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Crop Diagnostic Lab Report

Week of July 26 - July 30, 2010

Cereals One wheat sample with heavy development of Septoria leaf spot was received (Red River). One sample of wheat with physiological stem purpling was received (Red River). One sample of wheat with leaf rust was received (Southwest). One sample of wheat with a combination of Fusarium head blight, tan spot and Septoria leaf spot was received (Southwest).

Oil Seeds Two samples of canola were diagnosed with blackleg (Southwest, Central Plains). One sample of canola was diagnosed with root callousing due to group 4 herbicide injury (Southwest). One sample of canola with group 2 herbicide injury was received (South Parkland). One sample of camelina with staghead caused by white rust was received (North Parkland). Staghead causes a deformity in the flowering raceme. It often has the disease known as downy mildew associated with it and downy mildew was observed as a heavy coating of white fungus over the affected tissues of the sample.

Camelina – deformity in the raceme is called staghead and is caused by white rust but the white coating on the stem is downy mildew.

Two samples of flax with symptoms consistent with a group 2 herbicide injury were received (Southwest). One sample of sunflower with a combination of Alternaria leaf spot and rust was received (Southwest).

Forages One sample of bird’s foot trefoil was diagnosed with blossom blight caused by anthracnose (Red River). Anthracnose lesions were also observed on some stems.

Bird’s foot trefoil – the anthracnose blighted flowers had a somewhat orange appearance in this field.

Bird’s foot trefoil – the somewhat granular appearance on the petal surfaces is due to sporulation of Colletotrichum, causal agent of anthracnose.

Beans/Peas/Lentils Two samples of field peas had development of both anthracnose and Ascochyta as well as root rot (Southwest, South Parkland). Two samples of field bean were diagnosed with common bacterial blight (Central Plains, Red River).

Three samples of soybean were diagnosed with Phytophthora root rot (South Interlake, Eastman). Three samples of soybean were diagnosed with Fusarium root rot (Red River). One sample of soybean was diagnosed with group 4 herbicide injury related to soil carryover (South Interlake)

Soybean – group 4 herbicide can cause parallel leaf venation and narrowing of leaflets similar to what occurs on some other plants.

Fruit Again this week cherry leaf spot was diagnosed but this time on chokecherry (Red River) rather than dwarf sour cherry. The chokecherry sample showed a symptom known as shothole where the spotted tissue falls out leaving holes in the leaves that are sometimes mistaken as an insect injury. One sample of raspberry with cane blight and spur blight was received (South Interlake). One sample of raspberry with anthracnose and mites was diagnosed (Pembina). One sample of raspberry was diagnosed with Botrytis fruit rot (Central Plains). One sample of saskatoon with Entomosporium leaf spot was diagnosed (Red River). One sample of saskatoon was diagnosed with powdery mildew (South Parkland). One sample of apple had cracking and spotting of fruit that was diagnosed as caused by apple scab (South Interlake).

Chokecherry – cherry leaf spot causes a symptom known as shothole which causes holes in the leaves sometimes mistaken for insect injury.

Apple – these fruits show heavy development of lesions caused by the disease known as apple scab. Cracking of affected fruit can occur.

Vegetables/Potatoes/Herbs One sample of beets was diagnosed with root rot caused by Pythium (Central Plains). Pythium root rots occur on many different hosts and are favoured by moist soil conditions. One sample of rutabaga with a dry rot lesion on the root was found to be infected by Phoma lingam, the same fungus that causes black leg in canola (Central Plains). One sample of climbing bean and one sample of green bean were diagnosed with common bacterial blight (Southwest). One sample of carrot was diagnosed with root rot caused by Fusarium solani (Central Plains).

One sample of potato was diagnosed with black leg (Red River).

Trees and Shrubs Two samples of poplar with Marsonnina leaf spot were received (Red River). This leaf spot covers the leaves with numerous small spots and can cause premature defoliation. One sample of Amur maple was diagnosed with iron chlorosis (Red River). One sample of willow was diagnosed with chemical injury (Red River). One sample of spruce was diagnosed with an infestation of adelgids (North Parkland). These insects appear as small cottony spots on needles and can be identified more specifically by the types of galls they cause on twigs. One sample of poplar with leaf yellowing that could not be attributed to disease was received (Central Plains). One sample of ash with dieback and wilt symptoms had an undetermined vascular impairment (South Parkland). Trees can be affected by various vascular problems that will not always be detectable in samples submitted to the laboratory. Two samples of elm were diagnosed with Verticillium wilt (Red River) and two samples were diagnosed with Dutch Elm Disease (Red River). One sample of spruce was diagnosed with needle rust (Eastman)

Poplar – Marsonnina leaf spot causes numerous small spots on the leaves and can result in early defoliation

Spruce – needle rust can be common in some seasons and almost nonexistent in others.

Weeds Weeds this week included hemp dogbane (Southwest), common evening primrose (Southwest), thimbleweed (North Parkland), spotted knapweed (Red River), and water parsnip (Pembina).

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.

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