Vineyard Weed Management
Chemical Weed Control
Chemical weed control in vineyards uses pre-emergence (like oryzalin, simazine) for seed germination and post-emergence (like glyphosate, glufosinate) herbicides for existing weeds, often combined for effectiveness and resistance management, requiring shielded sprayers and careful application to avoid crop damage, especially with systemic herbicides like glyphosate, which needs careful handling around young vines. For organic weed control in vineyards, use OMRI-listed contact herbicides such as those containing ammonium nonanoate, caprylic/capric acids, or d-limonene for spot treatments.
Herbicides
When used correctly, herbicides registered for vineyard use can effectively control most weed species. In many vineyards, combinations and/or sequential applications of herbicides are necessary to achieve effective and economical control. Before using any herbicide, identify the weed species to be controlled, then read and follow product label directions carefully. More commonly, growers apply herbicides as vine-strip (under-vine) treatments rather than in alleys (inter-row). It is not necessary to maintain a completely clean strip under the trellis throughout the entire summer.
Preemergence Herbicides
Preemergence herbicides for vineyards control weeds by preventing germination, and popular options include products containing oryzalin, oxyfluorfen, simazine, and pendimethalin. For best results, apply to a clean soil surface and activate with rain or irrigation within a few weeks, using tank-mixes or rotating products with different modes of action to manage resistance.
Postemergence Herbicides
Several selective postemergence herbicides are registered for use in vineyards. They usually work best when applied to seedlings that are less than 4 inches tall. Time the application so that the maximum number of seedlings have emerged, but the largest seedlings are not too large to control. Glyphosate (Roundup) controls many weeds, but it must be applied at the correct stage of weed growth to achieve maximum movement into the roots.
Soil-Active Herbicides
Several herbicides with soil residual activity (i.e., soil-active herbicides) are labeled for use on vines. These herbicides prevent annual weeds and sometimes perennial weeds from emerging or establishing, but they do not typically kill weeds that have already emerged. Combining an herbicide with soil residual activity with glyphosate or another postemergence herbicide can significantly extend the period of weed control and reduce or eliminate the need for multiple glyphosate applications.
Herbicide Treatment Options
Treatment Options in Young Vineyards
Weed management is critical around young vines where weeds compete for nutrients, water, and light. Weedy vineyards may take 1 to 2 years longer than those that are weed-free to become economically productive. (From an economic standpoint, however, it is important to compare the costs of weed management with the benefits of earlier production.)
Treatment Options in Established Vineyards
It takes 3 to 4 years for a vineyard to become established under normal growing conditions. Established vines are more tolerant of many herbicides than newly planted vines, thus increasing the options available for weed control. There are three programs growers can consider. They include a spring preemergence application, which is a traditional approach; the delayed pre-emergence option; and the fall/ spring split option (Mitchem et al. 2005).
Spring Pre-emergence Option. Traditionally, a vineyard herbicide program has consisted . . .
Delayed Spring Pre-emergence Option. The delayed pre-emergence herbicide program requires a spring glyphosate application. The spring application should be made prior to bud break.
Fall/Spring Split Option. The fall/spring split is the third option that growers should consider. This program begins with a fall pre-emergence application in combination with non-selective burn down herbicide like Gramoxone Max or Rely applied after harvest.
Spring/Summer Split Option. In addition, the grower has the option with a spring/ summer split. This option consists of an early spring application of glyphosate with Chateau. Another application of glyphosate with Chateau should be applied mid-summer when control from the initial application begins to fail and emerging weeds are 2 to 4 inches tall.
Application Rate of Herbicides
The appropriate rate of herbicide to apply in the vineyard depends on several factors. Pre-emergence herbicides are soil active, and the effective concentration to use depends upon soil type. Generally, more preemergence herbicide is needed to control weeds on finer texture soils (clays and silts) than on coarser soils (sands and gravels). For some herbicides, the rate should be increased when the soil has a high organic matter content. The proper rate of both pre- and post-emergence herbicides to be used is also influenced by the species of weeds to be controlled.
Timing of Herbicide Applications
The correct timing of herbicide application in the vineyard depends on several factors. Some herbicides are more soluble than others, and move more quickly through the soil. More soluble herbicides should be applied just prior to weed emergence in the spring; fall application might result in movement in the soil below the weed seed germination zone.
Equipment Used in Applying Herbicides
To reduce the hazard of injury to vines as well as to ensure the maximum effectiveness of the herbicides applied, select your equipment and its use carefully
Other Herbicide Considerations
Symptoms of herbicide activity may not be noticeable for up to 14 days after application when using glyphosate, sethoxydim, clethodim, or fluazifop (Roundup, Poast, Select, Fusilade, respectively). Effects of glufosinate, and paraquat (Rely and Gramoxone, respectively) are noticeable within 1 to 3 days. Some post-emergence herbicides require the addition of a surfactant or crop oil concentrate to improve herbicide activity.
Herbicide Resistance
Herbicide resistance is the inherited ability of a weed to survive an herbicide application that would usually control that species. This problem is especially prevalent in vineyards due to the repeated use of the same herbicides (e.g., glyphosate), which selects for resistant weeds, such as Italian ryegrass or glyphosate-resistant horseweed. To manage herbicide resistance, use a diverse range of weed-control methods, rotate herbicides with different modes of action, apply herbicides at the correct growth stage, and employ cultural practices such as mulching and cultivation.
Herbicide Spray Drift
Herbicides recommended for use in the vineyard are usually very safe if the user follows the product label directions. When a slight injury does occur, yield and fruit quality are rarely jeopardized. Drift can occur in two ways: particle drift or vapor drift. When small spray droplets move long distances due to wind, it is referred to as particle drift. To minimize particle drift, it is recommended to use air induction nozzles and/or low-pressure nozzles, in addition to spraying during low wind conditions. Vapor drift is when a pesticide volatilizes or evaporates into the atmosphere and moves off-site, damaging non-target plants.
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