Results from six Pinus taeda nursery trials with the herbicide pendimethalin in the USA

Abstract

Pendimethalin is used by some nursery managers to control weeds in Eucalyptus and Pinus seedbeds and cutting beds of Pinus. Six trials were implemented in open-rooted seedbeds to test the response of Pinus taeda to postemergence (to the crop) applications of 2.2 kg ha⁻¹ active ingredient of pendimethalin (the formulation contained 455 g l⁻¹). No stunting was noticed when treating seedlings with 2.2 kg ha⁻¹ four to 10 weeks after sowing. In one study, treated seedlings were larger than those not treated. Although the 2.2 kg ha⁻¹ rate provided good control of the prostrate weed Chamaesyce maculata, pine seedlings developed herbicide galls on the stem near the groundline. The frequency of herbicide galls at 2.2 kg ha⁻¹ varied by study and ranged from 0 to 28%. At present, it is not known if the frequency of gall formation depends on environmental or genetic differences.