Juniper-pear trellis rust

Asked November 8, 2019, 2:08 PM EST

Hi, I have about 10 pear trees of different varieties on my 1.4 acre residential property near Wilsonville (and 10 apples as well, plus a few plums). Five of the pear trees are right next to a large mature juniper hedge, and I'm fairly certain they are (badly) infected with juniper-pear trellis rust. (The apples have codling moth and scab.) A complication is that our well water is drawn from beneath the orchard (on the other side of the house away from the junipers). I've had an an arborist out and he has recommended a pesticide spraying program starting in late winter. However, he apparently isn't familiar with trellis rust and has been calling it cedar-pear rust, which looks different to me. I'd greatly appreciate any guidance you might have regarding treatment options that would minimize pesticide infiltration to the well water. We'd be willing to take out the trees adjacent to the juniper hedge, as they aren't doing well anyway. Thanks in advance for any suggestions.

Clackamas County Oregon fruits rust

5 Responses

Thank you for your question. Before any pesticide applications are applied, the correct disease needs to be identified. I suggest you bring samples of the plant tissue with the fungus to the Clackamas County Extension office, where it can be identified using a microscope and comparing it to known species. The office is at 200 Warner-Milne Road, Oregon City, and has staff to help between 9 and noon, and 1:00 and 4:00 pm on weekdays (closed Veteran’s Day). Good luck!

Thanks for the suggestion. I took a leaf sample to the extension office. Definitely juniper-pear trellis rust. They recommended "one-cut pruning". I think I'll start by taking out the 5 badly infected pear trees right next to the juniper hedge and see if the 5 remaining pear trees on the other side of the house will get less infected due to the distance from the hedge.

I've read that this fungus requires rainy weather to propagate from the junipers back to the pears. Possibly covering the juniper hedge with plastic sheeting in April and May to keep it dry might discourage the spread of the fungus?

Glad to know you got help at the Extension office! I have searched for preventative measures to take to prevent rust (other than from removing or moving host plants), and covering with plastic isn't one of them--primarily because it reduces air circulation, which causes other fungi to develop. Here is an Extension article on rust prevention generally: http://ipm.ucanr.edu/PMG/GARDEN/FLOWERS/DISEASE/rusts.html

Hope this is helpful. Good luck!

Thanks much, Kristena, I appreciate the pointers.