Three tree fruit organizations put on grower training workshops in Washington State in March to raise awareness of postharvest storage diseases associated with Manchurian crab apple pollinizing trees. The diseases speck rot and sphaeropsis can be spread in apple orchards by water contact with unmanaged Manchurian crab apples.
In the videos below, Tom Auvil from the Washington Tree Fruit Research Commission talks about the problem and the proper pruning method growers can do to mitigate the diseases.
The reason growers need to be concerned about these diseases is that they can infect commercial apples in the orchard and cause postharvest storage decay. These diseases are quarantined by China, who now requires that Washington orchards have pruned pollinizer trees to qualify apples for export.