Low-Cost Technology for Soybean Pests
Ways of protecting soybeans before and after harvest from insect pests
Low-Cost Technology for Low-Income Farmers
New agricultural technology often needs expensive inputs and advanced skills. However, some scientists are working on improved technology that uses resources freely available on small farms. Like biotechnology, this kind of technology is biologically based. However unlike biotechnology, it is available for little or no cost, and poses no threat to the environment.
Rice Hull Ash Protects Stored Soybeans
Soybeans stored in simple containers on small farms in Asia are often infested with pests such as bruchid beetles. In Indonesia, there have been good results from adding rice husk ash to stored beans. The ash is mixed with the soybeans at a rate of 1 part per 100 (by weight).
Fresh, dry ash should be used, and the beans should be dried well before they are mixed with the ash and stored. The beans are put in a large metal can (from six to eighteen liters), and the ash spread and mixed in gently by hand. The lid is then placed tightly on the can, which should be stored in a cool, dry place.
Since rice husk ash is freely available on local farms, this technology does not cost the farmer anything but a little labor. The treatment is also non-toxic, and very effective. Tests on soybean/ash samples deliberately infested in the laboratory with beetles showed 100% mortality, which lasted three months after treatment.
How Does It Work?
Rice husk ash is not poisonous in itself. Its lethal effect on the beetles is not yet fully understood. However, the main ingredient of rice husk is silica. When the husk is burnt, the ash has almost the same composition as diatomaceous earth, a light chalky material which occurs naturally in some parts of the world.
Diatomaceous earth has many uses in both industry and agriculture. It is often used as a filler in paint or pesticide dusts, and also as an abrasive. One product is explicitly used for the control of pests of stored grain, and is very effective. Perhaps the high silica content of the rice husk ash has a similar lethal effect.
Rice husk ash also contains a large number of needle-like particles. These are probably derived from the setae, the fine hairs on the outer surface of the rice hull. These may damage the skin of the beetles, and induce a reaction that leads to their death.
Controlling Soybean Pests by Synchronized Cropping
Traditional cropping practices may also control pests. In parts of North Aceh, Sumatra, Indonesia, damage to soybeans from Etiella podborers is consistently very low, at around 1%. Farmers in this area seldom use pesticides. In other parts of Indonesia damage is severe, especially in the dry season when 50% of pods may be damaged.
Cropping in these parts of north Aceh is intensive, with as many as three crops of soybean each year. Scientists looking for the reason why pest damage is so low found that soybean crops were synchronized over a wide area. When it is time to sow, farmers meet in the village and hold special ceremonies. The village leader then instructs the farmers to prepare their land and soybean seed. As soon as the rains begin, farmers go out into the fields to sow their crops.
Since all the soybean crops mature at the same time, there is a period between the harvesting of one crop and the planting of the next when there is nothing for soybean pests to eat. Population levels of pests plunge. There is never time for them to recover to the level found in areas where soybeans are cultivated throughout the year.
Farmers in North Aceh also plant a wider range of varieties than is normal elsewhee. This too may help protect their crops from pests.
Trap Crops
Growing soybean plants are often infested with various species of stink bug. These may cause severe damage to young seeds ripening in the pod. Various kinds of trap crop were tested in Indonesia, including long bean, cowpea and pigeon pea. Sesbania (Sesbania rostrata) was one of the most effective.
It has several of the characteristics of a good trap crop. It is attractive to the pest. It grows taller than the crop it is protecting, and takes longer to mature. Like other ideal trap crops, it is also a useful plant in itself.
Sesbania As a Trap Crop for Soybean
Trap crops should occupy a small space, not more than 5-10% of the total planted area. They must be planted earlier than the main crop, and remain attractive to pests until after the main crop is harvested. If the population of pests in the trap crop is too high, the pests should be controlled with insecticide or some other method, to stop them from reproducing.
Soybean fields with a trap crop of Sesbania had only about one-tenth the number of stink bugs found on unprotected soybeans. Only 17% of the soybean seeds were damaged by stink bugs, compared to 43% damage when Sesbania was not used.
The effective control area of the Sesbania seems to extend about 15 m. In smaller fields, the Sesbania is planted along two sides of the field, usually on opposite sides (i.e. running north/south, or east/west). In large fields, the Sesbania can be intercropped with the soybean in rows about 15m apart.
(For more information, see FFTC Extension Bulletin No. 468, by the same author, on this
database)
Index of Images
Figure 1 Farmer in Java, Indonesia, with Tins for Storing Soybeans. the Plastic Bag on the Tin Is Full of Rice Husk Ash.
Figure 2 Stinkbugs on the Trap Crop Sesbania Rostrata
Figure 3 a Fine Crop of Soybeans Grown without Pesticides in Aceh, Indonesia
