Prepared: February 2005
*The Virginia Agricultural Statistics Service and the National Agriculture Statistics Service no longer reports on the general production or value of squash in Virginia.
In Virginia, there are many varieties* of summer squash available to growers. Variety selection depends on several factors such as market acceptability, yield, and horticultural characteristics. Crookneck (yellow) varieties recommended in Virginia include: Prelude II and Sundance. Straightneck (yellow) varieties include: Seneca Prolific, Lemondrop L, Multipik, Fortune, Superpik, Monet, Goldbar, and General Patton. Scallop varieties available include: Peter Pan (green), White Ruffles, and Sunburst (golden). Finally, zucchini types include: Zucchini Elite, Revenue, Independence II, Cashflow, Dividend, Milano, Select, Tigress, Seneca Zucchini, and Gold Rush. Because of virus pressure in the fall, only those varieties with virus resistance should be planted for the fall crop. These include Prelude II, Revenue, Independence II, Dividend, and Tigress.
* All summer squash varieties are hybrids. Varieties are listed by maturity within each type, earliest first.
Planting dates for transplants vary from April 15 in southern regions to June 1 in northern areas. Container-grown plants should be transplanted through plastic mulch when daily temperatures have reached 60°F. Early plantings should be protected from winds with hot caps, tents, row covers or windbreaks. Direct seeding occurs April 15 through August 15 in Virginia and usually 4-6 lb. of seed are needed per acre.
Mulching with plastic conserves moisture, increases soil temperature, and increases early total yield. Fumigated soil also aids in control of weeds and soilborne disease. Plastic and fumigant, metam-sodium (Vapam HL), should be applied on well-prepared planting beds 30 days before field planting. Fertilizer must be applied during bed preparation and the soil should be moist when laying the plastic. Clear plastic mulch is mainly only used on small acreage because weed control may be unsatisfactory even with the use of herbicides and fumigation. However, black plastic or paper can be used without a herbicide under the mulch. But weed control between the beds is essential. Foil mulches can be used to repel aphids that transmit cucumber mosaic virus in fall-planted (after July 1) squash. Direct seeding through the mulch is recommended for maximum virus protection. Transplants should not be used with foil or other repellent mulches. Fumigation will be necessary when there is a history of soilborne diseases in the field.
The recommended spacing for squash is 5-6 ft. apart with plants 2-3 ft. apart in the row.
Honeybees are important for proper fruit set and pollination. Populations of pollinating insects may be harmed by insecticides applied to flowers or weeds in bloom. Apply insecticides only in the evening hours, or wait until bloom is completed before application.
Summer squash usually takes 50 to 65 days to mature. Usually harvested by hand, squash should be harvested two to six days after blossom falls off, when the fruit are 6-8 inches long or 4-7 inches for crookneck varieties. At this point in its development, the squash is more tender as well as sweeter than at later stages. Squash should be harvested every other day to prevent fruit from getting too large on the vine and promote continuing flowering and fruit set. If the rind is too hard to be marked by the thumbnail, the fruit is too old. Remove the old fruit to allow new fruit to develop. When the squash is cut from the plant, 1-2 inches of the peduncle should be left on the fruit.5 Harvest dates typically range from the middle of June through October.
Worker Activities
During the growing season, worker activities in the field include direct seeding (April-August), transplanting (April-June), cultivating, irrigating, scouting, spraying, occasional hand weeding, and harvesting (June-October). Strictly following re-entry intervals (REIs) should minimize any risk of exposure to pesticides during these activities. If workers are required to go back in the field before the proper time limit has expired then personal protective equipment (PPE) is worn. Activities that bring workers in direct contact with the plants during the growing season are generally limited to harvest time because the fruit is hand-picked by the workers.
Special Use Labels
Section 18 Emergency Use Exemption and Special Local Need 24(c) labels are used to supplement the chemical tools available to producers for pest control. Once the problem or gap in pest control has been identified, specialists submit the proper documentation for the Emergency Use/Special Local Need label. Thus far, Extension specialists have been successful in obtaining these labels. Special Local Need (SLN) labels in Virginia are granted by the Virginia Department of Agriculture and Consumer Services (VDACS) and are usually only valid for limited time intervals. Section 18 Emergency Use labels are evaluated and granted by the Environmental Protection Agency (EPA) and can be renewed annually. Without these temporary use labels, pest control can be extremely difficult for producers.
Control recommendations found below were modified from information presented in the 2004 Commercial Vegetable Production Recommendations-Virginia6, unless otherwise noted.
INSECTS7
In general, cucumber beetles, pickleworms, squash bugs, and squash vine borers are the most economically important insect pests of squash in Virginia. Other important pests include: spider mites, which can be particularly devastating in hot, dry years, and aphids, especially after cool springs. Other minor pests include: seedcorn maggots, serpentine leafminers, cabbage loopers, and cutworms.
Aphids
Green Peach Aphid, Myzus
persicae
Melon Aphid, Aphis gossypii
Both the green peach aphid and the melon aphid are pests on squash. However, the latter is the primary species infesting squash plants in Virginia. In general, aphids feed on plant sap, which may reduce plant vigor, size, and yield. Also, as they feed on the underside of the leaves, aphids excrete honeydew. This, in turn, leads to the growth of black, sooty mold, which may block out sunlight and thus reduce plant yield. In addition, aphids can vector certain plant viruses. In particular, the melon aphid is instrumental in transmitting the cucumber mosaic virus, which can be devastating to squash production.
Monitoring: If a systemic insecticide such as imidacloprid or thiamethoxam is not applied at planting, then aphid scouting is recommended. Scouting for melon aphids should begin as soon as plants form runners. Examine two runners at five sites in the field. Record the number of runners with live aphids present. Treatment is recommended if more than 20% of runners have aphids.
Chemical Control: Systemic insecticides applied at planting are the best method of control. If foliar sprays are used, then thorough spray coverage beneath leaves is important. Treat seedlings every five to seven days or as needed. See the Chemical Insect Control section for more information.
Biological Control: A number of natural enemies such as lady beetles (adults and larvae), lacewing larvae, syrphid larvae, parasitic wasps, and fungal pathogens will reduce aphid populations. Natural enemies will often keep aphid populations below damaging numbers and, therefore, should be considered before making an insecticide application. However, if the spread of virus is of concern, chemical treatment will be necessary.
Cultural Control: Virus-resistant cultivars including transgenic varieties are commercially available and should be considered in the pest management decision-making process for aphids. Plant disease-free certified seed. Avoid planting fields immediately downwind of a barrier such as hedgerows or woodlots, which reduce wind velocity and increase the number of dispersing aphids falling into fields. These barriers can also cause overfertilization with nitrogen, which results in lush growth attractive to aphids.
Cabbage Looper, Trichoplusia ni
Cabbage loopers may be identified by their pale green color, thin white stripes down the back and sides, and by their doubling-up or looping as they move. These insects feed on the underside of leaves, producing ragged holes of various sizes. Feeding begins in late July or early August and usually continues through harvest. Healthy plants can usually sustain feeding injury unless populations become exceedingly large. Several generations can occur during a year. Loopers are not usually serious pests of squash in Virginia.
Monitoring: Check leaf-feeding levels in the field at least weekly. Healthy and older plants can usually withstand moderate defoliation before economic yield loss to the fruit occurs. Moth activity can be monitored at blacklight traps.
Chemical Control: See the Chemical Insect Control section for more information.
Biological Control: There are several parasitic wasps and predators that attack the cabbage looper. Also, a nuclear polyhedrosis virus (NPV) can substantially reduce population levels of larvae, especially after a period of precipitation.
Cultural Control: No current recommendations for commercial production.
Cucumber Beetles (Rindworms)
Spotted Cucumber
Beetle, Diabrotica undecimpunctata howardi
Striped Cucumber
Beetle, Acalymma vittata
Both the spotted and striped cucumber beetles (adults and larvae) may severely reduce squash productivity. These pests are the number one concern of growers in Virginia. Adults overwinter in wooded areas and fields, then migrate in the spring to cucurbit crops. Adults mass on plants and feed voraciously on the foliage and stems, often causing girdling, which will greatly reduce plant stands. Adults will also feed on the blossoms of developing plants, causing later scarring of the fruit8. Cucumber beetles also have the potential to transmit bacterial wilt.
In addition to the damage adult cucumber beetles cause, the larval stage, otherwise known as a rindworm, feeds directly on the roots and on the fruit as well. This feeding typically occurs at the bottom of the fruit where it comes in contact with the soil, rendering the squash unmarketable. Direct control of rindworms is difficult; however, management of adults (beetles) will reduce rindworm populations.
Monitoring: Scout twice a week, especially when plants have less than five leaves. At each of the five sites, scout five plants for beetles. Treat when an average of two beetles/plant are found.
Chemical Control: Cucumber beetles can transmit bacterial wilt and cause stand losses by direct feeding injury. If adult beetles are abundant and there is a history of disease problems, insecticides should be applied before beetles feed extensively on the cotyledons and first true leaves. If foliar insecticides are used, begin spraying shortly after plant emergence. Repeat applications at weekly intervals if new beetles continue to invade fields. To provide additional pest control, a Special Local Need 24(c) label has been approved in Virginia for the use of carbofuran (Furadan 4F) at planting. See the Chemical Insect Control section for more information.
Biological Control: No current recommendations for commercial production.
Cultural Control: Plant varieties resistant to bacterial wilt. Always cultivate the soil thoroughly before planting. The use of plastic or straw as bedding for the developing fruit may deter rindworm feeding. In the fall, eliminating surrounding weeds will reduce the overwintering sites for the beetles.
Cutworms
Black Cutworm, Agrotis
ipsilon
Variegated Cutworm, Peridroma
saucia
Granulate Cutworm, Feltia subterranea
Cutworms are sporadic pests of many crops. Several species of cutworm may be found in Virginia. Most are night feeders that hide under plant and soil debris common in weedy or minimum-tillage fields. Another distinguishing quality is their habit of rolling into a tight C-shape if disturbed. Newly hatched cutworm larvae feed on young plants at the soil line, often severing the stems. Later generations of cutworms feed on developing fruit and in severe cases may tunnel completely through the fruit. This greatly diminishes marketability.
Monitoring: Even if a preplant broadcast insecticide treatment is used, fields should be scouted for cutworm damage within a week of planting or plant emergence. Cutworms are not typically seen in the open during the day; however, digging in the soil around injured plants may reveal them. If cutworms are actively cutting plants, a postplant contact treatment may be used.
Chemical Control: See the Chemical Insect Control section for more information.
Biological Control: Cutworms are attacked by numerous ground-dwelling insect predators, especially carabid beetles. Also, pathogens such as Beauveria bassiana and entomopathogenic nematodes often will infect larvae.
Cultural Control: Proper tillage will help eliminate some species of cutworms that may move off of cover crops.
Leafminers
Serpentine Leafminer,
Liriomyza brassicae
Leafminers injure leaves primarily by mining the leaves, which results in the destruction of leaf mesophyll tissue. As the larvae hatch from eggs deposited within the leaf tissue, they create slender, winding white tunnels in their search for food. Mature larvae emerge from inside the leaf and drop to the soil, where they pupate in soil crevices or, in rare cases, the leaf. Leaf mining depresses the level of photosynthesis and may result in leaf droppage. Fewer leaves in the canopy can result in sun scalding of fruit. Many generations occur annually in Virginia, but the first is usually the most damaging.
Monitoring: The economic consequences of leaf mining are not well understood; thus, adequate scouting procedures have not been developed.
Chemical Control: See the Chemical Insect Control section for more information.
Biological Control: Parasitoids often provide excellent suppression of leafminers if broad-spectrum insecticides are not applied to the crop.
Cultural Control: No current recommendations for commercial production.
Pickleworm, Diaphania
nitidalis
Melonworm, Diaphania hyalinata
The melonworm is generally a foliage feeder (unlike the pickleworm, which attacks the developing leaf and flower buds) but also damages the vines and fruit. The adults overwinter in the warmer southern regions and begin to migrate north when temperatures warm. Females deposit eggs on the leaf surface, and the larvae emerge several days later, feeding on the flowers, vines, and fruit for up to two weeks. Several generations can occur during a year, allowing pickleworm and melonworm to be considered serious pests of squash in Virginia.
Monitoring: As soon as pickleworms or their damage appears, begin insecticide treatments.
Chemical Control: Make one treatment before fruit set, and then treat weekly. See the Chemical Insect Control section for more information.
Biological Control: No current recommendations for commercial production.
Cultural Control: After harvest, remove all debris from the field, destroy vines and unused fruit, and control adjoining weeds. Also, plowing early in the fall will bury the pupae. In the spring, planting early will help the crop establish itself, thus preventing major damage. Resistant varieties are also available.
Seedcorn Maggot, Hylemya platura
The seedcorn maggot is most noted for its damage to seeds or seedlings in bedding trays and early-planted fields, especially during cool, wet growing seasons. Adults emerge in early spring to lay their eggs, preferably in moist, organically rich soils, such as freshly plowed fields or greenhouse flats. Larvae or maggots hatch from the eggs and bore into seeds, cotyledons, or rotting crop debris. The maggots feed for one to three weeks before tunneling into the soil, where they pupate for about one to four weeks or for the duration of the winter. Multiple generations occur annually in Virginia.
Monitoring: Once seedcorn maggot damage has been observed, treatments are ineffective. Therefore, management options must be applied to high-risk fields before planting. High-risk fields can be defined as those having previous seedcorn maggot infestations or soils high in organic matter.
Chemical Control: Control is best achieved by using insecticide seed treatments such as chlorpyrifos (Lorsban SL) or diazinon (Agrox D-L Plus, Diazinon 50W, Germate Plus, Kernel Guard, or KickStart). The use of imidacloprid (Admire 2F) at planting will also reduce seedcorn maggot populations. See the Chemical Insect Control section for recommendations. Seed treatments containing malathion or lindane or seed commercially treated at low rates for seed storage will not control seed maggots. Do NOT use treated seed for food or feed.
Biological Control: No current recommendations for commercial production.
Cultural Control: Several management practices can be used to reduce the potential for damage resulting from seedcorn maggot infestations. These include plowing weeds or cover crops at least two weeks before planting or transplanting, avoiding overfertilization with manure, and completely plowing under crop debris immediately after harvest to eliminate plant remnants.
Squash Bug, Anasa tristis
Squash bugs destroy plant tissue by secreting a toxic saliva into the plant, sucking out the sap from the leaves and stems, which depletes nutrients from the plant. This feeding causes leaves to wilt and dry out. They eventually turn black and fall off the vine. Adults can be seen feeding on the main stems, but they also feed on leaves and fruit. Nymphs are more likely found feeding on the underside of the leaves. The adults are brown or black, flat-backed, and 1/2 to 3/4 inch long. Nymphs have gray-green bodies with red or black legs. Adults overwinter in garden debris and emerge the following spring to lay eggs. When the plants develop runners, elliptical brown eggs are laid in groups on the underside of the leaves.
Monitoring: All stages of plants may be attacked by squash bugs. If wilting is observed in a field, check the underside of leaves for egg masses, nymphs, or adults. Adults are often cryptic and hide in plant debris on the ground. A treatment is recommended if >1 egg mass or aggregation of nymphs is found per plant.
Chemical Control: Begin treatments if more than 1 egg mass per plant is present. Sprays should target nymphal stages. Note: Use of Metasystox-R for aphid control will reduce squash bug populations. See the Chemical Insect Control section for more information.
Biological Control: No current recommendations for commercial production.
Cultural Control: After harvest is complete, deep tillage or removal of crop residue will help to delay and/or reduce infestation the next spring. Since squash bugs like to hide in residue, mulching may increase squash bug pressure.
Squash Vine Borer, Melittia cucurbitae
The squash vine borer injures plants by tunneling through the stems. This interferes with nutrient transfer in the plant, eventually causing the plant to wilt. Borer feeding weakens plants, providing the opportunity for secondary infections. The larvae have a brown head, white body, and are rarely found outside of the vine. The adult moths may be mistaken for a wasp. The body is orange and black, often in a ringed pattern surrounding the abdomen. The squash vine borer overwinters as a pupa, and adults emerge in the spring to lay eggs.
Monitoring: There are no practical methods for direct sampling of adults or eggs in the field. Plants are checked for general vigor and other factors, and borer damage may be detected, but no regular monitoring is done specifically for this pest.
Chemical Control: When vines begin to run, apply to bases of plants four times at seven day intervals. Note: Use of SpinTor for looper control will reduce squash vine borer populations. See the Chemical Insect Control section for more information.
Biological Control: No current recommendations for commercial production.
Cultural Control: Proper cultural control may kill many overwintering pupae, reducing the following year's population. Soil should be disked after harvest, then plowed the following spring. Destroying vines after harvest prevents borers still in the larval stage from completing their development.
Thrips, Thrips tabaci
Thrips are small, slender insects, pale yellow to dark brown. The adult may be winged or wingless. When present, wings are narrow and fringed with long hairs. The larvae are wingless and may be green or yellow with red eyes. Both larvae and adults feed in the plants, causing silvering and sometimes deformation of the leaves; edges of the leaves tend to curl upward.
Monitoring: Yellow sticky cards can be used to monitor the incidence or timing of thrips entering fields; however, there are no current recommendations for commercial production.
Chemical Control: See the Chemical Insect Control section for more information.
Biological Control: No current recommendations for commercial production.
Cultural Control: Weed control and destruction of crop residues after harvest eliminates reservoir host plants and overwintering sites.
Two-Spotted Spider Mites, Tetranychus urticae
Spider mites can be a very serious pest of cucurbits. Typically, they feed on the undersides of leaves, often causing them to turn brown and fall off. Severe infestations, especially of smaller, stressed plants, may cause death. Mite infestations are often associated with hot, dry weather and as such have become a regular problem in Virginia during years with low rainfall.
Monitoring: Scout fields, especially areas that border roadsides or weedy edges or sandy areas of the field. Examine both the upper and lower sides of five crown leaves from five to ten locations and look for white stippling. Also note the condition of terminal leaves. Treatment should be made when 10%-15% of the crown leaves are infested early in the season, or when 50% of the terminal leaves are infested later in the season.
Chemical Control: Spot treatment of "hot spots" and areas along the edges of fields is recommended to control mite populations when problems are first noticed. Use of dimethoate for leafminer control will reduce mite populations. The products Agri-Mek, Kelthane MF, and Capture are excellent miticides. Continuous use of carbofuran (Furadan), carbaryl (Sevin), or the pyrethroids for other pests may cause mite outbreaks.
Biological Control: Natural predators and diseases of mites are present in fields, but rarely at levels high enough for adequate control during outbreaks.
Cultural Control: If possible, avoid mowing field margins and grassy areas until after midsummer since this forces mites into the crop.
Chemical Insect Control
The list below contains all of the products available to producers for insect control in squash along with the recommended application rates. Always consult the label before making an application. PHI = Pre-Harvest Interval. REI = Re-Entry Interval.
Control recommendations found below were modified from information presented in the 2004 Commercial Vegetable Production Recommendations-Virginia.9
DISEASES
Disease in squash can slow down development and injure the leaves and fruit, greatly reducing the yield and making the crop less profitable. Each of the diseases listed below occurs within Virginia. These diseases depend primarily on weather conditions but also on a number of other factors such as site location, seed quality, and effective management procedures. Good sanitation and management practices are key to a successful disease control program. Powdery and downy mildew, blossom blight, and Phytophthora blight are the most common diseases affecting squash in Virginia.
Bacterial Wilt, Erwinia tracheiphila
Initially, the foliage becomes dull green in color, and individual leaves droop in the early stages of infection. Eventually, leaves and entire branches lose turgor, wilt, and die. Bacterial wilt is carried by the striped and spotted cucumber beetles. The bacteria live in the digestive tract of the beetle and invade the plant through the wounds caused by the beetles. The bacteria multiply within the xylem tissue of the plant until water movement is obstructed. Entire plants may collapse and die within a few days.
Monitoring: Weekly scouting for cucumber beetles should begin following transplant of plants or as soon as the plants emerge. When an average of two beetles per plant is found a treatment plan should be started. A good diagnostic field test is to cut the plant near the crown and squeeze sap from the newly cut stem. Heavily infected plants will ooze a milky sap. Regardless of whether you see the milky sap, touch a clean knife to the cut surface and draw the surfaces apart. If you see threads stringing from the stem and knife blade, then the plant has bacterial wilt.
Chemical Control: Bacterial wilt control is directly related to control of cucumber beetles. Soil-applied insecticides and repeated applications of foliar contact insecticides are necessary for adequate disease control. See the Chemical Insect Control section for more information.
Biological Control: No commercially effective controls are available.
Cultural Control: Control is aimed at prevention of the infection by the beetles. Since cucumber beetles overwinter as adults, early control measures are necessary. Young plants can be protected by row covers, cones, or other types of mechanical barriers. Infected plants should be pulled up and destroyed.
Blossom Blight, Choanephora cucurbitarum
Blossom blight is a fungal disease that attacks flowers and young fruit. It first attacks the blossoms and progresses into the developing fruit, causing a wet rot at the blossom end. The fungus appears as spines with dark heads on the surface of infected tissues. It develops during periods of rainy, humid weather and is a serious problem in some years. The spores can be spread by insects, wind, and splashing water.
Monitoring: Checking the current fruit set for decay on the blossom end can show whether aeration needs to be improved for the subsequent fruit.
Chemical Control: Fungal sprays are not particularly effective but in some instances may reduce fruit losses.
Biological Control: No commercially effective controls are available.
Cultural Control: Reduce the humidity around the plant by using raised beds and wider plant spacing, planting open foliage varieties, and maintaining good weed control. This allows air movement to dry the soil and the foliage. Avoid planting squash on heavy, poorly drained soils.
Damping-Off, Fusarium oxysporumi and Pythium spp.
These soilborne diseases cause young seedlings to wilt and die, or to not emerge at all. Generally, these diseases occur during wet soil conditions. Although Pythium is more commonly found causing damping-off in cucurbits, Fusarium is occasionally found.
Monitoring: Monitoring your crop just after transplant will enable replanting for the current crop and reveal fields that need treatment in future crops.
Chemical Control: To protect against all damping-off pathogens, seeds are usually treated with broad-spectrum contact fungicides. Ridomil Gold 4E or Ultra Flourish 2E can be used for Pythium disease control. See the Chemical Disease Control section for more information.
Biological Control: No commercially effective controls are available.
Cultural Control: Practices that promote water drainage such as planting on raised beds can help to reduce Pythium damping-off.
Downy Mildew, Pseudoperonospora cubensis
Downy mildew is most prevalent during extended periods of cool, moist weather conditions. Symptoms appear as irregular yellowish to brown spots on the upper leaf surface, eventually becoming more distinct on both sides of the leaves. On wet mornings, the underside of the leaves may exhibit a brown to gray fungal growth. These spots grow rapidly and turn black, eventually causing the leaf to wilt and die. This can lead to a major foliage loss in the crop and to sunscald in fruit.
Monitoring: Scout fields for disease incidence beginning in mid-July, even though generally this disease does not occur until mid-August. Downy mildew comes to Virginia from the South. Check the website www.ces.ncsu.edu/depts/pp/cucurbit/ to see if the disease has been detected in your region.
Chemical Control: Begin sprays when vines run or if disease occurrence is predicted for the region. Use chlorothalonil or mancozeb every seven days. Other effective fungicides such as mefenoxam plus chlorothalonil (Flouronil or Ridomil Gold Bravo), mefenoxam plus copper hydroxide (Ridomil Gold Copper), mefenoxam (Ridomil Gold), pyraclastobin plus boscalid (Pristine), and cymoxanil plus famoxadone (Tanos) should be applied every 14 days. Apply chlorothalonil or mancozeb on alternate weeks. See the Chemical Disease Control section for more information.
Biological Control: No commercially effective controls are available.
Cultural Control: Crop rotation has little effect on prevention of downy mildew. It is important to promote healthy, vigorous growth and a good nutritional program in the crop, as plants under nutritional stress are more likely to develop the disease. Also, avoid overhead irrigation.
Plectosporium Blight, Plectosporium tabacinum
Plectosporium blight, formerly called Microdochium blight, has been present in Virginia every year since 1994. This disease infects stems, leaf veins, and fruit. The symptoms are very distinctive and easily distinguished from other cucurbit diseases. Initially, lesions on stems and leaf veins are small, white, and diamond-shaped. Lesions quickly coalesce, causing the entire surface of the vine or leaf vein to turn white. Because leaf lesions are restricted to the veins and do not spread to the interveinal tissue, they may be overlooked in the early stages of disease development. Leaves on severely affected vines die, and complete defoliation may occur in severe cases. On the fruit, the white lesions are more circular and less diamond-shaped. Spots on the flesh remain small and scattered. Spores are most likely spread by wind and rain.
Monitoring: Check the field weekly for tan flecks developing on the stems early in the season and on the petioles and fruit later in the season.
Chemical Control: It is important to achieve maximum foliage coverage with the fungicide application. Once symptoms appear on petioles or after fruit form, apply chlorothalonil (Bravo, Echo, or Equus) and repeat every 7-10 days. A spray schedule that alternates Cabrio or Flint with chlorothalonil will also provide control. See the Chemical Disease Control section for more information.
Biological Control: No commercially effective controls are available.
Cultural Control: Rotate with noncucurbit crops for at least three years. Plant in sites with good air circulation, and plow under crop debris after harvest.
Phytophthora Blight, Phytophthora capsici
This highly destructive disease can cause many different problems for a crop, including: seedling damping-off, leaf spots and fruit rot, and possibly total crop loss. Stem and leaf petiole lesions appear as light to dark brown, water-soaked, and irregular in shape, eventually becoming dry, brittle, and papery. Older plants with root infections may suddenly wilt, even though they show no signs of stem or vine lesions. In fruit, the symptoms begin as small, water-soaked lesions in the rind, which enlarges quickly and becomes a soft, sunken area covered with white fungal growth. This eventually will lead to fruit collapse in the field or in storage. During periods of heavy rainfall, this disease can spread rapidly, quickly becoming a very serious problem.
Monitoring: Monitoring your crop on a regular basis for disease will allow you to apply pesticides when needed.
Chemical Control: Mefenoxam applied preplant can provide some early-season protection and late-season protection if applied for downy mildew control. For protection against the stem and fruit rot phase of the disease, dimethomorph (Acrobat) plus fixed copper or mancozeb plus zoxamide (Gavel) may be applied. See the Chemical Disease Control section for more information.
Biological Control: No commercially effective controls are available.
Cultural Control: To reduce the risk of infection, a complete management program should be implemented with emphasis on water management. Fields should be adequately drained to ensure that soil water does not accumulate around the base of the plants. In addition, when the vines begin to run, trench between rows to allow for faster drainage following rainfall. Avoid overhead irrigation, and rotate out susceptible crops for two or more years.
Powdery Mildew, Sphaerotheca fuliginea
Initial inoculum may come from old cucurbit debris left in the field, or it may be blown in on air currents from infested areas south of Virginia. The plants reveal the characteristic white mold when infected. The mold occurs on both sides of the leaves and often results in an upward cupping effect of leaves with a severe mildew infection. The resulting decrease in photosynthesis may cause significant reductions in the quality and yield of fruit. In contrast to downy mildew, which is more severe during wet weather, powdery mildew is actually inhibited by free moisture on leaf surfaces. Dense plant growth, low light intensity, and high fertility favor disease. Powdery mildew usually occurs from mid-July until the end of the growing season.
Monitoring: Check with upper and undersides of leaves by turning over at least 100 leaves in a field. If one infection site per 45 leaves is found, fungicides need to be applied.
Chemical Control: Make the first application when powdery mildew is observed in the area or is detected by scouting. The fungus that causes powdery mildew has developed resistance to several classes of fungicides. The fungicides at risk for resistance development are in the class of strobilurans and should be tank-mixed with a different class of fungicide to delay onset of resistance. See the Chemical Disease Control section for more information.
Biological Control: No commercially effective controls are available.
Cultural Control: Crop rotation and tillage options will have only a minor effect on powdery mildew control. However, removing plant debris at the end of the season may reduce overwintering of the fungus.
Scab, Cladosponum cucumerinum
This fungal disease can attack all parts of the plant but is most damaging because of the unsightly scab lesions that develop on fruit, usually making it unmarketable. The first signs of disease are usually pale green, water-soaked areas on the leaves and runners. These spots gradually turn gray to white and become angular in shape. The only disease that scab may be confused with is angular leaf spot. Many of the symptoms are the same. However, angular leaf spot is more likely to infect only the foliage, whereas scab infection occurs on both foliage and fruit. Scab usually occurs during cool periods of weather.
Monitoring: Check for leaf lesions and lesions on runners during periods of cool, wet weather.
Chemical Control: Begin chlorothalonil sprays as true leaves form. Repeat every five to seven days. See the Chemical Disease Control section for more information.
Biological Control: No commercially effective controls are available.
Cultural Control: Choose sites that have well-drained soils and are conducive to good air drainage to allow for rapid drying of foliage. Crop rotation with noncucurbits for two or more years is also very important. Use resistant varieties when possible.
Viruses (CMV, WMV-2, PRSV-W, and ZYMV)
Viruses can be spread in the field by insect feeding, cuttings, and infected seeds. In the cucumber mosaic virus (CMV), the leaves show a distinctive yellow and green mosaic pattern on the youngest leaves near the growing tip. Over time, the leaves become malformed and curled, stunting of the vines occurs, and little fruit is produced. The watermelon mosaic virus - II (WMV-2) causes the leaves to become distorted and blistered and displays the same yellow and green mosaic pattern on the newest leaves. If plants are infected young, they can become stunted. The fruit can become misshapen, dwarfed, mottled, or spotted. Papaya ringspot virus (PRSV-W), formerly known as watermelon mosaic virus - I (WMV-1), causes severe plant stunting. A green mosaic pattern is visible on the leaves and is usually accompanied by malformations, leaf distortions, and narrowing leaf blades. The fruit can be malformed and present a break in color pattern. Zucchini yellow mosaic virus (ZYMV) also causes plant stunting and exhibits a yellow mosaic pattern, leaf malformations, and dead patches on the leaves. In the fruit, deep cracks can occur, allowing secondary bacteria to invade the flesh of the fruit.
Monitoring: Monitoring your crop on a regular basis for disease will allow you to apply pesticides when needed.
Chemical Control: Soaps and oils can be used to control virus-transmitting aphids, but once the virus is established in the crop, there are no effective chemical controls available. Reducing insect vectors with insecticides is an option, but remember that insecticides are not always effective in reducing virus spread because the virus may have been transmitted before the insecticide kills the insect.
Biological Control: No commercially effective controls are available.
Cultural Control: Always use virus-resistant cultivars whenever possible, and keep weeds mowed around fields that may harbor viruses over the winter. Plant crops early to escape peak aphid season, and plant as far away from existing cucurbit plantings as possible to prevent aphid transmission of viruses from existing fields to new fields.
Chemical Disease Control
The list below contains all of the products available to producers for disease control in squash along with the recommended application rates of these chemicals. Always consult the label before making an application. PHI = Pre-Harvest Interval. REI = Re-Entry Interval.
Control recommendations were taken from 2004 Commercial Vegetable Production Recommendations-Virginia.10
NEMATODES
The root-knot nematode (Meloidogyne spp.) is the most important species of nematode affecting squash in Virginia.11 These nematodes restrict water and nutrient uptake, giving the plant a stunted, wilted appearance. The diagnostic feature of root-knot nematode infection is the presence of galls on roots of affected plants. Severely affected plants may have galls as large as 1 inch in diameter. Nematode problems can be magnified by hot, dry summers. Symptoms and damage can mimic other diseases and pests, making identification nearly impossible to determine on site. Soil and root samples should be collected and analyzed by an expert.
Monitoring: Both diagnostic and predictive nematode assay programs in Virginia provide data to producers on the numbers and kinds of nematodes in soil along with recommendations for control. Soil samples for diagnostic assays are processed without charge to determine the cause of production problems during the growing season. Predictive nematode assays are done on samples collected after harvest.
Chemical Control: When using soil fumigation, it is important that the fields be sufficiently prepared for planting. All crop debris and clods should be removed, and soil moisture should be adequate. Otherwise, soil fumigation will not be effective due to lack of penetration of all soil particles by the gaseous fumigant. It is also necessary to allow an aeration period between fumigant applications and planting. Otherwise, crop injury will occur. For recommendations, see the Chemical Nematode Control section below.
Biological Control: No commercially effective controls are available.
Cultural Control: Sanitation and good cultural practices are the best preventive measures against nematodes. Examples include obtaining nematode-free roots and washing soil from machinery and tools before using them at different locations. Crop rotation with nonhost crops to lower their population size is highly recommended in the event of nematode activity.
Chemical Nematode Control
Several chemicals are currently available for nematode control, although this may change in the next few years. Currently, the multipurpose soil fumigants chloropicrin, chloropicrin plus dichloropropene (Telone C-17, Telone C-35), metam-potassium (K-PAM HL), metam-sodium (Vapam HL), and methyl bromide (Terr-O-Gas 67, MC-33) are recommended for use in Virginia. In addition, dichloropropene (Telone II) is a soil fumigant used only for nematodes. The nonfumigant nematicide, oxamyl (Vydate L), is also recommended for use in squash. Typically, chemical controls are used only when cultural practices cannot provide adequate control. However, these chemicals are still important tools when other methods of control have failed.
Control recommendations were taken from 2004 Commercial Vegetable Production Recommendations-Virginia.12
WEEDS
The herbicides currently labeled for weed control in squash work on annual grasses, certain perennial grasses, and certain broadleaf weeds, including common lambsquarters, jimsonweed, and pigweed species. However, producers in Virginia are faced with many broadleaf weed problems, including morningglory species, mustards, and yellow nutsedge. Successful weed management is vital to the production of quality squash. Weeds compete with the crop for light, space, nutrients and, particularly, water. Weed growth promotes disease problems and can harbor harmful insects and diseases. Weeds also impair the ability to harvest effectively, reducing the quantity of marketable fruit and increasing labor costs. If not controlled, weeds can greatly reduce fruit quality and may interfere with the harvest.
Monitoring: Proper weed identification is an important part of effective weed control. Weeds observed in previous crops within a given field should be noted to aid in future herbicide decisions. It is also important to monitor the effectiveness of preplant incorporated and preemergence herbicides once the crop emerges.
Chemical Control: To provide additional pest control, a Special Local Need 24(c) label has been approved in Virginia for the postemergence and postharvest use of paraquat (Gramoxone Max 3SC). Recommended rates can be found in the Chemical Weed Control section below.
Biological Control: No commercially effective controls are available.
Cultural Control: Cultivation is a very important component of weed control. Weeds will compete with a crop for nutrients, water, and sunlight, reducing yield and making the crop less profitable. Mechanical cultivation provides effective weed control but is limited to small weeds that can be easily uprooted or covered. More importantly, mechanical cultivation should not be performed on varieties of squash that vine ("run"). These vines are very tender and are easily damaged by tractor wheels or cultivators. Mechanical control must be supplemented with chemicals or hand weeding to remove weeds in the rows or after the plant produces vines. Hand weeding provides effective weed control and is safe to the crop. Weeding should be performed when the crop and weeds are small to reduce crop damage. Removing large weeds with extensive root systems may damage crop roots or vines. Hand weeding, however, is costly in terms of labor. Using cultivation with herbicides is the most cost-effective way to combat weeds and to produce a high yield. Crop rotation is also important to prevent domination of any one weed species year after year. Also, avoiding fields with a history of severe weed infestations may be appropriate.
Chemical Weed Control
The list below contains all of the fully labeled products available to producers for weed control in squash; however, these are subject to change. Always consult the label before making an application. PHI = Pre-Harvest Interval. REI = Re-Entry Interval.
Use the following herbicides for weed control under plastic mulch or crop injury and/or poor weed control may result.
Black plastic mulch effectively controls most annual weeds by preventing light from reaching the germinated seedlings. Herbicides are used under plastic mulch to control weeds around the planting hole, and under the mulch when clear or black plastic is used. Trickle irrigation tubes left on the soil surface may cause weed problems by leaching away herbicide at emitters. The problem is most serious when clear plastic mulch is used. Bury the trickle tube several inches deep in the bed to reduce this problem. Delay punching the planting holes until seeding or transplanting.
Note: All herbicide rate recommendations are made for spraying a broadcast acre.
Preemergence
Postemergence
Use the following herbicides when seeding into soil without plastic mulch or crop injury and/or poor weed control may result.
Note: All herbicide rate recommendations are made for spraying a broadcast acre.
Preplant Incorporated or Preemergence
Preemergence
Postemergence
Postharvest
Table 1: Effectiveness of herbicides recommended for weed control in summer squash.13
Developed and Written by:
Therese N. Schooley
Project Manager
Virginia Polytechnic
Institute and State University
Department of Entomology
Virginia Tech
Pesticide Programs (0409)
34 Agnew Hall
Blacksburg, VA 24061
Ph:
540-231-2086
Fax: 540-231-3057
E-mail: tschooley@vt.edu
Collaborating Authors:
Diseases:
Christine M. Waldenmaier
Research Specialist,
Plant Pathology
Virginia Polytechnic Institute and State
University
Eastern Shore Agricultural Research and Extension Center
(0512)
33446 Research Drive
Painter, VA 23420-2827
Ph:
757-414-0724
Fax: 757-414-0730
E-mail: cwalden@vt.edu
Insects:
Thomas P. Kuhar
Assistant Professor,
Entomology
Virginia Polytechnic Institute and State University
Eastern
Shore Agricultural Research and Extension Center (0512)
33446 Research
Drive
Painter, VA 23420-2827
Ph: 757-414-0724
Fax:
757-414-0730
E-mail: tkuhar@vt.edu
Pesticides:
Michael J. Weaver
Professor and Extension
Pesticide Coordinator
Virginia Polytechnic Institute and State
University
Department of Entomology
Virginia Tech Pesticide Programs
(0409)
34 Agnew Hall
Blacksburg, VA 24061
Ph: 540-231-6543
Fax:
540-231-3057
E-mail: mweaver@vt.edu
Weeds:
Henry P. Wilson
Professor, Weed
Science
Virginia Polytechnic Institute and State University
Eastern Shore
Agricultural Research and Extension Center (0512)
33446 Research
Drive
Painter, VA 23420-2827
Ph: 757-414-0724
Fax:
757-414-0730
E-mail: hwilson@vt.edu
Cultural Practices:
Rikki Sterrett
Associate
Professor, Horticulture
Virginia Polytechnic Institute and State
University
Eastern Shore Agricultural Research and Extension Center
(0512)
33446 Research Drive
Painter, VA 23420-2827
Ph:
757-414-0724
Fax: 757-414-0730
E-mail: mailto:vators@vt.edu
Edited by:
Susan E. Nessler
Project
Coordinator
Virginia Polytechnic Institute and State University
Department
of Entomology
Virginia Tech Pesticide Programs (0409)
34 Agnew Hall
Blacksburg, VA 24061
Ph: 540-231-8956
Fax: 540-231-3057
E-mail: snessler@vt.edu
On-Line Resources
C&P Press Online Crop Protection Reference
http://www.greenbook.net/free.asp
Crop Data Management Systems - Pesticide Labels
http://www.cdms.net/pfa/LUpdateMsg.asp
Insects and Related Pests of Vegetables
http://ipmwww.ncsu.edu/AG295/html
Pests of Vegetables and Fruit Trees
http://everest.ento.vt.edu/~idlab/vegpests/vegfact.html
Virginia Agricultural Statistics Service
http://www.nass.usda.gov/va/
Virginia Tech Pesticide Programs
http://www.vtpp.ext.vt.edu/
Virginia Tech Weed Identification Guide
http://www.ppws.vt.edu/weedindex.htm
2 Virginia Tech Cooperative Extension Publication 426-406, June 2000. Cucumbers, Melons and Squash: http://www.ext.vt.edu/pubs/envirohort/426-406/426-406.html.
3 Bratsch, A. D., Kuhar, T. P., Phillips, S. B., Sterrett, S. B., Waldenmaier, C., and Wilson, H. P., 2004. Commercial Vegetable Production Recommendations (No. 456-420), Virginia Cooperative Extension.
4 Swaider, J. M., Ware, G. W., and McCollum, J. P., 1980. Producing Vegetable Crops (4th ed.). Interstate Publishers, Inc. Danville, IL.
5 University of Georgia, Department of Horticulture. Vegetable Crops: http://www.uga.edu/vegetable/squash.html.
6 Bratsch, A. D., Kuhar, T. P., Phillips, S. B., Sterrett, S. B., Waldenmaier, C., and Wilson, H. P., 2004. Commercial Vegetable Production Recommendations (No. 456-420), Virginia Cooperative Extension.
7 Capinera, J. L., 2001. Handbook of Vegetable Pests. Academic Press, San Diego, CA.
8 "Cucumber Beetles." http://ipmwww.ncsu.edu/AG295/html/cucumber_beetles.htm.
9 Bratsch, A. D., Kuhar, T. P., Phillips, S. B., Sterrett, S. B., Waldenmaier, C., and Wilson, H. P., 2004. Commercial Vegetable Production Recommendations (No. 456-420), Virginia Cooperative Extension.
10 Bratsch, A. D., Kuhar, T. P., Phillips, S. B., Sterrett, S. B., Waldenmaier, C., and Wilson, H. P., 2004. Commercial Vegetable Production Recommendations (No. 456-420), Virginia Cooperative Extension.
11 Eisenback, J. D., Professor. Virginia Tech Department of Plant Pathology, Physiology, and Weed Science. Communications via email, September 6, 2003.
12 Bratsch, A. D., Kuhar, T. P., Phillips, S. B., Sterrett, S. B., Waldenmaier, C., and Wilson, H. P., 2004. Commercial Vegetable Production Recommendations (No. 456-420), Virginia Cooperative Extension.
13 Bratsch, A. D., Kuhar, T. P., Phillips, S. B., Sterrett, S. B., Waldenmaier, C., and Wilson, H. P., 2004. Commercial Vegetable Production Recommendations (No. 456-420), Virginia Cooperative Extension.
