What is in this article?:
- Wine grape season shaping up for powdery mildew
- Sulfur defense
- Once powdery mildew gets established, it does not need water or rain for infection – in fact, heavy rain is detrimental because it washes the spores from the leaves and causes them to burst.
Sulfur remains an effective and inexpensive protectant fungicide for powdery mildew control in non-sulfur-sensitive grape varieties. The most effective systemic fungicides for powdery mildew control are the sterol inhibitors (Rally, Elite/Orius, Procure, etc.) and the strobilurin fungicides (Pristine, Sovran, Abound and Flint). However, do be careful with these products, especially if you suspect fungicide resistance; strobilurin resistance has been found in powdery mildew and sterol inhibitor resistance is suspected in some vineyards in Michigan that have received many applications in the past.
Do not rely solely on strobilurins or sterol inhibitors during critical times for infection. Alternate or tank-mix fungicides with different modes of action; tank-mixing with contact fungicides like sulfur or ziram may also be helpful. Systemic fungicides with different modes of action against powdery mildew are Vivando, Luna Experience, Inspire Super, Quintec and Endura. Do not apply Pristine, Flint, Adament, Inspire Super or Revus Top to ‘Concord’ grapes, as crop injury may result. JMS Stylet Oil and Sulforix are good eradicant materials to knock down colonies after they start to show up. Apply these materials in sufficient water to get excellent coverage because these compounds have to contact the fungal colonies to be effective. Do not apply Sulforix to sulfur-sensitive grapes or close to harvest as sulfur residues may affect fermentation.