Virus Diseases of Geraniums.

One of the most common disease problems associated with geraniums is caused by viruses. Plant viruses are relatively common in geraniums, however in most cases they are not responsible for any major economic damage.

The plant viruses that are most commonly found to infect geranium are tomato ringspot virus (TomRSV), tobacco ringspot virus (TRSV), pelargonium flower - break virus (PFBV), cucumber mosaic virus (CMV), and tobacco mosaic virus (TMV). Of these five, TomRSV, TRSV, and PFBV appear to be the most common. I hope that you noticed that I didn't mention impatiens necrotic spot virus (INSV) or tomato spotted wilt virus (TSVW). Although geranium is an experimental host, these two viruses are very rarely found in geraniums. That has to be good news to anyone who grows geraniums.

The symptoms associated with viruses in geranium are varied, but the most common symptoms are yellow ring spots and leaf mottling. Leaf mottle is caused by PFBV (Figure 1). This symptom is very suttel and tends to be more visible during the early stages of production, especially when greenhouse temperatures are cool (60 - 70 degrees F). The symptoms of this virus appear as light colored spots on the leaves. When the zonal portion of the leaf is affected the symptoms are much easier to recognize. Yellow ring spots are caused by TomRSV and TRSV. Like PFBV, these symptoms are more evident during cooler temperatures. However, unlike PFBV they are much easier to recognize. The symptoms appear as yellow ringspots of various sizes (Figure 2).

Other virus - like symptoms can appear on geraniums from time to time. Things like genetic variation and a disease called yellow net vein are relatively common (Figure 3) and (Figure 4). Although some feel yellow net vein is caused by a virus, it has never been proven to be the case.

Even though geraniums show symptoms of virus infection from time to time, in most cases the viruses are not a problem and the infected plants are sellable. Evidence of virus infection should not be a major cause for alarm. Once temperatures start to warm and the plants start to grow rapidly, the symptoms tend to disappear. The plants are still infected mind you, however the symptoms are no longer evident.