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.

Voles, Hares and Moose

These are the most common and problematic "pests" on trees in the interior of Alaska. For information about how to avoid damage, see our Tree Planting and Care page.

Snow

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 branches 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. We recommend going around the trees and loosening the trapped branches in early March in Fairbanks. That will help with the snow pack ripping off branches.

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

Disease

This site from the University of Minnesota allows you to click on symptoms and find what might be wrong with your tree. There is information on a variety of different fruits on this site.

Powdery Mildew

We believe that the trees shown above are exhibiting symptoms of powdery mildew. In 2022, those most affected were those that had been damaged by snow during that rough winter. In previous years, a cold snap in the midst of bloom time seemed to contribute. One treatment is to spray with sulfur, beginning during the tight bud phase.

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

Fire Blight

This is a common and destructive bacterial disease that has 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.

Anthracnose

We believe that this fungal disease is present in orchards in the Fairbanks area. We have seen cankers on branches and spots on leaves, but so far have been lucky enough not to see it affecting our apples. To prevent the spread of this infection we prune away and dispose of infected branches and spray each spring with Bordeaux Mixture

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.

Sunscald

Sunscald damage can look a lot like sunburn, but it can also be more subtle.

This is the south side of a tree several years after suffering from sunscald. You can see that the bark on this part of the tree was completely killed and eventually fell off.

Sunscald usually occurs on the south or west side of the tree trunk. Sunscald is most common on tree species that have thin bark, like most fruit trees.. Because younger trees have thinner bark, they are the most susceptible. The damage is caused by large temperature fluctuations during the early spring months. Sunscald can occur when the bark is exposed to warm daytime temperatures followed by freezing temperatures at night. The sensitive cells in the cambium are killed when they fill with water during the warmth of the day which then freezes and expands at night. Skin may blister, crack, and peel away. Milder symptoms include discolored reddish or brownish bark, often somewhat sunken in appearance. As well as killing cambial cells, damage from sunscald can also provide an entry point for disease causing fungi and bacteria. Reflective surfaces (in Fairbanks, this is most commonly snow) contribute to sunscald by reflecting additional light onto the tree's bark. To test if damage has occurred, cut or scrape a small section of the outer bark away. If the inner bark is soft and green, then it is still alive.
Sunscald can be prevented by shading trees in the spring or by painting them with a light colored paint (this can be dilute latex paint or white wash) so that the bark absorbs less sunshine. While it is impossible to paint every twig, we have found that by painting the main trunk and limbs of younger trees, the most damaging sunscald can be prevented.

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.

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

Scorch

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

Rose Sawflies on Saskatoons

Rose sawfly larvae have 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. We've tried treating with Neem oil with some success, but not total success. The larvae eventually pupate and overwinter in the leaf litter below the tree.One year we put diatomaceous earth around the base of the tree but this strategy was unsuccessful, What has actually seemed to work best is leaving all the fallen leaves on the ground through the winter, then raking well in the spring. This seems to remove most of the overwintered pupae before they can hatch into adult flies and lay eggs on the leaves. It isn't a perfect cure, but it is easy and it seems to work better than the other things we've attempted.

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

Rust on the bottom side of the currant leaves.

Rust on Red Currants

In 2017 and 2018 we had very damp springs and this weather led to rust on our red 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. We see this same rust on wild roses, and it does not appear to affect the black currants or gooseberries.

A Mystery

Photos are from June 2022

We really don't know what causes these holes on our plum leaves. Do you have any ideas?

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