Improving Yield Safety of Glyphosate

Josh McGill Tip of the Week, weeds

By Ramdas Kanissery

Florida citrus growers face weed management problems throughout the year because of conditions that favor rapid weed growth in groves. A weed-free tree row is desired in a citrus grove to minimize weed competition with trees. Hence, chemical weed control using post-emergent, systemic herbicides like glyphosate has become a vital production practice in the Florida citrus industry.

Citrus fruit damage due to spray contact from glyphosate application
(Photo by Mongi Zekri, University of Florida Institute of Food and Agricultural Sciences)

Although glyphosate is a widely utilized and essential weed management tool in citrus groves for controlling emerged weeds, its extensive and non-judicious application has drawn increasing concerns about its unintended effects on citrus. Some of these concerns are linked to its possible impacts on preharvest fruit drop.

In a two-year study (Gairhe et al. 2022), glyphosate application in citrus groves during early spring, close to fruit harvest in Valencia, did not cause any significant effect on preharvest fruit drop. However, a slight reduction in fruit detachment force (FDF), an indicator of fruit holding force to the bearing branch, was observed in trees located in the glyphosate-treated plots. Glyphosate exposure can possibly decrease FDF and make fruit prone to premature drop. However, other factors, such as biotic and abiotic stresses, may be necessary for the occurrence of fruit drop.

Below are a couple of strategies based on the information generated from this study for fine-tuning glyphosate’s crop-safe usage in citrus.

  • Avoid glyphosate sprays close to the harvesting date (e.g., within 10 weeks of harvest) in citrus. For example, in late spring-maturing varieties like Valencia, early spring season sprays can be avoided to ensure the yield safety of glyphosate-based herbicide programs.
  • Adopt proper herbicide application practices such as maintaining a safe spray boom distance and carefully positioning the angle of off-center spray nozzles. This will prevent any glyphosate spray contact with the citrus fruit, foliage and trunk and will also help enhance the crop-safe use of glyphosate in citrus.

Ramdas Kanissery is an assistant professor at the University of Florida Institute of Food and Agricultural Sciences Southwest Florida Research and Education Center in Immokalee.

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