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What to Do Now in the Vineyard: Bud Break

Author: Annie Klodd, Extension Educator - Fruit and Vegetable Production

Photo: Bud break on a Marquette grapevine

First, a webinar alert: For a discussion of bud break tasks in the vineyard, please attend our webinar on May 19 at 1:00pm. We will start with a 20 minutes discussion of how to plan ahead for bird management (by popular demand) and then have 30 minutes of Question & Answer time on bud break tasks. A plant pathologist and weed management specialist will be there to answer questions and prepare you to start the season off on the right foot. Register for the webinar here.

 Summary of bud break tasks:

  • During bud break, you will be making your first or second fungicide application of the season. 
  • Within a couple of weeks, you will begin the process of shoot thinning, so keep a close eye on shoot growth. 
  • Insect pest concerns are few at this time, but look out for flea beetles and phylloxera. 
  • If you are using herbicides for weed control and have not yet applied a spring postemergent and preemergent tank mix, make this application before weeds become 6 inches tall. 

Fungicide application

Yield-limiting diseases including Phomopsis, black rot, powdery mildew, and downy mildew are infecting and spreading on grapevine tissue at this time, even though we can't see them. It is especially important to control Phomopsis between bud break and pre-bloom (the next month). 

The first application should occur when the new shoots are between 1-3 inches long, which means you can spray shortly after the first leaves emerge from the buds. 

Many growers apply mancozeb (i.e. Manzate, Dithane, Penncozeb, Roper, others) in combination with a fungicide active on powdery mildew. Captan can also be used in place of mancozeb, but it is not as effective on black rot. 

There are many fungicide options, differing in efficacy for each disease. Please refer to the Midwest Fruit Pest Management Guide (Section: Grape Spray Schedule) to find product lists and application information.

Make a Plan for Shoot Thinning

It is not time to shoot thin yet, but it will be soon. Shoot thin when the shoots are between 4-11 inches long; do not wait longer than that. This means that you will begin shoot thinning sometime in the next couple of weeks. 

A grapevine shoot 6 inches long. Photo: Annie Klodd
A grapevine shoot ready for thinning on May 29, 2020.

Since shoot thinning must be done in a very short span of time, make a plan now for how you will complete this task later this month. Do you need to hire temporary labor? Do you need to set some time aside after work for a week in late May? Whatever you need to do, just don't neglect shoot thinning.

Shoot thinning makes sure the vines doesn't have more shoots or fruit than it can support. Shoot thinning is especially important if you left extra buds on the vines during dormant pruning. Generally, each vine only needs 2 shoots per spur, assuming spurs are placed roughly every 3-5 inches down the cordon. So if you did a "long prune" and left 3-4 buds per spur during pruning and all of those buds survived to produce shoots, the extras should be removed. 

Not every vine needs to be shoot thinned to the same extent; if a vine already has just two shoots per spur (or less) it probably doesn't need thinning. Treat the vines equitably, not equally.

Insect Pests During Bud Break

As buds break and leaves rapidly grow, the time to worry about grape flea beetles is coming to a close. Flea beetles are not a problem in most years - they are only an occasional economic issue. When we do see them cause damage, it is during bud swell. They chew holes in the buds that impact their chances to produce healthy shoots and fruit. Once leaves emerge, their impact is negligible because the leaves can easily outgrow any minor feeding damage. Read more on grape flea beetles. 

Flea beetle feeding on a grapevine bud. Photo: David Wett
Grape flea beetle feeding on a grapevine bud. Photo: David Wett.

Grape phylloxera will begin forming galls on grapevine leaves in the next few weeks. Grape phylloxera only impacts the leaves (not the roots) of cold climate hybrid varieties. While many find leaf galls "ugly," it takes a lot of foliar phylloxera to impact the yield of the vines. Do not panic if you see phylloxera galls. 

Fresh grape phylloxera galls on May 29, 2020. They can be reddish or green.

If your vineyard has a history of phylloxera leaf galling and you wish to control it, you may apply Admire Pro to the soil for systemic control. But do it soon, between bud swell to the first expanded leaf. It works by being absorbed by the roots and transported into the leaves, which takes several weeks. If you miss this interval for applying Admire Pro, wait until the 4-10-inch shoot stage and apply Movento 2SC. Read more on grape phylloxera in Minnesota.

Weed Control

A vineyard in southern Minnesota. Photo: Annie Klodd
Vineyard rows need not be completely weed-free to support healthy and productive vines. However, strong weed control as shown here can be achieved with just 2-4 careful herbicide applications per season.

Not all grape growers use herbicides. If low-growing groundcovers or mowing under the vines is sufficient for your operation, you may not need to use herbicides regularly or at all. Grapevines can tolerate some weed competition, especially in temperate climates where water and soil nutrients are plentiful. However, many Minnesota grape growers still rely on herbicides as an effective and efficient way to keep weeds out of the rows. Herbicides (or mulch, in organic vineyards) are especially important for newly-planted vineyards, as young vines become severely stunted if they have to compete with weeds.

If using herbicides, your first application should occur in the spring once weeds are actively growing but are no taller than 6 inches. Therefore, many growers do their first application between late-dormant and bud break stages. 

Use a tank mix containing a preemergent and postemergent herbicide. Preemergent herbicides prevent new weeds from emerging, and they remain active in the soil for several weeks; for many growers, this means they can spread out the time between applications and apply less herbicide overall. Choose your herbicides based on the most common weed species in your vineyard. For instance, if most of the weeds are grasses, include at least one herbicide that has strong activity on grasses. Use the Growing Grapes in Minnesota guide or the Midwest Fruit Pest Management Guide to choose your pre- and postemergent herbicides.

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