File:Some diseases of Puerto Rican forage crops (1953) (20352711558).jpg

Title: Some diseases of Puerto Rican forage crops
Identifier: CAT10398040 (find matches)
Year: 1953 (1950s)
Authors: Theis, Thomas
Subjects: Forage plants Diseases and pests Puerto Rico
Publisher: Federal Experiment Station of the United States Dept. of Agriculture
Contributing Library: U.S. Department of Agriculture, National Agricultural Library
Digitizing Sponsor: U.S. Department of Agriculture, National Agricultural Library

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Figure 23.—A, Rust on Tripsacum laxum (Guatemala grass) caused by Puccinia polysora. Reduced 2.3 percent. B, Spores of P. polysora. X 528. LEGUMES Tropical Kudzu Powdery mildeiv Powdery mildew of Pueraria phaseoloides (Roxb.) Benth. (tropi- cal kudzu) is caused by a species of Oidium. It occurred to some extent throughout the year but was most prevalent during the dry winter months. During these periods se- vere infection has been observed. Defoliation of infected leaves was sufficient to reduce the amount of forage produced. A number of powder)' mildew fimgi thrive best in dry weather. This is due in part to the ability of their short-lived spores to develop in air that is devoid or very low in moisture (5, 6). In addition, the dryness of the atmosphere retards the growth of other fungi parasitic on the mildews (5). Powder)" mildew infects the leaves (iig. 24, A). It appears first as white spots on the surface of the leaves; ultimatel)^ these coalesce and involve the entire leaf surface. The leaf becomes puckered, then brown and dry, and finally drops. The spores (fig. 24, B) are hyaline and measure 14-24^ x 31-40pt. Complete identification of the causal organism has not been pos- sible because the perithecial stage, necessary for identification of the fungus, has not been found. Ste- vens (32), though he observed the conidial stage of powdery mildew on many hosts in Puerto Rico, was not able to find the perithecial stage. According to Bessey (5) perithecial production by powdery milde w is rare in the Tropics. Velvetbean Stem spot A stem spot on Stizolobium deer- ingianum (Bort.) (velvetbean, ha- bichuela terciopelo) has been ob- served, the cause of which has not been determined. This disease oc- curred only on heav)' clay soils during periods of high rainfall. During such periods, it became so severe that large patches in velvet- bean plantings were killed. The stems and petioles develop black, sunken spots (fig. 25), the size of which are 1-3 mm. x 4-7 25

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