Citrus Disease, Insects Causing Concern for Growers

Internal dry rot of satsuma fruits. (Photo by Dan Devenport, LSU AgCenter)

Internal dry rot of satsuma fruits. (Photo by Dan Devenport, LSU AgCenter)

Citrus harvest is in full swing in Louisiana, and people are enjoying the sweetness of satsumas, but some have complained about internal dry rot of fruit this year.  

Mature fruit looks otherwise healthy from the outside, but internal dry rot can be seen after peeling the fruit, said LSU AgCenter “Plant Doctor” Raj Singh.  

“This internal dry rot is caused by a yeast called Nematospora coryli, which is transmitted by the western leaf-footed bug,” Singh said.  

The leaf-footed bug is widespread and is a pest of many crops, including fruits, vegetables, grains, nuts and ornamentals.  

“It is a major pest of citrus and primarily attacks satsuma mandarins,” he said. “It feeds by inserting its piercing-sucking mouthparts in the fruit, and feeding on ripening fruit causes premature color break and fruit drop.”

Injury usually occurs as the fruit matures in the fall, Singh said. He added, the leaf-footed bug transmits yeast responsible for internal dry rot.  

Adults can fly considerable distances and move from other crops to satsumas during fruit ripening. 

The leaf-footed bugs will aggregate in large colonies on individual trees while neighboring trees are completely free of bugs. Adult bugs are dark brown, their back legs are flattened, and they appear leaf-like.  

Nymphs, the immature bugs, look totally different from adults. Their body color ranges from orange to reddish brown with black legs.  

Leaf-footed bugs are primarily managed by using insecticides, but biological control using other insects and fungi is also available, Singh said.  

Homeowners may spray horticulture oils or Malathion 57EC for managing leaf-footed bugs in backyard trees, but malathion shoud not be applied to plants in full bloom and fewer than seven days before harvest.  

Commercial citrus producers are advised to follow the citrus spray schedule recommended in the LSU AgCenter Insect Pest Management Guide (www.lsuagcenter.com).  

For more information on citrus problems, contact Singh at 225-578-4562 or email rsingh@agcenter.lsu.edu