Crop advisers in North Dakota are keeping a watchful eye on the northward advance of soybean cyst nematode (SCN) — and so should Manitoba growers, said a cropping systems specialist.
SCN, a round worm that parasitizes roots of soybean and can reduce yields anywhere from 15 to 30 per cent before ground symptoms are present, has been in the neighbouring state for at least a decade and much longer in other parts of the U.S., said Greg Endres, area cropping specialist with North Dakota State University Extension Service, while speaking at a Northstar Genetics’ grower information day in Morris March 23.
Endres shared survey data showing the incidence and evidence of SCN’s steady migration in a northward and westward direction from the southeastern portion of the state. Maps reveal its documented presence in North Dakota counties including Cavalier, Towner, Rolette and Renville. It’s at a point where it’s likely crossing into Manitoba, Endres said.
“I can only speculate but there is very high probability that SCN exists in Manitoba.”
The good news is that there’s still plenty of time to monitor and manage the disease here.
That essentially means not waiting to see the above-ground symptoms present before deciding to do something about it, he said.
SCN which causes yellowing in the plants can be confused with drown-outs or iron chlorosis. The right approaches include a mix of basic prevention and continuous monitoring with soil testing, the specialist said.
Prevention means keeping it out using clean equipment. But those activities in reality are “easier said than done,” said Endres, adding that wind, water and waterfowl commonly transport the disease.
It’s monitoring that’s key to identify SCN presence and the far most effective way to detect it is by soil testing. The recommendation is to do this around harvest time, or just before and take a soil sample from right in the root system of the plant where you have the best chance of finding SCN eggs. Sampling is best done on suspected areas such as field entrances, fencerows, flooded areas or alkaline areas.
“Soil sampling is by far the best way to give us an early alert so SCN can be effectively managed,” he said.
Managing SCN involves avoiding tight rotations, including edible beans, and using resistant varieties.
Crop rotation can help to reduce the egg levels but be mindful that rotation won’t eradicate SCN, said Endres.
There are also seed treatments available and more products are being tested and entering the marketplace all the time. But the debate continues as to how effective these are, Endres said.
“We don’t want those used alone as a strategy for cyst, but in combination with resistant varieties they may be useful.”
While SCN is a new disease, it’s far from the only one growers grapple with.
Endres said phytophthora, a disease that develops with wet and warm soil conditions is North Dakota’s No. 1 root rot concern.
“And it probably will be yours sometime in the future,” he added.
Field scouting is very important, said Endres. “The disease can occur throughout the soybean growing season.
Signs of phytophthora are water-soaked lesions at the base of the stem which will move upwards. Another sign it may be present is if the plant is dead but the leaves remain attached. It will occur in patches or sometimes single plants, he added.
Varietal selection is the key management strategy for phytophthora.
“The key is to use varieties with resistant genes as a major way to manage this disease,” he said. Seed company and university information includes resistance genes present (or not) in soybean varieties.
“There are many different races of phytophthora so if the disease is present at substantial levels in the field, then it would be good in the future to change varieties, that have a different type of resistance in them, also selecting varieties having good field tolerance to the disease.”
Endres said there is one race of phytophthora present right now in N.D. for which there are no genes to combat it. It’s been detected in the extreme southeastern portion of the state.
“We’re concerned about that.”
There are effective seed treatments for phytophthora, but protection only lasts during early plant establishment, not season long.
Endres also spoke about the use of fungicides and how various row spacing scenarios can impact sclerotinia or white mould.
Growers should be aware that only fairly high levels of the disease merit the use of fungicides from an economics perspective, he said. With dryland soybean, the disease does not consistently occur each year in N.D. at levels warranting economic use of fungicides.
It is challenging figuring if fungicide should be applied or not because incidence level must be predicted prior to disease symptoms present in the field, Endres said.
A reference he offered growers at the Morris meeting is that a 20 to 40 per cent sclerotinia incidence in a non-treated check would indicate it would have been economical to use a fungicide
Endres also presented detailed research related to row spacing to manage for sclerotinia. Commonly, growers will opt for the wider 30-inch rows to reduce disease incidence, he said. However, wide-row soybean without white mould will have lower yield potential across years.
“With the disease and narrow rows, the disease likely will bring yield potential down but probably just to the yield level of the wide rows without sclerotinia,” he said. “It’s a balance you must consider.”
Researchers in N.D. recommend, with a potential of moderate sclerotina incidence, going with 21- or 22-inch rows.
“I really question going to wide rows only because of sclerotinia management because in the long run I would speculate that you’re going to lose yield and ultimately profit.”
More information can be found on the website of the North Central Soybean Research Program at www.ncsrp.com/.