Roberts: Late Season Pest Management Considerations

Terminating Insecticide Applications: The decision to terminate insect controls can be challenging in some fields but a few basic considerations will assist in that decision. When evaluating a field a grower must first identify the last boll population which will significantly contribute to yield (bolls which you plan to harvest). In some situations the last population of bolls which you will harvest is easy to see (i.e. cotton which is loaded and cutout). In others, such as late planted cotton, the last population of bolls you will harvest will be determined by weather factors (the last bloom you expect to open and harvest based on heat unit accumulation). Once the last boll population is determined the boll development or approximate boll age should be estimated. Depending on the insect pest, bolls are relatively safe from attack at varying stages of boll development.

The table below list approximate boll age in days which bolls should be protected for selected insect pests. Cooler temperatures will slow plant development and subsequent boll age values may increase in such environments. It is assumed that the field is relatively insect pest free when the decision to terminate insecticide applications for a pest is made.

Defoliate in a Timely Manner to Manage Silverleaf Whitefly Populations and Preserve Yield and Fiber Quality:  Silverleaf whitefly (SLWF) infestations have been common in some cotton producing areas. Historically, SLWF infestations are highest in areas which grow both cotton and vegetables. In these areas we grow crops 12 months out of the year which SLWF feeds and reproduces on. The primary cropping systems that drive overall SLWF populations in Georgia include:

  1. Winter vegetables such as cabbage, collards, and kale.
  2. Spring vegetables including cucurbits (cantaloupe, cucumbers, watermelons, and squash) and fruiting vegetables (tomato and egg plants), and others.
  3. Agronomic crops such as cotton and soybean.
  4. Fall vegetables which include a similar crop mix as spring vegetables.

Management of SLWF in these individual cropping systems affects infestations in subsequent crops as SLWF move from one cropping system to the next. Failing to properly manage SLWF in any one of these systems can have negative consequences for subsequent cropping systems. It is important that we properly manage SLWF in all cropping systems to manage the overall SLWF population. The SLWF population is somewhat like a snowball and just grows larger and larger during the summer. Have you ever considered how many SLWF are produced per acre if   we defoliate 1, 2, or 3 weeks late? Timely defoliation will also lower the risk of having fiber quality problems related to whiteflies. Ultimately how we manage SLWF now will have impacts on us in 2023. By in large, Georgia growers have done a good job managing SLWF in cotton. Keeping in mind that SLWF requires management until harvest, one of the best practices is to defoliate in a timely manner.  For more information on this subject see the following publication: Cross-Commodity Management of Silverleaf Whitefly in Georgia at the following website: https://secure.caes.uga.edu/extension/publications/files/pdf/C%201141_1.PDF

Phillip Roberts
UGA Extension Entomologist

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