Brown rot bites into cherry, berry yields

Control available | Chokecherry, sour cherry and saskatoon berry growers can use the same fungal applications

Losing an intensely managed crop can be disastrous in the fledgling prairie fruit industry, especially for new businesses.

The latest threat is a new infection that hit sour cherries last year.

“It wiped out some crops last fall,” Saskatchewan’s provincial fruit specialist said.

However, Forrest Scharf had good news for producers attending the Saskatchewan Fruit Growers’ Association’s recent annual conference held during Crop Week.

Regional research into disease management is delivering advice they can use on their farms starting this spring.

A new disease started showing up in Saskatchewan sour cherry crops in the fall of 2011 after two years of above normal moisture. Growers reported dead blossoms and large crop losses.

Scharf investigated and identified the culprit as American brown rot, also known as brown blossom rot.

Brown rot, the product of the fungus monilinia fructicola, had been a problem in North Dakota’s chokecherry crops in the 1990s.

“It was considered to be new here, but so is the (sour cherry) crop and largely so are the conditions,” Scharf said.

It was initially thought to be one or two isolated incidents, but provincial cherry growers realized the problem was widespread after receiving extension information about the disease.

Producers noticed some incidence of the blossom rot in the spring of 2012, but it was not until closer to the August harvest that they felt the full effect of the disease.

“It was very severe for many growers,” said Scharf.

Brown rot develops during early bloom periods if enough moisture is present and temperatures are moderate.

The blossom blight spends the winter as shriveled pieces of infected fruit hanging on the shrub. It can also remain in cankers and on twigs, waiting for spring.

The spores (condidia) develop if the weather is cool and moist and move via wind and rain to blossoms and nearby branches. The blossoms die and the plant may develop mummy berries. The cycle then starts over again.

The disease appears to be endemic on the Prairies, hosted by the numerous chokecherry bushes that populate farms throughout the region.

“We just tend to be a dry climate and so we don’t see these problems that often,” said Scharf.

Moose Jaw area producer and processor Sandra Purdy of Prairie Berries said the pest can also hurt saskatoons.

However, most commercial producers already spray for entomosporium leaf and berry spot disease, and the brown rot is killed along with other more damaging pests.

Spray applications cost about four cents per harvested pound of berries, and Purdy said the more established saskatoon plantations wouldn’t dream of not using them.

Scharf said sour cherry producers will likely have to move to a two or three application strategy to deal with brown rot, provided the conditions are favourable to disease development.

“We are pretty sure we can avoid the problem with fungicide applications,” he said.

Scharf said the large amount of inoculum that has built up after three wet seasons will force producers to make spraying a routine procedure.

Recent research funded by the fruit growers association has experimented with timing of fungicide applications in saskatoons to control blossom-period diseases and will likely be just as effective with brown rot in sour cherries.

Propiconazole (Jade-Topas) and a mix of boscalid and pyraclostrobin (Pristine), when used in split applications with a “light application just ahead of blooming and a second during bloom and potentially one of Pristine after blooming, should deal with the problem and potentially other fungal issues in the crop and could also extend shelf life of the harvested fruit,” Scharf said.

“An organically acceptable solution that can suppress the disease is Serenade Max. Whatever you use, you should try to use more than one application and of different (active ingredients) to prevent tolerance building up.”

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