White pine weevil and your spruces and pines

Spray time is approaching rapidly for this pest of spruces and pines.

With the last several days of warm weather, the frozen tundra is springing to life. Along with the grass, the trees have buds rapidly swelling and soon will explode with a flurry of tiny, perfect leaves. It’s also the time that the universally hated white pine weevil makes her appearance. As everyone is rejoicing in spring, the female white pine weevil is making her way to the leader or the tallest part of a pine or spruce near her. She will lay her eggs in the next several weeks. Her eggs hatch into larvae and they begin the destruction of the new leader that is forming.

Emergence hole of a white pine weevil.
Round larva emergence hole is visible in the center.

By June, that new leader is beginning to bend over in a characteristic shepherd’s crook and turning pale green as it dries up. Soon, that promising new growth at the top of the tree has turned tan and dead. The kiddies have destroyed the interior of the new leader.

Dead tip of the tree forms a "shepherd's crook."

This sad event can be prevented by smart gardeners. By spraying the leaders of all your pines and spruces, you are preventing a problem. It is critical to get there first to stop the loss of the tree’s leader. If the timing is wrong, the larvae will continue on their path of destruction. The critical part is to time the spraying of the pesticide correctly before mommy arrives. The next critical part is to spray only what is necessary on the tree to protect it.

The product is a pesticide with the active ingredient of cyfluthrin. An example of a product that contains cyfluthrin is Bayer Advanced Garden Multi-Insect Killer. Mix in a pressurized tank sprayer following the directions. Then spray the leader of all pines and spruces on your property. Spray until the leader is wet or, as the phrase goes, to the point of runoff.

Timing of the insecticide is usually the middle of April. Or a plant indicator that lets you know it is at a critical time is the blooming of the silver maples. They produce flowers that look like yellowish green fringe and appear before the leaves pop out. For southern Michigan, that could be within days. That’s when the mommies are out stalking the trees. One application should be adequate unless it rains hard after you have sprayed. By the beginning of May, mom has either connected with a leader or been unsuccessful. Spray and ruin her day.

Michigan State University  Extension’s Horticulture Hotlines (888-678-3464) will receive hundreds of phone calls when homeowners begin to see the leaders dying in June and July. But at that time, there is nothing to do except cut off dead leaders and learn how to create new ones for the damaged trees. No one can predict which pines or spruces the females may go to so it is important to spray them all. Consider it your insurance policy so a year of upward growth will not be lost on your trees.

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