Pecan scab facts for kids
Pecan scab is the most economically significant disease of pecan trees (Carya illinoinensis) in the southeastern United States. Venturia effusa is a fungal plant pathogen that causes 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. Wind and rain spread the fungus to a susceptible host. Control of the disease is achieved by fungicide, sanitation and, in some cases, quarantine.
Since its first description in 1882, the pecan scab fungus has been reclassified ten times, with other names such as Fusicladium caryigenum, Cladosporium effusum and Cladosporium caryigenum commonly associated with the fungus.
Environment
A conducive environment for the propagation of pecan scab requires wet weather. For the spores to inoculate the host, there must be a period of wet weather in order for the infection to occur. The amount of rainfall is not as important as the frequency of rainfall and length of time that the leaves and fruit stay wet. For example, the optimal time for a rain would be right before dusk because the plant will stay wet overnight, thus increasing the period of time the pathogen has to infect the plant. The temperature is not as critical of a factor in the environment. The pathogen thrives in adequate temperatures of spring and summer ranging from 20–30° Celsius (68–86 °F). When there is a pecan orchard, cultural practices that increase the humidity levels also provide a good environment for the pathogen. These practices include close tree spacing, low limbs, and dense ground vegetation.
Importance
Pecan scab disease is the most economically damaging disease of pecans in the Southeastern United States, which is one of the major pecan producing regions in the world. It infects the leaves, shucks, and nuts thus reducing crop yield. In addition, the cost of fungicide application reduces the profitability of pecan production. Because of the cost of fungicides, pecan scab also prevents small orchards and yard trees from producing high quality nuts. The average cost of pecans ranges from $2.86–$3.50 per pound. Prices may fluctuate slightly with demand. An average tree will yield 40–50 pounds of nuts, thus equating to roughly $135 per tree. At 27 trees/acre, the total profit would be $3,645 per acre. Pecan scab is a devastating disease that can significantly impact the amount of quality pecans produced in a year. For example, during the summer of 2013, the estimated potential for the year was around 90 million pounds; however, the weather conditions were conducive for pecan scab growth and the actual total went down to 65 to 70 million. Pecans are valuable crops that are economically valuable to the farmer and also the farming industry. Devastating diseases like pecan scab can result in major financial loss that can hurt growers and also economic development.
