INSECT ENEMIES AND DISEASES.
The fig is usually spoken of as being comparatively free from insect enemies, and the literature of its diseases, of which there are a number, is scanty. It is probably true that in most localities it is less frequently injured from these causes than are other fruit trees.
Among the diseases reported from the South the one causing most widespread injury is doubtless root knot.
FIG-TREE BORER.
A longicorn beetle, Ptychodes vittatus, has caused considerable injury at some points in Louisiana and Mississippi by burrowing into the trunk and larger branches. In reply to inquiries regarding this insect, Director W. C. Stubbs, of the Louisiana Experiment Station, says:
The damage done in Louisiana is to a large extent conjectural. In our groves we have lost several trees temporarily, all being bored into by this borer. They, however, start up again quickly from the roots and soon replace the injured trees. We have had no remedy against this invasion except to dig it out while very young with a penknife. We have tried various insecticides without any apparent results.
FIG-LEAF MITE.
A browning and subsequent premature falling of the leaves, caused by the work of a minute mite, is reported as rather common in Florida by Mr. H. J. Webber, of the Subtropical Laboratory. It has not been studied.
Mr. Ellison A. Smith, jr., botanist and entomologist of South Carolina Experiment Station, has published a list[[1]] of insects observed feeding on ripe figs, but he does not mention any that injure the tree.
ROOT KNOT.
This disease is caused by a microscopic nematode or true worm, Heterodera radicola,[[2]] that infests the soft fibrous roots causing small galls or swellings. When present in sufficient numbers it causes the death of the roots and the consequent starvation and death of the tree. It is by no means confined to the fig, but attacks the roots of many other fruit and ornamental trees and shrubs and is especially injurious to many garden vegetables and farm crops.[[3]] This pest thrives best in moist sandy soils, and is troublesome throughout the entire coast region.
No effective remedy is known when a tree is once infested, hence the necessity for planting on land known to be free from the pest, and the importance of not growing vegetables between the trees that will act as a nurse crop for the disease.
Neal recommends thorough drainage of the land and the application of tobacco dust mixed with unleached ashes or lime as the most promising remedial measures. He advises against the excessive use of ammoniacal manures as producing a soft, succulent root growth favorable to the growth of the nematode. (See Bulletin No. 20, previously cited.)
FIG-LEAF RUST.
Brown spots frequently appear on the foliage during the summer, and, if numerous, cause the leaves to fall prematurely. These spots are caused by a true rust fungus, Uredo fici Cast. It occurs quite frequently widely, and abundantly, but as it usually does not develop enough to be noticeable until after the crop is ripe, it seems to do but little harm. No attempt has been made to find a remedy.
FIG CERCOSPORA.
A somewhat similar injury to the leaves is known in Europe, caused by an entirely different fungus, Cercospora bolleana (Thum) Sacc. It had not been observed in this country until the summer of 1895, when it was found abundantly in Mississippi by S. M. Tracy. A cercospora, probably the same species, is also reported from Florida by H. J. Webber. It probably occurs quite commonly, but has been overlooked, its injuries being confounded with those caused by the Uredo.
DIE BACK.
A dying of the young shoots in the fall and early winter is sometimes noticed. This occurs before they can have been injured by severe cold and its cause is not known. It usually occurs in feeble trees, those injured by previous winter killing or perhaps those suffering from root knot. A similar trouble is noted by A. F. Barron, of Chiswick, England, (The Garden, June 20, 1891, p. 577). He finds it occurring in trees grown in pots, and says it is there seldom noticed in trees growing out of doors.
ROOT ROT.
The fungus Ozonium auricomum Lk., which causes a root rot of cotton and of many other plants and trees, has been reported upon the fig,[[4]] but the extent of damage caused by it is not known. Several other species of fungi are known to occur on the fig, but none of them can be classed as disease-producing organisms.