When one thinks of the typical geranium diseases, the fungal root rots (Pythium and Rhizoctonia), Botrytis infections of the flower, leaf, and stem, plus the catastrophic bacterial wilt disease Xanthomonas are at the top of the list. With plant breeders having implemented clean stock programs and regular virus screening, rarely does one observe ring spots and mottling of a viral infection.
However, when two North Carolina State University researchers recently visited a grower, they found three plants, all different cultivars from the same breeder, with ring spots and mottling. With distinct ring spots on the leaves, it was easy to know it was a virus, but it was uncertain as to which one.
A recent e-GRO alert highlights why the grower was fortunate that only three plants exhibited viral signs. Given the oldest leaves were asymptomatic, the severity of the symptoms that had developed in only four weeks after transplanting, and that the problem was observed on three different cultivars, it was doubtful the infection had occurred in the mother stock. Testing protocols at the mother stock facilities also help to avoid problems. More likely infection occurred during rooting or at the greenhouse that reported the problem.
Both impatiens necrotic spot virus (INSV) and tomato spotted wilt virus (TSWV) are thrips vectored, with the Western flower thrips (WFT) being the most common thrips species observed in greenhouse operations. It has been observed that WFT will feed on geranium leaves and flowers, but it does not seem to be a preferred host.
Learn more in the original e-GRO alert here.