Stem borers
How to get rid of the pests
Stem borers belong to the family of nematodes. They enter plants through stomata, where they begin to feed. Their excrement is toxic to the plant. Leaves and stems swell, twist and turn a bluish colour.
Treatment
At the first sign, remove the affected plant and surrounding soil. Planting calendula and marigolds is a preventative measure; if infested, spray the plant with calendula or marigold broth.
Ed Kurtz, Bugwood.org / CC BY (https://creativecommons.org/licenses/by/3.0)
