Rootstocks and OTC

The University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Citrus Research and Education Center hosted a May OJ Break educational seminar. Ute Albrecht, UF/IFAS associate professor of plant physiology, spoke during the event and gave an update on oxytetracycline (OTC) therapies being applied in citrus groves over the past two seasons.

She gave a summary of research she and her colleagues have been conducting on trunk injection of OTC. One study looked at how six different rootstocks (US-942, US-812, US-897, Carrizo, UFR-4 and UFR-2) responded to the therapy at a trial site on the Ridge. The trial also compared rootstock injection versus scion injection versus no injection. The trials used the higher rate of 1.1 grams of OTC per tree.

Across all rootstocks, the injection improved fruit yields by 24%. There was no difference in performance whether the rootstock or scion was injected. The overall best performer in terms of yield was the popular US-942 rootstock, but all rootstocks responded well to the treatment.

The pounds solids showed an 11% increase with OTC treatment on average in the trial. The best-performing rootstocks for pounds solids were US-812 and US-897.

Albrecht also presented data from UF/IFAS citrus economist Ariel Singerman on the yield increase needed to offset the cost of trunk injection. In the rootstock trial, essentially all of the rootstocks broke even or returned more than the investment required to apply OTC.

In another Ridge trial, there was an average 58% yield increase response with the OTC application. However, Albrecht noted the yields were much lower in this trial site than the aforementioned trial.

“We see this in other trials. If you have a generally well performing grove, the response to OTC will not be as strong as if you have a poorer performing grove,” she said. “This shows why we had a stronger response to the OTC in this trial.”

But again, there were differences in rootstock performance. The best performer was US-812 followed by US-942. Sour orange (the standard rootstock) did poorly in this location. For pounds solids, the OTC-treated trees were more than 20% higher than the control. Here, too, according to Singerman’s calculations, the yield increase was more than enough to offset the cost of treatment.

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