Guide to Commercial
Summer Squash Production

Historical Perspective

Unlike many vegetable crops cultivated in the United States, summer squash originated in the New World. It is found from the southern temperate zone of North America to the northern subtropical zone of South America. Worldwide, summer squash ranks high economically among other vegetables produced.

There are four groups of summer squash: (1) straightneck, yellow cylindrical or bottle shaped fruit with a straightneck; (2) crookneck, yellow elongated fruit with a narrow, long curved neck; (3) scallop, white, green or striped flattened fruit with scalloped or ridged edges; and (4) zucchini and cocozelle, green or yellow cylindrical fruit, referred to as vegetable marrows. The zucchini is uniformly cylindrical and green.

Planting Recommendations

Planting Dates

Summer squash is typically direct seeded after all danger of frost is passed. Soil temperatures should be between 70°F and 90°F for optimal seed germination. Although direct seeding is the best method, growers can transplant summer squash provided great care is taken. If transplants are used, always use containerized plants (never bare root transplants) that are no more than 3 weeks old. Many growers opt for transplants to enhance earliness and uniformity of plant stands, but great care must be taken when transplanting squash and most other members of the Cucumber family as roots of young plants are easily damaged.

When transplanting or direct seeding, plant summer squash no earlier than March 10 to 30 in south Alabama; April 1 to 15 in central Alabama; and April 15 to May 10 in north Alabama. Make successive plantings of summer squash every 10 to 14 days throughout the summer and fall to ensure a steady supply of fruit. For plantings in the late fall, sow no later than 60 to 70 days before the first frost date.

Soil and Fertility

Timely and appropriate applications of fertilizer can make a significant difference in the quality and quantity of fruit, and may promote earlier harvests. In the winter or early spring, collect soil samples from each area you intend to crop and have a soil analysis performed on each sample. Soil testing eliminates much of the guesswork involved in a fertilizer program. Be sure to apply lime several months prior to planting. Contact your county Extension agent for information on how to collect and submit a soil sample.

If a soil test is not done, a general recommendation is to apply enough fertilizer to supply 60 to 80 pounds of nitrogen (N), phosphorus (P₂O₅), and potassium (K₂O). This can be done by applying 500 pounds of 8-24-24 in the row before planting; then sidedress with 30 to 40 lb. of nitrogen when the plants are 8 to 10 inches tall (3 to 4 weeks after planting).

Seeding Rate and Spacing

Seed the summer squash to produce stands with plants spaced 18 to 24 inches apart in rows on 36 to 48 inch centers. Plant seeds ¾ to 1½ inches deep. To achieve the maximum stand, plant two to three seeds per hill and thin to a single plant leaving the healthiest seedling.

Direct seeding will require three to five pounds of seed per acre. Summer squash contain about 3,500 seeds per pound (220 seed/ounce). Use Table 1 to determine the number of plants per acre required at various spacings. Note: if you are using double-rows of plants within a bed such as with polyethylene mulch, the number of plants per acre will double at the various spacings in the preceding table. On plastic, plant double rows of summer squash per bed with plants spaced 18 x 18 inches.

Table 1. Spacing And Number Of Plants Per Acre.
Between row spacing	Spacing between plants              18"                         20"                         22"                         24"
36"	9,680	8,712	7,920	7,260
42"	8,297	7,467	6,788	6,222
48"	7,260	6,534	5,940	5,445

Varieties

Successful Pollination of Squash

Several factors play a significant role in effective pollination of a crop. Among these, weather is one of the most important. Bees are less likely to forage for nectar and pollen during bad weather. If poor pollinating conditions exist during the flowering period, additional beehives may have to be supplied to the crop above the recommended level in order to compensate.

A second factor in managing bees for pollination is the presence of “competing blooms” during the flowering period of summer squash. Most cucurbit flowers are poor sources of nectar and pollen. They may be less attractive to bees than adjacent flowering weeds or other crops. In such cases, crops which may attract bees away from summer squash during the blooming period should not be planted nearby (at least a ½ mile buffer is desirable). Similarly, destroy weeds adjacent to the crop which may serve as competing blooms before the crop begins to bloom. Although such wild flowers can be detrimental if they are blooming in mass at the same time as the target crop, their availability during other times helps assure that bee colonies are well nourished and remain healthy.

The use of domesticated honey bees is the most effective means to pollinate cucurbit crops. However, wild bees or feral honey bees can be extremely important as pollinators. Wild bees include several species of native, ground nesting bees that prefer pollen and nectar from squash and other cucurbits. The abundance of wild bees varies greatly by location and from year to year, making them less dependable than domesticated bees. For this reason, it is strongly recommended that managed honeybee colonies supplement any wild bee activity.

Fruit size and seed set of cucurbits are strongly related to bee activity as movement of pollen to female flowers by insects is essential for fruit production. Cucurbit flowers are open for only 1 day, and squash are usually open only in the morning. Because of the large size of flowers and pollen, the small honey bees do not pollinate squash as efficiently as do the larger native bees. The pollination requirement for squash and pumpkin is similar to cantaloupe; one bee per ten “female” flowers is considered the minimum level of activity to maximize production. A minimum of one honey beehive per acre is normally necessary to achieve this level of activity. Yield increases have been achieved with up to three hives per acre.

Irrigation

Mulching and Drip Irrigation

These benefits promote increased quality and quantity of fruit yields, as well as earlier production, especially when used in combination with transplants. The use of transplants with plastic mulch generally results in harvests that begin 7 to 14 days earlier in comparison to bare ground production.

Although using mulch will increase production costs, increased profits from earlier and larger yields offset those costs. Drip irrigation systems must be used with plastic mulch. In addition, growers can plant multiple crops (double-cropping) into the plastic mulch provided care is taken to avoid excessive damage (tears, holes, etc.) to mulch. With summer squash, double rows of plants within each row can be used. Be sure to place drip tape down the middle of the bed, buried 2 to 3 inches deep. Contact your county Extension agent for more information regarding the use of plastic mulch and drip irrigation.

Controlling Weeds, Insects, Diseases, and Other Pests

Weed Control

Insect Management

Insect Scouting Methods

Soil Insects

Make the decision to treat for soil insects on the basis of field cropping history and the potential of the field to have pest problems. A pre-planting application of a soil insecticide is recommended if summer squash is planted in an area previously in pasture or was infested with weeds. If cutworm damage is suspected, check the soil around the plants for dark caterpillars that roll into a “C” shape when disturbed. Control cutworms after planting by using a recommended insecticide spray directed towards the base of the plants.

Cucumber Beetles

The critical period for cucumber beetle control is within the first 2 to 3 weeks after plant emergence. Apply a recommended insecticide if beetles are detected on plants during this period, particularly if the field has a history of bacterial wilt disease. Alternatively, use row covers to protect plants from beetles during the period from emergence to bloom. Weed control reduces the amount of bacterial wilt inoculum transmitted by beetles.

Squash Bug

Adults and nymphs suck sap from the plant. If feeding is severe the leaves turn brown and die. Vines that are fed upon wilt from the point of attack to the end of the vine. Large populations of squash bugs can cause plants to wilt under hot, dry conditions. However the plant can recover if squash bugs are controlled in time. Feeding may also occur on squash fruit, causing deformities.

There are two critical periods for management of squash bugs—the seedling stage and the early flowering stage. Monitor newly planted squash fields for squash bug adults and/or wilting of plants. If wilting is observed, check the underside of leaves for squash bug adults or for evidence of their feeding. An application of a pyrethroid insecticide will control adults during this stage.

Once plants are established, monitor at least once a week for adults and eggs. A foliar insecticide application is recommended if the average number of egg masses per plant before or after flowering exceeds 1 per plant. Time sprays to kill small nymphs, which are more susceptible to insecticides than older nymphs and adults. Good spray coverage is important (at least 30 GPA by ground application) for effective control with insecticides.

Removal and destruction (shredding and disking) of crop debris after harvest reduces overwintering squash bug populations. Hand destruction of adult squash bugs and egg masses is effective in home gardens. Place boards on the ground near squash plants to trap squash bugs. The bugs gather under the boards at night. Collect and destroy them the next morning.

Pickleworm

The pickleworm moth is small, and the body and wings are yellowish brown with a purplish sheen. The wings have a broad, light brown border. The tip of the abdomen contains dark, brush-like hairs that are waved in the air when the moth is resting. Pickleworm moths fly mostly between dusk and early morning, and are not usually seen in fields during the day. Female moths lay eggs on leaf and flower buds, leaves, stalks, and young fruit. Young pickleworm larvae are a pale, yellowish-green with many black spots. Older larvae are yellowish-green or coppery with no spots and a brown head (about ¾ inch long) (Figure 3).

Newly hatched larvae can feed on leaves, but prefer to move into protected areas like developing leaf and flower buds and stems. Young larvae may also create a “feeding chamber” by rolling up young leaf tissue or boring into stems. Later, mature larvae tunnel into vines and fruit (Figure 3). Pickleworms may reduce fruit set due to feeding on leaves and flowers. Feeding tunnels in fruit reduce quality and introduce secondary fungi and bacteria. Because of a low tolerance for fruit damage, particularly in the pickling cucumber industry, treatment threshholds are very low. However, because pickleworm do not overwinter to any great extent in Alabama, moths relocate to fields each year. Therefore, insecticide controls, particularly in early plantings, may not be necessary during each season.

Scouting for pickleworm larvae is the best method to determine whether insecticide sprays are needed. Scout at least once a week and begin when plants are still small before the flower buds form. Scouts can detect pickleworm larvae by opening up the newly developing leaf and flower buds. This should be done in approximately 10 to 20 representative locations in each field. At each location, examine the foliage on 12 to 18 feet of row. A 10X hand lens will be helpful to detect small larvae.

If larvae are detected, a labeled insecticide (such as Asana XL; 6-9 fl. oz per acre) is recommended at 7 to 10 day intervals; 7 day intervals for heavy infestations and 10 day intervals for lighter infestations. Refer to Extension publication ANR-0500-A, Alabama Pest Management Handbook—Volume 1, for insecticide recommendations and harvest interval restrictions.

Scouting is important because it provides growers with knowledge about pickleworm presence and density that can be used to determine if insecticide sprays are needed. If scouting is not feasible, growers can decide not to treat and risk damage, or they can apply insecticides and risk making unnecessary treatments.

If insecticide treatments are applied for pickleworm “prophylactically” without scouting, begin spraying when the first flower buds are present, but before the flowers open. Studies in Alabama indicate that if pickleworm is present, delaying sprays until the open flowering stage will not protect fruit from damage. This is likely because larvae may already be inside the leaf or flower bud tissue and protected from sprays by the time the flowers begin to open.

Squash Vine Borer

The adult vine borer is a “clear-wing” moth that resembles a wasp more than a moth. The body is reddish-white, with black bands on the abdomen. Females lay eggs at the base of the plant and the emerging larvae enter the plant stems just above the soil line. Larvae feed inside the stem or vines resulting in wilt and eventual death of occupied parts of the plant (Figure 4). Infested stems can be identified by entry holes with piles of “frass” or excrement. Squash vine borers prefer squash varieties with largediameter stems, such as Hubbard.

In areas with a history of vine borer problems, monitor plants regularly for the presence of borer frass and entry holes. If frass is found, split stems to check for presence of young borers. If young larvae are detected, further infestation by hatching larvae may be reduced by two insecticide applications spaced 5 to 7 days apart. In home gardens, remove larvae by hand and place soil around the stem to facilitate new growth. Plantings in late summer or fall usually escape vine borer infestations.

Aphids

Fortunately, aphids have many parasite and natural predator enemies that help keep populations in check. Application of insecticides that wipe out natural enemies may actually result in increased numbers of aphids. Insecticides are not effective in preventing aphid transmission of viruses because the virus is passed very quickly to the plant, before the aphid is killed by contact with the insecticide.

Insecticides are only recommended to control aphids if they are present in sufficient numbers to cause direct damage to plants. An insecticide application is warranted if aphids are present on 10 to 20 percent or more of leaves, and their feeding is causing obvious stress to the plants.

Cultural or mechanical control methods are usually more effective than insecticides for aphid and virus management. Elimination of weeds in and around crop fields that may be alternate hosts for aphids and for viruses will decrease their chances of movement into the squash. The use of reflective mulch under squash repels aphids from young plants delaying infection of aphid-transmitted viruses.

Virus effects on fruit yield and cosmetic quality are much less severe if infection occurs after plants have set fruit. Covering plants with row covers until bloom will protect young plants from aphids and virus infection. Late summer or fall plantings of squash are more likely to experience severe virus problems than are earlier plantings.

Spider Mites

The first signs of feeding is the appearance of light-colored specks on the upper leaf surface. Leaves turn yellow, then bronze, and eventually turn brown and dry-up. Once mite populations become large with large amounts of webbing and plant damage, they are nearly impossible to control. Hot, dry conditions favor mite development. Mites, lifted by wind currents, “float” onto plants using their silk as a parachute.

Mite infestations usually begin on field borders. Check field borders regularly, particularly during hot, dry weather. Plants that become covered with dust raised by vehicular traffic are also more prone to severe mite infestations. If mites are found along a field border, examine the interior of the field to see how far the infestations has spread. If only the border is affected and conditions favor mite development, spot-treat the border and about 100 feet beyond the infestation with a recommended miticide.

Some insecticides, particularly carbamate and pyrethroid insecticides, can worsen mite problems by destroying natural enemies. Insecticidal soap is effective for control of soft-bodied pests like aphids and mites without destroying natural enemies.

Cucurbit Diseases, Nematodes, and Their Control

Downy Mildew

SYMPTOMS. The first symptom of downy mildew is the appearance of pale green areas on the upper leaf surface, which may be confused with symptoms of a mosaic-type virus. These areas eventually turn into angular (limited by leaf veins), yellow to tannish-brown spots (Figure 5). During periods of wet weather the corresponding lower leaf surface may show a white to grayish-purple mold. Spots may enlarge rapidly during warm, moist weather, causing the leaves to wither and die. Dead leaves often remain erect while the edges of leaf blades curl inward.

Downy mildew first infects the older crown leaves, usually about the time of fruit set. Severe infections result in defoliation, stunted plants, and poor fruit development. Symptoms of downy mildew do not occur on squash fruit.

TRANSMISSION AND PERSISTENCE. The fungus survives season to season in contact with a cucurbit host. Also, air currents can carry spores of the fungus long distances. Spread of the disease within a field is usually by wind, rain, insects, or by contact with field workers or tools. The disease develops very rapidly in moderate to warm temperatures (between 61°F and 72°F) provided there is moisture on the leaves. Fog, dew, frequent rains, and high relative humidity provide conditions favorable for disease development. Extended periods of hot dry weather reduce the severity and spread of the disease.

CONTROL. Practices that reduce leaf wetness and lower relative humidity within the plant canopy will reduce disease development. Choose planting sites with all-day sun, good soil drainage, and free air movement. Increase row spacings to avoid dense plant canopies. Avoid overhead irrigation. Maintain adequate, but not excessive, nitrogen levels to help reduce damage from downy mildew.

A fungicide program is usually necessary to control downy mildew when favorable weather conditions persist. Fungicides with the active ingredient metalaxyl, chlorothalonil, maneb, mancozeb, or copper are effective in controlling downy mildew. When using a fungicide it is important to get good coverage on the lower leaf surfaces, since infections commonly occur on the underside of leaves. Follow all of the manufacturer’s label directions and restrictions when using any pesticide.

Powdery Mildew

SYMPTOMS. Powdery mildew first appears as pale yellow spots on stems, petioles, and leaves (Figure 6). These spots expand and merge and become covered with a superficial, powdery, white to gray fungal growth. This white growth may also appear on the lower leaf surface (Figure 7). Mature, fruit bearing plants are usually affected first and the older, shaded leaves are most susceptible. Severely infected leaves gradually turn yellow, then wither and die becoming brown and papery. Early leaf drop results in fruit of poor quality. Fruit may be malformed, sunburned, and ripen prematurely resulting in poor flavor and texture. Under favorable conditions an entire field may appear white from mildew within a week.

TRANSMISSION AND PERSISTENCE. The powdery mildew fungus commonly overwinters on weeds. The disease spreads from plant to plant by insects and farm machinery. Air currents can carry spores of the fungus long distances. Infection can take place when the leaves are dry although high humidity (50 to 90 percent) is necessary for infection to occur. Disease development is favored by excessive plant growth, moderate to high temperatures, low light intensity, and dews.

CONTROL.. The principal control measures for powdery mildew are the use of resistant varieties and timely applications of fungicides. A few summer squash varieties with resistance to powdery mildew are available. Consult current seed catalogs and trade publications for varietal availability. Weed control and good sanitation practices will help control powdery mildew. Crop rotation has no beneficial affect on managing this disease.

Apply a recommended fungicide beginning when symptoms of powdery mildew are first observed. Continue applications at 7 to 14 day intervals throughout the season. Fungicides with the active ingredient benomyl, chlorothalonil, or triadimefon are effective in controlling powdery mildew. Thorough coverage of the foliage is essential for good control. Adequate management requires that the fungicide reach the underside of leaves and the lower part of the plant. Always follow the manufacturer’s label directions and restrictions when using any pesticide.

Choanephora Wet Rot

SYMPTOMS. Fruits rot rapidly and white fungal mold appears on the infected area. With time, fruit look like a pin cushion with numerous small, black-headed pins stuck in it (Figure 8). Initially, the heads are white to brown but turn purplish-black within a few days. Affected flowers, pedicels, and immature fruit become water-soaked, and a soft, wet-rot develops. An entire fruit can rot in a 24 to 48 hour period. Symptoms usually begin on the blossom end of the fruit.

PERSISTENCE AND TRANSMISSION. The fungus overwinters as a saprophyte (living on dead plant tissue) and/or in a dormant spore form (such as a chlamydospore or zygospore). In spring, fungal spores are spread to squash flowers by wind and by insects such as bees and cucumber beetles. Infection occurs through the blossom, into the fruit and stem. Development of wet rot is favored by high relative humidity and excessive rainfall.

CONTROL. There are no effective control practices available for wet rot at this time. Fungicide sprays are impractical because new blossoms open daily and need to be protected soon after development. Drip irrigation may reduce development and spread of the disease during dry seasons.

Mosaic Viruses

Cucumber Mosaic Virus (CMV)

When plants become infected in the six- to eightleaf stage, symptoms first appear on the youngest, still expanding leaves. A mosaic pattern develops (healthy dark green leaf tissue intermingled with light green and yellow tissue). Leaves are often distorted, crinkled, curled, and stunted. Vines may appear bushlike due to the shortening of the internodes. In severe cases, older leaves may die. Typical mosaic symptoms develop only on actively growing leaves.

When a plant becomes infected at mid-season, previous growth remains normal and produces healthy fruit. Few fruit set on plants infected early in the growing season. Fruit that do set are often of poor quality and may be mottled green and yellow or have dark green warts (Figure 9).

PERSISTENCE AND TRANSMISSION. CMV survives in close to 800 species of plants, including many weeds found in Alabama. These weeds often act as reservoir hosts and allow the virus to overwinter. CMV is spread and transmitted by more than 60 species of aphids.

Squash Mosaic Virus (SqMV)

PERSISTENCE AND TRANSMISSION. SqMV overwinters in weeds, seed, and cucumber beetles. Cucumber beetles are efficient vectors of SqMV, spreading the virus during feeding.

Watermelon Mosaic Virus (WMV)

PERSISTENCE AND TRANSMISSION. WMV overwinters in seed or infected weeds. In spring, the virus is spread by many species of aphids. Later plantings risk greater damage as disease incidence and aphid populations increase during the growing season.

CONTROL OF CMV, S_QMV, AND WMV. Control of mosaic viruses in squash begins with eradication of biennial and perennial weeds and wild reservoir hosts in and around gardens and fields. Applications of insecticides to prevent the buildup of large aphid and cucumber beetle populations, as well as other insects, may reduce virus incidence and spread. When possible, plant certified virus-free seed and plant resistant varieties. Isolate later planting as far away as possible from earlier settings, especially if virus incidence was high. Removing infected plants when symptoms first appear may reduce or delay spread of the virus. Reflective mulches and row covers also reduce damage from insect transmitted viral diseases.

Root-Knot Nematodes

SYMPTOMS. When root-knot nematode populations are high, plants are often stunted and may wilt during dry conditions or during the hottest part of the day. Root-knot in the field is easily detected by examining roots of symptomatic plants. The nematodes cause knots or galls to develop on both large and small roots (Figure 11). Knots range in size from the head of a pin to 1 inch in diameter.

PERSISTENCE AND TRANSMISSION. Root-knot nematodes have a wide host range that includes summer squash and many other cultivated crops as well as many weed species. The nematodes survive in the soil from year to year and become active as soil temperatures increase in the spring.

CONTROL. Crop rotations with grasses or nematode-suppressive crops and clean fallowing during the off-season will reduce nematode populations (see Extension publication ANR-0856, “Nematode Suppressive Crops”). Soil fumigation is an effective means of reducing damaging population levels temporarily (one growing season). Soil solarization is effective in reducing nematode populations when environmental conditions are favorable for its use. See Extension publications ANR-0030, “Nematode Control in the Home Garden,” ANR-0500-A, Alabama Pest Management Handbook—Volume 1, and ANR-0713, “Soil Solarization for the Control of Nematodes and Soil-Borne Diseases.”

Harvesting

The first squash harvested from a planting are generally the best quality. Plan to harvest any given planting only 2 to 3 weeks and then start harvesting from another planting as quality decreases as plantings age. This will ensure that harvested fruit is of high quality. A good yield of summer squash is 300 cwt./acre. Table 2 lists the approximate number of days from pollination to market maturity for several types of summer squash under warm growing conditions.

Table 2. Time From Pollination To Market Maturity.
Type of squash	Time to Market Maturity (days)
Crookneck Straightneck Zucchini	6-7* 5-6* 3-4*
* for a weight of 0.25 to 0.5 lb. per fruit (adapted from Knott's Handbook for Vegetable Growers, 1988, O. Lorenz and D. Maynard, John Wiley & Sons, NY.).

Storage

Summer squash are quite perishable, as its skin is tender and easily wounded in handling. Normally fruit is not stored except for normal delays in marketing such as holidays and weekends. Fruit can be held 1 to 2 days below 41°F with no discernible damage. Avoid prolonged storage since summer squash are chilling sensitive (damaged by exposure to low temperatures). Holding summer squash longer than 4 days at 32°F will cause chilling damage (surface browning, pitting) and rapid deterioration of the fruit. The recommended storage temperature range is 41°F to 50°F with 95 percent relative humidity. The storage life is only 1 to 2 weeks.