KC Gardens

2015: The Year of Disease

Pear rust
Pear rust

From Dennis Patton:

Up to this point no one is really complaining about the summer of 2015. Yes, it has rained more than usual but for the most part that is a good thing. If you had to come up with a criticism in the gardening world there could be one small issue. Don’t get me wrong, I am not complaining, just pointing out one of the consequences of abundant rainfall.

2015 may be remembered as the summer of disease. I cannot remember a period where there have been so many pathogens affecting our vegetables, trees, shrubs and flowers. Let’s take a look at some or the issues we’ve experienced.


Fruit just seems to get harder to grow, especially for those that want to go organic. This year we saw the typical peach leaf curl, apple scab and cedar apple rust. These happen just about every year. But we also had what I would call a record amount of fire blight on apples and pears. Newer to me was a widespread outbreak of pear rust. This disease not only attacked the edible pears but also the ornamental ones in the landscape. Peach trees were loaded with fruit only to be attacked by brown rot which decreases fruit quality.

Grapes and strawberries had issues. Black rot seriously put a dent into a good harvest. Strawberry fruits ripening in the spring rains developed soft fruit rots and many of the berries turned to mush before making it to the table.


The combination of rain and cooler temperatures slowed the development of summer vegetable crops. Tomatoes and peppers just seemed to sit there, not growing for weeks. Once they did, foliage leaf diseases such as early blight and Septoria leaf spot started attacking the lower leaves, weakening the plants. Vine crops such as cucumbers were covered with a couple of leaf diseases that riddled the vines, but fortunately did not cut down yields that much.

Trees and Shrubs

Just about every species of ornamentals have come down with a case of foliar leaf disease this summer. Leaf spots attacked oak, elm, maple, magnolia and hydrangea to name a few. The leaves were spotted and many withered and fell from the tree. The good news is that for the most part these are considered secondary and do not cause long lasting problems.

You might be asking, what is the relationship between the rainfall and disease. The answer is really pretty simple. Spores of fungal and bacterial pathogens require moisture to germinate and grow. The foliage is damp and the spores are just floating on the wind current. They hit and land on a leaf, start to grow and the result is the lesion or spot on the leaf.

That’s why when we talk about watering plants the recommendation is not to get water on the foliage or not water in the evening. The key to reducing disease pressure is to have the leaf dry out as quickly as possible. But when the moisture comes from Mother Nature there is really nothing that can be done. Treating to prevent these issues is also not that easy because in the spring the new growth continues to develop for several weeks. If you were to treat, the fungicide would be washed off by the frequent rain.

The good news is the vast majority of these issues tend to be more cosmetic and have no long lasting effects on the overall health of the plant. The bottom line is they just don’t look that great but will recover.