Preliminary evaluation of soil-residual herbicides for the control of silver-leaf bitter apple (Solarium elaeagnifolium Cav.)
South African Journal of Plant and Soil
Agricultural Research Council, Plant Protection Research Institute, P.O. Box 318, Uitenhage, 6230, South Africa; Agricultural Research Council, Biometry Unit, Private Bag X5013, Stellenbosch, 7599, South Africa; Hofmeyer Street, Despatch, 6220, South Africa
Solatium elaeagnifolium Cav., commonly known as silver-leaf bitter apple, silverleaf nightshade or "satansbos",has become one of the most important emerging weeds in South Africa, with the potential to spread throughoutsome of the major crop growing areas of the country. Consequently, it has been declared a weed of nationalimportance. Previous research revealed the difficulty in killing the extensive root system when using foliarapplied herbicides. The small leaf area for herbicide absorption relative to the large root system and apparentinability to translocate sufficient herbicide beyond the root crown are believed to be some of the main reasonsfor the poor levels of control achieved. Since herbicides capable of being absorbed by the roots may be moreeffective, a study was undertaken to evaluate a range of soil-residual herbicides in the hope of improving control.While imazapyr 250 g V SL applied at 81 ha"1initially caused the most significant reduction in weed populationlevels, it was ultimately tebuthiuron 500 g !"1 SC and a bromacil/tebuthiuron mixture 250/250 g ("1 SC applied at32 J ha"1 that sustained the best long-term control. However, the high cost and long soil residual nature of theseproducts would seriously limit their application value in cropping areas and sensitive habitats. Nonetheless, theymay be useful for controlling isolated dense patches on fallow land and along roadsides, away from desirablevegetation, steep slopes or watercourses. The registration holders of these products are encouraged to conductfurther evaluations using lower rates, as well as combining these products with foliar applied herbicides, toreduce costs and potential environmental impacts if used in sensitive habitats.
dicotyledon; environmental impact; herbicide; pesticide residue; root system; tolerance; translocation; weed control; South Africa; Citrullus colocynthis; Solanum elaeagnifolium; Solarium