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Control winter annual
weeds now The best time to control annual weeds is just before you can see them. Timing of the herbicide (weed killer) application is of utmost importance in controlling winter weeds that are about to sprout in home lawns all over North Florida. Common winter weeds that germinate during fall include annual bluegrass (Poa annua), chickweed, henbit, hop clover, lawn burweed and Carolina geranium. These and other winter annual weeds germinate from seeds during fall as the soil temperature cools and the day length shortens. The little seedlings usually go unnoticed at this time but continue to slowly grow through the colder winter months. Approaching spring, as the day length becomes longer and the soil temperature warms, all of these previously inconspicuous weeds put on a growth spurt and go to seed. The majority of calls for advice on winter annual weed control come to me in late February through April when these weeds are most visible. By then, it's too late. The parent plants are dying and seeds have been scattered all over the yard. You should now see why timing is important when controlling these weeds. If you intend to use a preemergence herbicide, apply it during late September to early October when nighttime temperatures drop to 55° to 60°F for several consecutive days. This will be just before the weeds emerge. Timing of a preemergence herbicide application for warm season weeds such as crabgrass should be during mid February to March 1 when day temperatures reach 65° to 70°F for four to five consecutive days. This generally coincides with the blooming of azaleas, dogwoods and forsythias. Some preemergence herbicides to look for include oryzalin (Surflan), benefin (Sta-green Crabgrass Preventer, Hi-Yield Crabgrass Preventer), pendimethalin (Pre-M, Pendulum, Turf Weedgrass Control, Halts Crabgrass Preventer), benefin + oryzalin (XL) and DCPA (Dacthal). I've placed common names for products first followed by examples of brand names for those products in parenthesis. You may find other brand names on the market that contain the same active ingredient. All of these products are safe to use near ornamental trees, shrubs and flowers. Atrazine (Purge II, Atrazine, Aatrex) is another common herbicide that has both preemergence and postemergence activity on a wide range of weeds. It also can be purchased as a weed-and-feed product. One of the more common weed-and-feed products containing atrazine is Bonus S. Do not apply an atrazine product over the root zone of desirable trees, shrubs and flowers. Also, atrazine can injure certain types of lawngrasses. For season-long weed control, a second application should be made about nine weeks after the initial application. To activate some products, irrigation or rain may be necessary following application. Because many preemergence products may interfere with lawngrass seed germination, delay reseeding six to sixteen weeks after application. This applies to overseeding a lawn with ryegrass seed, also. Overuse of some types of preemergence herbicides can cause your lawn grass to produce short stubby weak roots. So as is true with all pesticides, only apply the product if there is a pest to control – in this case, if you have had a history of winter annual weeds. Otherwise, save your money and time. It is the user's responsibility to read and follow all label directions and precautions when using any pesticide, including herbicides. Larry Williams
Copyright 2005
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