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Crop Diagnostic Lab Report

Week of August 2 - August 6, 2010

Cereals Two wheat samples with symptoms of stem purpling were received (Red River, Southwest). Stem purpling has been reported to be linked to genetics of the cultivar with purpling being expressed under certain stress conditions. Copper deficiency has also been reported to be a factor in some cases. Production of purple pigment (anthocyanins) in plants is known to be enhanced by light exposure, therefore, on some stems showing the purpling, it may be more intense on one side of the stem depending on how the stem is exposed to sun. On some of these stems, the difference in pigment is great enough that the stem looks purple on one side but if flipped over it may appear unpigmented on the other. One sample of wheat showed leaf spotting related to injury following an application of fungicide (Red River).

Wheat – stem purpling is a physiological reaction of the plant to environment. The portion of the stem that was covered by sheath on this sample is unpigmented since it was not exposed to light.

Oil Seeds One sample of canola with symptoms of stem purpling and aborted pods on some areas of the racemes was received (Pembina). Symptoms were found to be related to environmental stress with the purpling also being tied to light exposure. As in wheat as mentioned above, the stem purpling in canola can be more intense on one side of the stems and pods, the “sunny side”. One sample of camelina was found to be affected by staghead (white rust) and downy mildew (Southwest).

Canola – stem purpling is often more noticeable on one side of the stem than the other. Both pieces in the picture are similarly pigmented but appear green on one side and purple on the other due to the role of light exposure in the pigment development.

One sample of flax was found to be affected by a combination of pasmo and Alternaria blight (Pembina).

Forages One sample of alfalfa was found to be affected by Botrytis flower blight and common leaf spot (North Interlake). The Botrytis fungus uses the flower petals as a food base and moves down onto the reproductive parts of the flower and even down the flower pedicel. High humidity favours development of the disease.

Alfalfa – flowers of this sample are blighted by Botrytis which can destroy the flower raceme and prevent seed production.

Beans/Peas/Lentils One sample of peas was found to be severely affected by a combination of anthracnose and Ascochyta blight (Southwest). One sample of soybean was found to be affected by a combination of Phomopsis and root rot (Eastman). One sample of soybean had heavy development of downy mildew (Red River). One sample of soybean was found to be affected by Septoria leaf spot (Red River). One sample of soybean showed symptoms consistent with group 4 herbicide exposure (Red River).

Soybean – downy mildew causes spotting of the leaves and fluffy growth of the fungus can sometimes be seen on the underside of the leaflet as on the leaflet on the right side of the picture.

Fruit One sample of apple was found to be affected by iron chlorosis (Eastman).

Trees and Shrubs One sample of amur chokecherry with dieback symptoms was diagnosed with diaporthe canker (Eastman). One sample of amur chokecherry with severe wilt symptoms indicating a vascular impairment was received (Red River). In this case, no pathogen was recovered from the small twigs submitted but since only shoot tips were submitted, sample type would not have allowed detection of vascular disease present further along the affected branches. One sample of green ash was found to be affected by anthracnose (Red River). Two samples of elm were diagnosed with Verticillium wilt (Red River). Five samples of elm were diagnosed with Dutch elm disease. Several samples of elm were diagnosed with canker disease caused by one of Botryodiplodia or Sphaeropsis. One sample of spruce showed needle damage from feeding activity by sawfly larvae (Central Plains). More than one species of sawfly can occur on spruce in Manitoba with the yellow headed spruce sawfly the most commonly encountered.

 

Spruce – sawfly larvae may consume entire needles or leave stubs of needles along twigs and the egg shaped pupal cases of the sawfly are visible on this sample twig.

Weeds Weed identifications for this week were water hemlock (Central Plains), one sided wheat grass (South Parkland), fringed brome (South Parkland) and Canada wild rye (South Parkland).

Insects A sample of insects from sunflower was identified as minute pirate bug which is a predatory insect, not a pest (Red River).

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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