Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Ascomycota
Subphylum	Pezizomycotina
Class	Dothideomycetes
Subclass	Pleosporomycetidae
Order	Pleosporales
Family	Venturiaceae
Genus	Venturia

Scientific Name

Venturia effusa

Scientific Name Synonyms

Cladosporium caryigenum

Cladosporium effusum

Fusicladium effusum

Common Name

pecan scab

Author: Paul Bertrand, University of Georgia

Symptoms

Pecan scab generally shows up as small black spots on the new leaf parts (Figure 1). Later, similar spots may be present on the small nuts (Figure 2). With heavy infection, the lesions may grow together resulting in large irregular black areas on leaflets or nuts. Early lesions may grow together resulting in large irregular black areas on leaflets or nuts. Early infections may become large, 1/4 inch or more across, and sunken in the center by late season. Old lesions, particularly in late season, are often overgrown by other fungi, giving them a white moldy look.

Disease Development

The pecan scab fungus overwinters on shucks and shoots infected the previous season. Infections can occur as soon as green tissue appears in the spring. They continue to occur throughout the season on any growing tissue. The value of prepollination disease control was known before 1930. Prepollination leaf infections arise from overwintering inoculum. Spore production on overwintering inoculum drops sharply between pollination and the onset of nut growth (early May to June). Most of the inoculum available for infection of the nut crop in June and July arises from early leaf infections. Pecan scab seldom causes significant leaf drop though leaf infection may be common. Nut infection can result in crop loss from nut drop and from failure of nuts to reach full size.

Pecan Scab Evaluation

When evaluating pecans for scab severity, observations should be made on a single variety. In most older groves, Schley or Desirable will be the best choice. For leaf scab, estimate the percent of leaflets with scab. For nuts, estimate the percent of shuck surface covered. The rating system illustrated for pecan scab can be modified for use on all nut and leaf diseases of pecan.