Vegetable Seed Production: Pumpkin and Squash

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Common Name: Pumpkin and squash Scientific Name: Cucurbita pepo Family: Cucurbitacea

Soil Nutrition

Pumpkins and squash require soils that are fairly fertile, and well drained. Maximum yields are achieved on medium-textured soils with high water-holding capacity and good internal drainage. They can be grown on a wide range of soils, although peat and heavy clay soils are not recommended. Clay soils generally have poor aeration and restricted drainage, which can be detrimental to root growth and increase fruit rot.

Pumpkins and squash are sensitive to acid conditions, but will grow well on slightly acidic (pH 6.8) to moderately alkaline (pH 8.0), soils. Pumpkins and squash are quite sensitive to salinity.

A crop rotation cycle of several years between planting members from the family Cucurbitaceae is required if pathogen populations are very high and fumigation is not used. When possible, grasses, corn or sorghum are good rotation crops. However, care must be taken that there are no carryover herbicide residues, which might inhibit growth.

Planting

In the Western US and some places in the East, pumpkins and squash are generally grown on raised beds (6 to 8 inches). Final spacing of the beds in furrow irrigated culture is generally 80 inches center-to-center.

Many growers in the East grow pumpkins without irrigation or mulch. Plastic mulch is sometimes used for pumpkins and winter squash production primarily for weed control, to keep fruit clean, and for moisture conservation since earliness is not a big issue except for summer squash production. Studies have shown that yields can be increased by plasticulture. Planting is by direct seeding or occasionally transplanting through holes punched or burned in the plastic cover. Drip irrigation or fertigation is used with the plasticulture system. Black plastic aids weed control, clear is used in northern areas to increase soil temperatures especially for early season planting of summer squash.

No-till pumpkin production works well and is rapidly gaining popularity. A cover crop is used and pumpkins are seeded directly or transplanted into the dead cover crop residue when the soil is sufficiently warm in the early summer.

Pumpkins and squash are generally planted from seed. However, both crops are sometimes transplanted in northern areas but are very sensitive to transplant shock and should be planted only as a plug with a root ball. The minimum, optimum, and maximum soil temperatures for seed germination are 65 F, 95 F and 100 F, respectively. Germination is slow and erratic when soil temperature is below 68 F. Fruit maturing when daily mean air temperatures are below 70 F have poorer quality. Pumpkins do well in hot weather, but very high temperatures (110-115 F) can cause temporary vine wilting, sunburned fruit, and soft fruit at harvest with reduced shelf life.

Spacing depends on whether cultivars are bush or vining. Large fruited pumpkins and squash are often planted in hills 6 to 8 feet apart with rows 6 to 8 feet apart. Bush cultivars are planted at much closer spacing with in-row spacing as close as 3 feet with 6 feet between rows. Large acreages can be seeded in rows six to ten feet apart. Seeds are placed at 0.5 to 1.0 inches deep. In-row spacings of 6 inches are common and plants may be thinned to a final spacing at the 2 to 4 leaf stage.

Fruit size may be modified by plant spacing. Closer spacings generally produce smaller fruit and wider spacings generally result in larger fruit. Hybrids usually are less affected by close spacing than open-pollinated cultivars, but more affected by wider spacings. This is due to their greater vigor throughout the vine-growth and fruiting cycles.

Irrigation

Squash and pumpkin have extensive, moderately deep, root systems that efficiently explore the soil for water. Pre-plant or post-plant irrigations should be applied to ensure seed germination, emergence and stand establishment.

Drip irrigation is increasingly used, particularly in the Eastern US. Drip irrigation provides the most uniform application of water with the least amount of water used. Sprinkler irrigation is frequently used during stand establishment, but this is not a good system once the vine canopy has become large, because it may result in significant vine and fruit disease. Furrow irrigation is the least efficient, least uniform, but is a common method of irrigation in the Western US.

Botany

Cultivated Species (All with 20 Pairs of Chromosomes)

• Warm-season, frost sensitive annuals
  • Cucurbita pepo L., - Pumpkin, Winter squash, Summer squash, Gourds
  • Cucurbita moschata - Duch., Pumpkin, Winter squash
  • Cucurbita maxima - Duch., Pumpkin, Winter squash
  • Cucurbita argyrosperma - Pang., Pumpkin, Gourds
  • Cucurbita ficifolia - Bouche, Malabar or Figleaf Gourd (not widely grown in US)
• Perennial
  • Cucurbita foetidissima HBK, Buffalo gourd

• C. lundelliana Bailey (Central America)
• C. martinezi Bailey (east coast Mexico)
• C. andreana Millan cross fertile with C. maxima (South America)
• C. texana Gr. Millan cross fertile with C. pepo (Southern U.S. and Northern Mexico

The various species of Cucurbita are very similar and often difficult to tell apart. The following characteristics are used to differentiate the species: Tabulation of Key Characters Differentiating the Cultivated Species of Curcurbita

Isolation

The recommended isolation distance between seed crops within this group is 1000 m. It is also important to avoid areas where even a few of these types are grown domestically for fruit production.
Crops for basic seed production should be isolated by at least 1500 m.

Pollination

Cucurbits require that pollen move from staminate to pistillate flowers or from the anthers to the stigma of perfect flowers. Honey bees are the msot reliable and cost-effective way to achieve pollination. One to two hives per acre are introduced when 5 to 10 percent of the plants have open flowers. If hives are placed in weedy areas or close to other flowering crops, the number of hives per acre should be increased. Hives should be placed in clusters around the periphery of fields, with additional hives placed inside of larger fields.

F1 hybrids dominate the market for most commerical cucurbit crops due to their greater vigor, higher yield, and greater uniformity than open-pollinated varieties. In addition, since parent lines are proprietary and seed cannot be propagated for a second generation from hybrid seed, seed company investments in varietal research and development are more secure.

In hybrid squash production, ethylene-releasing compounds suppress male flower production; the treated plants will produce mostly female flowers. Adjacent rows of the male parent lines are not sprayed. In both the genetic and chemical methods, only the female rows are harvested for hybrid seed.

Roguing

1. Early vegetative stage: Check that vegetative characters (e.g. bush or trailing type), foliage and vigor are in accordance with cultivar. Resistance to specific pathogens according to the cultivar description.
2. Before first flowers open: As above, and check that undeveloped fruit characters on female flower buds are true to type.
3. First female flowers setting: Check that developing fruits are true to type, and as above.
4. Fruit developing: Fruit characters true to type, and resistance to specific pathogens according to the cultivar description.

Seed Harvest

All squashes, pumpkins and marrows take approximately sixteen weeks from anthesis to seed maturity. By this stage the rind has hardened and changed color. The green types change to a yellow-orange color and the yellow-gold colored types change to a straw color.

For large-scale production fruit may be placed in windrows ready for the mobile thresher and extractor. Alternatively they are left on the vine for an automatic vine harvester to pass through the field.

The fruits of some cucurbits such as winter squashes are relatively dry by the time the seed is mature and ready for extraction. In this case water has to be introduced into the separator to wash the seeds free from fruit debris.

Cleaning

After extraction the seeds are washed in troughs and dried (as described for watermelon). Cucurbita seeds are not fermented during the cleaning process as this tends to discolor them and reduce the potential germination.
After drying, seeds are passed through an aspirated screen cleaner to remove pieces of dried fruit debris and any light seeds.

Seed Yield

The average seed yield is about 500 kg per hectare (446 pounds per acre), but under good pollination and cultural conditions up to 1000 kg per hectare (892 pounds per acre) can be obtained.

Seed Identification:

From: Whitaker, T.W. and G.W. Bohn. 1950. The Taxonomy, Genetics, Production, and Uses of the Cultivated Species of Curcurbita. Econ. Botany 4(1) 52-81.

Scientific Name:	Cucurbita pepo, Cucurbita maxima
Common Name:	Pumpkin and squash
Family:	Cucurbitacea
Weight:	The 1000 grain weight is approximately 200 g, depending on the cultivar.
(Note: 1 small square in above image = 1 mm)
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