Page:Report of the Puerto Rico Experiment Station (IA CAT31294391015).pdf/22

 An experiment was conducted to test repeated applications of the most promising herbicides in controlling nutgrass. The following treatments were applied to replicated plots: (1) Santobrite at 60 pounds per acre alone, and (2) with 5 pounds of sodium 2,4-D; (3) Santobrite at 60 pounds per acre alone, and (4) with 10 pounds of sodium 2,4-D; (5) sodium 2,4-D alone at 5 pounds per acre, and (6) at 10 pounds per acre; (7) Sinox A at 12 gallons per acre, and (8) Sinox AE at 12 gallons per acre. The results indicated that Santobrite at 30 pounds per acre and 2,4-D at 5 pounds per acre, applied three times at monthly intervals, was effective in controlling a heavy infestation of nutgrass under conditions of high rainfall. The experiment also showed that under these conditions the suppression of one weed pest, such as nutgrass, resulted in the substitution of another weed pest, Bermuda grass.

A combination of 2,4-D, tillage, and smother crop was tested to control nutgrass. Repeated applications of 2,4-D at 2.6 lb. per acre and tillage were ineffective. However, it was found that areas heavily infested with nutgrass can be used successfully for growing vigorous leguminous cover crops, such as velvetbeans, without mechanical or chemical weed control. The legume seed planted in the nutgrass germinated and grew vigorously when adequate soil moisture was available. The legume did not eradicate the weed pest but competed successfully by shading out and temporarily suppressing it.

In previous preemergence weed-control experiments there was some indication that the effectiveness of the herbicide was increased if it was applied several days after the land was plowed and prepared for planting. An experiment was conducted in which 2,4-D and Santobrite were applied at intervals of 2, 5, 9, and 16 days after plowing. The data obtained showed that both 2,4-D and Santobrité controlled weeds most effectively when applied as a preemergence spray 9 days after the land had been plowed. Earlier or later applications gave less efficient control of weeds, under the conditions of this experiment. These results indicate that sufficient time should be allowed after plowing for weed seed and vegetative parts to start growth before the herbicide is applied.

In cooperation with a local sugarcane grower, test trials of the herbicidal combination of Santobrite at 30 pounds and 2,4-D at 5 pounds per acre were made in a newly planted canefield. The results of these preemergence weed-control trials indicate that weed competition in newly planted canefields can be reduced to a minimum for a period of 2 months or longer without mechanical cultivation. Weeds are controlled before they have a chance to compete with the young cane.

An experiment was conducted during the rainy season to compare 12 preemergence weed-control treatments in newly planted sugarcane. The following treatments were applied to four replications of 40-acre plots: 2,4-D as the acid and as the sodium salt at 1.3, 2.6, and 5.6 pounds per acre; Santobrite at 21.5, 43.0, and 64.5 pounds per acre; Dow Contact at 12 gallons per acre; Santobrite at 43 pounds, combined with sodium, 2,4-D at 2.6 pounds per acre; and, check. Four weeks after the treatments were applied all weeds, with the exception of nutgrass, were controlled satisfactorily except in the check and the Dow Contact plots. The plots treated with 2,4-D even at