Crop Diagnostic Lab Report

 

Week of August 3 - 7, 2009

One sample of wheat streak mosaic virus was diagnosed this week (Pembina).  One sample of oats with glume discoloration related to environmental factors was received (Southwest).  One sample of barley was diagnosed with a combination of spot blotch and net blotch as well as showing evidence of bleaching of stem sheaths related to feeding injury by thrips (Southwest).One sample of barley with purpling on the heads believed to be a physiological response to environment was received (Red River).  One sample of wheat and one sample of barley with suspected injury from a glyphosate tank contamination were received (South Interlake).

Two samples of soybean with Phytophthora root rot were diagnosed (Red River).  Two samples of soybean with Fusarium root rot were diagnosed (Red River).  One sample of soybean with iron chlorosis was received (Red River).  One sample of soybean with leaf spotting was found to be free of pathogens indicating the spotting to be related to environmental or other abiotic factors (Central Plains).  One sample of soybean showed symptoms consistent with group 4 chemical injury (Red River).  One sample of peas was found to be affected by stem rot caused by Rhizoctonia (Red River).  In this case there was high moisture in the canopy and stems laying on the ground had become infected by the fungus

Soybean – with iron deficiency in soybean, leaf veins tend to be greener than interveinal areas, just as in other plants.  The chlorotic tissue is delicate and easily injured, resulting in browning.

 

 

Soybean – Phytophthora root rot in these plants has resulted in browning moving far up the main stem.

Two samples of canola were diagnosed with blackleg (Red River).  In both cases, the plants had lodged or bent at the soil line due to stem weakening from the blackleg canker.  One sample of canola with chemical injury was received (Red River).  One sample of flax with apical yellowing due to a suspected chemical exposure was received (Southwest) and one sample of flax with severe stunting and chlorosis of original growing points due to chemical was received (Eastman).  One sample of flax was diagnosed with brown stem blight (South Parkland).  Brown stem blight can cause leaf spotting and stem spotting but is most often recognized when it causes a blight of the flowers and developing bolls.  One sample of sunflowers was received showing symptoms consistent with a group 4 chemical exposure (Red River).

 

Flax – yellowing of the growing points on flax can be caused by exposure to glyphosate or group 2 herbicides.

Flax – the growing points of the flax yellow off when exposed to group 2 herbicides or glyphosate.  These flax plants were exposed at an earlier stage of growth than the above picture.  You can see the arrested original growing point clearly in the plant on the right and subsequent growth of additional branches from below.

One sample of lettuce with gray mould, one sample of corn with Fusarium root rot and one sample of beet with root rot were diagnosed (Valleys North).

In July we had some reports of severe injury to leaves of green ash from ash plant bugs where as much as 50% or more of the leaves had completely browned off.  Some of the injured trees are now putting out new shoot growth.  Since it is late in the season for new growth, new shoots may not harden off properly for winter and some twigs may suffer winter injury.

 

Green ash – a large percentage of leaves browned off on some ash trees from earlier ash plant bug activity.

 

Green ash – when most leaves are lost in an early part of the season, regrowth will sometimes occur later in the season as seen on this branch.

Weed identifications for this week were water parsnip (Central Plains) and shore buttercup (North Parkland).

An interesting beetle was submitted for identification and turned out to be a burying beetle.  These beetles are normally associated with carrion but this one was found in a bertha armyworm trap (North Parkland).

Burying beetle, a Nicrophorus sp.

 

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.