. California plant diseases. Plant diseases. 1120 UNIVERSITY OF CALIFORNIA—EXPERIMENT Fig. 48.—Leaf spot of iris (Hetero- sporium gracile). Irrigating and fertilizing abundantly will control this disease. Spraying with Bordeaux mixture and other fungicides is sometimes resorted to, but this treatment is not very satisfactory. IRIS. Leaf Spot (Ilctcrosporium gracile). Figure 48. Large, elliptical dead spots appear on the leaves, with a yellow margin between the dead and the green tissue. Quite disfiguring, but no treatment ordinarily considered necessary. LEMON. Gummosis. Figure 49. C
. California plant diseases. Plant diseases. 1120 UNIVERSITY OF CALIFORNIA—EXPERIMENT Fig. 48.—Leaf spot of iris (Hetero- sporium gracile). Irrigating and fertilizing abundantly will control this disease. Spraying with Bordeaux mixture and other fungicides is sometimes resorted to, but this treatment is not very satisfactory. IRIS. Leaf Spot (Ilctcrosporium gracile). Figure 48. Large, elliptical dead spots appear on the leaves, with a yellow margin between the dead and the green tissue. Quite disfiguring, but no treatment ordinarily considered necessary. LEMON. Gummosis. Figure 49. Characterized by the exudation of gum from the trunk of the tree just above the point of budding. The tree appears yellow and dies when badly affected. Occurs on poorly drained, heavy soil, especially if the point of budding is deeply covered with earth and where the soil about the trunk is undisturbed by cultivation. This trouble is more common on lemons than on oranges. Gumming is a characteristic of the citrus tree when affected by any injurious condition. Frequently, for instance, when trees have been extremely dry and suffering from a lack of moisture gum will break out at the crotches or twig axils when an abundant supply of water is furnished. If the twigs in this or any other manner are caused to die back for a short distance gum is very likely to exude after irrigation at the point where the dead portions of the twig join the live tissue. Any injury or irritation may have the same effect. When citrus trees are budded, either in the nursery or in the case of orchard trees, gum- ming often occurs at the point of budding, particularly if a large supply of moisture is furnished soon after the budding is done. Many buds are often killed in this way as a result of rain or irrigation. Such effects as these are not usually very serious, except that in the case of budding the process may have to be repeated. Orange or lemon nursery trees one or two years of age sometimes gum
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