A leaf blight on hawthorn was diagnosed recently in the PlantDisease Clinic. The disease is caused by the fungus Fabraeathuemenii. Symptoms of leaf blight begin in spring and earlysummer as small, angular, reddish-brown spots on the upper surfaceof leaves. The spots increase in size and run together, causingpremature defoliation during wet years. From a plant pathologist'sview point, the disease is very interesting because of thecharacteristic spores, which resemble minute, winged insects. Thefungus survives the winter on stems and fallen leaves, infectingnew leaves as they emerge the following year. Raking and disposingof fallen leaves will reduce the amount of inoculum and perhaps theseverity of the disease. Applications of Daconil 2787 or Bordeauxmixture, beginning when the leaves are half unfurled and continuingat 2-week intervals while conditions favor disease development,will control the spread of the disease and prevent prematuredefoliation. During a "normal" Iowa summer, with low to moderaterainfall, Fabraea leaf spot probably poses little threat of damageto hawthorns.
This article originally appeared in the August 11, 1993 issue, p. 136.