As grape harvest progresses throughout Michigan, it is time to consider controlling weeds in the field after crop harvest. After grape harvest, weed control might not be the top priority for many vineyards, but this is the best time to start a weed management program for getting ahead of next year’s weed issues. After grape harvesting, the most important step is to perform thorough scouting of your vineyard and prepare the list of weeds that are problematic in your vineyard. The next step is to select the herbicides in combination with non-chemical management tools that are effective against these weed species.
Fall is a good time to take action for controlling woody perennials such as poison ivy, Virginia creeper, wild grape and tree seedlings (poplar, maple). At this time, perennial plants translocate carbohydrates towards underground plant parts such as crowns, rhizomes and fleshy roots to reserve food for starting growth during the following season. Applying systemic products such as glyphosate is appropriate as it will translocate to kill below-ground parts and inhibit growth during the upcoming season. For effective results, treat these perennials before leaves senesce. Take extreme care at the time of application so that glyphosate does not come in contact with grape vines. Glyphosate absorbed by leaves and bark moves with in the vines and can show significant injury symptoms during the following season. In most cases, these woody perennials may need to be removed manually from the grapevines.
At this time, the risk of grape vine injury due to herbicide exposure is less as vines are shedding leaves and not growing actively. Fall is the best time for applying preemergence herbicides. However, if weeds are growing and have sufficient amount of green tissue, then a tank mix with post-emergent herbicides helps to clear the ground under the vines, which is critical for preemergence herbicides to reach the soil surface. It is also advisable to mow or use a hedge trimmer to remove the large or dead vegetation under the vines before applying any preemergence herbicides because this will help the residual herbicide penetrate into the soil that is essential for herbicide activation and control of emerging weed seedlings.
Aim (carfentrazone), Rely (glufosinate) and Gramoxone (paraquat) provide quick burn-down of weeds. Rely and Gramoxone control both broadleaves and grasses, but Aim is only effective for broadleaves and does not control grasses. Including Venue (pyraflufen-ethyl) with these post-emergence broadleaf herbicides improves burn-down and broadens the weed control spectrum. Post-emergent graminicides including Poast (sethoxydim) and Fusilade (fluazifop-p) are selective for controlling annual and perennial grasses. Fusilade is more effective on quackgrass than Poast. The addition of non-ionic surfactant or crop-oil-concentrate improves the efficacy of Aim, Poast and Fusilade.
Fall applications of preemergence herbicides should be made before the soil freezes or in early spring before the weeds begin to grow. Fall application may also be considered as a proactive weed control action especially due to unpredicted spring weather when herbicide application may be skipped or delayed due to wet and cold weather and early start of vine growth. There may be some loss of herbicides through water runoff or wind erosion, but on the other side cooler weather reduces herbicide degradation and winter time rainfalls help to move herbicide into the upper soil surface.
Several preemergent herbicides with different modes of action (MOA) are labeled for use in vineyards for fall application (Table 1). A general rule is to apply at least three residual herbicides with different MOA each year (fall, spring or during the season) to achieve effect weed control. Alion (indazaflam), Princep (simazine), Solicam (norflurazon), Casoron (dichlobenil), Kerb (pronamide), Goal Tender (oxyfluorfen), Prowl H2O (pendimethalin), Chateau (flumioxazin) and Matrix (rimsulfuron) may be applied in fall.
Each herbicide product should be selected based on its efficacy on weeds and grapevine safety. Detailed information related to the herbicide rates and efficacy on weeds can be obtained from labels and in the Herbicide section of Michigan State University Extension bulletin E0154, “Michigan Fruit Management Guide,” which contains lists of all currently labeled herbicides along with specific remarks for their use in vineyards. — By Sushila Chaudhari, Michigan State University Extension