For most pumpkin growers, it is too late to take any corrective action against diseases for the 2023 crop. However, it might be wise to determine what disease problems were present during the 2023 season. This article will discuss two relatively unusual virus diseases of pumpkin.
Recently, I visited several pumpkin fields in northern Indiana. I found what appeared to be virus symptoms in many of the fields. It is not unusual to find virus symptoms on pumpkin plants this time of year. The most common viruses to find in pumpkins in the Midwest are the potyviruses: Papaya Ringspot Virus, Watermelon Mosaic Virus, and Zucchini Yellow Mosaic Virus (plant virus disease are named for the first host they are found in). However, the viruses that I found in my trip to northern Indiana in mid-September were Tobacco Ringspot and Squash Mosaic Virus. Although the symptoms of these viruses appear similar to the common potyviruses, the biology and management of these diseases vary.
Tobacco Ringspot Virus-Whereas the usual potyviruses mentioned above are transmitted (vectored) by aphids, Tobacco Ringspot Virus (TRSV) is vectored by the dagger nematode. Dagger nematodes feed on the outside of the roots of a number of different crops. It isn’t clear how much damage the dagger nematode causes by feeding, but it is known that this nematode may also transmit viruses.
Managing the Tobacco Ringspot Virus can be difficult. TRSV can be a problem in weedy areas, especially areas that have been meadows or pastures for years. If these areas are intensely cultivated, weeds that may be a reservoir of the disease may be eliminated. Unfortunately, there are no sources of resistance to TRSV.
Squash Mosaic Virus. This virus can be transmitted through seed. Although most seed is screened for this virus, the virus transmission rate can be from 0.1 To 10% in some circumstances. Also, the virus can be transmitted to volunteer plants at the edge of the field. Once in a field, the virus can be spread from plant to plant through the feeding of the cucumber beetle.
The first step in managing Squash Mosaic Virus (SqMV) is to use seeds free of the virus. Although most seed is tested for the virus, it might make sense to check with your seed supplier. Do not allow pumpkins to volunteer along fence rows since this might lead to transmission for the next crop season. It may make sense to limit beetle populations if SqMV is present. Host resistance to SqMV is possible in squash and pie pumpkin but currently is unavailable.
Most pumpkin virus diseases in Indiana are caused by the potyviruses mentioned above. For these viruses, planting early to mid-June will allow the fruit to develop before virus pressure becomes severe. It usually does not make sense to try to control the aphids that spread potyviruses since these viruses can be transmitted in seconds. It is my experience that viruses on pumpkins do not usually result in significant economic damage.
It is not clear to me how frequently Tobacco Ringspot Virus and Squash Mosaic Virus may be present in Indiana. It may make sense to keep track of virus symptoms in 2024 to determine what virus is present.