UF/IFAS researchers want citrus growers to know that “Managing weeds in citrus groves isn’t just about what you spray; it’s about when you spray.” This is because the age of the weeds affects the effectiveness of herbicides. Similarly, the age of your citrus trees can also have an effect on how the herbicides affect your citrus.
Getting Weed Management Timing Right
For Pre-Emergent (or Residual) Herbicides. As pre-emergent herbicides target the seeds of weeds and keep them from germinating, they work best if weeds have not yet begun to sprout. It is advised to use pre-emergent herbicides on areas that have been cleared of weeds, such as a tree row. The pre-emergent herbicide will create a barrier that keeps weeds from germinating.
For Post-Emergent Herbicides. These herbicides target weeds that have already begun to grow, but the older and more mature the weeds get, the less effective the herbicide. Young weeds have underdeveloped root systems that make them more susceptible to herbicides.
In contrast, older weeds that have transitioned into their reproductive stages are much less responsive to herbicide treatments due to their established root systems. This leads to the need for multiple sprays of higher rates of the herbicide; this is obviously undesirable due to the higher cost and the danger of the weeds developing a tolerance to the herbicide.
Herbicide Treatments and Your Citrus
The age of your citrus trees also matters as you don’t want your herbicide treatments to affect your trees. Younger citrus trees—those under three years old—have a greater sensitivity to herbicides. Their smaller root systems and thin bark are not protection enough to withstand spray drift, and they can suffer chemical injury. The recommendation is to protect the trunks of young citrus trees when spraying herbicides and to keep the herbicide from making contact with the green tissues of young citrus trees.
It is also advised to always read the product labels of herbicides, even if it’s being used around mature citrus trees.
The Bottom Line
In conclusion, citrus growers should be targeting weeds when they are young and then following up with a pre-emergent herbicide. Growers should also protect young citrus trees from herbicides, and they should also be cautious with herbicides around more mature trees, reading product labels fully to understand the impact the product will have on mature citrus trees.