Agronomists say the biggest threat facing Manitoba sunflower growers is sclerotinia (head and stem rot), but the fungal disease can be managed with proper crop rotation and fungicide applications.
This formed part of the message of a presentation submitted to the Manitoba Agronomists’ Conference at the University of Manitoba in December. According to Troy Turner, an agronomist for the National Sunflower Association of Canada, pest management — which includes weed, insect and disease control — is the chief challenge facing sunflower growers in the province.
“The question each year is, ‘What type will be the worst pest?’ Will it be early insects or insects in the head? Will disease be the biggest pest?” says Turner. “But sclerotinia is the biggest issue sunflower growers are facing, especially confection sunflower growers.”
Turner says sunflower acreage was down in 2014 due to extreme moisture in the province’s southwest corner. “Over the past five to six years, acres have been down overall, but they’re now on the increase and looking to be back to a more normal number of 130,000 to 180,000 acres,” he says.
The southern region of Manitoba is known as Canada’s “Sunflower Belt” due to its long, dry growing season and soil fertility. This area produces over 90 per cent of the country’s total sunflower crop. A majority of that crop is confection-type.
Sclerotinia can be devastating for confection-type sunflower growers. Many major field crops are susceptible to the pathogen, including canola, mustard, edible beans, soybeans and flax, and when sunflower is grown near other susceptible crops the impact can be severe. Sunflower crops can develop either root infections, which cause stem breakage, or head infections, which impact seed yield and quality.
“Sclerotinia can be a big yield robber, and what’s worse, it can affect your quality so badly that some crops can be deemed unmarketable product,” Turner says. Although this is very rare, he says, the risk keeps Manitoba growers on edge.
According to Turner, one of the biggest problems with sclerotinia management in sunflowers is that the potential infection period can be extremely long, ranging anywhere from 10 to 14 weeks. “The fungicides we currently have only protect the crop for up to two weeks, and can only be applied once a season, or twice in the case of one product,” he says. “So this leaves a large window of opportunity for infection.”
Turner stresses that no one management strategy will be effective on its own. “Each field of sunflowers can be extremely different from the next, so treating them all the same can lead to disappointment,” he says.
However, proper management strategies can have a major impact in controlling sclerotinia. Chief among these is crop rotation. Turner says a one in four rotation, away from crops that are affected by sclerotinia, is very important.
Short rotations are not effective against sclerotinia due to the pathogen’s large host range and ability to live in the soil for long stretches of time. The disease’s impact is greatest when susceptible broad-leaf crops are grown consecutively. Its impact is least significant when diverse crops are used in a lengthy rotation.
Turner calls sclerotinia a “social disease,” meaning that it can spread very easily from one field or one crop to the next. “This can be a problem because if fields that are surrounding yours were susceptible fields last year and they belong to your neighbour this may cause you problems in-season,” he says.
As a result, growers should ensure that other sclerotinia susceptible crops are managed properly as well, and communicate with their neighbours as much as possible.
Fungicides should also be used as part of the grower’s management toolbox for sclerotinia. Turner says three fungicides that are labelled for suppression against sclerotinia have been registered in Canada over the last three years — Vertisan, Proline, and Lance.
Other management strategies include frequent and regular scouting, developing a good understanding of cultural and environmental triggers for sclerotinia, and keeping abreast of research related to the disease.
Besides sclerotinia, Manitoba growers will be on the lookout for downy mildew and rust this year, both of which can cause major losses in sunflower crops. The use of resistant varieties is key for downy mildew management. For managing rust in sunflower, scouting is key, as once the disease has taken root in a field there is no “curative” treatment.
Turner says that time and effort can pay off for sunflower growers, but it sometimes means a little extra attention to detail. “Sunflowers can be extremely profitable to a producer if they spend a little extra time ‘smelling the flowers,’ as I like to call it,” he says.