Q & A WITH PAMELA SHERRATT

Editor ’ s Note : This month ’ s Q & A article was written by Dr . David S . Gardner , professor of Turfgrass Science , Dept . of Horticulture and Crop Science , The Ohio State University .

Weeds like speedwell and hairy bittercress are becoming more of a problem on our rec . soccer fields . What herbicides are best for winter annual control ?

Winter annual weeds germinate in autumn , persist vegetatively over winter , and then grow rapidly and flower / set seed in late spring . They die on their own by early summer . However , control in the spring with postemergence herbicides can be difficult . If you have trouble controlling winter annuals this spring , plan for either a preemergence or postemergence application in the fall , either of which may be more effective for control .

Weeds you can target in spring ( but preferably in fall ) include winter annual broadleaf weeds . Henbit and chickweed have always been around , while species such as creeping speedwell , hairy bittercress and veronica have become more widespread in the Midwest ( possibly because our winters have been milder ). Each is highly competitive in thin or dormant turf or in newly seeded areas ; so , the best defense is to properly maintain your turfgrass . A concern is that a dense mat of winter annual weeds — after they die in the spring — will open a bare spot in the turf that may be filled in with crabgrass and other summer annuals .

Winter annuals can be controlled preemergence with an early fall application . Note that a fall application will likely degrade and not be effective against crabgrass and other summer annuals the following spring , so a specific preemergence application targeting winter annuals should only be used when you have a severe infestation . Spring is the time to map out infestations so you know where to apply the preemergence herbicide in fall . Pendimethalin , prodiamine , dithiopyr and isoxaben are labelled .

Best control of winter annuals with postemergence herbicides is with applications in late fall to actively growing plants . Postemergence herbicides can be used in the spring ; however , this is sometimes not as effective because the weeds have hardened off over winter . You should apply no later than when the weed is flowering , which can be a challenge if temperatures are cool . Combination herbicides containing esters and protox inhibitors may give more consistent results . Florasulam is also effective against winter annual broadleaf weeds and has good activity in cool weather . Annual bluegrass is opportunistic but technically a winter annual with a primary flush of germination in fall . Effective annual bluegrass control has been elusive , but control with two or three applications of amicarbazone in early spring can be effective ( consult the label for specifics ). Some also report good success with ethofumesate applied in fall , which has both pre and postemergence activity . Some preemergence herbicides are labeled for annual bluegrass control ; however , they may reduce — but usually do not eliminate — annual bluegrass .

A weed to target in early spring is lesser celandine , which is an ephemeral — meaning that the leaves and flowers are only visible in the early spring . Control with herbicides can be difficult . Try manual removal by digging the bulbs . You can also apply glyphosate ( non-selective ). Some selective control in turfgrass may be achieved if you apply a combination herbicide that contains at least two of the following active ingredients : MCPA , triclopyr and dicamba .

Weeds to target in early spring include wild garlic , wild onion and spring beauty . These are ephemerals that persist vegetatively year over year , but the foliage is only noticeable or a nuisance in late winter / early spring . They green up and grow a few weeks before the turf , and tend to be visible as clumps of foliage up to 12 inches in height in otherwise still dormant turf . They are monocots but they are not grasses . Just as sedges are different than grasses , so too are the Allium and Claytonia species , which are more closely related to amaryllis and daffodils . If you have a serious problem , you can attempt to treat them with herbicides that contain either 2,4-D or sulfentrazone ( or both ). Another strategy is to keep them cut short — either by mowing or with hand shears — which weakens the plant and reduces its ability to develop as vigorously the next year .

Winter annual weeds are usually not our most serious weeds in turf , but they can become quite noticeable and problematic . The key is to recognize the uniqueness of the life cycle and target your herbicide application for the right time of year . SFM

Questions ? Send them to Pamela Sherratt at 202D Kottman Hall , 2001 Coffey Road , Columbus , OH 43210 or sherratt . 1 @ osu . edu

Or send your question to Dr . Grady Miller , North Carolina State University , Box 7620 , Raleigh , NC 27695-7620 , or grady _ miller @ ncsu . edu

50 SportsField Management | February 2024 sportsfieldmanagementonline . com