Alerts › Weed Alerts ›

Winter Weed ALERT!

October 16, 2009
by Travis Gannon and Fred Yelverton

WINTER WEED IMAGES

Winter Weed Alert!

By: Dustin F. Lewis, Travis W. Gannon, and Fred H. Yelverton

Annual and perennial winter weeds are ahead of schedule this fall due to unseasonably cool temperatures coupled with frequent rain.  Common chickweed (Stellaria media), mouseear chickweed (Cerastium vulgatum), and henbit (Lamium amplexicaule) are common winter broadleaf weeds that emerged early this year.  Annual bluegrasss (Poa annua) also emerged early this year and has begun to tiller.  Of course, in established turf stands, winter annual weeds may not be as mature as other areas.

What does this mean for turfgrass managers?  This means turfgrass managers may need to adjust typical herbicide programs for controlling winter annual weeds this year.  Simazine and atrazine are very effective and economical herbicides for winter annual weed control in warm-season species; however, they will not control mature winter annual weeds.  Typically, atrazine and simazine applied as a single application (2 lb ai/a) early- to mid-November or a split application (1 lb ai/a) applied mid-October and mid-December provide acceptable winter annual broadleaf and annual bluegrass control.  This year, it is strongly recommended to go ahead and apply your initial or only application of atrazine or simazine immediately!  Additionally, turfgrass managers should survey the areas they manage.  If you note properties or areas where winter annual weeds are beyond seedling stage, you should consider mixing a postemergent herbicide with your simazine or atrazine application.  Common postemergent herbicides which are effective include three-way (2,4-D + MCPP + dicamba) or sulfonylurea (metsulfuron, trifloxysulfuron, etc.) herbicides and may be tank-mixed with simazine or atrazine.

Another common question we receive:  “Does bermudagrass or zoysiagrass need to be dormant to apply simazine or atrazine?”  NO!  Bermudagrass and zoysiagrass DO NOT need to be dormant prior to the application of atrazine or simazine but should not be applied after January 01 each year to avoid the potential of delaying spring greenup.

For Tall Fescue and other cool-season grasses, the triazines or sulfonylureas cannot be applied.  However, many 3-way and 4-way herbicides that contain 2,4-D, MCPP, dicamba, triclopyr, fluoxypry, etc can be applied.  As with warm-season species above, these application procedures should proceed as soon as possible. 

Figure 1:  Common chickweed (small plants) and henbit (larger plants) taken on October 13th.
Figure 1: Common chickweed (small plants) and henbit (larger plants) taken on October 13th.

winter weed
Figure 2: Mouseear chickweed taken on October 15th.

Figure 3:  Henbit taken on October 13th.
Figure 3: Henbit taken on October 13th.

Figure 4:  Annual bluegrass with multiple tillers taken on October 13th.
Figure 4: Annual bluegrass with multiple tillers taken on October 13th.