Prostrate Knotweed

Description

Prostrate knotweed is a low-growing summer annual or perennial which is very competitive in compacted soils. It is often a problem along driveways, sidewalks, and beaten paths. The slender stems radiate from a central taproot and produce a tough mat-like growth. Leaves are dull, blue green, small, smooth and arranged alternately along the stem. This weed germinates with the first warm temperatures in the spring. Newly emerging seedlings are often mistaken for grasses in very early stages of development.

Cultural Control

Prostrate knotweed is very competitive in infertile and compacted soils and often invades turfgrasses along driveways, sidewalks, and beaten paths across lawns. 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 weed in late spring or early summer because it is easier to control at this time and the turf will have a greater chance of recovering the areas previously occupied by weeds.

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.​
Postemergence Control
dicamba, MOA 4 (4 SL) (various brands) 1 to 2 tsp 0.5 to 1 pt 0.25 to 0.5
Precaution and Remarks: Apply as foliar spray to growing weeds. Prevent injury to ornamentals. Avoid rooting zone of shallow-rooted trees and shrubs.​
diglycolamine, MOA 4 (4 SL) (various brands) 1 to 4.5 tsp 0.5 to 2 pt 0.25 to 1
Precaution and Remarks: Do not exceed 1 pint per acre on bentgrass, carpetgrass, buffalograss, and St. Augustinegrass. Apply to newly seeded grasses after the second mowing. Do not exceed 0.25 pint per acre on extended sensitve plant roots on sandy soils and 0.5 pint per acre on clay soils.​
[2,4-D amine + fluroxypyr + dicamba], MOA 4 + 4 + 4 (4 SL) (various brands) 0.36 to 1.1 fl oz 1 to 3 pt 0.5 to 1.5
Precaution and Remarks: Use on perennial bluegrass and ryegrass, tall fescue, creeping bentgrass (excluding greens and tees), bermudagrass species, bahiagrass, zoysiagrass, and St. Augustinegrass in residential, industrial, and institutional lawns, parks, cemeteries, athletic fields, golf courses, and sod farms. Use on St. Augustinegrass sod farms only. Apply 1 to 2 pints per acre on creeping bentgrass and 1.5 to 1.8 pints per acre on warm season turf grown for sod. Apply 2 to 3 pints per acre to all other turf areas. For non-turf areas, rate can be increased to 2 to 5 pinst per acre. Application can be made to grass seedlings after second mowing and to newly sodded, sprigged, or plugged grasses 3 to 4 weeks after operations.​
[MCPA amine + fluroxypyr ester + dicamba], MOA 4 + 4 + 4 (4.8 SL) (Change Up) 0.73 to 1.1 fl oz 2 to 3 pt 1.2 to 1.8
Precaution and Remarks: Same turf tolerances and uses as [2,4-D amine + fluroxypyr + dicamba] in addition to centipedegrass. Only spot treat St. Augustinegrass when temperature exceeds 80 degrees F. Do not apply more than two applications per year totaling 3 pints per acre. For non-turf areas, rate can be increased to 2 to 5 pints per acre. Application can be made to grass seedlings after second mowing and to newly sodded, sprigged, or plugged grasses 3 to 4 weeks after operations. Sod farm rates include 1.25 pints per acre for creeping bentgrass, 2 to 3 pints per acre for all other cool season grasses listed on label and 1.5 to 1.8 pints per acre for all warm season grasses listed on label.​
pyraflufen ethyl, MOA 14 (0.177 SC) (Octane 2% SC) 0.016 to 0.092 fl oz 0.7 to 4 fl oz 0.000938 to 0.0055
Precaution and Remarks: Used in established sod farm and ornamental turf by commercial applicators and professional landscapers only. Turf can be newly seeded, sodded, or sprigged as long as it is established and not under stress. Tolerant turfgrasses include bermudagrass, centipedegrass, St. Augustinegrass, zoysiagrass, tall fescue, perennial ryegrass, perennial bluegrass, and creeping bentgrass (not greens or tees). Apply 1 to 4 fluid ounces alone to 3- to 6-inch tall weeds. For larger weeds and broader spectrum control, apply 0.75 to 1.5 fluid ounces and tank mix with 2,4-D, mecoprop, dicamba, chloroprop, MCPA, triclopyr, or fluroxypyr.​

Species Data

  • GROWTH SEASON / LIFE CYCLE
    • summer annual or perennial weed
  • GROWTH HABIT
  • LEAFLET NUMBER
  • LEAF MARGIN
    • smooth
  • LEAF HAIRS
    • none
  • LEAF / LEAFLET SHAPE
    • linear/oblong/oval/egg-shaped/elliptical
  • LEAF WIDTH
    • 1/2 - 1 inch
  • LEAF VENATION
    • pinnate
  • LEAF ARRANGEMENT
    • alternate
  • ROOT TYPE
    • taproot
  • FLOWER COLOR
    • white to pinkish in color
Prostrate Knotweed growth habit.Figure 1. Prostrate Knotweed growth habit.Prostrate Knotweed growth habit.Figure 2. Prostrate Knotweed growth habit.Prostrate Knotweed growth habit.Figure 3. Prostrate Knotweed growth habit.Prostrate Knotweed leaflet number.Figure 4. Prostrate Knotweed leaflet number.Prostrate Knotweed leaflet number.Figure 5. Prostrate Knotweed leaflet number.Prostrate Knotweed leaflet number.Figure 6. Prostrate Knotweed leaflet number.

Written By

Photo of Dr. Charles PeacockDr. Charles PeacockProfessor and Extension Turfgrass Specialist (919) 515-7615 charles_peacock@ncsu.eduCrop and Soil Sciences - NC State University
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This Extension factsheet can also be viewed at:
https://content.ces.ncsu.edu/prostrate-knotweed