Late Leaf Rust

Raspberries and white spruce share a disease called late leaf rust and raspberry rust.

Raspberry plant infected with raspberry rust (Scot Nelson) Public Domain

Mid to late summer, spores of this fungal disease infect red and purple raspberries. Yellow rust is similar but produces yellow to orange pustules in early to mid-summer.


Late leaf rust symptoms

The first symptom of late leaf rust (Pucciniastrum americanum) is small yellow (chlorotic) spots on the top of older leaves. These spots generally begin appearing in lower portions of the plant, slowly spreading upwards into younger leaves. As the disease progresses, reproductive uredinia form on the underside of leaves, containing masses of spores.


Extreme infestations can defoliate the entire plant. Fruit and flowers can also be infected, which causes them to rot. Of course, if all the leaves have fallen off due to disease, there probably won’t be any fruit or flowers. If the fruit has already formed, late leaf rust will appear as tiny orange spots on individual drupelets. Affected fruits will also ripen unevenly.


Late leaf rust lifecycle

Spores of this disease overwinter in white spruce and infected raspberry canes. Wind can spread these spores, so your upwind neighbor’s raspberries can directly impact yours.


Late leaf rust control

Like other rusts, late leaf rust is best avoided by pruning plants for good airflow and avoiding overhead watering. Also, be sure to remove spent canes each year. Throw infected plant material in the trash, not the compost pile.


​Fixed copper sprays may help prevent and treat late leaf rust.