Toward the end of August, when everything else was suffering, the winter annual weed seeds were just waiting to flourish. They have been dormant since last spring, when you couldn't control their parents, and they will quietly hide until you can't control them either. At the first drop of moisture, or even heavy dew, they start to come alive. Now in September, they will start to become visible as small seedlings. These small plants will overwinter and begin active spring growth before all else. When these reach the flowering stage, they may be next to impossible to control. Now is the most effective, easiest and least expensive control opportunity.
Henbit, chickweed and dandelion are the most common weeds; however, control is the same for even the lesser-known varieties. Pre-emergence herbicides are applied to the soil before the weed seed germinates and stops this germination. These are most effective on summer annuals, such as crabgrass, and not as effective on winter annual weeds because of the various germination times. Post-emergence herbicides are used after the weeds have emerged from the soil and while they are actively taking in nutrients for growth. These seem to be the most effective for fall weed control.
These herbicides are available in liquid, granular and granular fertilizer-herbicide combinations. The fertilizer combination is attractive now because this is a very good time to fertilize your lawn. Take care to count this application into the yearly fertilizer needs for your lawn. If you have just planted new grass, you must wait until it has been mowed three times before chemical weed treatment. None of these products will distinguish weeds from newly planted grass. The pre-emergence will stop the desirable grass seed from germinating, and the post-emergence will damage the new grass plants.
Post-emergence herbicide is absorbed though the leaves. The longer it stays in contact with the plant, the better. Keep the mower off the grass two to three days before and after application. Apply the product when rain is not expected for 24 hours after application, and do not water for the same time. The air temperature should be between 70 and 90 degrees. Granular application while the morning dew is on the grass is perfect. Not only is there adhesion to the leaves, but your spreader tire tracks are plainly visible, aiding in accurate application. Liquid application follows the same general rules.
These herbicides likewise do not distinguish between weeds and desirable perennials. These perennials are at less risk now than during their spring growth, but care must be taken. Weed treatment in a flower or perennial garden is different from this lawn application.
A strong health lawn is always your best defense against weeds.