University researchers in Florida and California are studying the effect of using mesh screenhouses to grow citrus greening-free trees. ( Courtesy University of Florida )

The U.S. Department of Agriculture has awarded the University of Florida a $3.5 million grant to study using mesh screenhouses to guard grapefruit against huanglongbing (HLB).

At a Fort Pierce research field, the university is using four half-acre white mesh screenhouses to study the effects of “Citrus Under Protective Screen,” aka CUPS, and how the mesh can guard against HLB. There are 512 “Ray Ruby” grapefruit trees in the four screenhouses, according to a news release from the university.

“The primary purpose of growing citrus under screen is to exclude psyllids and therefore block transmission of CLas, the bacterial agent of HLB disease,” Arnold Schumann, who is leading the CUPS research as project director, said in a news release.

Schumann is a professor of soil and water sciences at the University of Florida Institute of Food and Agricultural Science’s Citrus Research and Education Center in Lake Alfred, Florida.

Trees have recently been grown in screenhouses to shield the crop from the Asian citrus psyllid, an invasive insect that carries the pathogen that causes HLB, aka citrus greening.

HLB has reduced Florida’s citrus production from 292 million boxes in the 2003-04 season, to fewer than 78 million boxes at the end of the 2016-17 growing season, according to the USDA.

The project will support CUPS research at the Lindcove Research and Education Center at the University of California, according to the release.

“Growers and buyers share a mutual desire to restore the grapefruit industry that was once a highly profitable export business,” said Rhuanito “Johnny” Soranz Ferrarezi, a citrus horticulture scientist at the UF/IFAS Indian River Research and Education Center in Ft. Pierce, in the release.

Nine scientists and Extension agents will work on grant objectives. Six collaborators represent Florida; there are two in California and one in Australia, according to the release.