Pecan scab

The fungus causes lesions and tissue death on pecan twigs, petioles, leaves, nuts and shucks beginning in early spring, with multiple cycles of infection repeating until late summer.

[5] Common symptoms of pecan scab disease include light brown to black lesions on stems, leaves, shucks and nuts.

[1][6] Visible circular lesions begin to develop 7 to 14 days after infection, and first appear on young tissue as olive-green spots that turn black as they age.

[1] Numerous lesions can coalesce into larger dead areas on infected tissue and can cause early leaf loss.

[7] Venturia effusa over-winters in plant debris, such as shucks, leaf petioles and stems, as well as in lesions on the tree from the previous season.

[7] Conidia are moved by wind and water to a susceptible host, but they cannot germinate and infect without several hours of sustained wet weather.

Venturia effusa commonly reproduces asexually via conidia, but it may also produce a teleomorph stage like other Dothideomycetes in which pseudothecia carrying asci and sexual ascospores grow out of the hyphae.

Trees in the latter category experienced the greatest disease severity around mid-season (mid-July through August), roughly 1.5 to 2 months after inoculation.

[9] When there is a pecan orchard, cultural practices that increase the humidity levels also provide a good environment for the pathogen.

[11] The fungicides have not been shown to have any adverse effects outside of the warnings of all chemical control impacts on environmental and human health.

Removal and destruction of all fallen leaves, shucks, and nuts each winter or early spring helps reduce tissue that is often involved in the primary infection.

[10] Also, selective pruning of infected tissue during the dormant season may help reduce the level of scab disease.

Because of the cost of fungicides, pecan scab also prevents small orchards and yard trees from producing high quality nuts.

Devastating diseases like pecan scab can result in major financial loss that can hurt growers and also economic development.