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Crop Diagnostic Lab Report

Week of June 21 - June 25, 2010

Cereals Leaf spots on wheat are still coming into the lab with Septoria leaf spot (Stagonospora) now becoming more common. Septoria was detected on 5 wheat samples (North Parkland, Red River), tan spot was detected on 4 of those same samples and one also had spot blotch present as a third disease in the same sample (Red River). Humidity and wet weather favour development of fungus leaf spots. One sample of wheat was diagnosed with root rot from a combination of Pythium and Fusarium (Valleys North). Barley yellow dwarf virus was diagnosed on one wheat sample (South Parkland). For wheat streak mosaic virus, this week brought five samples with the disease (Southwest, Pembina, South Parkland).

Again this week, oats with bacterial blight were received (Central Plains). One sample of oats showing symptoms consistent with exposure to a contact herbicide was received (South Interlake).

Oats – bacterial leaf blight can have small spots on the leaf blade, blighting back from the leaf tip or long necrotic streaks

Oats – contact herbicide can cause yellow blotching and necrotic spotting of leaves.

One sample of barley was diagnosed with net blotch (Southwest). The spotting initially appeared to be spot blotch but lab tests indicated presence of the net blotch fungus. Net blotch has two subspecies of the fungus. One produces a netted type spot and one produces a discrete spot type very similar to spot blotch. One sample of barley was found to be affected by root rot caused by Rhizoctonia and Fusarium (Southwest). One sample of barley had symptoms consistent with a nutrient deficiency (Southwest).

Barley net blotch – the spot form of net blotch is difficult to distinguish from spot blotch without lab testing.

Oil Seeds One sample of canola leaves with severe necrotic leaf mottle from downy mildew was received (Red River). Humidity in the canopy is highly favourable for downy mildew and when severely affected, the leaves can tatter easily. On one leaf of that same sample, a small Phoma leaf spot (blackleg) was detected. One sample of canola had an unusual chlorotic leaf mottle suspected of being caused by abiotic factors since no pathogens were detected (Red River). One sample of canola with severe leaf burn consistent with contact herbicide was received (Pembina). One sample of canola showing symptoms of loss of chlorophyll consistent with exposure to a group 27 herbicide was received along with peas and alfalfa showing similar symptoms (South Parkland). One sample of canola with symptoms of group 4 herbicide injury was received (Eastman). One sample of canola with symptoms consistent with a group 2 herbicide exposure was received (South Parkland).

Canola – downy mildew (top side of leaf) causes a necrotic mottle of leaves.

Canola - downy mildew (underside of leaves)

Canola – group 27 herbicide causes a loss of chlorophyll which can cause the affected tissue to appear almost bleached.

Legume Crops One sample of peas was diagnosed with root rot caused by Fusarium solani (Southwest).

Forage Legumes One sample of alfalfa had symptoms consistent with a potassium deficiency (Central Plains).

Fruit One sample of saskatoon showed a marginal leaf browning consistent with a vascular impairment and also had a leaf spot caused by Phyllosticta (Pembina).

Vegetables/Potatoes/Herbs One sample of tomato showing symptoms of stress, possibly nutritional in nature, was received (Central Plains).

Trees and Shrubs One sample of oak was diagnosed with anthracnose (Eastman) and was also found to have a leaf spot caused by Monochaetia. Anthracnose of oak is an interesting disease since susceptibility can vary from tree to tree and within a population, some can be severely affected while others show minor symptoms. Two samples of elm with branch dieback were found to be affected by a canker disease (Winnipeg). One sample of ornamental plum was found to have leaf blighting caused by two fungi, Pestalotia and Phyllosticta (Red River). One sample of mountain ash showed symptoms of a marginal necrosis of leaflets indicating a possible vascular problem as well as development of leaf spot caused by Phyllosticta (Red River). Vascular impairments in woody plants can be caused in roots, main stems or individual branches and can cause symptoms far beyond the place in the tree/shrub where the problem is located. If the problem is disease related, the disease can be undetectable in samples submitted to the lab if they are distal to the point of infection. A sample consisting of various tree species showing symptoms of glyphosate translocation injury was submitted (Central Plains). One sample of ornamental apple showing symptoms of apple scab was received (Valleys North). One sample of caragana with a curling and cupping of leaflets consistent with a growth regulator herbicide injury was received (Valleys North).

Mountain ash – browning of leaf margins is often an indicator of a vascular problem in trees and shrubs. Symptoms could be related to root problems or infection of the vascular system by fungi or bacteria.

One sample of spruce with stress symptoms and no evidence of disease was submitted (Pembina). Again this week we received a spruce sample showing twig damage from the ragged spruce gall adelgid along with the fungus Stigmina on needles (Winnipeg).  

The Diagnostic Lab Report is prepared by Mardi Desjardins, Crop Diagnostic Centre, Manitoba Agriculture, Food and Rural Initiatives, 201-545 University Crescent, Winnipeg, Manitoba R3T 5S6. Phone: 204-945-7707 Fax: 204-945-4327.


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