Parthenium hysterophorus (Asteraceae), of South American origin, is considered to be one of the worldÕs most serious invasive plants, invading Australia, Asia and Africa. As part of an international collaborative project, this study attempted to improve the understanding of the geographical distribution of P. hysterophorus in eastern and southern Africa. The climate modelling program CLIMEX was used to assist in the selection of survey localities. Roadside surveys of the distribution of the weed were conducted in Botswana, Ethiopia, South Africa, Swaziland and Uganda. Prior to these surveys, only limited P. hysterophorus locality records existed; substantially more records were obtained from surveys. Most infestations were high density (>3 plants m )2 ). Distribution records were used to validate the CLIMEX model, which proved a useful tool. This study increased current understanding of the distribution of P. hysterophorus and developed a baseline from which to monitor future spread and abundance of P. hysterophorus. Additional surveys are required in other countries in Africa which are predicted by CLIMEX to be at risk. This will enhance integrated management decisions for the control of a weed which has implications for food security and human health.
Metalaxyl is a systemic fungicide commonly used in citrus production to control Phytophthora root rot and foot rot. When applied as a drench, injury was observed on newly planted, young citrus trees. The visual injury symptoms ranged from light- to bright-yellow leaves. It was learned that the commercial formulation of metalaxyl contained various isomers and that these isomers may vary in phytotoxic effects on citrus leaves. The objective of this study was to determine the difference in herbicidal activity between the two optical isomers of metalaxyl on pepper plants and citrus leaves. The phytotoxicity of the fungicide metalaxyl and its optical isomers (CGA76538, S+; CGA76539, R-) was determined using a pepper seedling growth bioassay and by measuring protein synthesis as estimated by the incorporation of 14C-leucine by citrus mesophyll cells. The two isomers and metalaxyl differed in their herbicidal activity to pepper plants and citrus cells. Pepper seedlings treated with R- had significantly higher mean fresh weight than plants treated with metalaxyl or S+ at 0.1, 1.0, 10.0, and 100 ppm. Protein synthesis, as measured by the inhibition of 14C-leucine incorporation by citrus mesophyll cells, also was inhibited more by metalaxyl and the S+ isomer than by the R- isomer. After 30 min of incubation at 100 μM, the R- isomer inhibited 14C-leucine incorporation by 29%, whereas incorporation of 14C-leucine in the metalaxyl and the S+ isomer treatments was higher (46 and 81%, respectively). Similarly, the highest 14C-leucine uptake at 60 min was obtained by R- at all concentrations. The assays showed that the R- and S+ isomers differ in their biological activity as expressed by weight loss of pepper plants and inhibition of protein synthesis and that the S+ isomer is responsible for the phytotoxicity of metalaxyl. The findings in this study show that the phytotoxicity of metalaxyl was due to the presence of the S+ optical isomer. Removal of this isomer from metalaxyl has enabled the continued use of this fungicide for control of foot rot and root rot in citrus.
The presence and spread of Listronotus setosipennis (Coleoptera: Curculionidae) and Zygogramma bicolorata (Coleoptera: Chrysomelidae) released in 2017 for the control of Parthenium hysterophorus (L.) (Asteraceae: Heliantheae) at two locations in Ethiopia (Arba Minch and Mojo) were assessed twice (July, September) in 2018. At Arba Minch, no L. setosipennis was found, only Z. bicolorata established and the number of eggs varied from 1.4±0.71/plant (July) to 7.41±4.52/plant (September) at the release site and from 0.52±0.18/ plant (July) and 0.68±0.24/plant (September) at the dispersal site. At Mojo, only L. setosipennis established with 3.87±1.18 eggs/plant (July) at the release spot and 10.76±1.64 eggs/plant in September whereas after dispersal the eggs numbered 8.69±3.2/plant (July) and 14.98±1.73/ plant (September). After one year, L. setosipennis and Z. bicolorata were found 51.75±3.95 m and 94.15±13.66 m away from the release spots, respectively. The results show that the biocontrol agents have started to establish and have dispersed at the two locations in Ethiopia.
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