LIVINGSTON COUNTY – Though all tomatoes and potatoes in Western NY and the Finger Lakes Region are at high risk of infection by late blight following the summer’s heavy rains, our local strain of the fungus is especially weak to a specific type of fungicide.
According to the Cornell Cooperative Extension Vegetable Program, last week late blight was confirmed in potatoes in Livingston and Wyoming Counties, but the Livingston County strain, US-23, is sensitive to Ridomil (mefenoxam fungicides) made by Syngenta.
“Continuing frequent rainfall has been extremely favorable for the development of late blight (LB),” said the Cornell co-op. “LB forecast programs have been indicating extremely high risk of disease development week after week.”
The co-op recommends that growers and farmers scout fields twice a week, especially in low spots and protected areas, and destroy all potato culls and volunteers now.
All tomato and potato growers should be applying fungicides on a regular basis, at no longer than seven day intervals. At some locations, less than a 5 day spray interval may be needed to protect potatoes and tomatoes according to the LB Decision Support System (DSS) forecast. Use alternate fungicides and always follow label directions.
Organic growers should also be applying a fungicide regularly. There are copper formulations approved for organic production. Fungicides differ in how long they will provide protection from infection.
The co-op added that potatoes have many serious insect and disease pests. Late blight can be a devastating disease, capable of completely destroying an unprotected crop within 3 weeks in wet weather, and rotting the tubers. It also affects tomatoes. Late blight was the major cause of the Irish Potato Famine.
New, more virulent strains of late blight fungus began showing up 20 years ago and the disease has been harder to predict and control ever since. Early blight is a common fungal disease on both potatoes and tomatoes which survives over-winter in the soil.