Crop Profile for Iceberg Lettuce in California

 PEST MANAGEMENT

All information on pests and pesticides listed in this report relate to the production of iceberg lettuce in California. All pests and pesticides mentioned in this report are listed in alphabetical order, and each such listing may, or may not, have any relationship to the importance of the pest or the use of an individual pesticide. Appendix 1 contains a summary of the amount of individual pesticides applied to the three primary production regions in California in 1999 (7).

When considering chemical controls the multiple use of individual products for the management of one, or more, pests that may be present at the time of the application is usually considered. For example, an application of acephate might be considered if aphids are the primary concern, or if both aphids and loopers are present, while acephate and thiodicarb or acephate and spinosad might be substituted if both aphids and the beet armyworm are present. Other likely foliar combinations for aphids and worms include: acephate and methomyl; imidacloprid and spinosad; and imidacloprid and methomyl. It is also quite common to include a fungicide with an insecticide if both insects (e.g., aphids) and fungal pathogens (e.g., downy mildew) are present at the time of treatment.

The management of insect populations is extremely critical to the production of iceberg lettuce. Not only do insects damage lettuce foliage, they also contaminate lettuce by their presence, from their feeding, or from the depositing of excrement. In addition, a number of insects (e.g., aphids, leafhoppers, and whiteflies) are vectors of virus diseases. The high quality standards currently in place in the iceberg lettuce industry allow for minimal, if any, contaminated products reaching the market place as whole lettuce heads. Quality standards are even higher for those products destined for sale as packaged salad mixes and for export, where product contamination from any source is not acceptable.

APHIDS

Lettuce aphid (Nasonovia ribis-nigri): This aphid is a new pest of iceberg lettuce having originally been identified in the 1998 production season in the Salinas area. This aphid feeds deep inside the plant on young lettuce leaves as opposed to the green peach and potato aphids which primarily feed on the external portions (i.e., older leaves) of lettuce plants. This aphid also has a tendency to disperse within the plant rather than forming colonies which other aphids (e.g. green peach aphid and potato aphid) might do. Contact aphicides are, for the most part, ineffective and the primary treatments for this aphid are endosulfan, imidacloprid (i.e., soil treatment only), and oxydemeton-methyl with a soil applied treatment of imidacloprid followed by 1 to 2 foliar applications, or 2 to 3 foliar treatments required to maintain acceptable control. CLRB funded research has shown that two new aphicides (e.g., triazamate and pymetrozine) provide effective control of this aphid.

Lettuce Root aphid (Pemphigus bursarius): This aphid is an occasional problem in the coastal production regions. It occurs in colonies on lettuce roots. Plants are severely stunted under high population conditions, while moderate populations cause heads to soften and fail to properly mature. The primary materials used for this pest involve either a preplant or postplant/banded application of disulfoton or a treatment at planting of imidacloprid. Oxydemeton-methyl also provides some control of established colonies of this aphid as a foliar treatment.

Potato aphid (Macrosiphum euphorbiae): This aphid is a sporadic problem but is causing increasing problems in the coastal regions. Like the green peach aphid, this insect deposits honeydew, and under high populations causes quality problems on lettuce. Feeding damage, and resultant honeydew, is usually located deeper into the head than the green peach aphid thus causing increased problems at harvest. The primary materials used for this aphid are acephate, diazinon, dimethoate, endosulfan, imidacloprid, and oxydemeton-methyl. If necessary, up to 2 total annual treatments are applied, primarily in the coastal regions.

The following information is provided to indicate the importance of each individual aphid pest by production region (8):

PEST	SB/SC/SC/MO				SB/SLO				FT/KE				IM/RIV
	P	S	O		P	S	O		P	S	O		P	S	O
Green peach aphid	X					X			X				X
Lettuce aphid	X				X					NA				X
Lettuce root aphid			X				X				X				X
Potato aphid		X					X				X			X
The four major production regions by county are: San Benito, Santa Clara, Santa Cruz, & Monterey (SB/SC/SC/MO ); Santa Barbara & San Luis Obispo (SB/SLO); Fresno & Kern (FR/KE); and Imperial & Riverside (IM/RIV). The importance categories are: P = Primary; S = Secondary; and O = occasional. NA indicates that the listed pest is not yet known to be a problem in that region.

CONTROLS

A number of predators feed on foliar aphids (e.g., green peach and potato aphids) including the following: convergent lady beetle (Hippodamia convergens); lacewings (Chrysoperla spp.); and syrphid flies ( Family: Syrphidae ).

A fungus (Entomophthora aphidis) can reduce populations of the green peach and potato aphids.

Use of predators, and the fungus, however, are limited because of the short time the lettuce crop is in the field, the transitory nature of aphids, high crop quality standards, and a low tolerance for insect contaminated products, especially in packaged salad mixes and the export market.

One of the primary means of biological control of the lettuce root aphid is through the removal of its alternate host the Lombardy poplar. As a result of a county ordinance, the removal of most Lombardy poplars in Monterey County has reduced the number of outbreaks of this pest. CLRB funded research has shown that some iceberg lettuce germplasm has a high level of resistance to this pest.

Reports from Europe indicate that there are some iceberg lettuce cultivars with a degree of resistance to both the green peach and lettuce aphids. CLRB funded research is examining the source(s) of resistance and exploring the potential to develop germplasm and/or iceberg lettuce cultivars with resistance to both of these aphid species.

Chemical

Acephate - Labeled PHIs are 21 days (coastal) and pre-head formation (desert). Typical PHIs range from 21 to 40 days in the coastal areas and pre-head formation in the desert (4, 6). Acephate is applied as a foliar treatment at a typical rate of 0.75 lb. a.i. per acre (6). The preharvest interval in the coastal regions (21 day PHI) allows for more use than the desert regions where use is limited prior to head formation. Loss of this product would impact aphid, looper, lygus bug, and thrips resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., carbamates, nicotinyls, and pyrethroids). Acephate, applied as a foliar treatment, provides the best control of the green peach and potato aphids for the longest period of time, and is the most cost effective foliar treatment (6).

Diazinon - Labeled PHI is 14 days. Typical PHI ranges from 20 to 50 days (4,6). Diazinon is applied as a foliar treatment at a typical rate of 0.5 lb. a.i. per acre (6). Research data indicates that diazinon is not an effective treatment for the lettuce aphid. Loss of foliar treatments of this insecticide would impact aphid and lygus bug resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., carbamates, nicotinyls, and pyrethroids).

Dimethoate - Labeled PHI is 7 days. Typical PHI ranges from 10 to 50 days (4, 6). Dimethoate is applied as a foliar treatment at a typical rate of 0.4 lb. a.i. per acre (6). Loss of this product would impact aphid and lygus bug resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., carbamates, nicotinyls, and pyrethroids). In addition, it is one of two (other treatment is imidacloprid) of the primary foliar aphicides allowed use close to harvest (7 day PHI).

Disulfoton - Labeled PHI is 60 days. Disulfoton is applied as an at-planting at a typical rate of 1.0 lb. a.i. per acre (4). Primary use is in the coastal regions as an at-planting treatment for root aphid control. Loss of this product would have some economic affect on coastal iceberg lettuce production.

Endosulfan - Labeled PHI is 14 days. Typical PHI ranges from 20 to 50 days (4, 6). Endosulfan is applied as a foliar treatment at a typical rate of 1.0 lb. a.i. per acre (6). Use is limited in all regions, particularly in the coastal areas, by environmental constraints on the label (e.g., endosulfan is toxic to fish, birds and other wildlife, and risks are associated with runoff and drift). Loss of this product would impact aphid and worm resistance management and IPM programs, especially in the desert regions, as it is used as an alternative treatment to other products (e.g., organophosphates, carbamates, and pyrethroids).

Imidacloprid - Labeled PHIs are 21 days (soil) and 7 days ( foliar). Typical PHIs range from 60 to 120 days for the soil treatment and from 7 to 21 days for the foliar treatment (4). Imidacloprid is applied as a preplant, in-furrow or post-seeding drench treatment at a typical rate of 0.375 lb. a.i. per acre or as a foliar treatment at a typical rate of 0.05 lb. a.i. per acre (6). Primary use in the desert is as a soil treatment for the control of whiteflies. Research data indicates that imidacloprid as a foliar spray is not an effective treatment for the lettuce aphid. Loss of this product would impact aphid and whitefly resistance management and IPM programs. In addition, it is one of two (other treatment is dimethoate) of the primary foliar aphicides allowed use close to harvest (7 day PHI).

Malathion - Labeled PHI is 7 days. Typical PHI ranges from 10 to 40 days (4). Research data and grower experience indicates that malathion is not an effective treatment for any of the aphid species attacking iceberg lettuce (4, 9). Loss of foliar treatments of this insecticide would have little, if any, impact on aphid resistance management and IPM programs.

Oxydemeton-methyl - Labeled PHIs are 14 days with 1 application, 21 days with 2 applications, and 28 days with 3 applications or for use in the desert. Typical PHIs range from 20 to 50 days with 1 application, 25 to 50 with 2 applications, and 35-50 with 3 applications or for use in the desert (4, 6). Oxydemeton-methyl is applied as a foliar treatment at a typical rate of 0.5 lb. a.i. per acre (4). Use is limited in the spring and summer crops (coastal regions) by the number of applications in relation to the PHI (i.e., 1 application = 14 days; 2 = 21 days; and 3 = 28 days). Use in the desert regions is restricted to 28 day PHI regardless of number of applications. Research data indicates that oxydemeton-methyl as a foliar spray is an effective treatment for the lettuce aphid. Loss of foliar treatments of this insecticide would impact aphid resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., carbamates, nicotinyls, and pyrethroids).

LEPIDOPTEROUS LARVAE

Beet Armyworm (Spodoptera exigua): This insect causes serious damage to lettuce, and is more prevalent during fall production in the desert regions. Reduced stands can result from high insect populations. The primary materials used for this pest are cypermethrin, methomyl, permethrin, tebufenozide, thiodicarb, and spinosad, with 1 to 2 total annual treatments applied in the coastal and desert regions (winter and spring) and 3 to 6 total applications under the high populations in the desert in the fall.

Cabbage Looper (Trichoplusia ni): This insect can cause serious damage to lettuce in all areas, but is more of a problem in the desert regions. It is particularly a problem near harvest when larvae enter heads causing internal damage and deposit frass. The primary materials used for this pest are acephate, Bt, cypermethrin, endosulfan, methomyl, permethrin, thiodicarb, and spinosad with 1 to 2 total treatments applied primarily in the desert region on an annual basis.

Corn Earworm (Helicoverpa zea): This insect can cause serious damage to lettuce in all areas, but is more of a problem in the desert regions. It is particularly a problem near harvest when larvae enter heads causing internal damage and deposit frass. The primary materials used for this pest are Bt, cypermethrin, endosulfan, methomyl, permethrin, thiodicarb, and spinosad, with 1 to 2 total treatments applied in the desert region on an annual basis.

The following information is provided to indicate the importance of each individual lepidopterous pest by production region (4, 8):

PEST	SB/SC/SC/MO				SB/SLO				FT/KE				IM/RIV
	P	S	O		P	S	O		P	S	O		P	S	O
Beet Armyworm	X					X			X				X
Cabbage Looper		X			X				X				X
Corn Earworm		X				X			X				X
Alfalfa Looper		X				X				X				X
The four major production regions by county are: San Benito, Santa Clara, Santa Cruz, & Monterey (SB/SC/SC/MO ); Santa Barbara & San Luis Obispo (SB/SLO); Fresno & Kern (FR/KE); and Imperial & Riverside (IM/RIV). The importance categories are: P = Primary; S = Secondary; and O = occasional.

CONTROLS

The most common parasites of the beet armyworm are wasps (e.g., Hyposoter exiguae and Chelonus insularis), and the tachinid fly (Lespesia archippivora).

Parasites that feed on lepidopterous looper eggs or larvae include the following: parasitic wasp (Trichogramma spp.); tachinid fly (Voria ruralis); and other wasps (Copidosoma truncatellum, Hyposter exiguae, and Microplitis brassicae).

Predators also play a role in reducing populations of lepidopterous larvae. Two predators that feed on lepidopterous eggs are minute pirate bugs (Orius spp.), and big eyed bugs (Geocoris spp.).

Viral diseases (e.g., nuclear polyhedrosis virus) also play a role in reducing populations of lepidopterous larvae.

Parasites, predators, and viral diseases may assist in reducing lepidopterous larval populations, however, their use is limited because of the short time crops are in the field, high crop quality standards, and a low tolerance for insect contaminated products, especially in packaged salad mixes and the export market.

Chemical

Acephate - Labeled PHIs are 21 days (coastal) and pre-head formation (desert). Typical PHIs range from 21 to 40 days in the coastal areas and pre-head formation in the desert (4, 6). Acephate is applied as a foliar treatment at a typical rate of 0.75 lb. a.i. per acre (6). The preharvest interval in the coastal regions (21 day PHI) allows for more use than the desert regions where use is limited prior to head formation. Loss of this product would impact aphid, looper, lygus bug, and thrips resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., carbamates, nicotinyls, and pyrethroids).

Bacillus thuringiensis (Bt) - 0 day PHI. Bts play an important role in IPM programs. However, they usually require additional applications to be as effective as other products (e.g., organophosphates, carbamates, pyrethroids and IGR), and leaf and head damage normally occur from feeding while worms are ingesting toxic amounts of Bt type products.

Carbaryl - Labeled PHI is 3 days. Typical PHI ranges from 7 to 21 days (4). Carbaryl is primarily used as a bait and only used on a minimal number of acres for worm control. When used, it is applied as a foliar treatment at a typical rate of 2.0 lb. a.i. per acre (4). Research data and grower experience indicates that carbaryl is not an effective treatment for any of the worm species attacking iceberg lettuce. Loss of foliar treatments of this insecticide would have little, if any, impact on worm resistance management and IPM programs.

Cypermethrin - Labeled PHI is 5 days. Typical PHI ranges from 5 to 10 days (4, 6). Cypermethrin is applied as a foliar treatment at a typical rate of 0.08 lb. a.i. per acre (6). Loss of this product would impact worm resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., organophosphates, carbamates, and IGR).

Endosulfan - Labeled PHI is 14 days. Typical PHI ranges from 20 to 50 day (4, 6). Endosulfan is applied as a foliar treatment at a typical rate of 1.0 lb. a.i. per acre (4). Use is limited in all regions, particularly in the coastal areas, by environmental constraints on the label. Loss of this product would impact aphid and worm resistance management and IPM programs, especially in the desert regions, as it is used as an alternative treatment to other products (e.g., organophosphates, carbamates, pyrethroids, and IGR).

Esfenvalerate - Labeled PHI is 7 days. Typical PHI ranges from 7 to 21 days (4, 6). Esfenvalerate is applied as a foliar treatment at a typical rate of 0.04 lb. a.i. per acre. Loss of this product would impact worm resistance management and IPM programs as it is used as an alternative to other products (e.g., organophosphates, carbamates and IGRs).

Lambda-cyhalothrin - Labeled PHI is 1 day. Typical PHI ranges from 1 to 21 days (4, 6). Lambda-cyhalothrin is applied as a foliar treatment at a typical rate of 0.03 lb. a.i. per acre (6). Loss of this product would impact worm resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., organophosphates, carbamates, and IGRs).

Methomyl - Labeled PHI is 7 days at <0.5 lb. a.i. and 10 days at >0.5 lb. a.i. use rate. Typical PHIs range from 10 to 50 days at <0.5 lb. a.i. and 15 to 50 days at >0.5 lb. a.i. use rate (4, 6). Methomyl is applied as a foliar treatment at a typical rate of 0.9 lb. a.i. per acre (6). Loss of this product would impact worm resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., organophosphates, pyrethroids, and IGR). Resistance to the beet armyworm has been documented in the desert however, resistance varies with geographical production region. Use in the desert regions, where worm pressure is severe, could be significantly impacted if this product were no longer available.

Permethrin - Labeled PHI is 1 day. Typical PHI ranges from 1 to 50 days (4, 6). Permethrin is applied as a foliar treatment at a typical rate of 0.125 lb. a.i. per acre (6). Loss of this product would impact worm resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., organophosphates, carbamates, and IGR).

Spinosad - Labeled PHI is 1 day. Typical PHI ranges from 1 to 10 days (4). Spinosad is applied as a foliar treatment at a typical rate of 0.1 lb. a.i. per acre (4). Use of this material is expected to increase, and the loss of this product would impact worm resistance management and IPM programs as it is used as an alternative treatment to other products. (e.g., organophosphates, carbamates, pyrethroids, and IGR).

Tebufenozide - Labeled PHI is 7 days. Typical PHI ranges from 7 to 21 days (4). Tebufenozide is applied as a foliar treatment at a typical rate of 0.125 lb. a.i. per acre (4). Use of this material is expected to increase, and the loss of this product would impact worm resistance management and IPM programs as it is used as an alternative treatment to other products. (e.g., organophosphates, carbamates, and pyrethroids).

Thiodicarb - Labeled PHI is 14 days. Typical PHI ranges from 14 to 21 days (4). Thiodicarb is applied as a foliar treatment at a typical rate of 0.75 lb. a.i. per acre (6). Use of this product is expected to increase, and the loss of this product would impact worm resistance management and IPM programs as it is used as an alternative treatment to other products. (e.g., organophosphates, pyrethroids, and IGR).

Tralomethrin - Labeled PHI is 3 days. Typical PHI ranges from 3 to 21 days (4, 6). Tralomethrin is applied as a foliar treatment at a typical rate of 0.02 lb a.i. per acre (6). Loss of this product would impact worm resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., organophosphates, carbamates, and IGRs).

OTHER INSECT PESTS

LEAFMINERS

The primary materials for control of the larval stage of this insect are abamectin and cyromazine, with plantback restrictions currently limiting the use of cyromazine. Reductions in adult fly populations may be achieved with foliar treatments of acephate, cypermethrin, diazinon, and permethrin. However, these chemicals do not provide economic control of adults and do not control fly larvae (9).

The control of adult flies is, at best, not an effective management technique. For example, under normal adult fly population conditions, achieving 90% control, which most of the aforementioned materials do not provide, still could result in populations in the range of 1/4 to 1/2 million flies per acre (9).

Under normal population conditions, the larval treatments would be applied a total of 1 to 2 times and the adult materials a total of 1 to 3 times. Under high population pressure, total treatments would increase to 2 to 3 for larval control and 2 to 4 for adults.

CONTROLS

CLRB funded research has identified resistance sources, and is exploring the development of resistant germplasm.

CLRB funded research is also exploring those factors affecting parasite abundance and the impact of parasite and predators on IPM programs for the management of leafminers. Initial results indicate that parasitism rates, even under IPM regimes, are very low and rarely above 5%.

Chemical - Management of fly larvae

Abamectin - Labeled PHI is 7 days. Typical PHI ranges from 7 to 30 days (4). Abamectin is applied as a foliar treatment at a typical rate of 0.01 lb. a.i. per acre (4). Abamectin is the product of choice for the control of leafminer larvae. Loss of this product would impact leafminer resistance management and IPM programs as it is used as the primary treatment for the control of leafminer larvae (other treatment is cyromazine).

Cyromazine - Labeled PHI is 7 days. Typical PHI ranges from 7 to 30 days (4). Cyromazine is applied as a foliar treatment at a typical rate of 0.1 lb. a.i. per acre (4). Loss of this product would impact leafminer resistance management and IPM programs as it is used as one of two (other treatment is abamectin) primary treatments for the control of leafminer larvae. Use is limited by plantback restrictions (e.g., 300 days for brassica vegetables).

Azadirachtin - Labeled PHI is 0 days. Typical PHI ranges from 1 to 50 days (4). Azadirachtin is applied as a foliar treatment at a typical rate of 0.1 lb. a.i. per acre (4). Azadirachtin does not control leafminer larvae, but restricts their ability to pupate thus reducing overall field populations.

Chemical - Management of adult flies

Acephate - Labeled PHIs are 21 days (coastal) and pre-head formation (desert). Typical PHIs range from 21 to 40 days in the coastal areas and pre-head formation in the desert (4, 6). Acephate is applied as a foliar treatment on a small percentage of the coastal acreage at a typical rate of 0.75 lb. a.i. per acre (4). The preharvest interval in the coastal regions (21 day PHI) allows for more use than the desert regions where use is limited prior to head formation. Loss of this product would impact aphid, looper, lygus bug, and thrips resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., carbamates and pyrethroids).

Cypermethrin - Labeled PHI is 5 days. Typical PHI ranges from 5 to 10 days (4, 6). Cypermethrin is applied as a foliar treatment on a small percentage of the coastal acreage at a typical rate of 0.08 lb. a.i. per acre (4). Resistance to pea leafminer adults has been documented for cypermethrin in the coastal regions (2, 9). Loss of this product would impact worm resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., organophosphates and carbamates).

Diazinon - Labeled PHI is 14 days. Typical PHI ranges from 20 to 50 days (4, 6). Diazinon is applied as a foliar treatment on a small percentage of the coastal acreage at a typical rate of 0.5 lb. a.i. per acre (4). Loss of foliar treatments of this insecticide would impact aphid resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., carbamates and pyrethroids).

Lambda-cyhalothrin - Labeled PHI is 1 day. Typical PHI ranges from 1 to 21 days (4, 6). Lambda-cyhalothrin is applied as a foliar treatment at a typical rate of 0.03 lb. a.i. per acre (6). Loss of this product would impact worm resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., organophosphates, carbamates, and IGRs).

Permethrin - Labeled PHI is 1 day. Typical PHI ranges from 1 to 50 days (4, 6). Permethrin is applied as a foliar treatment on a small percentage of the coastal acreage at a typical rate of 0.125 lb. a.i. per acre (4). Resistance to pea leafminer adults has been documented for permethrin in the coastal regions (2, 9). Loss of this product would impact worm resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., organophosphates and carbamates).

Tralomethrin - Labeled PHI is 3 days. Typical PHI ranges from 3 to 21 days (4, 6). Tralomethrin is applied as a foliar treatment at a typical rate of 0.02 lb a.i. per acre (6). Loss of this product would impact worm resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., organophosphates, carbamates, and IGRs).

LYGUS BUG (Lygus hesperus)

CONTROLS

There are no current methods of providing biological control for lygus bugs.

Chemical

Acephate - Labeled PHIs are 21 days (coastal) and pre-head formation (desert). Typical PHIs range from 21 to 40 days in the coastal areas and pre-head formation in the desert (4, 6). Acephate is applied as a foliar treatment at a typical rate of 0.75 lb. a.i. per acre (4). The preharvest interval in the coastal regions (21 day PHI) allows for more use than the desert regions where use is limited prior to head formation. Loss of this product would impact aphid, looper, lygus bug, and thrips resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., carbamates and pyrethroids).

Cypermethrin - Labeled PHI is 5 days. Typical PHI ranges from 5 to 10 days (4, 6). Cypermethrin is applied as a foliar treatment at a typical rate of 0.08 lb. a.i. per acre (4). Loss of this product would impact worm and lygus bug resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., organophosphates and carbamates).

Diazinon - Labeled PHI is 14 days. Typical PHI ranges from 20 to 50 days (4, 6). Diazinon is applied as a foliar treatment at a typical rate of 0.5 lb. a.i. per acre (4). Loss of foliar treatments of this insecticide would impact aphid and lygus bug resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., carbamates and pyrethroids).

Dimethoate - Labeled PHI is 7 days. Typical PHI ranges from 10 to 50 days (4, 6). Dimethoate is applied as a foliar treatment at a typical rate of 0.4 lb. a.i. per acre (4). Loss of this product would impact aphid and lygus bug resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., carbamates and pyrethroids).

Lambda-cyhalothrin - Labeled PHI is 1 day. Typical PHI ranges from 1 to 21 days (4, 6). Lambda-cyhalothrin is applied as a foliar treatment at a typical rate of 0.03 lb. a.i. per acre (6). Loss of this product would impact worm resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., organophosphates, carbamates, and IGRs).

Malathion - Labeled PHI is 7 days. Typical PHI ranges from 10 to 40 days (4). Malathion is applied as a foliar treatment at a typical rate of 1.25 lb. a.i. per acre (4). Approximately 50% of use is in the coastal regions and 50% in the San Joaquin Valley/Desert regions (7).

Methomyl - Labeled PHI is 7 days at <0.5 lb. a.i. and 10 day PHI at >0.5 lb. a.i. use rate. Typical PHIs range from 10 to 50 days at <0.5 lb. a.i. and 15 to 50 days at >0.5 lb. a.i. use rate (4, 6). Methomyl is applied as a foliar treatment at a typical rate of 0.9 lb. a.i. per acre (4). Loss of this product would impact worm and lygus bug resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., organophosphates and pyrethroids).

Permethrin - Labeled PHI is 1 day. Typical PHI ranges from 1 to 50 days (4, 6). Permethrin is applied as a foliar treatment on a small percentage of the coastal acreage at a typical rate of 0.125 lb. a.i. per acre (4). Loss of this product would impact worm and lygus bug resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., organophosphates and carbamates).

Tralomethrin - Labeled PHI is 3 days. Typical PHI ranges from 3 to 21 days (4, 6). Tralomethrin is applied as a foliar treatment at a typical rate of 0.02 lb a.i. per acre (6). Loss of this product would impact worm resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., organophosphates, carbamates, and IGRs).

WHITEFLIES

CONTROLS

Several wasps including those in the Encarsia and Eretmocerus genera parasitize whiteflies.

Big eyed bugs (Geocoris spp.) and larvae of lacewings (Chrysoperla spp.) feed on whitefly nymphs as does the lady beetle (Delphastus pusillius).

The presence of parasites and predators minimally reduces populations of whiteflies, and economic control is not obtainable, due to high whitefly population levels.

CLRB funded research is exploring two programs: 1) the development of iceberg lettuce germplasm which is resistant to whiteflies; and 2) the development of iceberg lettuce germplasm which is resistant to Lettuce Infectious Yellows and related viruses.

Chemical

Imidacloprid - Labeled PHI is 21 days. Imidacloprid is applied as a preplant, in-furrow or post-seeding drench treatment at a typical rate of 0.375 lb. a.i. per acre (4). Primary use in the desert is as a soil treatment for the control of whiteflies. Loss of this product would impact aphid and whitefly resistance management and IPM programs.

SOIL INSECTS

CONTROLS

Several soil dwelling arthropods may occasionally feed on soil pests, but none are effective in significantly reducing populations.

Chemical

Carbaryl - Labeled PHI is 3 days. Carbaryl is applied as a bait treatment for the control of cutworms at a typical rate of 2.0 lb. a.i. per acre (4). Carbaryl is the only bait product registered for this use, and the loss of this material would result in an increase in losses from cutworms.

Diazinon - Labeled use is as a preplant treatment. Diazinon is applied as a preplant granular treatment at a typical rate of 2.0 lb. a.i. per acre (6). Loss of the granular product would result in an increase in losses from soil insects as it is the only product registered for this use.

WESTERN FLOWER THRIPS (Frankliniella occidentalis)

CONTROLS

Biological

General predators such as minute pirate bugs (Orius spp.), big eyed bugs (Geocoris spp.), and predatory thrips (Order Thysanoptera) feed on pest thrips. These predators usually only become common when populations of F. occidentalis are well above damage thresholds, and thus are not effective management strategies.

Chemical

Acephate - Labeled PHIs are 21 days (coastal) and pre-head formation (desert). Typical PHIs range from 21 to 40 days in the coastal areas and pre-head formation in the desert (4, 6). Acephate is applied as a foliar treatment at a typical rate of 0.75 lb. a.i. per acre (4). The preharvest interval in the coastal regions (21 day PHI) allows for more use than the desert regions where use is limited prior to head formation. Loss of this product would impact aphid, looper, lygus bug, and thrips resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., carbamates and pyrethroids).

Cypermethrin - Labeled PHI is 5 days. Typical PHI ranges from 5 to 10 days (4, 6). Cypermethrin is applied as a foliar treatment at a typical rate of 0.08 lb. a.i. per acre (4). Loss of this product would impact worm and lygus bug resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., organophosphates and carbamates).

Lambda-cyhalothrin - Labeled PHI is 1 day. Typical PHI ranges from 1 to 21 days (4, 6). Lambda-cyhalothrin is applied as a foliar treatment at a typical rate of 0.03 lb. a.i. per acre (6). Loss of this product would impact worm resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., organophosphates, carbamates, and IGRs).

Methomyl - Labeled PHI is 7 days at <0.5 lb. a.i. and 10 days at >0.5 lb. a.i. use rate. Typical PHIs range from 10 to 50 days at <0.5 lb. a.i. and 15 to 50 days at >0.5 lb. a.i. use rate (4, 6). Methomyl is applied as a foliar treatment at a typical rate of 0.9 lb. a.i. per acre (4). Loss of this product would impact worm and lygus bug resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., organophosphates and pyrethroids).

Permethrin - Labeled PHI is 1 day. Typical PHI ranges from 1 to 50 days (4, 6). Permethrin is applied as a foliar treatment at a typical rate of 0.125 lb. a.i. per acre (4). Loss of this product would impact worm and lygus bug resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., organophosphates and carbamates).

Tralomethrin - Labeled PHI is 3 days. Typical PHI ranges from 3 to 21 days (4, 6). Tralomethrin is applied as a foliar treatment at a typical rate of 0.02 lb a.i. per acre (6). Loss of this product would impact worm resistance management and IPM programs as it is used as an alternative treatment to other products (e.g., organophosphates, carbamates, and IGRs).

The management of diseases is extremely critical to the production of iceberg lettuce. Not only do diseases damage lettuce foliage (e.g., anthracnose, bacterial leaf spot, and downy mildew), they also contaminate lettuce as a result of tissue decay (e.g., lettuce drop and bottom rot) during shipment. The high quality standards currently in place in the iceberg lettuce industry allow for minimal, if any, contaminated products reaching the market place as whole iceberg lettuce heads. Quality standards are even higher for those products destined for sale as packaged salad mixes and for export, where product contamination is not acceptable.

FUNGAL DISEASES

Bottom Rot (Rhizoctonia solani): This disease causes yield losses primarily in the San Joaquin Valley and desert production areas. Dicloran, iprodione, and vinclozolin provide some relief from this disease. Economic control, however, is seldom obtained and losses of up to 50% have been observed in individual fields in the desert.

Downy Mildew (Bremia lactuca): This is the most serious foliar disease of iceberg lettuce in California. It is found in all areas, but is more prevalent in the coastal regions. Resistant cultivars have been developed through CLRB funded plant breeding programs. Unfortunately, this disease has the ability to overcome this type of resistance, and many of the originally resistant cultivars are no longer useful. Maneb and fosetyl-al are the fungicides of choice for downy mildew control, with the number of foliar applications per acre per season ranging from none up to 4 in the coastal regions and from none up to 2 in the desert. Metalaxyl use has declined due to the ability of the fungus to become tolerant to this fungicide, and recent research has indicated that insensitivity to fosetyl-al also exists (2, 11). Ground applications are the preferred method for applying fungicides. However aerial treatments are also used, especially under wet field conditions. CLRB funded research has shown that the use of downy mildew resistant cultivars in combination with weather forecasting and models related to leaf wetness, rainfall, irrigation, and other downy mildew infection parameters has resulted in improvements in application efficiency and a reduction in fungicide use.

Lettuce Drop (Sclerotinia minor and S. sclerotiorum): Lettuce drop is an extremely important disease of lettuce. Although both species may be present in all lettuce production regions, the soilborne species (S. minor) is more prevalent in the coastal production areas while the airborne species (S. sclerotiorum) is more prevalent in the San Joaquin Valley and desert regions. S. minor populations occur in most production regions and the sclerotia of this species may remain viable in the soil for prolonged periods (e.g., up to 8 to 10 years). Soil applied fungicides such as dicloran, iprodione, and vinclozolin provide some relief from this disease, but timing of applications is extremely critical to achieving economic control. Under normal disease conditions, approximately 2/3 to 3/4 of the lettuce acreage is treated for lettuce drop, and even with the use of these fungicides losses from this disease range from 5 to 20%. CLRB funded research is exploring the development of resistant cultivars.

Powdery mildew (Erysiphe cicoracearum): Powdery mildew is primarily a problem in the desert production regions during the winter months. Sulfur is the primary treatment for powdery mildew control.

Verticillium Wilt (Verticillium dahliae): Verticillium wilt has only recently been identified as a disease of iceberg lettuce, and the current known infestations are limited to Monterey and Santa Cruz Counties. Combination treatments of methyl bromide and chloropicrin treatments may reduce soil infestations of this disease.

The following information is provided to indicate the importance of each individual disease by production region (8):

PEST	SB/SC/SC/MO				SB/SLO				FT/KE				IM/RIV
	P	S	O		P	S	O		P	S	O		P	S	O
Anthracnose		X					X				X				X
Bottom Rot		X					X				X			X
Downy Mildew	X				X					X					X
Lettuce Drop	X				X				X					X
Powdery Mildew			X				X			X			X
Verticillium Wilt			X		NA				NA					NA
The four major production regions by county are: San Benito, Santa Clara, Santa Cruz, & Monterey (SB/SC/SC/MO ); Santa Barbara & San Luis Obispo (SB/SLO); Fresno & Kern (FR/KE); and Imperial & Riverside (IM/RIV). The importance categories are: P = Primary; S = Secondary; and O = occasional. NA indicates that the listed pest is not yet known to be a problem in that region.

CONTROLS

CLRB funded research has resulted in the release of germplasm and/or iceberg lettuce cultivars with varying degrees of resistance to downy mildew. CLRB funded research is also exploring the development of resistance to anthracnose, bacterial leaf spot, lettuce drop, and verticillium wilt.

CLRB funded research has shown that lettuce drop caused by S. minor can be reduced by the use of drip irrigation and also by a crop rotation with broccoli. Both of these techniques are used when not constrained by economics and/or crop rotation practices.

Chemical - Foliar Disease Management

Acibenzolar-S-methyl - Labeled PHI is 7 days. Acibenzolar-S-methyl was just recently registered for downy mildew control in California and no data are available on use.

Azoxystrobin - Labeled PHI is 1 day. Typical PHI ranges from 7 to 28 days (4, 6). Azoxystrobin is used as a preventative fungicide and is applied as a foliar treatment at a typical rate of 0.025 lb. a.i. per acre (6). Azoxystrobin is the current product of choice for anthracnose management.

Copper - Although not labeled as such, there is a 1 to 2 day PHI which is related to the REI of 24 to 48 hours on individual labels. Copper is applied as a foliar treatment at a typical rate of 1.5 lb. a.i. per acre (4). Copper provides a degree of control of downy mildew and anthracnose. Applications of copper can be injurious to lettuce, especially under periods of excessive leaf moisture. Injury from copper is exacerbated when it is combined with acid-based products (e.g. fosetyl-al) and these types of mixtures should be avoided (5).

Fosetyl-al - Labeled PHI is 3 days. Typical PHI ranges from 3 to 14 days (4, 6). Fosetyl-al is applied as a foliar treatment at a typical rate of 2.75 lb. a.i. per acre (4). Loss of this product would impact downy mildew resistance management and IPM programs as it is used as an alternative treatment to maneb. Fosetyl-al also may be used closer to harvest (3 day PHI) than maneb (14 day PHI) and thus is available to maintain lettuce quality just prior to harvest. Recent research indicates possible downy mildew insensitivity to fosetyl-al (2, 11).

Maneb - Labeled PHI is 14 days. Typical PHI ranges from 14 to 20 days (4, 6). Maneb is used as a preventative fungicide and is applied as a foliar treatment at a typical rate of 1.6 lb. a.i. per acre (6). Maneb is the current product of choice for downy mildew management, and the loss of this product would severely impact resistance management and IPM programs as it is used as an alternative treatment to fosetyl-al. Maneb use is somewhat restricted by the number of total applications (i.e., 4) allowed per crop, and due to the 14 day PHI.

Metalaxyl - Labeled PHI is 7 days. Typical PHI ranges from 20 to 40 days (4, 6). Metalaxyl is applied as a foliar treatment at a typical rate of 0.125 lb. a.i. per acre (4). Label restrictions only allow use in a tank mixture with full labeled rates of other fungicides. Insensitivity of downy mildew to metalaxyl has been documented (2).

Sulfur - Although not labeled as such, there is a 1 day PHI which is related to the REI of 24 hours on individual labels. Sulfur is applied as a foliar treatment at a typical rate of 4.0 lb. a.i. per acre (4). Sulfur is currently the only labeled product for the control of powdery mildew. The degree of control with sulfur is influenced by temperature, and the warmer the temperature, the better the control. Sulfur can cause phytotoxicity following repeated applications.

Chemical - Soil Disease Management

Dicloran - Labeled PHI is 14 days. Typical PHI ranges from 35 to 70 days (4, 6). Dicloran may be applied either preemergence and/or immediately after thinning at a typical rate of 2.5 lb. a.i. per acre for the control of S. sclerotiorum or immediately after thinning at a typical rate of 3.5 lb. a.i. per acre for the control of S. minor (4). Usually only 1 application is made to an individual lettuce crop. Dicloran is one of three fungicides (iprodione and vinclozolin are the others) used in rotation for the control of lettuce drop in the coastal regions. Even with fungicide use, losses from this disease range from 5-20%, and the loss of any one of these fungicides would have serious economic impacts on iceberg lettuce production.

Iprodione - Labeled PHI is 14 days. Typical PHI ranges from 35 to 70 days (4, 6). Iprodione may be applied at the three leaf stage to just after thinning and again 10 days later at a typical rate of 1.0 lb. a.i. per acre (4). Usually only 1 application is made to an individual lettuce crop. Iprodione is one of three fungicides (dicloran and vinclozolin are the others) used in rotation for the control of lettuce drop in the coastal regions. Even with fungicide use, losses from this disease range from 5-20%, and the loss of any of one of these fungicides would have serious economic impacts on iceberg lettuce production.

Methyl Bromide - PHI is restricted by use prior to planting. Methyl Bromide (MeBr) and chloropicrin are applied in combination as a soil treatment prior to planting at typical rates of 250 lb. a.i. MeBr and 120 lb. a.i. of chloropicrin per acre (4). Methyl Bromide and chloropicrin provide considerable control of verticillium wilt and lettuce drop (e.g., S. minor), but the cost of treatment limits their use.

Vinclozolin - Labeled PHI is 28 days. Typical PHI ranges from 35 to 70 days (4, 6). Vinclozolin is applied immediately after thinning with additional treatments based on weather conditions at a typical rate of 1.0 lb. a.i. per acre (4). Usually only 1 application is made to an individual lettuce crop. Vinclozolin is one of three fungicides (dicloran and iprodione are the others) used in rotation for the control of lettuce drop in the coastal regions. Even with fungicide use, losses from this disease range from 5-20%, and the loss of any of one of these fungicides would have serious economic impacts on iceberg lettuce production.

BACTERIAL DISEASES

Corky Root - (Rhizomonas suberifaciens): This soil borne bacterial disease is primarily a problem in areas that have been continually farmed in lettuce over an extended period of time. The primary means of controlling this disease are through the introduction of iceberg lettuce cultivars with corky root resistance. Crop rotation also reduces soil populations of this disease.

 CONTROLS

CLRB funded research is developing germplasm with resistance to bacterial leaf spot. CLRB funded research is also exploring various methods of controlling bacterial leaf spot, including the potential to determine if lettuce seed is pathogen-free, or if there is an economical seed treatment that will eliminate this disease.

CLRB funded research has resulted in the release of germplasm and/or cultivars with varying degrees of resistance to corky root.

Crop rotation with brassica species (e.g., cole crops) or cover crops has been shown to reduce soil populations of corky root. Both of these techniques are used when not constrained by economics and/or crop rotation practices.

Chemical

Copper - Although not labeled as such, there is a 1 to 2 day PHI which is related to the REI of 24 to 48 hours on individual labels. Copper is applied as a foliar treatment at a typical rate of 1.5 lb. a.i. per acre (4). Copper is only marginally effective as a foliar treatment for bacterial leaf spot. Applications of copper can be injurious to lettuce, especially under periods of excessive leaf moisture. Injury from copper is exacerbated when it is combined with acid-based products (e.g. fosetyl-al) and these types of mixtures should be avoided (5).

VIRAL DISEASES

Lettuce Big Vein (LBV): LBV is associated with a soil borne fungus and is present in all lettuce regions. CLRB funded research is exploring resistant cultivars. At the present time the only control for this virus is the use of tolerant cultivars.

Lettuce Infectious Yellows Virus (LIYV): LIYV has been an extremely destructive virus in the desert production regions and is transmitted by whiteflies. LIYV is currently not a problem due to a change in whitefly populations that is presently dominated by one species that is not an efficient vector of this disease and the use of imidacloprid.

Lettuce Mosaic Virus (LMV): LMV is transmitted by the green peach aphid, and can be an extremely serious virus on iceberg lettuce. LMV is currently under acceptable economic control through the use of a seed testing program, use of virus free seed, some iceberg lettuce resistant cultivars, and a lettuce free period.

The following information is provided to indicate the importance of each individual virus by production region (8):

PEST	SB/SC/SC/MO				SB/SLO				FT/KE				IM/RIV
	P	S	O		P	S	O		P	S	O		P	S	O
BWYV			X				X			X				X
LBV		X				X				X				X
LIYV	NA				NA				NA					X
LMV	X					X			X						X
The four major production regions by county are: San Benito, Santa Clara, Santa Cruz, & Monterey (SB/SC/SC/MO ); Santa Barbara & San Luis Obispo (SB/SLO); Fresno & Kern (FR/KE); and Imperial & Riverside (IM/RIV). The importance categories are: P = Primary; S = Secondary; and O = occasional. NA indicates that the listed pest is not yet known to be a problem in that region.

CONTROLS

CLRB funded research has resulted in the release of germplasm and/or cultivars with varying degrees of resistance to BWYV, LBV and LMV. CLRB funded research is also exploring iceberg lettuce resistance to LIYV and related viruses.

LMV is primarily controlled through the use of virus-indexed seed. The most common techniques involve enzyme-linked immunosorbent assay (ELISA). Monterey and Imperial counties have ordinances that require LMV testing for all iceberg lettuce seed lots. There is also a lettuce free period in Monterey County.

Chemical

There are no known chemical controls for viruses other than reducing the insect vectors that transmit them.

There are only a limited number of herbicides available for use in controlling weeds in iceberg lettuce. The wide range of production areas and the extreme diversity of weed species allow for many problems in maintaining acceptable control during the production season. No individual herbicide or combination of materials will control all weed species under all production conditions and soil types.

The high quality standards currently in place in the iceberg lettuce industry allow for minimal, if any, contaminated products reaching the market place as whole lettuce heads. Quality standards are even higher for those products destined for sale as packaged salad mixes and for export, where product contamination from any source is not acceptable.

CONTROLS

There are no current methods of providing biological control for either annual or perennial weeds that infest iceberg lettuce.

Cultivation and hand weeding are used on iceberg lettuce following crop emergence. Hand weeding is done in conjunction with the thinning operation, which occurs early in the production cycle, and usually once more later in the season. Mechanical cultivation of the bed top and furrow areas is often done in conjunction with an application of fertilizer. Weeding and cultivation crews require careful supervision to reduce the potential for yield reductions resulting from plant damage or the loss of plants during these operations. Under normal plant-population conditions, losses of one plant per 10 bed feet can result in yield reductions of approximately 50 cartons per acre.

Chemical

Control of weeds prior to planting is usually accomplished through the normal preplant ground preparation procedures or with preplant or fallow bed treatments of glyphosate, oxyfluorfen, or paraquat. The use of herbicides in this period varies from year to year primarily depending upon weather conditions, with increased use during wet periods when cultivation is not possible. In most instances, herbicide use at this time is followed by a light cultivation to eliminate any remaining plant material prior to planting.

Pronamide is the most widely used herbicide on lettuce in California. It is used in all production areas, and is the predominant material used in the coastal regions for annual broadleaf weed control. Pronamide is usually applied postplant-preemergence as a banded bed-top treatment followed by sprinkler irrigation. Its use is restricted to one application per crop. Benefin and bensulide are two other broadleaf herbicides used in California with their use more prevalent in the San Joaquin Valley or desert production areas. Sethoxydim is used on a small percentage of the acreage where grassy weeds present problems.

The economics of annual broadleaf weed control involving pronamide has been examined in Monterey County, the primary production area in California. Applying pronamide saved growers $29 to $57 per acre in weed control costs. At very high weed densities, additional hand weeding ranging from $404 to $770 per acre would be necessary to reduce or prevent yield losses. Without pronamide, weed control costs could be as high as $3,301,420 more per year just for Monterey County, and even worse under very high weed population densities (2).

Fallow Bed Uses

Glyphosate - PHI is restricted by use as a fallow bed treatment prior to planting. Glyphosate is applied as a preplant - fallow bed treatment prior to planting at a typical rate of 1.0 lb. a.i. per acre (4). Glyphosate is used on a minimal number of acres, with increased use under wet conditions.

Oxyfluorfen - PHI is restricted by use as a fallow bed treatment prior to planting, which requires 90 (i.e., up to 0.25 lb. a.i. rate) and 120 (i.e., up to 0.5 lb. a.i. rate) day intervals between treatment and planting. Oxyfluorfen is applied as a preplant - fallow bed treatment prior to planting at a typical rate of 0.5 lb. a.i. per acre (4). Oxyfluorfen is used on a minimal number of acres in California.

Paraquat - PHI is restricted by use as a fallow bed treatment prior to planting. Paraquat is applied as a preplant - fallow bed treatment prior to planting at a typical rate of 0.9 lb. a.i. per acre (4). Paraquat is used on a minimal number of acres in California.

Preplant, Preemergence, or Postemergence Uses

Benefin - PHI is restricted by use as a preplant incorporated treatment. Typical PHI ranges from 60 to 110 days (4). Benefin is applied as a preplant incorporated treatment at a typical rate of 0.9 lb. a.i. per acre (6). The loss of this product would have serious economic impacts on the production of lettuce in the San Joaquin Valley and desert areas.

Bensulide - PHI is restricted by use as either a preplant or a preemergence treatment at planting. Typical PHI ranges from 60 to 110 days (4). Bensulide is applied as either a preplant or preemergence treatment at a typical rate of 5.0 lb. a.i. per acre (6). The loss of this product would have serious economic impacts on the production of lettuce in the desert areas, and would also impact a percentage of the summer coastal production regions where it is combined with pronamide (10).

Metam-sodium - PHI is restricted by use as a preplant treatment. Typical PHI ranges from 90 to 120 days (4). Metam-sodium is applied as a preplant treatment at an average rate of 130 lb. a.i. per acre (4). Metam-sodium is used on a minimal number of acres in California.

Pronamide (propyzamide) - Labeled PHI is 55 days. Typical PHI ranges from 60 to 110 days (4). Pronamide is applied as a preemergence treatment at a typical rate of 1.0 lb. a.i. per acre (4, 6). The loss of this product would have serious economic impacts on the production of lettuce in all regions, but particularly in the coastal areas, where the two other available herbicides are not as effective (4, 10).

Sethoxydim - Labeled PHI is 30 days. Typical PHI ranges from 30 to 60 days (4). Sethoxydim is applied as a postemergence treatment at a typical rate of 0.3 lb. a.i. per acre (4). Sethoxydim use is restricted to the control of grassy species. Sethoxydim is used on a minimal number of acres in California.

Edward A. Kurtz
Manager
California Lettuce Research Board
512 Pajaro Street
Salinas, CA 93901
TEL: 831-424-3782
FAX: 831-424-3785

1. United State Department of Agriculture - Vegetables - 2000 Summary - January 2001.
2. California Lettuce Research Board Reports.
3. California Agricultural Resource Directory - 2000
4. Personal Communication - CLRB members and/or their PCAs.
5. Compendium of Lettuce Diseases - American Phytopathological Society - 1997.
6. Grower-Shipper Vegetable Association of Central California - Pest Management Committee - Reports to the Environmental Protection Agency - 1998.
7. California Department of Pesticide Regulation - Use Reports - 1999.
8. Reduced Risk Pest Management Programs for Iceberg and Leaf Lettuce - California Department of Pesticide Regulation - Contract #97-1267 - 1998.
9. Personal Communication - Bill Chaney - University of California Cooperative Extension - Monterey Co.
10. Personal Communication - Harry Agamalian - University of California Cooperative Extension - Monterey Co.
11. Personal Communication - Richard Michelmore - University of California @ Davis.

• Integrated Pest Management for Cole crops and Lettuce - UC Publication 3307 1987
• Iceberg Lettuce Production In California - University of California Vegetable Production Series - Publication 7215 - 1996.
• Ryder, E. J. 1999. Lettuce, Endive and Chicory, Crop Production Science in Horticulture.
• UC IPM Pest Management Guidelines: Lettuce - December 1996