Manitoba Insect & Disease Update

 

 

Thistle caterpillar and their webbing continue to be quite noticeable in some soybean fields.

Aphids are at high levels in some cereal fields in the Central region.

Soybean aphid has been found in some fields in the Central region, but currently just at low levels.

 

Pathogens: Additional reports of stripe rust across Manitoba, with high severity showing up in fields/plots that did not receive a fungicide application. If the crop is past the flowering stage, a fungicide application is likely not warranted.

 

 

There have been continued reports of stripe rust in wheat crops across the province. In the MCVET trials (which do not receive a fungicide application), symptoms are severe with pustules even forming on the glumes and awns. If stripe rust has recently shown up in your crop it is important to assess the staging before considering a fungicide application. Research indicates that high severity of rust (or any leaf disease) on the flag leaf after the flowering stage is less likely to have an impact on yield. The table below illustrates the severity of leaf rust on the flag leaf and the predicted yield loss based on the stage of the crop.

 

Growth Stage	Severity of Leaf Rust on Flag Leaf (%)
	10	25	40	65	100
Flowering	10% yield loss	15% yield loss	20% yield loss	30% yield loss	35% yield loss
Milk	2% yield loss	5% yield loss	8% yield loss	14% yield loss	20% yield loss
Soft Dough	1% yield loss	3% yield loss	4% yield loss	7% yield loss	10% yield loss
Hard Dough	1% yield loss	1% yield loss	1% yield loss	3% yield loss	5% yield loss

 Adapted from: Hunger, B. and K. Jackson. Foliar Fungicides and Wheat Production in Oklahoma. Oklahoma Cooperative Extension Service. Oklahoma State University.