Effects of ammonium sulphate on leaf growth inhibition by glyphosate in Cyperus esculentus L.

Abstract

The influence of ammonium sulphate (AMS) on glyphosate ( N-(phosphonomethyl) glycine) efficacy on Cyperus esculentus L. var. esculentus was measured under several conditions. Measurements of leaf growth from 1 to 5 days after treatment were highly correlated with visual estimates of efficacy and fresh weight of foliage at the end of the experiment. Reductions in leaf growth from glyphosate could be measured long before changes in coloration or other symptoms appeared. This is a quick and reliable non-destructive method for predicting foliage control from glyphosate. AMS increased the rate at which glyphosate affected leaf growth, indicating that absorption rate of the herbicide was increased. The effects from adding AMS were especially significant when the foliage was washed (simulating rainfall) shortly after treatment, or when the spray solution contained simazine (6-chloro- N,N′-diethyl-1,3-5-triazine-2,4-diyldiamine) or calcium ions. However, when treated leaves were removed 1 day after treatment, AMS sometimes reduced glyphosate effects on the remainder of the plant, suggesting that the rate of translocation could be inhibited under some conditions. In a field experiment in North West Spain, a 2% solution of AMS did not affect C. esculentus reinfestation during the year following treatment with glyphosate at 2·16 kg/ha. In general, the addition of AMS to glyphosate may be advantageous in the field when rainfall is received soon after spraying or when glyphosate is applied in hard water or mixed with simazine. There seem to be no long-term benefits when those conditions are not present.