Timing Insecticide Applications for Best Effects

Daniel CooperPests, Tip of the Week

Citrus leafminer adult (Photo by Lyle Buss)

By Lukasz Stelinski

Here are some basic guidelines that growers can follow to manage pests successfully and economically in their groves:

  • Apply broad-spectrum insecticide at general budbreak to reduce psyllids before they have a chance to begin reproducing in the spring.
  • Monitoring for psyllids with tap sampling can inform spray decisions. When tap samples reach 1.0 psyllid per tap, it’s time to spray. This is based on an average sample from 10 trees per block.
  • An attempt can be made to keep psyllids below damaging levels with three to four sprays per year. Piggyback leafminer sprays onto those targeting psyllids.
  • It is important to make leafminer sprays count. It’s best not to apply leafminer products until larvae infest leaves (active mines). These products only work on living larvae in mines.
  • For best control of leafminer, apply leafminer-specific sprays 13 days after general budbreak at the earliest. The last potential date for leafminer application is 31 days after budbreak.
  • If diaprepes are a problem in your grove, combining Mustang + Micromite rotation is a good start to reduce populations. After that, rotate in soil applications of a neonicotinoid with Verimark to kill larvae in soil at times when psyllid applications would be made for combined benefit of reducing psyllid populations.
  • For diaprepes, spray in the canopy for adults and use soil-applied formulations against larvae to make headway. Both the adults in the canopy and the larvae in the soil need control to break the lifecycle.
  • For reducing the HLB pathogen, initial results indicate that trunk-injected oxytetracycline should provide much more benefit than earlier attempts with foliar sprays.

Take-home messages include the following:

  • As psyllid density increases, trees receive greater stress. This compromises tree health (yield).
  • Spray for adults at budbreak at the beginning of spring before there is feather flush on which adults can lay eggs.
  • Approximately one psyllid per tap sample works as an effective nominal threshold.
  • The window for spraying against citrus leafminer is 13 to 31 days after budbreak.
  • Several insecticides used against psyllids are also effective against diaprepes.

Lukasz Stelinski is a professor at the University of Florida Institute of Food and Agricultural Sciences Citrus Research and Education Center in Lake Alfred.

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