It’s So Galling!


I were pretty excited over the last week or two because I found not one, not two, but three examples of different kinds of gall diseases in trees and shrubs. Gall #1, which I mentioned last week, is cedar apple rust.

The second disease that I found recently is Phomopsis gall on forsythia. I saw this disease in a forsythia shrub row just around the corner from my house about a week ago. I have seen this disease but don’t know too much about it, and, apparently, I am not alone. I looked up some information, and there is not much. Back when the bacterial disease crown gall was being investigated, galls were discovered on plants such as viburnum, oak, maple, elm, rhododendron, and forsythia. However, these were not caused by the crown gall pathogen but rather a fungus in the genus Phomopsis. Little is known about the life cycle, how it spreads, and we do not even have an identification to species, just to the genus. The individual galls usually live a few years then die out. The disease can cause some twig dieback, so pruning them out is a good idea. Sterilize tools in a 10% bleach solution or rubbing alcohol in between cuts.

The third gall disease I recently found is black knot. Black knot causes thick, warty, irregular growths and occurs on cherries, plums, and other members of the Prunus group.  The fungus survives the winter in the knots, and in springtime spores are spread to new, succulent growth during wet weather leading to new infections. Black knot can eventually trigger severe dieback and can cause major losses in commercial plum or cherry orchards. When it comes to home plantings of fruiting or ornamental cherries, plums, etc., sanitation is key. Scout trees in the winter and prune out affected branches before bud break, cutting a few inches below the visible gall. Don’t drop the prunings to the ground burn, bury, or discard them or they will serve as a source of spores just as if they were still in the tree.

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