Poison Ivy in Hay Field
Hello, We own a 40 acre parcel of land in Leelanau County just west of Northport. Currently (7) acres is planted in Riesling, Chardonnay, Pinot Gris and Marquette. We are experiencing a significant amount of poison ivy growth in the vineyard. We have been spot treating the poison ivy with 2,4-D before bud break and now (after bud break) we are spot treating using a hand spray with a shield around the nozzle head with round up. Is there another chemical that would be more effective. We also have (15) acres of field that we had contracted with someone to come in and cut to use as hay for cows. When they came this week, they decided not to take the hay because there was significant amount of poison ivy in the fields as well. We need to get rid of the poison ivy. What is the most effective way to do this? We also need to be careful of spraying anything that will drift onto our vines. Thank-you, Theresa Holmstrom 517-614-4466
Leelanau County Michigan weed issues
This is a difficult situation. Unfortunately, grapes are very sensitive to the growth regulator herbicides (aka synthetic auxin; Group 4) that are most effective on poison ivy. You are already using one such product 2,4-d when the grapes are dormant, but probably the most recommended product for poison ivy control is triclopyr (e.g. Garlon and Bayer Advanced Brush Killer Plus). These compounds are volatile, can be prone to drift depending on the formulation, and therefore are not recommended for use anywhere around grapes. Within the grapes, continued shielded spot treatment with glyphosate is probably your best option. It may take several applications, but it should be effective over time and will not cause issues due to volatilization.
You may be able to use triclopyr in the hay field early in the season before the grapes have started to grow. Crossbow is an example of a product that contains both 2,4-d and triclopyr that may be effective, but you’ll note that the label specifically warns against drift and volatility being concerns near grapes. If the infestation is bad enough that they will not harvest it may be time to replant all or some of the hay after first spraying with glyphosate and later tilling to be rid of the ivy. Currently, if the ivy present is killed in the hay, the dried material present will still have the irritant substance (urishol), which does not degrade rapidly. As with any herbicide application you should read and follow all labeled instructions and you will want to pay special attention to any restrictions on hay harvest or grazing.