Degradation and residual efficacy of insecticides in Citrus Under Protective Screen (CUPS) differ from traditional citrus orchard.

Abstract

Citrus Under Protective Screen (CUPS) protects trees from huanglongbing (HLB) by excluding the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), the vector of the bacteria responsible for the disease. Nevertheless, small arthropods such as crawlers of the hibiscus mealybug, Nipaecoccus viridis (Newstead) (Hemiptera: Pseudococcidae), a newly invasive pest in citrus, can enter the structure and infest trees. Environmental conditions in CUPS are different compared to open citrus groves with lower solar radiation and higher maximum temperatures which can influence insecticide breakdown and efficacy. From June to December 2024, the residual activity and degradation of 4 foliar insecticide applications in CUPS and open orchards were evaluated. Hibiscus mealybugs were exposed to treated leaves for 14 d on samples collected on different days after treatment (DAT). Mortality of the hibiscus mealybug was higher in CUPS than in the open orchard for all sprays except the last one containing fenpropathrin, abamectin, and tolfenpyrad. For cyantraniliprole and thiamethoxam, leaf residues were higher in CUPS for up to 14 d suggesting that photodegradation could be reduced in this system. Abamectin also appears to degrade more slowly in CUPS, although due to its short half-life and low residue levels, this trend was only observed for the first 3 d following application. For malathion, residues were consistently higher in the open orchard, indicating that thermodegradation could be potentially increased in CUPS due to higher temperatures, specifically during summer. Combined with further studies, these results will be used to tailor IPM programs in CUPS.