Herbicidal Properties of the Antibiotic Monensin

Abstract

The agricultural antibiotic monensin caused herbicidal injury to 1- to 2-week-old seedlings of seven weed and two crop species when applied at 10 -4 M as a foliar spray in the greenhouse. The non-ionic surfactant tergitol TMN (0.1 ml litre -1 ) aided foliar absorption of monensin and increased herbicidal injury. Fresh weight reductions ranged from 20 to 75% (compared to control seedings treated with tergitol alone) 65 h after spray application of 10 -4 M monensin with tergitol. When root-fed at 10 -4 M, monensin (without tergitol) caused death in all nine species within 24-72 h after treatment. Monensin supplied to roots at 10 -5 M caused fresh weight reductions in spurred anoda [Anoda cristata], velvetleaf [Abutilon theophrasti] and prickly sida [Sida spinosa] of 43, 32 and 23%, respectively. Substantial growth effects also occurred in hemp sesbania [Sesbania exaltata] and sicklepod [Cassia obtusifolia] (33 and 15% reductions in fresh weight, respectively) ; jimsonweed [Datura stramonium] and johnsongrass [Sorghum halepense] had the least fresh weight reductions. Injury included chlorosis, necrosis, desiccation and leaf abscission. Cotton and okra were the most tolerant of all species tested ; however, three malvaceous weeds were severely damaged by the compound. When root-fed at 10 -6 M, monensin caused limited injury. Monensin exhibited some degree of selectivity among these crop and weed species and caused greater injury in light-treated than dark-treated plant tissues.