Page:Report of the Puerto Rico Experiment Station (IA CAT31294391015).pdf/21

 increased rather than decreased with the passage of time at the low temperature. The cucumbers were affected to a greater extent by the pentachlorophenate than the corn, possibly because the corn has a larger seed.

In plots treated with 90 or 60 pounds per acre, the cucumber seed either failed to germinate or, if they did germinate, grew very poorly. The results of this experiment, insofar as they are applicable to field conditions, indicate that prolonged toxic effects of sodium pentachlorophenate would be expected during cold weather. They also indicate that higher rates of application can be made with greater safety in warm weather than in cool. The data obtained in the soil-moisture study indicated that the toxicity of sodium pentachlorophenate was not reduced any appreciable extent with the passage of time when applied to air-dry soil. The toxicity of the herbicide persisted somewhat longer in soil that contained a medium moisture level than in saturated soil. The toxicity had almost completely disappeared at all levels of application after 1 month in saturated soil; whereas 2 months were required for the toxicity to disappear in soil with a medium moisture content.

The results obtained in the soil-texture study showed that the toxicity of sodium chlorophenate persisted for a longer period of time when applied to heavy clay soil than when applied to sandy soil or sandy-clay mixture. One month after application there was no appreciable reduction of toxicity of the herbicide in the clay soil. The reduction in toxicity in the sand-clay mixture was more or less the same as in the sandy soil. The toxicity of sodium pentachlorophenate was reduced at about the same rate in autoclaved soil as in unautoclaved soil.

Preliminary analysis of plants treated with 2, 4—D showed a higher concentration of inorganic phosphates in treated plants than in untreated ones.

A. J. Loustalot and R. Ferrer Delgado

The effect of six pre-emergence weed-control treatments on yield of USDA-34 sweet corn was tested in a Latin square design. The results indicated that USDA-34 field corn can be grown successfully without cultivation in Puerto Eico by using Sinox at 12 gallons per acre plus 2.6 pounds of butyl 2, 4-D or Santobrite at 43 pounds per acre as a pre-emergence treatment. The latter treatment is preferred because of lower cost.

Considerable mechanical weeding is frequently necessary to establish a planting of tropical kudzu from seed. An experiment was conducted to determine if pre-emergence weed control treatments with Santobrite would enable a planting of tropical kudzu to be established without mechanical weeding. Santobrite in aqueous solution was applied to planted plots in a replicated experiment at the rate of 0, 20, 40, and 60 pounds per acre. The results indicated that a good stand of tropical kudzu can be obtained in a relatively short time, without mechanical weeding, by using Santobrite at the rate of 20 to 40 pounds per acre as a pre-emergence weed control treatment. The 60-pound rate was injurious to the kudzu seed.