--- Michael Persiano wrote:

Nina:

With respect to Cedar-Apple Rust, what do you
recommend for prevention as well as for treatment
(barring the removal of complete shoots and
branches)?

There was a good article on this a few years ago in the ABS journal (I
was a co-author with Andy Walsh and I drew the illustrations). But the
upshot is: Cedar apple rust *itself* is not much of a problem on
junipers, because it infects single needles, so the whole gall can be
removed with little trauma to the tree. Also, the galls only live one
season, then die. But spores from the juniper gall infect roseaceous
hosts, (primarily crabapple and apple), which get leaf spot symptoms. A
few spots won't harm them. However, if the roseaceous bonsai are kept
close to a big infected landscape juniper, they could suffer
defoliation and twig death. The solution is to move them away from the
juniper. If you live in an area with lots of junipers, the solution
would be to move the roseaceous trees to a sheltered place during rainy
spring weather or spray them with an appropriate fungicide as directed
(Cooperative Extension should be able to recommend a fungicide and
spray schedule for your region).

BUT: There's also Hawthorn rust. It also infects junipers, but it
causes galls on twigs, so the twig must be removed to get rid of the
gall. Luckily, the galls only live a few years, so they don't get too
big. The alternate host is hawthorn. This is a less common rust, but
when it's present, it can cause design headaches when you have to
remove galled twigs.

FINALLY: There's quince-apple rust. The galls will live and grow
indefinitely, so if it is found on a juniper trunk or main branch, it
can't be pruned off without ruining the bonsai aesthetically. On the
alternate hosts, it infects fruits, particularly on hawthorn, apple and
amelanchier. The infection on the fruits look like little papery
cigarettes filled with orange dust; they're pretty obvious. The worst
they do to roseaceous bonsai is make them ugly, but if you see this
kind of infection on fruit, you know your junipers are at risk. You
could spray during the infectious season (again, Cooperative extension
for your state will tell you what that season is for you), but I
wouldn't bother. When I lived on Long Island, I had all three rusts on
my landscape junipers, and my yard was filled with apples and wild
hawthorn. All I did was watch my junipers REALLY carefully in spring
and remove galls as soon as I saw them. Quince apple galls have to
start on green tissue, so if you catch them early they won't be too
damaging. The problem is that they aren't weird like cedar-apple and
hawthorn rusts, with those orange gelatinous horns sprouting
everywhere, so you have to look harder to see the young galls. The
gelatin is still bright orange; examine your junipers after a rainstorm
and look for orange gum on the branches.


Nina