Though crabgrass germination is likely a month or more off with the cold temperatures, it will be here before we know it. Following is a quick summary on maximizing crabgrass control with preemergence (PRE) herbicides from Zac Reicher, Professor of Turfgrass Science, University of Nebraska at Lincoln:
1. Mow as high as practical all year to maintain turf competitive with crabgrass, 3” at a minimum for most homelawns and other turf according to their use. Mow often enough not to remove more than a third of the leaf blade on any single mowing. For homelawns, this will likely by every 5 days during the aggressive spring growth and less frequent during the rest of the season.
2. Irrigate deep and infrequently, wetting to the depth of rooting only after the grass shows signs of drought stress.
3. For those not using sequential applications of PRE herbicides, your application should be made late April to early May in eastern Nebraska assuming “typical” spring weather.
4. When using only a single application of PRE herbicide, the highest label rate will provide the maximum control.
5. For the most reliable crabgrass control, sequential applications of PRE herbicides are needed. The first application can be applied almost anytime from November to April and the second application should be early to mid-June.
6. For sequential applications of PRE herbicides, the highest label rate can be divided by two and then two equal applications applied.
7. For sequential applications of PRE herbicides, it doesn’t matter if active ingredients are switched between the first or second application as long as one half the high label rate of the respective active ingredient is used in each app.
8. To maximize control from PRE herbicides, water within 24 hours or try to schedule before a rainfall to move the active ingredient off the leaf blades.
9. Try to minimize N fertilizer applied with the PRE herbicide since cool-season grasses are naturally growing quickly in the spring. This can be done by using fertilizer/herbicide combination products either low in nitrogen and/or with most of the nitrogen in slow release forms that will release after the early spring growth flush.
10. As always, avoid applications to impervious surfaces and sweep or blow product off these surfaces back into the turf.
More details are available at: Application timing of preemergence herbicides: http://turf.unl.edu/pdfctarticles/Janpreestrategies.pdf
Research update: Is it important to use the same preemergence herbicide for both the initial and
sequential application?: http://turf.unl.edu/pdfctarticles/May%20seq%20with%20unlike%20pree.pdf
Crabgrass Control in Home Lawns (Turf 2010b):
Crabgrass and Other Summer Annual Grassy Weeds (Turf 2010d Professional Series)
Zac Reicher, Professor of Turfgrass Science, firstname.lastname@example.org