Implementing Insecticide Sprays for Winter Management of Psyllids

By Jawwad A. Qureshi

In winter, citrus trees enter a state of quiescence due to lower light and cooler temperatures, which slows their metabolic activity. Therefore, most citrus trees do not produce new shoots during this period. These young shoots are essential for the growth of the Asian citrus psyllid (ACP), Diaphorina citri. The ACP is a small sap-feeding insect that causes damage to citrus trees by feeding on the leaves and, more importantly, by transmitting the bacteria that cause huanglongbing (HLB) or citrus greening disease.

The ACP has a simple life cycle consisting of eggs, five nymphal instars and winged adults. Adults lay most eggs in the buds and unfolded leaves of developing young shoots, while nymphs develop into adults feeding on these soft tissues. The eggs and nymphs are yellowish-orange in color, and the adults are mottled brown. Nymphs and adults are easily spotted on developing shoots, feeding and producing white, waxy honeydew tubules abundant during the growing season. Adults also exhibit a distinct head-down, tail-up posture (Figure 1).

In winter, due to the scarcity of young shoots, the ability of the ACP to reproduce and increase its population is reduced. Therefore, eggs and nymphs, as well as their natural enemies such as predators and parasitoids, are rare or absent from citrus orchards. Meanwhile, low numbers of adult ACPs survive in the orchards, waiting for spring growth to start reproducing. This situation presents the weakest link in ACP biology in relation to citrus phenology and an opportunity for a preemptive approach to its management. 

A dormant spray refers to a foliar application of an insecticide (Figure 2) targeting the overwintering adult ACPs. This tactic provides significant suppression of the low-surviving pest populations in winter, an effect that translates into the growing season. The strong impact of winter suppression of ACP, resulting in reduced populations during the growing season, has been observed in large-scale studies.

The female ACP has a high reproductive rate, so suppression before spring growth is critical. Dormant sprays may use broad-spectrum insecticides, such as pyrethroids or organophosphates, to achieve significant ACP knockdown with minimal or no impact on beneficial insects, which are rare or absent at that time.

Jawwad A. Qureshi is an associate professor at the University of Florida Institute of Food and Agricultural Sciences Southwest Florida Research and Education Center in Immokalee.