Tuesday, March 3, 2009

Weekly Word on Weeds

Even though the record cold weather may damage some of our desirable landscape plants – don't worry about those weeds. They will be just fine.

Winter annuals will need to be controlled
Chickweed, henbit, annual bluegrass and vetch are lurking; insulated under a blanket of snow they are protected from the harsh weather and will be ready to grow, flower and seed when the snow melts. Control these weeds while they are small and before they set seeds. Most winter annual weeds can be controlled with non-selective postemergence herbicides such as diquat (Reward) or glufosinate (Finale). What about glyphosate you may ask. Glyphosate does work on these weeds but it works very slowly in this cold weather.

Annual bluegrass can be selectively controlled in landscape beds with clethodim (Envoy). It will take several weeks for the annual bluegrass to die, but Evoy is selective and can be applied over the top of many broadleaf ornamental plants.

Vetch can be particularly difficult to control in landscape plantings. Clopyralid (Lontrel) controls vetch but must be used as a directed application around woody plants – not over the top of ornamentals. Lontrel works by foliar absorption but has some root uptake as well, so follow the label directions for dose and avoid applications near sensitive species – particularly herbaceous perennials in the aster and legume families.

Sureguard – a new herbicide labeled for use in landscapes:
Sureguard is a sprayable formulation of flumioxazin. This herbicide has been labeled for directed applications in field nurseries for preemergence control of broadleaf weeds. It has also been popular as a sanitation treatment in gravel areas of container nurseries. It is now labeled for use around woody landscape plants and for weed control in and around hardscapes. Advantages include good broadleaf weed control, no staining, some postmergence as well as preemergence weed control. Disadvantages: Sureguard will injure herbaceous ornamentals, will injure woody ornamentals if applied to the foliage or green stems, and will damage turf if applied directly to the grass.

My highly opinionated advice on Sureguard for landscape use:
This may be a good option for weed control in hardscapes where weeds emerge in the cracks around brick or stone pavers. Also, in woody plant beds such as tree islands, median strips, or along fence rows. Sureguard is a good partner with postemergence herbicides such as glyphosate, glufosinate or diquat.

For more information contact your local Cooperative Extension Center and ask for the Commercial Horticulture Agent.