Southwest Michigan grape scouting report for August 25, 2015

Fruit are entering veraison and grape berry moth egglaying is winding down for the year.

Weekly scouting report

More rain has necessitated more frequent sprays for leaf protection. Veraison is underway in different stages, depending on the variety. The third generation of grape berry moth continues to lay eggs on the surface of maturing fruit. Weather continues to be conducive to development of down mildew on leaves and botrytis on susceptible fruit.

Enviro-weather growing degree day summary for 2015 (GDD50 from March 1)

We are 200 GDD50 behind the five-year average for this time of year, which puts us just a few days ahead of last year.

GDD summary since March 1

Location

Aug. 24

Aug. 31 (projected)

Berrien Springs

2,147

2,254

Lawton

2,152

2,257

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

We are in the midst of the third generation egglaying of grape berry moth. No fourth generation is expected this year.

Grape berry moth GDD summary

County

Wild grape bloom

Current GDD after wild grape bloom (as of Aug. 24)

Fourth generation egglaying (2,430 GDD after wild grape bloom)

Berrien

May 26

1,982

Not expected

Van Buren (Lawton)

May 28

1,954

Van Buren

(Mattawan)

May 29

1,828

Allegan

June 3

1,825

Berrien County farms visited Monday, Aug. 24

Concords are in veraison and berry diameters are up to 1.75 centimeters. Vignoles are at tight cluster with the largest berries just over 1 centimeter.

The third flight of grape berry moth males is continuing, but the number of moths caught in traps has remained relatively low. On the last scouting visits to these farms, captures ranged from zero to 13 moths per trap. Growers at these farms applied insecticides to target eggs and young larvae for control of this early activity when Enviro-weather’s grape berry moth model predicted the start of egglaying for the third generation on Aug. 9, and grape berry moth control appears to be very good in vineyards that we visited this week. In vineyard hotspots, some clusters have signs of grape berry moth damage, but most of this damage involves only a small entry wound on a single berry with no further increase in the severity of damage. In the vineyards we scouted Aug. 24, infestation ranged from 12 to 64 percent of clusters with grape berry moth feeding damage on vines that are adjacent to woods containing wild grape. Very little damage was recorded on vines in vineyard interiors.

Japanese beetles were not seen during scouting this week. Overall, beetle numbers are still low and declining; juice vineyards with a full canopy should not need to treat in most cases. Growers with susceptible vinifera and hybrid varieties should still scout regularly to detect possible build-up of Japanese beetle populations and plan to treat if canopy protection is needed. Potato leafhoppers were not seen during scouting at these farms and eastern grape leafhoppers were only seen in one vineyard with 2 percent of leaves with leafhoppers, but growers and scouts should continue looking for these pests on foliage.

At this time of year, we are scouting leaves for active infections of downy mildew and powdery mildew, and examining clusters for developing downy and powdery mildews, as well as botrytis and sour rot infections. The incidence of disease symptoms at the Berrien County scouting sites remains low. No black rot infections were seen on Concord clusters, but downy mildew was seen on 4 percent of leaves. In Vignoles, old infections of phomopsis were seen on 15 percent of clusters. Single black-rot infected berries were seen on 20 percent of clusters, but no further infection is expected. Downy mildew and powdery mildew was not observed on leaves or clusters in Vignoles, but we did note a small number of clusters with botrytis symptoms – one cluster in a sample of 25.

Michigan State University Extension recommends continuing monitoring leaves for downy and powdery mildew, and especially in tight clustered varieties, growers should check clusters for developing symptoms of botrytis and sour rot infections. Treatment may be necessary to control these late-season diseases to ensure the canopy and fruit remain healthy. Leaf pulling around clusters is helpful for control of bunch rots by increasing air flow and sun exposure.

Van Buren County farms visited Monday, Aug. 24

Niagara are at veraison and clusters are continuing to tighten with berries starting to soften and diameters up to 1.75 centimeters. Chancellor is well into veraison and berries are 0.75 centimeters in diameter and clusters are tightening.

The number of grape berry moth males caught in traps ranged from zero to eight moths per trap, showing that the third flight is also underway in this region. The Enviro-weather grape berry moth model predicted egglaying by the third generation to begin Aug. 11 in Van Buren County. Grape berry moth damage in these vineyards has increased over the past two weeks and feeding by third generation larvae ranged from 60 to 100 percent of clusters with damage. The incidence of damage in these high pressure vineyards is highest at vineyard borders, but the severity of feeding remains low and most of the damaged clusters contain only one or two damaged berries. At this point in the year, we are not expecting a fourth generation of grape berry moth; however, depending on the length of the third generation and the level of grape berry moth pressure, an additional insecticide application may be required in some vineyards before harvest.

Potato leafhoppers and grape leafhoppers were not seen during scouting on Aug. 24, and no Japanese beetles were observed. Growers should continue scouting for these pests from now until harvest.

The vineyards in Van Buren County were last scouted for diseases Aug. 17, and diseases have been well-managed in these vineyards. Downy mildew and powdery mildew symptoms were absent from clusters in Niagara and Chancellor, even though these varieties are susceptible to these pathogens. Downy mildew leaf lesions, or “oil spots,” were seen in Niagara vineyards, and the incidence of infected leaves has approximately doubled. We now see about 20 percent of leaves with symptoms, but the disease has not moved onto fruit. It is important to ensure foliar infections do not continue unabated; severe downy mildew can lead to premature defoliation and delayed ripening of fruit. A few old black rot lesions were seen on fruit in Niagara – 4 percent of clusters with symptoms – so it appears these infections were held in check by fungicide applications. In Chancellor vineyards, old symptoms of downy mildew, black rot, phomopsis and botrytis were seen on leaves, but we have not seen any new symptoms on fruit.

Growers and scouts should still be checking vineyard canopies for active infections of downy mildew and powdery mildew on leaves (fruit are no longer vulnerable to new infections of downy or powdery mildews), and botrytis and sour rot infections on clusters. It will be important to ensure these pathogens do not increase between now and harvest, so additional fungicide applications may be needed before season’s end.

Please consult the “Michigan Fruit Management Guide” (E0154) for management options for insects, diseases and weeds.

This scouting report is supported by the Michigan Grape and Wine Industry Council and the National Grape Cooperative.

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