Page 45 - Grapevine NovDec 2021
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Around The Vineyard
Scout for Lingering Powdery clear, up-close photo to your local Extension spe-
and Downy Mildew cialist.
First, take an hour to scout the vineyard for pow- When to Reach for the Sprayer
dery and downy mildew on the leaves. If visible
infections are few to none, you can consider skip- It is best to make applications when you first
ping this step and start winterizing the sprayer. observe the signs of infection. Disease control
becomes more challenging the longer you wait.
However, also remember that minor infections Protectant products can be used to prevent new
might keep growing until the leaves senesce. infections, in combination with a systemic fungicide
When scouting, know how to correctly identify the to stop active infections.
diseases in order to apply the right fungicides.
This proactive approach is most important if
Check out the upper surfaces of the leaves for you still have a while between now and when the
white or greyish-white blotches – this is how pow- grapevine leaves start to senesce for the winter.
dery mildew infections appear. You might also see Infections can spread surprisingly quickly under the
them on the undersides of the leaves. The blotches right fall weather conditions.
begin sporadically and then merge into one large
patch. The optimal temperature range for powdery
mildew is 68-77F, but infections can still occur
Once a leaf is severely infected it can curl, dry up between 59-90F. This makes fall a time for fast
and fall off. A heavy infection can cause an entire spread of this disease.
vine to defoliate early in the fall, impeding its abili-
ty to acclimate for winter. Similar to powdery mildew, downy mildew can
occur during peak fall temperatures. It does best
Downy mildew is most obvious on the upper sur- between 64-76F but can infect when temperatures
faces of the leaves, as yellow or greenish-yellow are anywhere between 54 to 86F.
blotches. But the infection actually shows up first
on the lower surface of the leaves. Turn the leaves A new vine infected
over to look for a white or greyish cotton-like with powdery mildew
growth. As the infection gets worse the blotches in late September. The
spread in size and dry up, causing the leaves to infection may spread
drop if the disease doesn’t slow down. and kill the leaves if
not controlled.
Yellow blotches
indicating downy Many fungicides will
mildew. control either downy
mildew or powdery
Both patho- mildew, but the list of
gens can damage effective products dif-
shoots, petioles, fers quite a bit between the two diseases. Consult
and rachises (the the Midwest Fruit Pest Management Guide (MFPM)
branches of the or your regional university-based spray guides for
cluster), especially the latest fungicide recommendations.
in fall. Therefore, keep an eye out for them during When selecting fungicides for during or after har-
harvest to help decide if a post-harvest fungicide is vest, consider:
needed.
• Cost – consider whether the application is import-
If you need help identifying a disease, send a ant enough to you to justify the cost, as some
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