Many of you have had frost by this time and your lawn is showing the effects of a very dry summer unless you irrigated. If it seems that there are more weeds than ever, you are exactly right. Some weeds thrive in droughty conditions and that makes this the best time to get a handle on some of them.
Looking at our own lawn, the crabgrass seems like the dominant species in many parts of the lawn. If you have crabgrass, get down and take a very close look at it. Notice how it spreads out and hugs the ground? That is a survival tactic that lets crabgrass bloom and seed while unaffected by close mowing or grazing (not that many of you have sheep or cattle in your yard). Notice also that the plant is brown and dying. Crabgrass in an annual grass but has already left thousands of seeds for next year. Don’t bother with it now; the effective control is a pre-emergent herbicide applied 2-3 weeks before the seeds germinate in the spring.
Three weeds that get top billing in many yards are dandelion, plantain, and ground ivy or creeping Charlie. Fall is an excellent time to control these because they are sending nutrients to the root to survive the winter and grow with reckless abandon in the spring. Other perennial weeds have already started to go into dormancy and control does little good now. Look at poison ivy for example; the leaves have started to turn red and yellow. (It is really very pretty!)
The first method of control for these weeds is always cultural practice. Mowing high, reducing compaction, fertilizing (or reducing fertilizing), and adjusting the acidity or alkalinity of the soil to give grasses an advantage over weeds is a long-term solution that is both economical and environmentally friendly.
When infestations are severe or there are patches of these weeds to deal with, chemical control may be necessary. Master Gardeners do not make recommendations for specific chemicals; we have not been trained for that. In general, there are two choices for chemical control. One is a nonselective herbicide.
Nonselective herbicides are effective on anything green. In other words they will kill annual and perennial weeds as well as all grasses. If you want to kill everything in an area and start over, that is the choice and there are several on the market. However, they only work when the plant is actively growing and the temperature is above 60 degrees.
Selective post emergence herbicides are effective on annual, biennial, and perennial broadleaf weeds so would be the choice for dandelion, plantain, dock, thistle, ground ivy, knot weed, or clover to name a few. You can choose granular or spray but make sure you get good advice from a trained pesticide dealer. Again, they are effective when the temperature is above 60 degrees and there is no rain forecast for 48 hours. Be very careful with herbicides that contain dicamba since the herbicide can be taken up by the roots of adjacent shrubs. Sprays are more effective because you can be very selective about what you spray and you can tell if the weed was thoroughly covered.
With all chemicals, read the instructions carefully and use protective gear when applying. Now if there were a spray that was effective against intolerance, bigotry, and incivility this fall, we would really have something! More information about conventional fall weed control is available at: http://www.extension.umn.edu/distribution/horticulture/dg1137.html.
Up-to-date information on seasonal problems can be found at blog.lib.umn.edu/efans/ygnews/. For personal help with gardening questions, call 444-7916, leaving your name, number, and question. A master gardener will call to assist you.
