Response of Soil Algae to Picloram-2,4-D Mixtures

Abstract

The effects of an approximate 1:4 commercial mixture of 4-amino-3,5,6-trichloropicolinic acid (picloram) and (2,4-dichlorophenoxy)acetic acid (2,4-D) on a natural population of soil algae were studied at dosages of 0.28, 0.56, and 1.12 kg/ha of picloram. No change in the composition of the algal flora was noted over an 18-month period, regardless of dosage. In vitro studies indicated that mixtures of picloram and 2,4-D inhibited growth of Chlorella vulgaris Beyer. at concentrations above 100 ppm, but concentrations above 250 ppm were needed for growth inhibition of Cylindrospermum licheniforme (Bory) Kuetz. or Chlorococcum sp. Picloram alone inhibited all three algae at 50 ppm, while 2,4-D produced no inhibitory effects at concentrations less than 400 ppm.