For Release October 20, 1998

Fall Lawn Weed Control

    by Chuck Otte, County Extension Agent

It seems that all of our fall lawn chores have been pushed back a few weeks by the summer like weather that doesn’t want to go away. Well, now we’ve had good fall rains, noticeably cooler weather has arrived and before we know it there will be snow flying. So we now have to rush around and treat those seedling broadleaf weeds or be plagued with a lawn full of flowers next spring.

What weeds are we targeting? Primarily we are looking at four species: dandelion, pretty yellow flowers; henbit, a mass of K-State purple flowers; chickweed, dainty little white flowers and speedwell, small blue-violet flowers with a white center. All of these are annual weeds, except dandelion which is a perennial. The annuals, as well as seedling dandelions, sprout in the fall anytime from late August to early November whenever there is good moisture and the weather cools off.

If you aren’t looking for these in the fall, you probably won’t see them. But if you go out into your lawn and look close, especially in areas where the grass is a little thin and there’s bare soil, you are probably going to see a LOT of little green weeds. These may not look like much now, but do nothing and you’ll be surprised how much they will have grown by March and April! These weeds are often referred to as winter annuals. They sprout and start growing in the fall. While there may not be a lot of plant visible above ground they are busy forming one heck of a root system and crown below ground. These plants will not go dormant until the thermometer falls well down into the teens.

In the spring these plants explode to life, often blooming as early as late February if we have a warm spell. By the time these plants start to bloom in the spring it is literally too late to treat. Spraying in the spring will kill them, but it will take a lot more spray, and by the time they have died they will have gone ahead and made seed. Spring spraying also brings an extra risk to other plants. Many other plants are producing new leaves, in the spring, when homeowners are spraying for weeds. The herbicides we use to control these weeds can partially vaporize and the new tree and shrub leaves are very sensitive to these vapors. You probably won’t kill other plants but you can sure mess up leaves and branches.

In the fall we have a completely different scenario. These plants are small and moving lots of food into the roots. You can use lower rates of chemicals and these chemicals are going with the flow, into the roots, creating a very effective control situation. In the fall we have cooler temperatures so there will be less vaporization of herbicides. Additionally, plants are going dormant. Old leaves that are getting ready to fall off aren’t prone to being damaged by herbicide drift. You can’t be sloppy with your herbicide, there’s just less chance of a problem developing.

(The following has been requested by numerous parties and is reprinted from a column that I wrote in 1988.) One other seasonal weed I want to mention. This weed is a peculiar one that only shows up about every other year, but real heavy every fourth year. It is almost always found in the front yards of homes. It grows from 2 1/2 to 6 feet tall, generally has one thick woody stem, though sometimes two. These stems will normally be fairly shallow, 3 to 8 inches deep, with few if any lateral or feeder roots. The leaves on this thing are only 1 or 2, fairly large and thick, quite pale with an almost word like etching on the surface sometimes in different colors. The life span of this weed is generally short. Chemical control is seldom needed since they quickly disappear after election day.


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