This newsletter is being sent to Michigan Grape Society members who have paid their annual dues for 2002. If you have received this newsletter, you are a paid member for 2002. If you know someone who did not receive the newsletter and they wonder why they did not receive their copy, it is because they did not pay their 2002 annual membership.

We reduced our mailing list from 763 to 146 members. Since there are 400 grape growers in Michigan we had hoped to cut our mailing list in half. We hope that serious grape growers will subscribe and help the Michigan Grape Society build the Michigan grape industry.

In the past few years, MSU’s grape pest management program has blossomed (or should that be bloomed?). This is partly due to the hiring of new Extension specialists with small fruit focus. However, there has been a limited amount of space for testing unregistered insecticides and fungicides in vineyards that also have high populations of insects and diseases. The Trevor Nichols Research Complex (TNRC) in Fennville provides these unique conditions and is expanding it’s vineyard acreage to keep up with demand for research vineyards. This article is to update Michigan growers on the recent changes in our grape acreage, and the projects that are underway.

During 1999, a 3 acre Niagara vineyard was planted and it will bear its first crop this summer. This has been established to a top-wire cordon system, and the grapes are growing well in this sheltered site. Our Concord vineyard has served the needs of the grape industry for over 20 years, but it was on an old head training system that is now rare in Michigan. To better represent the juice grape vineyards found in Southwest Michigan, we have initiated a change to the top-wire cordon training system. During 2001, work in this vineyard by farm management included installation of new posts, installing a higher top wire on each row, and training suckers up to the top wire for establishment of the new system. Because we cannot do our testing without fruit and foliage, we will leave the old system in place while we establish the new trunks. In a few years, the old Concord vines will be rejuvenated and the training system and vineyard conditions will better represent Michigan vineyards when we test insecticides and fungicides.

We are currently conducting a research project on the nitrogen nutrition of Concord and Niagara grapevines in southwest Michigan. As a part of this project we tested grower vineyards to learn how useful measurements of total nitrogen and nitrate nitrogen at bloom and veraison are for measuring vine nitrogen status. In Michigan and other viticultural areas in the eastern U.S. total nitrogen content of leaf petioles at veraison is the typical measurement taken to monitor vine nitrogen status. However, in the California industry, nitrate nitrogen measurements taken at around bloom time are used for measuring vine nitrogen status. Our current research is investigating the value of both of these types of nitrogen measurement. Over the past two years we have collected approximately 200 petiole samples from several commercial farms in southwest Michigan and we thank the cooperation of Bob Blum, Cronenwett Farms, Mark Epple, Phil Falak, Grandview Orchards, Herman Farms, Kerlikowske Farms, Mike Nitz Farms, Rambo Farms, Dan Stockton, Twin Oaks Farms and Totzke Farms that have made this work possible. Our work on nitrogen will be presented separately at the conclusion of our research next year. We will briefly summarize our findings from these petiole tests other than nitrogen as they were presented in more detail at the Southwest Michigan Horticultural Days this past February.

We'll first begin with the macro-nutrients, i.e., those that are present in relatively large amounts from about 0.5 to 4% by dry weight.

Potassium (potash) is very important to vine function. Deficiency of potash can cause scorching of leaves (Fig. 1), reduced vine growth and fruit set (Fig. 2) and shattering of berries at the time of harvest. Most southwest Michigan vineyards tested had adequate to excessive amounts of potassium with only 2% of the samples in 2000 and 26% in 2001 having less than optimum (1.5 to 2.5%) amounts of potassium. The viticultural literature indicates that vine performance is not actually affected until the potassium petiole concentration is less than 0.6%, thus making an even lower percent of vineyards at risk of potassium deficiency. In fact, none of the samples taken over the 2-year period had less than 1% potassium suggesting that no vineyards were at severe risk of potassium deficiency. Perhaps the more important information was that 49% of the samples in 2000 and 38% of the samples in 2001 had greater than optimum concentrations of potassium. This suggests that many of the vineyards sampled may be experiencing excessive rates of potash fertilization. Higher than optimum levels of potassium in grapevines are not considered advantageous to vine performance. Such high levels are considered "luxury consumption" by grapevines. High levels of potassium in grape juice processed into wine may actually be detrimental to wine quality. In addition, high levels of potassium can actually induce magnesium deficiencies in the soils and vines if the levels become high enough. Therefore, these data suggest that timely petiole testing of southwest Michigan vineyards may identify as many as 40-50% of the vineyards with more than adequate levels of potassium. In those situations potash fertilization need not be performed for one or several years. Such testing may also identify those vineyards that truly have low levels of potassium so that potassium fertilization can be more efficiently directed to those vineyard blocks that are in need.

Approximately 11% of the samples in 2000 and 17% of the samples in 2001 had less than optimum (0.25-0.4%) levels of magnesium. Whereas magnesium deficiency that results in extensive degradation of vine leaf area can be a serious problem, most levels of magnesium deficiency found in southwest Michigan vineyards result in only modest leaf degradation. A grower needs to be aware of the symptoms of magnesium deficiency (Fig. 3), but if only small percentages of leaves are affected in a particular vineyard block, there need not be concern or corrective measures undertaken. When leaf petiole test concentrations drop below 0.15% then there is a significant risk of reduced performance of Concord vines. However, none of the samples in the 2-year period were less than 0.15% magnesium.   None of the petiole testing indicated any problems with the macro-nutrients calcium or phosphorus.

When looking at the micronutrients, i.e., those present in parts per million on a dry weight basis, it was surprising that only 2% of the samples in 2000 and 4% in 2001 had Boron levels below the optimum (25 to 50 parts per million). It was also surprising that 36% of the samples in 2000 and 45% of those in 2001 had less than 10 ppm copper. Deficiencies leading to poor vine performance can occur when copper is present at 4 ppm or less. The lowest levels of copper concentration from all the tests were about 7 parts per million, which is considered borderline. Therefore, we will be inspecting those vineyards this growing season to see if any real problems of copper deficiency exist in southwest Michigan vineyards. Although a whopping 57% of the samples taken in 2001 had less than the optimum (20 to 100 parts per million) levels of iron, general vineyard observations suggest that there are no real problems with iron in southwest Michigan vineyards. Iron deficiency expresses itself as creamy-white chlorosis of the leaves at the terminal portions of a shoot (Fig. 4). These symptoms simply are not widespread in southwest Michigan vineyards. On occasion excess liming can induce iron deficiency when the pH levels of the soil become greater than 7.0.

Systemic fungicides are absorbed into the plant and kill the fungus early in the infection process before symptoms appear. Systemic fungicides kill fungi by blocking specific biological pathways in the fungus. Since a minor change in the pathway is all that is needed to get past this “roadblock”, development of resistance in target pathogens can be a problem. Systemic fungicides need to be applied before the infection process is too advanced and the fungus is big enough to shake off the dose and continue growing. (Think of this as stepping into to boxing ring with Mike Tyson. We could’ve all beat Mike when he was 6 years old, but no one wants to fight him now.) With systemic fungicides we talk about days of “back action” or post-infection activity. This is actually the amount of time we have before the fungus becomes too big to control. We can apply a systemic fungicide after a rain (infection period) and get control. Since these fungicides are absorbed into the plant we do not need to worry about washoff. Systemic fungicides also provide protection for several days before plant growth or fungicide movement within the plant dilutes them. My rule of thumb is that if the material has been on for a day, most of it has been absorbed so you don't need to reapply. Systemic fungicides do not protect new growth. In grapes we have three types of systemic fungicides: 1) The SI’s or sterol-inhibiting fungicides, such as Nova and Elite, 2) the strobilurin fungicides or strobys: Abound, Sovran, and Flint, and 3) Ridomil.

Due to the warmer than normal temperatures this past winter, grape growers face the potential for an early bud break. With an early bud break comes the possibility of spring frost damage. Washington State University conducted a study a number of years ago on the critical temperatures at which 10% and 90% of the primary buds would be killed.

At full bud swell (which is described as when young leaves become pink but are still closed around the growing point) a temperature of 21 degrees F will result in 10% bud kill, and a temperature of 10 degrees F will kill 90% of the buds.

Once bud burst occurs (this is described as when young leaves separate at the tip to show the growing point) 10% of the buds will be killed at 25 degrees F and 90% of the buds will be killed at 16 degrees F.

When the first leaf is out of the bud and makes a right angle with the stem, 10% of the buds will be killed at 27 degrees F and 90% of the buds will be killed 21 degrees F.

It is during these three stages when freezes are most likely to occur. One should recognize that these are not absolutes. Temperature duration and humidity are additional factors that can alter the extent of bud kill at any temperature.

The terms frost and freeze are often used interchangeably, but are really associated with two different weather events. The term “frost” is associated with radiational cooling where skies are clear and wind speeds low. During the night of a frost, heat is sent back up to the sky from soil or plant tissues that have absorbed heat during the day. Under these conditions, the coldest temperatures occur at the ground or cover crop level, and a layer of warm air forms that is as much as 10 degrees F warmer at the 25-to-200 foot level. This layer of warm air aloft is known as an inversion layer. Under radiational frost conditions, wind machines or helicopters can be employed to cause a mixing of the warmer air aloft with the cooler air at the bottom. This can result in a temperature gain at ground level of 2-to-5 degrees F. Heaters can also be used to increase temperatures.

The term “freeze” is usually associated with a cold air mass that is most likely accompanied by relatively high winds and cloudy conditions. There is little one can do to mitigate the temperatures associated with a freeze under these conditions.

The dew point will also have an impact on the severity and likelihood of frost damage conditions. If the dew point is low, there are two issues to be aware of. First, nighttime temperatures can drop extremely rapidly. Second, a low dew point raises the critical temperature at which damage can occur. For example, if the critical temperature for damage is 27 degrees F but the dew point is 18 degrees F, actual tissue damage may begin at 29 to 30 degrees F. As a result, frost control measures (such as wind machines or vineyard heaters) should be started at a higher temperature than under conditions of a higher dew point.

The late Dr. Nelson Shaulis of Cornell University used to use the analogy that air flows just like water. Think of water flowing to the lowest spot in the vineyard. The coldest air will also flow to the lowest portion of the vineyard. This could be the bottom of a slope, or the top of your cover crop. One of the practices currently employed by many grape producers is to grow a cover crop that is killed by application of a contact herbicide a few weeks before bloom. While this practice is good for limiting soil erosion and building humus, it is not good for minimizing frost damage in the vineyard. As previously mentioned, the coldest air will settle at the lowest point in the vineyard. That lowest point could be at the top of the cover crop and, if frost conditions occur, could result in substantially more frost damage than if there were no cover crop. A high cover crop can also restrict the natural air drainage down slope and result in temperatures 6-to-8 degrees colder than they might otherwise be without the cover crop. Keeping any cover crop closely mowed during the frost-susceptible period can help minimize damage potential.

However, having firm, bare soil during radiational frost conditions provides much greater benefits and can result in a 2-to-4 degrees F higher temperature than without bare soil. In order to maximize this benefit, the soil must be tilled several days in advance of a possible frost. If the ground is tilled the day of the frost the temperatures at ground level can be 2 degrees F colder than with soil tilled several days earlier. Maintaining a damp soil surface will allow more solar radiation to be stored in the soil during the day for release at night to gain higher nighttime temperatures. Irrigate early in the day with short sets to dampen the soil. The goal is to dampen the soil, but not cool it through excessive irrigation water. Irrigating early in the day allows the soil to absorb solar radiation throughout the balance of the day. It is also very important to allow foliage to dry before night falls. Damp foliage will lose heat more quickly due to evaporative cooling and sustain more damage than dry foliage.

Installing wind machines, heaters, or sprinkler systems are not short-term solutions to minimizing damage from a frost. If an early bud break occurs this year, and/or your vineyards have a history of frost damage, you should consider the one alternative that may help limit damage – maintain firm, bare soil under the trellis as described above.

By: Linda Jones, Michigan Grape & Wine Industry Council

Studies by Michigan State University (MSU) and the Michigan Agricultural Statistics Service demonstrate the growing significance of Michigan’s grape and wine industry to Michigan agriculture and the state’s overall economy, according to Michigan Department of Agriculture (MDA) Director Dan Wyant.

Wyant said MSU researchers, in a recently-released study entitled “A Marketing and Economic Analysis of Michigan’s Wine Industry and Winery Tourism,” estimate that Michigan’s grape and wine industry contributed more than $75 million in state economic activity in 2000. Of this, over $16 million is directly attributed to winery tourism.

“This study confirms the important and increasing role that Michigan’s grape growers and wineries play in our state’s agricultural diversity and strength, as well as the contribution they add to the state’s overall economy,” Wyant said.

This report also provides detailed information regarding the characteristics and behaviors of winery tourists, including the fact that these travelers come from a variety of in-state and out-of-state locations and tend to extend their stays in local communities by at least one half-day to specifically include winery visits in their overall travel experience.

Michigan Agricultural Statistics of 2000-2001 also document the growing contribution of the grape and wine industry with statistics showing that Michigan wine grapes purchased by state wineries increased from $800,000 in 1996 to more than $2.5 million in 2000. Part of this increase is due to increased acreage devoted to wine grapes (a 24-percent increase from 1997 to 2000) and part is attributed to the change in the varieties of grapes grown for winemaking in the state.

“Michigan wine grape growers are becoming very skilled at growing the varieties of grapes that are in high demand for top quality table wines,” said Linda Jones, executive director of the Michigan Grape and Wine Industry Council (GWIC), which is housed and overseen by MDA. “Our growers are producing wine grapes that can go ‘toe-to-toe’ with the world’s best when crafted by our talented winemakers into fine wines. Michigan wines continue to win awards regularly at national and international wine competitions.”

For more information on the state’s wineries and wine grape production, or to receive a complimentary magazine with a map highlighting Michigan’s wineries, visit www.michiganwines.com or call MDA’s GWIC office toll-free at 800-292-3939. Copies of the MSU report’s executive summary or its complete 75-page analysis are also available by contacting the GWIC.

MDA is the official state agency charged with serving, promoting

and protecting the food, agriculture and agricultural economic interest of the people of the state of Michigan. Its programs serve all sectors of agriculture, which is Michigan’s second-largest industry. (This news release can also be viewed at www.michigan.gov/mda.)

By: Al Gaus, Berrien County MSU Horticulture Agent

By: Rodrigo Mercader and Rufus Isaacs, MSU Entomology

In the coming year, we are hoping to measure beetle densities and damage in Michigan vineyards, and we need your help! We are mostly interested in rosechafers and Japanese beetles. This is part of a project underway at MSU to understand how much damage vines can tolerate from insects and diseases, before growth and yield are affected.

You can help us by allowing us to sample in your vineyards when you see these insects on the vines. Please contact us now if you have had problems with these pests in previous years. Also, if you let us know about vineyards with either of these pests during the coming growing season, we can take measurements of these pests when they appear. We would then plan to visit a few times to measure beetle abundance and the damage they have caused.

By helping us with this project, you can help us develop IPM programs tailored to Michigan vineyards and their pest complex.