Article: Disease Control After Spring Freeze Injury in Grapes: What are the Options?

By Annemiek Schilder, Michigan State University It is unfortunate that the Michigan grape industry has been hit with widespread freeze injury once again. In addition, there was hail damage in the Lawton area. A more accurate estimate of yield will not be possible until after fruit set. However, based on the number of surviving flower clusters and proportion of secondary buds, an initial assessment can probably be made. In previous years, the crop turned out to be harvestable in some vineyards that growers had given up on. One thing that is clear is that growers will need to reduce inputs, including fungicides. There are basically three different reduced cropping scenarios:

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1) There is no crop worth harvesting and you don’t care about inoculum build-up.
In this case, protecting the fruit from infection by black rot or Phomopsis is not necessary. If you’ve had good black rot control in previous years, you probably won’t have too much disease. If you’ve had black rot problems in the past, one more year of inoculum production won’t make much of a difference because you already have an “inoculum bank” in the vineyard. We have shown that even under conditions of high disease pressure, it is possible to produce an excellent crop with a standard spray program, which you would implement next year. As far as foliar diseases are concerned, vines with a low crop can tolerate more disease than vines with a full crop. Powdery mildew may infect Concord and, to a lesser extent, Niagara leaves, but if there is no crop, the vine can tolerate quite a bit of disease without ill effects. However, there is a risk that a severe downy mildew outbreak may defoliate Niagara, which may predispose vines to winter injury, even if there is a low or no crop. If downy mildew comes in early in the season (based on scouting) and if it looks like the weather will continue to favor downy mildew, a fungicide spray may be needed to knock back the disease to the point that it does not lead to serious defoliation.

2.) There is no crop worth harvesting, but you want to limit inoculum build-up.
In this case, we don’t want to protect the vine to preserve fruit quality as much as we aim to apply fungicides at a few critical times to knock back diseases to prevent large amounts of overwintering inoculum production. In this case, we can also opt for less expensive fungicides that have good to excellent disease control efficacy. This would include at least one protectant fungicide application (e.g., before a rainy period) to protect the young shoots and exposed flower clusters from Phomopsis. An SI spray could be applied at first postbloom if you are concerned about black rot. Scouting-based management of downy mildew in Niagara would occur as described above. If powdery mildew becomes severe on Concord leaves, you may consider an eradicant spray (e.g., JMS Stylet Oil) to knock down colonies and cleistothecium formation.

3.) There is a harvestable but reduced crop.
In this case, protecting the fruit from black rot and Phomopsis is the most important activity and will require a few more sprays than the two scenarios above, e.g., one or two pre-bloom protectant sprays to protect against Phomopsis, one or two postbloom sprays to protect against black rot and Phomopsis (while also controlling powdery and downy mildew), and curative/protectant sprays against foliar powdery and downy mildew only if scouting indicates a need.

To cut input costs, you can use lower-cost fungicides (e.g., generics, older protectant fungicides, phosphites) and reduce the number of fungicide applications only to critical times. Watching the weather and stretching spray intervals during dry periods also helps to lower the number of sprays. It is important to also take labor and fuel costs for applying fungicides into account. The fewer times you have to drive through the vineyard, the better. A way to reduce the number of applications is to tank-mix fungicides with insecticides (most growers are already doing this), apply products at higher rates, or apply products with longer-lasting residuals for extended coverage. Adding a sticker-extender (e.g., NuFilm) can be a low-cost way to make a fungicide last longer and obtain better coverage. Ensuring thorough coverage by spraying every row at an appropriate spray volume (at least 50 gpa after the canopy fills in) will increase the “bang for your buck” of the fungicides you use. This is especially important for protectants like Ziram, Captan, and Manzate.

This article was published on the Integrated Pest Management Resouces, CAT Alert webpage. (follow the link below to view article tables) https://ipmnews.msu.edu/fruit/Fruit/tabid/123/articleType/ArticleView/articleId/2686/Disease-control-after-spring-freeze-injury-in-grapes-What-are-the-options.aspx.

Grape Biopesticide Report 2009 by Annemiek Schilder, Michigan State University.

This report evaluates biopesticides for control of black rot and Phomopsis in organic grape production in 2009. The experiment was conducted in a mature ‘Niagara’ vineyard at the Trevor Nichols Research Complex in Fennville, MI. Here is a summary of the report. Apply Serenade (+ Nu-film-P), Sonata (+Nu-Film-P), Kaligreen and JMS Stylet Oil for disease control, see attached report (put in WEB link of table after you put on our web site here Danielle). Everything on this list is organic except the blue-lettered treatments, which are conventional fungicides for comparison .Dr. Annemiek Schilder (Dept of Plant Path-MSU) would consider Serenade and Sonata to be the strongest of the bunch against most grape diseases (be sure to add Nu-Film-P as a spreader-sticker). JMS Stylet oil is most efficacious against powdery mildew (but does suppress the other diseases as well) and Kaligreen is good for powdery mildew and black rot (and provides some suppression of other diseases). (To read full report visit www.michiganorganic.msu.edu <https://www.michiganorganic.msu.edu/> under the fruit production tab).
Managing Row Covers to Avoid Heat Injury and Poor Pollination <https://ipmnews.msu.edu/vegetable/vegetable/tabid/151/articleType/ArticleView/articleId/2738/Managing-row-covers-to-avoid-heat-injury-and-poor-pollination.aspx>  by Mathieu Ngouajio, Department of Horticulture, Michigan State University
Row covers are used as a means to modify the microclimate around the crop. Attempts to modify the environment for enhanced crop production dates back to the 16th century. Since the early 1960s, the introduction of plastics in agriculture helped develop new and efficient row cover technologies for open field vegetable production. Row covers are used for a number of reasons such as, season extension (frost protection), insect exclusion, heavy rain and hail protection. Regardless of the primary goal of the row covers, their management should help avoid excessive heat that can injure the crop and also avoid poor pollination that may reduce yield.

Row covers and heat injury
When using row covers, always keep in mind that they are more efficient at increasing temperature, especially during a sunny day, than protecting against frost. Even in the absence of a frost risk, some growers may consider using row covers because most warm season vegetables stop growing at temperatures below 40-50oF. A row cover may increase the temperature enough to promote the growth of these warm season vegetables.

When outside temperatures are high, it is recommended to remove row covers. Temperatures inside row covers can get extremely high and injure crops, especially when row covers without perforations or holes are used.

Under a sunny day with a calm wind, we have observed about 20 to 30 degree temperature increases inside row covers when compared to outside. Depending on the outside temperature, this extreme heat can easily damage certain crops like tomato. Under those conditions, it is recommended to open the row covers for ventilation.

Row covers and pollination
Many crops require insects, especially bees, for pollination. In cucurbits for example, there are separate male and female flowers. For adequate pollination and fruit set, the pollen needs to be moved from the male flower to the female flowers. Row covers present physical barriers for insects including bees. Even when the row covers are perforated, most insects normally stay outside. In a recent study conducted by our team, we observed a significant reduction in slicing cucumber yield when the row covers were removed two to three days after appearance of the first flowers. It is important to know that flowers of most cucurbit crops remain open for only 24 hours. It is therefore important to remove the rows covers before cucurbit flowers open to facilitate pollination and proper fruit set.

This article was published on the Integrated Pest Management Resouces, CAT Alert webpage https://ipmnews.msu.edu/vegetable/vegetable/tabid/151/articleType/ArticleView/articleId/2738/Managing-row-covers-to-avoid-heat-injury-and-poor-pollination.aspx.