Crop Diagnostic Lab Report

 

Week of August 24 - 28, 2009

This week we had one oat sample with suspected chemical injury (Central Plains).  There were a few inquiries about wheat with purple stems.  One sample of wheat with purple stems (Central Plains) was submitted to the lab.  Stem purpling can be highly visible.  It is not disease related but is a physiological response of the plant to environmental stresses.  Some cultivars seem to be more likely to show this condition than others.

Wheat – stem purpling is a physiological response of plants to environmental conditions.  In 2007 the Diagnostic Centre received reports of stem purpling in wheat similar to what has been occurring this season.

Two sample of field beans this week, both with anthracnose and one of those also with bacterial blight lesions on pods (Red River).

This week there were two samples of canola with blackleg (South Parkland, Southwest).  One sample of hemp was found to be affected by Alternaria leaf spot (Valleys North).

One sample of corn was diagnosed with Phyllosticta leaf spot (North Parkland), also known as yellow leaf blight.  One sample of corn was diagnosed with the bacterial disease known as Goss’s wilt (Red River).

One sample of alfalfa was diagnosed with root rot caused by Fusarium spp. fungi as well as leaf spot disease and possible fertility issues (North Parkland).  One sample of alfalfa was found to be affected by severe development of spring black stem (North Interlake).

One sample of potato with early blight and gray mould was received (Central Plains).  One sample of potato with just early blight was received (Red River). 

One sample of tomato with severe Septoria leaf spot was received (Red River).  Conditions for Septoria on tomato have been ideal this season.  In the case received at the laboratory, plants were reported to have been more than 70% defoliated in about 9 days from the time spots were first observed on the plants.  Septoria will cause spotting of the stems and leaves but not of the fruit itself.

Tomato – Septoria leaf spot causes numerous small spots on leaf and stem tissue and can cause rapid defoliation if weather conditions favour the disease.

One sample of lawn grass with severe powdery mildew was received (North Parkland).  Powdery mildew is favoured by high humidity in the grass canopy and can be particularly severe in shaded locations or if mowing height is long.  Powdery mildew can result in yellowing and dying off of affected grass blades.

Grass – powdery mildew has resulted in dying of the grass blades in this sample.  A thick white coating of the fungus is visible on some blades.

One sample of silver maple was received that showed bladder galls caused by eriophyoid mites (Red River).  The galls would have been present all season but at this time of the year, the gall tissue tends to die showing the presence of black bumps on the leaves.  Leaf galls do not harm the tree but may be highly visible if the tissue is blackening at this time of the season.  An assortment of deciduous tree samples have continuted to arrive at the lab from various areas of the province with complaints of wilting off of leaves.  Vascular problems of various kinds can cause the disruption of water flow to the affected areas of the tree resulting in wilting or browning off of leaves.  Problems in roots or main stems will affect the whole tree. When individual branches are affected, localized stem cankers may be involved.  Samples from wilting branches may not allow detection of the causal agent since symptoms can be displayed on leaves long distances from where disease is present in a tree.

Silver maple – mite galls on this leaf have darkened as the galled tissue has died giving the appearance of black bumps on the leaf surface.

 

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.