Friday, May 2, 2008

Landscape and Turf - Weed Control in Landscape Beds and More

The following is information from Dr. Steve Hart, extension weed specialist from Rutgers, on weed control options in landscape beds and turf as well as newer herbicide products coming to market.

In landscape beds, it is important to place herbicides in the proper location with respect to mulch. Ronstar, Goal, Rout and OH2 require light to be effective and must be placed on top of mulch. Devrinol, Treflan and Snapshot have the potential to volatilize, therefore must be placed below mulch. Gallery, Pennant and Surflan can go under or on top of mulch.

Some landscapers like to use landscape fabric under mulch to reduce weeds in landscape beds. Fabric can work in shrub beds, but is not effective for annuals and perennials, when too many holes are punched in the fabric. Spun-bonded fabric is better for weed control than woven fabric, but it has limited friction and will not hold mulch on a slope.

Snapshot, Rout and OH2 are great on annual grasses (They also are effective on a wide range of annual broadleaf weeds) and should be applied as a preemergent in early spring and late summer. Ronstar and Casoran are other preemergent products. Casoran is especially useful for controlling really tough perennial weeds, like Canada thistle and mugwort in an existing groundcover, like blue rug juniper. But, Casoran is tricky to use. Only apply Casoran when it is cold because it is highly volatile. The ideal time to apply is in February, when there is a layer of snow on the ground. As the snow melts, it carries the herbicide into the soil.

When applying a granular herbicide, don’t let the granules collect leaf whorls. Some landscapers effectively use leaf blowers to blow granules off plants and onto the soil where they belong. Allow soil to settle around newly planted perennials before applying herbicide. Air pockets become flow channels and you will loose the herbicide from the zone where it provides control. Pennant is a good preemergent to use for yellow nutsedge control.

Post emergent products for landscape beds include Sedgehammer (new name for Manage), Basagran, and Lontrel for broadleaf control; Acclaim, Fusilade, Vantage and Envoy for grass control; and Roundup and Finale for non-selective control. Basagran is good for Canada thistle and yellow nutsedge. Fusilade is the best grass herbicide to use for bermudagrass in beds. The grass herbicides can generally be used over the top when beds contain broadleaved plants.

Many suppliers now carry a glyphosate product. Fortunately, the formulations are all 41% active ingredient (except Glypro). All manufacturers have also followed the convention of calling their product “pro” or “plus” if it contains a surfactant. When people complain about poor control with glyphosate, it is usually a timing issue. Spraying glyphosate in April on tough weeds will kill topgrowth but since there is very little translocation to the roots at this time of year, the plant is not completely killed. If you are managing difficult weeds like mugwort, the best thing to do is to keep the mugwort in check until about July 15 (but you won’t be able to kill it). Then allow it to grow to about 6 inches. Control with an application of glyphosate on August 15 (with a second application in September).

Steve Hart’s recommendation for control of bermuda grass in lawns is to apply 3-4% Round Up Pro mixed with a post emergence grass herbicide. Then wait four weeks to see what comes back. Retreat (maybe as many as two-three times) and reseed in August.

Yellow nutsedge is another difficult to control weed. Glyphosate usually just burns the tops without killing roots. The product formerly called Manage, is now Sedgehammer, and can be used by professionals for excellent nutsedge control. You need a significant amount of foliage present to get good control. Sedgehammer failures are usually due to one of the following reasons: lack of high quality non-ionic surfactant – you must add a surfactant when using Sedgehammer for nutsedge control; degradation in solution – Sedgehammer degrades in solution with a complete breakdown in 5-7 days. That means if you mix a tank, don’t use it all, save it for 5 days and try to use then, it won’t work.

Mugwort, another difficult weed, can be controlled with glyphosate in late fall. Lontrel and Casoran (applied during winter) can also control mugwort.

Phragmites can be controlled with Rodeo (the aquatic formulation of glyphosate) but you need to use a high rate and apply in the fall. Renovate has an aquatic label, contains triclopyr and has good activity on phragmites if applied in late June.

Glyphosate will control poison ivy, but only with a fall application. Use a rubber glove, covered by a cotton glove and brush a 10% glyphosate solution on the plant.

Some new products for weed control include:

mesotrione – This product will replace Tupersan. It provides a longer window for crabgrass control by providing early postermergent activity. Unfortunately, it turns foliage white for about 2 weeks before it kills the weed. It will control creeping bentgrass and nimblewill in cool season turf and has some activity on zoysia and bermudagrass in cool season turf. For commercial nursery production, it may have a use as a preemergent to control yellow nutsedge.
Mesotrione is currently labeled as Tenacity but is only registered on golf courses and sod farms.

Dismiss – This is a new nutsedge material. It controls other sedges as well and has rapid activity.

Quicksilver – This product provides more rapid injury and will control moss and Star-of- Bethlehem (at high rates).

Spotlight – This new formulation removed clopyralid since clopyralid can’t be used on material destined for compost (i.e. lawn clippings).

Information compiled by Susan Barton, Extension Horticulture Specialist, UD

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