Manitoba Insect & Disease Update

Insects: Some field edges and a few fields have had grasshopper populations controlled. Some field edges are being watched for grasshopper levels and whether there is much feeding to crops. Aphid levels in peas and cereal crops are still quite low. No soybean aphids have been reported yet. 

 

 

Canola plants showing clubroot symptoms were observed last week (Figure 1). The affected plants are located along a waterway in the field and the affected area covers at least 7 acres. The field, while a new clubroot case, is located in a rural municipality where clubroot symptoms have been previously observed. This finding will not change the Manitoba Clubroot Distribution Map. Best management practices for fields where clubroot is suspected or fields at higher risk (in RMs where clubroot has been detected) include a 3- or 4-year rotation, growing clubroot resistant varieties, and practicing good sanitation (knocking off soil, completing field work on affected fields last). Early detection is important for clubroot management, so be vigilant about scouting areas where plants are less vigorous and consider having a soil test done for the presence of clubroot DNA.

 

 

Apothecia, the fruiting bodies of Sclerotinia sclerotiorum, were observed within the canopy of a wheat crop (on canola stubble) in the MacGregor area (Figure 2). This area has received more consistent moisture than many other areas of the province. In order for a sclerotia to germinate and produce apothecia, they require at least 10 days of moist soil conditions (surface soil - as only sclerotia within an inch or two of the surface will produce apothecia on the surface). Canola and dry beans in many areas of the province are through or at the stage when a fungicide application is being considered. Keep soil moisture conditions and humidity within the canopy in mind when making the decision of whether or not to spray.

 

 

 

There continues to be reports of suspected Phytophthora root rot in soybeans in the central region (Figure 3). Root rot in field peas is also showing up in the Hamiota area (Figure 3). If root rot is suspected in field peas samples should be sent in to the diagnostic lab to identify the causal agent. If Aphanomyces root rot is identified a rotation of 5 to 7 years between field pea crops is recommended. Typically when Aphanomyces root rot is present, Fusarium is present as well. Symptoms of Aphanomyces root rot include caramel-coloured root systems whereas Fusarium will show up as darker discolouration on the tap root.

 

 

Wheat streak mosaic virus is suspected in the RM of Macdonald. Spring wheat plants were submitted that exhibit typical symptoms of this disease (Figure 5) and a winter wheat field was located nearby. This disease is vectored by the wheat curl mite which overwinters on wheat and occassionally other grass species. The main method of control is by breaking the green bridge as the mites will not survive on plants that have dried down. If there is a period of time in the fall when the spring wheat has dried down and the winter wheat has not emerged the mites will be without a host and wheat streak mosaic virus will not spread. Samples from the suspected field have been sent to the Crop Diagnostic Lab for confirmation.

 

 

 

The aecial stage of the rust fungus in sunflower was observed this week in the Cypress River area on sunflower plants at the R1 stage (Figure 6). This disease overwinters on sunflower residue and it is typical to see the aecial stage at this time of year. If rust symptoms are observed it is important to continue scouting as the typical threshold for a fungicide application is 2 to 3% pustule coverage on the upper 4 leaves during the R5 growth stage.

 

 

Wheat midge emergence should be close to complte southern Manitoba, and around 50% in more northern areas. So for wheat fields that have headed but have not flowered yet, an evening trip to the field to assess levels of egg laying midge would be timely.