The cause of decline in vigor without visible symptoms is very difficult to diagnose. Many possible causes exist, most of which will lead to visible symptoms over time. Some of the more common are:
Virus symptoms may appear only at certain times of the year but could affect the vigor throughout the year. Clean nursery stock should be used for establishing new plantings. European plantings have many viruses which are not found in the United States. These viruses should not be brought into the United States. Ribes plants coming from countries, other than Canada, must go through U. S. National Plant Germplasm Quarantine in Beltsville, MD, for virus testing prior to entry into the United States.
Whole plant decline can indicate the presence of a root pathogen such as Armillaria, Phytophthora, orVerticillium. Nematodes, root weevils, and under ground rodents can also cause root damage resulting in gradual plant decline or collapse.
The use of heavy equipment in the field can slowly compact certain soils, leading to a decline in plant vigor. Clean cultivated fields are most vulnerable.