Disease Management Starts With Resistant Varieties

Even if you have no intention of spending money on a foliar fungicide treatment, you still want to know what diseases you have in a field. This is one reason why scouting is important. Certain diseases are more common in certain areas, often as a result of wind patterns, typical moisture, and the predominance of host crops. (Lots of barley in a region usually means lots of barley disease.) When you know what diseases are most common — and most costly — on your farm, you can choose varieties with the greatest degree of resistance.

Scouting your crops and choosing resistant varieties are two critcal factors in disease management. Two others are crop rotation and timely spraying.

Randy Kutcher, research scientist with Agriculture and Agri-Food Canada in Melfort, Sask., outlined these four steps in a presentation at Western Canadian Crop Production Show in January.

SCOUTING

You want to scout at least twice during the growing season. The first time is during crop development to check for pathogens that may need spraying. The next time is pre-harvest — even though it’s too late to spray — to see what you’ve got and whether it’s something to look for next year.

Standard scouting recommendation is to check 10 plants from 10 random locations throughout the field. Record what diseases you see, how many plants are infected and how much of each plant is infected. Record these details along with the crop growth stage. Keep this information as a log of disease presence in your farm over the years.

Some diseases you need to control before they show up, so if you know your farm has a history of this disease, it makes you more alert. If you see damage in a pre-harvest scout one year, you might be more prepared to spray in other years.

SPRAY ING

Sclerotinia of canola is one disease you need to spray for before it shows up. That’s because you need to get the fungicide on the petals. You protect the petals from the pathogen so that when the petals fall into the canopy, the pathogen isn’t present on the petals and therefore can’t infect the plant.

There are no sclerotinia-resistant canola varieties. Pioneer Hi-Bred has a new variety with improved tolerance, but you’ll still have to spray if conditions are right for intense sclerotinia infection. And rotation doesn’t really work for sclerotinia. Sclerotia can last a long time in the soil, and spores blow into a field from great distances.

Fungicides applied on the petals can be an effective strategy for disease management. But it still takes some analysis to judge the risk, and decide whether a spray — which costs $20 to $27 per acre — is effective and economical, Kutcher says.

He recommends you follow the sclerotinia checklist, which you can find online at the Canola Council of Canada website.

When you do spray, Kutcher recommends you leave a check strip to see how the spray worked. It doesn’t have to be a scientific study. Just leave a strip unsprayed and then go back during your pre-harvest scout and compare infection levels. If you have a yield monitor on the combine, you can also compare yield differences.

ROTATION AND RESISTANCE

Choosing varieties with improved resistance and using crop rotation are effective tools for cereal disease management in particular. If you do choose to grow barley back to back, you can reduce the effect of disease by rotating to a different barley variety the second year. Kutcher credits Kelly Turkington with Ag Canada in Lacombe for making this discovery.

But even with resistant varieties and with good crop rotation, you still want to scout for cereal diseases. You especially want to protect the top leaves from disease. If you let diseases destroy these top leaves, you lose photosynthetic area. “Destroyed photosynthetic area means yield loss,” Kutcher says.

Scout at flag leaf emergence. The earlier the disease appears and the longer it lasts, the bigger the yield loss, he says. Read up on the diseases you see. Find out the best control timing, products and rates. And again, if you want to know whether a fungicide works, leave a test strip.

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