Wednesday, October 30, 2013
Leaf scorch caused by pecan anthracnose
Leaf scorch is actually just one symptoms of a late-season disease called anthracnose which attacks both pecan leaves and nuts. Pecan anthracnose is caused by the fungus, Glomerella cingulata, a common plant pathogen that causes diseases in many fruit and vegetable crops.
On pecan leaves, anthracnose first appears as brown, irregularly shaped lesions along the edges of a leaflet. These lesions can spread rapidly over the entire leaflet ultimately causing early leaf fall. The advancing margin of the infection forms a distinctive dark brown line that separates healthy tissues from disease killed tissue (photo above).
The first thing I notice in the photo is that all 4 nuts are well filled with kernel. Looks like this year's anthracnose infection on nuts will have little effect on kernel quality. However, the nut on the far right was smaller than the others and the shuck did not peel off very easily. In this case, anthracnose probably got an earlier start on colonizing this particular nut.
Even though the kernel inside the nut on the far right looks good, this nut would probably not survive the nut cleaning process. Judging from the force I needed to apply to remove the shuck, this nut would probably be discarded off the cleaning table as a stick-tight. If anthracnose causes enough stick-tights, this disease can lead to significant yield losses.
Anthracnose can be controlled with fungicides and is largely suppressed when we spray fungicides to control pecan scab. However, this year's unusual weather patterns hit just right to promote an outbreak of anthracnose after we finished making fungicide applications aimed at controlling scab.