Technical Aspects of Spring Preemergence Herbicide Applications

Preemergence herbicides are the most effective way to control crabgrass and goosegrass in warm- and cool-season grasses. Here are some quick tips for on maximizing control from preemergence herbicides.

• Application timing
• PRE’s are primarily broken down by microbes and microbial activity is relatively low at cool soil temperatures. So applying PRE’s early is always better than applying late
• Crabgrass germinates when 4” soil temperatures average 53-55oF whereas goosegrass germinates later when 4” soil temps average 63-65oF. Preemergence (PRE) herbicides should be applied prior to these soil temperatures
• In cooler climates, PRE’s can be applied in the fall at the high rate and will provide season-long control of crabgrass the following year, especially when followed by a sequential application in late Spring
• Though most PRE herbicides can provide minimal POST control of 1-2 leaf stage annual grasses, they are much more effective as PRE’s applied prior to germination
• Sequential applications
  • Research shows sequential applications of PRE’s consistently improves long-term control compared to single applications at the same total rate
  • Depending on rate, sequential applications in spring and summer should be spaced 4 to 6 weeks apart
• PRE/fertilizer combinations
  • Smaller granules tend to provide better control. This is because PRE’s do not move in the soil and smaller granules provide a denser pattern and more consistent distribution of active ingredient compared to large granules
  • Higher spread rates from lower concentration products also can improve control
  • On cool-season grasses, chose combination products with low nitrogen since nitrogen is needed in limited amounts in the spring on cool-season grasses
• Use in winter-damaged areas or new seedings?
  • Most PRE herbicides cannot be used at seeding of cool-season grasses or at sprigging of warm-season grasses. So do not apply to warm season or cool-season grasses until winter survival is confirmed
  • Ronstar^® is one PRE that can be used at the time of sprigging bermudagrass to control annual grasses and not inhibit establishment. New restrictions on Ronstar will likely not appear on labels until late 2023 or 2024
• Herbicide resistance
  • Cases of herbicide resistance have been reported in goosegrass, crabgrass, and annual bluegrass as a result of using the same active ingredient or within the same group of active ingredients repeatedly over years
  • Preferably tankmix or at least rotate modes of action among PRE’s and POST’s as often as is practical (Table 1)
• Need more info? – Follow all label recommendations and contact your Envu sales manager if you need assistance

Figure 1. The compressed (flattened) sheaths of goosegrass are characteristic under lower mowing heights (Envu).

Table 1. Common PRE and POST herbicides used to selectively control annual bluegrass, crabgrass and/or goosegrass in cool- or warm-season turf. It is important to tankmix or rotate different types of herbicides and MOA's when possible to limit chances of resistance. Be sure to check specific labels for use on your turf species.