Black Spot on the Texas Madrone, Arbutus xalapensis

(March, 2016)     In our colony (Edwards Plateau, northeast Hays county), black spot on Madrone leaves first appeared last Fall and proliferation has been increasing for the past four months.  Previously seen during cold, wet stretches of winter, the black spot would usually be checked with drier weather and warmer temperatures.

This winter's temperatures have been warmer-than-usual and extremely dry and windy since the beginning of the year.  That combination should have controlled it, but it gained momentum and spread, with the Spring rains coming soon (we all hope).  Rainfall totals below show a pretty dry record, with October deluges and November significantly wet.  December, 2015 had only two days of significant rain.  January and February had only one day each of significant rainfall.

July: 0.03"   August: 0.28"   Sept: 0.87"   Oct: 13.44"
Nov: 3.05"   Dec: 2.62"       Jan.: 0.47"     Feb.: 1.18"

It appears similar to black spot on roses, the fungus Diplocarpon rosae, which is difficult enough to control in a cultivated setting.  Treatment of native plants in a natural environment is going to be tricky.
The black spots appear on older leaves and spread quickly up the trunk or stem, with younger and more dynamic leaves having more energy to resist but still susceptible.  At this point many trees are heavily defoliating with two negative results.  Losing their leaves weakens their photosynthesis now when they are gathering strength for April flower-production and therefore Fall seed production.  If the fungus is similar to Diplocarpon rosae, the spores of the fungus will survive the defoliation and lay dormant in the dead leaves to maintained their life cycle and be spread on wet winds.  But collecting the leaves in a native, natural setting is impractical.  I have no solution but am looking for feedback as well as whether this is happening in other colonies in the Hill Country or West Texas mountains.

While the spot is prevalent in the native setting, there is no sign as yet in the cold frame where I am growing them.

(June, 2016)   The spot nearly totally defoliated the large Madrone.  After three months of cooler, wet weather (March-May) the leaves re-sprouted and with cloud cover grew to wide, thick foliage.  [See photo.]  

Reply to 

Severe black spot on 3-inch cal. Madrone
Severe defoliation of lower leaves on 8-inch Madrone
After near-total defoliation, this ancient Madrone recovered with cooler, wet weather by June.