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A crop-by-crop rundown on sclerotinia control

Variety and fungicide are key for control, but for sunflowers there’s only one option — rotation

The good news is the hot, dry summer made sclerotinia somewhat scarce in canola fields this summer, but there was a minor downside — there weren’t many examples to show farmers attending a sclerotinia control session at this year’s Crops-A-Palooza, even in the inoculated demonstration plots at the Canada-Manitoba Crop Diversification Centre (CMCDC) here. But they still got plenty of useful information about managing the fungal disease which will no doubt return in future.

Canola Council of Canada agronomy specialist Nicole Philip was disappointed that she couldn’t actually show the comparisons between sclerotinia-tolerant and susceptible varieties or the effect of fungicide application timing, but had some take-home messages for producers.

Varieties and fungicide

“There are varieties out there that have some tolerance to sclerotinia,” said Philip. “They are not resistant but they can certainly help in some of the higher-pressure years.”

When it comes to fungicide timing, most are registered for application from 20 to 50 per cent bloom on canola. Philip said the 10 per cent flower stage is probably the earliest for application because the aim is to cover the flower petals which are the food source for sclerotinia spores.

“For control, if you’re spraying a fungicide, the earlier the better, usually at that 20 or 30 per cent flower, keeping in mind that the fungicide application is to cover the petals that’s the food source for all the sclerotinia spores that are being released,” said Philip. “Fungicide at 50 per cent flower is the end of the window and is too late in general, and we also want to make sure that there’s no pre-harvest concerns for using products closer to that 50 per cent flowering.”

Moisture is the biggest factor in sclerotinia incidence and severity, and infection starts in the leaf axis and works its way down the plant stem. A dense plant canopy provides a warm, humid environment that is ideal for the development of sclerotinia, which causes lesions on stems that prevent the plant from accessing the nutrients and water it needs.

“What’s really important is the moisture situation leading up to flowering, and of course crop rotation,” said Philip. “Sclerotinia has multiple hosts and we’ve grown many of them in Western Canada so it comes down to the disease triangle. You need the environment, the infection source and the host plant. For sclerotinia, environment is the biggest pressure.”

Reducing seeding rates for thinner plant stands might help reduce canopy moisture, but could mean flowering takes longer, so rainfall could be more of an issue. Either way there’s no substitute for careful monitoring of moisture conditions, said Philip. “That means going into the field, not just driving by or keeping an eye on the radar, it really is going in and seeing how moist that canopy is,” she said.

Fungicides don’t pay in soybeans

Managing sclerotinia in soybeans can be tricky, and the Manitoba Pulse & Soybean Growers has a network of on-farm plots across Manitoba where it is evaluating the effect of row spacing and fungicides on sclerotinia.

Jordan Karpinchick, a GIS technician with Tone Ag Consulting, has been evaluating the plots since 2014 and said it’s pretty hard to pencil out a benefit right now.

“Using fungicides on soybeans is not a feasible option at this point in time. We have seen a statistical yield response about seven times out of 41. Only once or twice have we broke even or made some money by applying fungicide. Where the costs are for the products at $24 to $25 an acre, it just doesn’t pencil out for soybeans.”

Row spacing, however, does appear to have an influence on sclerotinia, with narrow spacing increasing incidence of sclerotinia in soybeans but not necessarily decreasing yield. “As we widen the rows, more air flows in between and it seems to keep levels quite low,” said Karpinchick. “There are many studies that show narrow row spacing in soybeans yields more, so even though there is more of a risk for white mould, it isn’t the yield robber.”

Plant early and rotate crops

Two things important for preventing sclerotinia in soybeans are planting as early as possible and crop rotation, Karpinchick added.

“What we’ve seen with the on-farm network studies, your best yield potential is usually planting earlier than later. Waiting until the third or fourth week of May sometimes isn’t the best option for yield,” he said.

Growing soybeans on canola, another highly susceptible crop, isn’t advisable. Growing soybeans on soybeans will increase the risk of not just sclerotinia, but phytopthora and fusarium root rot as well. “Eventually it catches up with you,” said Karpinchick.

Dry bean seeding density

Laura Schmidt, extension co-ordinator with the Manitoba Pulse & Soybean Growers, had some surprising results in the studies she conducted for her master’s degree on the effect of row spacing and seeding densities on yield and sclerotinia pressure in dry beans.

Pinto beans planted in narrow, 7.5-inch rows yielded 80 per cent more than those on 30-inch rows in the studies, but as plant density increased from 40,000 plants per acre to 200,000 plants per acre, there was very little yield change.

“Typically, in a crop what we expect to see is as you increase density, you have corresponding increase in yield until a plateau is reached,” said Schmidt. “Our dry beans weren’t doing that.” Average recommended seeding rates for pinto beans are 90,000 to 100,000 plants per acre.

When it came to sclerotinia, higher seeding densities significantly increased the risk of white mould pressure, but, counterintuitively, because the assumption is that there is less airflow in narrower rows causing more likelihood of sclerotinia, the wider-spaced rows were hit harder with the disease than narrow rows.

“Each row had the same plant population of 120,000 plants per acre, but there was more space in the row between plants in the 7.5-inch row than in the 30-inch row where they are almost touching,” said Schmidt. “You get plenty of airflow in between the 30-inch rows, but as soon as you have sclerotinia in that row, it’s just moving from plant to plant so much quicker because they’re so much closer together, at least that’s our thinking right now.”

There was still a lot of white mould present in the narrow rows, but the yield increase more than compensated for the disease, she added. “We’re seeing that in North Dakota and Saskatchewan work as well, that the narrow rows are just doing so much better than 30-inch rows despite the disease pressure,” she said. “It really is more of a plant population story with disease pressure in dry beans.”

Sunflowers — rotation only

With no fungicides currently registered for sclerotinia on sunflowers, and no resistant varieties, the only management option available for growers right now is crop rotation. “You need at least four years between susceptible crops, so if you’re really heavy into canola, it’s probably a bad choice to be also really heavy into sunflowers,” said Elizabeth Karpinchick, a crop production adviser with Tone Ag Consulting. “Sunflowers can get infected basically their entire life cycle, so, you only start seeing it once the flowers come out. You can get an infection in the root, stem, leaves, head, flowers, all over the place. They’re just very susceptible.

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