I had problems with yellow jackets in my backyard last year, which made eating outside challenging at times. Is there something I can do to prevent problems again this year? I have a large garden with many different plants.
— Reese Pollack, Oak Park
It certainly is annoying to battle yellow jackets as you are eating. Even keeping them out of open soda cans can make outdoor dining tricky. Populations of yellow jackets build up in summer. These yellow-bodied social wasps are considered beneficial insects that pollinate flowers and prey on grubs and beetles. They prefer sugary foods and nectar from flowers, but will eat meat, garbage, and picnic food that’s left outside. The yellow jackets’ wide diet attracts them to urban areas because a lot of what we eat and throw away is food to them. They are particularly attracted to sweet things like soda and dessert. They may crawl into your soda can in between sips if you do not pay attention. Yellow jackets will continue to return to a site once they find a good source of food, so the best way to reduce this pest problem is through good sanitation to attract fewer to your dining area. Be sure to thoroughly clean up food and drink residue when you are finished eating and dispose of it in a covered trash can. There are traps that you can buy for yellow jackets, but since they use a pheromone to attract the insects, you may end up drawing even more of them to your eating area rather than controlling them. You will get the best results by keeping the area clean.
I have not yet seen many yellow jackets in home gardens, but it is getting to be the time of year to watch more carefully for yellow jacket nests in the garden. The first hard frost will kill most of the yellow jackets. Queens do not use the same nest in the following year but may use a site close by if it is favorable. Yellow jackets are especially active on warm sunny days in late summer and fall. The best way to spot them is as they fly in and out of the nest. Yellow jackets tend to nest in more secluded places like brush piles, ground cover beds, rotted logs, cracks or holes in the ground or pavement, under steps or porches on a house, in house walls and foundations and at the base of trees and shrubs. Just because they are present during your meals does not necessarily mean there is a nest in your garden. They will aggressively sting if you happen to disturb their nest with typical gardening tasks such as planting, pruning, raking or weeding. Vibrations of a mower adjacent to or over a nest or the impact of a wayward basketball can also disturb them enough to swarm and attack a person close by. Their stingers are smooth, which means they can sting more than once, and the stings are painful. There is no need to treat a nest though unless it happens to be in an area that poses a hazard to pets or people. Simply avoid the nest as you work in the garden. I currently have a nest located under an evergreen next to the front steps of my house. I plan to leave it alone as it can easily be avoided. Walking by this nest to the front door does not pose a problem.
Bald-faced hornets construct large paper nests in trees at head height and above, so you should also watch out for them as you are working in the garden. Garden staff found the first one last week at head level. You will be most likely to disturb them by pruning a tree or bumping into a nest with a piece of equipment. Bald-faced hornets are black and white wasps and are aggressive if disturbed. Bald-faced hornet nests that are high up in trees pose very little danger. Paper wasps build nests under eaves, signs, benches and fence railings and will sting if disturbed. These are beneficial insects, so control them only if they pose a safety hazard. Unfortunately, the response of most people is to destroy any nest that is discovered.
If you find a nest that poses a danger to your family, use an aerosol insecticide formulated for wasps and bees to thoroughly soak the nest. Spray the nests from a distance to reduce the chance of being stung. It is best to treat the nest at dusk or early in the morning when there are more wasps in the nest and they are less active. Stay away from the area for a day or so as the treatment will agitate them. Check the nest the next day and treat it again if necessary. Whenever possible, I avoid killing a nest.
For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at plantinfo@chicagobotanic.org. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.
