Horseweed

Description

Horseweed is a winter or summer annual found in waste areas, roadsides and turf. It can vary greatly in height according to the soil it grows in, and the immature rosette looks much different than the mature plant. The erect stem is usually hairy, and is generally branched near the top with small inconspicuous white flowers. The lower leaves are 1 - 4 inches long and toothed, while those scattered along the stem are narrow and smooth. From June to November the plant produces numerous heads of small, inconspicuous white flowers, followed by an abundance of seed.

Cultural Control

Proper turf management is important for biennial broadleaf weed control. Maintain a dense, actively growing turf through proper mowing, fertilizing, and watering practices. Mow at the proper height for your selected adapted turfgrass. Coring and traffic control reduce compaction and encourage desirable turfgrass competition. It is best to control this biennial broadleaf weed in spring or fall, if actively growing at these times.

Chemical Control

Herbicide and Formulation Amount of Formulation per 1,000 sq ft Amount of Formulation per Acre Pounds Active Ingredient per Acre
Preemergence and Postemergence Control
mesotrione, MOA 27 (4 SC) (Tenacity) 0.092 to 0.183 fl oz 4 to 8 fl oz 0.125 to 0.25
Precaution and Remarks: Use on residential turf, golf courses (not greens) and sod farms for pre- and postemergence weed control. Tolerant turfgrasses include St. Augustinegrass, centipedegrass, tall fescue, fine fescue, Kentucky bluegrass, and perennial ryegrass. Add a nonionic surfactant and repeat application after 2 to 3 weeks for improved postemergence control. Tank mix with prodiamine 65 WG for extended preemergence grassy weed control. Can be applied at seeding to all tolerant grasses except fine fescue. After turf germination, wait 4 weeks or until turf has been mowed twice before making a postemergence application. Also controls henbit, chickweed, dandelion, white clover, Florida betony, Florida pusley, ground ivy, oxalis, wild violet, creeping bentgrass, and yellow nutsedge.
[sulfentrazone + prodiamine], MOA 14 + 3 (4 SC) (Echelon) 0.184 to 0.826 fl oz 0.5 to 2.25 pt 0.25 to 1.125
Precaution and Remarks: For use in residential and institutional lawns, athletic fields, sod farms, golf course fairways and roughs, roadsides, utility right-of-ways, railways, and industrial areas. Apply to turf following a second mowing if a good root system has been established. Apply up to 12 fluid ounces per acre to bentgrass at 0.5 inch or higher, fine fescue, and perennial ryegrass. Apply 18 to 24 fluid ounces per acre to perennial bluegrass, tall fescue, and all warm season grasses except St. Augustinegrass (do not apply) and bermudagrass (apply 18 to 36 fluid ounces per acre). For sod production, apply 6 months after establishment, and do not harvest within 3 months. Do not apply with adjuvants or surfactants. [Sulfentrazone + prodiamine should not be applied to cool-season turf with N-containing fertilizers unless some short-term discoloration is tolerable.​

Species Data

  • GROWTH SEASON / LIFE CYCLE
    • summer or winter annual weed
  • GROWTH HABIT
  • LEAFLET NUMBER
    • one
  • LEAF MARGIN
    • smooth or serrated/toothed
  • LEAF HAIRS
    • upper / lower surface
  • LEAF / LEAFLET SHAPE
    • linear / oblong / oval / egg-shaped / elliptical; leaves along stem on the mature plant have no petioles
  • LEAF WIDTH
    • <12 inch; leaves along stem on the mature plant are about 0.4 inches (10 mm) wide
  • LEAF ARRANGEMENT
    • alternate; whorled or basal rosette
  • FLOWER COLOR
    • white
Horseweed growth habit.Figure 1. Horseweed growth habit.Horseweed growth habit.Figure 2. Horseweed growth habit.Horseweed growth habit.Figure 3. Horseweed growth habit.Horseweed growth habit.Figure 4. Horseweed growth habit.Horseweed growth habit.Figure 5. Horseweed growth habit.