Features Agronomy Cereals
Learning from 2009 cereal crops

Every year provides a learning experience in cereal crops. Although the 2009 growing season did not produce the diversity or severity of diseases that 2008 season saw, it did produce its share of trouble in both spring and winter wheat.

Although not a problem with spring wheat, powdery mildew can hit winter wheat particularly hard as a result of cool spring days.

“Diseases are all about weather,” says Peter Johnson, provincial cereals specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs. “And it’s weather that drives the difference in disease outbreaks in the two crops.”

While winter wheat is often plagued with powdery mildew, it is not found very often in spring wheat. Powdery mildew is a cool weather disease, so once the weather warms up, mildew stops. In winter wheat, it starts growing in cool spring days; by early May, it has produced a fairly thick canopy just perfect for mildew development. At the same point in the growing season, spring wheat has not yet emerged, and by the time it has canopied, usually around the first of June, the temperature goes up and mildew is done.

It is the opposite scenario with rust, where spring wheat is a prime target. Rust moves north from Mexico and the southern US. By the time rust spores arrive, winter wheat has headed out and is well on its way to maturity. Spring wheat, however, is at a very vulnerable stage when rust arrives, especially in southern and central parts of Ontario. “New Liskeard spring wheat crops usually escape rust, but in Wellington County, the crop is not so lucky,” says Johnson. “The saving grace is that the spring wheat genetics that perform well in Ontario have better leaf rust tolerance than the winter wheat varieties.”

In 2009, winter wheat across much of Ontario escaped major outbreaks of Fusarium because although the weather was wet, cool nights (below 10 degrees C) stopped sporulation of the fungus. In spring wheat, however, wet weather arrived at heading and temperatures stayed above the critical 10 degree C mark, creating conditions conducive to disease development. “Outbreaks were regional. The Ottawa Valley got hid hard but the spring wheat growing areas around Grey, Bruce and Dufferin counties had some but it wasn’t epidemic,” says Johnson. “Seventy-five percent of the crop in that area was good quality.”

It was a big year for septoria in both spring and winter wheat crops. The disease started early with a vengeance. Normally, wheat grows faster than the disease, but in 2009, it was the disease that moved faster. Early applications of Stratego at T1 (Zadoks 21 to 37) helped keep the disease in check.

Stagnospora showed up in a number of areas of the province, too. “When it comes early on the glumes, it can slash yields by 20 percent,” says Johnson. “Unfortunately, a lot of septoria and stagnospora were misdiagnosed as physiological leaf fleck.”

So what about 2010?
November of 2009 allowed the 750,000 to 825,000 acres of winter wheat planted last fall to produce healthy stands and luckily, temperatures were not low enough during the winter of 2009/2010 to cause winterkill. If thin stands are evident in the spring, applying about one-third of planned nitrogen applications early before the frost is out will help give it a boost. And growers should be prepared to control weeds in thin stands.

Another disease that was a problem in 2009 was septoria, often misdiagnosed as physiological leaf fleck.  Photos courtesy of Bayer CropScience.

As the crop progresses, check early and check often for signs of disease. “Sound disease management strategies start with being able to identify diseases,” says Luc Bourgeois, research manager with Bayer CropScience. To help with identification, growers can go to CerealCentral.ca and download a
Disease Management Guide. “If you plan to only apply one fungicide, make it a Fusarium fungicide early on in the T3 timing (Zadoks 59).”

For high yield potential crops, it pays to apply an early season preventative application at T1 (Zadoks 21 to 37). “Scout and apply when disease pressure warrants an application,” says Bourgeois. “Proactively applying a disease control product at herbicide (T1) timing followed by a Fusarium fungicide at heading (T3) is a preventative approach that many growers employ.”

Other growers take a “wait and see” approach. For just-in-time decision making, consider the helpful management tools made available at WeatherCentral.ca, including DONcast, WHEATcast and SPRAYcast.

DONcast is a tool designed for wheat producers to provide a means of predicting deoxynivalenol toxin (DON) concentration in wheat at harvest. The forecasting model uses actual and historical weather data along with field-specific data to predict the risk of DON. The tool can help producers make informed management decisions about fungicide application at heading and which field to harvest first, and can provide an advance warning of DON levels so producers can look for appropriate markets.

WHEATcast provides farmers advice on when to more intensely scout wheat fields for the development of septoria and powdery mildew and to determine whether or not a T1 fungicide is warranted. SPRAYcast is a tool to help producers identify times during the day that are more or less favourable for spraying to reduce drift.

DONcast and WHEATcast require site-specific information about specific fields. Growers can sign up for a user account to access the most precise forecasting models for their farm at WeatherCentral.ca. “Growers have a host of new technologies to help them grow profitable cereal crops,” says Bourgeois. “When you employ these forecasting models with timely scouting and highly effective fungicides such as Stratego, Folicur and Proline, chances of maximizing yield, quality and profitability are much greater than they were just a few years ago.”

Is it disease or just sunburn?
It is difficult to tell the difference between physiological leaf fleck, essentially sunburn, and a disease. The easiest way is to look for dark, pepper-like spots called pycnidia on the lesions. By the time these fruiting bodies have formed though, it is too late to spray. Growers need to catch foliar diseases when there are only one or two lesions on leaves.

If there are chlorotic spots with a halo around them or little yellow pin pricks, a grower needs to determine quickly what is going on. A simple test can help.

Growers can take eight or 10 suspicious leaves and put them in a zip lock bag with two or three drops of water to create humidity. Do not drown them, just use a couple of drops of water. Seal it, leaving air in the bag. Put the bag someplace dark and warm and check it in 24 hours for pycnidia in the centre of the lesions. If nothing is forming, it is probably a physiological condition. Leave it for another 24 hours and check again just to be sure. However, if there are  pycnidia, a foliar fungicide is in order immediately.