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Corn+Soybean Digest

Leafy Spurge "Surge" Means Extra Control

Leafy spurge seems to have "surged" this spring, according to Leon Wrage, extension weed specialist at South Dakota State University. Wrage says the yellow-green leaf bracts make this serious noxious weed easy to spot along roadsides, in fence lines, field corners and pastures.

The South Dakota Weed and Pest Commission and the South Dakota Department of Agriculture have declared leafy spurge as one to be emphasized for control this year. Wrage notes the apparent increase follows the last few years of thistle "explosion," giving weed fighters a real "double-barrel" challenge this season.

Several factors may be involved in the surge: Fall spraying was very limited due to dry weather, spraying that was completed was less effective, or fall growth was poor and soil residual was less active.

Wrage says grass growth is less vigorous and less competitive this spring, yet the deep rooted spurge seems almost ahead of normal development schedule.

While Wrage says there’s still time to take action, the next week or two is critical to stop seeding. "The yellow-green bracts are not really the flower, the true flower forms about two weeks after the first color appears and seed continues to develop for the next 20-30 days," says Wrage.

The most effective timing for herbicide treatment is during the first part of the true flowering period – sometime during the next one to two weeks. Wrage says that infestations previously treated are delayed in development, so there is extra time for those sites.

Wrage claims treatment is tough because leafy spurge roots go deep. "A 100% control is hard to get, but it’s possible to reduce the stand and stop the spread with a treatment this year. Reports show 300,000 acres are infested in South Dakota. Research shows seedlings are capable of producing re-growth four days after emergence. After two seasons plants grown in a test had over 1400 buds on the roots," says Wrage.

Seed change in color from yellow to yellow with brown tips to brown seeds to reddish brown to brown, gray brown gray and finally mottled. Seeds are viable when they become brown – usually 10-14 days after fertilization.

Spring treatments that have been evaluated in SDSU extension demonstrations include 2,4-D at 1.5 lbs/acre, applied in spring and fall to reduce the stand in a long-term program. Wrage says Tordon is more effective in spot treatments at 2 quarts/acre or 1.5 pints combined with 1 lb/acre 2,4-D. These can be used in rights-of-way and grass pasture. Use mowing or low 2,4-D rates now to set up the weeds for fall spraying. Plateau is another option for fall, including many tree plantings. Special labeling for pasture or grass hayland has been approved.

Wrage says leafy spurge fighters should consider biological agents to help. "There are collection opportunities in South Dakota. Contact your county weed and pest supervisor for information. The flea beetles have been very effective in some locations. Grazing goats or sheep works for some situations. It’s important to use all the tools available for this weed," he says.

Source: Leon Wrage, 605-688-4591

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