Crop Scene Investigation - 49: Why was Richard's field infected with septoria?

Thursday, January 2, 2014

When Paul Sullivan pulled into Richard's twin wheat fields near Pakenham, west of Ottawa, in late May, septoria leaf spot disease was one of the last things he expected to see.

Richard, who farms with his son, Bill, had planted two 15-acre adjacent fields to spring wheat on April  23. As he walked the first field, Sullivan noticed obvious signs of septoria.

"We scouted the fields at the three-to four-leaf stage as the crop was just starting to tiller. You could see the small, light green and yellow lesions on the leaves and the tips were discoloured and yellowing," recalls Sullivan. He also noted that the disease pattern was uneven and patchy across the first field.

Richard and Sullivan then walked to the adjacent field where the same wheat variety was planted on the same day. This field was clean. There were no signs of septoria. "I asked Richard if he had used the same seed in both fields and he confirmed that it came from the same lot," says Sullivan. "We then reviewed seed treatments and there was no difference between the fields. We also checked the fertility and the fields were pretty much the same."

Sullivan's thoughts then shifted to rotation. The disease symptoms looked typical of fields in his area where wheat had been seeded after a wheat or barley crop. "That's a no-no," says the agronomist. "In these situations, we typically see a lot of disease early on and you have to use a fungicide to make sure the disease doesn't overrun the crop."

But Sullivan quickly crossed that potential answer off his list after he reviewed field history. Both fields had the same rotation. A 2010 wheat crop had been followed by corn in 2011 and then soybeans in 2012. It was a solid rotation that should have broken the disease cycle.

With no obvious answers, Sullivan delved further into field history. Richard explained that they had run into a stretch of wet weather earlier in the spring, which was much different from 2012 when his no-till soybeans had to fight for every ounce of moisture to make a crop in a very dry year. 2011 was also uneventful, according to Richard, who noted that he minimum-tilled the fields in the spring and then planted a pretty successful corn crop in another dry year.

Then there was 2010. Digging through his memory bank, Richard recalled that he and Bill had planted a wheat crop intended for seed. With that in mind, they decided to forego a pre-harvest treatment and ended up wrestling with a high population of green weeds after harvest. They also left the straw, so they decided some tillage was needed to ready the fields for the following crop. They tried to work down the first field with a regular field cultivator, but it kept getting plugged. "It kind of piled up the straw and green material throughout the field," recalled Richard. As they moved into the second field, they changed their tillage approach, switching to a cultivator with more clearance which did a much better job of residue management across that field.

It took some digging, but Sullivan figured he had finally solved the puzzle. Do you know why septoria infected the wheat in Richard's first field? Send your solution, along with complete contact information, to Better Farming at: rirwin@betterfarming.com or by fax to: 613-678-5993.  

Correct answers will be pooled and one winner will be drawn for a chance to win a Wireless Weather Station. The correct answer, along with the reasoning followed to reach it, will appear in the next issue of Better Farming. BF