Cedar Apple Rust on Juniper
Cedar apple rust, a truly colorful disease, rarely causes significant damage to junipers, but the mere presence of the rust galls on twigs may be considered unsightly, especially when the woody galls "bloom" in April and May. In mid-spring, when conditions are right, the galls produce gelatinous bright orange tendrils that release millions of fungal spores. And although cedar apple rust may not damage the junipers, this disease does cause serious damage on non-resistant apples and flowering crabapples, on which it can initiate premature defoliation and fruit distortion.
There are several ways to tackle the problem of cedar apple rust. In landscape situations where only a few junipers are present, pick off the rust galls in late winter. The galls are killed once they are detached from the tree.
You can apply fungicides at 7- to 21-day intervals from early June through August to prevent infection and gall formation on the junipers. (During this period, the fungal spores are being released from the apple, crabapple host trees back to the junipers.) Fungicides will not control the active gelatinous galls in the spring.
Likewise, controlling the disease on apple and crabapple with timely applications of fungicides will help to reduce re-infection of the junipers. Call the Extension Office for a list of fungicides rated for cedar apple rust control on juniper and apple.
Select resistant junipers when choosing new plant material. Keep in mind, too, that there are other rusts hosted by junipers that attack other members of the rose family, namely cedar hawthorn rust and cedar quince rust. The fungi manifest themselves in much the same way as cedar apple rust, and the diseases are controlled in the same way.