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Crop Update - 6/21/2007
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UPCOMING EVENTS REMINDER: COFFEE POT MEETINGS - Wednesdays from 10 a.m. until 12 noon 6/27/07 Rick Walker vineyard Forestville, NY 7/11/07 Freedom Run - Larry Manning vineyard Lockport, NY 7/18/07 Militello's Forestville, NY 7/25/07 Gary Youngs vineyard North East, PA

From the Desk of...

Dr. Terry Bates

June 19th Precipitation Fends Off Vine Water Stress...   For the short term.

Official Concord bloom at the Fredonia Vineyard Lab was marked on June 9th. On June 13th, mid-day stem potentials (a measurement of vine water status) were taken because weather records indicated a 4 inch precipitation deficit from average - and my lawn was turning brown. The readings indicated mature Concord vines on gravel-loam soil were experiencing a slight amount of water stress. This mild stress is often associated with a slight reduction in shoot growth and a drop in photosynthesis by only about 10%. Certainly, this was nothing to get too worried about and the reduction in shoot growth may even improve fruit set (yet to be measured). Stem potential readings taken on June 20th (after the rain) indicated no vine water stress, as you would expect.

However, the early stress should also be raising your awareness for the potential for more severe and damaging water stress if the dry weather pattern continues. Despite the rainfall amounts (anywhere from 0.6 to 1.5 inches) from the June 19th storm, WE ARE STILL 4 INCHES BEHIND NORMAL in precipitation for this time of year with the highest plant water demand still to come.

Here are the FACTS:

1. From bloom to about 30 to 40 days after bloom, Concord leaf area and canopy fill goes from about 40% to 100% and canopy water demand increases with leaf area. Research on Concord in Washington State estimates a Concord vine with a full canopy on a sunny, warm, low-humidity afternoon used about one liter of water per hour! That's a lot of water.
2. The Concord grape berries are going through rapid cell division at this time. Early season berry cell division impacts late season berry size potential. (Wine grape growers use water stress during cell division to make smaller berries with higher skin to pulp ratios at harvest). If you want the greatest berry size potential in your Concord fruit at harvest, don't water stress them through cell division.
3. Most Concord growers do not replace soil water with irrigation; therefore, soil water conservation is the main strategy for vineyard water management. Did I mention that we are STILL 4 INCHES BEHIND NORMAL.
4. Weeds are the number one enemy to vineyard soil water conservation - especially on own rooted Concord vineyards where the grapevine roots are primarily shallow rooted.

You should currently have an aggressive weed management program in place in your vineyard. You need to conserve what soil moisture you have and fully capture any precipitation that falls for the grapevines. Yes, this is a risk management strategy. If the sky opens up and we have plenty of rain late in the season (like in 2006) then your aggressive weed control would not be needed. However, if the weather stays dry, a weedy vineyard runs the risk of low vine water status which leads to low photosynthesis, low fruit ripening, as well as incomplete periderm formation for next year.

Vineyard row-middle management research from Pool and Lakso has shown that when it comes to vineyard water conservation, treatments ranks like this:

1. Hay mulch - blankets the ground, smothers weeds, prevents evaporation.
2. Killed annual rye grass - covers like hay and extends weed free period.
3. Herbicide - eliminates weed competition.
4. Light Cultivation - eliminates weed competition. Cultivation can cut shallow roots but in a dry year it is better to get rid of the water competition than to do nothing.
5. Anything green - weeds have higher rooting density than grapevines and out compete the vines for water every time. Therefore, get rid of the weeds! Mowing doesn't count.

Figure 1: From the Weather Channel Web Site: Storm precipitation totals from the June 19th storm. Most of the Lake Erie belt received between 1 and 1.5 inches of rainfall with some localized heavier spots (less in Niagara County).

Figure 2: Warm and Still Dry! Growing degree and precipitation accumulation. The blue line is average, the black line is 2007, and the additional data shows some extreme years.

Figure 3. A root trench in a gravel-loam Concord vineyard (Betts) this spring. Notice the shallow rooting nature of own rooted Concord grapevines. This makes weed control for water conservation so important in a dry growing season.

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In the Vineyard

Andy Muza

Concord and Niagara berries are sizing up quickly across the Lake Erie Belt and the rainfall received on Tuesday should help vines continue growing rapidly. Insect and disease levels remain low in vineyards examined but the season is early. Looking at scouting records from last season (same week and same vineyards) pest levels are similar.

I received a call a few days ago (before the rain) asking if a first postbloom spray should be applied at this time due to the hot, dry conditions. The answer was easy - YES. Even though the incidence of disease is low and environmental conditions have not been favorable for diseases, Concords and Niagaras are still in a critical stage as far as susceptibility to infections. If we get into a pattern of frequent thunderstorms then the disease situation could change dramatically in unprotected vineyards. If a first postbloom spray has not been applied yet (i.e., within 10 - 14 days of immediate prebloom spray) then make an application as soon as possible. Repeating what I said in last week's Crop Update, choose fungicides that are effective against all of the major diseases (phomopsis, black rot, powdery, and downy) and don't skimp on rates or coverage (spray every row).

Insects and Diseases observed in vineyards this week include:

Grape berry moth - webbing has increased slightly in clusters at high risk sites. High risk sites should receive an insecticide at the first postbloom application. Continue to scout low and moderate risk blocks for signs of GBM webbing.

Grape leafhopper - early instar nymphs (i.e., wingless, immature leafhoppers) are now present in vineyards. However, only small numbers were seen and stippling on leaves is still low in vineyards examined.

Rose Chafer - only a few rose chafers observed. Berries have sized enough in Concord and Niagara vineyards that no more feeding will occur in clusters and leaf feeding will be minimal.

Powdery mildew - again this week, observed only a few small patches of powdery mildew on Concord leaves and none on clusters.

Black rot - more leaf lesions were observed this week compared with last week in a vineyard which has only received copper and lime applications for disease management. This serves as a reminder that even though weather has been dry, black rot infection periods have occurred and disease symptoms are present in some vineyards. Vineyard blocks with a history of black rot problems should be scouted for disease symptoms.

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