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CONTROL NEXT YEAR’S WEEDS THIS YEAR
Contrary to popular belief, fall is the best time to treat turfgrass for broadleaf weed problems in cool season turfgrasses such as Perennial Ryegrass, Kentucky Bluegrass and Tall Fescue. Herbicides are one tool in reducing the weed population in a stand of grass. According to The Lawn Institute (www.thelawninstitute.org) the best defense against weeds is a healthy strong stand of turf. A fairly hard to spot fall weed becomes a spring problem in a hurry. Dandelions, clover, chickweed and a plethora of other broadleaf weeds are present in the fall but not flowering. Treating them in the fall ensures they are dead before spring arrives when they would have a chance to flower and go to seed. This repeated reduction in seeds will decrease the future need for herbicide use.
There are two options in fall weed control, pre-emergent and post-emergent. Pre-emergent chemicals are often not the best choice. These stop weeds from germinating, which sounds great, however they do not last a long time in the soil and would need to be reapplied to ensure all weed seedlings are halted. However, most of these pre-emergent products stop all seed from growing including grass seeds. This means no fall over-seeding to thicken your turf stand. An exception to this would be Siduron or Tupersan which allow cool season grasses to germinate.
Post-emergent weed control is your best option for many reasons. Weeds can be killed in the fall beginning when air temperatures decrease below the herbicide label temperature thresholds, but if you are going to over-seed the area, applications should be held off until the seedlings have developed enough to be mowed. Actually the later you wait to treat with your post-emergent attack on the weeds the more likely you will kill them all. If you were to apply a post-emergent herbicide in early September there is a good chance that more weeds could germinate after that time and cause problems come spring.
Applications of broadleaf weed control chemicals such as 2,4-D, MCPP and Dicamba should be made late September thru late October. If you have difficult to control weeds such as ground ivy or wild violet, two applications spaced 2-3 weeks apart may be needed. As the weeds die remember that good cultural practices (mowing, fertility and irrigation) will promote the grass to fill-in and decrease the chance the weeds will return.
Do not worry about treating for crabgrass and other spring annuals in the fall as they will die after the first frost anyway.
Lawn chemicals such as those used to treat broadleaf weeds are safe when used according to the label instructions. Always follow all label instructions when using any type of chemical.
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