When the proper environmental conditions exist, the fungus Cristulariella moricola (Hino) Redhead causes a target or
zonate leaf spot on a myriad of woody and annual plants. Susceptible host plants (Alfieri et al. 1994) which can become
infected in Florida are:
Acer sp.
A. rubrum L.
A. saccharinum L.
Ailanthus spp.
Aleurites fordii Hems
Ardisia crenata Sims
Bucida buceras L.
Caladium x hortulanum Birdsey
Catalpa spp.
Carya illinoinensis (Wangenh.) K. Koch
Chionanthus virginicus L.
Cornus florida L. Vitex sp.
Fraxinus spp. Vitis rotundifolia Michx.
F. pennsylvanica Marsh.
Hibiscus cannabinus L.
Lagerstroemia indica L.
Lycopersicon esculentum Mill.
Magnolia sp.
Malus spp.
Pentas lanceolata (Forssk.) Deflers
Platanus occidentalis L.
Prunus persica (L.) Batsch
Punica granatum L.
Ulmus parvifolia Jacq.

SYMPTOMS: Susceptible foliage infected by Cristulariella displays symptoms quickly. During periods of cool moist weather entire leaves may become blighted. Initial symptoms vary from host to host, but generally, watersoaked, greenish-gray, circular or irregularly-shaped leaf spots develop, which may be accompanied by a chlorotic halo. Spots eventually produce alternating concentric bands of lighter and darker tissue, giving these lesions their common zonate or target appearance. Depending on the host and weather conditions, lesions may coalesce and give a scorched appearance. Rapid tissue death is due to a combination of toxic and enzymatic processes. Cristulariella produces oxalic acid in toxic amounts and the pectic enzymes that degrade cell walls are synergized by the acid.

[PHOTO] Foliar symptoms of Cristulariella leaf spot on Lagertroemia indica (crepe myrtle) showing typical concentric ring pattern and rapid expansion of leaf spots.

PATHOGEN: Cristulariella sporulates readily on infected tissue and can be observed easily with a hand lens or dissecting microscope. The conidia or propagules produced by the fungus are characteristically pyramidal or coneshaped and are off-white in color. Sporulation may occur on both sides of infected foliage. Propagule production varies with the host, temperature, and relative humidity. Cool, wet weather during mid- and late summer is optimum for disease development. Sclerotium cinnamomi Sawada, the sclerotial stage of Cristulariella, may also develop on diseased plant tissue. These sclerotia appear as black, crusty, irregularly-shaped structures approximately 2-5 mm. in diameter.

SURVEY AND DETECTION: Look for circular target or zonate type leaf spots with concentric rings. Target lesions usually have a tan or light-colored center. If Cristulariella is actively sporulating, small, white or cream-colored pyramidal or cone-shaped propagules should be easily observed within leaf lesions on either leaf surface. Black, crusty, irregularly shaped sclerotia may be observed on older infected foliage or fallen leaves.

- Robert M. Leahy: (March/April 1995) Cristulariella Leaf Spot on Florida Ornamentals^©