Know When to Spray for Weeds

By Ramdas Kanissery

Managing weeds in citrus groves isn’t just about what you spray; it’s about when you spray. The effectiveness of your weed control program largely depends on the growth stage of both the weeds and the citrus trees in your grove. Getting the timing right can make a big difference in how well your weed control program works and how safely it fits into your grove.

WEED GROWTH STAGE

The best results are achieved when weeds are targeted early. At this stage, they are much more responsive to herbicide treatments. In contrast, mature weeds with established root systems and in their reproductive stage are far more difficult to manage. Controlling them often requires higher herbicide rates or multiple applications, which increases costs and the risk of developing herbicide tolerance. This is especially true for post-emergent herbicides. If applied too late — when weeds are larger and more advanced in growth — the effectiveness of these products can drop significantly.

By aligning your herbicide applications with the proper growth stages, odds of weed control success can be increased. Post-emergent herbicides are most effective when weeds are young — while they’re still small and actively growing. Figure 1 shows examples of what early-stage citrus weeds look like.  Weeds in such young growth stages are the ideal targets for post-emergent control.

For pre-emergent (also called residual) herbicides, timing is just as important. These products work by preventing weed seeds from germinating. To get the best results, apply them before weeds start to emerge — ideally on a clean tree row, after any remaining weed stubble from earlier post-emergent treatments has been cleared. This allows the herbicide to form a strong barrier against new weed growth.

TREE GROWTH STAGE

Citrus trees in their first one to three years are more sensitive to herbicides. Their smaller size and thin bark make them more vulnerable to spray drift and chemical injury. This means herbicides that are safe around mature trees might damage young trees if applied without proper care. Shielding young trunks and avoiding contact with green tissue are key precautions.

As trees mature and develop hardened bark, they become more tolerant to a broader range of herbicides. This gives growers more flexibility with pre- and post-emergent herbicide products. However, that doesn’t mean you can skip caution. Understanding what your tree can handle at each stage helps you avoid mistakes. Always read product labels carefully and adjust your approach depending on whether you’re working with young plantings or established trees.

BOTTOM LINE

Understanding the growth stages of both weeds and citrus trees is essential for building a strong, cost-effective weed management plan. When you time herbicide applications correctly, you’ll get better results, save money and protect your citrus trees in the process.

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

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