Blueberry vigor 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. Viruses occur mainly in older plantings, or in plantings where clean nursery stock was not used. Special tests are required to diagnose the presence of virus, and these tests produce many false negatives.
Symptoms usually appear only after infections are severe.
Dig up plants and examine the roots for lesions, tunnels or feeding damage. Nematodes and grubs prefer lighter soils, whereas voles prefer heavy mulch and grassy alleyways. The presence of ants around the root system is usually an indication that mealy bugs are present on the roots. 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.