Vineyard IPM scouting report for September 8, 2014

Berry ripening is slowly progressing and harvest of some early varieties is set to begin. Be on the lookout for late season insect pests and bunch rots in clusters.

A few days of warm weather has advanced fruit development in some vineyards and harvest of early varieties such as Marechal Foch, Marquette and Vignoles has started at some warmer sites in southwest Michigan. With this recent heat and the passage of some strong storms, we have seen an increase in sour rot and Botrytis infections in some vineyards. The excess water from the recent rainfall has also caused some berries to split and this is likely contributing to increased levels of sour rot.

Additionally, these split berries are also very attractive to some late season pests such as fruit flies, ants and wasps. Growers, consultants and scouts should check ripening clusters for the presence of these insects and diseases in case a clean-up spray is warranted and fits in with the harvest schedule. For more information on management of cluster rots, see “Don’t let bunch rots ruin your grapes” from Michigan State University Extension.

Cooler temperatures will return to the region by the middle of this coming week, with highs predicted to be only in the upper 50s or low 60s for the end of this week. Currently, we are about 90 growing degree days (GDD) GDD base 50, or about one week, behind last year and about 275 GDD, or about three weeks, behind the accumulation for this date averaged over the past five years.

MSU Enviro-weather GDD summary for 2014 (GDD50 from March 1)

Site

Sept. 8

Sept. 15 (projected)

Berrien Springs

2,339

2,392

Lawton

2,281

2,342

The incidence of powdery mildew in clusters and on leaves has continued to increase in some southwest Michigan vineyards that we scout regularly. Downy mildew, black rot and Phomopsis symptoms on leaves and clusters have remained steady. Berries are now largely resistant to infection by black rot, powdery mildew and downy mildew pathogens, but current infections by these pathogens may continue to rot or sporulate, and symptoms may become more evident in infested clusters. Growers should be checking to see if these diseases are present or increasing to help determine if an additional fungicide application is needed.

Egglaying by the third generation of grape berry moth is still occurring, and damage is easy to see in clusters on vines that are adjacent to wooded areas. However, it appears that new egglaying and damage from newly hatched larvae have slowed considerably over the past two weeks at the vineyards we scout in Berrien and Van Buren counties. Based on the slow growing season, we do not expect a significant grape berry moth fourth generation this year.

We have seen an increase in the number of common fruit flies and ants in some vineyards with split berries, but the other insect pests that can appear at harvest time, such as multi-colored Asian lady beetles, brown marmorated stink bugs, wasps and mealybugs, were not seen during our scouting. We are still catching spotted wing Drosophila (SWD) in traps on vineyard borders, but because we generally have to deal with common fruit flies at this time, we do not expect this pest to pose many additional problems.

Harvest time insect pests can appear quickly, so regular scouting is required to check whether their numbers are increasing. Insecticides with short pre-harvest intervals (PHI’s) are important tools for controlling pests during this time of year. The following insecticides all have a one-day PH. Mustang Max (zeta-cypermethrin) is a pyrethroid with broad spectrum activity on insect pests. Scorpion contains dinotefuran, which is a third generation neonicotinoid, having activity on mealybugs, stink bugs and other harvest-time insect pests. Belay (clothianidin) is also a third generation neonicotinoid, has a zero-day PHI and activity on lady beetles, mealybugs, leafhoppers and berry moth. Be sure to consult the “2014 Fruit Management Guide” (E-154) for a more comprehensive list of late season insect and disease control options.

MSU Enviro-weather grape berry moth model summary (GDD47 from wild grape bloom)

County

Date of wild grape bloom

Current GDD after wild grape bloom as of Sept. 8

Predicted start of fourth generation egglaying (2,430 GDD after wild grape bloom)

Berrien

May 29

2,264

Not expected to occur

Van Buren

June 2

2,134

Not expected to occur

Berrien County farms scouted Friday, Sept. 5

Concord is ripening and berries continue to increase in size and many are over 25 millimeters, or about 1 inch, in diameter. The Vignoles vineyard we scout is ripening and the grower expects to begin harvest late this week.

Eastern grape leafhoppers and potato leafhoppers were not seen in the vineyards we scouted. No Japanese beetles were seen during scouting and there is no new feeding damage on leaves. We do not expect a large increase in this pest and it is likely that treatment for this pest will not be needed again this season. Low numbers of SWD continue to be trapped in vineyards. Our experience in the four years since this pest has been arrived in Michigan indicates that SWD is much less of a problem in grapes than the common fruit flies that are present in much higher numbers at harvest.

The third flight of grape berry moth males is still going and the number of males captured ranged from zero to 18 per trap. A few newly laid grape berry moth eggs are present in clusters, but fresh feeding by third generation larvae has decreased over the past two weeks. In some border areas, as many as 50 percent of the clusters have damage from third generation larvae. In vineyard interiors, grape berry moth damage ranged from 4 to 20 percent of the clusters with grape berry moth damage.

Disease incidence has generally remained steady over the past two weeks, except for an increase in the number of clusters showing signs of Botrytis and sour rot infections. In Vignoles, 26 percent of clusters showed symptoms of Botrytis infection while 53 percent of clusters were infected with sour rot. Phomopsis leaf lesions are widespread, but no Phomopsis symptoms were seen on clusters during scouting. In the Concord vineyards we visited, disease pressure is at very low levels, with downy mildew on 3 percent of leaves with lesions and black rot on 2 percent clusters with symptoms. Powdery mildew was not observed on leaves, and no disease symptoms were seen on clusters during scouting.

Van Buren County farms scouted Monday, Sept. 8

In the Niagara vineyards we scouted, the fruit is past veraison, berries are sizing rapidly and Chancellor is also past veraison, with harvest likely to occur in the next two weeks.

Over the past week, captures of grape berry moth males have increased at the Van Buren County vineyards that we monitored, with six to 44 moths per trap, but we did not see an increase in egglaying or new damage. Compared to our scouted sites in Berrien County, we observed a higher percentage of grape berry moth-damaged clusters at the vineyards we scout in Van Buren County. In these high pressure vineyards, damage ranged from 56 to 100 percent of clusters infested on borders and from 10 to 74 percent of clusters infested in vineyard interiors. As was seen in Berrien County, grape leafhoppers, potato leafhoppers and Japanese beetles were not present in the vineyards we scouted.

This week in the Chancellor vineyards we scout in Van Buren County, we did not see new Phomopsis or black rot leaf lesions, however powdery mildew incidence on leaves and clusters has increased. In one vineyard, over 30 percent of the clusters and 18 percent of the leaves were infected with powdery mildew. In the Niagara vineyards we monitor as part of this project, black rot symptoms are becoming more evident in clusters and ranged from 6 to 66 percent of clusters infected. Downy mildew lesions (oil spots) were seen on 12 percent of the leaves that we checked, and this is similar to levels observed over the past month. Botrytis was recorded on 19 percent of the sampled clusters, and this also is similar to results of our scouting over the past month.

Our vineyard scouting and this report is supported by the Michigan Grape and Wine Industry Council and the National Grape Cooperative.

Drs. Schilder and Isaacs’ work is funded in part by MSU‘s AgBioResearch.

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