Now is a Good Time to Assess Your Vineyard Weed Control Program
By: Lee Stivers, Extension Educator, Penn State Extension, Washington County
With the grapes all harvested, and frosts already visiting the vineyards, it might seem an odd time to be thinking about weeds. However, fall is not a bad time to take a walk through your vineyard and makes some observations about weed control. At this time of year, it is still possible to recognize summer annual weeds, even those that are not frost-tolerant, as well as to identify stubborn perennials, and young winter annual and biennial weed species. You may even want to draw up a weed map of your vineyard to help you next year when making weed control decisions.
I recently took a vineyard weed walk with Rich Ripepi of Ripepi Winery and Vineyards in Monongahela. We discussed his cultural and chemical weed control practices, what worked and why, and talked about several of the weed species that we found.
The rainy season this year made it a challenge to control weeds in the vineyard rows. In early August at Ripepi Vineyard, weeds in most of the vineyard rows were weed-whacked back to approximately 8 inches in height, followed by an application of glufosinate herbicide (Rely, Liberty). Two and half months later, we see that few new weeds had emerged in this dead residue (photo 1). But in several rows where vine growth was too vigorous to allow for the herbicide application, we found a variety of annual and perennial weeds. Here’s a few of the species we found, and how they might be controlled next season.
Canada thistle: A common perennial weed throughout Pennsylvania, Canada thistle spreads from rhizomes. Uncontrolled, Canada thistle can form large patches in the vineyard. Glyphosate applications made in late summer or fall are the most effective chemical control. Pre-emergence herbicides will not control Canada thistle.
Foxtail: Yellow foxtail, green foxtail, and giant foxtail are all clump-forming annual grass weeds often found in vineyards. Because they germinate anew from seeds each spring, they can be controlled using pre-emergence herbicides (e.g. Chateau or Devrinol). But there are also several post-emergence grass herbicides such as Select or Fusilade that can also provide excellent control.
Hemp dogbane: Another perennial plant, hemp dogbane spreads by both rhizomes and seeds. Glyphosate herbicides will provide only fair control of hemp dogbane; glufosinate and paraquat are not very effective against this weed.
Sow-thistle: There are a number of sowthistles, both annual and perennials, members of the genus Sonchus, that are common in vineyards. Spread mostly by seeds, they form rosettes during the fall, tightly hugging the ground. Another weed species that resembles sow-thistles in form and habit is prickly lettuce. Sow-thistles are usually controlled by weed control measures used against more troublesome weeds, but they can be quite abundant in the fall.
Identifying and mapping weeds in the fall is a valuable IPM practice, and you can learn a lot from taking a weed walk through your vineyard. To help you identify the weeds you find, I highly recommend purchasing a copy of Weeds of the Northeast by Uva, Neal and deTomaso to use as a reference. This field guide to common weeds covers nearly three hundred weeds common to our area, and includes photos of each weed at different growth stages.