“There have been lots of yellow jackets in our backyard recently, making our outdoor dining challenging at times. What can we do to eliminate or reduce them? My garden is large with many different plants.”

— Laura Yee, Lake Villa

Populations of yellow jackets build up in summer. They are considered beneficial insects that pollinate flowers and prey on grubs and beetles. This is the time to year to watch more carefully for yellow jacket nests in the garden.

Continue this watchfulness until there has been a hard killing frost that will kill the yellow jackets. The yellow jackets are especially active on warm, sunny days in late summer and fall. You can spot them flying in and out of the nest. Yellow jackets tend to nest in more secluded places such as brush piles, ground cover beds, rotted logs, cracks or holes in the ground or pavement, under steps or porches on a house, house walls and foundations, and at the base of trees and shrubs.

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 prefer sugary foods and nectar from flowers but will eat meat, garbage, and picnic food that’s left outside. They will 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 in your dining area. There are traps that you can buy for yellow jackets, but since they use a pheromone to attract them, you may end up attracting even more of them to your eating area versus controlling them. You will get the best results by keeping the area clean.

Just because they are present during your meals does not necessarily mean there is a nest in your garden. They will aggressively sting you if you happen to disturb their nest with typical gardening tasks such as planting, pruning, raking and 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 nearby person. 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 to my house. I plan to leave it alone, since it is easy to avoid.

Bald-faced hornets construct large paper nests in trees and large shrubs at head height and above, so also watch out for them as you are working in the garden. You are most likely to disturb them by pruning a tree or bumping into a nest with a piece of equipment. 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.

If you find a nest that poses a danger to your family, a good way to proceed is to use an aerosol insecticide formulated for wasps and bees to thoroughly soak the nest. You should be able to spray from a distance to reduce the chance of being stung. It is best to treat the nest at dusk 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 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.