Winter Annual Weeds Making Their Exit

Every year in early to mid-spring, I receive questions regarding identification and control measures for winter annual weeds in the landscape. In the recent weeks, the 2004 season has been no exception. Why do we wait until now to decide upon finding out the proper identity and which control measures should be taken? The obvious answer is that these plants are much more noticeable in their flowering and reproductive stages of growth, and we are all outside in our landscapes now and we easily see them as we are mowing and doing other activities. What can I do to control these weeds?

First, let’s review some plant biology regarding life cycles, since life cycles are very important to understand in timing control measures. Plants or weeds that complete their life cycles within a year are classified as annuals. Annuals are categorized into two groups – summer and winter. Summer annuals are the weeds we see emerge in the spring; they flower and set seed prior to frost in the fall. Some common examples of summer annual weeds that occur in the landscape include crabgrass, carpetweed and common purslane. Winter annuals are many of the flowering plants we see at this time of the year. They generally germinate in the fall or late winter, and then go through the reproductive phases prior to the summer. At this time, some of the common winter annuals we notice are common chickweed (small, white flowers), henbit and purple deadnettle (pinkish-purple flowers). With the onset of temperatures consistently reaching daily highs of 80 degrees F, winter annuals die fairly quickly.

Biennials are plants that require two years to complete their life cycles. During the first year, they progress through the vegetative stage, usually having a rosette appearance, which is a cluster of basal leaves. During the second year, they bolt, or produce a flowering stem. Biennials are not very common in landscapes; some of the most common biennials include many of the thistles.

Perennials are those that live longer than two years. They have a wide range of germination and reproductive patterns and are generally the most difficult group of weeds to control in any setting. Besides reproducing from seed, this group of plants has means of vegetative reproduction through structures such as bulbs, underground rhizomes and extensive rootstocks. Some of the most common weeds in our landscapes are perennials such as dandelion, wild garlic and poison ivy.

Now, let’s go back to the original question regarding control of winter annuals. At this time, winter annuals are fading out of the picture. There is no reason to spend the time and money making herbicide applications targeting this group of weeds as they are dying back. After noticing these plants in the fall or late winter, postemergence herbicide applications at those times will be more effective and warranted. There is a wide variety of products available for home use on the shelves at lawn and garden centers . Many various trade name products contain some combination of 2,4-D, dicamba and mecoprop (MCPP) as their active ingredients, but there are several others as well. These products can easily be applied through hose-end or pump sprayers and control a wide variety of broadleaf weeds; be sure to read their labels and understand the directions. It’s critically important to properly identify weeds targeted for control in the landscape; since a product’s label will specifically list those species for which it claims control. Weed species not listed on a product’s label are anyone’s guess as to whether or not that product will provide adequate or even any control.

So for now, with the heat setting in, don’t worry about the winter annuals; you have enough to worry about with the summer annuals rushing in and the perennials setting new growth. Much information regarding weed control in lawns may be found by obtaining MU Extension Publication IPM1009, Turfgrass and Weeds. This full-color guide has many photographs and written descriptions of the common weeds found in our landscapes. The guide also has listings of products and their active ingredients that are recommended for control of many of these common weeds. It may be ordered through the MU Extension Publications Center by calling 1-800-292-0969 or online at http://muextension.missouri.edu/explore/agguides/pests/ipm1009.htm. A Website that can assist you in matching your weeds for proper identity is Missouri Weeds at http://www.psu.missouri.edu/fishel/.

Fred Fishel, Extension Pest Management/Pesticide Training Coordinator, UMC (573) 884-6361