Crop Diagnostic Lab Report

 

Week of July 20 - 24, 2009

Two samples of wheat were diagnosed with leaf tip browning due to environmental causes (Red River).  Five samples of wheat (cultivar KANE) were received over the past two weeks with symptoms of necrotic blotching and purpling/reddening of leaves, sometimes mid-story leaves affected and sometime flag leaves (Red River, Southwest, Valleys North, Pembina).  No disease has been found associated with the symptoms which are believed to be a physiological reaction to stress.  The reddening purpling symptom seems to be more intense on the underside of some affected leaves.  Another sample of wheat with a non-pathogenic leaf spot was received (Valleys North).  One sample of wheat with wheat streak mosaic virus was received (Pembina).  One sample of barley had leaf crinkling symptoms believed to be caused by rapid growth (Red River).  One sample of fall rye had stem injury believed to be caused by grasshoppers (South Parkland).

Wheat – abiotic spotting and purpling on KANE wheat.  The two leaves on the left and the one on the far right show the discoloration on the leaves. 

 

One sample of sunflower with rust and Alternaria leaf spot was diagnosed (Red River).  Four samples of sunflower with group 4 chemical injury were received (Central Plains, South Parkland).  Group 4 herbicides can cause an assortment of leaf deformities and distortions with parallel leaf veins being common.  Sometimes the veins are arranged so as to cause large areas of light coloured tissue that may be mistaken for downy mildew disease.  One sample of sunflower was received that had both downy mildew and group 4 herbicide injury (Central Plains).  One sample of sunflower was received that had browned leaf areas related to rapid moisture loss from environmental factors (South Parkland).

Sunflower – growth regulator (group 4) herbicides can cause an assortment of leaf distortions.  Development of parallel leaf veins often occurs.

 

Eight samples of canola were received that displayed symptoms of group 2 chemical injury (Red River, North Parkland, Central Plains). One symptom associated with group 2 injury in canola is development of growth from axillary leaf buds that tends to give the plant a bushy appearance.  One sample of canola with blackleg and downy mildew was diagnosed (Southwest).  One sample of canola with identical right angle bends at the ground and higher up the stem caused by lodging followed by continued growth was received (Valleys North).  The stem bends that occur in this way are sometimes mistaken for chemical damage.  One sample of canola with sulphur deficiency symptoms was diagnosed (Red River).  One sample of canola with purpling on pods and upper stems was received (South Parkland).  This purpling on the upper stems is sometimes mistaken for nutrient deficiency but is usually a physiological reaction to sun and may be more intense on one side of a pod or one side of a stem.

Canola – group 2 injury can cause development of growth from leaf axils giving the plants a bushy appearance.

 

One sample of flax with iron deficiency symptoms (iron chlorosis) was received (Red River).  Two samples of flax with chemical injury were received (Red River, Southwest). 

One sample of field beans with halo blight and iron deficiency was received (Red River).  One sample of peas with a combination of Septoria blotch and Ascochyta leaf spot was diagnosed (Eastman).

One sample of potato with the leaf spot known as brown spot was diagnosed (Central Plains).

One sample of alfalfa with Stemphylium leaf spot was diagnosed (Red River).  One sample of alfalfa with poor growth suspected to be affected by nutritional problems was diagnosed (North Parkland) 

Two samples of strawberry with severe iron chlorosis were diagnosed (Red River, South Interlake).  One sample of apple with iron chlorosis was diagnosed (South Parkland).  Iron chlorosis can weaken the plant causing greater susceptibility to disease and winter injury.  One sample of pear was diagnosed with group 4 herbicide injury (Pembina).  One sample of seabuckthorn was diagnosed with Verticillium wilt (Central Plains).  One sample of crabapple with fireblight was diagnosed (Red River).

 

Iron chlorosis – (apple on left, strawberry on right) iron deficiency causes yellowing between the veins of the leaves with veins tending to remain green.  The chlorotic tissue is easily damaged by environmental conditions such as wind and high temperature.

 

For spruce, one sample was diagnosed with Rhizosphaera needle cast (South Parkland).  One sample of green ash was diagnosed with anthracnose (Red River).  One sample of ash had environmental leaf scorch and Phyllosticta leaf spot (South Parkland).  One sample of ash with severely browned leaves caused by ash plant bug was received (Red River).  The plant bugs have caused leaves on large areas of some trees to brown off this season.  The symptoms have been reported to be most severe on the lower half of tree canopies in some cases and although more than 50% of leaf area has been lost on some trees, there should not be any significant effect on an otherwise healthy tree.

Weed identifications for this week were small snapdragon (North Parkland), northern willowherb (Eastman, Red River) and bird’s foot trefoil (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.