Preliminary evaluation of residual herbicides for the control of camelthorn bush (Alhagi maurorum Medik.)

Abstract

Camelthorn bush (Alhagi maurorum Medik.) invasion in South Africa is a serious, but still relatively localized problem, with the potential to spread into many other parts of the country. Previous research revealed the difficulty in killing the deep extensive root system when using foliarapplied herbicides. The small leaf area available for herbicide absorption relative to the large root system and the apparent inability of foliar-applied herbicides to lranslocate in sufficient quantity beyond the root crown are probably some of the main reasons for the poor levels of control normally achieved. It stands to reason that residual herbicides that are root absorbed may be a better option to enhance control. Tebulhiuron 200 g kg¹ (Molopo 200 GG) is an example of such a herbicide and is presently the only product registered for control of camelthorn bush in South Africa. However, since the plant is often a problem in cultivated areas and since tebuthiuron has a long-term soil sterilizing effect, this product has limited practical application value for control of camellhorn bush. The objective of this study was to investigate other residual herbicides that would have a lower residual impact on the soil. Results showed that both imazapyr 250 g ℓ ^-1 SL (8 ℓ ha^-1) and metsulfuron-methyl 600 g kg^-1 WP (13.33 kg ha^-1) outperformed all other treatments and sustained good levels of population control for at least 2 years after application. It is recommended that the registration holders of these products conduct further trials for the purpose of registration to control camelthorn bush.