The saying, “Timing is everything,” could never be more true. Proper timing of herbicide applications can not only save you the frustration of having a lawn full of weeds, but it can also lead to better control of those pesky plants. Properly identifying the weed and knowing its growth habit is helpful in knowing if or when is the best time to apply herbicides for the best results.
Knowing the type of plant you are dealing with is crucial in its control. Annual weeds require a little different approach than perennial weeds. Annual weeds are those that sprout, grow, set seed, and die all within a year. Annual weeds fall into one of three categories. There are the spring annuals, like crabgrass; summer annuals, like knotweed or sandbur; and winter annuals, like henbit. Each one has a different set of temperatures and requirements it needs in order to germinate. Perennial weeds can grow and set seed in a year, but they continue to come up year after year, like clover and ground ivy.
There are several options for control of weeds. Knowing the plants’ life cycle and when it germinates will help in the timing of herbicide applications or if hand pulling is needed. Preemergence herbicides keep the seeds from germinating, or sprouting, which keeps the weeds from becoming a problem, and are usually used to control annual weeds. Once the seeds have germinated, the preemergence herbicides are not effective at controlling the growing weeds. Postemergence controls will do a much better job of controlling the weeds once they have germinated. Perennial weeds come up every year from the crown of the plant. This makes preemergence herbicides not effective in controlling these weeds as they only have an effect on seeds. Postemergence herbicides or hand removal are two common methods of control. Hand pulling or digging the weed may require a little elbow grease, but it is an effective method of control if you get the whole root system and have the time.
Timing of post emergent control is just as important as the timing of preemergence herbicide. Early season control of many weeds can give you better efficacy. As in the case with some perennial weeds, summer applications of broadleaf weed killers might just burn back, or brown, the foliage for a little while, only to have it regrow new leaves a little while later. Comparatively, later season applications to annual weeds might make you feel better, but it might only kill the plant a month earlier than it normally would have died due to frost.
There are some products that can be affected by the heat. Some broadleaf weed killers, like 2, 4-D, in the heat can volatize, or switch from a liquid to a gas. When this happens, the product that was applied to the weed can drift over and damage nearby sensitive plant material. The most common indicators in the garden are peppers, grapes, potatoes, redbud, and tomatoes. Symptoms can be leaf yellowing, distortion, and cupping upward of the leaf. Sometimes the herbicides can also cause a twisting, curly-q appearance to stems and petioles, leaf stems. To prevent herbicide damage, avoid applying herbicides for weed control during the hottest months to sidestep injury to non-target plants.
Proper timing, identification, and the right product/method are the secrets for good weed control. With a little luck, your weeds might have met their match.
Elizabeth Killinger is the Horticulture Extension Educator with Nebraska Extension in Hall County. For more information contact Elizabeth at firstname.lastname@example.org, her blog at https://huskerhort.com/, or HuskerHort on Facebook and Twitter.