Fall lawn weed control strategies
The fall season and even some of the milder weather periods of early winter present great possibilities in weed control, particularly if you are interested in using recommended herbicides. Any time of year is appropriate to hand-remove weeds and for common lawn weeds such as dandelion and plantains, there are a host of tools available (commonly called ‘weed poppers’) that are extremely effective in the complete removal of ‘tap-rooted’ weeds. If you don’t mind bending over or getting on your hands and knees, you can achieve the same result with a sturdy pocket knife. If you commit a few minutes a day to hand-removal, you will be surprised what an impact you can have over several days of effort. However, hand-removal of creeping weeds with fibrous root systems is often very limited in success and can be quite frustrating in terms of the effort expended and the limited level of control. In these cases, herbicides are often the most effective option in control.
What does the season have to do with control? There are a few major reasons: 1) Many of our most problematic weeds in Virginia homelawns are cool-season broadleaf perennials, and fall is a time when they are actively growing and translocating food and water throughout the plant. Perennials (plants that live for 3 or more years) are some of Mother Nature’s hardiest, most durable plants, and in order to control them with a herbicide, it is important to get the chemical translocated throughout the entire plant in order to control growing points beneath the ground as well as above. Weeds such as dandelion, plantains, wild violet, creeping Charlie, mock strawberry, and even the ‘grass-like’ weeds of wild onion/wild garlic are ideally treated with appropriate broadleaf herbicides in the fall. 2) Tolerance levels of most broadleaf landscape plants (i.e. trees, shrubs etc.) to potential exposure to a broadleaf herbicide are quite high in the fall because these plants have been ‘hardened-off’ by the stresses of summer. In contrast, these same plant materials are usually very sensitive to the same herbicides in spring applications when the desirable plants are loaded with very succulent plant tissues that are just emerging and developing. Factor 3) fall is an ideal time to control the majority of winter annual broadleaf weeds that emerge from September through mid-October. Plants such as henbit/deadnettle, chickweeds, Carolina geranium, and buttercup are prominent winter annual broadleaf weeds that can easily be controlled by herbicides when they are young and actively growing.
What can/should be done about summer annual or perennial weeds in the fall? The basic answer is ‘nothing to very little’. These weeds have either just completed their life cycle and will die upon first frost (the annuals, things like crabgrass, foxtail, or spurge) or they have begun to enter their winter dormancy period (weeds like dallisgrass, wiregrass, or Virginia buttonweed). Other than mechanically removing them, there is no point in trying to control them now with selective herbicides.
A complete list of weed control products and their application levels can be found in the Virginia Tech Pest Management Guide – Lawns (http://pubs.ext.vt.edu/456/456-018/Section_5_Lawn-4.pdf). Pictures and descriptions of many of Virginia’s most troublesome lawn weeds can be found at www.TurfWeeds.net. And there is a host of fall management strategies detailed in a Virginia Cooperative Extension publication entitled ‘Fall Lawn Care’ that can be found at http://pubs.ext.vt.edu/430/430-520/430-520.pdf.