Notes on Poison Ivy

Poison Ivy 3' from the sidewalk. Not on my client's property but on Leonard Street in Eaton Rapids.

The number of poison ivy plants seem to positively correlate with the number of feral asparagus plants, Virginia creeper and grape vines.

The poison ivy, VC and grapes fill a similar ecological niche so it is not surprising that they run together. They are vines that produce small, persistent (i.e. hang well into winter) berries so birds that eat PI berries are also feasting on VC and grapes and poop-them-out in the same places.

An implication of that is that if you only control the PI but give the Virginia Creeper and wild grapevines, then the birds who are attracted to the VC and grapes will replant the PI. Even though they are competing for the same niche, they are passively cooperative in terms of spreading seeds.

The asparagus is the flier and was likely present when the grounds were converted from agriculture. I believe the berries of the female asparagus plants were the food that originally attracted the berry-eating birds.

Another implication is that landscaping plants like Washington Hawthorn (small persistent haws) will likely have PI infestations beneath them.

The common practice of using glyphosate in the spring to control grass in the landscaping beds favors poison ivy because it leafs out much later than the grass greens up. Spraying glyphosate in May (in Michigan) gives PI a competitive advantage. One work-around is to spray herbicide in mid-June once every three years rather than always spraying in early-May.