Raspberry Mosaic Virus
Raspberry mosaic virus is one of the most common and damaging diseases of raspberries, but it’s not caused by a single pathogen. The raspberry mosaic complex includes many viruses, including Rubus yellow net, black raspberry necrosis, raspberry leaf mottle and raspberry leaf spot virus, which is why mosaic symptoms in raspberries can vary significantly. Mosaic virus on raspberry usually causes a loss in vigor, reduced growth and a significant loss of fruit quality, with many fruits becoming crumbly as they mature. Leaf symptoms vary from yellow mottling on developing leaves to puckering with large dark green blisters surrounded by yellow halos or yellow irregular flecks throughout leaves. As weather warms, mosaic symptoms in raspberries may disappear entirely, but this doesn’t mean the disease is gone – there is no cure for raspberry mosaic virus.
Preventing Mosaic in Brambles
The raspberry mosaic complex is vectored by very large, green aphids known as raspberry aphids (Amophorophora agathonica). Unfortunately, there’s no good way to prevent aphid pests, but careful monitoring will alert you to their presence. If any of the raspberries in your patch carry any virus in the raspberry mosaic complex, raspberry aphids may vector it to uninfected plants. Once these pests are observed, immediately treat them using insecticidal soap or neem oil, spraying weekly until the aphids are gone, to slow the spread of raspberry mosaic virus. A few raspberries appear to be resistant or immune to the effects of the virus, including the purple and black raspberries Black Hawk, Bristol and New Logan. Red raspberries Canby, Reveille and Titan tend to be avoided by aphids, as does the purple-red Royalty. These raspberries can be planted together, but may silently carry the virus into mixed beds with susceptible varieties since they rarely show mosaic symptoms. Planting certified virus-free raspberries and destroying virus-carrying plants is the only control for mosaic virus on raspberry. Sterilize your tools between plants when thinning or pruning the raspberry brambles to prevent spreading hidden pathogens to uninfected plants. Also, resist the temptation to start new plants from your existing brambles, just in case your plants have contracted a virus in the raspberry mosaic complex.
