Jack, a farmer from Eston, Sask., thought he had a major problem on his farm at the end of June 2011. “My lentil field is dying off and I don’t know if it’s anthracnose, root rot, or what,” he said. “This is a critical time for my lentils, and whatever is happening in my field is going to affect my final yield!” He told me that off-colour patches of plants had developed over the past week.
In Jack’s lentil field, I could see scattered patches of brown-coloured plants. It appeared as though the plants were prematurely dying. Up close, I could see spots ranging from cream to tan in colour spread across the leaves. The spots were evidently then infecting the whole leaflet, as well as the rest of the plant. Even the pods were turning light brown.
The occurrence of the patches was heavier toward the edge of the field Jack shared with his neighbour. “I know my neighbour had disease pressure last year. I’m not sure what the problem was,” Jack said.
As the result of premature plant death, plant density was lower within the patches when compared with the surrounding areas. As I peered through the canopy I could see a mould-like fuzzy growth on some of the leaflets and lower stems of the plants.
Jack was dealing with a fungal infestation of some kind — root rot, anthracnose, ascochyta blight, fusarium wilt, stemphylium blight. The list of potential candidates was long. Some we could eliminate easily. For example, the plants were at an advanced stage with the canopy closing in, so root rot probably wasn’t the problem. The brown lesions on the lower leaflets and the blackening of the stem characteristic of anthracnose infection were also absent. The pods of stempyhlium blight-infected plants do not turn brown, and there were no tan lesions on the lower leaflets of the plants in Jack’s field, eliminating this disease from the list.
I dug up some of the plants and examined their roots. If fusarium wilt had infected this field, I would have expected to find reddish to brown discolouration of the roots, but they looked completely healthy and normal.
The small black pycnidia (asexual fruiting bodies) and spot-like lesions on leaves, stems, and pods characteristic of ascochyta blight infection were also not present on the plants in Jack’s lentil field.
There are only two fungal diseases of importance in Saskatchewan that produce mould growth on the plant. White fluffy mould can be found on plants infected with the pathogen responsible for sclerotinia white mould, and the roots of these plants are often infected and rotting. However, the roots of Jack’s plants were healthy, eliminating this disease as the possible cause of damage to his lentil crop. There was now only one pathogen left to consider. “I know what’s growing in your field, and I think your neighbour can confirm my diagnosis,” I said.
What disease has infected Jack’s lentil field? Send your diagnosis to Grainews, Box 9800, Winnipeg, MB, R3C 3K7; email [email protected] or fax 204-944-5416 c/o Crop Advisor’s Casebook. Best suggestions will be pooled and one winner will be drawn for a chance to win a Grainews cap and a one-year subscription to the magazine. The reasoning which solved the mystery, will appear in the next Crop Advisor’s Solution File. †