This week at Wilbur-Ellis was focused largely on finding diseases in cherries. The most concerning disease was Cherry Leaf Spot. This is a fungus that grows on cherry leaves in hot and humid weather. It creates spots on the top of the leaf with spores that grow underneath the leaf. These spores eventually get displaced and land on other wet leaves and spread the infection. The pictures below show the spots on top of the leaf(left picture) and the spores on the bottom of the leaf(right picture).
The big concern with leaf spot is how easily it spreads and its widespread effects. Leaf spot causes the leaves to dry up and fall off the tree. This makes trees weaker and more likely to have problems throughout the winter. As you can imagine this effects the yield on the cherry crop in the following season.
The last week or so the conditions in Traverse City have been perfect for the growth and spread of leaf spot. It has rained several times and been in the 80 degree range for several days. That has really increased the amount of leaf spot I have found in orchards throughout the area. The farmers are somewhat frantic because the spread of leaf spot means they need to find a break in the weather to spray so that the fungus does not spread. Once the farmers have sprayed, the white spores on the bottom of the leaf die and turn brown. That is how you tell the difference between active leaf spot and burned out leaf spot.