Rainfall has been plentiful this spring and early summer in many areas across the Southeast, which is a considerable change from last year in many of the same areas. A wet summer can put additional stress on weed management programs and result in escaped weeds that thrive.
If you have young, newly planted vineyards make sure to take care of weeds that have escaped your herbicide program. Research in NC has shown that in order to maximize vine growth in the establishment year the vineyard must be maintain weed free through July. If you have applied only a single preemergence application it is not too late for an additional preemergence herbicide application in those new plantings. Chateau has proven to be a better option than oryzalin for late summer residual both broadleaf and annual grass weed control.
In established vineyards vines tend to be more competitive with weeds since more shading is available to cover the vineyard floor, however given the weather and depending on the your herbicide choice summer weeds may be escaping your control measures. Perennial weeds like horsenettle, Johnsongrass, and bermudagrass are not be controlled with preemergence herbicides. Perennial grasses can be controlled in bearing vineyards with postemergence herbicides like Poast and Fusilade. Application timing is the key to success. Bermudagrass should be treated when it has 6 to 8″ of new growth while Johnsongrass should be treated when it is 8 to 12″ tall followed by a second application when regrowth occurs. Horsenettle is very difficult to control and options are limited to the use of either paraquat or glufosinate (Rely) to burn it down. In my opinion glufosinate is the better of the two. Both of these herbicides are non-selective and effectively control most annual weeds.
In closing, it is imperative that you do not make any additional applications of glyphosate from now until next winter. Grape sensitivity to glyphosate increases as we move into later summer, through fall until complete leaf drop has occurred. I have seen glyphosate injury in grapes in the spring following late summer and fall glyphosate applications the previous year. Glufosinate in nearly as effective and a much safer herbicide choice.
