Effective pest management in organic rice production

Rice is not very susceptible to many pests, except stem borers whose effect differs depending on the region. Even when rice is attacked by pests, they cannot cause significant yield loss despite damage to the plant. Rice can recover very well and still deliver more or less the same yield as the non-damaged crop. Research and observations have shown that there is no direct relation between moderate damage and yield loss as trials with farmers in many integrated pest management training programs have demonstrated. These trials show that up to 30 to 40 % of damage to leaves and 10 to 20 % of damage to tillers will not result in any yield loss because the rice plant is able to compensate for lost leaves and tillers.

However, stem borers can be devastating in rice if not properly managed and can delay flowering and time of harvest and reduce yields e.g. such cases have been reported especially in West Africa. The stem borers attack the panicles and result in dead shoots.

Generally, rice pests can be categorised into three main groups depending on the stage of the rice growing cycle when they are most likely to attack:

a. Seedling pests which attack seedlings during the younger stages of the rice crop include rice gall midge, snails, crabs and thrips.

b. Leaf and tiller feeding pests, sucking leafhoppers and stem borers which bore in the tillers include Chilo zacconius (striped borer), Marliarpha spp. (white borer), Scirpophgaga spp. (yellow borer), Sesamia calamistis (pink borer) common in uplands, Diopsis thoracica (stalk-eyed fly) and Orselia oryzivora (African rice gall midge) common in lowland rice.

c. Pests in ripening rice include birds, rats and bugs (stink bug, rice bug, mealy bug and rice weevil). While bugs stay on the young panicles and suck the milky juice causing staining of the grains (lowering grain quality), rodents (e.g. rats) cut down the rice plant and feed on the soft parts and on the mature grains. Birds feed on the filling grain as well as mature grains.

Generally, there are many preventive methods of managing rice pests which have proved very effective, and thus direct pest control is rarely needed. Some of the popular and widely used methods in organic cropping systems are:

Good land preparation whereby all material remaining after harvest is ploughed/dug into the soil during land preparation will minimize the incidence of most pests, especially stem borers as they are covered and killed under the soil. Proper plant spacing also allows sunshine to penetrate into the basal portion of the rice plants and thus conditions like coolness and humid environment which favour the growth of pests are reduced.
Mosaic planting can be achieved by growing different rice varieties of varying growth patterns and resistance to pests and diseases on the same land at the same time or through varietal diversification. Varietal diversification can be achieved by planting at least three rice varieties on the same fields to create a mosaic pattern of varieties. Due to the differential resistance of varieties to pests and diseases, any devastative effects from any pest or disease outbreaks can be avoided. Likewise, varieties with varying plant maturity duration in terms of planting and harvesting dates can be considered to distribute labour requirements on the farm.
Intercropping has a high potential as a cultural method of controlling the major stem borers on rice. Maize is a suitable trap crop for stem borers. Strip cropping of four rows of maize alternating with an equal number of rice plants (NERICA) rows has been found effective in controlling stem borers.
Proper water management in irrigated lowland systems: especially if the water level can be raised up to 10-15 cm so that it can drown and wash out any worms, bugs or leaf hoppers during drainage.
Birds are a problem in most rice growing areas, however, they can be effectively controlled. They do most harm in the early morning and late evening, and with routine monitoring and scaring, the damage caused will be reduced significantly. Scaring them away by hanging old tins in the field to make noise, use of scarecrows, catapults or shielding the field with nets have proved effective to some extent. Shooting to kill and trapping the birds are not friendly practises to the ecosystem. They are, therefore, not recommended in organic farming.