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Crop Diagnostic Lab Report

Week of July 19 - July 23, 2010

Cereals Two samples of wheat with Fusarium head blight were diagnosed (Red River, South Interlake). In both cases, darkening of the stem just below the head was observed and agar plate test recovered Fusarium from the stem tissue as well as the blighted heads. Two samples of wheat with a necrotic leaf spotting which appeared to be injury related were received (Pembina, South Parkland). Cause of the injury is not positively determined but is suspected of being related to a fungicide application. One sample of oats had symptoms of blasting of lower panicle branches caused by stress conditions prior to head emergence (Eastman). One sample of oats was diagnosed with Septoria leaf spot (Eastman).

Wheat – Fusarium head blight. Pink colour of the fungus mycelium is visible on some glumes and the orange coloured areas indicate sporulation of the fungus.

Wheat – Fusarium head blight. Dark discoloration of the stem below the heads on this sample was found to be caused by Fusarium graminearum.

Fusarium graminearum – this fungus usually has a pink to red colour growing on potato dextrose agar and is one of the Fusarium spp. that can cause Fusarium head blight.

Oil Seeds One sample of canola with symptoms of pinching off root and lodging of plants was diagnosed with brown girdling root rot caused by Rhizoctonia solani (Southwest). Two samples of canola with leaf spotting caused by Phoma, causal agent of black leg, were received (Southwest, Eastman). One sample of canola with complaints of lodging and obvious pinching and cankering of lower stems was diagnosed with black leg (Red River). One sample of canola with basal black leg cankers was received (Pembina). One sample of canola with symptoms indicating exposure to group 2 and group 4 herbicide was received (South Parkland) and one sample of canola with only group 4 symptoms was received (Southwest). Both samples showed a symptom caused by group 4 herbicides that is commonly referred to as callousing because of the roughened nature of the root. It is caused by adventitious rooting which sometimes can also be observed occurring on the lower stem. One sample of canola with leaf mottle consistent with contact herbicide was diagnosed (Southwest).

Canola – the roughened root symptom caused by some group 4 herbicides is referred to as root callousing. The lower stem area on some of these stems also shows the production of adventitious root tissue.

One sample of sunflower with only cotyledon leaves was received (Red River). In this case, scattered plants had failed to grow beyond the cotyledon stage. No apparent disease was observed and the problem was suspected to be related to injury to the embryo of the seed. One sample of flax with symptoms of a group 2 or glyphosate herbicide exposure was received (South Parkland).

Beans/Peas/Lentils One sample of field pea was diagnosed with Rhizoctonia root rot and Ascochyta (Red River). One sample of peas was diagnosed with Aphanomyces root rot (Red River). One sample of peas was diagnosed with Fusarium root rot and Ascochyta (Southwest). One sample of field peas with complaint of stem rot on lodged plants was found to be affected by Sclerotinia stem rot (Pembina).

One sample of lentils was diagnosed with a combination of Ascochyta blight and Stemphylium leaf spot (Southwest). One sample of fababean with problems of stunting and yellowing was found to be affected by Fusarium root rot (South Parkland).

Several samples of soybean have been diagnosed with root rot (South Interlake, Red River). All of these have been found to have Phytophthora root rot and all had additional root rot agents such as Pythium, Rhizoctonia and Fusarium also present.

Fruit One sample of sour cherry had the disease known as cherry leaf spot (Red River). One sample of raspberry showed development of the disease known as crown gall, an unusual bacterial disease that causes gall formations on stems and roots (Southwest). One sample of strawberry showed severe iron deficiency characterized by interveinal yellowing (South Parkland).

Dwarf sour cherry – cherry leaf spot is a common disease of sour cherry. The underside of the two leaves in the lower part of the picture show a pinkish ooze of spores released from the fruiting bodies on the leaves.

Strawberry – iron deficiency causes interveinal yellowing in strawberry and other susceptible plants.

Raspberry – the rough warty looking bumps on the cane are caused by the disease known as crown gall.

Vegetables/Potatoes/Herbs One sample of pepper was diagnosed with Fusarium root rot (Central Plains). One sample of green beans was diagnosed with environmental leaf injury (Central Plains). One sample of red beet was diagnosed with a virus disease (Central Plains). There is a complex of viruses affecting beets known as the Yellows Complex and is comprised of 5 different viruses with affected plants often having more than one of the viruses present at the same time. Leaf vein clearing or vein yellowing and sometimes general leaf yellowing are symptoms commonly associated with the virus complex.

Red beet – the yellow net net-like pattern of vein discoloration is commonly associated with virus infection.

This week two samples of potato had leaf symptoms consistent with environmental injury (Red River, Central Plains) and one of those also had stem infections of the disease known as black dot. When stem or root diseases are present in potato, the compromised vascular tissues may contribute to environmental leaf injury symptoms since water flow in the plant is somewhat impaired. Three samples of potato were diagnosed with late blight (Red River, Central Plains).

Trees and Shrubs Two samples of oak with the leaf disease known as anthracnose were received (Red River, Eastman). One of those oak samples was also found to be affected by the bacterial disease known as slime flux or wetwood (Eastman). Two samples of elm were diagnosed with Verticillium wilt, a vascular disease producing symptoms very similar to Dutch Elm Disease (Red River). One sample of spruce with poor growth and suspected stem canker disease was received (North Interlake).

Miscellaneous One sample of red baneberry was diagnosed with downy mildew and Ascochyta leaf spot (Red River). The plant had been incorrectly identified as a nightshade weed affected by late blight and the concern was the possibility it was harbouring late blight as a threat to the potato crop. Baneberry is not in the same family as potato and does not get the late blight disease.

Weeds Weeds this week included cow parsnip (Red River, Valleys North), rough cinquefoil (Central Plains), goldenrod (South Parkland), hoary alyssum (South Parkland, Eastman), Canada wild rye (Southwest), and bird’s foot trefoil (Southwest).

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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