By Ramdas Kanissery
The use of compost in tree rows is receiving increasing attention among citrus growers. The use of weed-free certified products can considerably minimize the weed emergence issues associated with compost use. However, eventually, weeds will start to grow in the composted areas in the grove. As compost and similar soil amendments prove to be very rich in nutrients, they may potentially stimulate the weeds’ germination and growth (Figure 1). Here are some tips to help growers manage the weeds in citrus tree rows after applying compost and other soil amendments.
KNOW YOUR WEED … IT HELPS
It is essential to identify the weeds that are emerging in the composted areas in the tree rows. This helps to select an appropriate management strategy to tackle them. Determining the type of weed that needs to be controlled and its growth stage (seedling, vegetative growth and seed production) will make it easier to choose the correct herbicide product and application rate. Check out the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) resources that help identify the weeds (broadleaf, grasses, sedges and vines) commonly found in a citrus grove.
LET THEM GROW … BUT TEMPORARILY
Let the weeds germinate and grow in the composted areas. Once the weeds emerge several inches above the soil and are in an active vegetative growth stage, apply an appropriate post-emergent herbicide. They must be sprayed when in the seedling stage. Generally, the weeds are less vulnerable to herbicide application as they advance to a mature growth stage due to reduced uptake and translocation of herbicides within the plant. Also, follow-up applications may be necessary for heavy weed pressure areas for accomplishing better control. This quick reference table from UF/IFAS provides growers with information on different post-emergent herbicides used in citrus.
HOLD OFF THE RESIDUALS … FOR SOME TIME
It may be worth holding off the residual (pre-emergent) herbicide application immediately after composting in the grove. Residual herbicides need to be applied directly into the soil to work effectively; fresh compost can potentially prevent the herbicide’s contact with the soil and its subsequent incorporation into it. Therefore, it is usually better to start the residual herbicide program after the compost is blended well into the soil. The impacts of different soil organic amendments, including compost, on herbicide’s behavior and soil half-life in the citrus grove is not well known and is currently under investigation.
Read more about compost use and weed management here.
Ramdas Kanissery is an assistant professor at the UF/IFAS Southwest Florida Research and Education Center in Immokalee.