The Harm Weeds Do

Before HLB, canker and diaprepes root weevils became major problems for Florida citrus growers, weeds were among the constant and major annoyances in groves. Even with the pests and diseases growers have faced over the past five decades, the need for weed control may be as important, and costly, as ever. A University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) report indicated weed control accounted for about 20% of processed orange production costs in Southwest Florida in 2021–22.

In a May 20 virtual presentation, two UF/IFAS speakers told why weeds remain a concern. Horticultural sciences Associate Professor Ramdas Kanissery was the main presenter, and host Mongi Zekri, citrus Extension agent for Southwest Florida, contributed with opening remarks.

MAIN PROBLEMS

Kanissery’s presentation, “Managing Aggressive Weeds in Citrus,” cited three main problems that weeds cause:

• They affect the health and productivity of citrus. (Zekri added that weeds reduce crop yields and increase production costs.)
• They provide competition for resources. (Zekri said they compete with trees — particularly young trees — for water, nutrients, space and even light in the case of climbing vines, which can easily cover trees. “The more competitive the weeds, the more adversely they alter tree physiology, growth, fruit yield and quality,” Zekri said.)
• They increase susceptibility to pests and diseases. (Zekri noted that weeds may also harbor insect pests, mites and plant diseases.)

Zekri pointed out that “weeds have various effects on tree performance, including reduced efficiency of low-volume irrigation systems and interception of soil-applied pesticides and fertilizer.”

HARD-TO-CONTROL WEEDS

Kanissery said hard-to-control weeds share several key traits:

• They are tolerant to herbicide programs.
• They grow aggressively.
• They have deep or extensive root systems.
• They have high reproductive capacity.
• They are highly adaptable.

Kanissery cited the following as examples of hard-to-control weeds in citrus:

• Spanish needle
• Horseweed
• Dayflower
• Parthenium
• Bermuda grass
• Nutsedge
• Goatweed
• Guinea grass