Spring is usually the time of year we see multiple advertisements for lawn care product, especially weed n' feed products. The labeling on these products always contains a photo of a weed-free lawn with photos of weeds the product will control. What is the weed most commonly shown? Dandelions!
Dandelion is a perennial broadleaf similar to other perennial broadleaf weeds (broadleaf plantain, buckhorn plantain, ground ivy, violets, clover, etc.) that have a central taproot. In the spring, weeds such as these will flower and produce seed. When this happens, plant foods and energy move upward in the plant for reproduction of seed. In early fall, perennial broadleaf weeds prepare for winter by building up carbohydrate reserves. The storage vessel is the large, central taproots characteristic of perennial broadleaf weeds. Therefore, most internal plant activity is carrying these reserves downward.
Broadleaf weed numbers are best reduced by maintaining a taller mowing height (3.5 to 4"). While we know that taller mowing heights reduce weed populations up to 80%, you will still notice some weeds like dandelions and others. Increased mowing heights may provide you some savings in weed control by resorting to some hand pulling or spot spray applications of broadleaf herbicides. Blanket applications of broadleaf herbicides are usually not necessary for just a few weeds and are costly. A ready-to-use spray product for broadleaf weeds takes just a few minutes to treat a few weeds for the desired result.
So, why is fall the best time to control perennial broadleaf weeds? All broadleaf herbicides sold over-the-counter for homeowners are considered systemic herbicides. This indicates that the plant absorbs the product then is translocated throughout the plant to disrupt normal plant functions. That large taproot we discussed in the engine house for that plant to survive. If the taproot lives, so does the plant. Therefore, that downward movement of food reserves into the taproot during fall allows the herbicide to translocate more easily into the root for a more efficient control. Broadleaf herbicides are also considered selective herbicides, which indicate they will control the broadleaf weeds without harming your desirable turfgrass.
One precaution to keep in mind when controlling perennial broadleaf weeds in fall is to read the label concerning re-seeding intervals. Fall (September) is also a great time to over-seed lawns. Many broadleaf herbicides require a wait time of 3 to 4 weeks following an application of product before seeding. In some situations it may be better to seed first for proper timing, and then follow up with broadleaf weed control.
Broadleaf weed control products will contain some combination of various active ingredients. They usually include some three-way or four-way mix of the following - 2,4-D, MCPA, MCPP, sulfentrazone, dicamba, or triclopyr. Most products are three-way mixes of 2,4-D, MCPP and dicamba. Some products have removed 2,4-D and replaced it with triclopyr. These products tend to do a better job on the tougher perennial broadleaf weeds like ground ivy and violets. Active ingredient of the products can always be found on the front panel/label of the container under the ACTIVE INGREDIENT section. Some of the more common trade names include: Ortho's Weed b Gon and Weed b Gon MAX, Pbi/Gordon's Trimec, and Spectracide's Weed Stop for Lawns.
For best results, it is recommended not to mow two days prior to two days following applications. Do not irrigate the lawn following applications for at least 24 hours. Always check the forecast for rain prior to applications as well.
All product information is presented with the understanding that no endorsement of named products is intended, nor criticism implied of similar products that are not mentioned. Before using any weed control product please read the label carefully for directions on application procedures, appropriate rate, first aid, storage and disposal. Make sure that the product is properly registered for the intended use (specific weeds and site).
REVISED: September 29, 2015