Monday, March 24, 2014

Jumpin' Junipers - Red Cedar Problems

Dr. Chuck Hodges at age 82.99.
This blog post is dedicated to our esteemed colleague and expert on tree diseases and on molds, Dr. Charles Hodges, who celebrates his 83rd birthday today. He collected some eastern redcedar (Juniperus virginiana) branches from a golf course last Thursday that demonstrate several problems we'll be seeing over the next few weeks.

One branch was remarkable in that it had not one but two Gymnosporangium rusts, indicated by the arrows in the photograph below.
Infections of quince rust (left) and cedar-apple rust (right) on the same eastern redcedar branch.

The large woody galls on the right are produced by cedar-apple rust (Gymnosporangium juniperi-virginianae), which will be exuding gelatinous orange telial horns when the warm rains arrive in April or May. The spores produced on those horns (basidiospores from teliospores, if you want to get technical) will blow on the wind and infect the leaves and fruit of nearby apple and crabapple trees. Those infections will result in the production of another kind of spore which - if fortunate enough to get a ride on the wind to a juniper - will cause a new infection in summer. Eastern redcedar and Rocky mountain junper are the principal hosts. Those infections will not develop into galls until the year, and they'll mature the following spring. For more information and some nice pictures, see last year's blog post on this disease.

Quince rust infection on an eastern redcedar branch.
The smaller orange-colored swelling on the branch is the telial stage of quince rust. By the last week of March we already see this one forming spores on juniper in eastern North Carolina. The gelatinous telia function the same way as those of cedar-apple rust but are not as large and showy. Another difference is that quince rust infections on juniper are perennial, whereas the cedar-apple gall dies out after producing its spores.
The quince rust fungus, Gymnosporangium clavipes under the microscope.
The two-celled orange teliospores are only 1/500 of an inch long.
Carrot-shaped pedicels beneath are diagnostic for the species.
Quince rust affects not only quince and flowering quince but also hawthorn, serviceberry, and very commonly ornamental pear, where it sporulates abundantly on fruits and less so on swollen twigs in the early summer.
Ornamental pear fruits covered with the white papery peridia of the aecia of quince rust.
Shed spores from the fruit give an orange cast to the leaves. Note: This stage is still months away.
 What about control measures? On juniper you can prune out the galls if they are unsightly or if the branch dies. On susceptible cultivars of apple grown in the vicinity of junipers, fungicide sprays may be needed to avoid losses.

Symptoms of Kabatina tip blight on juniper.
The other disease that Chuck brought in was Kabatina tip blight. The last several inches of the affected twigs had died and faded. When tip blight occurs on juniper in North Carolina in the late winter, Kabatina is the prime suspect. This is also a fungal disease, but you have to look hard with young eyes or a handlens in order to see the tiny gray/black spore-producing bodies (acervuli) at the base of the dead twig. These spores are probably moved by rain splash rather than the wind. In this case the spores are capable of infecting juniper rather than some alternate host. Infection requires some sort of injury either by insects or physical damage. References disagree on whether infection occurs in the fall or spring, but the tip does not die until the following year. Not just eastern redcedar but also other Juniperus spp. are susceptible. No control measures are needed.