Bramble Disease - Managing Orange Rust

Photo 1 shows the appearance of infected plants in late spring. Primocanes and shoots on floricanes are spindly and numerous, and are pale green with a yellow-orange hue. Besides being off-color, leaves are narrow and have a twisted or cupped edge. Bright orange rust pustules will eventually be apparent on the lower side of the leaves of these plants. This is a good stage at which to dig out the entire infected plant, being careful to remove as much of the root system as possible. At this time, you can remove the plant before the spores are produced, which have the potential to spread the disease to healthy plants. In the following years, new plants are likely to grow from left-behind root pieces. These plants will already be infected because of the systemic nature of the disease, so they should be removed.

Photo 2 below shows some eruptions of blister-like rust pustules of various sizes on the leaf undersides, which are often described as "waxy" in appearance at first. Some are quite small, and much of the leaf underside still appears green. Spores will be produced shortly, followed by their release and spread primarily by wind.

Photo 3 shows the same plants about 2 weeks later. This is the most apparent stage of the disease cycle, as much of the leaf underside is covered with orange pustules. Abundant spores are being released at this time.

Finally, in Photo 4, the severely affected leaves dry, curl up, and die and will eventually fall off the plant. In this last photo, you can see the accumulated spores lying on the upper surface of the leaves in the background. Because the leaves with orange rust symptoms have fallen off, it may be mistakenly assumed that the disease has disappeared.

There are several other rust diseases that affect the various types of bramble plants, such as cane and leaf rust on blackberry, late leaf rust on red and black raspberry, and yellow rust on red raspberry. These diseases are not systemic, and plant removal is not necessary, so it is important not to mistake them for orange rust.

How can orange rust be managed?

First, since orange rust is a systemic disease, any plants propagated from infected plants will also be infected, including canes dug from infected plants or plants grown from root pieces of infected mother plants. Thus, it is important to start out with clean plants from a reputable nursery source.

Scout nearby wooded edges for wild black raspberries and blackberries in the spring, and remove any that show symptoms of orange rust if possible. When choosing a location for a new planting, stay as far away from wild brambles as possible, and choose fields on the upwind side of wooded areas not only to minimize the chances of orange rust spores being blown into your planting, but also other pests that might transmit viruses, such as aphids.

If plants in your planting show symptoms of infection, remove the entire infected plants early in the year as described above. If the ideal timing is missed, canes should be carefully cut, bagged, and disposed of before attempting to dig the plants out.

Fungicides in categories 3 and 11 may be applied to assist in protecting uninfected plants at the time of spore release. A second type of spore is produced in the summer, but it is difficult to tell when this is taking place, making use of cultural controls even more important.