Spring 1995
Some Crop Development Factors may Influence Scab
by Tracy Sayler, Communications Specialist; Minnesota Wheat Council
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Prairie Grains is the
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the Minnesota
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Wheat Growers,
North Dakota Grain
Growers Association,
South Dakota Wheat,
Inc., and the
Minnesota Barley
Growers Association.
Stover explains that all other things being equal, including genetic resistance, the taller varieties should have a slight "microclimate" advantage over varieties with a shorter, more compact canopy.
"The tall varieties will wave back and forth in the breeze allowing them to dry out a bit," he says.
For the same reason, location can also make a difference; wheat that receives less wind or is shaded, such as alongside shelterbelts, may be more vulnerable to scab in wet conditions.
The spikelet formation on the heads of some varieties is tighter, which may affect scab infections, says Stover.
Some varieties seem to linger at the milk stage longer than others- increasing exposure to scab infection, and more importantly, increasing the duration of disease progress.
Further, some varieties bred with a longer duration of green leaf area are normally ideal for maximum yield potential -- but consequently may also be more vulnerable to a longer duration of scab susceptibility. Thus, rapid grainfill and maturation may sometimes be beneficial, particularly in weather conditions that favor scab development.
These are just some observations as to why scab may be more severe in some varieties than others, although Stover stresses that these observations need to be researched further before any firm conclusions can be made.
More of Stover's observations on scab:
- Early in last year's growing season, Stover could find the scab fungus growing on previous year crop residue, on the ground in the canopy. "I could see early on what could happen if we would have bad weather at anthesis and the milk stage," he said.
- Seed growers may want to consider Benlate applications, if only to help boost grain test weights. "But at the same time, fungicides won't be the salvation in solving our scab problems. It will come in breeding and better weather."
- Burning theoretically is no better than moldboard plowing in ridding scab. Still, destroying scab inoculum by burning or moldboard plowing should give a slight advantage in wheat recropping situations compared to chiseling or no-till.
- Once a wheat head is infected, is additional moisture needed for the infection to spread? The answer is a bit complicated, says Stover. The initial infection continues to grow within the plant tissue under normal growing conditions, regardless of rain. However, new or secondary inoculum won't develop and spread without adequate wetness in the canopy.