Recent cold weather in some regions has slowed down weed growth in lawns. However, they will continue to grow when it gets warmer.
The unseasonably warm weather experienced in early January in the same regions has many cool-season annual weeds growing like it's spring.
Winter annuals such as chickweed, henbit and annual bluegrass seem to pop out when they are least expected. Controlling winter annuals with preemergent herbicides before they germinate is tricky.
Unlike summer annuals such as crabgrass, which germinates when the soil warms in the spring, winter weeds germinate when soil temperatures drop in September. Therefore, applications of preemergent herbicides to prevent germination of these weeds must be applied in mid-September. Most don't apply preemergent herbicides to lawns with good reason. Preemergent herbicides, as a rule, are not applied when lawns are over-seeded. Most lawns are over-seeded in the fall, eliminating the chance to reduce winter weed germination.
Commercial lawn care companies and home owners are now scrambling to apply postemergent herbicides to control winter weeds that seem to be out of control. It is important to control the weeds now because weeds such as chickweed and henbit are almost impossible to control in bloom. Some of the weeds are approaching this stage, so it is important to apply post-emergence herbicides soon.
Cold weather, below 40 degrees, impedes the effectiveness of some postemergent herbicides. Watch the weather forecast and apply when day temperatures are approaching 50 degrees or more for a few days. It's best to apply blended herbicides since many weeds are difficult to kill with one particular herbicide.
Winter weed populations can be reduced with a healthy lawn. Healthy, vigorous lawns shade the soil, preventing seed germination in the fall. This is another issue that takes a bit of skill, but is not impossible. Those with healthy lawns that don't want to use herbicides often overlook a few winter weeds in the spring. When June arrives, winter weeds are gone.
Darrell Blackwelder is an agricultural agent in charge of horticulture with the North Carolina Cooperative Extension Service in Rowan County. For archived garden columns or other information, visit the Rowan County Master Gardener Web site at www.rowanmastergardener.com, e-mail Darrell_Blackwelder@ncsu.edu.
--The Salisbury (N.C.) Post