SUCCEED WITH WATER MELONS - Water melons are a simple crop to grow and generally thrive in hot and humid climatic regions. Water melons in Zimbabwe are generally consumed by all sections of society and are quickly gaining popularity with health activists. Marketing water melons is generally easy as commercial entities and informal vegetable markets easily retail the crop. In a country engulfed with liquidity challenges, one may consider water melons as an alternative stream of income source. This guideline is, therefore, designed to assist the reader with the fundamentals in order to obtain good returns. Climatic Requirements Water melons are generally sensitive to cold temperatures and even a mild frost can severely damage the crop. The best average temperature range for water melon production during the growing season is between 18 oC and 35 oC. Temperatures above 35 oC or below 10 oC will slow the growth and maturation of the crop. Soil Requirements Watermelons grow best on non-saline sandy loam or silt loam soils. Fields with light textured soils warm up faster in the spring and are, therefore, favoured for early production. Very sandy soils have limited water holding capacities and must be carefully irrigated and fertilised to allow for high yield potential. Clay soils are generally avoided for water melon culture, but they can be productive if irrigated with care to prevent prolonged saturation of the root zone (a condition that favours the development of root rot pathogens) and to allow good drainage between irrigations. The soil should have a pH of 5.8 to 6.6. Fields should be prepared thoroughly by ploughing and harrowing and removing the different types of plant debris. It should also be pulverised and levelled. Furrows are made 2 m apart. Water melon is known to be sensitive to manganese toxicity, a frequent problem in low-pH soils. Further research studies indicate an association between high leaf manganese concentration and poor growth and yield of water melon. Seedlings of water melons react to manganese toxicity with stunted growth and yellowish, crinkled leaves. Older plants generally exhibit spots on leaves that may be mistaken for symptoms of gummy stem blight. Manganese toxicity is usually associated with soils having a pH below 5.5. However, in wet seasons the condition may occur at higher pH levels. This condition was also noted in several water melon fields with pH ranges at 5.8 or slightly higher when the crop was planted on the flat. Planting water melons and other cucurbits on a bed is good insurance against manganese toxicity during a wet season. The best solution to manganese toxicity is to apply lime in autumn at rates based on the results of a soil test. A pH of 6.0 should be maintained for maximum yields. Planting Period and Days to Maturity In Zimbabwe, water melons can be planted in the Lowveld from June to August and in the rest of the country from August to October. The crop matures three months after planting, and the yield varies from 5 to 72 ton/ha. It is usually takes about 80 to 90 days for baby bush varieties and 90 to 100 days or more for the large varieties to reach maturity. Spacing In large-scale production, few seeded varieties are currently grown. Watermelons are planted on flat beds 2 m wide and 20 cm to 30 cm high. In direct-seeded plantings, seed is placed 1.2 cm to 1.9 cm deep. After thinning and side dressing, furrows are reformed to the condition prior to furrow irrigation. For transplants, a single drip irrigation tape is laid 15 cm to 20 cm below the bed surface. Black plastic film, 1.8 m wide, is then laid flat on 2 m beds to heat the soil and reduce weeds. Seeds or transplants are then planted directly through the plastic. Transplants are set 60 cm to 90 cm apart. About 15 cm of the plastic is covered with soil at the edges to hold the mulch in place. Common seedless water melon planting configurations are 1 row of the seed variety (pollinator) for every 2 to 3 rows of the seedless variety. However, other novel configurations are being used. The most popular is the mixing of seedless and pollinator plants from 2:1 to 5:1. As the seedless to pollinator ratio increases, the number of beehives should be increased to ensure pollination. The seed rate is 16 to 25 seeds per 10 m2 (1.0-3.0 kg/ ha). Fertilisation Water melons have moderate nutrient requirements compared to other vegetable crops, and because of its deep rooting it is efficient in extracting nutrient requirements from the soil. We recommend compound L (4:17:11) or Compound C (5:15:12) for basal fertiliser application, and Ammonium Nitrate (34.5 % N) as top dressing. Weed Control Shallow mechanical cultivation and hand-hoeing are needed to control weeds before plants have developed vines. Pruning roots and vines with cultivating equipment slows melon development and reduces yield. Several pre-emergence herbicides are available that will control germinating broad leaf weeds and grasses in seeded and transplanted water melons if used properly. Chemicals are economical when used as narrow band applications in the planted row. Other chemicals can be used as a lay by application between the rows before vines begin to run. Herbicides are applied with shallow incorporation and transplants are placed with the roots below the treated zone. Post-emergence herbicides such as Agil 100EC are used to control grasses. Methyl bromide was commonly used in the past in field fumigations, but currently metham sodium is used to control weeds pre-emergent. Common Pests and their Remedies Cutworm - Fenvalerate/Lambda-cyhalothrin Aphids - Dimethoate 40 EC, Malathion 25 WP Fruit fly - Lebaycid 50 EC, Malathion 25 WP, or Dipterex 95 SP. Common Diseases and their Remedies Watermelons are susceptible to several diseases that attack the roots, foliage, and fruit. Disease control is essential in the production of high quality water melons. A preventative program that combines the use of cultural practices, genetic resistance, and chemical control as needed usually provides the best results. Cultural practices are useful for limiting the establishment, spread and survival of pathogens that cause water melon diseases. Many of the fungal, bacterial, and nematode pathogens survive in old crop debris and in the soil. Fields with the proper soil characteristics should be selected. (Disease Symptoms Control) Verticillium Wilt Yellowing of the foliage and wilting. Copper oxychloride 85 WP Anthracnose Early signs of infection by this bacterial disease are water-soaked spots on the leaves and fruit. Mancozeb, hlorothalonil. Fusarium Wilt Affects runners of the plant, at advanced stage may cause wilting Benomyl 50 WP Powdery Mildew Premature defoliation, and reduced crop growth. Wettable sulphur, Bavistin, Benomyl 50 WP. Charcoal Rot Death of crown leaves combined with grey stem lesions. Apply potassium and phosphorous fertilisers Downey Mildew Initial symptoms include large, angular or blocky, yellow areas visible on the upper surface. Polyram DF, Copper Oxychloride 85 WP Rhizoctonia and Soil-borne Diseases. “Damping off”, or the failure of infected seeds to germinate. Seed dressings with Vitavax Plus or Thiram 80 WP. Fruit Pruning Fruit pruning in water melons should begin as soon as defective melons are noticed. Remove misshapen and blossom end rot fruit to promote additional fruit set and better size of the remaining melons. If a market demands larger melons, remove all but two or three well-shaped melons from each plant. To avoid disease spread, do not prune melons when vines are wet. Physiological Disorders Physiological disorders are caused by non-pathogen agents that affect fruit quality. Usually, aesthetic quality is negatively affected. The cause can be either one or a combination of environmental, genetic or nutritional factors. Below is a list of some of the common fruit disorders: • Misshapen melons (gourd-necked or bottlenecked) are frequently produced by varieties with long fruit. Moisture stress is a cause. Occasionally melons of any variety may misshape because they lie on uneven ground or were damaged when small. Misshapen or pear-shaped fruit can also be caused by poor pollination that leads to restricted growth at the stem end because of the absence of developing seeds. Poor pollination can be minimised by increasing the number of beehives in the field. Low temperatures can also cause misshapen fruit. • Blossom end rot is a deterioration of the blossom end of the fruit. The usual order of development is softening, slight shrivelling, browning, blackening with extensive shrivelling, and sometimes secondary decay. Poor calcium nutrition and moisture stress cause blossom-end rot. Hot, dry winds, nematode damage, excessive fertiliser, low levels of calcium in the soil, pruned roots from late cultivations, and other conditions are contributing factors. • Bursting may result from an uneven growth rate, which is particularly associated with heavy rainfall or irrigation when the fruit is maturing. The percentage of bursted fruit is usually low, and types with round fruit are more susceptible. • White heart consists of white streaks or bands of undesirable flesh in the heart (centre) of the fruit. This is caused by excessive moisture (and too much nitrogen) during fruit maturation. • Hollow heart is a disorder that varies among varieties. Hollow heart is marked by cracks in the heart of the water melon fruit owing to accelerated growth in response to ideal growth conditions facilitated by ample water and warm temperatures. • Sun Scald (burn) results from exposure to intense solar radiation that leads to dehydration and overheating damage of the rind tissue. Sun Scald can be alleviated by covering the fruit with vines or straw materials. • Sun burn occurs most frequently in varieties that have dark green rinds. Charleston Grey types and other melons with grey grin rinds rarely suffer from sunburn. Good healthy foliage will minimise sunburn damage as well as favour good yields and quality. Strong winds can blow unprotected vines away from the developing fruit along the edges of the rows and cause full exposure of the fruit to the sun. • Rind necrosis is an internal disorder of the watermelon rind. Symptoms are brown, corky, or mealy textured spots on the rind which may enlarge to form large bands of discoloration that rarely extend into the flesh. Experienced pickers often can detect affected melons by the subtle knobbiness that is visible on the surface of the affected melons. The cause of rind necrosis is unknown. Bacterial infection has been reported to be a cause, although similar bacteria are found in healthy melons. Drought stress also is reported to predispose melons to rind necrosis. • Cross stitches are elongated necrotic wounds (2 cm long) that are perpendicular to fruit length. The cause of cross stitches is unknown. Harvesting Determining optimum maturity of a water melon can be difficult. Water melons reach harvest maturity five to six weeks after pollination, depending upon variety and season. Varieties may differ in certain characteristics that include maturity. An experienced person can identify a ripe water melon just by glancing at the glossy rind surface. Other indications of ripeness include a change in the colour of the ground spot from white to light yellow, a change of tendrils nearest the fruit from green to brown and dry. Thumping the fruit, a metallic, ringing sound indicates immaturity and a more muffled or dull sounds indicates maturity to over maturity in round-shaped melons. The best method is to cut a few melons in various parts of the field. Harvesting and marketing green or over-ripe melons lessens the damage by the consuming public. Sugar content does not increase after the harvest. However, a red colour will continue to develop after a slightly immature melon is picked. Harvesting Methods Watermelons do not slip from the vine or emit an odour when ripening, unlike muskmelons. Indicators for picking watermelons include colour change (the most reliable), blossom-end conditions, rind roughness and drying of the nearest tendril to the fruit (less reliable). A sharp knife should be used to cut melons from the vines. Melons pulled from the vines may crack open. Harvested fruit is windrowed to nearby roadways, often located ten beds apart. A pitching crew follows the cutters and pitches the melons from hand to hand, then loads them in trucks to be transported to a shed. Melons should never be stacked on the blossom end, as excessive breakage may occur. Loss of foliage covering the melons can increase sunburn. Exposed melons should be covered with vines and straw as they start to mature to prevent sunburn. Each time the field is harvested, the exposed melons must be re-covered. Most fields are picked at least twice. Some fields may be harvested a third or fourth time depending upon field conditions and market prices. Harvest Recommendations Melons should be cut from the vine rather than pulled, twisted or broken off to reduce the chances of stem decay. Leave a long stem on the fruit. To avoid bruising melons, handle them carefully at all times. Never stand melons on end to avoid bruising and flesh separation from the rind. Do not place melons with the bottom sides turned up as the ground spot is easily sun-scalded. Haul melons from the field in straw or paper padded vehicles to reduce bruising, punctures, and rind abrasion. To help prevent bruising, put them directly into trucks for ferrying to the market, or haul them to a central grading station for reloading and transportation. Melons are usually graded and sized during the loading operation. Traditionally, melons have been bulk- hauled in trucks. The use of containers has gained popularity because they are more efficient in unloading and damage caused by rough handling during loading and unloading is reduced. Bulk bins made of corrugated fireboard and holding around 450 kg as well as cartons holding three to five melons are also used.
Posted on: Sat, 08 Nov 2014 12:02:17 +0000