What are those odd-looking plants?

2010 - Issue 16


number of odd looking plants have generated calls and questions lately. Some are tall, monstrous looking plants. These are called off-types. Many seed companies conduct seed multiplication in the southern hemisphere and these off-types result when pollen transfer occurs with winter canola. Another anomaly showing up is aster yellows.  Affected plants show a bunched appearance at the tips of branches where blue-green, sterile, hollow bladders are formed in place of normal pods. Normal appearing pods may be present on the lower portions of infected plants but fail to set seed. Aster yellows is caused by a phytoplasma, a plant pathogenic micro-organism. The phytoplasma is carried from plant to plant by sap-sucking leafhoppers. Off-types and plants infected with aster yellows are usually found in extremely low levels within a field and are not economic. A third odd-looking plant symptom being reported this year is stag head or white rust. This plant disease thrives under wet conditions and appears as white to cream-coloured pustules on the underside of leaves from the seedling stage onward. Following infection of the stems and pods, raised green blisters form that turn white during wet weather. The most conspicuous symptom is the presence of swollen, twisted and distorted inflorescences called “stagheads” that become brown, hard and dry as they mature. Stag head is not an economic pest of canola except in B. juncea varieties.

Canola infected with aster yellows.

Canola infected with white rust, commonly known as stag head.

 

Canola Watch