Controlling Psyllids: A Threshold Approach

Citrus growers should consider controlling HLB-spreading Asian citrus psyllids (ACP) only when a prescribed ACP population, or threshold, is reached. Entomologist Lukasz Stelinski suggested this approach in a virtual Citrus Expo presentation. Stelinski is a University of Florida Institute of Food and Agricultural Sciences researcher at the Citrus Research and Education Center in Lake Alfred.

A summary slide Stelinski showed stated that psyllid density is related to tree stress; more psyllids lead to more damage and compromise tree health. “If the pest population (and the resulting damage) is low enough, it does not pay to take control measures,” the slide stated. “As the pest population continues to rise, it reaches a point where the resulting damage would justify taking control measures; 0.7 ACP per (scouting) tap is a ‘working ballpark’ threshold.”

Another slide stated that long-term ACP feeding suppresses plant immunity and inhibits growth, “which explains the importance of vector suppression as part of HLB management.” The slide added that while ACP management is beneficial, “we need to make it more sustainable.”

Stelinski also presented a typical recent model for ACP sprays and a possible better alternative. In the typical model, a dormant spray has usually been timed after harvest and before major spring flush using pyrethroid or organophosphate. In that typical model, sprays are made on a schedule with intervals somewhat determined by the length of efficacy of a particular insecticide.

In the alternative model, growers would spray for adults at bud break at the beginning of each new flush before there is feather flush on which adults can lay eggs. They would apply a second spray on the flush as ACP begin to reappear. “This seems to achieve more than 60 days of low ACP populations,” a slide stated. Growers would hold off spraying until the ACP hit a threshold of 0.2 to 0.7 per tap. Maintaining ACP below a threshold of one ACP per tap was associated with better yield, according to Stelinski.

See Stelinski’s full presentation here. All Citrus Expo presentations and the CEUs that can be earned by watching them will remain available through the end of 2020.