How to Manage Horseweed

University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) weed scientist Ramdas Kanissery recently shared information about management of horseweed, a common Florida citrus broadleaf weed. Kanissery is an associate professor at the Southwest Florida Research and Education Center. Following are highlights from his article in the August 2026 UF/IFAS Citrus Magazine. 

Horseweed is found in citrus tree rows, ditch banks and along grove edges. It can spread quickly through a grove if it is not managed early.

Horseweed grows as a single, upright stem covered with short, stiff hairs and can reach up to 6 feet tall. A single plant can produce approximately 200,000 seeds.

Horseweed is also known as marestail, coltstail and Canada fleabane. The names marestail and coltstail refer to the plant’s tall, narrow flowering stalk, which resembles a horse’s tail or upright broom.

Horseweed holds a spot in weed history as the first broadleaf weed found to survive glyphosate, first reported around 2000. Glyphosate-resistant horseweed has since spread across much of the country, which is a big reason it can be so hard to control.

CONTROL YOUNG PLANTS

Young horseweed in the rosette stage is far easier to control than tall, mature plants that have formed a woody stem. Scout tree rows often and treat while plants are small and actively growing.

STAY ON TOP OF MOWING

In the row middles, keeping horseweed in check usually comes down to routine mowing as part of normal vegetation control between the tree rows. Running the mower before flowering keeps a mature horseweed from dropping its heavy load of seed and helps stop seed from building up in the soil and spreading into the tree rows. However, mowing can cause horseweed to grow back with several stems, so it pays to stay on top of it and mow while plants are still young and well before they set flowers and seeds.

INCLUDE PRE-EMERGENT HERBICIDES

Products containing indaziflam, diuron, flumioxazin, norflurazon or simazine can help reduce new horseweed emergence. Pre-emergent herbicides work best on clean soil, so clear existing weeds and debris from the tree row before applying.

USE EFFECTIVE POST-EMERGENT HERBICIDES

Systemic herbicides such as glyphosate, 2,4-D, and saflufenacil are commonly used to control actively growing horseweed. Because horseweed has developed resistance to glyphosate and some other herbicides in many areas, rotating herbicides with different modes of action is important for keeping control effective. Always read and follow herbicide label directions to achieve good weed control and avoid injury to citrus trees.