Crop Diagnostic Lab Report

 

Week of August 10 - 14, 2009

Only two small grain samples into the lab this week, a spring wheat with significant development of wheat streak mosaic virus (WSMV) in the field due winter wheat plants present in the field from a previous attempted crop (Red River).  That same sample had a significant level of Septoria leaf spot.  Some of the plants were severely stunted and although attempting to head out, many were sterile empty heads with plants starting to die.  The second was a wheat sample with purpling of glumes consistent with a physiological reaction to environment (Southwest).

Wheat – wheat streak mosaic virus caused varying degrees of stunting in these plants.

 

Wheat – this leaf shows the yellow mosaic pattern caused by WSMV as well as Septoria leaf spot.  In earlier stages of the disease development, the yellow mosaic pattern is more subtle and yellowing less intense.

 

Wheat – yellow mosaic of the flag leaf from WSMV and an unemerged head.

Six samples of soybean with Phytophthora root rot were diagnosed (Red River, South Interlake).  One sample of soybean with iron chlorosis was received (Red River).  One sample of soybean showed symptoms consistent with group 4 chemical injury (Red River).  One sample of peas was found to be affected by Fusarium root rot (Southwest).  One sample of field beans with halo blight, a bacterial disease, was diagnosed (Red River).

Bean – halo blight is a bacterial disease that causes large yellow halos around infection points.

One sample of canola with chemical injury was received (South Interlake).  One sample of flax was diagnosed with brown stem blight and root rot (Southwest).  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 canaryseed with common root rot was diagnosed (South Interlake).  One sample of field corn with Goss’s wilt was received.

One sample of potato with blackleg was received (Central Plains).  One sample of potatoes with symptoms of chemical injury was received (South Parkland).

Potato – blackleg is a bacterial disease of potato that causes a black or dark brown discoloration of affected stems.  The affected tissue often has a foul odour because of the bacteria.

One sample of tomato with Septoria leaf spot and a problem of cat facing of the fruit was received (Red River).  Two samples of cucumber and one of watermelon with leaf whitening symptoms consistent with temperature injury were received (Central Plains, Red River).  Cold temperature would be suspect in these cases but warm temperature could cause similar injury.  Cucurbit family plants are known to be injured by temperatures below 10^oC and there have been some nights below that in recent weeks in some areas.  One sample of cucumber fruit with skin scarring due to an undetermined cause was received (Red River).  In this case, cool temperature would also be a possible cause.

Cucumber leaves and melon leaf – cucumber leaves on top and the melon leaf on the bottom of this picture show whitened areas on leaves consistent with temperature related environmental injury.

Two samples of raspberries with severe leaf injury caused by spider mite infestations were received (Central Plains).  Two samples of raspberry were diagnosed with anthracnose, a disease that can attack canes, leaves and fruit (Central Plains, Red River).  One sample of grape with leaf discoloration due to suspected nutrient deficiency was received (Central Plains).  One sample of saskatoons with Entomosporium leaf spot was diagnosed (Red River).

Raspberry – this berry shows some areas of the berry that appear to be diseased and tested positive for the anthracnose fungus.

Raspberry – this cane shows lesions from anthracnose.

One sample of trees was submitted with suspected chemical injury (North Parkland).  One sample of poplar and one sample of elm with suspected vascular impairment were received (Valleys North).  Tree problems can be very difficult to diagnose since symptoms of a vascular impairment can be displayed well beyond the location of the impairment.  Obstruction of the water conducting vessels of a tree can be caused by disease or injury to roots, trunk or branches with dieback or wilting symptoms of various kinds then being displayed on leaves above the point of obstruction.  Some disease can be detected in symptomatic sample pieces but many times, the samples contain no apparent cause for the symptom.  The symptoms tell us that a vascular problem is occurring but not the cause. 

Poplar – this sample of poplar shows symptoms of a vascular impairment but no disease was found in the vascular tissues of the sample piece.  Symptoms in trees can be displayed well beyond the point where the problem is located.

Weed identifications for this week were false flax (North Parkland), kochia (South Parkland), and northern willowherb (Southwest).

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.