Hi Carrie, What kind of fruit tree is it? Do you have lawn in and around the tree?
Yes, you can kill grubs at root level only if you have turf in and around (but most of the time adults might fly long distance to feed and lay eggs). According to University of Minnesota, the best time to apply insecticides for grubs is from mid-July until the end of September (later the grubs will move deeper as the top soil become cooler).
To control adult insect
1. If the tree is small you can hand pick the beetles and put them in a soap solution (1 tablespoon of liquid dishwashing detergent and water) to get rid of some population. Or place the drop cloth and shake the tree in early morning to collect beetles and place them in soap solution.
2. Also you can cover the tree with the net to prevent further attack (if the tree is small).
3. Organic insecticides like neem oil and sprays containing potassium bicarbonate found to be effective in controlling beetles in rose plants.
4. Spray home made soap and vegetable oil solution (mix 1 tablespoon of regular dish soap in 1 cup of vegetable oil, then add it to 1 quart of water. Later add 1 cup of rubbing alcohol and shake vigorously to emulsify, mix well and pour it into a spray bottle. It needs to be shaken often as you are using it. Spray at ten-day intervals on pests. The best time to spray is during early morning or late evening when the temperature is cool. Improper use of home made solution may cause leaf burn.
5. Use bait like fruit cocktail to attract and kill beetles. Buy the fruit cocktail can and ferment it in the sun for a week after opening it. Later put the fermented can on top of bricks or wood blocks in a light-colored bucket, and fill the bucket with water to just below the top of the can. Place the bucket about 25 feet from the tree. The beetles will attracted to sweet bait and get killed by drowning in water. Change the bait if it gets diluted by rainwater.