Virus Diseases of Cucurbits
Many viruses affect cucurbits and cause mosaic diseases. The most important of these viruses are cucumber mosaic virus (CMV), squash mosaic virus (SqMV), watermelon mosaic virus (WMV), zucchini yellow mosaic virus (ZYMV), and papaya ring spot virus (PRSV). The viruses differ in the range of host plants they infect, how they survive between crops, and the ways in which they are transmitted. Since control programs are based on this information, it is important that the virus or viruses involved be identified. This virus complex has caused growers in certain areas to stop growing these crops.
The symptoms caused by different cucurbit viruses are commonly very similar. It is impossible to identify these viruses with certainty based on symptoms alone. Usually special laboratory tests are required to correctly identify a cucurbit virus.
Leaves of virus-infected plants often appear mottled and distorted. Pumpkin plants infected early in their development (near or before the time of flowering) are severely affected and produce few fruit, and most of the pumpkins that are produced are likely to be misshapen or off-color. However, plants infected after fruit reach full size may not show any effect on yield or quality. Late-season pumpkins are especially prone to losses associated with virus disease.
Viruses survive in infected weed hosts. SqMV is seed-borne. These pathogens are spread by insect vectors (especially aphids) and mechanical operations that disturb plants and bruise leaves and vines.
Virus diseases of cucurbits can be controlled by planting resistant varieties (wherever available), using virus-free seed, cultural practices, and insect control. Early planted field tend to have less damage than those that are planted later. Weed control within and around field is important. Avoiding mechanical transmission of viruses is important. Insect control for reducing incidence of virus diseases is effective. However, Attempts to control insects for virus disease control may be futile, because insects may transmit the virus before insecticides are effective.