Yao S.-L.,Zhejiang University |
Ying S.-H.,Zhejiang University |
Feng M.-G.,Zhejiang University |
Hatting J.L.,Small Grain Institute
BioControl | Year: 2010
Conidia of Beauveria bassiana and Metarhizium spp. smeared on glass slides were assayed for their responses to irradiation with weighted 312-nm UV-B and 365-nm UV-A at gradient doses of 0.005-1.1 and 1.0-18.0 J cm-2, respectively. All inverted, sigmoid dose-survival trends showed good fit to a survival model (r2 ≥ 0.97), yielding respective UV-B LD50s of 0.23-0.59 and 0.05-0.65 J cm-2 for 24 B. bassiana and 36 Metarhizium isolates, and UV-A LD50s of 2.78-10.46 J cm-2 for 24 Metarhizium isolates. Myzus persicae apterae on detached leaves were sprayed with a concentrated spore suspension of B. bassiana or M. anisopliae, followed by exposure to the UV-B doses to cause 10-90% viability losses. These doses caused aphid mortality reductions as expected but affected neither spray-to-death period nor fungal growth on cadavers. The results highlight the merits of using UV-tolerant candidates and photoprotection measures in fungal formulations for pest control. © 2010 International Organization for Biological Control (IOBC).
Hatting J.L.,Small Grain Institute |
Brand J.,Rooibos Ltd. |
Damavandian M.R.,Stellenbosch University |
Damavandian M.R.,Sari University of Agricultural Sciences and Natural Resources
African Entomology | Year: 2011
Production of 'rooibos' or red bush tea from Aspalathus linearis (Burman f.) Dahlgren (Fabaceae) is unique within the greater Cederberg region, Western Cape Province, South Africa. One of the principal insect pests associated with A. linearis production is the root-boring clearwing moth, Monopetalotaxis candescens Felder & Felder (Lepidoptera: Sesiidae). Annual moth flights peak during November/December, resulting in young plantations being targeted during the hot, dry summer conditions prevailing at this time. Average infestation levels progressively increased from 28 ± 2 % in year 1, to 53 ± 2 % and 72 ± 1 % in years 2 and 3, respectively. A second, 4-6 years old plantation during the three-year survey period was found to be severely infested (average 92 ± 1 %) with virtually no additional infestation over time. Estimated losses to borer infestation were calculated at 4, 24, 27 and 36 % in plantations that were 1-4 years old, respectively. Significantly more eggs were laid on leaves (66 ± 4 %) compared to woody tissue, stems and twigs. Most eggs hatched between 02:00 and 04:00, with neonates migrating down to the stem base and entering the root just below the soil surface. A control strategy, exploiting aspects of neonate migratory and feeding behaviour, should result in both yield increases and prolonged survival of plantations beyond the typical 4-5-year cycle.
Dube E.,Small Grain Institute |
Sibiya J.,University of KwaZulu - Natal |
Fanadzo M.,Cape Peninsula University of Technology
South African Journal of Science | Year: 2014
Home-saved bean (Phaseolus vulgaris L.) seed can be hand-sorted to remove discoloured seed, thereby reducing the level of contamination by certain seed-borne fungi and improving seed germination. In this study, the effect of planting date on the infection and discolouration of bean seed by seed-borne fungi was investigated in order to improve the quality of hand-sorted, farm-retained bean seeds used by resource poor smallholder farmers. The germination quality and level of seed-borne fungi in hand-sorted first-generation bean seed harvested from an early-, mid- and late-summer season planted crop was therefore assessed. The highest percentage of discoloured seed (68%) was obtained from the mid-summer season planting. Non-discoloured seed from early- and late-season plantings had significantly (p<0.001) higher normal germination (82% and 77%, respectively) than that from the mid-season planting date (58%). Irrespective of planting date, unsorted seed and discoloured seed had higher levels of infection by Fusarium spp. and Phaeoisariopsis spp. than the non-discoloured seed. Removal of discoloured seed by hand sorting eliminated Rhizoctonia spp. from all seed lots. Farmers can eliminate this pathogen by simply removing discoloured seed. Non-discoloured seed from the early-planted crop had the lowest level of infection by Fusarium spp. and Phaeoisariopsis spp. The results indicate that planting date is an important consideration in improving the quality of hand-sorted farm-retained bean seed. © 2014. The Author(s).
Richter J.M.,Private Bag X |
Richter J.M.,University of the Free State |
Prinsloo G.J.,Small Grain Institute |
Van Der Linde T.C.D.K.,University of the Free State
African Entomology | Year: 2014
Volatile compounds present in essential plant oils are known to influence insect behaviour. They are generally of low molecular weight, highly volatile, have a unique mode of action and are sometimes of low toxicity to non-target organisms. One example of a volatile compound extracted from a plant is methyl salicylate which is being used to reduce aphid infestation on barley in some European countries. The use of such volatile compounds was therefore considered as an alternate control option to be included in the control programme of Diuraphis noxia (Kurd.) after plant resistance-breaking bio types started to develop in South Africa. The aim of this study was to test the response of alate D. noxia to plant extracts from four plant species in a four-arm olfactometer. Aqueous and light mineral oil extracts of Artemisia afra (Jacq.), Datura stramonium (L.), Tagetes minuta (L.) and Tulbaghia violacea (Harv.), which grow naturally in some dryland wheat production regions of South Africa, were tested. These plants were chosen based on possible insect repelling properties known to occur in other species of the same genera. Aphids were strongly repelled by the oil extract of T. violacea and the aqueous extract of A. afra. The oil extract of A. afra, both T. minuta extracts and T. violacea aqueous extract were less repellent but still elicited an exceptional repelling response. Aphids were not repelled by D. stramonium extracts. The effectiveness of these basic extracts in repelling D. noxia should, however, be tested under field conditions before they can be recommended as a control option.
Jankielsohn A.,Small Grain Institute
Journal of Economic Entomology | Year: 2013
The incidence and host associations of Russian wheat aphid were investigated in the wheat-growing areas of South Africa from 2009 to 2011. Most Russian wheat aphid samples were collected on dryland wheat, while few samples were collected on irrigation wheat. Volunteer wheat and rescue grass were the preferred alternative host plants to cultivated wheat for all three biotypes. NoRWASA1samples were collected from oats, butRWASA2seemed to be able to survive successfully on oats, with 12.26% of the total RWASA2 samples collected on oats and 2.83% RWASA2 samples on wild oats. The intrinsic rate of population increase (rm) has often been used as an index of herbivore performance, and alternative host suitability can be quantified using growth rate parameters, such as the intrinsic rate of increase. The rm was determined for the three South African biotypes - RWASA1, RWASA2, and RWASA3 - on seven different host plants. Russian wheat aphid biotypes showed a positive intrinsic rate of increase on all host plants tested, indicating that these host plants were all suitable hosts to support populations of all three biotypes. The rm on TugelaDn, which is resistant to RWASA1 but susceptible to RWASA2 and RWASA3, was significantly higher for RWASA3 and lowest for RWASA1. The rm for RWASA2 and RWASA3 was significantly lower on TugelaDn5, which is resistant to these two biotypes. The rm for RWASA2 and RWASA3 was significantly higher than for RWASA1 on both oats and wild oats. Aphid infestation of winter wheat in the spring may be directly influenced by their success and abundance in noncultivated host plants between harvest and emergence of the cultivated wheat. Therefore, it is important to consider the success of different Russian wheat aphid biotypes on host plant alternatives to cultivated cereals when planning a management strategy for Russian wheat aphid in an area. © 2013 Entomological Society of America.