MSU Extension

As harvest gets into full swing and everyone becomes increasingly busy with picking, we will be closing down our vineyard scouting reports. We hope these reports have provided timely information to reminded you when to scout, what to look for in your vineyards and offered options to help with pest management in your vineyards. We will continue to scout some representative vineyards through much of the harvest period and will report any significant increases of insect pests and diseases should they occur.

We do recommend that growers, scouts and vineyard managers continue to check vineyards until they are harvested to help identify any increases of cluster rots and late season insect pests such as common fruit flies, multi-colored Asian lady beetles, brown marmorated stink bugs, wasps, spotted wing Drosophila and mealybugs. Although we do not expect a significant fourth generation of grape berry moth this year, and the window has passed for using fungicides to control many diseases, a walk through the vineyard will let you know if there are problem areas where special care should be taken during picking.

Recently, we have seen mature grape berry moth larvae in clusters on the borders of vineyards near woodlots, and sour rot and Botrytis have increased in some vineyards as well. It is more than likely that these problems will persist in vineyards with heavy grape berry moth populations and substantial disease pressure through the period of Niagara harvest. We do, however, expect these issues to be less of a problem for later harvested varieties. Pre-harvest is a good time to reflect on the past season, and we recommend growers make note of areas of high grape berry moth infestation or high incidence of diseases to help with management plans for the future.

This season was one of the coolest and wettest in the recent past, and this made management of diseases and insect pests very challenging for some growers. Not only did the abundant rain provide moist conditions that favor disease development, but pesticide wash-off led to the need for reapplication of some sprays, or resulted in less effective control of insect pests and diseases. Many growers had a particularly tough time controlling powdery mildew in both wine and juice grape vineyards, and cluster rots were especially prevalent in varieties with compact clusters. Grape berry moths were also out in force this year, and we observed some of the highest infestation levels of this insect in the vineyards we monitored for this newsletter. Luckily, many other insect pests including flea beetle, rose chafer, grape and potato leafhopper and Japanese beetles were not problematic in most vineyards this year.

We will have some dry, pleasant weather this week just in time for the start of Niagara harvest in southwest Michigan. Highs are predicted in the 70s with lows in the 40s and 50s for the next week to 10 days, and there is little rain in the forecast for southwest Michigan for the coming week. Currently, we are about 180 growing degree days (GDD) base 50, or about 10-14 days, behind last year and about 350 GDD, about three weeks, behind the accumulation for this date averaged over the past five years.

Good luck with harvest, and we will see you this winter!

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

In general , the incidence of powdery mildew, downy mildew, Phomopsis and black rot in clusters and on leaves has remained steady or declined over the past couple of weeks in the southwest Michigan vineyards that we scout regularly. We have seen an increase in cluster rots at some sites. Egglaying by third generation grape berry moth has been very low due to cool nighttime temperatures, but larvae can be found in clusters on vines that are adjacent to wooded areas. We expect this trend to continue for the next two weeks at the vineyards we scout in Berrien and Van Buren counties.

MSU Enviro-weather grape berry moth model summary (GDD47 from wild grape bloom). We do not expect a significant fourth generation of grape berry moth 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 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. Insecticides with short pre-harvest intervals (PHI) such as Mustang Max (PHI of one day), Scorpion (PHI of one day) or Belay (PHI of zero days) can be valuable tools for controlling pests during this time of year. Be sure to consult the “2014 Fruit Management Guide” (E-154) from Michigan State University Extension for a more comprehensive list of late season insect and disease control options.

Berrien County farms scouted Friday, Sept. 19

Concord continues to ripen well and berries continue to increase in size. The Vignoles vineyard we scout was harvested late last week, so no specific data are available for that vineyard.

No big surprises were seen this week during scouting as eastern grape leafhoppers, potato leafhoppers and Japanese beetles were not seen in the vineyards we scouted. Low numbers of spotted wing Drosophila (SWD) continue to be trapped in vineyards across southwest Michigan, but in our experience, SWD is much less of a problem in grapes than the common fruit flies that are present in much higher numbers at harvest.

The cool weather has slowed grape berry moth activity to a crawl; no males were caught in traps this week. This is most likely due to the cool nighttime temperatures and not necessarily the end of the third flight. A few newly laid grape berry moth eggs are present in clusters, but fresh feeding by third generation larvae decreased over the last two weeks. In some border areas, as many as 68 percent of clusters have damage from third generation larvae. In vineyard interiors, grape berry moth damage ranged from 0 to 4 percent of clusters with grape berry moth damage.

Disease incidence has generally remained steady over the past two weeks. In the Concord vineyards we visited, disease pressure remains at very low levels with downy mildew at 2 percent leaves with lesions and Botrytis at 2 percent clusters with symptoms. Powdery mildew was not observed on leaves or on clusters during scouting.

Van Buren County farms scouted Friday, Sept 19

In the Niagara vineyards we scouted, the fruit is ready for harvest, and Chancellor is also likely to be picked the next two weeks. Similar to the situation in Berrien County, no grape berry moth males were captured over the past two weeks at the vineyards that we monitored, and we did not see an increase in egglaying or new damage. In contrast to the 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 32 to 100 percent of clusters infested on borders and from 0 to 80 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, and powdery mildew does not appear to be actively growing. In one vineyard, 34 percent of the clusters and 10 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 8 to 88 percent of clusters infected. The incidence of Botrytis has also increased and symptoms ranged from 16 to 78 percent of the sampled clusters. Downy mildew lesions (oil spots) were seen on 12 percent of the leaves that we checked. However, these appear to be old infections that are not actively growing.

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.