FOCUS on Entomology: May 2019

Tuesday, May 21, 2019

Texas High Plains cotton: Time to scout for thrips and wireworms

With the cotton planting in full swing and the early-planted crop making its way up, it is time to begin scouting for early-season insect pests. Wireworms are a growing problem in the region especially in fields with reduced tillage and those following grain crops. Wireworm larvae damage cotton by feeding on the root, hypocotyl (stem of the germinating seedling), and cotyledon of plants before emerging from the soil. Wireworm injury usually results in stunting; however, heavy pressure can kill plants and reduce plant stand substantially. There are no rescue treatments for wireworms--early field scouting will help making timely replant decisions if necessary.

Wireworm injury (Photo: Pat Porter)

Thrips are the number one insect-pest of seedling cotton in the region. Their feeding causes foliar deformity (leaves crinkle and cup upward), plant stunting and delays in maturity. Thrips species composition in the Texas High Plains region is mainly formed by onion thrips and the western flower thrips. Preventive insecticide seed treatments provide good control against these species up to 3 weeks after planting. However, this can vary with growing conditions and the weather. When scouting for thrips, there is truly no substitute for whole plant inspections from a representative sample from across the whole field. It is important to remember that there will always be adult thrips on cotton. If plants are growing well, presence of adult thrips alone will not warrant foliar insecticide application. The presence of immature thrips (wingless) is a good indicator of whether the seed treatments are running their course and reproduction is taking place. Consider applying a foliar insecticide at the first or second true leaf stage when the emerging leaf shows signs of thrips injury and especially if immature thrips are present. Also, beware of “look-a-like” thrips symptoms from sandblasting, residual herbicides and high temperatures. As the cotton emerges, it is very important to keep a close watch at the early season pests to make timely management decisions and give a good head start to the crop.