Constant Vigilance

Watch for root rot, even in dry years

by Noelle Chorney

With a dry year behind us and another dry year in the forecast, growers may be tempted to relax their vigilance toward root rot. Even in dry years, however, the problem does not go away. 

Dr. Sabine Banniza, Plant Pathologist at the University of Saskatchewan, was involved in a root rot survey in 2017. “The Aphanomyces pathogen is widespread,” she says. “It was present in the vast majority of fields that we studied. What we know now is that while it was likely always present, short crop rotations of peas and lentils, and a string of wet years made it a more serious problem.”

“There are no in-crop management options for root rot, but keeping an eye on roots enables growers to develop longterm strategies to manage the disease,” says Banniza. Here is what you can do to protect your fields in the coming growing season.

Assess Risk

Do you have a field adjacent to another field that you know to be infected and which may still contain infected crop residue? Do you have a field that has high moisture levels? Start there, as the risk is highest.

Watch for Signs

“Generally, root rots have the highest impact during the seedling stage, but even later growth stages are affected,” says Banniza. Head into the field and scan for signs of plant weakness. Check your peas and lentils at the seedling stage for signs of  chlorosis (yellowing), stunted plants, or weedy areas where your plants are having more difficulty competing.

Test Your Soil

If you see warning signs, get your soil tested, or better yet, test the roots of lentils and peas in a lab. If Aphanomyces is present, it is recommended you start taking measures to control the disease. 

Dr. Syama Chatterton, Research Scientist at the Agriculture and Agri-Food Canada, Lethbridge Research and Development Centre, has confirmed through 2017 infectivity modeling that the fungus spores are usually uniformly distributed throughout the soil. She still recommends collecting samples from lower areas where water accumulates, as well as getting roots tested. “Testing roots give you better positive results. Soil-only testing is more likely to give a false negative because it is more difficult
to extract DNA from soil,” she says.

The infectivity modeling is also closer to confirming the threshold of oospores in the soil that will cause disease. One hundred or more oospores per gram of soil is detectable, and at that rate infection is likely. Fewer than 100 oospores per gram may still cause disease, however, but has a 30 to 40 per cent false negative rate.

Prevent the Spread of Disease

Aphanomyces is entirely soil bound, so it cannot be spread on seed or by the wind. However, you can spread it by moving clumps of soil from an infected field onto another field. If you know a field is infected, plan to harvest or seed that one last, Dr. Chatterton suggests, or wash your equipment before moving to a different field.

Crop Rotation

If you have proof from soil or root testing that Aphanomyces is present, says Banniza, “the recommended crop rotation is six to eight years.” If you do not have proof of Aphanomyces, it is still wise to use a four-year rotation for prevention purposes.

Resistant Cultivars Are on the Way

“We have identified partial resistance in lentil and in pea,” says Banniza. “In pea we are further ahead and hope to have the first lines with partial resistance ready for registration by the end of 2020.”

Aphanomyces-resistant lentil strains are farther off because researchers have to do the ground work that had already been done for peas, beginning with making crosses with wild relatives of cultivated lentils, which have good resistance. With resistant
cultivars two or more years off, crop rotation and good crop management are the only sure prevention for Aphanomyces.

Grow Healthy Crops 

The best resistance to disease is soil and plant health. Make sure your fields are planted at the appropriate density, have adequate nutrients, and are as weed-free as possible. “Keep your plants stress-free and happy, whatever it takes,” says Banniza. “Know your plants’ optimal growing conditions and do what you can to provide them.” 

Reconsider the temptation to plant lentils and peas in high-risk fields, even if it is likely to be a dry year. “In the case of Aphanomyces-infested fields you are not contributing to reducing the inoculum if you grow susceptible crops in close rotations because you can get away with it in the drier weather.” Take the long view — and keep Aphanomyces in check for future economic success.