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Be on the Lookout for Early Season Insect Pests

Safer, Less Expensive Biologic...

BY HOLLY DAVIS

s planting gets underway for sor ghum, cotton and sesame, remember to keep an eye out A for seed and seedling insect pests, including wireworms and cutworms. They can be tricky to recognize as they have a secretive lifestyle. The damaging immature stages remain on or under the soil surface thus it’s often the losses resulting from their feeding that alerts growers to their presence. Wireworms are not typically a major pest in the Lower Rio Grande Valley but may be an occasional problem when land taken out of fallow, there is significant crop residue, or where there was heavy weed pressure in previous years.

These cylindrical, shiny, hard-bodied, yellowish to brown “worms” are the immature stages of click bee-

tles (true wireworms) or darkling beetles (false wireworms). They mainly feed on seeds, leading to large skips in the row where plants fail to emerge, but may also feed on seedling plants, reducing vigor. You can determine if you need to plan for wireworm management prior to planting. Sampling can be done by examining a one square-foot area of soil, four inches deep, in several locations throughout the field. Bait traps can also be set several weeks before planting using corn or sorghum seed. An average of one wireworm per sampling area or two per bait station may warrant the use of insecticide-treated seed or an at-plant insecticide application. In some cases, replanting areas with large skips due to wireworm feeding is the most economical option. For more information on wireworm sampling, please see Managing Insect and Mite Pests of Texas Sorghum, AG-085.

Several species of cutworms may attack seedling plants. The adults (moths) deposit eggs in weedy areas along field margins and/or on the stems or leaves of crops. Larvae emerge in 2-14 days and, depending on the species, may range in color from grayish white to grayish-black and reach 1-2 inches long, often curling into a c-shape when disturbed. They remain at the base of plant and feed, cutting plants off at, just above, or a little below, the soil surface. A few species, such as the variegated cutworm and army cutworm, will feed on foliage. When scouting for cutworms look for severed, dead and dying plants. Seed treatments will not provide good control of cutworms, but at-plant treatments may be warranted in areas with a history of heavy cutworm pressure, i.e. fields near banks, along tree lines and other weedy areas. Typically cutworms are best controlled with rescue, post-emergence applications, applied where established stands are at risk or when above ground (foliar) feeding reaches 30% or more on seedling plants. Because larvae are active at night, insecticide applications made in the late afternoon or evening will be more effective.

Several cultural practices can help reduce wireworm and cutworm problems. These include destroying weeds and cultivating to reduce plant material 4-6 weeks before planting, preparing good seed beds and planting when soil moisture and temperatures will promote rapid germination and seedling growth.