Flowers of bitter gourd are first developed 45 to 55 days after sowing and vines will bloom for about six months. Flowers are cross-pollinated by insects, especially bees. Pollination can be a problem during the wet season since bees are less active during overcast conditions. Each flower opens at sunrise and remains viable for only one day. Pollen loses viability as the day advances and may be fully inviable by midday. To ensure good pollination and avoid the need for hand pollination, introduce beehives or blow pollen around with an unloaded mister.
Bitter gourd is monoecious, in other words, male and female flowers are borne separately on the same plant (Fig. 8). The male flowers normally exceed the females by about 25:1. Long days cause male flowers to bloom up to two weeks before female flowers, while short days have the opposite effect. Spraying vines with flowering hormones after they have six to eight true leaves will increase the number of female flowers and can double the number of fruits.
For example, one application of gibberellic acid at 25–100 ppm increases female flowers by 50% and can work for up to 80 days. Other hormones have similar effect, but may reduce vine length and leaf area resulting in decreased total yield. As mentioned earlier, pruning the lower lateral branches increases the number of flowers per plant by increasing the number of flowers on higher laterals.
In Taiwan, yield of bitter gourd is increased by grafting with luffa (Luffa spp.). Luffa resists fusarium wilt and is more tolerant to flooding, which allows bitter gourd to survive in waterlogged soils.
Mulching is commonly used for bitter gourd crops grown on raised beds (Figs. 4–6). Use organic or plastic mulch depending on availability. Organic mulch such as dry rice straw or grass is usually available and cheaper than plastic mulch. If you use organic mulch, be sure that it is free of weed seeds. Mulch can be laid down before or after transplanting and after sowing. Several herbicides are available, but make sure that you select a herbicide recommended for bitter gourd. Hand or hoe weeding can be performed as needed.
Controlling Diseases and Pests
Bitter gourd is susceptible to many of the same diseases that affect other cucurbits. It is a host of watermelon mosaic potyvirus (Fig. 9) and is infected by downy mildew (Fig. 10), Cercospora leaf spot, bacterial wilt, fusarium wilt, and root knot nematode. Fungal infections often occur during prolonged wet periods. Fungicide sprays may be used under such conditions to prevent infection. The use of resistant varieties is the best defense for most of these diseases.
Figs. 9, 10. Symptoms of watermelon mosaic potyvirus on cucumber (left) and downy mildew on luffa (right)
Fruit fly is the most destructive insect pest of bitter gourd. This fly is difficult to control because its maggots feed inside the fruits, protected from direct contact with insecticides. Bury any infested fruits to prevent the build up of fruit fly populations. To prevent flies from laying eggs inside the fruits, enclose the gourd in paper while it is on the vine. A cylinder of paper, longer than the fruit, is tied with string around the stalk. Where consumers want their bitter gourd straight rather than curved, tie a pebble at the end of a long piece of string to the flower end to weigh down the fruit and keep it from curling. Double layer paper bags may be used against fruit fly and are applied when gourds measure 2–3 cm in length.
Beetles, thrips, cutworms, bollworm, aphids and mites are other common pests of bitter gourd. Chemical control of insect pests should be done only when significant damage occurs. Avoid pesticides that kill or inhibit the development of beneficial organisms especially the pollinators. Choose pesticides that last only a few days. Wear protective clothing and follow all instructions carefully on the label when applying pesticides.
Harvesting and Handling
Bitter gourd requires close attention at harvest time. The fruits develop rapidly and must be harvested frequently to keep them from becoming too large or too bitter. Normally it takes 15–20 days after fruit set or 90 days from planting for fruit to reach marketable age, however, bitter gourd can be harvested at earlier stages depending on the purpose for which it will be used. Fruit should be light green, thick and juicy, and the seeds should be soft and white.
Harvest every 2–3 days using a pair of scissors or a sharp knife to cut the fruit stalk. If a fruit remains too long on the vine, it will turn spongy, sour, yellow or orange, and split open (Fig. 11).
Bitter gourd yield can vary depending on variety and crop management. Average marketable yields are 8–10 t/ha. A yield of 20–30 t/ha is excellent and some F1 hybrids yield up to 40 t/ha.
Fruits of bitter gourd do not keep long and should be sold in the market immediately. Remove damaged and deformed fruits. Carefully arrange fruits in bamboo baskets or boxes (Fig. 12) and store in a cool place at 12–13°C with 85–90% relative humidity. Under this condition, fruit storage life can be extended 2–3 weeks. Bitter gourd is chilling sensitive and damage may occur if kept below 10°C.
Do not store fruits at temperatures above 13°C, as this will result in fruits turning yellow and splitting open. Keep harvested fruits away from other fruits (such as banana, pineapple and apple) that release large amounts of ethylene, a ripening hormone.
source: Marid Digest, authored by AVRDC’s Dr. Manny Palada and LC. Chang, World Vegetable Center, Taiwan