Alberta weekly pest and disease report

In his weekly Call of the Land interview, Alberta Agriculture pest specialist Scott Meers says cabbage seedpod weevils and cereal leaf beetles are dying off faster in the recent heat. He says seedpod weevil activity has slowed and does not recommend spraying at this time even where infestation is fairly high.

Despite earlier concerns, diamondback moths have not proven to be a major concern, perhaps due to heavy rain and parasitism. While there might be hot spots, "We’re not finding the numbers of diamondbacks that we expected," Meers said.

Some grasshoppers are being reported in the Peace River region, and Meers warns that the insects thrive in hot weather. "Any grasshoppers that are just emerging now will do extremely well given this heat."

Meers says wheat is at the most susceptible stage — "Fields that are just heading out now are at risk" — and scouting is recommended.

Diseases — excerpts from the weekly report

Alberta Agriculture’s weekly surveillance update says that AAFC pathologist Byron Puchalski reports that stripe rust is now common on wheat in the Foremost area. Stripe rust was also obseved July 11 on barley at Lacombe, the first report on barley.

The following counties are on stripe rust alert: Cardston, Lethbridge, Forty Mile, Taber, Warner, Willow Creek, Foothills, Vulcan and Newell. Additionally, the disease has been observed around the Olds, Trochu and New Norway areas of central Alberta.

Winter wheat has become seriously infected in the alert areas with hot days bringing any slow or latent infections into severe pustulation/sporulation. In addition to hot days, there is still high humidity and heavy dew in crop canopies for extended periods.

Under these conditions, stripe rust can progress very rapidly due to abundant inoculum, lots of susceptible host tissue and high humidity. Spring wheat is beginning to be infected in the counties on alert and will need to be monitored carefully and regularly.

Scouting every second day is recommended, and then daily when stripes appear. Keep in mind that it may not be necessary to apply fungicides to crops with intermediate or strong resistance. Thresholds for fungicide applications are:

• Susceptible types:  2% incidence, 4% severity =  spray.
• Intermediate resistance 10% incidence, 10% severity = spray
• Resistant 15% incidence, 15% severity and increasing = spray.
• 70% incidence, 45% severity =  too far gone to spray.
Incidence  is based on the number of plants in the field with stripe rust symptoms. Severity is  the average percentage leaf area showing symptoms of stripe rust on any given plant.

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