Mike Roberts

Controlling Primary Infection in Young Plantings

At the 2020 Citrus Show in January, Mike Irey, the Chief of Plant Sciences at the U.S. Sugar Corporation, gave a presentation concerning research utilizing computer models his company had done in conjunction with two professors of mathematics with the University of Florida titled “Controlling primary HLB infection.” Irey maintained that “the continued success of the citrus industry will depend on bringing young groves into production,” and keeping them free of citrus greening for as long as possible. The research simulated the rate of infection when different spray frequencies are utilized between a mature grove that is 100 percent infected with citrus greening and a young grove that is not yet infected. The simulations showed interesting results.

Spray Results

The simulations utilized three different spraying schedules. In the first, the mature, infected grove was sprayed every 10 days, while the young grove was sprayed every 30 days. In the second, both groves were sprayed every 15 days, and in the last, the mature grove was sprayed every 30 days and the young grove was sprayed every 10.

The first spray schedule, with the mature grove receiving intense sprays, resulted in a 23.71 percent infection rate after 720 days. The second schedule, where both groves were sprayed at the same rate, had an infection rate of 9.38 percent after 720 days. Lastly, the third schedule, where the young grove received intense sprays, had an infection rate of 6.69 percent.

Irey concluded that a once-a-month spraying schedule is not enough to disrupt the life cycle of the Asian citrus psyllid, which is 14 days. However spraying twice a month “is sufficient to disrupt the psyllid life cycle and mostly protect the young planting.”

When the simulations were extended to three blocks of groves—one mature, infected grove and two young, noninfected groves, with the mature block being on the left and the two young grove blocks with one in the middle  and the other on the left, simulation resulted in the same pattern. When the mature grove was sprayed every 10 days and the young groves every 30, infection spread deep into the young grove adjacent to the mature grove and into the farther, young grove. When all groves were sprayed every 15 days, the middle young block saw reduced infection rates, but infection spread— however sparingly—into the third, far block. When the two young blocks were sprayed every 10 days, infection rates into the middle block were the lowest of all the simulations, and it never spread into the last, far block of young citrus grove.

Irey concluded that surrounding blocks should be treated two or more times a month and younger blocks one to two times a month, with the yield versus cost model utilized.

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