Summer is “a field day for weeds,” Ramdas Kanissery said in a March 29 presentation about weed control for citrus. The University of Florida Institute of Food and Agricultural Sciences assistant professor provided a progressive step-by-step approach to suppressing weeds during the summer.
CONTROL EXISTING WEEDS
Growers can get off to a good start by controlling existing weeds with post-emergent herbicides. Learn about suggested herbicides in the weeds section of the 2022-23 Florida Citrus Production Guide. Kanissery suggested ways to get the most out of post-emergent herbicides, including:
- Achieve adequate coverage on weed foliage; optimum spray volume is the key.
- Use optimum rates; use high-labeled rates for heavy weed infestation and for weeds in a mature growth stage.
- Use an appropriate surfactant to improve herbicide retention, coverage and efficacy.
- Use suggested adjuvants.
- Rotate post-emergent herbicides with different modes of action to reduce selection pressure on weed populations and to help manage weed tolerance.
- Apply when there is ample sunlight. Midday applications generally provide higher levels of efficacy than early-morning and late-afternoon applications.
- Spray when there is low wind.
- Apply when weeds are non-stressed, actively growing and in an early growth stage.
SUPPRESS WEED GERMINATION
Growers can prevent weed germination from the soil seed bank with pre-emergent herbicide programs. Kanissery’s tips for getting the best out of pre-emergents include:
- Apply residual herbicides to bare soil for maximum soil incorporation.
- Turn on irrigation to activate residual herbicides in the soil.
- Include a compatible post-emergent tank-mix partner if there is already some weed growth.
- Tank-mix pre-emergent herbicides with different modes of action to increase the spectrum of weed control and to reduce tolerance/resistance issues.
WEATHER TIP AND TREE SAFETY
Growers should recognize that the efficacy of post-emergent systemic herbicides is reduced when temperatures are above 90 degrees. Kanissery recommended avoiding spraying 2,4-D products when temperatures are higher than 90 degrees because the potential for herbicide injury is high then.
To help ensure tree safety when using herbicides, Kanissery suggested that growers:
- Maintain proper spray boom height.
- Deliver herbicide to the target.
- Avoid tree stem and foliage contact.
- Install protective wraps around trunks of young trees.
- Don’t use high herbicide rates on new plantings.
Kanissery reported that avoiding glyphosate sprays close to harvest for Valencia oranges may improve yield safety. He also noted that cover crops in row middles suppress weed growth, in addition to providing other benefits.
The weed-control presentation was made to an in-person audience at the Southwest Florida Research and Education Center and was also available virtually. Multi-county citrus Extension agent Mongi Zekri served as host.
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