Cherry Leaf Spot

I planted four young plum tree this spring and was hand watering them every day until recently I started using a sprinkler.  Last night I noticed what appears to be Cherry Leaf Spot on one of the trees.  There is a lot of information about the fungus that causes this and how to prevent, but not a lot about whether using an anti-fungicide spray right away will help or do I need to wait until the end of the season.  And, I'm a newbie so this question may be fairly basic: do I need to change the way I water the trees (i.e., stop using a sprinkler) to help prevent in the future?

Thanks in advance for any help.

Hey John, welcome to Permies!

Yeah I bet the watering is the issue. The watering of the leaves with the sprinkler is probably making them more susceptible to the leaf spot disease.

Also, plums, along with peaches and cherries, seem to actually do better for me with less water than the average tree. They seem to get unhappy and disease prone when we get too much rain.

Steve

Steve,

thanks for the info, this is very helpful.

Water on the leaves and where branching occurs seems to be the vector that allows the spores to enter the plant.  If leaves have growths on them or stems or leaves have black spots it is best to remove them and dispose of them in a way they do not remain a source of contamination.  I built a high tunnel over my peach trees so that spring and fall rains do not contribute to the spread of disease between them and the neighboring plums that are mostly resistant. The ground under the trees remains dry so only the perennial rhubarb flourishes there but there is plenty of water soaking into the root zone from the edge of the enclosure.  The warmer dryer conditions also makes for higher pollination rate which can be a positive or negative depending on whether you want larger size or numbers of fruit. I definitely get earlier fruit and help my mason bees get started in the spring.