Pair of Problems for Louisiana Satsumas

Josh McGillLouisiana, Mandarins, Pests

Plant Diagnostic Center Director Raj Singh at the Louisiana State University Agricultural Center (LSA AgCenter) recently addressed two stresses that impact yields in Louisiana citrus — internal dry rot and puffy fruit.

Western leaffooted bugs carry a yeast that causes internal dry rot. (Photo by Raj Singh, LSU AgCenter)

Mature fruit affected by internal dry rot may look healthy on the outside, but peeling the fruit reveals dry, discolored flesh. This internal dry rot is caused by a yeast called Nematospora cordylid transmitted by the western leaffooted bug (Leptoglossus zonatus).

The leaffooted bug is widespread and a pest of many crops including fruits, vegetables, grains, nuts and ornamentals. It is a major pest of citrus and primarily attacks satsuma mandarins. It feeds by inserting its piercing-sucking mouthparts in the fruit. Feeding on ripening fruit causes premature color break and fruit drop. Injury usually occurs as the fruit matures in the fall. While feeding, the leaffooted bug transmits the yeast responsible for internal dry rot.

Adults can fly considerable distances and move from other crops to satsumas in fall during fruit ripening. Leaffooted bugs will congregate in large colonies on individual trees while neighboring trees are completely free of bugs.

Adult bugs are dark brown in color, and their hind legs are flattened and appear leaflike. Nymphs, or immature bugs, look totally different from adult bugs. Their body color ranges from orange to reddish brown with black legs.

Leaffooted bugs are primarily managed by using insecticides, but biological control using other insects and entomopathogenic fungi is also available. Horticultural oils or Malathion 57EC can be sprayed for managing leaffooted bugs. Do not spray Malathion on plants in full bloom and make sure to wait at least seven days after spraying to harvest fruit.

Puffy fruit is primarily a satsuma problem but is shown here on a navel orange tree. (Photo by Raj Singh, LSU AgCenter)

Puffy, misshapen fruit is mostly a problem on young, vigorously growing satsuma trees. As the tree becomes older, the occurrence of puffy fruit decreases. Puffy fruit on older trees results from fruit that sets on late blooms during periods of warm weather.

Puffy satsumas have thick, wrinkled rinds and appear pear-shaped as compared to round, smooth, healthy fruits. When peeled, the satsumas look dry and do not have any juice.

Little can be done to prevent puffy fruit. But good growing conditions, proper fertility and pest control are always helpful in maintaining the health of citrus trees.

Source: LSU AgCenter

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