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’s the first of a series on maximizing control from preemergence herbicides.
  • Application timing
    • Preemergence (PRE) herbicides are primarily broken down by microbes and microbial activity is relatively low at cool soil temperatures. So applying PREs early is always better than applying late.
    • Crabgrass germinates when 4" soil temperatures reach 53-55°F whereas goosegrass germinates later when 4" soil temps reach 63-65°F. Preemergence herbicides should be applied prior to these soil temperatures.
    • In cooler climates, PREs can be applied in the fall at the high rate, providing 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 PREs applied prior to germination.
  • Sequential applications
    • Research shows sequential applications of PREs consistently improve 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 PREs 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 also can improve control.
    • On cool-season grasses, choose 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.
  • 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 many years.
    • Tank-mix and/or rotate modes of action among PREs and POSTs as often as is practical. (Table 1)
  • Need more information? – See the linked Solution Guides below and contact your Bayer sales manager if you need assistance.

Figure 1. The compressed (flattened) sheaths of goosegrass are characteristic under lower mowing heights. Photo: Bayer Green Solutions Team.

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 tank-mix or rotate different types of herbicides and MOAs when possible to limit chances of resistance. Be sure to check specific labels for use on your turf species.

Spring Application Chart

  Bayer Solutions – Crab Goosegrass – Cool
  Bayer Solutions – Crabgrass – Warm
  Goosegrass Warm-Season Golf Solutions Sheet

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Laurence Mudge

by Laurence Mudge , Green Solutions Team Manager

Monday, January 07, 2019