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Crop Diagnostic Lab Report

Week of July 5 - July 9, 2010

Cereals Two samples of wheat were diagnosed with tan spot (Red River) and one of those also had Septoria. Three samples of winter wheat were diagnosed with physiological leaf spot (Red River, Eastman). Three samples of wheat were diagnosed with root rot caused by one or more of Fusarium, Rhizoctonia or Bipolaris (Central Plains). Two samples of wheat were received (cultivar Kane), with purpling on leaves and some of the leaves also showing yellowing or some necrosis associated with the purpling. This type of symptom was commonly observed on this cultivar last season and is believed to be a reaction to stress conditions and associated with the genetics of the cultivar.

One sample of oats showed symptoms consistent with a glyphosate exposure (North Interlake). One sample of oats was diagnosed with Septoria leaf spot (Eastman).

Wheat – in these leaves from the cultivar Kane, purple leaf discoloration is believed to be a reaction to stress.

Oil Seeds Two samples of canola with leaf spotting from Phoma, causal agent of black leg, were diagnosed (Eastman). One of those also had water soaked lesions on leaves found to be caused by Sclerotinia. Two samples of canola showed symptoms of group 2 herbicide injury (Southwest, North Parkland). One sample of canola showing spotting on the stem and some leaves was found to be affected by the physiological condition known as oedema (Southwest). The spotting initially is slightly raised and can later become collapsed and necrotic looking. In this sample the spotting was purple in colour. Oedema is caused by the plant being unable to release water through transpiration at a rapid enough rate resulting in the swelling of cells which may then burst and collapse. Environmental conditions are usually involved in the symptom development.

Canola – oedema in this sample was observed as a spotting along the stem and on some leaves.

One sample of sunflower showed leaf symptoms consistent with a group 4 herbicide injury and stem bending consistent with a lodging incident and not related to the chemical injury (Central Plains). A second sample of sunflower with only leaf abnormalities consistent with group 4 herbicide was also received (Pembina).

One sample of flax was determined to have Fusarium wilt and root rot (Pembina).

Beans/Peas/Lentils One sample of soybean showed symptoms of root rot and was found to be affected by an assortment of root disease organisms including Pythium, Phytophthora and Fusarium (Red River).

Fruit One sample of plum was found to be affected by the insect known as plum curculio. This is a snout beetle that lays eggs in the developing fruit resulting in loss of the fruit (Red River).

Vegetables/Potatoes/Herbs One sample of tomato was diagnosed with Septoria leaf spot (Red River). This disease results in development of numerous small circular spots on leaves that will later move on to stems.

Tomato – Septoria leaf spot tends to start on lower leaves and moves up the plant, often resulting in defoliation.

Eight samples of potato were received with leaf injury symptoms caused by environmental factors (Central Plains, Red River). The symptoms on these samples were consistent with a rapid loss of moisture from leaves that the plants were unable to replace quickly enough resulting in a wilted or blighted appearance to leaves. Wind, sun, and high temperature can individually or in combinations cause such symptoms. Four samples of potato were diagnosed with late blight (Central Plains, Red River). One sample of potato was diagnosed with the bacterial disease known as blackleg (Red River).

Potato – environmental injury may give the leaves a blighted look.

Potato – black leg is a bacterial disease that may cause a wilted look and can rot the stems and tubers.

Trees and Shrubs Two samples of elm were diagnosed with Verticillium wilt (Red River). This fungus disease causes symptoms similar to Dutch Elm Disease. One sample of poplar had symptoms of a vascular impairment indicating a possible canker disease as well as having the poplar petiole gall aphid on leaves (South Parkland). One sample of an assortment of trees showed symptoms consistent with a contact herbicide exposure (Valleys North). One sample of spruce showed wilting of new growth and was found to be affected by the insect known as white pine weevil (Southwest).

Spruce – white pine weevil destroys the vascular tissue under the bark leaving a brown mess of frass instead of healthy white tissue.

Weeds One sample of Canada thistle was submitted to enquire about the yellow tops on the plants (Eastman). Thistles are susceptible to a bacterial disease known as ‘apical chlorosis’ which results in the tops (the apical growing point) becoming severely chlorotic. Although this can be quite eye catching, it does not seem to have any significant impact on the survival of the thistles. It was at one time evaluated as a possible biological control for thistle.

One weed sample was identified as Shepherd’s purse (Eastman). One sample was identified as vetchling (Red River). Two grasses were identified as redtop and Nuttall’s alkali grass (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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