Citrus greening has been affecting Florida’s citrus industry for over a decade, but growers and researchers are still figuring out the “best practices” when it comes to treatments for the disease. An entomologist with the USDA, David G. Hall, has released guidelines to growers for the optimal use of insecticides aimed at the Asian citrus psyllid, the insect vector for the Huanglongbing bacterium (HLB) that causes citrus greening.
Hall and his team explored whether a citrus tree’s flush cycle mattered in terms of insecticide applications. Flushing is part of a citrus tree’s growth cycle where the tree produces new leaves, and it occurs a few times a year. Hall’s team wanted to find out if citrus trees were more susceptible to HLB infection during flushing. They trimmed trees to stimulate an ‘old flush’ stage (about three weeks after trimming), a ‘new flush’ stage (two weeks after trimming) and conditions for a tree not in flush (just trimmed). Then, they released psyllids infected with HLB to feed on the trees.
After six months, the trees were inspected for HLB infection. They found that trees exposed to HLB during the ‘old flush’ phase had the highest infection rate; one trial showed an infection rate of 80 percent for ‘old flush’ trees. Trees in ‘new flush’ had the second highest rate of infection while ‘no flush’ trees had the lowest. In that same trail as above, ‘new flush’ trees showed a 23 percent rate of infection, and the ‘no flush’ trees showed only a three percent rate of infection. According to Hall, the research shows that growers should monitor the trees for psyllids when they are in flush, and that targeting ‘old flush’ trees with insecticides is best.
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