*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:

*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) *
.** ***

* *

*Grape Biopesticide Report 2009 *by* *Annemiek Schilder, Michigan State

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 ** under the fruit production tab).
Managing Row Covers to Avoid Heat Injury and Poor
*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 *

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