Crop Profile for Cantaloupes and Muskmelons in Kentucky


Prepared: June, 2003

General Production Information

Production Statistics

The total commercial acreage in Kentucky was estimated to be approximately 470 acres produced by 210 growers in 2002. The melon production in Kentucky during 2002 was estimated to be valued at US $2,000,000. Melons are marketed on a wholesale and retail basis.

Production Regions

Melon production generally occurs in clusters of small farms scattered across the state. Melons are wholesale marketed through formal grower coops as well as retailed through roadside markets. The map below indicates the commercial melon acreage by county reported in a survey of Kentucky Cooperative Extension Agents in the Fall of 2002. Melon acreage is relatively stable, but increasing in the state.



Cultural Practices

Muskmelons (cantaloupes) are a warm season crop. They require a relatively long growing season of 80 to 100 days from seeding to marketable fruit. Well drained, lighter textured (sandy or sandy loam) soils are considered best for cantaloupes although medium textured soils can be just as productive with good management practices. Lighter textured soils warm up faster than heavier soils. However, in Kentucky, most melons are grown on clay-loam soils. Because of potentially serious disease problems, melons are best grown on land that has not been in vine(cantaloupes, watermelons, squash, pumpkins, etc.) or solanaceous crops for at least three years.

The vining habit of the plant and its large leaves make it especially susceptible to wind damage. Planting cantaloupes between strips of annual rye or some similar, taller-growing plant will provide windbreak protection. In addition, growers should orient rows in the direction of prevailing winds (usually winds blow from the southwest in most parts of Kentucky) so that wind blows down rows rather than across them.

Cantaloupes are direct seeded to the field or grown as transplants in the greenhouse or hotbed and transplanted to the field. When direct seeded, rows should be 5 to 6 feet apart with plants thinned to hills 2 to 3 feet apart in the row, with 2 or 3 plants per hill. Generally, 2 pounds of seed is sufficient to direct seed an acre while 1/4 to 1/2 pound per acre is sufficient for transplants. Plant the seed 1/2 to 3/4 inches deep after danger of frost is past.

Transplants produce earlier ripening fruits that bring much higher early prices. With transplants, plant the seed 3 weeks before the plants are to be transplanted to the field. The plants should have 2 or 3 true leaves. For transplants, plant 2 or 3 seeds each in 3 or 4 inch round or square peat pots or plug trays. Do not allow pots to dry out.

Black plastic mulch on raised beds with drip irrigation is often used to obtain higher yields and to encourage faster growth and earlier maturity. Photodegradable mulches (break down over time from exposure to sunlight) can also be used but should be formulated to remain intact for at least 45 to 50 days; such mulches can considerably reduce plastic removal and disposal costs. Bed shapers/plastic mulch layers and waterwheel setters are commercially available to make raised beds, lay plastic and drip lines, and to aid in transplanting. Single plants are usually spaced 18 inches apart in the rows on plastic; some growers use two plants per hill spaced 3 feet apart in the row. A fine, well-prepared seedbed is essential before plastic is laid down. For small plantings, transplants can be planted through plastic by making holes with a bulb setter or similar device. Fertilizer is applied preplant and through the drip system (see next section).

It is crucial that plants be protected from cucumber beetle feeding from the day of seedling emergence or from the day of transplanting to reduce the risk of bacterial wilt disease (vectored by the beetles). The insecticide Admire has provided good early season systemic control of cucumber beetles on melons in Kentucky. This reduces the potential for bacterial wilt while the plants are small. Although several soil application methods may be used with this product, the post-transplant drench is recommended for best control: a small amount of the Admire solution is applied at the base of each plant immediately after transplanting. With proper calibration, this can be done quickly and accurately using a backpack sprayer with the nozzle removed (see the "Insect Control" table and current label for recommended rates). It is strongly recommended that Admire not be used in the setter tank water because of the potential for worker exposure during transplanting.

Since male and female flowers are separated on the same plant, growers with large acreage should provide one to two hives of bees for each acre of plants to ensure good pollination. Spraying for insect control should be done late in the day to avoid unnecessary bee kill.

Recommended Cantaloupe Varieties


Cultural Practices Reported by Growers

Commercial melon growers were surveyed in the spring of 2002 to obtain information on production practices that are being used on farm. There were 35 completed and usable surveys from melon growers. Melons are commonly grown by Amish and Mennonite growers in Kentucky, and two of the three grower groups that were surveyed represented these groups.


Survey question Answer Percent responding
Do you grow your own transplants? (35) Yes

No

80.0
20.0
When do you begin to germinate your seeds? (28) March 20
March 25
April 1
April 10
April 15
April 24
10.7
7.1
32.1
32.1
14.3
3.6
Do you use raised beds? (35) Yes
No
17.2
82.8
Do you cover the beds with plastic? (35) Yes
No
91.4
8.6
Do you use trickle irrigation? (35) Yes
No
57.1
42.9
What melon varieties do you grow? (35) Athena
Eclipse
Minerva
Aphrodite
RML 8793
Jubalee
94.3
28.6
17.2
8.6
2.9
2.9
How many melon plants per acre? (35) 1500
1900
2000
2250
2500
3000
3600
4200
2.9
2.9
42.9
2.9
28.6
2.9
8.6
2.9
What are the spacings between plants/rows? (35) 32"/2'
18"/4'
30"/6'
32"/5'
28"/3'
30"/4'
20"/5'
3'/6'
2'/6'
1.5'/6'
2.9
2.9
14.3
2.9
2.9
2.9
2.9
54.3
8.6
2.9
When do you begin transplanting melons? (35) April 20
May 1
May 5
May 10
May 15
May 30
11.4
22.9
14.3
31.4
8.6
2.9

Sequential transplanting, at 10 day to three week intervals, were used by 77% of the growers to spread harvest dates. Growers used between 2 and 5 sequential planting dates.


Worker Activities

Much of the Kentucky melon and watermelon crop is produced by Mennonite and Amish growers. The culture of these communities strongly affects the manner in which these crops are managed. There is a strong emphasis to use little to no mechanization and rely on farm animals and families for labor to raise the crop.

Land Preparation

Growers using tractors to cultivate will generally use open cab tractors, while Mennonite and Amish producers use team-driven equipment to prepare the soil. Growers will cultivate the soil and most will then lay drip irrigation and plastic before setting transplants.

Planting Method

All of the crop is transplanted from the greenhouse to the field. Generally, four-week old, greenhouse-grown transplants, are used. Many growers use waterwheel setters, some use carousel tobacco setters. Either of these two systems can be used with tractors or horse-driven equipment. Transplants are grown in plastic or styrofoam trays which are used to transport plants to the field. Plants are removed by hand from the trays and either placed directly into the ground (waterwheel setter) or placed into the carousel setter. No hand thinning of plants is needed, although some growers may replace plants by hand that did not establish.

Irrigation

Most of the crop is drip irrigated as indicated in the table above. T-tape is placed beneath the plastic crop cover during land preparation, prior to transplanting. Some use municipal water, others use well, stream, or pond water. As the crop matures, the need for irrigation increases.

Cultivation

As indicated in the weed control table, on average growers will cultivate four times for weed control. Most growers are not using pre-emergent herbicides for weed control. Mennonite and Amish growers rely heavily on hoeing and hand weeding by family members. This may require as many as four to eight trips through the field with the equivalent of one to eight 8-hour days required for each pass. This may comprise half of the melon acreage in Kentucky.

Pest Monitoring

This is done by the grower or family member once or twice per week. Most use fungicides on a regular-scheduled basis, but use post-emergent herbicides and foliar insecticides on an as-needed basis.

Pesticide Applications

About half of the applications are made with tractor mounted equipment. Many of the tractors are open cab. Many growers are using backpack sprayers as well. Aerial applications are not used for melons in Kentucky. The grower generally does the mixing, loading and application.

Harvest

The crop will be harvested two to four times per week for three to four weeks. The entire crop is hand harvested, however, there is minimal post-harvest handling.



Insect Pests

The most common insect problems are cucumber beetles, squash bugs, aphids, and spider mites. As melon cultivars are susceptible to bacterial wilt, cucumber beetle control must begin as soon as plants emerge. A newly recognized disease of cucurbits, yellow vine decline, is persistently vectored by squash bugs. This has changed the pest status of squash bugs and has resulted in an increased need for early and effective control of squash bugs.


Squash Bug
Anasa tristis

While, squash bug is a common pest of melons, it prefers other cucurbit crops, pumpkins and squashes, over melons. This insect can be very difficult to control. Squash bugs damage plants by removing sap, causing leaves to wilt and collapse. Young plants and infested leaves on older plants may be killed.

Only unmated adults overwinter in Kentucky with flight into fields beginning about the time the plants begin to run. They remove plant sap with their piercing-sucking mouth parts. Squash bugs do not lay eggs in melon crops to the extent they do in squashes and pumpkins, so the nymphs are not common. Squash bugs spend most of their time around the base and stems of the plants and on the undersides of leaves, they are common underneath the plastic used to cover the beds. There is a single generation per year in Kentucky.

Transmission of Yellow Vine Decline Agent

During the summer of 2001, a new disease of cucurbits was identified in central Kentucky, yellow vine decline. The disease was widespread throughout Kentucky in 2002. It is likely that this disease had been present for some time, but not recognized. The causal agent of the disease is persistently vectored by squash bugs. As with other persistent insect-disease relationships, control of the disease is dependent on control of the insect vector. This has changed the pest status of squash bug in melons from an occasional pest to a key pest and disease vector.

Controls

Monitoring

Timing is the key to successful squash bug control and control of yellow vine decline. Insecticide sprays should target adults at transplanting. Research at the University of Kentucky indicates that transmission of the bacteria that causes yellow vine decline occurs either before or shortly after transplanting. Growers must ensure that squash bugs are not able to feed on seedlings prior to transplanting.

Application Alternatives Used in Kentucky


Cucumber Beetles
Acalymma vittatum, Diabrotica undecimpunctata

Striped and spotted cucumber beetles can cause serious losses in melons. Cucumber beetles are a major concern because they vector the pathogen that causes bacterial wilt of cucurbits. While the adults feed mainly on foliage, pollen and flowers, their feeding on melon rinds just prior to harvest reduces market quality. Larvae of these insects feed on roots and stems, but this damage is minimal compared to the potential losses due to bacterial wilt.

Cucumber beetles overwinter as adults in protected areas near buildings, in fence rows, or wood lots. They become active in mid-spring, when temperatures begin to increase. Currently, there is no good method for predicting when activity will begin. Beetles quickly locate host plants in the spring. The adults feed and females deposit eggs in cracks in the soil at the base of plants. The eggs hatch and the larvae feed on the roots. These larvae will pupate in the soil, later in the summer the next generation of beetles will emerge. These beetles will also feed on melon fruit and overwinter until the next spring.

Transmission of Bacterial Wilt Agent

The bacterium that causes bacterial wilt overwinters in the gut of some of the striped and spotted cucumber beetles. When beetles become active in the spring and begin feeding, they spread the bacterium either through their feces or from contaminated mouthparts.

Chewing damage on young leaves or cotyledons open entry points for the pathogen. Once inside the plant, the bacterium multiplies quickly in the vascular system, producing blockages that cause the leaves to wilt. Beetles are attracted to infected plants and can pick up the bacterium and move it to healthy plants.

The first symptom of bacterial wilt on melon is a distinct flagging of lateral and individual leaves. Beetle feeding is not always obvious on wilted leaves. Soon, adjacent leaves and finally the entire vine will wilt. The wilting spreads as the multiplying bacteria move within the vascular system of the plant. Eventually, the entire plant wilts and dies. Cantaloupes are very susceptible to losses by this disease.

Controls

Application Alternatives Used in Kentucky


Melon Aphids
Aphis gossypii Glover

Melon aphid is an infrequent, secondary, indirect pest of melons in Kentucky. While melon aphid can be found in virtually all fields, in most fields and years densities are below economic levels due to the beneficial action of predators and parasitoids. Melon aphid is a sucking pest that removes sap from leaves and vine terminals. Excessive aphid levels can stunt plants, reduce melon yield and quality, and produce large amounts of honeydew. Honeydew and the resulting sooty mold reduces the appearance of melons. Prolonged use of some broad-spectrum insecticides can deplete the natural enemies of melon aphid and foster rapid aphid population increases.

Various winged aphids can vector a group of viruses that infect melons. These viruses are common in some years and are more prevalent with late plantings, as winged aphid activity generally increases and the season progresses. Good aphid control helps to reduce secondary spread.

Control

Application Alternatives Used in Kentucky


Two Spotted Spider Mites
Tetranychus urticae

Two-spotted spider mites are occasional pests that can cause serious damage to some vegetable crops during hot dry weather. Mites can injure tomatoes, beans, muskmelons, watermelons, and sweet corn. Extended periods of hot, dry weather favors mite buildups. Infestations usually first occur at the edge of a field, typically near rank weed growth or dirt roads. Generally mites feed on the undersides of leaves. They use their sucking mouthparts to remove sap from plants, giving the upper leaf surface a speckled or mottled appearance. Leaves of mite infested plants may turn yellow and dry up, and plants may lose vigor and die when infestations are severe. The undersides of affected leaves appear tan or yellow and have a crusty texture. Heavy infestations of the two-spotted spider mite produce fine webbing which may cover the entire plant.

Controls

Monitoring: Mites can be identified by shaking symptomatic leaves onto a sheet of white paper or by observing infected leaf areas with a hand lens. Mites can easily be moved to infested plants on clothing, so always examine infested last during inspections.

Application Alternatives Used in Kentucky

When possible, select pesticides for other pests which will have the least impact on beneficial insects.

Insect Management Practices Reported by Growers

Survey question (responses) Answer Percent responding
What are your major insect pests? (34) Cucumber beetles
Squash bug
Aphids
Wireworms
Spider mites
91.2
14.7
11.7
2.9
2.9
How do you monitor for insect pests? (34) Scout field
Spray
73.5
26.5
How often do you monitor fields? (33) Daily

Twice a week
Weekly
Every other week
Occasionally
12.0
27.3
42.4
3.0
9.1
Do you use insecticides during transplant production? (32) Yes


No
15.6
84.4
What insecticide do you use during transplant production? (5) Pounce
Sevin
80.0


20.0
Do you use insecticides during or just after transplanting? (34) Yes

No

94.1
5.9
What insecticides are used during or just after transplanting? (34) Admire
Asana
Diazinon
Endosulfan
Furadan
Pounce
Sevin
65.6
6.3
3.1
3.1
3.1
21.9
3.1
How many insecticide applications are used prior to harvest, including those used at transplanting? (35) 3
4
5
6
7
8
10
5.7
22.9
25.7
22.9
14.3
5.7
2.9
Which insecticides are used? (35) Admire
Asana
Malathion
Pounce
Sevin
Thiodan
Capture
28.6
40.0
5.7
85.7
48.6
8.6
8.6
What is the interval between insecticide applications? (35) Weekly
7 to 10 days
10 days
2 weeks
As needed
68.6
22.8
2.9
2.9
2.9
How do you decide when to apply an insecticide? (33) When insects seen
According to schedule
45.4
54.5
When is the last insecticide application made prior to harvest? (30) 0 days
1 day
2 days
3-4 days
5 days
1 week
According to label
Not necessary
13.3
10.0
3.3
3.3
3.3
33.3
30.0
3.3
Which insecticide is used close to harvest? (31) Asana
Pounce
Sevin
3.2
83.9
25.8
Are insecticides used once the harvest period has begun? (30) Yes
No
90.0
10.0
What insecticides are used once harvesting has begun? (28) Asana
Pounce
Sevin
3.6
89.3
14.3



Weeds

As with many other Kentucky crops, weed control in melons presents an ongoing management problem. For economy and efficiency, melon growers should view weed pests as a complex. Specific plant pests which interfere with melon production are both diverse and unpredictable. A specific plant or two may present more of a challenge for a period of time only to be replaced by another dominant pest or a mixture of weeds with individually low populations.

Overall, thinking in terms of creating a good field management history is central to making decisions about addressing the weed population presented during any specific year. Melon production needs to be supported by a balance involving intelligent cultural practices and modest chemical weed control practices.

Beyond the obvious issue of pest presence, a farmer's decisions are strongly impacted by costs. Many farmers, knowing that they can neither afford to apply herbicides for each and every significant plant pest nor expect weed free fields, are strongly impacted by manufacturer's marketing strategies.


Common Weeds in Kentucky Melons:
(Common Name, Scientific Name, Life Cycle)

Monocots: Grasses and Grass-like Plants

Dicots: Broadleaf Plants

* A = annual and P = perennial


Controls

Application Alternatives Used in Kentucky

Weed Management Practices Reported by Growers

Survey question (responses) Answer Percent responding
Do you monitor for weeds? (35) Always
Usually
Sometimes
85.7
9.1
4.5
Do you cultivate for weeds? (35) Always
Usually
Sometimes
Seldomly
54.3
25.7
11.4
2.9
Number of cultivation passes for weed control? (35) 1
2
3
2 or 3
4
6
Weekly
As needed
5.7
14.3
14.3
17.1
22.9
11.4
11.4
2.9
Do you use herbicides for weed control? (35) Yes
No
42.9
57.1
Which pre-emergent herbicides are used prior to transplanting? (35) None 100.0
Which pre-emergent herbicides are used after transplanting? (35) None
Curbit
Command
91.4
5.7
2.9
Which post-emergent herbicides are used prior to transplanting? (35) None
Roundup
Poast
Gramoxone
80.0
14.3
5.7
5.7
Which post-emergent herbicides are used after transplanting? (35) None
Roundup
71.4
28.6
List your top five problem weeds for melon production. (35) Pigweeds
Lambsquarter Johnsongrass
Crabgrass
Ragweed
Cockleburr
Nutsedge
Nightshade
Foxtail
Jimsonweed
Prickly sida
Fall panicum
Smartweed
Bindweed
Horsenettle
74.3
48.6
60.0
25.7
14.3
14.3
11.4
8.6
5.7
5.7
5.7
2.9
2.9
2.9
2.9



Diseases

Field selection, crop rotation, sanitation, resistant varieties, seed treatment, and fungicide use are important disease control practices with melons. Select fields with good soil and air drainage and those that have not been used during the past three years for any cucurbit crop, tobacco, peppers, or tomatoes. Bacterial wilt and yellow vine control is critical in Kentucky. An abundance of healthy leaves through the harvest period should be an important objective in muskmelon production because these leaves are needed during ripening to produce quality fruit. Fungicides need to be applied timely and with excellent coverage. Fungicide options need to be carefully considered with the labeling of new fungicides, strobilurins (Flint and Quadris), and Nova. Kentucky growers can also benefit from the Botany and Plant Pathology Department at Purdue University, which has an excellent research program on diseases of muskmelons. Much of this work is conducted in southern Indiana. Their expertise and findings have been drawn upon in the preparation of this section. They offer an excellent publication on diseases of melons (Diseases and Pests of Muskmelons and Watermelons, bulletin BP44, $15.00) available from Agric. Communications Service, Media Distribution Center, 301 South 2nd St., Lafayette, IN 47901-1232.


Alternaria Leaf Blight
Alternaria cucumerina

This disease usually starts as yellow spots on the older leaves near the crown; these spots subsequently become brown, circular, and usually have concentric rings. This disease can cause extensive damage to melon crops, especially during wet weather on vines with heavy fruit loads as the leaves roll and die leaving the fruit exposed. Failure to control this disease is directly linked to poor melon flavor/quality.

Cultural: This pathogen survives on crop debris so crop rotation to non-cucurbits for 3 or more years significantly reduces the disease potential by eliminating most of the primary inoculum. Because this pathogen is apparently also seedborne at low levels and can produce much secondary inoculum, fungicides are usually still needed in Kentucky even with rotation during normal and wet seasons.

Monitoring: Start scouting as vines begin to run and check weekly.

Application Alternatives Used in Kentucky: Start sprays with the initial appearance of symptoms or preventively by initiating sprays when vines first touch within the row (even if the disease is not detected) if rotation intervals are not followed. Regular fungicide applications (at 7 to 10 day intervals) are needed to delay the onset of disease and slow development.

Use chlorothalonil (2 to 3 pts/A for flowable formulations or 1.5 to 2.5 lbs/A for dry formulations WP, DF, or DG), Mancozeb (2 to 3 lbs/A for dry formulations or 2 to 3 pts/A for flowables), or Quadris at 11 to 15 oz/A. The availability of Quadris adds a most valuable tool in battling Alternaria, but this new fungicide must be alternated with either chlorothalonil or mancozeb to manage fungicide resistance-check the label carefully.


Angular Leaf Spot
Pseudomonas syringaep.v. cachrymans

This bacterial disease is usually a minor problem on muskmelon in Kentucky, but some locations with red clay soils have damaging levels, especially if either potassium levels are low or manganese toxicity (acid soils) is present.

Lesions first develop as small water-soaked spots on leaves. With angular leaf spot, the lesions become angular and irregular in shape and size as they contact the veins, while others are more circular. Under wet conditions the lesions later develop a white to gray crust, turn brownish, and often drop out leaving a tattered appearance. Petioles, stems and fruits are also affected. These pathogens are seedborne, persist in crop residues, and can be spread rapidly by natural and mechanical means during wet weather. The causal agents are bacteria, and as with most bacterial diseases, a comprehensive management program is needed. No single control measure is adequate in wet seasons.

Cultural: Use disease-free seed (hot water, acid, or bleach treatments) and crop rotations of 2 or 3 years with non-cucurbits, if weedy cucurbits-including volunteers- are controlled. Severity is enhanced with high nitrogen and low potassium levels. Once active, the bacteria are easily spread while working the vines during wet periods, so work crops only when they are dry. Increased incidences of this disease have been noticed at times when air blast sprayers are used on cucurbits, probably because the sprays are being made while the foliage is wet and copper was not in the spray program. It is important to slow early outbreaks, but spray materials sometimes cause a marginal leaf burn or yellowing of the leaves.

Application Alternatives Used in Kentucky: At first evidence of this disease, include a fixed copper (Champion WP or Kocide DF at 2 to 3 lbs/A, or Citcop 5E at 3 pts, for example) and keep copper in the spray program or alternate with fungicides (to control fungal diseases) until dry weather has lasted for two weeks. Mixing coppers and mancozeb (used for fungal diseases) will improve control of bacterial leaf spots. Resistant cultivars are not available, but muskmelons have considerable tolerance, especially as the plants age.


Anthracnose
Colletotrichum orbiculare

On muskmelons, anthracnose causes sunken lesions/spots (with a pink-red ooze upon reproduction of the pathogen) on fruit, stems, petioles, and leaves. The lesions darken with age. This disease persists on seed and crop residues.

Cultural: Rotate to unrelated crops for 2 or more years. Use western-grown, disease free seed. Clean up cucurbit fields at the end of the growing season by removing and destroying or plowing under crop debris.

Application Alternatives Used in Kentucky:Scout crops regularly for this disease and begin fungicide sprays when the first symptoms appear or as a preventive measure no later than when vines touch within the rows. The fungicide options are the same as those listed under Alternaria Leaf Blight.


Damping Off and Seedling Rots
Pythium

Pythium is a major problem in floatbed produced transplants.

Cultural: Buy treated seed or treat with thiram (about 0.5 tsp/lb of seed). Planting into warm, well-drained soils greatly reduces the risk of seedling death.

Application Alternatives Used in Kentucky:


Bacterial Wilt
Erwinia tracheiphila

Bacterial wilt is the most serious disease threat to muskmelon production in Kentucky, but marked improvement in the control potential is now available. Sudden wilting of individual runners or the whole plant is typical of this disease. A diagnostic tip is to cut wilted runners near the crown and squeeze sap from the newly cut stem. If a white exudate is present, touch a knife blade to it. If you are able to slowly string out the material, it's a strong indication that bacterial wilt is present. Unfortunately, by this time it is too late to control the disease for that particular crop.

The bacterium causing this wilt overwinters in and is carried (vectored) by cucumber beetles so that the disease is especially serious following mild winters. When beetles begin feeding in the spring, they spread the bacteria either through their feces or from contaminated mouth parts. Beetles feeding on young leaves or cotyledons open entry points for the pathogen. In order to control bacterial wilt, it is essential to control these insects before they feed on the plant, starting from the day of plant emergence through fruit set. Once the bacterium has been introduced into the plant, no control is known. Beetles are attracted to infected plants and can pick up the bacterium and move it to healthy plants. Use appropriate insecticides (see insect control section). The Admire insecticide program (post-transplant drench method) has greatly improved the control of this disease in Kentucky.

Cultural: Plant late on land which has been plowed early in the spring or in the fall and cultivate frequently before planting so that all vegetation has been kept down.

Monitoring: Begin monitoring for cucumber beetles as soon as seedlings emerge. There is usually a peak in beetle activity each spring that lasts two to four weeks. This is the most important time to control the beetles. Early control and effective control of the beetles is needed to manage bacterial wilt.

Application Alternatives Used in Kentucky: See insect control section


Gummy Stem Blight
Didymella bryoniae

Gummy stem blight has been increasing in importance in Kentucky, especially during the hottest weather. Greenhouse produced transplants have been involved in some very serious outbreaks. It first occurs as a leaf disease, usually as water-soaked spots that turn to dark brown areas, often concentrated at the leaf margins and appearing as a marginal burn to only a portion of the leaf. Stem cankers also occur as cracks on the stems with gummy ooze.

Cultural: Use disease-free seed and clean, uncontaminated trays for transplant production. Plant into land that has not been planted with cucurbits for more than 3 years. Plant western-grown certified seed.

Application Alternatives Used in Kentucky: Waiting until the disease is evident before starting fungicide sprays usually does not work if there has been a history of cucurbits on the site. Start preventive sprays when vines begin to touch in rows or earlier at the very first indication of symptoms. See Alternaria Leaf Blight section for fungicides and rates. In addition, adding Topsin M at 0.5 lbs/A to chlorothalonil or mancozeb/maneb will significantly improve control of gummy stem blight if benzimidazole resistance is not present, but Topsin M alone will not provide adequate control. Fungicide sprays should be maintained starting with vining and continued until harvest.

Quadris is highly effective against gummy stem blight and will be especially valuable if benzimidazole resistant strains are present, but the potential for resistance is high and already reported in the south, so follow the labels closely concerning resistance management with this product.


Downy Mildew
Pseudoperonospra cubensis

Initial symptoms are light green, irregular shaped spots or areas on the leaf, sometimes confused with virus infections. In time, downy mildew lesions turn yellow to brown, remain irregular shaped and bounded by the veins, with a blue to gray mold usually present under moist conditions. The disease is usually found first on the center (older) leaves of the vine. This disease is closely related to tobacco blue mold so it has potential for rapid spread with a short incubation period that yields massive loads of wind blown spores. Because of the difference in leaf hairs between the two crops, downy mildew sporulation is not as obvious on cucurbits as it is with tobacco. Another important difference is that the cucurbit pathogen also produces swimming spores in dew drops, so once active in the planting, it can destroy a crop more quickly than tobacco blue mold; these swimming spore spread to all parts of the plant under wet conditions.

Downy mildew appears erratically in Kentucky but can be quite damaging, especially during and following prolonged cool, wet weather in the late summer and fall.

Cultural: Most varieties popular in Kentucky are susceptible, but resistance is available. Rotate 2 to 3 years after outbreaks and control volunteer cucurbits in the rotation.

Monitoring: Watch for advisories (see the Kentucky Blue Mold Warning System web page at <http://www.uky.edu/Agriculture/kpn/kyblue/kyblue.htm> for updates on this downy mildew). Tobacco blue mold (which is downy mildew of tobacco) advisories in the area are a good indication that conditions also favor downy mildew development on other crops. These advisories can be especially helpful in alerting one about possible outbreaks occurring before mid August, but they have limited value later because the tobacco crop is far enough along that few of the blue mold advisories are reported locally. The Kentucky Blue Mold Warning System in now linked to a national effort to forecast downy mildew outbreaks in cucurbits.

Application Alternatives Used in Kentucky: If chlorothalonil, mancozeb, or coppers are being used in protectant sprays against anthracnose, leaf spot, or gummy stem blight, expect significant protection against downy mildew. Continue with them but alternate weekly with one of the materials in the 14-day program below. For example, if you have been spraying mancozeb weekly, and Flouronil is started on a 14-day interval with the appearance of downy, continue to make mancozeb applications a week after the Flouronil spray. This is a key point in keeping other diseases under control.

Under serious downy mildew pressure, apply (at 14 day intervals) mefenoxam+chlorothalonil (sold as Ridomil GoldBravo or Flouronil) or Ridomil Gold Copper 2.0 lbs/A. Aliette 80 WDG at 3.0 lbs/A and Ridomil Gold MZ at 2.5 lbs/A are also labeled. The strobilurin-fungicides (Flint at 4 oz/A and Quadris at 11 to 15 oz/A) are now labeled for mildew control on this cucurbit crop when alternated with one of the above effective products. These can be expected to provide a high level of control although consideration should also be given to cost, fungicide resistance management, and improved pesticide safety.


Fusarium Wilt
Fusarium oxysporum f. sp. melonis

This wilt is caused by a soilborne fungus. Preliminary data indicate that race 2 is common in Kentucky, but other races may also be present. Fusarium wilt is characterized by stunting, yellowing, and a slow death-not the sudden wilting caused by bacterial wilt. A diagnostic tip is that with Fusarium wilt, water-soaked to dark brown streaks usually develop at the soil line on the side of the plant most affected. Cuts made into the stem should reveal a brown discoloration of the vascular system if Fusarium wilt is the problem.

Cultural: Resistant varieties offer the best control. Use those with resistance to Race 2 on sites with a history of the disease; if these varieties also contract Fusarium wilt, consider varieties with resistance to other races. For example, Athena has resistance to races 1, 2, and 3. Although this specific Fusarium infects only Cucumis melo (muskmelons, cantaloupe, crenshaw, and honeydews), it may survive in the root zone of nonhost cucurbits. Rotation to crops other than melons for 3 years (5 years if the disease is known to be present on the site) should help reduce buildup of the disease. Rotation alone is not an adequate control

Application Alternatives Used in Kentucky: Fungicide sprays with materials effective against the fungus have not proven adequate; this is probably related to inadequate coverage of the fruit. Taking steps to control insects and other diseases during production and until harvest and is suggested.


Root Knot Nematode
Meliodogyne spp.

Root Knot Nematode is very damaging to muskmelons and results in stunting and root galling. This has been especially common where melons follow tobacco without rotation. Tobacco under Kentucky conditions can support a high nematode population before serious damage occurs, while melons sustain major damage with small populations.

Cultural: Rotation with small grains and grasses (especially tall fescue) has long been the primary control in Kentucky, and proper rotation remains an excellent option. Control of broadleaf weeds and volunteer crops must be included for the rotation to be effective, since the nematodes of most concern have a wide host range. Fortunately, nematodes decline rapidly without a host. Reduced income from the site during the rotation is the primary disadvantage. Endophyte-infected tall fescue is recommended as the rotational tool of choice in management of nematodes. This recommendation stems from the fact that most of the work in Kentucky on rotation was done with Ky 31 and related fescues that were endophyte-infected at the time of the studies. We do not have proof that other fescues (with or without the endophyte) are equally effective. In one preliminary evaluation the data showed that populations of plant parasitic nematodes were reduced faster with endophyte-infected fescue (Ky 31) than with endophyte-free fescue (Johnstone) or other grass species (orchardgrass and ryegrass). However, no differences in vegetable crop performance after the two-year rotation were detected among the rotational grasses.

Management of the field immediately after harvest is an important step in nematode control. Prompt crop destruction after harvest and replanting with a non-host cover crop prevents further increases in the nematode population and even traps some nematodes in the middle of their reproductive cycle. Some cover crops are naturally suppressive to some nematode species, although no single crop will control all. Non-host cover crops suppress nematodes by starving them and preventing reproduction. Antagonistic crops (French marigolds or certain rapeseed crops) suppress through direct toxic effects to the nematodes. Cover crops that are hosts of the nematode can be, with care, used to trap and reduce nematode populations by destroying the host plant (cover crops) before the nematode can reach a reproductive life stage from which it can survive to the next crop. Timing with trap crops is critical, because even more serious problems exist when crop destruction is delayed until after nematodes have reproduced. In general, the introduction of large amounts of organic matter in the soil is suppressive to plant parasitic nematodes. As the plant material decomposes, toxic chemicals are released that will damage nematodes and certain plants (organic matter toxicity). Maximum benefit is achieved when large amounts of organic matter are incorporated as green manure; however, sufficient time must be allowed for adequate decomposition to avoid crop damage.

Application Alternatives Used in Kentucky: Vydate L at 1 to 2 gallons/A applied broadcast and incorporated 2 to 4 inches deep 14 to 21 days prior to transplanting can be helpful, but it is not an equal substitute to fumigation.


Powdery Mildew
Erysiphi cichoracearum and Sphaerothecia fuliginae

Powdery mildew affects the crown leaves first, occurring as white, powdery mold on the leaf surface followed by withering and death. The powdery mildew pathogen is airborne from outside the planting initially but then spreads quickly on air currents within the planting. It occurs in Kentucky from mid July until the end of the season; earlier outbreaks are most always connected to using greenhouse-infected transplants.

Since two separate fungi (Erysiphi and Sphaerothecia) are involved in Kentucky, submit samples showing fresh lesions to the UK diagnostic labs for identification of the fungus involved.

Cultural: Control weeds near fields and gardens to help reduce the overwintering population of the powdery mildew fungus. Powdery mildew resistant muskmelon cultivars with acceptable yield and quality are now available and their use is strongly encouraged. Mildew is especially serious in Kentucky on late summer/fall plantings, so resistant varieties are highly recommended for late plantings.

Monitoring: Poor spray coverage and poor timing of fungicide applications are the major reasons this is such an important disease in Kentucky. Plantings should be scouted for the first signs and symptoms of powdery mildew at least weekly starting in mid-July. With the first evidence of powdery mildew (usually late July or early August), initiate a more aggressive and effective fungicide program.

Application Alternatives Used in Kentucky: Chlorothalonil or coppers used for other diseases will also significantly suppress powdery mildew, but mancozeb and maneb are not effective. Other narrow-spectrum, non-systemic, but effective powdery mildew materials are: AQ10, mineral oils, Nutrol, Armicarb 100, and sulfur. Sulfur is highly effective but may cause crop damage in hot/humid periods; do not apply if temperatures exceed 90F.

A major problem with controlling powdery mildew is the need to have the material on both the bottom and top of the leaf surface. Excellent coverage is needed with all these materials. Superior control can be achieved by tank mixing Nova 40WP at 2.5 oz/A with a chlorothalonil-containing material; this mixture is applied on a 7-day schedule. This combination is alternated with a strobilurin-containing fungicide (Flint at 4 oz/A or Quadris at 11 to 15 oz/A). These fungicides can be expected to provide a high level of control although consideration should also be given to cost, fungicide resistance management, and improved pesticide safety. Topsin M at 0.5 lb/A tank mixed with chlorothalonil also gives excellent control.

These are effective when applied at the first appearance of symptoms (repeated as needed) and if resistant strains of the fungus are not present. If one fungicide is not effective, and it is being applied correctly, switch immediately to a new class of chemicals. If you grow other cucurbits, appreciate that failure to control powdery mildew on early melon crops can lead to earlier and more serious mildew problems on later cucurbits, especially pumpkin. Strains of this pathogen resistant to Reach (triadimefon) and Benlate and Topsin (benzimidazoles) have been confirmed in Kentucky with triadimefon resistance being very common.


Virus Complex

A variety of viruses (Cucumber Mosaic, Watermelon Mosaic, Papaya Ring Spot, and Zucchini Yellows Mosaic) are common and often severe in some years in Kentucky. Serious damage has usually been limited to late plantings, especially on truck farms using sequential plantings of cucurbits. These viruses overwinter in perennial weeds and are spread into melon plantings by aphids.

Cultural: Elimination of perennial weeds within 150 ft of the planting by using grasses or nonsusceptible annual crops around the melon planting is helpful. Maintaining good aphid control helps to reduce secondary spread from within the planting only. Planting melons adjacent to earlier cucurbit plantings presents a high risk situation. Where practical, also avoid planting adjacent to peppers, tomatoes, and tobacco as these host some of the same viruses. Aphids are excellent vectors of some of these viruses and can easily transfer them from one crop to the other.


Yellow Vine Decline
Serratia marcescens

Yellow Vine Decline of Cucurbits is a new disease. During the past decade, a disease causing yellowing and sudden decline of vines has been recognized in cucurbits, especially those planted early in the season on plastic mulch. The disease was initially reported from Texas and Oklahoma, but other states south and west of Kentucky have also reported it. Symptoms are variable depending on plant age and include the following: Affected young fast growing plants may suddenly collapse without yellowing while older plants develop striking yellow vines and decline slowly as the fruit approach maturity. Phloem tissues in the primary root and crown develop a distinct honey-brown discoloration. The roots and lower stems of such plants are quickly colonized by a number of microbes that help finish the kill, and these secondary invaders have complicated the diagnostic efforts.

It is now known that the causal agent is a bacterium, Serratia marcescens, and it appears to survive in, and be vectored into the cucurbit plants by the squash bug, Anasa tristis. Although this bacterium has strains that are human pathogens, preliminary research indicates cucurbit strains are not human pathogens. Any relationship to human pathogens, however, is enough to raise some red flags.

Cultural Control: Destruction of crop residues immediately after harvest is complete will disrupt the feeding of squash bugs nymphs and limit the number that become adults and are able to overwinter.

Application Alternatives Used in Kentucky: Control is based on preventing squash bugs from feeding on the plants. Thorough, early control of squash bugs is needed. See insect controls for details.

Disease Management Practices Reported by Growers


Survey question (responses) Answer Percent responding
What are your major diseases? (31)
Gummy stem blight
Bacterial wilt
Powdery mildew
Alternaria
Anthracnose
Downy mildew
Yellow vine decline
Stem rot
Fusarium
Mosaic virus
25.8
54.8
16.1
29.0
9.7
9.7
6.4
3.2
3.2
3.2
Do you use fungicides for transplant production? (33) Yes
No
24.2
75.8
What fungicides do you use for transplant production? (35) Bravo
Ridomil
Quadris
Topsin
11.4
11.4
2.9
2.9
Do you use fungicides at transplanting or just afterward? (33) Yes
No
15.1
84.9
What fungicides do you use at transplanting or just afterward? (35) Ridomil
Bravo
2.9
11.4
How many fungicides applications made prior to harvest? (28) 3-4
4
4-5
5
5-6
6
6-8
6-10
8-9
8-10
weekly
14.3
14.3
10.7
3.6
3.6
14.3
14.3
2.9
2.9
7.1
10.7
What fungicides are used prior to harvest? (35) Bravo
Quadris
Copper
Ridomil
Benlate
Dithane
Terranil
Maneb
Topsin
94.3
54.2
22.8
11.4
8.6
11.4
11.4
2.9
2.9
How often are fungicides applied prior to harvest? (35) 7 days
7 - 10 days
7 - 14 days
14 days
57.1
34.3
2.9
5.7
How do you determine if and when to apply a fungicide? (35) Routine/schedule 100.0
Are fungicides used after the harvest period has begun? (35) Yes
No
62.9
37.1
What fungicides are used after the harvest period has begun? (33) Bravo
Copper
Quadris
60.0
5.7
5.7



Contacts

Dr. Ric Bessin
Extension Entomology
S225L Agricultural Science Building-North
University of Kentucky
Lexington, KY, 40546
Phone: (859) 257-7456
E-mail: rbessin@uky.edu

Dr. Brent Rowell
Extension Vegetable Specialist
N-308D Agricultural Science Building-North
University of Kentucky
Lexington, KY, 40546
Phone: (859) 257-3374
E-mail: browell@uky.edu

Dr. Bill Nesmith
Plant Pathology Vegetable Specialist
S307B Agricultural Science Building-North
University of Kentucky
Lexington, KY, 40546
Phone: (859) 257-3991
E-mail: wnesmith@uky.edu

Dr. R. Terry Jones
Extension Vegetable Specialist
University of Kentucky, Horticulture
130 Robinson Road
Jackson, KY 41339-9081
Phone: (859) 257-9511
E-mail: tjones@uky.edu

Lowell Sandell
Extension Specialist
Coordinator, Kentucky Pest Management Center
S225 Agricultural Science Building-North
University of Kentucky
Lexington, KY, 40546
Phone: (859) 257-6693
E-mail: lsandell@uky.edu



References

  1. Commercial Vegetable Crop Recommendations (2000-2001). ID-36: University of Kentucky Cooperative Extension Service.

  2. Cucurbit Diseases ID-91: University of Kentucky Cooperative Extension Service.

  3. Purdue University Center for New Crops and Plant Products. 1998. www.hort.purdue.edu/newcrop/cropmap

  4. 2001 Crop Protection Reference, C & P Press, 17th Edition.