Nov. 1996
Kurt Spingath

Weeds are back! You know this as you get out to do the work necessary to get the trees out of the field. Those of you who have been successful with your spring residual weed control undoubtedly saw a flush of weeds, like crabgrass, after the July rains. Many have been asking us what can be done to clean up late emerging weeds after the residuals have stopped being effective. Here are a few ideas to consider. Always read and follow label directions for all pesticides.

Broad Spectrum Weed Control
Roundup has been the premier product used for foliar broad spectrum weed control. Roundup will control most annual and perennial grasses and broadleaf weeds and woody brush. Roundup was changed this year by replacing the old surfactant with a new surfactant system that precludes the need to add any spreader. This gives the product advantages as well as disadvantages. The old Roundup was never labeled for over the top use though many have used it that way during the conifer dormant season. The new products, represented by Roundup Pro and Roundup Ultra, are not labeled for over the top use. The surfactant that is now used can cause Roundup to damage conifer foliage, even during the dormant timing. Do not use over the top. On the other hand, Roundup Pro and Ultra will have a faster burndown of many weeds, as little as one week versus four to six weeks. The old surfactant required application four to six hours before rain to allow absorption. Now one hour is all that is needed before rain for effective control. Accord, the glyphosate used in forestry, is also labeled for Christmas trees for broadcast site preparation and directed spray release. Accord has no surfactant in the jug and should be mixed with 0.5% R-11 or 0.25 Sylgard 309. Any glyphosate product can do damage to conifer foliage and is not labeled for over the top applications. Use Roundup Pro, Roundup Ultra or Accord at a 2% solution for annual and perennial weed control in directed spray release applications.

Specific Weed Problems
Canadian thistle and bull thistle are problems that can persist even after soil residual products are used. Canadian thistle emerges over time from underground roots during the entire spring and is less susceptible to soil residual products. Stinger can be used over the top of the trees during the entire growing season. Wait until the thistles have emerged entirely (this has been accomplished by the time thistles have reached the bud stage in early May) and apply Stinger at 8 to 10 ounces per acre. Stinger is also active on several other weeds such as dandelion, lambsquarters, groundsel and clover.

Vantage and Prism will control most annual grasses and some perennial grasses except fine fescues. Consult the labels for a listing of susceptible weed species. They can be used in broadcast applications without damage to conifers before budbreak at the recommended rates. Directed spray treatments must be made after budbreak. Most effective application are when actively growing grasses are less than 6 inches in height. Higher rates are needed for weeds 6 to 12 inches in height. Grandstand is a new product that is expected to be available for broadleaf weed and woody brush control. The active ingredient will be triclopyr, the same as in Garlon 3A and will be fully labeled for Christmas trees. The weeds susceptible are field bindweed, clovers, dandelion, Canadian and bull thistles, blackberries and most woody species that tend to invade plantations. It will most likely be labeled for directed spray release and site prep broadcast applications as triclopyr can damage conifer foliage. Editor's Note: Kurt Spingath is a forester with the large chemical supply firm of Wilbur Ellis Co.