Only a weakly virulent strain of the fungus was found in the seed. Apparently infection by the local, nonvirulent strain occurs with some regularity, but virulent strains infect the seed only in unusually wet summers. It produces ascospores that are ejected into the air, and these spores can infect the seed pods, increasing the danger of having infected seed. Bonman concluded that the ability of virulent strains to persist in the seed-producing regions of the West is not known. The presence of avirulent strains in seeds complicates seed sales.
Most countries require a phytosanitary certificate.
If Phoma is found on the seed it should be tested for virulence. If avirulent, the seed is still safe to use. If virulent, the seed should be condemned. All seed labs are not equipped to perform the virulence test. The studies of Bonman confirmed the avirulence of strains that persist in the Pacific Northwest.