INEFFECTIVENESS OF THE OVERHEAD-IRRIGATION METHOD FOR THE APPLICATION OF INSECTICIDES TO CONTROL THE SUGARCANE MOTH STALK-BORER, DIATRAEA. SACCHARALIS (FABRICIUS)

The use of the overhead-irrigation system established at Colonia Juana Díaz, near Central Cortada, Santa Isabel, P. R., makes possible the application of fertilizers dissolved in water, and of insecticides for the control of soil-insect pests. Experiments were conducted during the crop years 1950 and 1951, using the overhead-irrigation system as a means of applying insecticides, in an attempt to control the sugarcane moth-stalk borer, Diatraea saccharalis (Fabricius). Thirteen different kinds of insecticides, namely: Aldrin, Chlordane, Dieldrin, Ryania, Rhothane (DDD), Benzene hexachloride, CPR Emulsion Concentrate, Gy-phene (Toxaphene), Muriate (Methoxychlor), Kryocide (natural cryolite insecticide), Dilan 25 EM, Heptachlor 2E Emulsion Concentrate, and Dr. Wolf's Insecticide A, were used. Each insecticide was applied at two different concentrations. Thirty-one plots planted with sugarcane, each having an area of 214 acres, were used in the experiment, 20 of them being treated with insecticides and 11 being used as checks. The insecticides were applied at 15-day intervals; there were four sprayings during each season. The experiments were initiated during the fall of 1950 and 1951, respectively, when the sugarcane plants were still small and had just begun to develop the first joints at the base of the stalks. The tables and analyses of the work conducted demonstrated that these insecticides, at least when applied by this method of spraying, were completely ineffective in the control of the insect. In many cases the check plots showed less borer infestation than those treated with insecticides; in others, the insecticide was more effective at low concentration than when used at twice that concentration. The ineffectiveness of the insecticides might be due, in part, to the large amount of water used which reduced the concentration of the chemical so much as to make it valueless in controlling the moth-borer.

SUCROSE CONTENT OF SUGARCANE AS AFFECTED BY MOTH-BORER, DIATRAEA SACCHARALIS (FABRICIUS), INFESTATION

More than 1,000 samples of stalks of sugarcane were milled and their juices analyzed in attempting to obtain a more accurate estimate of the losses caused by infestation of sugarcane in Puerto Rico by the moth stalk-borer, Diatraea saccharalis (Fabricius). The samples were divided into (1) whole-canes unbored, (2) whole-canes bored, (3) tops unbored, (4) tops bored, (5) central portions unbored, (6) central portions bored, (7) bases unbored, and (8) bases bored. The statistical analyses showed that the highest percentage of sucrose in cane is found in the central portion, less is found at the base, and the least in the top joints. By using a factor of 0.03549 (as determined by the junior author), which represents the loss of available sucrose per 1 percent of joint infestation, one can calculate the losses of sucrose caused by moth-borer damage in any given area. Thus it was found that Colonia Juana Díaz, near Santa Isabel, P. R. had an estimated total loss of $49,326 in the 3 years 1950, 1951, and 1952, from borer injury. It is estimated that the average annual losses in Puerto Rico amounted to approximately $2,500,000 in the 12-year period from 1940 to 1951.