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Crop Diagnostic Lab Report

Week of May 31 - June 4, 2010

Cereals This week has brought 5 additional samples of wheat with wheat streak mosaic virus (Red River, Pembina, Southwest). In one of those samples, plants were very small, in about 3 leaf stage, many showing severe yellowing and even necrosis of leaves. Symptoms could easily have been attributed to environmental problems due to size of the plants and severity of the chlorosis. Chlorosis was so severe, the streaking pattern often association with WSMV was not clearly visible. No field history was given. Because of the presence of what appeared to be some dead winter wheat plants in soil sent with the sample, a microscope scan was done of the seedlings which revealed presence of the wheat curl mites. This sample was the most severely WSMV infected sample we have seen this season. Three samples of wheat have been received with some yellow mottle of older leaves which has been attributed to activity by thrips. The yellow mottle was caused by the ovipositing activity of the thrips resulting in a slight yellow mottle of the affected leaves (Pembina). On these samples, the silvery white streaking on upper leaves caused by feeding activity of thrips could also be seen. One sample of wheat with suspected glyphosate injury was received (Valleys North).

Wheat – these leaves show chlorotic streaking and mottle typical of wheat streak mosaic virus samples.

ELISA test wells – these test wells show positive (yellow) and negative (no colour) results for samples tested for WSMV. The – and + signs are the control wells used for comparing to the sample results.

Wheat seedlings – these seedlings were found to have wheat curl mites and were positive for WSMV. Plants infected at this early stage will be sterile if they survive till later in the season.

One sample of oats was diagnosed as being affected by seedling blight and possible environmental stress (Red River).

Two samples of fall rye showing stunting and lack of tillering were diagnosed as being affected from an undetermined stress (South Interlake). Although symptoms of root rot were present on some of the plants, it was not present on all the plants and therefore could not account for the general poor growth of all the plants.

Oil Seeds One sample of canola was received showing symptoms consistent with exposure to group 2 and group 4 herbicide (Red River).

Special Crops One sample of corn showing deformed and curled seedlings was received (Pembina). Symptoms in this case were attributed to problems associated with difficulty emerging due to a soil crust.

Corn – deformed seedlings caused by difficulty emerging through a soil crust.

Fruit One sample of raspberry was diagnosed with a combination of spur blight and suspected glyphosate translocation injury (Central Plains).

Raspberry – the new growth has a tufted appearance and has small misshapen leaves consistent with a glyphosate translocation injury. This symptom is typical of injury from a glyphosate exposure in the previous season and similar symptoms can occur on a wide range of trees and shrubs.

Vegetables/Potatoes/Herbs One sample of peas was received affected by a group 4 herbicide injury (Red River). Leaves were normal to the fifth internode above which point all were narrowed and cupped.

Peas – narrowed, cupped leaflets on the top portions of the plants indicates exposure to a group 4 herbicide.

One sample of potatoes from storage was found to be affected by a disease known as rubbery rot caused by the fungus Geotrichum candidum (Red River). This disease results in a rubbery texture of the affected tubers which have a foul odour and leak fluids. When cut, the surfaces can take on a smoky gray colour after several hours.

Potato – with rubbery rot, tubers may show small tufts of mycelium coming from lenticels or breaks in the periderm.

One sample of basil came from a greenhouse and had symptoms of darkened patches on leaves. It was diagnosed with damage from an infestation of thrips (Eastman).

Trees and Shrubs Three samples of maple were received with complaints of poor growth (Red River). No disease was detected and the poor growth was suspected of being related to winter injury.

One sample of ninebark was received showing leaf chlorosis with a mainly interveinal pattern indicating a micronutrient deficiency (Red River).

Two samples of green ash showing development of the leaf disease known as anthracnose were received (Eastman). One of those also displayed symptoms consistent with a group 4 chemical injury.

One sample of spruce was received showing twig galls known as ragged spruce galls. These are caused by the ragged spruce gall adelgid. Several different species of adelgids are known to occur in the prairies and each causes a gall with a different appearance. Adelgids do not spend their entire life cycle inside galls and when free and distributed on twigs or needles will appear as tiny cottony tufts as was observed on another sample this week (Pembina).

Spruce – the ragged spruce gall adelgid causes a swelling of the twig and bases of needles look somewhat enlarged. Galled twigs often die off.

 

 

Spruce – the small white cottony tufts seen on the needles are adelgids that will cause galls at one stage of their life cycle.

One sample of spruce was received that showed development of two needlecast diseases, Lirula needle blight and Stigmina (Pembina).

Weed Identifications Weed identifications for this week were Canada fleabane (South Parkland), narrow-leaved hawk’s-beard (South Parkland) and 2 samples of Kentucky bluegrass (Red River, South Parkland).

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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