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Archive for Thursday, March 30, 2006

Diligence required to control pesky weeds

March 30, 2006

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Although the recent rains and warmer days have brought about a welcome change in the landscape, several less-than-desirable plants are out-greening the lawn, shrubs or flowers. A combination of grassy and broadleaf weeds are quickly becoming the focal point of the spring show, taking away from the hyacinth, forsythia and quince. Here are some tips and tricks to help you get a handle on these plants before they turn the spring zing into a spring flop:

Henbit is a rather showy spring-blooming weed. The violet flowers, born on stems 8 to 12 inches tall, are quite striking on a warm March day. They are commonly found in cultivated areas such as farmers' fields, flower beds, gardens and in the lawn. Chickweed, on the other hand, has a lower growth habit with creamy yellow blooms. Mix the two plants together, and you can create a beautiful spring display with little effort. Keep in mind though, as with most weeds, they can be invasive and easily take over if left unattended.

Because both weeds are self-seeding, the plants that were there last year are not the same plants we're finding this year. They are, however, plants that sprouted from seeds that were dropped last spring. As the days get longer and the temperatures rise, both have started to bloom to start the process again.

Unfortunately, control options are limited this late in the growth cycle. Start with mechanical controls. Hoe or lightly till bare soil in the garden and around flowers, trees and shrubs. For added control, apply a fresh layer of mulch - 2 to 3 inches should be enough. For hard-to-reach or noncultivated areas, the broadleaf weed killers Trimec and carfentrazone are the two best products to use. Spray on a sunny day when the air temperatures are above 55 degrees.

Avoid spraying newly sprouted grass seed as dieback may occur. Likewise, avoid spraying desirable trees and shrubs. As always, read and follow all label directions. Don't expect miracle results as these plants mature and are less affected by the sprays.

Three grassy weeds that are growing full bore are wild garlic, wild onion and Star-of-Bethlehem. Though wild garlic and wild onion look much alike, each has an odor that is characteristic of its name. These plants are perennials that also can reproduce by seed and aerial bulbil. Bulbils form at the top of the stem and are oval and smooth. Wild garlic also reproduces by underground bulb offsets, but wild onion does not. Both species produce a clump of plants that is unsightly in a lawn.

Control recommendations are the same for each. Traditionally we have used 2,4-D; 2,4-D + MCPP (i.e. Weed-B-Gon); or 2,4-D + MCPP + Dicamba (i.e. Trimec, Weed-Out and some formulations of Weed-B-Gon). These products should be sprayed on a day that is at least 50 degrees. The newer products available are Weed Free Zone and Speed Zone. Both are combination products that contain a formulation of Trimec plus carfentrazone. These may be used at lower temperatures than the traditional products (below 50 degrees). A spreader-sticker added to the spray should help any of these products be more effective. At times, the spreader-sticker is already mixed into the weed killer; no additional amount is needed.

Unfortunately, there is not a good chemical control for Star-of-Bethlehem. The best products currently used are Coolpower (31.3 percent active ingredient) and Turflon Ester (23.8 percent active ingredient). Coolpower is a commercial-only product, but Turflon Ester is available to both commercial and homeowner users.

However, some recent research out of Virginia Tech University has improved the outlook. Scientists there conducted a study in which they achieved 96 percent control of Star-of-Bethlehem one month after treatment by using Quicksilver, a formulation of carfentrazone at the rate of 4 fluid ounces to the acre. Quicksilver is a commercial-only product and therefore is not available to homeowners. However, both Speed Zone and Weed Free Zone contain carfentrazone and would certainly be worth a try if you have this troublesome plant.

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