As Mink slips into retirement he cautions that the industry can't afford to let down its virus guard. With all of the importing of varieties people are expanding the diversity of germ plasm used for fruit trees, especially in apples. They are going outside the traditional germ plasm to get disease resistance, improved horticultural characteristics and using new rootstocks. As they change from the old varieties to new ones, viruses that were no problem in old varieties can cause very serious problems in some of the new varieties. We're seeing this in stone fruit and apples.
Some new varieties are very, very sensitive.
When people bring in new rootstocks and graft them with varieties that are infected with viruses, trees may die outright because the viruses kill these new rootstocks. We've found this situation now in some of the most popular new sweet cherry rootstocks that came from Germany. Some of these varieties die within a single year, or two years, when infected by viruses that are common in our orchards now. While viruses haven't been a general problem throughout the industry for a couple of decades, none have disappeared. Not one of the viral pathogens that created major economic problems for U.S. or Canadian fruit growers in the past has ever been eradicated.