CANOLA QUIZ – Clubroot scouting

Seeing galls again? Or seeing galls for the first time? Here are four quick questions to guide your pre-harvest clubroot assessment for 2021.

1. Clubroot infection could be lower in dry soil conditions. One reason is that resting spores need moist soils to germinate into infecting zoospores. What is the other reason?

Zoospores swim through soil moisture to reach root hairs. No moisture, no swimming.

Root hairs have a waxy coating that is impervious to infection.

Moisture keeps soil cool. Clubroot spores don’t like warm soil.

Fungicide residual carryover will be high in dry soils. This will reduce spore viability.

2. Mud on equipment is a quick way to spread clubroot-infested soil. In dry conditions, what is the more likely way to spread clubroot-infested soil?

Tillage causes soil to blow, and carry clubroot.

Baling crops for feed picks up infested soil.

The combine header, working in low-stature crops, picks up soil.

All of the above

3. Biosecurity is important for farmers, agronomists and anyone accessing farm land. Disinfecting boots and scouting tools is a good step after each field visit. Select which two products are known to destroy P. brassicae resting spores when saturated for 10 minutes. (0.5 point each)

Ethanol

2% sodium hypochlorite (bleach) solution

SprayNine

Virkon

4. Lime will increase soil pH, making the soil less hospitable to clubroot. It can take a few tonnes per acre of lime to make a difference, so liming is probably most cost effective for patch management. What is the target soil pH when applying lime to manage clubroot?

6.0

6.6

7.2

7.8

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Pre-harvest is a good time to scout canola for yield-limiting levels of disease. This is when disease symptoms tend to be most obvious, which makes it easy to assess the degree of damage. Please read Disease ID tips for pre-harvest scouting.