The Great Lakes Fruit, Vegetable and Marketing Expo will be held in Grand Rapids on December 10th through the 12th. All Michigan fruit growers should attend this 3-day program. Last year was the largest show I had ever seen since I came to Michigan in 1988. The grape session will be from 2 to 4 PM on Tuesday, December 10th. This session will focus on grape production issues and one RUP credit will be available to attendees. Grape IPM topics will include grape berry moth and Phomopsis. These two significant vineyard pests in 2002 should be of interest to all grape growers. Production topics include fertilization and vine management practices.

Looking back on the 2002 season, grape berry moth (GBM) caused the greatest insect-related problems in Michigan vineyards. This was particularly true in Southwest Michigan, but we also saw increased infestations in vineyards around Traverse City. Reports of similar problems in the Lake Erie region also show that this was a region-wide issue. So, what happened? This article is intended to discuss why this pest was such a problem. An article in the spring issue will address approaches for GBM management in 2003.

We don’t think that any one thing was responsible for the outbreak this year. Instead, multiple factors combined to promote GBM development, leading to intense pest pressure in many vineyards. Infestation started to increase rapidly in the middle of August, and continued non-stop until harvest. This timing made effective control of this pest extremely difficult in vineyards with these high pressure conditions. The increasing infestations of clusters during the warm conditions of August and September caused secondary problems of cluster diseases, contributing further to decreased fruit quality (Figure 1).

In 2001 and 2002, we have taken weekly counts of grape berry moth eggs and larvae on clusters in vineyards near Lawton. We also monitored flight activity of adult moths using pheromone traps. The pattern over time from this year (Figure 2) was similar to 2001, although the amount of infestation was higher. Egg laying started at a low level after bloom, and remained low until early August. After that, the weekly counts show that egg laying continued to increase, and the number of larvae also increased.

There has been a lot of discussion among entomologists, growers, and consultants in the past 2 months about the factors that caused this increase in grape berry moth. The list below (in no particular order) outlines the main factors that contributed in Michigan. For different vineyards, some may be more important than others, but this should help you understand why we had the problems we did.

1. Frost effects on grape availability. Grape berry moth populations are usually abundant in woods with wild grape. But in 2002, few of the wild grape plants fruited because of the early frosts. We suspect that grape berry moth responded to the lack of fruit in the woods by moving to the vineyard. In addition, moths in the vineyard had fewer grapes to lay eggs on, so there was probably a concentration effect of moths having fewer clusters to lay eggs on.

2. Winter temperatures and snow cover. The relatively warm winter temperatures and snow cover in recent years have been ideal conditions for survival of grape berry moth pupae through the winter.

3. Unusual pest management year. Remembering back to the spring, many growers decided not to actively manage some vineyards to cut costs. Later estimates of the crop changed some minds, but without regular scouting it was hard to know whether berry moth had become a problem until it was too late.

4. Heat and drought in August and September. Conditions for development of grape berry moth were ideal this summer. Higher temperatures mean faster development, and with the night temperatures staying warm, the time from egg laying to burrowing into the berry was very short. This combined with the long period of egg laying made timing of insecticides extremely difficult. Higher temperatures also speed up the decline in insecticide residues, so during the burst of egg laying in August, there would have been gaps in the coverage of an insecticide program, even if sprays went on every 2 weeks.

5. Excess canopy. Many juice grape vineyards had a large canopy because of the lower crop this year. These conditions make it more difficult to get sprays onto the clusters, because the layers of leaves can deflect the air and spray materials. However, without residues completely covering the cluster, it is difficult to achieve good control of grape berry moth. As the grape canopy increases, spray water must increase to achieve good coverage, and techniques such as spraying every row should be considered.

6. Pesticide effectiveness. There have been some major changes in the types of insecticides available to grape growers in recent years. The calendar spray program relied heavily on getting two weeks of activity from Penncap or a similar broad-spectrum products. Most insecticides registered now don’t give that kind of longevity, and so effective pest management requires more information on pest development and the strengths and limitations of new products, so they can be used to maximum effectiveness at the best time.

A meeting of grape entomologists from Michigan, Pennsylvania, and New York has been planned by National Grape for early December to focus on grape berry moth. The discussion at this Grape Berry Moth Summit will be used to develop effective strategies for controlling this pest, and we will be reporting the results of our berry moth experiments at the upcoming winter meetings.

Figure 1. Concord grapes collected just before harvest showing (left to right) a healthy berry, a berry with grape berry moth and some disease, a berry hollowed out by a larva, and a berry completely collapsed from berry moth and disease.

Actually, the use of these 5-year averages (1996 - 2000) is also flawed because there was rapidly increasing acreage of Niagara in Michigan during that period. Therefore, if we use the most recent data (2000) for Concord and Niagara acreage in Michigan at 9200 and 3000 acres, respectively, then the 2002 marketed crop averaged 2.7 tons and 4.4 tons, respectively, for all the Michigan acreage of these varieties. That's amazing considering the acreage left un-harvested!

How did this happen? As many growers came to realize, the primary reason for this much larger than expected crop was due to the unusually high fruitfulness of secondary buds. The low crop levels in 2001 made ideal conditions for the development of fruitfulness on vines for the 2002 crop. It was amazing to see the number and size of clusters that developed on secondary shoots in both Concord and Niagara. Amazingly, the crop would have been even larger if there had not been a series of subsequent spring freezes in early- to mid-May after the first big freeze on April 23rd that whittled away at emerging secondary buds. Another factor in the development of the crop for 2002 was that in several locations there was actually little damage to primary buds. Factors that at times contributed to the survival of primary buds appeared to include: reduced pruning severity from mechanical pruning that allowed buds to develop more slowly in the spring, vineyards on "cooler", slower-to-develop north-facing slopes, vineyards proximate to structures like buildings or highways, and vineyards on fairly steep, sloping ground that facilitated cold air movement out of the vineyard site. As the season progressed towards harvest, it became apparent that more and more acreage had marketable yields.

A smattering of berries on the ground before harvest was unfortunately a common sight in many vineyards this year. The likely culprit: Phomopsis. Phomopsis is a fungus which infects both the rachis and berries of grape bunches. Niagara is a particularly susceptible variety. Most berries drop due to a withering of the berry stem, although whole clusters may break off if the cluster stem becomes infected near the top. Mechanical harvesters increase berry and cluster drop due to shaking of the trellis. Infected berries turn brown and rubbery. This brown discoloration can often be seen moving from the stem end of the berry to the blossom end, sometimes along the veins.

It is important to remember that most or all infections that take place during the growing season, from cane and leaf infections to rachis and fruit infections are coming from one source: overwintered infected canes. The fungus is present in these canes as mycelium and will produce fruiting bodies until it runs out of food or until the weather becomes too dry. Preliminary observations suggest that the more heavily infected the canes are the previous year, the longer the period of spore dispersal will last. The fungus usually does not produce fruiting bodies in current-year lesions, although at the end of the season some fruiting bodies may be noticed on infected berries as small black pimples. Spores may be seen oozing out as cream-colored droplets and can infect neighboring berries. If you let the fruit hang a long time, more and more berries become infected.

Due to the devastating spring frosts, most growers waited to see how much damage the vines had sustained before making decisions on pesticide and other inputs. Some growers applied few or no fungicides because expected yields were extremely low. This and a cool wet spring contributed to moderate to heavy Phomopsis infections in many vineyards.

To determine the effects of different fungicide programs on Phomopsis severity, and to determine the relationship between disease severity and berry drop, trials were conducted in Niagara vineyards in Keeler and Lawton in 2002. Penncozeb was used before bloom and Abound or Ziram were applied after bloom in various programs. The vineyard in Lawton had more rachis infection than the vineyard in Keeler. For the sake of brevity, only the former trial will be discussed. In Lawton, most fungicide programs had significantly less disease than the untreated control, with the program containing Abound (post bloom) performing best numerically. The data show that at least two sprays and possibly more have to be applied to get a decent level of control. The benefit of post-bloom sprays may be limited to the first post-bloom application. Spatial variability in infections in the vineyard, which is common for Phomopsis, probably contributed to variability between treatments. Yield loss was mostly due to berry drop. The number of berries on the ground after harvest was positively correlated with percentage of the rachis infected. Based on the data obtained, maximum losses of 0.62 tons/acre were estimated for the Keeler plot (~30% of total yield), and 1.2 tons/acre for the Lawton plot (~40% of total yield). It must be taken into account that overall yields were much lower than in normal years.

Figure 1. Percentage of the total rachis area infected as affected by fungicide treatment in a Niagara vineyard in Lawton, MI, 2002. (P=Penncozeb; Z= Ziram; A=Abound; *=no treatment; letters before the comma indicate pre-bloom sprays, letters after the comma indicate post-bloom sprays). Means followed by the same letter are not significantly different from each other at P=0.05.

The web site of the Michigan Grape and Wine Industry Council has a new look. A special section for industry members is now available that will host registration forms for the Council-sponsored industry meeting, competition entry forms and other useful resources to the industry. Watch for additional material to be added in the coming months.

The Michigan Grape and Wine Industry Council is one of the recipients of a Julian-Stille Value-Added Agriculture grant for $30,000, to create a web based resource kit for new and existing wineries. The work will be completed in phases over a two year period. Five Michigan wineries shipped wine to Germany for sale in September, as a result of the MIATCO Midwest wine promotion activities coordinated by the Agriculture Development Division.

2002 Dates:
Nov. 20–22 American Vintners Association Meeting, St. Louis, MO
Dec. 3, Michigan Grape/Wine Industry Council Meeting, Lansing

The Grape Society has generously supported the improvement program for the Concord and Niagara vineyards at Trevor Nichols Research Complex, in Fennville, where much of the insecticide and fungicide testing by Drs. Isaacs and Schilder is done. These funds are helping to transfer the vineyard from it's old kniffin system to a modern top-wire cordon system, and to replace old posts and wire. The presentation of the check was made at the ceremony to celebrate the opening of the Angus J. Howitt IPM Training Room, held on October 30th, 2002. This new MSU facility will be used to host research and extension meetings, and to train fruit growers, scouts, and consultants in integrated pest management.

Presenting the check to Jim Wise, Trevor Nicholas Coordinator and Gus Howitt, is Brian Cronenwett of the Michigan Grape Society and Rufus Isaacs, MSU Assistant Professor Small Fruit Entomology.

Another feature is a wine tasting on Wednesday evening. At 7:00 p.m., a wine tasting and hospitality session will be held poolside at the Benton Harbor, Ramada Inn. The Ramada Inn also offers a special conference rate for rooms in conjunction with this event. This low rate should encourage even local growers to participate in the evening's festivities. Mention "Southwest Hort Days" when making your reservations. We hope to again have door prizes and prize giveaways during the trade show. The show starts Wednesday morning with a general Farm Safety session, good for 2 RUP credits. On Wednesday afternoon there are concurrent Vegetable and Tree Fruit sessions. Thursday's concurrent sessions are for Tree Fruit and Grapes.

Do you have an implement, tractor, or tool you would like to sell?  Do you have a service you would be interested in offering?  Why don't you buy an advertisement in the Michigan Grape Society newsletter.  Our circulation is about 270 and is focused at grape growers who would be interested in what you have to sell.  If you have an item you would like to sell call Jerri at 269-657-7745 or email her at pursleyj@msue.msu.edu.