Sr. Walker et al., WEED-CONTROL WITH ATRAZINE AND CHLORSULFURON IS DETERMINED BY HERBICIDE AVAILABILITY AND PERSISTENCE IN SOILS, Australian Journal of Agricultural Research, 48(7), 1997, pp. 1003-1009
Effectiveness and length of weed control with atrazine and chlorsulfur
on can be variable in the field. While some of this may be due to clim
atic variations, differences in soil properties may also be important.
We tested this by recording changes in control of mintweed (Salvia re
flexa Hornem.) and turnip weed (Rapistrum rugosum L.) with time in dif
ferent soils, and comparing these results with the measured changes in
plant-available herbicide in the soils. Length of weed control with t
he same herbicide rate varied from 0 to >15 weeks. Mint Need and turni
p weed were controlled (85-100%) only when the soils had greater than
or equal to 0.1 mu g available atrazine/g and 0.8 ng available chlorsu
lfuron/g, respectively. This agreed with the sensitivity data for thes
e weeds when grown in a soil-free system. The herbicides were initiall
y more available in grey clays than in black earths, and soil pH accou
nted for most of the variations in the persistence of the available re
sidues. Thus, the efficacy of these herbicides in different soils coul
d be estimated if the available residues in the root-zone could be pre
dicted and the sensitivity of different weeds was known.