Squash

Cucurbita spp.

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Description

Squash is the collective name given to several species of plant in the genus Cucurbita, including C. maxima, C. mixta , C. moschata and C. pepo, which are widely grown for their edible fruit. Squash plants are are herbaceous annual plants which are either trailing vines or bush-like in morphology. Vines generally have large, lobed leaves and long vines which can climb by attaching to surfaces with their tendrils. Bushes generally take up less space than the sprawling vine types and may have prickly leaves. Squash plants produce yellow or orange flowers and green, white or yellow fruit in a variety of shapes and sizes with smooth or ridged skin. Vining squash varieties can reach several meters in length and, as annuals, survive only one growing season. Squash originate from North and Central America and are referred to by their cultivar name e.g. acorn squash, butternut squash, spaghetti squash, zucchini, banana squash, hubbard squash and buttercup squash.

Uses

Squash fruit can be cooked and eaten as a vegetable. Some varieties are grown as ornamentals.

Propagation


Basic requirements
Squash is a warm-season crop, requiring lots of sun and good drainage to develop optimally and growing best at temperatures between 18 and 25°C (65–75°F). Squash will yield best if grown in a fertile, well-draining soil, rich in organic matter and with a pH between 6.5 and 7.5. Squash should be planted in full sun and provided with ample soil moisture due to their shallow root system. Vining varieties can grow to very large sizes and require a good deal of space. Smaller bush varieties are available for more modest spaces.

Propagation
Squash is propagated from seed and can be direct seeded or sown indoors and transplanted. If direct seeding,seeds should be sown after the last frosts and when the soil has warmed to at least 15.6°C (60°F). Sow 1–2 seeds 1.3–2.5 cm (0.5–1.0 in) deep, at least 90 cm (~3 ft) apart if growing bush varieties and 120–150 cm (4–5 ft) apart if growing vining varieties. Allow a further 1–3 m (6–10 ft) between rows depending on the variety. If transplanting, seeds should be sown 3–4 weeks before the last frost date in your area and transplanted before the plants develop their second set of true leaves. Seeds in sown both indoors and out require lightly moist soil for germination, care should be taken to avoid overwatering. Seeds should germinate in 5–10 days depending on the soil temperature.

General care and maintenance
Squash vines are sprawling and require plenty space to grow. Vines can be trained to grow on a trellis or fence. Squash also require a continuous supply of water and where drip irrigation is not being used, plants should be watered deeply once per week, providing at least an inch of water. Shallow watering or watering less frequently encourages a shallow root system. Mulches can be used to conserve soil moisture and black polyethylene mulch has the advantage of warming the soil. All squash varieties produce both male and female flowers (monoecious) and are pollinated by insects such as bees.

Harvesting
Squash is ready to harvest when the rind is hard and cannot be punctured with a fingernail. The skin of mature fruits is dull and dry in appearance, especially when compared with the shiny skin of an immature fruit.

Diseases

Alternaria leaf blight Fungus Alternaria cucumerina

Symptoms

Small, yellow-brown spots with a yellow or green halo which first appear on the oldest leaves; as the disease progresses, lesions expand and become large necrotic patches, often with concentric patternation; lesions coalesce, leaves begin to curl and eventually die.

Comments

Disease is prevalent in growing areas where temperatures are high and rainfall is frequent.

Management

Cucurbits should be rotated with another crop every 2 years to reduce levels of inoculum; crop debris should be removed from the field as quickly as possible after harvest or plowed deeply into the soil; applications of appropriate protective fungicides can help to slow the development of the disease; water plants from the base rather than from above to reduce periods of leaf wetness which are conducive to the development and spread of disease.

Alternaria leaf spot (Brown spot) Fungus Alternaria alternata

Symptoms

Initial symptoms appear as necrotic flecks on leaves with chlorotic halos; as the disease progresses, the flecks grow into spots which may join together into large, roughly circular lesions; if infestation is severe, leaves begin to turn yellow and die.

Comments

Pathogen survives between growing season on crop debris.

Management

Crops debris should be removed from the field or plowed deeply into the soil after harvest; applications of appropriate protective fungicides can hep reduce the incidence of the disease.

Angular leaf spot Bacterium Pseudomonas syringae

Symptoms

Small water-soaked lesions on leaves which expand between leaf veins and become angular in shape; in humid conditions, lesions exude a milky substance which dries to form a white crust on or beside lesions; as the disease progresses, lesions turn tan and may have yellow/green edges; the centers of the lesions dry and may drop out leaving a hole in the leaf

Comments

Spread through infected seed, splashing rain, insects and movement of people between plants; bacterium overwinters in crop debris and can survive for 2.5 years

Management

Use disease-free seed; do not grow plants in field where cucurbits have been grown in the previous 2 years; protective copper spray may help reduce incidence of disease in warm, humid climates; plant resistant varieties

Aphids (Peach aphid, Melon aphid) Insects Myzus persicae
Aphis gossypii

Symptoms

Small soft bodied insects on underside of leaves and/or stems of plant; usually green or yellow in color, but may be pink, brown, red or black depending on species and host plant; if aphid infestation is heavy it may cause leaves to yellow and/or distorted, necrotic spots on leaves and/or stunted shoots; aphids secrete a sticky, sugary substance called honeydew which encourages the growth of sooty mold on the plants

Comments

Distinguishing features include the presence of cornicles (tubular structures) which project backwards from the body of the aphid; will generally not move very quickly when disturbed

Management

If aphid population is limited to just a few leaves or shoots then the infestation can be pruned out to provide control; check transplants for aphids before planting; use tolerant varieties if available; reflective mulches such as silver colored plastic can deter aphids from feeding on plants; sturdy plants can be sprayed with a strong jet of water to knock aphids from leaves; insecticides are generally only required to treat aphids if the infestation is very high - plants generally tolerate low and medium level infestation; insecticidal soaps or oils such as neem or canola oil are usually the best method of control; always check the labels of the products for specific usage guidelines prior to use

Armyworms (Beet armyworm, Western striped armyworm) Insect Spodoptera exigua
Spodoptera praefica

Symptoms

Singular, or closely grouped circular to irregularly shaped holes in foliage; heavy feeding by young larvae leads to skeletonized leaves; shallow, dry wounds on fruit; egg clusters of 50-150 eggs may be present on the leaves; egg clusters are covered in a whitish scale which gives the cluster a cottony or fuzzy appearance; young larvae are pale green to yellow in color while older larvae are generally darker green with a dark and light line running along the side of their body and a pink or yellow underside

Comments

Insect can go through 3–5 generations a year

Management

Organic methods of controlling armyworms include biological control by natural enemies which parasitize the larvae and the application of Bacillus thuringiensis; there are chemicals available for commercial control but many that are available for the home garden do not provide adequate control of the larvae

Aster yellows Phytoplasma Aster yellows phytoplasma

Symptoms

Foliage turning yellow; secondary shoots begin growing prolifically; stems take on a rigid, upright growth habit; leaves are often small in size and distorted, may appear thickened; flowers are often disfigured and possess conspicuous leafy bracts; fruits are small and pale in color

Comments

Disease is transmitted by leafhoppers and can cause huge losses in cucurbit crops

Management

Remove any infected plants from the field to reduce spread; control weeds in and around the field that may act as a reservoir for the phytoplasma; protect plants from leaf hopper vectors with row covers

Bacterial leaf spot Bacterium Xanthomonas campestris

Symptoms

Dark, angular lesions on leaves; leaf lesions may coalesce and cause severely blighted foliage; water-soaked lesions which enlarge and develop into tan scabs, or blisters, on the fruit; blisters eventually flatten as they reach their full size

Comments

Disease can spread rapidly in a field; disease can be introduced through contaminated seed

Management

Avoid overhead irrigation; rotate crops away from cucurbit species to prevent disease building up; use new seed each planting as saved seed is more likely to carry bacteria; apply appropriate protective fungicides; copper containing fungicides generally provide good control

Bacterial wilt Bacterium Erwinia tracheiphila

Symptoms

Severely wilted vines; leaves appear dark green; dark discoloration on leaves and stems; rapid plant death

Comments

Spread by striped or spotted cucumber beetles; disease can be confirmed by cutting the stem and slowly pulling the two ends apart - infected plants will ooze strings of bacterial exudate

Management

Control cucumber beetle populations on plants; hand pick adult beetles and destroy; soil and foliar application of appropriate insecticides may help to control populations

Blossom-end rot Nutritional disorder

Symptoms

Symptoms first appear on immature fruits as small light brown spots close to the blossom end of the fruit; as fruit grow, the spots enlarge, resulting in dark leathery lesions sunken into the fruit

Comments

Management

Blossom-end rot is caused by a lack of calcium in the developing fruit and it occurs when the uptake of nutrients to the plant is disrupted; factors which disrupt nutrient uptake include drought, root damage or high soil salinity; application of excess nitrogen fertilizer may also contribute to the development of blossom-end rot as it promotes vigorous growth of vegetative tissues and depletion of calcium in the soil; watering plants evenly and regularly reduces the incidence of blossom-end rot

Cabbage looper Insect Trichoplusia ni

Symptoms

Large or small holes in leaves; damage often extensive; caterpillars are pale green with a white lines running down either side of their body; caterpillars are easily distinguished by the way they arch their body when moving; eggs are laid singly, usually on the lower leaf surface close to the leaf margin, and are white or pale green in color

Comments

Insects overwinter as pupae in crop debris in soil; adult insect id a dark colored moth; caterpillars have a wide host range

Management

Looper populations are usually held in check by natural enemies; if they do become problematic larvae can be hand-picked from the plants; an organically acceptable control method is the application of Bacillus thuringiensis which effectively kills younger larvae; chemical sprays may damage populations of natural enemies and should and should be selected carefully

Cercospora leaf spot Fungus Cercospora citrullina

Symptoms

Initial symptoms of disease occur on older leaves as small spots with light to tan brown centers; as the disease progresses, the lesions enlarge to cover large areas of the leaf surface; lesions may have a dark border and be surrounded by a chlorotic area; the centers of the lesions may become brittle and crack

Comments

Fungus survives on plant debris; spread by wind and water splash; occurs mainly in tropical and subtropical growing regions

Management

Any diseased plants should be removed and destroyed to prevent further spread; crop debris should be removed after harvest or plowed deeply into the soil to reduce inoculum

Cucumber beetles (Western striped cucumber beetle, Western spotted cucumber beetle, Banded cucumber beetle) Insect Acalymma vittata
Diabrotica undecimpunctata
Diabrotica balteata

Symptoms

Stunted seedling; damaged leaves, stems and/or petioles; reduced plant stand; plants may exhibit symptoms of bacterial wilt; scars on fruit caused by beetle feeding damage; adult beetles are brightly colored with either a green-yellow background and black spots or alternating black and yellow stripes.

Comments

Beetles overwinter in soil and leaf litter and emerge from soil when temperatures begin to reach and exceed 12.7°C (55°F).

Management

Monitor new planting regularly for signs of beetle; floating row covers can be used to protect the plants from damage but will need to be removed at bloom to allow bees to pollinate plants; applications of kaolin clay can be effective for management of small beetle populations; application of appropriate insecticides may be necessary.

Cucumber mosaic Virus Cucumber mosaic virus (CMV)

Symptoms

Plants are severely stunted; foliage is covered in distinctive yellow mosaic; leaves of plant curl downwards and leaf size is smaller than normal; flowers on infected plants may be deformed with green petals; fruits become distorted and are small in size; fruit is often discolored.

Comments

Transmitted by aphids; virus has an extensive host range; can be mechanically transmitted via tools etc.

Management

Control of the virus is largely dependant on the control of the aphid vectors; reflective mulches can deter aphid feeding; aphid outbreaks can be treated with mineral oils or insecticidal soap applications; some resistant varieties are available.

Cucurbit yellow stunting disorder virus Virus Cucurbit yellow stunting disorder virus (CYSDV)
Genus: Crinivirus
Group: "Positive sense ssRNA viruses"

Symptoms

The symptoms generally appear on the older leaves first. Initially the symptom appears as chlorotic spotting which leads to intervenial chlorosis and followed by severe yellowing. The infected leaves may roll upward and become brittle. Also the infected plant may appear stunted.

Comments

The virus is mainly transmitted by whitefly Bemisia tabaci. The host range is restricted to the Cucurbitaceae (watermelon, melon, cucumber, squash, courgette etc.,).

Management

Grow virus free and whiteflies free seed materials. During the growing season use yellow sticky traps to monitor and control whiteflies. Remove the infected plants and burn them. Keep the field free from weeds. In case severe infestation of whiteflies, use suitable insecticides. After a growing season remove the crop debris, volunteer plants and destroy them.

Cutworms Insects Agrotis spp.
Peridroma saucia
Nephelodes minians
and others

Symptoms

Stems of young transplants or seedlings may be severed at soil line; if infection occurs later, irregular holes are eaten into the surface of fruits; larvae causing the damage are usually active at night and hide during the day in the soil at the base of the plants or in plant debris of toppled plant; larvae are 2.5–5.0 cm (1–2 in) in length; larvae may exhibit a variety of patterns and coloration but will usually curl up into a C-shape when disturbed.

Comments

Cutworms have a wide host range and attack vegetables including asparagus, bean, cabbage and other crucifers, carrot, celery, corn, lettuce, pea, pepper, potato and tomato.

Management

Remove all plant residue from soil after harvest or at least two weeks before planting, this is especially important if the previous crop was another host such as alfalfa, beans or a leguminous cover crop; plastic or foil collars fitted around plant stems to cover the bottom 3 inches above the soil line and extending a couple of inches into the soil can prevent larvae severing plants; hand-pick larvae after dark; spread diatomaceous earth around the base of the plants (this creates a sharp barrier that will cut the insects if they try and crawl over it); apply appropriate insecticides to infested areas of garden or field if not growing organically.

Downy mildew Fungus Pseudoperonospora cubensis

Symptoms

Small yellow areas on the upper leaf surface; brown lesions with irregular margins; gray mold on lower leaf surface.

Comments

Disease emergence favored by moist conditions.

Management

Do not overcrowd plants; avoid overhead irrigation, water plants from base; apply appropriate fungicide.

Flea beetles Insects Epitrix spp.

Symptoms

Small holes or pits in leaves that give the foliage a characteristic “shothole” appearance; young plants and seedlings are particularly susceptible; plant growth may be reduced; if damage is severe the plant may be killed; the pest responsible for the damage is a small (1.5–3.0 mm) dark colored beetle which jumps when disturbed; the beetles are often shiny in appearance.

Comments

Younger plants are more susceptible to flea beetle damage than older ones; older plants can tolerate infestation; flea beetles may overwinter on nearby weed species, in plant debris or in the soil; insects may go through a second or third generation in one year.

Management

In areas where flea beetles are a problem, floating row covers may have to be used prior to the emergence of the beetles to provide a physical barrier to protect young plants; plant seeds early to allow establishment before the beetles become a problem - mature plants are less susceptible to damage; trap crops may provide a measure of control - cruciferous plants are best; application of a thick layer of mulch may help prevent beetles reaching surface; application on diamotecoeus earth or oils such as neem oil are effective control methods for organic growers; application of insecticides containing carbaryl, spinosad, bifenthrin and permethrin can provide adequate control of beetles for up to a week but will need reapplied.

Fusarium crown and foot rot Fungus Fusarium solani

Symptoms

Wilting of leaves progresses to wilting of entire plant and plant dies within a few days; distinctive necrotic rot of crown and upper taproot when plant is uprooted; plant breaks easily below soil line

Comments

Fungus can survive in soil for 2-3 years

Management

Plant fungicide treated seed; rotate crops on 4 year rotation

Gummy stem blight Fungus Didymella bryoniae

Symptoms

Brown or tan spots of various sizes on leaves; leaves covered with lesions; stems splitting and forming cankers; wounds exude a brown, gummy substance; wilting vines; death of stems

Comments

Disease may be seed-borne

Management

Use disease free seed; treat seeds prior to planting; rotate crops every 2 years

Leaf miners Insect Lyriomyza spp.

Symptoms

Thin, white, winding trails on leaves; heavy mining can result in white blotches on leaves and leaves dropping from the plant prematurely; early infestation can cause fruit yield to be reduced; adult leafminer is a small black and yellow fly which lays its eggs in the leaf; larave hatch and feed on leaf interior

Comments

Mature larvae drop from leaves into soil to pupate; entire lifecycle can take as little as 2 weeks in warm weather; insect may go through 7 to 10 generations per year

Management

Check transplants for signs of leafminer damage prior to planting; remove plants from soil immediately after harvest; only use insecticides when leafminer damage has been identified as unnecessary spraying will also reduce populations of their natural enemies

Phytophthora crown and root rot Oomycete Phytophthora capsici

Symptoms

Sudden and permanent wilting of plant; leaves do not change color; plant death within a few days; roots and stem close to soil line discolored light to dark brown; plant easily removed from soil

Comments

Fungus can be spread through air; disease emergence favors high temperatures and water saturated soil

Management

Efficient management of water to avoid saturated soil; avoid long periods of irrigation

Powdery mildew Fungi Erysiphe cichoracearum
Sphaerotheca fuliginea
Podosphaera xanthii

Symptoms

White powdery growth on the upper surfaces of leaves and stems; infected areas stunted and distorted.

Comments

Disease emergence favored by dry weather and high relative humidity.

Management

Plant in sites with good air circulation and sun exposure; do not overcrowd plants; sanitize equipment regularly.

Septoria leaf spot Fungus Septoria cucurbitacearum

Symptoms

Initial symptoms of disease are small dark water-soaked spots on the leaves which turn beige to white in dry conditions; lesions develop thin brown borders and the centers may become brittle and crack; small white spots may erupt on the surface of infected butternut and acorn squash and pumpkin fruit

Comments

Pathogen can survive on crop debris for periods in excess of 1 year

Management

Scout plants during cool wet conditions for any sign of spots; early application of an appropriate protective fungicide can help limit the development of the disease if spots are found, cucurbits should be rotated with other crops every 2 years to prevent the build-up of inoculum; crop debris should be removed and destroyed after harvest

Squash bug Insect Anasa tristis

Symptoms

Speckled leaves which turn yellow and brown; wilting plants; dieback of runners; blemished fruit; fruit death; adult squash bugs are often misidentified as stink bugs; they are grey-black in color with orange and black stripes on the edges of their abdomen; nymphs are greenish gray in color and often covered in white powder; female squash bugs lay conspicuous copper colored eggs on the undersides of the leaves

Comments

Squash bugs overwinter in crop debris or under rocks and stones

Management

Destroy all crops residue as soon as possible after harvest or on plant death; apply row covers at planting; apply insecticidal soap or appropriate insecticide

Squash mosaic Virus Squash mosaic virus (SqMV)

Symptoms

Symptoms vary with variety being grown but plants can show symptoms which include include green veinbanding, mottled leaves, blisters, ring spots or potruding veins at leaf margins; some squash varieties may develop leaf enations; infected plants are often stunted and fruits may be malformed with mottled skin

Comments

Virus can be transmitted through infected seed and spread by striped cucumber beetles

Management

Use only certified disease-free seed

Squash vine borer Insect Melittia cucurbitae

Symptoms

Wilting plants; holes in vines or at base of petioles; green frass (insect excrement) visible around holes

Comments

Insect overwinters in soil as larvae or pupae and adults emerge in spring; adults lay eggs on leaves and larvae burrow intro stems to feed

Management

Apply appropriate insecticide if eggs are found on leaves; plow plants into soil after harvest

Stinkbugs (Various) Insect Various

Symptoms

Dark colored pinpricks on fruit surrounded by a lighter area that turns yellow or remains light green; stink bugs often carry pathogens in their mouthparts which can cause secondary infections and decay of fruit; adult insect is shield-shaped and brown or green in color; may have pink, red or yellow markings; eggs are drum shaped and laid in clusters on the leaves; larvae resemble the adults but are smaller

Comments

Adult insects overwinter under leaves, on legumes, blackberries or on certain weeds such as mustard or Russian thistle

Management

Remove weeds around crop which may act as overwintering sites for stink bugs and practice good weed management throughout the year; organically accepted control methods include the use of insecticidal soaps, kaolin clay and preservation of natural enemies; chemical treatments are not recommended for tomatoes that are to be processed for paste or canning unless secondary infections with other pathogens are a concern

Thrips (Western flower thrips, etc.) Insect Frankliniella occidentalis

Symptoms

If population is high leaves may be distorted; leaves are covered in coarse stippling and may appear silvery; leaves speckled with black feces; insect is small (1.5 mm) and slender and best viewed using a hand lens; adult thrips are pale yellow to light brown and the nymphs are smaller and lighter in color

Comments

Transmit viruses such as Tomato spotted wilt virus; once acquired, the insect retains the ability to transmit the virus for the remainder of its life

Management

Avoid planting next to onions, garlic or cereals where very large numbers of thrips can build up; use reflective mulches early in growing season to deter thrips; apply appropriate insecticide if thrips become problematic

Verticillium wilt Fungus Verticillium dahliae

Symptoms

Symptoms generally appear after fruit set; chlorotic leaves which develop necrotic areas; leaves collapsing; symptoms only on one side of vine; discoloration of vascular tissue in roots

Comments

Fungus can survive in soil for many years; disease emergence favored by cool or mild weather in Spring

Management

Do not plant in areas where other susceptible crops have been grown previously; delay planting until temperatures are warmer

Watermelon mosaic Virus Watermelon mosaic virus (WMV)

Symptoms

Symptoms vary widely depending on species, cultivar, virus strain and environmental conditions; symptoms on leaves may include green mosaic patternation, green vein-banding, chlorotic rings and disfigured leaves; infected fruits may develop green spots - particularly if fruit is yellow

Comments

Virus is found in almost all Cucurbit growing regions in the world; virus is spread by over 20 aphid species

Management

Use of resistant varieties can greatly reduce virus incidence; treatments that control populations of aphid vectors can also reduce the incidence of the virus; spraying plants with mineral oils or insecticidal soaps can help to reduce aphid numbers

Zucchini yellow mosaic Virus Zucchini yellow mosaic virus (ZYMV)

Symptoms

Infected plants are severely stunted and leaves can exhibit a variety of symptoms including yellow mosaic patternation, severe deformation, blistering, reduced size and necrosis; fruits are deformed

Comments

DIsease can cause devastating epidemics when present

Management

Use of resistant varieties, where available, is usually the most effective method of controlling the virus; control of aphid populations on the plants can be achieved through the use of mineral oils and insecticidal soaps but is rarely effective at controlling the virus

References

CABI Crop Protection Compendium. (2008). Cucurbita (pumpkin) datasheet. Available at: http://www.cabi.org/cpc/datasheet/17341. http://www.cabi.org/cpc/datasheet/17064. [Accessed 15 April 15]. Paid subscription required.

Heflebower, R. & Drost, D. (2010). Summer and Winter squash in the garden. Utah State University Cooperative Extension. Available at: http://extension.usu.edu/files/public.... [Accessed 15 April 15]. Free to access.

Polomski, B. (2003). Summer squash. Clemson Cooperative Extension. Available at: http://www.clemson.edu/extension/hgic.... [Accessed 15 April 15]. Free to access.

Zitter, T. A., Hopkins, D. L. & Thomas, C. E. (1996). Compendium of Cucurbit diseases. American Phytopathological Society Press. Available at: http://www.apsnet.org/apsstore/shopap.... Available for purchase from APS Press.