We have reached that point of the year where whiteflies are present in our cotton fields. While I have yet to see whiteflies above threshold throughout the county, we still need to be keeping an eye on this pest, as it can become a big issue in a relatively short amount of time. The following is an update from Dr. Phillip Roberts, UGA Cotton Entomologist, on silverleaf whitefly management:
Silverleaf whitefly (SLWF) populations have increased significantly in areas we most commonly observe whiteflies. Insecticide applications targeting SLWF began in some fields about ten days ago and the frequency of fields exceeding threshold has been increasing. Only time will tell how populations will expand from these core areas. Hot and dry conditions favor whitefly population buildup. It is extremely important that we scout all fields for SLWF and do everything we can not to exacerbate populations. Most importantly, we need to conserve beneficial insects, do not treat other pests unless thresholds are exceeded, and avoid using insecticides that are prone to flare SLWF populations.
The presence of SLWF in a field should influence every decision we make. It is also extremely important SLWF insecticides are applied in a very timely manner if SLWF infestations exceed threshold. Being late with the initial insecticide application will make management more difficult and expensive in the long run. Insecticides recommended for SLWF include Knack, Courier, Assail, Sivanto, PQZ, Venom, and Oberon. Knack and Courier are insect growth regulators (IGR) and have good residual activity and minimal impact on beneficial insects. In general, these IGRs are slow acting but perform well when applied in a timely manner.
Conservation and the presence of beneficial insects are an important part of the IGR program. Knack is active on large nymphs and eggs (eggs will not hatch), and Courier is active on nymphs only. Neither Knack nor Courier will control adults. Knack has a 24(c) Special Local Need label for a split application of whitefly on vegetative cotton. Knack should be applied at 5 ounces followed by an additional application of 5 ounces 14 days later. This split application allows for treatment of new plant growth, which occurs after the first application. If cotton is no longer vegetative or “cut out,” the rate of knack is 8-10 ounces per acre. Courier is labeled at 9-12.5 ounces per acre. We would expect 2+ weeks of residual activity of the IGRs. If you are late with the initial application, an IGR is not the most appropriate insecticide. Assail and Sivanto are active on all stages, immatures, and adults. Sivanto provides more consistent control of adults when compared with Assail. Assail or Sivanto would be a preferred choice over an IGR if you are late with the initial whitefly application. We would expect 2+ weeks of residual activity with Assail and Sivanto.
PQZ is a relatively new product that provides good control of adults and is also active on immatures. Residual activity of PQZ is less than that observed with Assail and Sivanto. Venom and Oberon are also labeled for whiteflies but are rarely used. It is extremely important that we as an industry manage SLWF on all fields. In addition to reducing yield, honeydew accumulation on lint can negatively impact fiber quality and spinning efficiency at mills. Yield loss can be devastating if high populations are not controlled.
Feel free to reach out to Aubrey or me at 912-557-6724 if you have any questions or concerns about whiteflies in your cotton crop!