Pest management

Insects

Understand the value of IPM in dealing with insects

How do insects reduce yields?

By physical damage: Insects reduce leaf area, and damage panicles and stems.

By spreading diseases Many insects (e.g., green leaf hopper) spread viral diseases like tungro.

Some insects like brown plant hopper

cause direct damage (hopper burn).

If you see insect damage consider the following:

If there is	remember that
leaf loss,	Early damage on the leaves is rarely a problem. The plant usually recovers, unless more than 50% of the leaves are damaged or lost, then there may be delayed development and maturity.
Tiller loss:	Early tiler loss before and just after panicle initiation may not be a problem, if other tillers can compensate.
Panicle and grain loss:	Late panicle and late grain loss will likely reduce yield, as rice has little flexibility to increase kernel weight to compensate. But it is not always that bad. For example, up to 1 whitehead/hill in hills producing 20 or more productive tillers do not generally affect yield.

Are pesticides the solution to deal with insects?

In a rice field, hundreds of species of insects, spiders, and other organisms are linked in a food web. Many insect pest problems in tropical rice have been found to be disruptions of this food web by weather extremes, cultivation practices, and pesticide use.

Based on scientific evidence, it is questionable whether routine insecticide treatment of rice is needed to protect the crop. In surveys of rice farmers in the Philippines,untreated fields yielded as much as fields treated with one to five or more pesticide applications. Sometimes pesticides can even cause pest outbreaks. Click here for an example out of Thailand.

Spraying pesticides may even cause more damage

as you also kill insects that are helpful!

The solution to deal with insects is through IPM

Based on experience and research findings during the 1970s, the advantages of combining several tactics in IPM systems instead of relying only on insecticides or host plant resistance became clearer.

In the meantime, thousands of rice farmers have learned to use IPM principles in their rice fields. Although this represents the largest crop-specific group of farmers practicing IPM anywhere in the world, it is still only a fraction of the total number of rice farmers in Asia.

Asian rice farmers often spray insecticides during the first 30-40 days after transplanting or seeding. Their main targets are leaf-feeding insect pests. The rice crop, however, can usually recover from early-season insect injuries with no significant loss in production.

Insecticide spraying during this early period increasingly appears to be unnecessary and can lead to secondary pest problems, such as brown planthopper. In Vietnam, farmer experiments on withholding insecticide sprays during the first 30-40 days after seeding helped to motivate the government’s decision makers to endorse the “no early insecticide spray” rule as a standard practice in rice production. (see picture below)

IPM in Vietnam: This posters explains rice farmers in Vietnam

not to spray insecticides in the first 30 days after transplanting.

Always consider the economics!

All losses and actions must be balanced against the cost. Calculate the amount of grain required to cover the cost of the application. Will you lose this much?

More information

Click on the icon to open a manual with more information on:

Control of insects on rice

Click on an icon to open a fact sheet with specific information about the following insects:

Army worm		Rice bug
Green leafhopper		Rice leaffolder IPM
Plant hoppers		Stem borer IPM

Next lesson

In the next lesson we will discuss the pest of weeds.