Pests, Diseases, and other Problems

We are lucky that in Alaska we have fewer pests and diseases to deal with than fruit growers in other parts of the country and the world. Unfortunately, we are not completely immune to these problems. Here is some information on problems that we or other fruit growers in the area have experienced.


We have had quite a lot of damage from snow. Early in the winter heavy, wet snow falling on trees with full leaves results in broken branches or tops snapping off. We have also had become trapped in the snow. Those branches can either be eaten by voles or be ripped off the trunk in the spring when the snow pack settles. I recommend going around the trees and loosening the trapped branches in early March in Fairbanks, at least that will help with the snow pack ripping off branches. Of course that is no longer a problem for many of our trees!!


This site from the University of Minnesota allows you to click on symptoms and find what might be wrong with your tree. There are pages for apples, ribes (currants), prunus (plums and cherries), saskatoons (service berries), as well as other plants you might be growing.

Fire Blight - This is a common and destructive bacterial disease that has recently appeared in Fairbanks and the surrounding area. Pears are very susceptible and apples can also become infected.

Fairbanks Daily News-miner article about fire blight - from 2015. Details of local infected trees as well as treatment.

Article from - Excellent article with lots of images, advice on treatments, etc.

Nutrient Deficiencies - Nutrient deficiencies can cause problems to both leaves and fruit. Potassium deficiency is a problem we suspect in some of our trees.

Diagnosing and Avoiding Nutrient Deficiencies - Article by Eric Hanson of Michigan State University

Powdery Mildew -This year, for the first time, we had powdery mildew on some of our apple blossoms and leaves. We are guessing that the spores are always present but that we don't usually see symptoms. This year we had a period of cold weather after the leaves and blooms had begun to open. They trees stopped growing allowing the mildew to gain a foothold. When warmer weather returned, the trees were able to outpace the infection. We had also sprayed with sulfur.

The Ontario Ministry of Agriculture - information on the biology, identification and management on powdery mildew in apples.

Two Prairie Sun Apples. The one on the left exhibits water coring.

Water Core

Water core is the accumulation of water and sugar between the cells of the apple, in spaces that might normally be filled with air. The apples are sweeter and denser but do not keep well, because the extra sugar between the cells leads to fermentation. One cause of water coring is a too high ratio of nitrogen to calcium. This can be either because of an excess of nitrogen or a deficit of calcium. Apples ripened too long. or ripened in sunshine are also more prone to water coring, as are large apples from young trees.

Water cored apples can be quite tasty, and are very juicy. They are chewy and sweet when dried, but they don't keep well and look unappealing to many.

Silver Leaf - This is another fungal infection that we have seen in Fairbanks. While it apparently can kill trees, it can also be something that trees can live with for a long time with no apparent damage. You can find more information in this article from Michigan State University.

Scorched leaves on an apple tree growing in a small pot and not getting enough water (click on the image to enlarge it).


Hey, guess what? Trees that are not getting enough water in hot weather will experience scorched leaves and eventually will die. The problem can be exacerbated by a small pot or root damage. Yes, I realize this sounds quite obvious, but we were watching for signs of wilting and, seeing none, thinking the trees were doing fine, until this happened. They don't wilt, apparently.

Sawfly larvae on Saskatoon leaves

Sawfly larvae on Saskatoon leaves

Rose Sawflies on Saskatoons

This has been a problem on our Saskatoons (Service Berries) for several years, although some years are worse than others. They eat the leaves, skeletonizing some and eating others almost completely, as you can see in the picture below. We've tried treating with Neem oil with some success, but not total success. This year I put diatomaceous earth around the base of the tree, hoping to stop the larvae before they could attack the tree, but this strategy was also unsuccessful.

Rust on the currants themselves (above) and on the currant leaves (below)

Rust on the bottom side of the currant leaves.

Rust on Currants

In 2017 and 2018 we had very damp springs and this weather led to rust on our currants for the first time. While this looks really bad, some of the berries were not affected and others seemed to survive, so we actually got a decent crop.