Tree removal, fungicide ward off cedar apple rust

Evergreen trees such as pines, spruce and cedar often are most enjoyed during the Christmas holiday season. The bright lights, shining star and wide array of ornaments adorn the tree, helping to capture all of Santa’s magic. However, this time of year, the juniper and cedar trees are loaded with seasonal ornaments that are neither charming nor magical. Rather, they are grotesque indications of something not right. So if your evergreens are full of orange slimy balls that have developed since the last rain, here is what they are and what you need to be doing:

Cedar apple rust is a common diseases of edible and flowering crab apples in Kansas. These rust fungi spend a portion of their life cycle on rosaceous hosts, such as apple and flowering crab, and another portion on species of Juniperus, mainly eastern red cedar.

All winter long, cedar apple rust has been lying dormant as reddish-brown galls on the twigs of juniper. These woody galls are from 1/2 to 2 inches in diameter. With the recent rains, the galls swelled and produced orange, 1-inch-long, gelatinous tendrils. The tendrils will remain on the galls through the month. The galls of cedar-apple rust last only one season. The spent galls dry and will fall from the tree during the summer months.

The problem with cedar apple rust is the infection on apple and crab apple trees. The disease causes round, bright orange 1/4-inch-diameter lesions on the leaves. Severely infected leaves will drop during the summer. Premature defoliation weakens the tree and reduces fruit set and yield the following year. Trees with severe defoliation also are susceptible to other diseases.

Removal of junipers within a 2-mile radius of apple trees will disrupt the life cycle of the rust fungi. This has been suggested as a control measure in some states. Unfortunately, in Kansas, eradication of the alternate host becomes an impossible task because of the large native population of eastern red cedar and the wide use of junipers in windbreak and ornamental plantings. Nevertheless, homeowners should avoid planting apples or flowering crabs near junipers.

Fungicides can be applied to apple or flowering crab in the spring to prevent rust infection. The first spray should be applied as soon as the gelatinous tendrils are noticed on the cedar galls. This typically occurs in early April. Continue applications on a seven- to 10-day interval as long as the galls remain active – usually until the end of May. Several chemicals, including ferbam, myclobutanil (Immunox) and triadimefon (Bayleton) are effective in controlling rust diseases. Captan and benomyl, labeled for control of apple scab, are not effective in controlling rust diseases. In areas where both rust and scab are a problem, be sure to select a fungicide or combination of fungicides that will control both diseases. Check fungicide labels for proper rates of application.

One way to avoid fungicide sprays each year is to plant tolerant or resistant cultivars of flowering crab and apple. For a list of resistant varieties, go to

Although the presence of galls on twigs of juniper and cedar trees may be unsightly, rust diseases generally do not cause serious damage. Nevertheless, susceptible trees may be protected from infection by three to four fungicide applications sprayed at 10-day intervals, beginning in early July. Because it takes two years for galls to develop, benefits of these sprays may not be noticed until the second year. Several cultivars of juniper are available with resistance to cedar apple rust.

– Bruce Chladny is horticulture agent at K-State Research and Extension-Douglas County. For more information, call him at 843-7058 from 8 a.m. to 5 p.m. weekdays.