Growers, Scientists Seeking Shelter From Citrus Greening

Growers, Scientists Seeking Shelter From Citrus Greening

Arnold Schumann, UF/IFAS CREC, stands next to a citrus screenhouse structure

UF/IFAS professor Arnold Schumann is among those leading the charge to test growing citrus under screen structures.
Photo by Frank Giles

Ten years ago, the idea of growing citrus under cover might have been laughable to some, but the arrival of HLB has changed the calculation. Constructing structures that are capable of virtually excluding the psyllid and thereby preventing HLB has a natural attraction in a period when crop forecasts flirt with disaster.

Because of the interest among growers, researchers have put in trials to test production methods under screen structures. And, citrus growers have proven it can be done before. Leading the charge has been Arnold Schumann, a professor of soil and water science and Brian Boman, a professor of agricultural engineering, both with UF/IFAS.

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“The crucial, successful conversion of Florida citrus nurseries from open-field production to screenhouse covered production inspired us to try this technology for high-value fresh citrus production in HLB-endemic environments,” Schumann says. “HLB prevention was the main motivation for testing the growing of citrus under cover, and is considered an interim HLB solution.”

There are other possible benefits of covered production that need testing: 1) the possibility of higher yields (greenhouse tomato yields are up to 30 times higher than field-grown); 2) higher-quality fruit and high packout percentage — less wind, therefore less wind scar, protection from hail, sunburn, and other pests, especially leafminer; 3) seedless fruit due to lack of cross-pollination in the absence of insect pollinators; and 4) the prospects of organic citrus production in a protected psyllid-free environment.

Job No. 1

Excluding the psyllid from a citrus planting is the biggest goal of citrus undercover production systems (CUPS). In fall 2014, Schumann constructed a 1.3-acre screenhouse for 1 acre of planted citrus at the Citrus Research and Education Center (CREC) in Lake Alfred. How well has the structure done keeping psyllids out?

Spraying indoor citrus

Working inside structures, some manual caretaking activities can almost be completely eliminated.
Photo courtesy of UF/IFAS

“Psyllid exclusion has been near perfect,” Schumann says. “After one year, we discovered one psyllid in a sticky trap near the service door of the structure. Very small numbers of psyllids entering the house are tolerated because the trees also are systemically protected via neonicotinoids, and we spray the entire screenhouse on a four-to six-week schedule with broad spectrum insecticides.”

Insecticide applications are made via a 48-inch electric golf cart paired with a conventional airblast sprayer or a twin vertical boom fan sprayer. The golf cart is semi-autonomous and remotely controlled so operators are not exposed to pesticides. An orchard tractor (48-inch cab) also can be used in the system.

While psyllids are excluded by the structure, smaller pests like thrips and mites can penetrate the mesh covering. Going forward, Schumann says he will be focusing more attention on managing thrips and rust mites inside the house.