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Cass County Extension

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Lawn Weed Control

How soon can newly seeded lawns be sprayed for weeds?

According to the directions on the spray container, you must wait until after the new grass has grown enough to be mowed 3 times. Don't worry about weeds in your new grass. They can always be gotten out once the grass is well established.

When are weed killers normally applied on home lawns?

Usually we recommend applying a weed killer in the spring and early fall. Weeds are more actively growing and the weed seeds in the soil will have germinated.

When is the right time to spray weeds in the spring?

As soon as they are actively growing and have enough leaf surface to enable the weed killer to be effective. Don't wait until the weeds have started to flower.

Is October too late to attempt weed control?

Definitely not, if the weeds are actively growing, applying a herbicide will give some weed control. The cooler the temperatures, the slower the weeds will respond to the herbicide.

Is August a good time to spray for lawn weeds?

Normally this isn't a good time but if we've had good rainfall and the weeds are actively growing, they may respond well to weed killers.

Why have so many new weeds appeared in lawns the last few years?

Several factors may have caused this to happen. Power raking and removing all the thatch also encourage any weed seeds laying in the soil to germinate and grow. During drought years, the grass may have thinned out and whenever we've had rain, the weed seeds in the soil will germinate and grow. 

Does 2,4-D do a good job of controlling lawn weeds?

2,4-D is very good in controlling dandelions and some of the easier to kill weeds but is fairly ineffective against many of the harder to control weeds.

Does a Weed & Feed fertilizer do a good job of controlling dandelions?

Yes, if everything works just right. You don't want rain for at least two days after applying the weed & feed. After the 2 day period it should be watered in to carry the fertilizer down to the grass roots.

How would you compare a Weed & Feed and a liquid weed killer?

Weed & Feed is obviously more convenient. It allows us to control weeds and fertilize at one time. Liquid weed killer gives us more versatility. It can be applied whenever needed without concern for fertilizer.

Are there any particular precautions which should be taken when applying a weed killer?

Yes, there are 2 conditions which should always be considered when applying a lawn weed killer. The day should be very still and the temperatures should not get above 85 degrees. These chemicals are very volatile and can drift a considerable distance.

What is the best spray for clover in the lawn?

Common lawn sprays such as Weed B-Gone and 2,4-D are not very effective in controlling Clover.  A special Weed B-Gone for chickweed, clover and oxalis is more effective than 2,4-D or regular Weed B-Gone. A lawn weed killer containing Banvel or dicamba would work good but be careful when using this material in an area with tree & shrub roots.

What can be used to control creeping Charlie and creeping bellflower?

They are both very difficult to control. Weed B-Gone is usually not very effective.   A special Weed B-Gone for chickweed, clover and oxalis is more effective than 2,4-D or regular Weed B-Gone. A lawn weed killer containing Banvel or dicamba would work good but again becareful when using it around and under trees & shrubs.

Can anything be done to eliminate quackgrass?

No, not unless you are willing to kill the lawn grass at the same time. Roundup will do a good job of killing all the grasses.

Is there any way to get rid of the undesirable grasses in the lawn?

That is a very difficult situation. There are no herbicides which will control the undesirable grasses such as quackgrass without killing the lawn grass. If these grasses have taken over complete areas of your lawn, they can be killed by spraying with Roundup.

Will the lawn grass eventually choke out the quackgrass?

No, quackgrass is very competitive and actually withstands stress better than Bluegrass. A good fertilizer program along with adequate watering helps the lawn grass compete. Mowing your lawn every 5 days will also help keep the undesirable grasses under control.

When should we apply a crabgrass killer?

Generally we don't recommend applying a crabgrass killer until between the 1st and 15th of May. Crabgrass is a fairly warm seasoned grass that doesn't germinate until the soil warms. Just a word of caution! Don't put a crabgrass killer on the lawn if you are trying to thicken up your lawn by interseeding.

What can be done to control crabgrass in the fall of the year?

Not much of anything besides pulling it out. The most effective way of controlling crabgrass is to apply a fertilizer with a crabgrass killer in the spring.


Todd Weinmann, Extension Horticulturist & Master Gardener Coordinator
Phone: (701) 241-5707
E-mail: todd.weinmann@ndsu.edu

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