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Crop Diagnostic Lab Report

Week of June 7 - June 11, 2010

Cereals Tan spot has been diagnosed on several samples this week (Red River, Southwest, South Parkland, Pembina). One sample of wheat affected by a combination of seedling blight and soil crusting was received (Valleys North). One sample of wheat showing severe stunting was received (South Interlake). Plants had some leaves and internodes only 1 cm in length with interveinal chlorosis on some leaves. Disease was ruled out but cause has not been determined. Six samples with wheat streak mosaic virus have been diagnosed again this week (Red River, Pembina, Southwest). One sample of wheat with both leaf rust and stripe rust was received (Red River).

One sample of barley with a combination of Pythium root rot and net blotch was diagnosed (Pembina).

Wheat – tan spot will often show chlorotic halos around the spots and severely infected leaves may become completely yellow.

Oil Seeds Two samples of canola were diagnosed with damping off (Southwest). Rhizoctonia and Fusarium spp. were the organisms involved. One sample of canola with yellow blotching of leaves from an undetermined abiotic cause were received (Southwest).

Canola – the 3 plants on the left are healthy, the 5 plants on the right show typical damping off symptoms of pinching and collapse of the root and stem tissue from soil borne fungi.

One sample of sunflowers with the aecial stage of rust was received (Red River).

Fruit One sample of strawberry with leaf injury from environmental causes was received (Southwest). One sample of strawberry with dieback from root and crown rot fungi was diagnosed (South Interlake). One sample of strawberry leaves with Botrytis, likely secondary to other problems, was diagnosed (Central Plains). One sample of raspberry with a suspected cane or vascular disease was received (Southwest). One sample of honey berry with leaf necrosis related to environmental injury and secondary fungi was diagnosed (Southwest). One sample of apple with suspected vascular problems was received (Central Plains). One sample of saskatoon with Botrytis blight of flower/berries and suspected canker was diagnosed (Southwest). A sample of apple and pear with symptoms suggesting a glyphosate translocation injury were received (Pembina).

Vegetables/Potatoes/Herbs Tomato and pepper plants with symptoms consistent with group 4 herbicide injury were received (Red River). Two samples of tomato transplants with gray mould blight were received (Central Plains, Southwest). Three samples of tomato transplants with late blight were diagnosed (Southwest, Red River). Symptoms of late blight and gray mould are similar.

tomato – late blight stem lesions have a brown appearance and edges of the lesion may appear somewhat diffuse.

tomato – sporulation of the late blight fungus occurs under conditions of high humidity and will appear as a whitish fuzz on the infected stem or leaf surface. 

Late blight sporangia – sporangia of Phytophthora infestans, causal agent of late blight, as viewed under the microscope.

One sample of potatoes showing poor emergence and suspected of having seed pieces contaminated with glyphosate was received (Central Plains).

Trees and Shrubs One sample of amur maple with shoot dieback caused by anthracnose was diagnosed (Red River). One sample of trees with symptoms of group 4 chemical injury was received (Pembina). One sample of green ash with some minor plant bug injury and ash flower gall was received (Red River). One sample of caragana with some leaf scorch was diagnosed with a combination of abiotic injury and Phyllosticta leaf spot (South Parkland).

Again this week, we received one sample of spruce that showed development of both Lirula needle blight and Stigmina (Pembina).

Spruce – this spruce sample shows needles with light straw colour caused by Lirula and darker brown needles with Stigmina.

Spruce – these needles show the fruiting bodies of Lirula as a black stripe running along the side of the needle. Fruiting bodies may be in one long stripe or broken into several smaller pieces. Ornamentals One sample of peony with crinkled leaves was diagnosed with environmental injury at an earlier growth stage (Southwest). One sample of perennial veronica was diagnosed with sclerotinia stem rot (Red River).

Weed Identifications Weed identifications for this week were Canada bluegrass (South Interlake), Kentucky bluegrass (South Interlake), marsh ragwort (Southwest), Dame’s rocket (Southwest), and one weed which was white cockle or night flowering catchfly (Southwest). White cockle and NF catchfly are difficult to distinguish accurately in the preflowering stage.

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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