Crop Diagnostic Lab Report

 

Week of June 9 - 13, 2008

This week brought several samples of winter wheat with powdery mildew (Eastman).  Affected samples showed yellowing of leaves with some leaves showing the green island effect of small green spots remaining in chlorotic leaf blade tissue.  The mildew was clearly evident on still green leaf blades of one sample, while a microscope was needed to observe the spots developing on another.  When the mildew is not easily detectable on the leaf blades, it can sometimes be observed low in the canopy on the stems.  Two samples of wheat with Wheat Streak Mosaic Virus were diagnosed this week (Pembina).  One sample of wheat with bacterial leaf spot was received and 2 with symptoms of stress were received (Southwest).  One field of wheat with scattered seedlings being killed was found to be affected by insect injury (Southwest).  One sample of barley showed symptoms consistent with a glyphosate exposure (Red River) and one sample of barley showed symptoms of group one herbicide injury (Southwest).  The necrotic spotting caused by group 1 herbicide can sometimes be confused with the disease known as scald.  The group 1 injury will usually have some yellow streaking associated with the necrotic spotting and the injury is often observed to be present on the same age leaves of each tiller and often in approximately the same leaf location.

Microscope view of powdery mildew on a wheat leaf

Winter wheat powdery mildew – green islands of tissue evident in the chlorotic tissue of some leaves.

Barley – group 1 herbicide injury on leaves.

Two samples of canola seedlings were agar plate tested for damping off and found to be affected by wirestem caused by the fungus Rhizoctonia (Red River).

One sample of alfalfa was received and showed symptoms of stunting in one part of the field due to abiotic factors, possibly winter injury (North Interlake).

One petunia sample with interveinal chlorosis suspected to be an iron deficiency was received from a greenhouse (North Interlake).  When a greenhouse experiences symptoms of nutrient deficiency, plant tissue analysis is recommended to determine the cause since similar symptoms can be caused by different deficiencies and sometimes diagnosis based on a visual assessment of symptoms is inaccurate or just plain wrong.  One golf turf sample was diagnosed with a combination of 4 different diseases that included Pythium blight, anthracnose, melting out and Septoria leaf spot (Southwest).  One marigold with a stem and root rot was received (Eastman).

Several spruce samples were diagnosed this week, one with the fungus Stigmina lautii on needles (Central Plains), two with a needle blight caused by a Lirula sp. fungus (Central Plains, Eastman), one spruce with spruce budworm (Southwest), two spruce samples with delayed bud growth due to winter injury and stress (Red River, Southwest) and one shelterbelt sample undergoing significant branch dieback due to Cytospora canker (Southwest).  One sample of poplar with the disease Cryptodiaporthe canker (formerly known as Dothichiza canker) was received (Southwest).  This canker disease is known to be severe on poplars that have been stressed from unfavourable growing conditions and can cause significant damage leading to loss of the affected trees.  A pine with Western gall rust was diagnosed via an email submission (Southwest).

Poplar stem – fruiting structures of the fungus Discosporium populeum (causal agent of Cryptodiaporthe canker) visible on the stem.

One insect identification request was received and found to be a ground beetle, Chlaenius sericeus (South Parkland).  This is an attractive but non-harmful insect.

Ground beetle – members of the ground beetle family eat other insects and are not a concern for plants.

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.