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Current Situation Regarding Chemical Sucker Control and Vineyard Weed Management

by Rick Dunst, Research Support Specialist, Fredonia Vineyard Lab

Mid-May marks an opportunity to consider chemical suckering options in your vineyard, and a chance to adjust your vineyard weed management program while there is still some time to consider a few effective options. You may even be able to address both concerns simultaneously. I'll review both topics here briefly so you can get back to work.

CHEMICAL SUCKERING

Chemical suckering of hardy varieties not needing sucker retention for trunk replacement is an attractive option from the standpoints of economics and effectiveness. Gramoxone® (paraquat) and Rely® (glufosinate) have been registered for this purpose for several years in vineyards. In 2005, Aim® (carfentrazone-ethyl) was also registered for this purpose. Aim® is used in many other crops to control some annual broadleaf weed seedlings. In our trials and experience, it provides very effective control of grapevine suckers at a material cost of about $3 per acre at the 2 oz. rate, plus surfactant or crop oil concentrate, applied on the herbicide strip under the vines. With labor issues coming to the forefront I don't need to explain the attractiveness of this approach.

I already mentioned that Aim® controls certain small seedling weeds (at the 2 to 3-leaf stage). It doesn't control some other annual broadleaf weeds, larger annual broadleaf weeds, annual or perennial grasses, or perennial broadleaf weeds. Think of Aim® as a sucker control agent, period. I'll review how to use it in combination with other herbicides for weed control a little later in this article.

Aim EW® is used at a rate "up to" 2 oz. per sprayed acre. I have not evaluated Aim® at less than the maximum use rate. In our experience and trials, Aim® provides more effective control of grapevine suckers than Gramoxone®. A combination of Aim® and Gramoxone® was somewhat more effective than Aim® alone in one trial a few years ago on the variety Dechaunac. When using Aim®, add non-ionic surfactant at 2 pints per 100 gallons or crop oil concentrate at one gallon per 100 gallons. Time the application when sucker growth is about 6" long, sometime between now (May 17) and next week. Depending on the vineyard, sucker regrowth may justify a second application in about 30 days.

Aim® can be used in a tank mix with other pre- or post-emergence herbicides. If you haven't already applied pre-emergence herbicide but plan to, you can tank mix Aim® with a registered pre-emergence material. Chateau® plus Aim® can be an effective combination for weed and sucker control (keep reading for more information on that). If weeds have emerged, choose an effective post-emergence herbicide for weed control (i.e., glyphosate, Gramoxone®, or Rely) and add Aim® for sucker control. If you want to obtain pre- and post-emergence weed control and sucker control with a single application, tank-mix a combination of pre-emergence herbicide, post-emergence herbicide, and Aim®.

WEED MANAGEMENT DURING THE GROWING SEASON

Conventional vineyard weed management usually includes an application of pre-emergence herbicide while vines are dormant. Grower experience indicates later applications can still be effective, especially if post-emergence herbicides are added to control suckers or established weeds.

For the past two growing seasons, we (Mike Vercant, Dennis Rak, and myself) have been investigating giant foxtail control in a vineyard that Dennis purchased a few years ago. Foxtail pressure in this vineyard is intense, with almost solid ground cover of giant foxtail growing into or above the grapevine canopy by the end of the season. For the past two years, no "conventional" herbicide application (herbicide applied at bud break) has provided effective season-long control of giant foxtail. Herbicides evaluated in these studies included Chateau®, diuron (trade name Karmex®), simazine (trade name Princep®), Solicam®, oryzalin (trade name Surflan®), two other non-registered herbicides (pendimethalin and rimsulfuron), and various tank-mix combinations of the listed herbicides. We did achieve effective giant foxtail control in this vineyard with a split application of Chateau®, and based on previous research, another effective approach should be two applications of post-emergence herbicide only. Application timing for the two effective approaches is different and will be explained in detail to follow. Meanwhile, we are continuing to search for other effective alternatives at the Rak vineyard in 2007.

EFFECTIVE WEED MANAGEMENT USING CHATEAU® HERBICIDE

Chateau® is a relatively new herbicide registered for use in grape. Our program evaluated Chateau® during the registration process, so we have a fair amount of experience regarding its effective use in vineyards.

In some cases, a single application of Chateau® applied at the maximum use rate (12 oz. per sprayed acre), has provided effective season-long weed control. Typically, that approach has worked in vineyards with well-drained soil and moderate weed pressure, such as the conditions at both the Fredonia and North East, PA grape labs. In 2006, we achieved effective weed and sucker control at the Fredonia Lab with a tank mix of 12 oz. Chateau®, 2 oz. Aim, and non-ionic surfactant applied in mid-May. However, in several other cases, a single application of 12 oz. Chateau® applied in early May did not result in effective season-long weed control. Those vineyard sites have typically had heavier soil and greater weed pressure from summer annuals such as foxtail and pigweed. What did work effectively in those situations was a split application of 6 oz. Chateau®, each tank-mixed with a post-emergence herbicide. The first application should be made in early May and the second in mid-June. We have included this treatment in our herbicide evaluations for the past four years and it has provided effective season-long weed control in all cases. Chateau® has some post-emergence activity on weeds and grapevine suckers, but needs to be tank-mixed with an effective post-emergence herbicide to obtain effective control of established weeds and suckers. If weed and sucker control is desired, make the first application when suckers are about 6" tall (mid-May or so). The second application should be made at least 30 days after the first application, but not within 60 days of harvest (as per label restrictions). Post-bloom applications must be made to avoid contact of spray or mist with developing fruit, as obvious injury will result.

EFFECTIVE WEED MANAGEMENT USING POST-EMERGENCE HERBICIDES ONLY

Effective weed management using post-emergence herbicides only is entirely possible, but timing is more critical than programs that use pre-emergence herbicides. Tim Weigle and I have conducted experiments in several commercial vineyards and post-emergence only programs were effective in every case. At least two annual applications of broad-spectrum herbicide such as Gramoxone®, Rely®, or glyphosate (if contact with green grape tissue can be avoided) are usually necessary. In our trials, the first application was made in early June before weed height exceeded 6" height, and before weeds begin competing with grapevines for water (especially) and nutrients. The second application was made in mid- to late July. We found the July timing was necessary under local conditions to prevent subsequent germination, growth, and weed production by summer annual weeds. Unfortunately, those timings don't coincide well with the optimal timing for grapevine sucker control, so effective post-emergence only control of suckers and weeds may require three application timings per season.

For additional information on weed and sucker control in vineyards, consult the 2007 New York and Pennsylvania Pest Management Guidelines for Grapes.

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