By Jawwad A. Qureshi
Several insect pests and mites colonize citrus crops in traditional open orchards. Most pests are localized and are suppressed by predators, parasitoids and entomopathogens to levels that are not economically damaging to the crops. The Asian citrus psyllid (ACP) is the primary vector of huanglongbing (HLB) disease. Despite biological and chemical control of ACP, growing a disease-free crop in open orchards is challenging.
The citrus under protective screen (CUPS) production system is an innovative approach to producing citrus in screened structures that are free from ACP and HLB. Although CUPS creates a controlled environment that reduces the incidence of this vector and disease, it increases temperature and humidity compared to the outside environment, which may favor the establishment of pests that enter the CUPS. The screens recommended for CUPS exclude larger pests and predators. However, small pests such as mites, thrips, citrus leafminers (CLM), scales and mealybugs may selectively enter through the permeable screen or entry points, including damage or tears in the screen.
Regular monitoring of CUPS screens for holes, tears or any other damage is important to reduce pest incursions and management needs. Pests can establish from planting an infested tree or a later incursion. Therefore, initiating tree examination and monitoring at and soon after planting helps in the early detection of pest infestations and the implementation of control measures.
Monitoring pests in CUPS involves regular inspection of trees using visual observations as well as other tools such as traps (sticky or pheromone) and tap sampling or suction sampling. Developing buds and young shoots, mature leaves and shoots, limbs and trunks are places to look for pest infestations. ACP, CLM and aphids prefer to develop and reproduce in the soft tissues of developing unfolded leaves. However, adults could be in the canopies and detected using the above-mentioned methods.
For two to three years, University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) researchers used multiple monitoring methods to determine pest incursions in CUPS structures with a 50-mesh screen. Only a few ACP were detected in the CUPS and mainly on the yellow sticky cards, which also detected thrips. Shoots infested with ACP eggs and nymphs were observed when hurricanes or storms damaged screens and CUPS were exposed to pest incursions. Infested shoots were removed manually, followed by insecticide sprays to control residual populations. Using magnifying lenses facilitated detection of ACP and CLM immatures in young shoots and thrips in flowers and young fruit at the stem and under the calyx.
CLM males were detected in the pheromone traps. Larval feeding and leaf damage was observed in the foliage but was reduced by 80% when compared to the open orchard. Localized infestations of different species of scales and mealybugs were also observed in the CUPS. Florida red scale was found infesting shoots, leaves and fruit on 11% to 12% of the trees. The most persistent pest problems were citrus rust mites and citrus red mites. Red mite populations were high in early summer, fall and winter, while rust mites were abundant from June to September.
Several species of predatory mites and parasitoids of CLM, scales and mealybugs were observed in the CUPS, suggesting potential for biological control. There are several chapters of the Florida Citrus Production Guide that provide detailed information on the reported pests and their biological and chemical control.
Jawwad A. Qureshi is an associate professor at the UF/IFAS Southwest Florida Research and Education Center in Immokalee.
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