Pest Management Challenges in CUPS

By Lauren Diepenbrock

Citrus under protective screen (CUPS) has provided growers with a profitable method for producing fresh fruit in Florida. Growers who have implemented this system have noted quality fruit production and reduced inputs. However, when changes are imposed to the production environment, they are also imposed to the invertebrate pest complex, which can be either beneficial or detrimental to production outcomes. The following is a discussion of pest challenges brought to my attention from growers, what has been learned and where knowledge gaps currently exist.

ASIAN CITRUS PSYLLIDS

CUPS structures do an excellent job of reducing Asian citrus psyllid (ACP) access to citrus trees. However, incursions can occur when screens are damaged in storms or from aging, and if psyllids hitchhike into structures on people or equipment. Because keeping psyllids out is of critical importance, most CUPS growers have plans in place should screen damage occur. This includes extra screen and prophylactic sprays to reduce the likelihood of survival should ACP gain entry.

CITRUS LEAFMINERS

Citrus leafminers are largely prevented from accessing citrus trees within CUPS as they cannot penetrate the mesh-covered structures. However, once they gain entry via screen damage or hitchhiking, they can be challenging to manage. Their life stages include larvae residing within leaves and mobile adults that seek shelter within the thick canopies of the healthy trees growing within CUPS.

This means that to get this pest under control, growers need to incorporate a systemic chemistry for the larvae and a contact chemistry for adults. And there is no guarantee this will work given that 1) the CUPS growing environment is different from that of traditional open groves and 2) thick, healthy canopies of CUPS-grown trees can reduce pesticide penetration into tree canopies.

MITES

Rust mites are the primary mite challenge reported by growers to date, though CUPS has been noted to support red spider mites in the past. Mites thrive in warm, dry climates, and rust mites perform well in shaded conditions. Given the heavy outbreaks of rust mites within CUPS, it is likely that the screening filters light sufficiently to make an ideal level of lighting for rust mites.

Growers should scout regularly for mites and use the fresh fruit recommendations from the Florida Citrus Production Guide for management planning until further research can be performed to determine if these recommendations need to be modified for CUPS.

THRIPS

Both flower thrips and chilli thrips have been noted to cause damage to fruit in CUPS.

Flower thrips cause the standard ring-shaped damage around the calyx. Flower thrips can pass through the screen walls of CUPS and are temporal pests during bloom. They feed on the young developing fruit, leaving behind their characteristic damage.

Chilli thrips have become problematic because of their damage in both nurseries and CUPS. In CUPS, chilli thrips migrate through the screen walls when weeds are flowering outside, and sometimes inside, of structures, which is also when we often start seeing citrus flowers.

Mixed populations of flower and chilli thrips within citrus flowers are often seen. However, unlike flower thrips, chilli thrips often persist within CUPS at lower numbers while both feeding and reproductive hosts are available.

Chilli thrips feeding damage generally stretches across large sections of the surface of the fruit (Figure 1), appearing similar to damage from broad mites. Damage is generally on young fruit, with the scarred surfaces expanding with the fruit. Leaf feeding (Figure 2) results in misshapen, cupped leaves similar to spider and broad mite feeding damage.

There are currently no chemical recommendations for chilli thrips in citrus. However, blueberry and strawberry studies have evaluated many insecticides that are also labeled for use in citrus. This data can be used to support management decisions until there are CUPS-specific recommendations. Additionally, removal of weeds both in CUPS and nearby fields can help reduce the initial invasion pressure of this pest in the spring.

MEALYBUGS

Citrus, long-tailed and lebbeck mealybugs have all been found in CUPS, with lebbeck causing the most damage. While the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) researchers have done extensive management work on this pest in traditional growing settings, the data do not smoothly translate into the CUPS production environment. There are multiple reasons why:

1. CUPS excludes the few critical predators that have been found for lebbeck mealybug that occur in open production systems.
2. The CUPS environment is favorable for mealybugs throughout most of the year, with temperature extremes being slightly mediated within the structures and no direct, heavy rainfall to dislodge mealybugs during vulnerable mobile periods.
3. Thick canopies reduce the ability of contact chemistries and/or oils to actually make contact with the pest.
4. The CUPS environment influences pesticides.

Within CUPS structures, infested young trees (Figure 3) have died from heavy lebbeck mealybug pressure over the course of a few months (Figure 4). Currently, there are no management recommendations specific to the CUPS-growing environment, so growers will need to watch for this pest and manage it before they lose limbs or entire trees.

Acknowledgments: Thank you to the Citrus Research and Development Foundation (lebbeck research) and the Citrus Initiative (chilli thrips research) for funding, and to the CUPS collaborators around Central Florida. None of this work can be done without collaborator input and support.

Lauren Diepenbrock is an associate professor at the UF/IFAS Citrus Research and Education Center in Lake Alfred.