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Crop Diagnostic Lab Report

Week of June 14 - June 18, 2010

Cereals Tan spot has been diagnosed on 9 wheat samples this week (Red River, North Parkland, South Parkland, Southwest). One sample of wheat affected by both tan spot and spot blotch was diagnosed (Red River). One sample of wheat with Septoria leaf spot was diagnosed (Red River). Two samples of winter wheat showing development of physiological leaf spot were received (Red River, Pembina) and both also had a low level of fungus leaf spots. One sample of wheat affected by root rot and seed decay was diagnosed (Pembina). One sample of wheat with symptoms of poor emergence similar to that caused by soil crusting was received (Pembina) but since no crusting was present, poor seedling vigour was suspected to be the cause. One sample of wheat showing symptoms consistent with barley yellow dwarf virus was received (Red River). Two samples of wheat with wheat streak mosaic virus have been diagnosed again this week (Pembina, Southwest).

One sample of oats with bacterial blight was received (Red River). One sample of oats was diagnosed with root rot caused by Fusarium graminearum (Eastman). One sample of oats was diagnosed with Septoria leaf spot.

Wheat – with barley yellow dwarf virus, symptoms can be highly variable in colour and pattern. One pattern is yellowing from leaf tip toward leaf base and from leaf margin toward midrib so that yellowing may appear to extend slightly farther along the leaf edges than in the center of the blade.

Oil Seeds Two samples of canola were diagnosed with damping off caused by Rhizoctonia (Pembina, Southwest). One sample of canola with poor emergence due to seed decay from Fusarium was diagnosed (Southwest). Two samples of canola with group 4 chemical injury were received (Red River, Pembina).

Legume Crops One sample of soybean was received with a complaint of chemical injury but no symptoms were evident (Red River).

Forage Legumes One sample of alfalfa was diagnosed with spring black stem and Phoma leaf spot (Pembina).

Fruit One sample of strawberry was diagnosed with root and crown rot suspected of being secondary to winter injury (Pembina). One sample of crabapple showing poor shoot development and small leaves was received from a young planting of multiple trees all with the same symptoms (Central Plains). Sample was negative for vascular pathogens and the problem was suspected of being related to transplant shock and winter injury. One sample of cherry showing a condition known as gummosis was diagnosed with fungus stem canker disease (Central Plains). Gummosis describes the oozing of sticky gummy globs of sap that seep through the bark and occurs with infection of Prunus spp. hosts by some canker fungi.

Vegetables/Potatoes/Herbs One sample of potato showing symptoms consistent with group 4 chemical injury was received (Red River). One sample of potato with a combination of silver scurf and black dot on tubers was diagnosed (Central Plains). These diseases cause lesions on the periderm of the tuber and have a similar appearance. Silver scurf affects only tuber surfaces but blackdot can infect roots, leaves and stems of plants as well as causing lesions on the periderm surface.

Potato – tuber piece on the left shows small discoloured circular lesions of silver scurf, tuber piece on the right shows many coalesced lesions of silver scurf and blackdot.

Trees and Shrubs This week another sample of amur maple with shoot dieback caused by anthracnose was diagnosed (Eastman). Foliar diseases like anthracnose are favoured by wet weather and humid conditions. One sample of poplar with iron chlorosis was received (Valleys North). One sample of basswood with mite galls on leaves was received (Central Plains). Two sample of poplar were diagnosed with anthracnose (Urban). One sample of green ash with suspected chemical injury was received (Pembina).

One sample of spruce with needle browning on some twigs and failed bud growth was diagnosed with winter injury (Southwest). One sample of spruce was diagnosed with Stigmina on needles (Valleys North). One sample of spruce with white pine needle scale insects and old galls caused by the cooley spruce gall adelgid was received (Valleys North). The white pine needle scale insect looks almost like flecks of white paint scattered over the needles. The scale insect can shorten needle life and produces excretions that sooty mould fungus can grow on.

Basswood – galls scattered over the leaf surface are caused by mites. The galls are not harmful to the tree.


Poplar – iron chlorosis shows a symptom pattern of leaf yellowing with veins tending to remain a darker green.

Weed Identifications Five grass samples were identified as Kentucky bluegrass, slough grass, quack grass, smooth brome and a Fescue sp. (all 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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