Vineyard IPM scouting report for August 25, 2014

Don't put away the sprayer yet. Grape berry moth egglaying is likely to be prolonged and late season insect and disease control may still be required.

Although the last few days have been hot, we are still in the midst of a cool year. In that respect, this year has been similar to 2013 and to the 2009 growing season. We have accumulated about 2,000 growing degree days (GDD) base 50 since March 1 in the grape growing areas of southwest Michigan. Long-term forecasts predict the cool trend to continue through harvest, and this means we will only add about 600 additional GDDs before harvest begins; this may be six to eight weeks for some varieties. Although the cooler weather may slow the development of some insects and diseases, it can also prolong the period of time when vines need protection from these issues.

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

Site

Aug. 25

Aug. 31 (projected)

Berrien Springs

2,059

2,192

Lawton

2,016

2,160

The incidence of powdery mildew and Botrytis in clusters has continued to increase in some southwest Michigan vineyards that we regularly scout. Bunch closure, veraison and pre-harvest are important spray timings for Botrytis bunch rot control, and growers should be scouting to determine if these diseases are present or increasing to decide if treatment is necessary. Downy mildew, black rot and Phomopsis symptoms on leaves and clusters have remained steady, but additional fungicide applications may still be needed to protect vines from foliar fungal diseases that are increasing because of recent rain. Generally speaking, berries are now resistant to infection by black rot, powdery mildew and downy mildew pathogens, but current infections by these pathogens may continue to rot or sporulate.

The third generation of egglaying has just started this past week in southwest Michigan. Fresh grape berry moth eggs and feeding damage by young larvae is generally easy to see in clusters on vines that are adjacent to wooded areas, and we are also seeing an increase in the number of grape berry moth males captured in pheromone traps.

Grape berry moth needs about 800 GDD to complete a generation (egg to adult), and with the predicted cool weather, it looks like it will not be warm enough for eggs that are laid now to make it through to emerge as adults. In addition, day length is getting shorter; currently we are getting about 13.5 hours of daylight. Grape berry moth eggs and young larvae that are exposed to 14 hours or less of daylight are automatically triggered to enter a resting state known as diapause when they pupate, and this is how they will spend the winter. So the good news here is that we do not expect a significant fourth generation of grape berry moth this season.

Nevertheless, we still have to deal with the third generation. So far this season we have seen some very high rates of damage along the edges of vineyards that are adjacent to wooded areas with wild grape. Vineyard interiors have generally experienced much lower rates of infestation. The high pressure at the borders is likely due to the cool, wet weather extending the lifespan of the moths, and increasing the duration of egglaying, and we expect these trends to continue for the third generation. The take-home message here is that one insecticide application may not be enough to control third generation grape berry moth at the edges of vineyards with high pressure, but vineyard interiors may not need additional insecticides for grape berry moth control.

Be sure to consider pre-harvest intervals (PHI) when choosing insecticide options for controlling grape berry moth. Intrepid, which is active on eggs and young larvae, has a 28-day PHI, so the window for using this compound is closing for many growers. Compounds that are active on eggs and larvae also include Altacor, 14-day PHI, and Belt, seven-day PHI. Like Intrepid, these types of compounds should be applied at the start of egglaying, and these would need to be applied very soon for maximum protection. Broad spectrum insecticides should be applied about 100 GDD, approximately one week, after egglaying begins. Options that have a long PHI include Brigade/Capture, 30-day PHI, and Danitol, 21-day PHI, which may be possibilities for some varieties. Insecticides with shorter PHIs include Imidan, 14-day PHI, Sevin, seven-day, Baythroid, three-day PHI, and Mustang Max, one-day PHI, which will likely be better options for most growers.

Other insect pests can also appear at harvest time, such as multi-colored Asian lady beetles, brown marmorated stink bug, wasps, ants, mealybugs, spotted wing Drosophila (SWD) and other common fruit flies. Here again, insecticides with short PHIs become increasingly important. The following insecticides all have a one-day PHI. 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 moths. 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.

We will continue to scout 20 southwest Michigan vineyards through harvest to monitor for late-season pests. Look for our reports on what we are finding at www.grapes.msu.edu.

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 Aug. 25

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

Berrien

May 29

1,933

Not expected to occur

Van Buren

June 2

1,910

Not expected to occur

Berrien County farms scouted Monday, Aug. 25

Concord is well into veraison and berries continue to increase in size and many are 20-25 millimeters, or about 1 inch, in diameter. Vignoles is also at veraison and clusters continue to ripen slowly with berry size at 10-13 millimeters, or about 0.33 inches, in diameter. Eastern grape leafhoppers and potato leafhoppers were not seen in the vineyards we scouted in this county. No Japanese beetles were seen during scouting and light feeding damage on leaves can be seen, but there is no need to treat for this pest at this time. Low numbers of SWD continue to be trapped in vineyards. Our experience in the four years since this pest has 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. Ants were seen in clusters in some vineyards, but other harvest-time pests were not observed during scouting.

The third flight of grape berry moth males is picking up and the number of males captured ranged from zero to 36 per trap. Feeding damage from second generation larvae can still be found in clusters in vineyard hotspots. Newly laid grape berry moth eggs are present in clusters and fresh feeding by third generation larvae is also evident. In some border areas, as many as 60 percent of the clusters have stings from third generation larvae entering berries. In vineyard interiors, grape berry moth damage ranged from 4 to 20 percent of the clusters with evidence of early grape berry moth feeding 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 or black rot infection. In Vignoles, 10 percent of clusters showed symptoms of black rot infection while 24 percent of clusters had Botrytis symptoms. Phomopsis leaf lesions are widespread, but no symptoms were seen on clusters during scouting on Aug. 25. In the Concord vineyards we visited, disease pressure is at very low levels: Phomopsis is at 2 percent leaves with lesions, and black rot is at 2 percent clusters with symptoms. Powdery mildew was found on 1 percent of the leaves during scouting.

Van Buren County farms scouted Monday, Aug. 25

In the Niagara vineyards we scouted, the fruit is at veraison and berries are sizing rapidly and Chancellor is at veraison, with most berries showing color. Over the past week, captures of grape berry moth males have increased at the vineyards we monitored at zero to 21 moths per trap. Early damage from third generation larvae in clusters is generally higher than what we have seen recently in Berrien County, ranging from 28 to 100 percent of clusters infested on borders and 6 to 18 percent of clusters infested in vineyard interiors. As was seen in Berrien County, grape leafhoppers, potato leafhoppers, Japanese beetles and other harvest-period pests were not present in the vineyards we scouted.

This week in the Chancellor vineyards we scouted in Van Buren County, there do not appear to be new Phomopsis or black rot leaf lesions, and powdery mildew incidence on leaves and clusters has also remained steady. In the Niagara vineyards we monitor as part of this project, we recorded black rot symptoms on 10 percent of the clusters and on 5 percent of the leaves. Downy mildew lesions (oil spots) were seen on 9 percent of the leaves that we checked, and this is similar to levels observed over the past month. Botrytis was recorded on 17 percent of the sampled clusters, and this represents a four-fold increase in this disease.

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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