The seasonal response of Lantana camara to selected herbicides

At 7- to 8-week intervals between September 1990 and February 1993, blocks of Lantana camara L. cv. `Helidon White' were treated with four herbicides (fluroxypyr, metsulfuron-methyl, glyphosate and dichlorprop) as an overall high-volume spray at the recommended label rates. Mortality for each treatment was recorded and correlated with climatic data (maximum, minimum air and soil temperature, rainfall, day length and humidity) recorded for the site. Fluroxypyr killed more than 90% of the L. camara if at least 35 mm of rain was received in the preceding 6 weeks and provided that the average minimum daily temperature for the week before the application was above 15 °C. Similarly, glyphosate caused more than 80% mortality when the rainfall was greater than 60 mm in the preceding 6 weeks, with a similar temperature requirement to fluroxypyr. In contrast, dichlorprop and metsulfuron-methyl caused maximum kills of 35–80% and 83% respectively. This occurred in the summer or early autumn (at times when fluroxypyr and glyphosate also gave maximum kills), but times of maximum kill for dichlorprop and metsulfuron-methyl did not correlate with any specific climatic characteristics. Current field practice is to apply all herbicides in autumn (March–May) when L. camara is growing actively. The consequence of this is that, if some plants are not killed, they can go undetected until the next growing season. However, this study shows that fluroxypyr and glyphosate can be sprayed earlier in the year, thus allowing for follow-up sprays later in the same growing season to kill any regrowth.