Concerned about one of his malt barley fields, Jim — a Saskatoon-area farmer — asked me to visit his farm. It was the third week of June, and until that point Jim’s crop had progressed normally, despite the heavy rain that had fallen on his fields that spring. Now, quite unexpectedly, some of the plants were showing signs of stress.
Many plants in Jim’s field appeared stunted in growth, with yellowing lower leaves and brown, discoloured crowns. These unhealthy plants were located randomly throughout the field, sometimes within the same seed row as healthy plants. Close by, Jim had planted another field with malt barley, and it was producing normal, healthy plants.
Half of the affected field had been seeded on oat stubble and the other half on yellow mustard stubble. The soil of both halves of the field was composed of wet, sandy loam, but it was moister and had a higher frequency of stressed plants, especially where its moisture level was highest, on the side seeded on oat stubble. However, the stressed plants were not exclusive to the moister parts of the field, but could be found in the drier areas as well. I thought excess moisture was one factor contributing to the crop’s stress, but not the only one.
After eliminating chemical damage and nutrient deficiency as possible sources of the problem, a closer inspection of the unhealthy plants helped reveal what was causing the stress on Jim’s crop. The plants were pale green to yellow in colour, and the lowest internodes were pink to brown. The root development of these plants was stunted. Laboratory analysis confirmed the plants had been infected with the fungal species fusarium. The plants were exhibiting symptoms of root and crown rot.
The fusarium pathogen is found in other cereal crops, including wheat and oats. The lab report noted that this might explain why the incidence of infected plants seeded on oat stubble was higher than that seeded on mustard stubble. In addition, the moist conditions provided an environment conducive for fungal pathogens to enter the plants at the crowns from sources above ground.
Soil-borne fungi can survive for a number of years. These fungi contribute to root and crown rot, explaining why the barley plants seeded on mustard stubble were also infected with fusarium — oats had been planted in this field in 2009, prior to mustard in 2010.
Finally, we examined Jim’s seed lot to determine whether it had become infected with fusarium or any other pathogens associated with root rot. Tests revealed that the seed lot was infected with fusarium and Cochliobolus sativus. Poor seed quality was one of the largest contributing factors to Jim’s unhealthy plant stand.
“I don’t understand why that other field is completely healthy,” I said to Jim.
“That’s easy — I used two different seed lots!” he replied.
Jim had started seeding his barley fields with new, certified seed, but he’d run out and switched to the infected seed lot. This seed lot had been tested for germination but not for disease.
I recommended that Jim test his seed lot for disease in the future, and that he only plant seed within acceptable levels of seed-borne disease. To avoid repeating this scenario, I also advised Jim to use a crop rotation that would eliminate seeding cereals into cereal stubble, and to use a seed treatment to protect seedlings from infection.
Seed quality testing for germination, vigour and disease is an integral part of growing a quality crop. A great crop starts with high-quality seed. †