This virus, abbreviated TSWV, has become a serious problem for some Iowa tomato growers in 1994. While most fields we have seen have only a few symptomatic plants, some fields have more than one-third symptomatic plants. Because plants showing symptoms this early in the season seldom produce marketable fruit, this means a yield loss of at least one-third. According to unconfirmed reports, some TSWV-stricken fields have been plowed down.
Symptoms vary depending on plant age, environmental conditions, and other factors.
Plants infected early in the season tend to be stunted, often dramatically, and may fail to set any fruit. These symptoms are often the first ones that catch a grower's eye. Typical foliar symptoms include yellowing and a bronze or purplish cast, especially in the upper leaves. Eventually, the discolored leaves wilt and die, at which point TSWV infection is often mistaken for bacterial or fungal diseases. If plants become symptomatic after fruit set, immature fruit sometimes show green or brown, concentric rings with raised centers.