By Ramdas Kanissery
Paraquat is an herbicide labeled for various crops, including citrus, for post-emergent weed control. When applied during the early growth stage, paraquat controls many annual grasses and broadleaf weeds commonly found in Florida citrus. Additionally, paraquat typically offers relatively good crop safety in citrus due to its lack of translocation in the plant. This makes it the herbicide of choice for quick post-emergence weed control in citrus.
The Environmental Protection Agency has implemented certain regulations on the use of paraquat in the last couple of years, including restricting the herbicide’s use to certified pesticide applicators only. Certified applicators must now take additional training before handling paraquat. The training covers new label requirements and restrictions, consequences of misuse, and other important information. Details on these new regulations and training can be found here.
With new paraquat use restrictions in place, citrus growers may be interested in other post-emergent herbicide options to burn down emerged weeds quickly. Some alternative options to paraquat are available, including carfentrazone-ethyl.
Carfentrazone-ethyl disrupts the cell membranes of weeds upon contact with the plant tissues and typically kills the weeds in one to three days after application. It’s a good substitute for paraquat for managing broad-leaved weeds in citrus; however, it will not provide a similar level of weed control on grass weeds. Carfentrazone has little to no control of grasses and will require selective grass herbicides (such as clethodim or sethoxydim) in the post-emergence herbicide program to manage grasses in the grove.
Glufosinate-ammonium is another contact herbicide option in citrus with a relatively broader weed-control spectrum. It controls both the emerged broad-leaved weeds and grasses. Glufosinate inhibits weeds’ nitrogen metabolism and kills the contacted weeds in approximately two to five days. It has restricted translocation in the plant and works best when weeds are not stressed. Bright sunlight and warm temperatures improve its performance.
Due to their contact activity and limited translocation, thorough spray coverage of carfentrazone-ethyl or glufosinate-ammonium on weeds is needed for effective control. This is achieved by the following strategies:
- Use of proper spray adjuvants (e.g., buffers, surfactants, etc.) will enhance the herbicide’s performance and increase leaf-surface contact and coverage. Find more information on herbicide adjuvants in citrus weed control here. Consult the specific product label for adjuvant compatibility and specificity.
- Utilize spray pressure and nozzles that produce medium-size droplets (250-350 microns). Larger-sized droplets can potentially result in reduced weed control.
- Using optimal spray carrier volume (for example, 20 to 40 gallons of water per acre) will help achieve good spray coverage of these herbicides.
Finally, the timing of application is critical since most of these paraquat alternatives require weeds in their young growth stage for successful control.
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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