10. Weed Management

OBJECTIVE: Determine pest management action levels for weed infestations. 

Develop site-specific action level guidelines for controlling weeds. 

  • No general action level guidelines for management of weed species in lawns are presently available. 
  • Pest management action levels for weed populations are very subjective and vary greatly based on the management program, desired quality and function for a lawn. 

Example: a moderate infestation of broadleaf weeds may be allowable on a seldom used residential lawn area but unacceptable on a high-profile commercial lawn. 

  • Weed species action levels can be established even for a specific use area on a specific property based on careful monitoring and the history of the site.  
  • Action levels may vary according to weed species present.  
  • In most cases control measures will be curative. Preventive control may be used based on scouting information and on potential for future infestation. 

OBJECTIVE: Establish and conduct a scouting program for weeds.

Scout regularly for weeds to inform management decisions. 

  • Scouting for weed species normally consists of visual observation and counting of the number of undesirable plants per unit area.  
  • Scouting should be done every time a turf manager is on a particular site, in addition to an all-inclusive, in-depth scouting event during late summer or early fall.  
  • The turf manager should use a back and forth or zig-zag pattern when scouting for weeds, with special attention to known problem areas.   
  • Observations can be recorded on a site map or added to a list with the location identified. 
  • In addition to recording weed species present, special attention should be given to areas of thin turf and possible causes, newly introduced weeds and historically problematic weeds that are not controlled with the current management program. 
  • Since many weed problems arise as a result of specific cultural problems, corrective action may be critical to minimizing future weed encroachment. 

OBJECTIVE: Discourage weed infestations with non-chemical means. 

Limit potential entry of weed seed into the system. 

  • Remove weeds, especially newly introduced weeds, by hand when appropriate. 
  • Prevent weeds from going to seed in lawns, adjacent gardens and border areas. 
  • Consider weed seed levels in selection of materials such as soil, amendments, compost, topdressing material, sod and other plant material. 
  • Use certified seed for establishment, making repairs, reseeding and overseeding. 
  • Use high quality, low weed level sod during renovation and establishment. 
  • Collect and remove clippings which contain weed seeds when appropriate. 
  • Set height of cut at maximum acceptable height. 
  • Reduce compaction and wear areas by re-routing traffic. 

Create a growing environment that makes weed species less competitive. 

  • Maintain a dense and deeply rooted turf as the primary means of integrated weed management. 
  • Water judiciously; timing irrigation events to prevent moisture stress and avoid over-watering. 
  • Aerate to relieve compaction. 
  • Avoid turf cultivation during periods conducive for crabgrass germination (spring) if it is considered a weed at the particular site. 
  • Avoid turf cultivation during periods conducive for Poa annua germination (fall, peak Poa annua germination), if species is considered a weed. 
  • Overseed with desired turfgrasses in late summer-early fall if turf has thinned due to drought dormancy. 

Supply adequate and balanced nutrition to yield a dense and well-rooted turf.  

  • Avoid high levels of fertility during the summer months when cool-season turfgrasses are stressed and easily out-competed by many weed species.  
  • If turf has thinned due to drought dormancy, provide adequate fertility once dormancy breaks to encourage recovery. 
  • Do not fertilize dormant or brown turf.

OBJECTIVE: Use herbicides intelligently when other means fail to acceptably control weed species present. 

Discourage herbicide resistance. 

  • Select from different herbicide groups whenever possible, not relying on a single “group” (class) or mode-of-action. 

Apply postemergence materials responsibly. 

  • Be familiar with weed life cycles to apply herbicides at most vulnerable growth stages of weeds. 
  • Limit blanket applications to avoid unnecessary pesticide use and undue turf stress. Spot treat weeds when appropriate. 
  • Do not apply herbicides if temperatures are above or forecast to exceed 85 °F. 

Apply preemergence materials responsibly. 

  • Use preemergence or preventive herbicides only in areas where weeds occurred and were documented the previous season and can be expected to occur in current season. 
  • Select and use preemergence herbicides so as not to interfere with overseeding opportunities. Follow label recommendations. 
  • If there is annual weed pressure and turf dormancy is going to be allowed to progress at a site during the summer months, consider applying a preemergence material in the spring. 
  • Water-in preemergence herbicides as appropriate and according to label directions. 
  • Avoid cultivation following preemergence applications to maintain the protective barrier. 

Consider fertility. 

  • When using herbicides containing nitrogen, factor the amount of N applied into the fertility program for the particular lawn. 
  • Fertilize lightly after postemergence herbicide application when appropriate to aid the turfgrass in the filling of canopy voids left by dying and dead weeds.