Is the blackberry leaf-rust safe?

Rust spores are not toxic to humans and animals but may cause irritation to people sensitive to pollens and dusts. In such cases, it is recommended to wear safety equipment such as goggles, a respiratory mask and gloves when handling rust spores or infected foliage.

The additional rust strains of the blackberry leaf-rust fungus (Phragmidium violaceum) were thoroughly tested before approval was obtained to release them in the environment. They were shown in host-specificity tests to be highly specific towards weedy European blackberries.

Results from these tests also demonstrated that that these additional strains pose no greater risk to commercial blackberry cultivars and Australian native Rubus species than the strains that already existed in Australia before their release.

There are a number of fungi that cause 'leaf spots' on cultivated blackberry: Cercospora rubi (causing Cercospora leaf spot), Elsinoë veneta (causing Anthracnose), Septoria rubi (causing Septoria leaf spot) and the rust fungus Kuehneola uredinis (causing cane and leaf spot). It is important for growers to be able to distinguish these leaf spots from those caused by the blackberry leaf-rust, the rust fungus introduced for the biological control of weedy blackberry.

Leaf-spot diseases may be causing isolated incidents of reduced fruit yield, but the contribution of the blackberry leaf-rust in relation to other fungi that cause leaf spots is probably negligible and should be determined in each instance. If rust occurs on raspberries, then it is most likely caused by Phragmidium rubi-idaei, a species related to the blackberry leaf-rust.

For the last three decades, exotic rust fungi have been used for the biological control of weeds in Australia without even an unpredicted shift between forms of the same host species. Their safety record is unblemished, indicating that the scientific guidelines followed prior to introduction of the fungi were appropriate.

The spectacular success of some of these fungi in reducing the impact of weeds, as seen with Puccinia chondrillina introduced in the early 1970s for the control of skeleton weed and more recently with the bridal creeper rust reminds us that there is a lot to be gained from this method of weed control.