Thursday, July 1, 2010

Hold off on lawn weed control

This is about the worst time of year to try to control those weeds that have been plaguing your lawn since last spring (or for the past decade). During the heat of July and August, the plants do not absorb herbicides into their leaves very well so most of it just runs off onto the ground.

The best time for lawn weed control is in the autumn. Actually, it is best to keep the sprayers in the garage until about the first week of October. During the cool part of the fall, perennial weeds such as creeping Charlie (ground ivy), violets and others begin to send carbohydrates produced in the leaves down to the roots for winter storage. Herbicides that land on the leaves are absorbed and transported down to the roots too.

Some of our weeds are “winter annuals” meaning that they germinate in the fall, grow for a while and then survive the winter as a plant. Next spring, they go to seed very early in the season and then sprout again next fall. An autumn application of an herbicide will help control these types of weeds too.

Do not be discouraged if the weeds do not shrivel up and die immediately. Often, it will look as if nothing has happened but the weeds will die over the winter and be gone when the lawn comes to life next spring.

Creeping Charlie, also known as ground ivy, is one of the most common and invasive weeds of lawns in Jackson County. As a member of the mint family, it has a square stem. Whenever the stem touches the ground, it has the ability to make roots and start a new plant. If you do not kill the entire plant, it will soon regenerate and that is why it is so tough to control.

A serious creeping Charlie infestation almost always indicates either a shady lawn or one that has a drainage problem. Turfgrass, even the shade resistant types, will not grow as thick and lush in these conditions as in more sun. Since the creeping Charlie thrives in shade and poorly drained soils, it often wins the battle for the ground.

Chemical treatment is only one part of the control process for creeping Charlie. You may have to try using a core aerator on your lawn each spring or fall to loosen up the soil. Removing certain tree limbs may help for a while but the branches will eventually grow back to fill the opening. In severe situations, you may need to kill the entire lawn with a non-selective herbicide such as Roundup and start all over again. Till the soil to loosen it, add organic matter such as compost and re-seed with a shade tolerant grass variety.

If all of this does not work, you have the alternatives of living with it or giving up and putting in a shade garden. The creeping Charlie will also try to invade your hosta beds but it is generally a little easier to control in that situation than in the lawn.