Biologically-Based Management of Citrus Pests

Josh McGill Biologicals, Pests, Tip of the Week

By Jawwad Qureshi

Management of the Asian citrus psyllid (ACP, Figure 1) is critical because it is responsible for spreading huanglongbing (HLB) disease. Although HLB is established in Florida, it continues to spread through ACP feeding in already infected trees and by infecting newly planted young trees. Some ACP control occurs naturally in the environment by beneficial organisms such as generalist predators (e.g., ladybeetles, lacewings, spiders, hoverflies and syrphid flies), entomopathogens such as Hirsutella citriformis and the parasitoid Tamarixia radiata.

Figure 1. Biological control can contribute to management of the Asian citrus psyllid. (Photo by Jawwad Qureshi, UF/IFAS)

University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) researchers evaluated the biological control of ACP soon after the advent of HLB in Florida and observed several species of predators causing 90% to 100% mortality of ACP immatures. The incidence of those predators has reduced over time due to the increased use of insecticides for several years to control ACP. However, predators are still present in citrus and other crops and contribute to the biological control of ACP in the groves.

In recent years, UF/IFAS researchers have conducted studies in young and mature citrus in commercial groves, including high-density plantings, and observed several species of ladybeetles, lacewings and spiders inflicting natural mortality of ACP averaging 40% to 85%. These predators have also been shown to kill and reduce populations of other pests, including citrus leafminers, aphids, mealybugs, scales, mites sand thrips.

The entomopathogenic fungus H. citriformis attacks multiple pests, including ACP, and is common in citrus groves and urban environments. The parasitoid T. radiata mass-produced and released in Florida is established and attacks ACP nymphs. Beneficial organisms provide significant reductions in ACP populations but are not enough. Therefore, chemical control is needed to enhance ACP suppression.

Selective insecticide approaches include:

1) Application of soil-applied systemic insecticides that avoid direct contact with natural enemies

2) Foliar sprays of insecticides directed mainly at adult psyllids, which are more vulnerable during winter when trees are producing little or no new growth, which limits ACP reproduction

3) Rotating mode of action of insecticides in applications

Predators are largely absent from groves in winter due to the shortage of prey. Foliar sprays of broad-spectrum insecticides tested in the winter before spring growth suppressed ACP into the growing season. These applications had no detectible impact on key natural enemies and, therefore, were helpful for conserving populations of beneficial organisms. An article (“Dormant Sprays for Asian Citrus Psyllid Management”) discussing the details of this tactic was published in the January 2021 issue of Citrus Industry.

Potential options and supplements to conventional insecticides can be used to control psyllids during the growing season and maintain citrus production, even under conditions of high HLB incidence. For example, a program of organic insecticides sequentially mixed and alternated with horticultural mineral oil to control psyllids produced similar or better yields than a conventional program in a mature block of HLB-positive Valencia oranges. Similarly, conventional insecticides rotated with organic insecticides integrating biological control have shown promising results in suppressing ACP.

Jawwad Qureshi is an associate professor at the UF/IFAS Southwest Florida Research and Education Center in Immokalee.

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