The following was received via email: We are experiencing some plants with dead sections. The leaves turn a reddish/brown. Are we over watering? Do we need to fertilize? The area approximately 30' x 8' and is in full sun. There are approximately 24 to 30 plants in this area and they are 3 years old. The soil appears to drain readily.
It sounds like the growing conditions for your Arctostaphylos are optimal (full sun + well-drained soil). The most likely problem affecting y our plants is leaf gall. "Green or reddish galls appear at the edges or tips of the newest leaves. The leaves are twisted and distorted. When the gall is torn open, a small (1/8 inch), dark green to black insect or insect excrement is seen. On kinnikinnich, the entire leaf may be thickened and reddish. Leaf galls appear in early summer. All new leaves may be disfigured, preventing growth and spread of the ground cover." (The Ortho Problem Solver, 1982). To control leaf gall, pinch off and destroy the affected leaves as soon as you spot the galls. Arctostaphylos uva-ursi requires light fertilizer and allow the soil to dry between waterings. If the above description does not match your problem, please let us know and we will do our best to find the answer.
More likely, the problem is a blight caused by a fungus. Coniothyrium is a genus of opportunistic fungi that cause leaf spots, twig dieback and cankers on Arctostaphylos species (and numerous other landscape plants, including roses, magnolias and junipers). It is a likely candidate for what you see on the kinnikinnick. However, there is strong evidence that Coniothyrium species are secondary pathogens; i.e., they attack already weakened or dying tissues, rather than initiating infection. Arctostaphylos species are particularly sensitive to both moisture and oxygen at their roots. If the soil in which the plants are growing is either waterlogged or compacted (oxygen is excluded), roots will die off and a corresponding amount of above-ground growth will also die back. Water-borne pathogens, such as pythium commonly infect plants in poorly drained sites, but these infections generally, eventually kill off the entire plant. The same thing can occur with droughty conditions or in even in loose soil, where there are large air pockets. Finally, Arctostaphylos are also sensitive to wounding. Foot traffic is often implicated in dieback, both from soil compaction (see above) and from physical damage to stems. Wounds in both stems and roots are classic entry points for opportunistic fungi such as Coniothyrium. The Arctostaphylos uva-ursi cultivar 'Vancouver Jade' -- a UBC introduction and one of the most widely grown cultivars in temperate climates -- is adapted to wetter conditions than many other cultivars, as it was selected from the Pacific Northwest. Nevertheless, like all kinnikinnicks, it is not a plant for poorly drained, shaded or high traffic areas. And unfortunately, it appears to be rather more susceptible to manzanita pod gall aphid than other cultivars. Populations of that insect pest can build up during "warm winter" periods (such as we've been experiencing in Vancouver over the past several years) and disfigure plants significantly.
