Page:Report of the Puerto Rico Experiment Station (IA CAT31294391015).pdf/16

 The 5,000-p. p. m. treatments caused delayed abscission with uneven, somewhat blackened leaf scars. The petioles had a water-soaked appearance but no damage was observed in the phloem or xylem. The highest concentration, 50,000 p. p. m., prevented abscission but the petioles rotted and eventually fell off. The injury penetrated into the xylem almost to the center of the stem and extended 1 to 2 inches above the point of attachment and ½ to 1 inch below, in a narrow strip. One to 3 leaves directly above the treated petioles also died, and a small area directly under their points of attachment blackened. Both the xylem and phloem between these injured areas were apparently undamaged. These disconnected, injured areas were always directly above the treated petiole. Apparently there was local concentration of the applied chemical substance only at the leaf base directly above the point of application.

R. H. Hageman

Germination tests were made of Manila grass seed harvested at 2 week intervals over a period of 2 months beginning February 10. The highest yield of viable seed was obtained from the initial harvest date. Of the seed collected on this date 12.9 percent were well filled or "heavy," and of these 17.2 percent germinated. The germination of the total seed collected during the entire season was less than 1 percent, which is in agreement with previous trials.

H. K. Plank and R. Ferrer Delgado

In a previous experiment it was shown that dipping bamboo for 10 minutes in a 5-percent solution of DDT in Diesel fuel oil maintained almost complete control of the bamboo powder-post beetle (Dinoderus minutus (F.) ) for 3 months. Examinations for external evidences of internodal infestation were continued at intervals of 3 months for 1 year to determine the lasting qualities of this treatment. The Diesel fuel solvent alone produced a small amount of control, significant only during the first 6 months after application on clump-cured material. The 5-percent DDT solution produced a highly significant degree of control that lasted for 12 months on both freshly harvested and clump-cured material, but this control tended to be more permanent on the freshly harvested culms: From 98 percent on both kinds of bamboo at 3 months the control decreased to 91 percent on the freshly harvested and to 88 percent on the clump-cured When split open at the 12-month at 12 months after treatment. examination all of the 300 internodes in the untreated freshly harvested culms, and all but 5 in the clump-cured culms, were found attacked by the beetle. Most of the former were riddled,, whereas those that had been clump-cured were lightly damaged.

Where DDT was applied, the control was still 91 percent in the freshly harvested culms, but 79 percent in the clump-cured culms, with the difference in number of damaged internodes being statistically significant. Apparently no improvement in control of inter-nodal infestation is to be derived from previously drying the culms, as in clump-curing, before dipping in DDT. The residue left by DDT treatment was still visible on some of the culms at 12 months the after treatment. Ring sections from both freshly harvested and