Monitoring early pests in rice
May 28, 2009 11:01 AM, UC Cooperative Extension, Colusa County
During the seedling stage, rice plants are susceptible to many pest problems. Arthropods and diseases can reduce stands, which could later translate into problems such as increased weed pressure, lodging, and ultimately, reduced yields.
Midges can greatly affect plant establishment. Adult midges look like mosquitoes but do not bite. They lay their eggs on the water surface once the field is flooded. Larvae hatch in one or two days. They live in the soil surface and can feed in germinating seeds and small seedlings.
Another important pest of the seedling stage is tadpole shrimp. Tadpole shrimp eggs can survive several years in dry fields and hatch once the field is flooded in the spring. This arthropod can feed on germinating seeds and uproot seedlings during foraging in the soil. Their foraging also muddies the water, reducing light penetration and slowing down seedling growth.
Crayfish can cause problems similar to tadpole shrimp. Additionally, their tunneling activity can disrupt levees and produce water leaks. This is especially critical during water holding periods after the application of a pesticide.
Check your fields during seedling development. Floating seedlings and muddy water is a good indication of tadpole shrimp activity. If the water is clear, you may see them on the bottom or you may see their shed skins floating in the water.
Also, examine injured seedlings for midge larvae and tubes. Monitor seedling establishment closely five to seven days after seeding. If you find less than 30 healthy seedlings per square foot and signs of midge or tadpole shrimp presence, a management action may be needed. Monitor again a week later. If the stand is below 25 seedlings per square foot and there are signs of midge or tadpole shrimp activity, a management action may be needed.
Currently, no insecticides are registered against midges or crayfish. Copper sulfate can be effective against tadpole shrimp; however, recent studies have shown that copper can bind to straw residue, reducing its efficacy. Cultural practices are a good option to manage these pests. Once seedlings have well established roots they are less susceptible to injury by these pests, therefore, anything that promotes quick seedling establishment will help reduce their impact.
Minimizing the time between flooding and seeding is an effective way to prevent the establishment of midges and tadpole shrimp during the period of seedling susceptibility. If crayfish becomes a problem, crop rotation may help reduce their numbers in the field.
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