Considerations for Fall Weed Control in Vineyards

Author: Thierry Besancon
Plant & Pest Advisory
November 15, 2019

Fall or early winter is the best time to consider the application of a residual herbicide that will help maintaining the ground clean in early spring and allow for delayed herbicide applications in spring. Most residual herbicides primarily control annual grasses or annual broadleaf weeds.  A combination of an annual grass herbicide and an annual broadleaf weed herbicide is usually recommended.  Rate ranges are recommended for most residual herbicides.  Use the lower rates in vineyards with coarse textured (sandy) soil low in organic matter, and the higher rate when soils are fine textured (silt and clay) and have higher organic matter.

Post-harvest application of a residual herbicide should be done in late fall after vines are dormant, but before the soil freezes, or in late winter before the weeds begin to grow in early spring.  This application targets the control of winter annuals and provides early season control of summer annual weeds.  Most growers are more easily able to apply herbicides to the vineyard in late fall, usually after Thanksgiving in New Jersey.  In March, growers find themselves scrambling to apply insecticides and fungicides, and prune.

Pruned wood must be removed or chopped before weed spraying can be accomplished. Weed residues from last season should also be removed as much as possible before considering application of a residual herbicide in fall. Too many leftover residues will prevent the residual herbicide to penetrate into the soil (the “activation” process), and the herbicide will lose efficacy at controlling the emergence of weed seedlings. If you plan hilling-up the vine, be aware that the de-hilling operations will break the residual herbicide coverage. Thus, hilling may not compatible with the use of residual herbicide in fall.

• Casoron (dichlobenil), applied in late fall, followed by a spring application of a residual annual grass herbicide is a very effective residual weed control program.  More different species of weeds are controlled than any other residual herbicide combination available.  Apply 4.0 lb active ingredient Casoron CS (2.7 gallons per acre) or 4.0 to 6.0 lb active ingredient Casoron 4G (100 to 150 lb per acre) in late fall when soil and air temperatures will remain below 50 degrees Fahrenheit until rainfall moves the herbicide into the soil.  The active ingredient in the granular formulation can be lost to volatilization in warm weather.  The Casoron CS formulation is encapsulated, which prevents loss due to volatilization.  Casoron provides annual broadleaf weed control through harvest and annual grass control until early summer the next year.  Certain herbaceous perennials, including goldenrod species, aster species, and yellow nutsedge will also be controlled or suppressed by Casoron applied in late fall.  Late winter applications provide less consistent winter annual and perennial weed control.  Apply an additional residual annual grass herbicide in the spring to provide late summer annual grass control following the late fall application of Casoron.
• For many years Princep (simazine) was recommended at 1.0 to 2.0 lb active ingredient per acre in the late fall/ winter, and Karmex (diuron) was recommended at 1.0 to 2.0 lb active ingredient per acre in the late spring.  Both herbicides have been safe and reliable, and cost effective choices for many years, and continue to be good options where their use provides good weed control.  Both Princep (simazine) and Karmex (diuron) share the same mode of action, inhibition of the light reaction in photosynthesis.  Unfortunately, triazine resistant weeds, with cross resistance to urea herbicides, including Karmex, are present at some sites. Where a triazine resistant weed has become established, switch to herbicide(s) a different herbicide mode of action.  Use Chateau or Tuscany (flumioxazin) at 0.19 to 0.38 lb of active ingredient per acre or Goal 2XL (oxyfluorfen) at 1.0 to 2.0 lb of active ingredient per acre in late fall or late winter. The activity of both Chateau and Goal occurs at the soil surface as sensitive BLW seedlings emerge.  Do not disk, till or otherwise mechanically mix Chateau or Goal into the soil after application, or the effectiveness of the herbicides will be reduced or eliminated.
• Alion (indaziflam) is a relatively new (2012) herbicide labeled for use in stone and pome fruit orchards, and in vineyards.  Alion is very effective at controlling a broad range of annual grasses and broadleaf weeds. Alion does not provide control of sedges or established perennial weeds. Alion is ideally applied in late fall at 0.045 to 0.065lb of active ingredient per acre in late fall. The most compelling characteristic of Alion is its VERY long weed control period (up to 6 months). However, the use restrictions for Alion are stricter in vineyards than in orchards:

1. Alion can only be applied in vigorous grapes that have been established for a minimum of three years after transplanting.
2. Alion can only be used in grapes that have at least 6 inches of soil barrier between the soil surface and the major portion of the root system.
3. Alion cannot be used on soils with 20% or more gravel content or on sand or loamy-sand soil.
4. Do not apply Alion prior to any type of soil disturbance, including hilling/dehilling operations, and only apply the herbicide after the soil settles.
5. Do not allow spray or spray drift to contact crop foliage, green bark, roots or fruit of the crop being treated as it may cause localized crop injury or death
6. Maximum use rate per application now has a restriction based on soil organic matter (OM) content: if soil contains less than 1% OM, maximum rate is 3.5 oz/A (0.045 lb ai) and if over 1% maximum rate is 5 oz/A (0.065 lb ai). In any case, maximum use rate cannot exceed 5 oz/A (0.065 lb ai) per year or in a 12 month period.
7. No irrigation can be applied within 48 hours following Allion application. This is designed to ensure crop safety by giving the herbicide enough time to bind to surface soils before rainfall or irrigation to ensure proper activation of Alion by allowing weed seeds or seedlings to come into contact with the herbicide.

The Alion label also lists some guidelines that will ensure efficient weed control:

• Soil should be free of debris, clumps or cracks at application time to ensure best weed control performance and prevent the herbicide from reaching the grape roots (this is true for best performance of ANY of our PRE herbicides).
• For best weed control, dry soil surface for 48 hours followed by rainfall or sprinkler irrigation within 3 weeks is ideal. If irrigation is used to activate, 0.5 inch of water is ideal (the idea is to incorporate the herbicide into the surface an inch or so, where the weeds germinate, but not go too deeply.  This is also true for all PRE herbicides.

Consult the New Jersey Commercial Grape Pest Control Recommendations for rates and additional information https://njaes.rutgers.edu/pubs/publication.php?pid=E283.

As with all herbicides, always  read and follow all label instructions and precautions.