Vineyard Weed Control
Joy Hollingsworth, UCCE Table Grape Advisor for Tulare and Kings Counties
Jorge Angeles, UCCE Weed Management and Ecology Advisor for Tulare, Kings, and Fresno Counties
How important is vegetation management in vineyard systems? Most mature vines can withstand some competition, but even the most robust vineyards can suffer from the effects of uncontrolled weed growth. Weeds compete for water, nutrients, and sunlight; newly planted vineyards are especially susceptible to competition. In the first three years, weed competition can reduce vine growth by 50% (Bettiga 2013). Weeds can also reduce the effectiveness of irrigation by disrupting the distribution and uniformity of water application. Another reason to keep weeds under control is because they can attract and harbor insect pests. For example, leaf hoppers cannot survive on dormant vines but can overwinter on weedy plants. If the weeds hosting the pest are not controlled before budbreak, it will be easy for the pest to move over to the new tissue, causing damage in the early part of the growing season. Controlling weeds helps remove habitat for rodent pests as well. Weeds can also be a nuisance that gets in the way of vineyard operations. Tall weeds such as horseweed and lamb’s quarters and vining weeds such as morning glory and field bindweed are especially problematic in this way, as are weeds species with sharp or sticky seeds. Further, weeds can affect the microclimate of a vineyard, such as increasing frost risk in the spring or increasing the humidity of a vineyard which creates ideal conditions for many fungal diseases.
Although weeds can cause many issues in a vineyard, the good news is that there are a wide variety of effective control options available. Multiple factors should be considered before choosing the methods that will work best for your operation. Before beginning any weed control, identify which weeds are present in your vineyard as different weed species require different control methods. This is true whether you are using chemical or mechanical control. For example, there is a saying that “nothing is resistant to steel,” which implies that even herbicide-resistant weeds can be controlled by tillage. While that is true for many species, some plants like bermudagrass propagate through underground rhizomes, and discing them will expand their population. Some common vineyard weeds are listed in Table 1, and there are resources to help you identify them at the end of this article.
Weed Control Options
Mechanical control options include tilling, mowing, and hand hoeing. Mowing may kill some small plants, but many plant species will eventually regrow. A benefit of mowing is that it does not disturb the soil, allowing for better water infiltration and reduced wind and water erosion. Discing effectively kills many weeds by breaking down the plants and incorporating them into the soil. However, discing can create compaction problems, and because it breaks down soil structure, it decreases organic matter, reduces water penetration, and increases soil erosion. In vineyards, only the row middles are disced. A French Plow can be used to cultivate soil in vine rows. As mentioned earlier, tilling will kill most weeds; however, be cautious tilling vineyards with rhizomatous weeds. Tilling weeds when the soil is moist will likely result in the pieces sprouting roots and their population increasing in the vineyard. Nutsedge and field bindweed populations can be reduced through plowing, but only if they are buried deep enough (12 inches or 16-18 inches, respectively). Shallower cultivation in dry soil can kill nutsedge by drying out the tubers, but they can resprout in moist soil. Shallow cultivation won’t kill field bindweed because it has very deep roots, and the root fragments can regrow even in dry soil conditions. However, you could prevent them from setting seed if tilled early enough.
For chemical control, herbicides can be divided into pre-emergents or post emergents. Pre-emergence herbicides only prevent weed seeds from germinating, and post-emergence herbicides only control actively growing weeds. To be effective, most pre-emergent herbicides need to be applied to a clean field (berm) and incorporated within two to three weeks after application. Pre-emergence herbicides are typically applied from late fall to early spring since they require rainfall for incorporation.
Post-emergent herbicides are typically used in combination with pre-emergent herbicides and used during the growing season. Post-emergent herbicides are foliar applied and are either contact or systemic. Contact herbicides work relatively quickly but will only kill what they touch, so coverage is important. Systemic herbicides move within the plant and work best when the plant is actively growing. Since the herbicide must move through the plant to kill it, a systemic herbicide will take longer to achieve control than a contact. Systemic herbicides can be used to control perennials and other weeds that can resprout from established root systems. Foliar herbicides often require adjuvants such as crop oil concentrates, methylated seed oils, or non-ionic surfactants to enhance their efficacy and performance. Depending on which weed species are present in your vineyard, you could apply grass, broadleaf, or broad-spectrum herbicides, which can kill both types. Carefully read the herbicide label to verify its effectiveness against specific weed species, particularly because certain weeds have developed resistance to herbicides. Calibrating spray equipment is needed to ensure safe application of herbicides and minimize drift.
Organic Weed Control
Most currently registered organic herbicides are post-emergent and contact-based. They tend to require higher volumes and cost more money than their conventional counterparts. Although they are not selective, they do tend to be more effective on broadleaf weeds than grasses and work best on small plants.
Other forms of organic weed control include tilling, mowing, hand labor, mulching, and cover crops. Hand labor is expensive and time-consuming but may be the most effective option in organic vineyards. It is also the most effective at controlling weed escapes. Mulch can be used to block light and prevent seed germination. It also increases organic matter and helps retain moisture. However, it can provide cover for rodents. Mulch can come in organic forms, such as wood chips or even mowed weeds or cover crops, but that material will decompose and must be replaced yearly. Synthetic mulches can also be used, which will hold up for longer periods. Similar to organic mulches, cover crops can be planted to compete with weeds. Other benefits of cover crops include reduced erosion and improved soil health. However, they should be mowed before budbreak to reduce frost risk and avoid competing with the vines for resources during the growing season.
Additional Concerns
As mentioned earlier, controlling weeds is most critical in young vineyards because their small size makes them less competitive for light, and a young vine's limited root system also makes them less competitive for water and nutrients. However, exercise caution when applying herbicides because contact with green wood or foliage can seriously injure the young plants. Even mature vines can suffer from crop injury when an herbicide spray is poorly timed. For example, some products like oxyfluorfen should not be applied after February 15th, and some are risky after budbreak, especially in table grapes where berry appearance is so important. Hooded sprayers can be used during the growing season to minimize herbicide drift. Also, be careful to avoid application when pruning or girdling has recently been done, as the chemicals can enter the open wounds.
Timing is critical no matter what type of weed control method is used. The older and larger a weed is, the harder it will be to kill. You’ll have much greater success if you can attack the weeds when they are young. For herbicides, larger plants mean a larger surface area that must be covered, and more of the plant to dilute the herbicide in. For mechanical control, larger plants take more effort, as more of the plant is below the soil surface, allowing it to regrow after being injured. It is also important to kill the weed before it sets seed, otherwise they will add to the existing weed seed bank.
Another important consideration is herbicide resistance. The number of weeds resistant to particular herbicides is ever-increasing, as are the weeds that have developed multiple resistances. It is very important to check the label before applying any herbicide and rotate your products to use multiple modes of action throughout the growing season.
Finally, properly calibrating your sprayer is incredibly important. Make sure your nozzles are the correct size and shape for your applications and do regular maintenance to replace worn-out or plugged nozzles. This can make a huge difference in the effectiveness of your herbicide application program.
New Trials
UCCE Weeds Advisor Jorge Angeles and I have recently begun working on several new herbicide trials at the Kearney REC in Parlier and at the West Side REC in Five Points. These trials are in young vineyards and examine both conventional and organic herbicide options. The results were promising, and we plan to continue these trials in 2025. Stay tuned for more information.
Image 1. An established table grape vineyard with palmer amaranth and morning glory weeds.
Image 2. A newly planted table grape vineyard and site of an herbicide trial.
Table 1. Some common weeds found in San Joaquin Valley Vineyards
References and Resources
Bettiga, L. J. (Ed.). (2013). Grape pest management (Vol. 3343). UCANR Publications.
Grape Pest Management https://anrcatalog.ucanr.edu/Details.aspx?itemNo=3343
Raisin Production Manual https://anrcatalog.ucanr.edu/Details.aspx?itemNo=3393
Weeds of California and Other Western States https://anrcatalog.ucanr.edu/Details.aspx?itemNo=3488
UC IPM Weed Photo Gallery https://ipm.ucanr.edu/PMG/weeds_intro.html
Grape pest management guidelines: Integrated Weed Management https://ipm.ucanr.edu/agriculture/grape/integrated-weed-management/#gsc.tab=0