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The value of oat and barley crops in wheat rotations

Most Ontario farmers fully understand the importance of rotating crops, especially when trying to avoid Fusarium.

“Ontario seems to be the epicenter for Fusarium, at least in wheat,” says Peter Johnson of OMAFRA. “It seems as if the fact that we’re surrounded by the great lakes, we have lots of corn out there in the countryside, and our weather conditions – the crops in the area seem to always make Fusarium the bullet that we’re trying to dodge. It is the number one issue in wheat production, bar none.”

Dr. Trevor K. Smith, a professor in the Department of Animal and Poultry Science at the University of Guelph, has devoted his entire career to the study of feed and food toxicology including the effects of feeding anti-nutritional factors such as Fusarium mycotoxins. Much of the information for this article has come from his research.

Fusarium head blight (FHB) is a mould or fungus that lives and overwinters in the soil. When the conditions are favourable, the fungus will grow in the soil and move up the stock of the plant, using the nutrients within the plant to promote mould growth. Fusarium produces mycotoxins, which are harmful compounds, especially to livestock, but they can also be harmful to plants.

Fusarium fungi produce a multiplicity of toxins, one of which is referred to as DON (deoxynivalenol), but is more commonly known as vomitoxin. When Fusarium head blight attacks the head of the wheat plant it will attack the grain and produce DON residues in the grain. When ingested, the DON toxin will act on three levels in animals. First, the farmers will see behavioural changes, including reduced feed consumption or loss of appetite, vomiting, loss of muscle coordination and lethargy (DON can act as a sedative). Secondly, it causes a reduction in immunity, making the animal more susceptible to disease. Thirdly, it causes damage to the intestinal tract, including ulcers and bleeding. Pigs are particularly susceptible to the presence of DON.

There are many different strategies you can use to minimize mould growth and toxin production, one of which is crop rotation. If you cultivate wheat endlessly in the same plot of land, the fungus will continue to grow and spores will be produced. “But if you rotate it with oats or with barley, for instance,” says Dr. Smith, “different species of Fusarium will develop, some of which will be more powerful in producing head blight than others.”

They will also produce different amounts of mycotoxins. Depending on what the crop is, whether it’s wheat, barley, oats or corn, you will see a proliferation of different strains of Fusarium. “So if you rotate the crops,” says Dr. Smith, “What’s going to happen is that the strains of Fusarium will start to change, and that means that you won’t have a proliferation of just one, which will then potentially reduce a large amount of mycotoxins.” Using crop rotation will minimize the chance that you will see severe disease in the plant, or severe production of mycotoxins, which will reduce the feeding value of the grain.

There are other strategies you can use too. Besides crop rotation, there is also the concept of no-till farming. No-till farming is great for soil conservation, which is something the province of Ontario encourages producers to practice, but not so great for minimizing the life cycles of fungal spores. “When you till the soil, it exposes the fungal spores to the air, which kills them,” says Dr. Smith. “So by tillage you minimize the life cycles of the spore. By practising no-till, you increase the chances that that’s going to happen. Crop residual remains on the ground, fungal spores thrive, and stay there.”

One other strategy that can be used to minimize fungal growth, and thereby reduce toxic residues, is the use of fungicides – a process that not only costs money, but which can also be a bit tricky. “It has to be applied at the right time in the growth cycle,” says Dr. Smith. “And that will depend on different times for different types of crops. It is also subject to the vagaries of weather.”

According to Peter Johnson of OMAFRA, Fusarium isn’t restricted to corn and wheat. Both barley and oats are susceptible too, but to a much lesser degree. “It’s much more difficult to see Fusarium in barley, than it is in wheat, because in wheat the kernels turn pink and you can see the bleached heads,” says Johnson. “In barley, you don’t get that same pink coloration. It’s a much paler pink. When you run barley for toxins, they will often come back with very
high levels.”

Johnson is a firm believer in crop rotation, as well. “Crop rotation helps with limiting the initial infection,” he says. “It is, by far, the largest management tool that a grower can employ to reduce the toxin in the grain. If I can grow cereal crop following a legume crop, I’m going to get a lot less Fusarium or toxin in the grain almost all the time.”

“Once you get that infection in the crop, it really doesn’t matter whether it’s grown after corn or after soybean or after alfalfa hay, it’s going to make the same toxin,” he continues. “If I get the infection, it’s still going to make vomitoxin. But I get way, way less Fusarium if I grow it in a good rotation.”

As the Cereals Specialist for Ontario, Johnson recommends that you do not grow wheat after corn, because corn is the big problem in creating the disease inoculum that infects the wheat crop. “I would say the same thing for barley and the same thing for oats.”

The dilemma, he says is deciding whether or not to spray, since it must be done on about the second day after it heads, which means making a decision on day 2 of a 42-day growth cycle. The weather in between those days, which has the biggest impact on the fungus, is another major factor of consideration.

“It’s a big guessing game,” says Johnson.

In recent years, there has been a dramatic increase in the use of fungicides on winter wheat. “The reason that we’ve seen that is that we’ve had a number of years with either a significant problem with toxins or a near miss.”

Johnson says that growers now have access to better fungicides that cost less, particularly in the past couple of years. “We’ve gone from 10 years ago spraying none of the crop,” says Johnson. “Five years ago we maybe sprayed 15% of the wheat crop, and last year we probably sprayed 70% of the wheat crop. It’s because growers just cannot afford to take the risks. From a safe food standpoint, it’s just the right thing to do.”

Currently, there are two products on the market for Fusarium. One is a BASF product called Caramba; the other is Prosaro from Bayer Crop Science. They both have equal efficacy, and they both cost about the same.

“From my perspective,” says Trevor Krauss of BASF, “whether you’re growing wheat, oats or barley, Fusarium is a significant disease that’s very difficult to predict. So it’s not something where you can say, ‘Oh, I anticipate a big problem so I’m going to use it.’ You use them as a matter of course every year with the goal of producing grain that’s low in vomitoxin.”

Both Prosaro and Caramba are currently on the market. Prosaro is registered for wheat and barley, but not for oats.

Caramba is registered for all three.

May 3, 2012  By Melanie Epp