Psyllid Exclusion and Screen Selection

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By Arnold Schumann and Timothy Ebert

As the adage goes, “necessity is the mother of invention.” Since the presence of huanglongbing (citrus greening) in Florida, new methods of managing the Asian citrus psyllid that transmits the bacteria have resulted in the growing of citrus in screen houses (CUPS, citrus under protective screen) and the use of individual protective covers (IPCs), especially for new trees.

Researchers at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) looked into which type of protective screen was the most effective in keeping psyllids away from trees in a CUPS environment.

Screens may get stretched through daytime heat, age, and stress from the weight of the screen or wind pushing on the screen (for CUPS) or the tree pushing on the screen (for IPCs). Everything is “flexible” if enough force is applied, and opportunities may develop for an insect to get through if it finds the right spot. Therefore, the openings need to be slightly smaller than the threshold value for excluding psyllids. Furthermore, psyllids range in size, just like people do, and it is not possible to test the entire range of sizes.

In lab tests, the PME1610 and Polysack40 screens prevented psyllids from reaching food and water in the arenas. See results for all screens tested and details of the lab tests.

After testing eight woven screens for hole size and fiber diameters, the team discovered that 40-mesh screen had the best results for keeping psyllids away from trees. While the 40-mesh screen cannot be said to be psyllid-proof based on finite laboratory test conditions, the researchers were confident enough in its effectiveness to use 40-mesh screen when the screen was replaced at the CUPS grove at the UF/IFAS Citrus Research and Education Center.

The use of screens with openings of 385 µm or less (~40 mesh or more) are suggested because they exclude the Asian citrus psyllid. In addition to excluding psyllids, the use of these screens further alters the pest management landscape by excluding larger insects like sharpshooters, stink bugs, weevils and many lepidopterous pests.

This approach to pest management can be adapted to other pests and other crops so long as the return on investment is profitable. However, the screen mesh size needs to be adapted to perform properly for each use. The knitted screen we examined would not be suitable for excluding the Asian citrus psyllid because the openings are too large. A more complete description of methods and results for the woven screen can be found here.

Arnold Schumann is a professor and Timothy Ebert is a post-doctoral associate, both at the UF/IFAS Citrus Research and Education Center in Lake Alfred.

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