Bob Mugaas, University of Minnesota Extension Educator
While this past May went down as one of the driest Mays ever, many areas around the Twin Cities have received some rain during the first part of June. That has both been very helpful for our lawn grasses and has also provided the needed moisture for many of our weed seeds, especially crabgrass to begin actively germinating. In most areas of southern Minnesota we are past the time when preemergent herbicides for crabgrass control will be effective. However, that doesn’t mean control is not possible. Those small crabgrass seedlings can effectively be controlled with postemergent herbicides. One of the newer active ingredients for crabgrass control is quinclorac. This is a very good herbicide for controlling crabgrass once it’s germinated and the seedlings are visible. However, it is usually mixed with other broadleaf control products and marketed for home use as general weed and crabgrass killers. However, it is important to note that with these combination products, you will be applying other herbicides that are not needed or even effective at controlling crabgrass. Hence, this unnecessarily introduces these other materials into the environment; something we try to minimize doing whenever possible.
Photo 1: This mixed stand of young crabgrass plants and other broadleaf weeds is a good candidate for a combination herbicide that will selectively control the crabgrass as well as the broadleaf weeds. Bob Mugaas
Photo 2: Dead grass spots resulting from using a glyphosate containing product designed to kill all vegetation that it comes in contact with. These areas will need to be resodded or reseeded. Bob Mugaas
Where you have a mixed stand of weeds, both broadleaf and crabgrass, a combination product like the one mentioned above, can be a good alternative to buying separate products for each category of weeds. Be careful to choose products that are safe for use on your lawn. Those containing the active ingredient glyphosate will kill all grasses and broadleaf weeds leaving the lawn scarred with unsightly brown dead spots that will need to be resodded or reseeded. Remember to always follow product label directions exactly regarding a products use. Where only a few crabgrass plants are present, they can easily be hand pulled from a moist soil thereby avoiding the use of an herbicide altogether.
Even though some rain has arrived to help out our lawns and gardens, many lawns are still showing signs of the very dry conditions encountered during the month of May. Those signs range from small brown spots intermingled with green grass to larger, completely brown areas. Future rainfall patterns and amounts for the remainder of June are, of course, not known. If we continue with our cool to mild temperatures and periodically receive some rainfall over the next couple of weeks, supplemental irrigation needs for most lawns should be minimal, if needed at all during that time. Avoiding excessive traffic and play on the lawn during those times when lawns are brown and dry will help avoid additional, often more permanent injury. Likewise, herbicide applications to lawns under drought stress can cause injury to lawn grasses that would otherwise be quite tolerant of those products.
Photo 3: Typical drought stress symptom with dry, brown patches interspersed with patches of green grass. Bob Mugaas
In general, lawn grasses should be mowed at higher heights of cut from now through the remainder of the summer. Flowering of our cool season lawn grasses is winding down. As those flower heads are being mowed off, remember that those shoots ultimately die after flowering. Hence, folks will often complain about a larger amount of course, brown grass stems in their lawns making them appear thinner and even a bit unsightly. In fact, our lawns are somewhat thinner this time of year due to the dying back of those spent flower stalks. It’s really nothing to worry about. This is a natural occurrence every year. Our lawn grasses begin to regrow new rhizomes and shoots in a few weeks, which will help thicken up the lawn. This regrowth process is one of the reasons why our fall lawn fertilization is so important to the long term health of our lawns. But more on that in later article.