By Dr. Jarrod Hardke
University of Arkansas
The three main insect pests of rice in Arkansas are grape colaspis (Lespedeza worm), rice water weevil and rice stink bug. Of these, grape colaspis and rice water weevil have traditionally been the most difficult to manage. The most damaging stage of both is the immature stage that feed on roots in the soil. Management of a pest you can’t see is always the most difficult.
In recent years, three insecticide seed treatment products have become available for use in rice: CruiserMaxx Rice, NipsIt INSIDE and Dermacor X-100. CruiserMaxx and NipsIt provide the best control of grape colaspis, while Dermacor provides the best control of rice water weevil. Knowing which pest you need to worry most about is critical when deciding which seed treatment to use.
Much of the acreage planted to rice in Arkansas is in annual rotation with soybean – this is where grape colaspis infestations can be the most severe. Acres planted continuously in rice or in rotation with other crops are less at risk of grape colaspis injury. If you have a problem with grape colaspis, CruiserMaxx or Nips It would be the logical choices to control colaspis and provide management of rice water weevil.
Rice Water Weevil
If rice water weevil is your only concern, Dermacor provides better control. Dermacor now has a label in Arkansas for use in waterseeded rice (dry seed only – cannot pre-soak seed). In water-seeded rice, water weevil infestations can be severe as they are attracted to open water and the small rice seedlings can have difficulty withstanding the level of insect feeding pressure that can occur.
If choosing to go without an insecticide seed treatment of any kind (not recommended), the window for insect management is very small. To control rice water weevil with a foliar insecticide application, treatments need to be made approximately seven to 10 days after flood establishment. Typically, leaf-feeding scars from adult rice water weevil can also be observed at this time, but not always. Once this window has closed, foliar applications have little or no impact on rice water weevil management.
Secondary pests can also be suppressed by insecticide seed treatments. CruiserMaxx and NipsIt can suppress chinch bugs, aphids and billbug (important in furrow-irrigated rice). Dermacor has little, if any, impact on those pests but can suppress stalk borers.
Length Of Seed Treatment Efficacy
Insecticide seed treatments are not designed to last throughout the growing season. A reasonable expectation would be for these products to maintain some level of efficacy out to 35-40 days, but no longer. Irrigation and rainfall can have a direct impact on this – studies have indicated that multiple irrigation flushes (or possibly heavy rainfall events) can lead to the loss of the treatments earlier than normal.
Dermacor appears to be more stable and less prone to this effect and may maintain activity longer under these conditions than the other insecticide seed treatments.
Plan to insure your rice crop with an insecticide seed treatment this spring. In over 40 trials since 2007, insecticide seed treatments have provided a positive net return 80 percent of the time with an average yield increase of eight bushels per acre. Choose the product that is most appropriate based on your needs and product pricing. Keep in mind when evaluating price that CruiserMaxx contains an insecticide and fungicides, while NipsIt and Dermacor are insecticides only, and fungicides will need to be added.
Dr. Jarrod Hardke is a rice Extension agronomist with the University of Arkansas, Cooperative Extension Service. Contact Hardke at firstname.lastname@example.org.