Bacterial Blight (bacterium – Pseudomonas syringae pv. mori): Watersoaked spots appear on leaves and shoots have black stripes. The leaves at the twig tips wilt and dry up. Some control is obtainable on young trees by pruning dead shoots in autumn and spraying with approved fungicides.
Leaf Spots (fungi – Cercospora moricola, C. missouriensis, and Cercosporella spp.): The leaves of mulberry are spotted by these fungi in very rainy seasons. The Cercosporella fungus can cause defoliation of older trees. Valuable specimens should be sprayed with approved fungicide if leaf spots are serious.
Popcorn Disease (fungus – Ciboria carunculoides): This disease, known only in the southern states, is largely confined to the carpels of the fruit. It causes them to swell and remain greenish, and interferes with ripening. The disease is of little importance. It does not lessen the value of the tree as an ornamental.
False Mildew (fungus – Mycosphaerella mori): The foliage of mulberries growing in the southern states may suffer severely from attacks of this fungus. It appears in July as whitish, indefinite patches on the undersides of the leaves. Yellowish spores emerge from the stomata on the underside and spread out so as to form a white, cobweb-like coating; the general appearance is that of a powdery mildew. The asexual spores are colorless, each composed of several cells. The infected leaves fall to the ground, and the overwintering or ascocarpic stage matures in spring on these leaves. Gather and burn all fallen leaves in autumn. Spray with approved fungicide mixture as soon as the mold appears in July.
Cankers: Cankers on twigs and branches and die back of twigs may be caused by at least six fungi: Cytospora sp., Dothiorella sp., Gibberella baccata, F. moricola, Nectria sp., and Stemphylium sp. These can be distinguished only by microscopic or laboratory tests. Prune and burn dead branches. Keep trees in good vigor by watering and fertilizing.
Powdery Mildews (fungi – Phyllactinia corylea and Uncinula geniculata): The lower leaf surface is covered by a white, powdery coating of these fungi. Valuable specimens can be protected by occasionally spraying with approved fungicide.
Mushroom Root Rot (fungus – Armillaria mellea): Attacks in its usual manner with hardwoods, in that while its rhizomorphs may occur generally on healthy root bark, pathogenic invasion and damage by A. mellea is almost always preceded by major root injury or other debilitation of the host.
Cotton Root Rot (fungus – Phymatotrichum omnivorum): White mulberry has been rated highly susceptible to cotton root rot. The Russian mulberry was tested for planting as a shelterbelt tree in the root rot prone areas of Texas and Oklahoma. Based on six years of records it was considered “intermediate in susceptibility, possibly usable on sandy sites.”
Root Knot Nematodes (Meloidogyne sp.): These nematodes attack seedlings in the East and Southwest. The problem can be serious on young trees but has less effect on older trees.
Summer Scorch (physiological): Leaves on affected trees have chlorotic margins. This condition is thought to be caused by low soil moisture and high atmospheric temperatures.