Managing Aggressive Weeds in Citrus

Ramdas Kanissery gave advice for growers in a May 20 virtual presentation about managing aggressive weeds in citrus. Kanissery is a University of Florida Institute of Food and Agricultural Sciences associate professor of horticultural sciences at the Southwest Florida Research and Education Center in Immokalee. A summary of his recommendations follows.

• Regular grove monitoring helps catch weed escapes from herbicide programs. If only one weed species escapes after treatment, it likely indicates herbicide tolerance in weeds, not overall herbicide failure.
• Rotate and tank-mix herbicide modes of action. Tank-mixing pre-emergent herbicides helps stop hard-to-control weeds from emerging.
• Spray when weeds are young. Never let weeds grow and adapt.

CULTURAL PRACTICES

• Mechanical mowing trims down the tall growing weeds (grasses at a height of about 1 to 2 feet). It must be done regularly, before seeding.
• Cover cropping may contribute to longer-term management of weeds in row middles. Planting cover crops in the row middles effectively reduced grass infestation in the tree rows.

PRACTICAL APPROACHES

• Using low herbicide rates reduces control and encourages weed tolerance. Always apply full rates.
• Skipping surfactants and adjuvants reduces herbicide effectiveness. Always include them for optimal results. Using an appropriate surfactant helps improve the herbicide retention, coverage and efficacy.
• Applying herbicides at the wrong time of day reduces effectiveness. Target ideal timing for best control. Apply when there is ample sunlight. Mid-day applications enhance effectiveness of glufosinate. Broadleaf weeds tend to be more sensitive to the time-of-day effect than grasses.
• Low temperatures affect herbicide effectiveness. Post-emergent herbicides do best when the temperature is between 65 and 85 degrees. In the summer, apply during the cooler part of the day.
• Applying herbicides just before rain can reduce effectiveness. Always check the forecast and avoid application between rains. Generally, rainfall within six hours after application may reduce effectiveness.
• Don’t skip pre-emergent herbicides. A square foot of soil 6 inches deep can have about 3,000 viable weed seeds. That’s 130 million viable seeds per acre.

As part of his presentation, Kanissery also discussed the harm weeds do.