Everything you need to know about summer squash cultivation, production and harvest. Learn about:- 1. Introduction to Summer Squash 2. Origin and Distribution of Summer Squash 3. Composition and Uses 4. Climate and Soil Required for Cultivation 5. Sowing Time 6. Manurial Requirement for Cultivation 7. Irrigation Requirement for Cultivation 8. Intercultural Operations and Few Others.
- Introduction to Summer Squash
- Origin and Distribution of Summer Squash
- Composition and Uses of Summer Squash
- Climate and Soil Required for Cultivating Summer Squash
- Sowing Time of Summer Squash
- Manurial Requirement for Summer Squash Cultivation
- Irrigation Requirement for Summer Squash Cultivation
- Intercultural Operations of Summer Squash
- Harvesting and Yielding of Summer Squash
- Physiological Disorders Seen in Summer Squash
- Cultivated Varieties of Summer Squash
1. Introduction to Summer Squash:
Summer squash is also known as vegetable marrow, Italian marrow and field pumpkin, however, in India, it is known by several names, like chappan kaddu, vilayati kaddu, kumra and safed kaddu. It is grown in many temperate and subtropical regions, ranking high in economic importance among vegetable crops worldwide. There are six extant groups of cultivars, viz. cocozelle, crookneck, scallop, straight neck, vegetable marrow, and zucchini, and most of them have existed for hundreds of years.
Their different fruit shapes determine their suitability for various methods of culinary preparation. The zucchini group, a relatively recent development, has undergone intensive breeding in the United States and Europe. It is the most widely grown and economically important group of the summer squashes.
Summer squash, which is harvested for culinary purpose at immature stage before the hardening of rind, differs from winter squash and pumpkin. Among summer vegetables, it appears earliest in the market. In India, it is cultivated in the states of Punjab, Haryana, Delhi, Uttar Pradesh, Jammu and Kashmir, Himachal Pradesh, and West Bengal.
Summer squash is an annual bush or vine often trailing in growth habit. Its leaves are deeply-lobed and petioles usually covered with prickly hairs. The plant produces stem with greatly shortened internodes and sets fruits in close succession. The yellow, green, or white colour fruits with white or pale-scentless flesh have a hard deeply furrowed five-angled peduncle.
Summer squash is usually monoecious but occurrence of an androecious mutant is also reported. The fruits sometimes have the bitter principles cucurbitacins- tetracyclic triterpines- that occur naturally in the family cucurbitaceae and cause bitterness. Such compounds can occur in all parts of the plant though the concentration, tends to be highest in roots. Plants may have exceptionally bitter fruits but non-bitter leaves or cotyledons.
Concentration of cucurbitacins may be several times higher in the placental region of the fruit compared to pericarp or the rind. The sporadic occurrence of bitter fruits has caused serious medical problems in a few cases. Ingestion of as little as 3 g of such fruits can cause nausea, stomach cramps, and diarrhea.
2. Origin and Distribution of Summer Squash:
Summer squash (Cucurbita pepo), the native of North America, is said to be originated from wild species Cucurbita texana, occurring in the south-central USA, and C. fraterna, occurring in northeastern Mexico. The word squash has been derived from native North American word asq (plural asquash), meaning ‘uncooked or unripe fruit’. It has been domesticated in North America for at least 10000 years ago.
Archeological records favour the idea that C. pepo was grown and domesticated in North America initially for consumption of its seeds. Squashes were introduced to Europe by returning Spanish explorers in the 1500’s.
Summer squash is an excellent source of minerals, particularly of magnesium, copper, and potassium. It also contains fairly good amount of fiber. Its fruit is a very rich source of vitamin A (β-carotene), riboflavin, vitamin B6, folic acid, niacin, and vitamin C. The summer squash seeds contain 30-51% oil rich in linoleic acid (43-55%) and oleic acid (27-38%). The seeds also contain good quantity of carbohydrates 6-10%, proteins 31-51% and minerals 4-5%. The composition of summer squash fruits is given in Table 17.1.
Summer squash fruits at immature stage are eaten as a cooked vegetable. Its tender male flower is also used in various preparations. There are some ‘naked seeded’ mutants of which the seeds are fried in oil, salted, and eaten as a snack.
4. Climate and Soil Required for Cultivating Summer Squash:
Summer squash is although a warm-season crop but being tolerant to low temperature it can be grown both under high and low temperature conditions. It cannot tolerate frost, thus, it should be planted when danger of frost is over. The plants can be grown successfully at a temperature range from 24° to 27°C. Optimum soil temperature for seed germination is about 30°C. Germination is severely reduced at temperature below 15°C, and yield is also affected adversely when temperature exceeds 35°C.
The environmental factors, i.e., temperature, light intensity, and photoperiod play a key role in the determination of flower gender/sex expression in cucurbits. Cool conditions generally favor the production of female flowers. Over all mean temperature is most important in sex expression, however, night temperature plays a significant role since warm nights lead to increased male flowers production at a given temperature compared to warm days.
The temperature effect may occur during differentiation of flower primordia or the development of flower to anthesis. Low temperature may inhibit development of male flowers after differentiation, resulting in precocious female flowering.
In brief, the conditions those encourage the buildup of carbohydrates and those reduce the amount of vegetative growth tend to favor female flower expression, on the contrary, the conditions such as high temperature, low light intensities, high fertility especially nitrogen levels, and close spacing, which promote stem extension and reduce carbohydrates buildup, also increase maleness.
High light conditions, generally, favor production of female flowers, while shading or low light intensity delays the onset of female flowering. Prevalence of low light intensity in association with high temperature predominantly favors the production of male flowers. The effect of photoperiod on sex expression appears to be less striking than the temperature and light intensity.
Short photoperiod tends to favour the production of female flowers. Cooler temperature and shorter photoperiod increases the proportion of female flowers than when the same cultivar is planted in contrast conditions, and where the conditions conflict temperature tends to be more important. Monoecious plants produce female flowers earlier under cool-long day conditions than in hot-short day conditions.
Summer squash can be grown on almost all types of soil, however, a well-drained sandy loam or loam soil rich in organic matter is considered the best for getting higher yield. Summer squash is sensitive to acidic and alkaline soils with high salt concentration. The soil pH should be 6.0 to 7.5 for its successful cultivation. The soil is prepared well to a fine tilth by repeated ploughing and planking.
5. Sowing Time of Summer Squash:
In northern plains of India, it is, generally, sown in February-March but in areas of frost-free, it can also be sown from October to January to take early crop. In hilly tracts, the optimum sowing time for summer squash is April to May, depending on altitude. However, in southern parts of India where winter is mild, the crop can be grown almost throughout the year.
Summer squash needs about 6-7 kg seed for sowing in a hectare area. Seed priming before sowing is found beneficial in enhancing seed germination and plant growth too. Seed priming in aerated solutions using PEG at -1.5 MPa, KNO3 at 2 or 3% or KNO3 + K2HPO4 (ratio of 1 : 1) at 2 or 3% in complete dark at 18°C for 2 days significantly improved the emergence of seeds; the priming treatments also improved the uniformity of seedlings compared irrespective of osmotic agent used or duration of treatment.
Soaking of seeds in 1 ppm continuously aerated cobalt solution for 48 h before sowing has been found to increase growth, femaleness, and fruit yield. Plants from cobalt soaked seeds produced significantly higher ethylene levels as early as the seedling stage (14-30 days after seed sowing).
Kamar et al. (1986) reported that seed soaking in Cu (300 ppm) + Mn (1000 ppm) solution significantly increased total yield of summer squash. Abed and Sharabash (1985) also reported that seeds soaking in Cu (500 ppm), Mn or Zn (2000 ppm) for 24 h before sowing gave higher seed germination, plant growth, and fruit yield compared with a untreated control.
Low temperature is limiting factor for early production of crop during spring-summer. Summer squash is very susceptible to low temperature (below 10°C). However, its seedlings can be raised during last week of December or first week of January under protected condition. Seedlings are raised in polythene bags of 15 × 10 cm size and thickness of 200 gauge. Bags are filled with well rotten farmyard manure and soil (1 : 1). In each bag, 2-3 healthy seeds are sown during last week of December or first week of January.
The seedlings as soon as attain a stage of 3-4 true leaf and the outside temperature becomes favouable are transplanted in the main field. The appropriate age for transplanting the summer squash transplants in field is 21 day old. Adopting such technique, the crop can be advanced by about 1 to 1½ month than the direct sown crop. In summer squash, about 8,500 to 10,000 seedlings are required for the planting of one hectare land area.
In spring-summer season, the pits of 45 × 45 × 45 cm size are dug 2-3 weeks before planting at a spacing of 1 × 1 m, and filled with a mixture of farmyard manure (3-4 kg/pit) and top soils, however, in rainy season, either the raised beds or the ridges are made to facilitate drainage. Usually, about 40 cm wide furrows are made at a distance of about 1 m in case of bush type cultivars and about 1.5-2.0 m for viny cultivars.
The seeds are sown at a plant-to-plant spacing of 75-100 cm in bush type cultivars and about 1.0-1.25 m in case of viny type. Per hill, at least 2-3 sprouted seeds are sown to avoid gap created due to failure of germination. In riverbeds of North India, the seeds are sown in deep pits or trenches of 1.0-1.5 m depth. The pits are filled with mixture of farmyard manure (10 kg), urea (40 g), diammonium phosphate (40 g) and muriate of potash (25 g), and thereafter, 3-4 seeds per hill are sown at a depth of 2-3 cm.
In summer squash for obtaining higher yield of better quality produce, it is important to maintain optimum plant population, which usually varies from 8 to 13 thousand plants per hectare, depending upon cultivar and method of growing. In a hectare area, around 9-10 and 12-13 thousand plants of bush and viny type cultivars can be accommodated, respectively.
6. Manurial Requirement for Summer Squash Cultivation:
The analysis of plant for nitrogen, phosphorus, potash, and calcium confirmed that nutrients removal by summer squash is relatively low, thus, about 15-20 t/ha of well rotten farmyard manure, which should be applied at the time of soil preparation, is enough for its successful cultivation.
Besides, nitrogen 40-60 kg, phosphorus 20-30 kg and potash 30 kg/ha are also needed. Full dose of phosphorus and potash and half dose of nitrogen are applied as basal at the time of last ploughing. Rest of the nitrogen is top dressed about four weeks after seed sowing.
Application of boron is also essential since it is required for continued DNA synthesis and cell division in root meristems of summer squash. Stephano et al. (1995) reported that application of boron (1 g borax/hill or two foliar sprays of borax at 0.03% applied at 30 days interval) significantly increased fruit yield. Soil application has been found more effective than foliar spray.
7. Irrigation Requirement for Summer Squash Cultivation:
Irrigation during summer should be given at an interval of 3-4 days depending upon weather and soil type. Vine growth, flowering, and fruit development are the most critical stages for irrigation requirement since water stress during these phases may reduce plant growth, flowering and fruiting. Moisture deficit during flowering and fruiting may cause wilting and drying of apical portion of the developing fruits, however, frequent and heavy irrigation should be avoided, especially in heavy soils, as it promotes excessive vegetative growth.
In rainy season, proper drainage is equally important to drain out the excess rainwater since water logging reduces the photosynthetic rate (Pn) by reducing stomatal conductance (gs) and chlorophyll content of leaf. Water logging also greatly reduces the root and shoot growth and fruit yield in summer squash.
Stansell and Smittle (1989) reported that the marketable fruit yield was higher, and production cost per kilogram of marketable fruit was least when the summer squash was irrigated at 25 kPa of soil water tension. Haynes and Herring (1980) found that trickle irrigation in summer squash at 700 mbars gave the highest marketable yield. However, the number of marketable fruits was highest with irrigation at 300 mbars.
8. Intercultural Operations of Summer Squash:
In early growth period, the weeds pose problem, therefore, weeding should be done frequently in order to keep the weeds under check. One manual weeding at about 20-25 days after seed sowing is usually recommended for summer squash. Pre-sowing incorporation of Bensulide (6.5 kg/ha) or Di-butalin (1.5 kg/ha) gives an excellent control of weeds in summer squash.
Pre-emergence application of pendimethalin or Alachlor @ 1 kg/ha is also very effective for the control of weeds. Application of weedicides controls weeds only for about 30-35 days, thus, thereafter one hand weeding may be supplemented, if required. Mulching is also found effective for controlling weeds in summer squash.
The use of plastic mulch or row covers can overcome the chilly and frosty weather conditions and result in an early crop production, and use of reflective films as mulch also increases yield, reduces aphids, and delays infection of mosaic virus in summer squash.
Jensen et al. (1999) found that infestation of whitefly, a vector for the transmission of Gemini virus in summer squash, can be avoided for 18 days just after transplanting/sowing by covering young seedlings or transplants with non-woven floating cover, and recorded an increase of 60% fruit yield with the use of floating covers, whereas, an increase of 160% yield was achieved with combined use of plastic mulch and floating covers.
Silver and polyethylene film mulches delays the onset of aphid-transmitted virus diseases, however, the water-soluble biodegradable silver mulch has more advantageous over polyethylene film mulch because of its biodegradation into the soil at the end of growing season. Brown et al. (1996) reported that aluminium painted plastic mulch (APM), white plastic mulch (WPM), and black plastic mulch (BPM) increased total yields of summer squash by 96, 98 and 75%, respectively than plants on bare soil.
The onset of mosaic disease infestation on plants was delayed by as much as 3 weeks in the APM treatment compared with bared soil treatments, and the minimum percentage (39%) of viral infection was observed in plants with APM treatment, whereas, the maximum infestation (72%) was observed in BPM.
Growth substances in summer squash are used for modifying sex, and increasing fruit set and yield. There are many reports that the production of male flowers can be temporarily suppressed for 2-3 weeks by spraying ethephon at first true-leaf stage. Application of ethephon (600 ppm) twice at 2 and 4 leaf stages results in complete suppression of male flowers and promotion of female flowers during early stage, which ultimately increases the yield.
Saimbhi and Gill (1988) reported that application of ethephon (390 ppm) advanced the production of female flowers and delayed and/or reduced that of male flowers in C. pepo. Ethephon also increased the number of female flowers and fruits per plant and total fruit yield.
Similarly, Gad et al. (1993) found that spraying of ethrel (225-300 ppm) over summer squash seedlings markedly reduced the number of male flowers and increased the number of female flowers within first 15-20 days from anthesis and increased both early and total yield.
Kasrawi (1995) also reported that foliar sprays of ethephon in bush type summer squash at 300-600 ppm completely suppressed staminate flower production for the first 16 nodes. Similarly, Singh et al., (1989) obtained highest early and total yield in summer squash (cv. Hisar Selection-1) with spraying ethrel 250 ppm at 2- and 4-true- leaf stages.
Arora et al. (1989) reported maximum early yield, number of fruits per plant and total fruit yield of summer squash with foliar spray of 100 ppm paclobutrazol (P333) at 6-8 full expanded leaf stage.
9. Harvesting and Yielding of Summer Squash:
Summer squash fruits develop very rapidly after pollination, thus, its timely harvesting is very important. The crop is ready for harvest in about 50-80 days after seed sowing, depending upon variety, soil fertility and weather conditions, and fruits after anthesis usually take 6 to 8 days to be ready for picking. Fruits should not be allowed to become too large, hard and seedy.
For optimum quality, harvest the fruits while they are tender and still have a shiny or glossy appearance. The quality of fruit is lost rapidly as the shiny color changes to a dull color. Actual fruit size at harvest depends on the market demand. Most elongated varieties are picked when they are 15- 20 cm long and 5 cm or less in diameter. The fruits of Patty Pan cultivar types are harvested when they are 7 to 10 cm in diameter. Harvesting is usually done every alternate day, and sometimes, every day.
At harvest, a short piece of peduncle attached to the fruit is kept intact. Using a sharp knife or pruning shear to cut the squash fruit peduncle from the vine and putting cotton gloves at harvesting to avoid scratching and puncturing the fruit are always better.
Summer squash fruits are generally stored at 10°C temperature and 90% relative humidity with a wind velocity of 10 feet per second. Storage at low relative humidity (40%) for 12 h results in excessive dehydration and shrinkage of fruits due to high rate of physiological loss in water and respiration, which is 2.7 times more rapid at a holding temperature of 35°C than at 10°C.
Smittle et al. (1980) observed minimal weight loss and physiological changes during a 9 days storage period when immature fruits were stored at 5°C temperature and 85 to 95% relative humidity. The weight loss was 4 times greater at 10°C and 6 times greater at 15°C. Generally, the fruits are harvested at immature tender stage. Hence, the deterioration of fruits is rapid. Fruits of summer squash should be handled carefully and used immediately after picking.
The yield of summer squash crop varies from 15 to 35 t/ha, depending upon variety, soil fertility, growing weather conditions and other inputs, like fertilizers, irrigation, intercultural operations and management of insect-pests and diseases. The average yield ranges from 20 to 30 t/ha in a crop duration of 65-90 days, however, the fruit yield up to 50 t/ha can also be obtained, if crop is grown under ideal conditions with good agronomic practices.
i. Precocious Flowering:
The induction of androecious flowers in summer squash is suppressed in temperate regions under cool conditions. Thus, precocious development of female flowers results low or no fruit set due to a dearth of male flowers. This disorder is less pronounced in open pollinated vine type cultivars. Spraying with GA4+7 at a stage of first flower appearance can hasten the induction of male flowers, which will solve the problem precocious flowering.
The ingestion of only 3 g of bitter fruit of summer squash may cause serious health hazards like, nausea, stomach cramps, food poisoning, and diarrhea. Such fruits contain an alkaloid-cucurbitacin (tetracyclic triterpenes), which is responsible for bitterness and other human disorders. This compound, generally, occurs in all plant parts but the levels tend to be highest in roots.
In fruits, its content may be several limes higher in placental region than the pericarp, thus, the bitter fruits of not only summer squash but also of all other cucurbits would potentially be more dangerous than those of which placenta is not consumed.
11. Cultivated Varieties of Summer Squash:
i. Punjab Chappan Kaddu:
It is an early maturing variety developed at Punjab Agricultural University, Ludhiana. It is an inbred selection from the segregating local variety of Punjab. Plants are bush-type, foliage erect, non- lobed and green without white specks, and stem is mildly ribbed with flat end.
It has a predominant female tendency, and bears about 10 fruits per plant with an average weight of about 80 g/fruit. It takes about 60 days from sowing to first harvest, and gives fruit yield of about 20-25 t/ha. It has been reported to have field resistance against downy mildew and red pumpkin beetle.
It is a bush type variety introduced from USA and recommended by Indian Institute of Horticultural Research, Bangalore for cultivation in India. Fruits are disc-shaped, chalky white, tender and very attractive at edible stage. It is a short-duration variety (85-90 days) with yield potential of about 54 tonne per hectare.
It is very early bush-type introduced variety, which was grown and acclimatized at Indian Agricultural Research Institute, Vegetable Research Station, Katrain. Fruits are 25-30 cm long, uniformly green with light green stripes, and very tender at edible stage. It bears 15-20 fruits per plant with an average yield of 15-16 t/ha.
It is an early bush type variety developed at Indian Agricultural Research Institute, Vegetable Research Station, Katrain. Fruits lire medium sized, waited and tapering towards stem end. Flesh is tender at edible maturity stage.
This cultivar is evolved at Indian Agricultural Research Institute, Vegetable Research Station, Katrain. It is an early maturing F1 hybrid between EC 207050 and Sel. 1 PI 8 (a selection from the cross of Chappan Kaddu and Early Yellow Prolific) with uniform dark green fruits, slightly tapering towards the stem. The flesh is tender and delicious at edible stage. It takes 45 to 50 days from sowing to first harvest, and gives a yield of about 20-30 t/ha.