Spraying for the HLB-spreading Asian citrus psyllid (ACP) is essential for HLB control even when virtually all trees are already infected with the disease. Entomologist Lukasz Stelinski made that declaration early in his virtual presentation at the April 6 Florida Citrus Growers’ Institute. Stelinski is an entomologist at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Citrus Research and Education Center.
Researchers have observed that reducing ACP populations increases fruit yield in groves, Stelinski said. He explained that tree defense against disease is compromised by psyllid damage. Reduction in disease defense leads to reduced yields. He added that ACP density is related to tree stress. More ACPs lead to more damage, which compromises tree health and yield, Stelinski explained.
Those findings have prompted Stelinski and other researchers to seek an ACP population threshold at which it makes economic sense to spray for the pests. Economic ACP control is needed because growers’ production costs have increased drastically while fruit yield has plummeted due to HLB. Stelinski said finding from 0.2 to 1.0 ACP per tap in a tap survey of trees seems like an effective threshold at which to initiate ACP sprays.
Stelinski suggested a possible “better alternative” to the typical recent grower model for ACP spraying in an effort to reduce ACP spray costs. Under the typical model, growers applied a dormant spray before the major spring flush using a pyrethroid or organophosphate. Then, sprays were made on a schedule with intervals determined by the length of efficacy of a particular insecticide.
Under Stelinski’s proposed alternative, 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. Growers would then apply a second spray on the flush as ACP begin to reappear. This seems to achieve more than 60 days of low ACP populations, Stelinski said. Under his alternative model, growers would hold off spraying until ACP reach the threshold of 0.2 to 1.0 ACP per tap in a survey.
Stelinski said growers can further reduce ACP control costs by protecting grove borders against the so-called “edge effect” with windbreak walls or sprays. Growers and researchers years ago discovered that HLB tends to be most prevalent on the edges of groves.
Learn how other UF/IFAS researchers are looking to increase the efficiency of ACP control techniques.
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