By: Alyssa L. Ochs
Like all plants that are grown commercially or even as backyard hobbies, grapevines are not immune to weeds and the damage they cause. Although your grapevines may not be growing at this time of the year, the weeds around them still are. In fact, the late fall season after harvest time is often considered to be the most important time for weed control. Here is some information about how vineyards can treat their soil for dormant weed control and tips for using herbicides after harvest.
The Importance of Dormant Weed Control
Weeds can take a lot out of grapevines after harvest, which is why this type of vineyard maintenance is so important to learn about right now. This is an ideal time to get a handle on your vineyard’s weeds while the vines are dormant and have no leaves.
Dormant weed control helps limit soil moisture loss and prevents more weed seeds from being deposited in the soil. Ultimately, it benefits next year’s crop yield by reducing the spread of disease and reducing competition between weeds and grapevines for both water and nutrients.
Patrick Clark, the technical marketing manager and research coordinator for BioSafe Systems, LLC, and Taylor Vadon, BioSafe’s technical sales representative, told The Grapevine Magazine how the possibility of crop injury is considerably low during dormancy due to the lack of vegetation. Headquartered in East Hartford, Connecticut but serving customers throughout North and South America, BioSafe is a family-owned manufacturer of biodegradable disease-control products. The risk of crop injury due to herbicide exposure increases when leaves and buds form during the growing season. This is why vineyard managers of conventional, mature vineyards are advised to apply herbicides during the dormancy period.
“The primary and most effective weed management options during this stage are pre-emergent herbicides used in conjunction with post-emergent systemic chemistries and burndown products,” said Clark and Vadon. “The use of systemic herbicides with a burndown product, such as AXXE, is ideal for removing the weeds from under the vines to ensure a bare soil area. By removing weeds from under the vines, a vineyard manager can maximize radiant heat from the sun to minimize possible frost injury leading up to and during budbreak. The reduction of weeds will also reduce nutrient and water competition when the vines transition from dormancy into the growing season.”
“Furthermore, having bare soil under the vines is critical in maximizing the efficacy of any pre-emergent herbicides, as it will allow for full coverage of the area,” Clark and Vadon said. “After adequate rainfall or irrigation water moving the pre-emergent herbicide into the soil, the performance of these products will extend well into the spring and summer, which will reduce the competition of weeds during the growing season.”
Types of Weeds in Vineyards
In many vineyards, you’ll find annual weeds that live less than a year and also perennial weeds that live more than two years. It is crucial that vineyard operators consider both types separately for dormant weed control strategies. Perennial weeds can include poison oak and Canada thistle. Meanwhile, some weeds should be controlled before the vineyard is established, such as bindweed and horse nettle. Weeds are also often classified as summer annuals and winter annuals. Weeds are very regionally specific, so take some time to learn about the weeds common to your area so you can devise a plan to kill them effectively.
One common mistake that vineyards make with regard to dormant weed control is not applying burndown products and other post-emergent herbicides at the right target plant height. Clark and Vadon from BioSafe recommend treating target weeds at one to three inches maximum height to ensure complete coverage when using a burndown herbicide.
“When weeds become too large or mature, obtaining adequate coverage by getting product contact throughout the target weeds becomes difficult, thus reducing efficacy,” they said.
Weather is another persistent concern for vineyards looking to get weeds under control because rainfast timing varies with different herbicides. If you apply the herbicide too early, the product can get washed off the plant’s surface, thereby minimizing the effectiveness of the herbicide’s active ingredient.
“It is important to note here that a vineyard manager or applicator should consult the product label to be sure of proper rates by plant height and best use recommendations,” said Clark and Vadon. “Understanding the products, proper timing and rates of application, tracking the weather conditions and good planning will ensure your chosen burndown product will be effective.”
Non-Chemical Weed Control Methods
Weeds can be controlled by both chemical and non-chemical methods, and the choice of method depends on the severity of the weed problem and whether you plan to make organic wine with your grapes. One chemical-free weed control method involves applying a synthetic mulch made of a plastic or geotextile; however, this material can be difficult to keep in place and expensive. You can also apply organic mulch that is several inches deep to reduce weed growth. But be mindful of the fact that organic mulch can offset the nitrogen balance, introduce new seeds from the content of the mulch or create a habitat that rodents love.
Black plastic and landscape fabrics work well for weed suppression if your vineyard can afford these materials and avoid damaging them during normal vineyard operations. Only the very tiniest vineyards can manage pulling weeds by hand, while machine weeders can assist larger vineyards if they are able to cut close enough to the roots or make multiple trips through the rows. Try planting a cover crop to out-compete weeds in your vineyard but ensure that your chosen cover crop doesn’t compete with the vines. Other organic weed control methods include soil solarization before planting and flaming with propane after planting. Animals, such as geese and sheep, can be used to control weeds without chemicals, as well as organic herbicides made with agricultural vinegar.
Weed Control with Chemical Aids
If these methods aren’t effective or based upon a vineyard owner’s preference, chemical-based herbicides are commonly used to kill seedings in their earliest stages of formation. Some options are Prowl, Surflan and Diuron, while other herbicides are not used for vineyards because they will harm the vines. Alion is an herbicide that is used in vineyards with grapes that are at least five years old and with root systems that are at least 12 inches deep.
Roundup PowerMaxx, Rely 280, Shark EW and AXXE are common systemic and burndown herbicides that control many plant species when rotated or tank-mixed. Clark and Vadon of BioSafe mentioned several pre-emergent herbicides for long residual management of tough-to-control weed species, including iChateau SW, Alion, Trellis and Matrix.
For annual weeds, it is common to use a pre-emergent herbicide to interfere with the weeds’ germination. Glyphosate is often used in pre-plant situations, with multiple applications necessary for perennials that are well-established. Meanwhile, systemic herbicides are most common for perennial weeds, such as poison ivy, poison oak and Canada thistle.
After harvest, you can apply a pre-emergent herbicide by itself or combined with another herbicide. This is usually done in both the spring and fall or done as a single winter treatment along with a post-emergent herbicide to address weeds that are currently growing in the vineyard. Coarse and sandy soil with little organic matter can use lower rates of herbicides, while silt and clay soil with high organic matter will need more of the product.
To help vineyards control weeds after harvest, BioSafe offers AXXE, a broad-spectrum herbicide used for non-selective, weed control of grasses and broadleaf weeds for herbicidal burndown applications in established vineyards during dormancy. AXXE provides fast-acting results on many weeds, mosses, lichens and sedges.
“This product is an herbicidal soap (40% ammonium nonanoate) comprised of a form of ammoniated pelargonic salts that provide rapid burndown of weeds and breaks down quickly leaving no harmful residue,” said Clark and Vadon. “These salts penetrate the cell walls of plants, disrupting the cellular functions of the targeted weeds and killing them within hours of application. AXXE is an American-made herbicide that is ideal as a tank-mix partner for systemic products to provide an innovative mode of action increasing efficacy and resistance management.”
Final Tips About Dormant Weed Control
Just after Thanksgiving is an ideal time to apply herbicide in many parts of the country before a second application of residual annual grass herbicides in the late spring for late summer control. Regardless of what herbicide you use, always spray it at the weed foliage and soil rather than the vines’ leaves, shoots, or young wood. If weeds are sparse, it may be best to use a visual weed-seeking sprayer to reduce unnecessary spread of the herbicide. It also helps to place a grow tube around the vines to spray for weeds without injuring vines. In addition to deciding on chemical and non-chemical weed control methods, vineyards also need to plan ahead for the equipment required, such as sprayer technology that can fit onto the front of a tractor, a spinning disk under a dome to shield vines from herbicide contact, or a backyard-type sprayer for small vineyards.
Clark and Vadon of BioSafe’s most important piece of advice about applying herbicide is that worker safety is always paramount. This means that vineyard managers, labor crews, and applicators must be aware of the rules and regulations of herbicide use and read product labels to understand handling and mixing procedures, personal protective equipment needed, and best use recommendations.
“Regarding weed management in established vineyards during dormancy, we would recommend rotating and/or tank-mixing products from varying modes of action when developing a weed management plan,” said Clark and Vadon. “This will reduce the likelihood of resistant weeds from developing, thus ensuring the industry will have effective products for many seasons to come.”