Crop Diagnostic Lab Report

 

Week of August 17 - 21, 2009

This week we have only two small grain samples to report on.  One sample of oats had leaf rust, Fusarium head blight and glume discoloration due to environmental factors (South Interlake).  One sample of wheat had poor head fill suspected to be caused by a combination of heavy leaf spot disease and root rot (Eastman).

Only one sample of soybean this week with symptoms consistent with exposure to a group 4 herbicide (Red River).  One sample of lentils this week with anthracnose (Central Plains).

One sample of canola with blackleg (Pembina) diagnosed this week.  One sample of flax had symptoms of chlorosis suspected to be caused by a combination of excess moisture and chemical injury (South Interlake) and another sample of flax had symptoms of apical chlorosis consistent with exposure to a group 2 herbicide or glyphosate (South Interlake).  One sample of flax was diagnosed with brown stem blight and root rot (Southwest).

Two samples of bird’s foot trefoil with blasting of flowers due to Botrytis gray mould were received (Eastman) and one of those samples also displayed rotting of pods caused by the Botrytis.  One sample of trefoil was found to be affected by a combination of anthracnose and Stemphylium leaf spot (Eastman).  One sample of alfalfa with blighted flowers due to Botrytis gray mould was diagnosed (Red River).

 

Bird’s foot trefoil – developed pods can be affected by gray mould (Botryis) or flowers can blight off and prevent development of pods.  The gray fuzz of the fungus can be seen on the pods in this picture.

 

One sample of potato with late blight was received (Valleys North).  One sample of potato with a combination of early blight and botrytis (gray mould) was received (Central Plains). 

Two samples of tomato with late blight were received (Valleys North).  One sample of tomato with fruit rot due to Botrytis gray mould was diagnosed (Red River).  One sample of onion with neck rot was received (Red River).  One sample of cucumber with angular leaf spot was diagnosed (Red River).

Only one fruit sample to report on this week.  One sample of apple was diagnosed with fireblight (North Parkland).  Fireblight is a bacterial disease that can spread quickly with rainy weather and can be severe following hail storms.

One amur maple sample and one ornamental crabapple showed symptoms of a vascular impairment (Red River).  In both cases, severe wilting was occurring on branches.  Testing of the samples did not recover a pathogen indicating that the problem was at a point distal to where the samples were collected.  One sample of mountain ash was diagnosed with a combination of fireblight and Botryosphaeria canker (Red River).  Botryosphaeria is a fungus that is commonly found on apple trees and is frequently found on trees that have been affected by fireblight.  Mountain ash and apple are in the rose family of plants and susceptible to some of the same disease problems.  One sample of spruce showed evidence of a spruce bud scale infestation as well as damage to needles from a chewing insect (South Parkland).  With recent humid conditions experienced in some areas of the province, growth black sooty mould is becoming conspicuous on some trees that have been affected by infestations of sucking insects.  Sooty mould grows only on insect excretions and does not harm trees but can be highly visible when conditions favour its growth.

Mountain ash – leaves tend to have a reddish brown appearance when affected by fireblight.

 

Botrytis gray mould as reported above in forage legumes, tomato and potato is highly favoured by humid conditions.  Flower gardens can also be affected by gray mould.  The fungus can grow on dead or senescent tissue but under favourable conditions can attack living tissue of some plants.  Plants used for flower gardens often have either abundant petals or very large petals.  Flower petals serve as an excellent food base for the Botrytis fungus.  During humid weather, regular removal of dead flowers can be helpful in reducing the occurance or severity of Botrytis blight in ornamental plantings.

One sample of iris leaves was received this week and was diagnosed with the disease known as Didymellina leaf spot (North Parkland).  Some references call the disease “Fire” due to the appearance of the leaf symptoms.  Rhizomatous iris is highly susceptible to the disease which survives from season to season on infected plant debris.  Removal of the dead plant material from the garden at the end of the season is important in reducing the inoculum available to start the disease cycle again the following season.

 

Iris – leaf tips were browning back on this iris infected with Didymellina leaf spot.  The fungus can infect all above ground parts of the plant including flowers.

 

Flixweed (South Parkland) was the only weed identification received this week.

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.