Wines & Vines

26 Wines&Vines March 2015 Grounded Grapegrowing V ineyard row middles are often covered with living vegetation at least part of the year, usually during the winter. Growers may plant row middles with cover crops or allow weeds and other self- seeding plants to grow, generating liv- ing material (biomass). In the past I have written about cover crops and the numerous benefits this plant material brings for vineyard soil health, chemi- cal and physical properties. Growing live vegetation in row middles can make huge differences for soil water storage, soil fertility and vine perfor- mance. In this part of the vineyard floor, it is fairly easy to control unwanted vegetation (weeds) by mowing, tilling and occasionally spraying herbicides (not needed in most cases.) The weed-free strip beneath the vines Beneath the vines, weed control is very important and often much more man- agement-intensive than the row mid- dles. You don't often see vineyards with vegetation growing directly be- neath the vines, and when you do, the vines often are not growing well. When weeds are left uncontrolled be- neath the vines, their roots are much better than grapevine roots at compet- ing for water and nutrients. Since weed root systems are more dense and grow rapidly, vines can't keep up. In fact, according to University of Cali- fornia weed scientist Kurt Humbree, if a grapegrower is lax on weed control during the first 12 weeks fol- lowing planting of a young vineyard, it will probably stunt the vines and delay full fruit pro- duction by one to three years. Such a vineyard likely would also lose vines that have to be replanted. On marginal sites with poor soils, s t a r t i n g v i n e s w i t h highly effective weed control is essential to establishing a healthy vineyard. You can learn by example from the early winegrowers in Northern California who chose upland sites with shallow soils and then never allowed any weeds in their unirrigated vineyards during the growing season. Some of these vineyards, planted more than 100 years ago, are still thriving today, and total weed control was an important strategy that made the vines survive for many years. Keeping the area beneath the vine clean has another important purpose. Damage from rodents such as gophers (root and trunk damage) and voles (trunk girdling) can occur as the weeds provide cover and protection from vari- ous predators that like to eat these little pests. Removing cover (habitat) helps to control these pests and is another important reason to keep a weed-free strip beneath the vines. Finally, weedy vegetation under the vines provides habitat for both good and bad insects. Unfortunately, the bad insect pests of vines often effectively use this area to get a head start on cre- ating harmful populations in the spring. Cutworms are well protected in weeds and can come out to attack the vines at night. Orange tortrix can survive in both weeds and dried grape clusters beneath the vines. Leafhoppers over- winter in this area, as the weeds and fallen leaves give them protection from cold weather and predators following the growing season. Keeping the area beneath the vines clean helps to mini- mize early season leafhopper pests. If you use herbicides, use them correctly The idea that you can control weeds year-round with one herbicide applica- tion probably isn't the best approach. In California, we are dealing with two sets of weeds that need to be con- trolled. n glenn t. mcgourty Creating effective Weed Control KEY POINTs While cover crops give numerous benefits to vineyards, weed control is still vital, especially in the under-vine row. young vines in particular can suffer from com- peting vegetation, and weeds can also harbor damaging rodents and insects. It's important to use herbicides correctly; one application per year is unlikely to suffice. Under-row weeds compete with grapevines for water and nutrients, and their roots are often much better at the task.

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