A Canola Watch reader emailed this question: I have been scouting a lot of canola fields and flea beetle stem feeding is evident. If flea beetles are just biting into the stem and not very deep, will the plants survive? How much of the stem needs to be gone before the plant is in danger of dying?
Answer: If the tissue underneath the bite is still living, the seedling will likely survive as long as (1) the stem can still bear the weight of the cotyledons and first leaves, (2) the stem is not to subjected to more feeding, and (3) weather conditions are good for plant growth. With decent soil moisture and limited stress, the plants can recover well. However, hot dry windy conditions could desiccate stem-damaged seedlings.
Always look at the stems as well as the leaves when making flea beetle spraying decisions. Action thresholds are based on leaf-area loss estimates, but stem feeding needs to be included in the spray decision. Seedlings that die from stem feeding should be counted as 100% leaf area loss in your averages. What about a stem that will pull through but can’t function at 100%? We don’t really know how to account for that, but you might want to take a fairly conservative approach if feeding seems to be getting worse and the crop is struggling.
As a general observational guide, if the field is thinner than it was the last time you checked and if flea beetles are the cause, action is likely required.