Garden Matters: Do Marigolds deter bugs?

Marigolds
Photo credit: Dale Odorizzi
Posted on: June 20, 2019

Do Marigolds deter bugs? If so how? This is something I have wondered about several times. The obvious answer is because the marigolds are smelly. This was brought out at a recent information session I attended about emerald ash borer. They didn’t mention marigolds but did mention elm and of course ash trees. It was said that the pruning of ash trees seemed to increase greatly the chance of that tree being infested with the borer. And apparently the same happened to elm and the elm bark beetle which transmitted Dutch elm disease back in the 60’s and 70’s. The cutting into live ash or elm wood emitted an odour attracting the insects to the trees. 
Has anyone ever grown sweet potato vine, which is an Ipomoea, or morning glory, and found the leaves chewed? This is caused by a gold coloured ladybug shaped beetle, also the red lily beetle or the iris borer. All of these plants and insects have a connection. Just like moths are attracted to each other by pheromones, these bugs are attracted to the only plants they survive on by the signature smell given off by these plants. 
So what to do to stop or at least control these insects? If you spray you must make contact with the insect. To do that, every leaf should be looked at, both top and bottom of the plants like morning glory or lilies. It would be easier to just squish or remove the insects when you see them. Wear gloves if you have to! In the case of the iris borer, infestation is not noticeable until it is too late. Because these insects find these plants by smell, masking the plants’ odor would be something to try. This is why planting marigolds among some of these plants will work: marigolds have a strong odor. Try other plants with a strong smell also, such as lilies, among other plants. One lily smells less than five lilies planted together. I found that out this spring when I grew morning glory from seed and had about twenty pots huddled together. The smell was like a magnet to the beetle. Spray lemonade (because it is smelly ) or tabasco sauce or a very light concentration of vinegar or add other smells to the garden like moth balls to hide the odour of these plants. This would have to be done early and on a regular basis to be effective. This may not work one hundred percent of the time but then nothing does.

Article by Paul Pietsch

Paul Pietsch is a member of the Lanark County Master Gardeners.  Want to know more about the Master Gardeners group or ask a gardening question? Visit our website at www.lanarkmg.blogspot.com or contact us at lanarkmg@gmail.com