In an attempt to manage HLB, streptomycin and oxytetracycline were allowed to be used in Florida’s citrus groves a little more than a year ago. The basic tenet for their use is not to eliminate the bacteria within HLB-affected trees, but to reduce its titer. The reduction in titer is expected to improve the trees’ condition, which, in turn would make them more productive. But, have streptomycin and oxytetracycline been effective from a biological standpoint after one year? And, if so, does their use make economic sense?
Regarding the biological effectiveness of bactericides, growers’ feedback has been mixed. Some growers have reported an improvement in the overall condition of their affected trees while others have reported no effect. A key aspect of the growers’ assessment in either case is whether they have an adequate control to be able to determine whether it is the bactericides, or a change in other factors that affect yield. Preliminary results from the Citrus Research Development Foundation (CRDF) trials presented at the 2017 Florida Citrus Growers’ Institute indicate that after one year, there are no statistically significant differences in bactericide-treated trees versus the control. Some suggest it will take more than just one year to start observing the positive effect of these compounds, asserting more time would be needed to fully assess the impact of bactericides.
Given the current uncertain effect of streptomycin and oxytetracycline, and therefore tweaking the second question posed above, what yield would be needed to make the use of streptomycin and oxytetracycline justifiable from an economic standpoint?
Using USDA’s planted area and its most recent production forecast, statewide yield for early-mids and Valencias in 2016-2017 can be estimated at 194 and 161 boxes per acre, respectively, down from 213 and 209 boxes per acre in 2015-2016. These estimates provide evidence that the statewide downward trend on yield observed in past seasons continues. So, on a statewide basis, bactericides have not been able to put a halt on the downward trend of citrus yields.
The underlying key assumption for the back-of-the-envelope calculation above is that all the citrus acreage in the state has been treated; such assumption may be debatable. But, the message to growers is that with an average cultural cost of production per acre of about $1,800 and a continued decrease in yields, profitability margins are very narrow — if positive at all. Therefore, growers need to make their own calculations to figure out whether bactericides, or any other treatment they apply within their groves, is worth the cost.