Battling Scorch And Shock In Blueberries

Blueberry Blues

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This past summer, two deadly viruses cropped up in Michigan: blueberry scorch and blueberry shock. In July, shock showed up at Michigan State University’s (MSU) Trevor Nichols Research Station in Fennville, MI, and scorch was found on three farms in the area, as well. While the viruses are unrelated, their symptoms can be similar, says Annemiek Schilder, associate professor of small fruit pathology at MSU. “You get blighting of the flowers and young leaves and such, except in shock it lasts a couple of years and the bush apparently recovers,” she says. “With scorch, it just keeps happening every year until that bush dies.”

According to Schilder, nearby farms have all been monitored and tested, and so far nothing has been found, which means it doesn’t appear to have spread. All the infected bushes will be pulled out this fall and winter. “They did a lot of backtracing from a nursery where it was originally detected, and they tested adjacent fields and have not been able to see any evidence of spread,” Schilder says. “We believe we have nipped the problem in the bud, but there will be at least three years of monitoring, and every year we’ll have to look to confirm that indeed the virus hasn’t spread in either case.”

The shock virus is spread via pollen transmitted by bees to healthy plants, and since all the infected plants are being removed, it would be extremely unlikely for it to spread next season. Blueberry scorch, on the other hand, is spread by aphids. However, Schilder says it hasn’t yet been determined if the aphids in Michigan are actually capable of spreading it. “That’s something we are investigating right now,” she says.

Be On The Lookout

For growers concerned about the virus, Schilder recommends taking precautions early on. Be on the lookout for symptoms like simultaneous blighting of flowers in the spring, which could be confused with diseases like botrytis or even a frost injury. “The difference would be that in the case of the virus, you will see one bush that is infected next to perfectly healthy bushes,” she says. “There might be more infected bushes, but it’d be very localized, and so with any of the diseases it’s unlikely that you would get one bush with entirely necrotic leaves and flowers with healthy bushes next to it.”

Preventive Measures

Schilder says the only way to truly prevent the viruses is to make sure you have plant material virus tested. In the scorch situation, the virus was linked to a specific variety — Legacy — which was not showing typical symptoms, so growers with that variety should be especially vigilant. Monitoring fields closely is also paramount.

She notes that if growers have purchased plants from the Pacific Northwest that were not virus tested, be particularly vigilant with those bushes, too, as both shock and scorch tend to occur in that region. This is the first time the viruses have showed up in Michigan, and this year, shock also was found in New Jersey, Massachusetts, and Connecticut.

So, why all the sudden outbreaks? “I think there’s a lot of planting going on, and people will get plants from any nursery,” Schilder says. “Sometimes they might go for the least expensive plants or wherever they can get sufficient numbers of the varieties they want, so it’s very much tied to national and international exchange of planting materials or distribution and sales.”

Overall, she believes this was an isolated find and that growers shouldn’t be overly concerned. They’ve surveyed about 50 fields where growers indicated there were some virus-like symptoms, but tests showed no signs of the viruses in any other blueberry growing areas in Michigan. “It’s not a huge concern, I think, as long as growers are aware and take precautions,” she says. “We know that the risk is there, and we just have to be vigilant.”