The relative seasonal abundance of indigenous heteropterans occurring on Litchi chinensis Sonn. was studied in the Mpumalanga province of South Africa. Litchi appears to be a good host for these insects as 669 individuals from 22 species were recovered during the study period lasting approximately 15 months. The coconut bug Pseudotheraptus wayi Brown was not the dominant stink bug as was expected, but rather Coenomorpha nervosa Dallas and Pseudatelus raptorius (Germar) which represented nearly 80% of the individual insects that were recovered. Not only were these two species numerically dominant, they were also the only species that were able to breed in this crop. Additionally, both species were also abundant when fruit was available on the trees. None of the other heteropterans were able to breed in litchis as only adults were recovered. These insects also occurred in low numbers and were abundant during autumn and winter when no fruit were available on the trees. This implies possible competitive displacement of lesser important heteropterans by C. nervosa. Damage previously ascribed to P. wayi may actually be caused by C. nervosa and possibly P. raptorius. P. wayi overwintered on litchis and could be controlled on this crop during this time in order to reduce their impact in adjoining alternative subtropical fruit tree hosts.
Citrus green mould, caused by Penicillium digitatum, is a serious postharvest disease which affects oranges during storage and in transit. The disease is mainly managed by application of postharvest fungicides. Some plant extracts have been shown to effectively inhibit P. digitatum growth. The aim of the study was to determine the efficacy of methanolic extracts of Monsonia burkeana and Euphorbia ingens on P. digitatum growth and citrus green mould severity under laboratory conditions. M. burkeana and E. ingens samples were collected from Sekhukhuni district in Limpopo, dried under shade and extracts were prepared using methanol. The final extract powder was used to amend growth medium and to prepare a water-based spray for artificial fruit infection. Both tested plant extracts inhibited P. digitatum growth in vitro. All concentrations of E. ingens had an equally significant effect on the pathogen growth when compared with the control. M. burkeana concentrations displayed varying suppressive effect on pathogen growth. Extracts of both plants were also able to significantly reduce disease severity in artificially infected citrus fruits when compared with the control. In conclusion, these results showed both extracts of M. burkeana and E. ingens had suppressive effects against P. digitatum.
The aim of this study was to determine the occurrence of mucoralean fungi as causal agents of fruit spoilage between different market types (small, medium-sized and large) in the Gauteng Province, South Africa. Samples of infected papaya, peach and strawberry were randomly collected at five different times, from three different markets around the Gauteng Province. Primary isolations were made from infected areas on the fruits, and the fungal colonies were identified morphologically. Mucoralean species associated with food spoilage were Rhizopus stolonifer, Rhizopus arrhizus, Mucor circinelloides and Mucor racemosus. Rhizopus stolonifer was the most prevalent species found with the highest numbers from strawberry in the small market, while R. arrhizus affected all three commodities at the same rate in the big market. Mucor racemosus were most prevalent on strawberry in the medium-sized market, while M. circinelloides were most prevalent on papaya in the small market. Rhizopus stolonifer is the main species associated with spoilage of peach, papaya and strawberry in all three markets.
Abstract The citrus mealybug, Planococcus citri, is a highly destructive pest of citrus, occurring only in the aerial parts of plants. Humidity will be one of the key factors to consider when using entomopathogenic nematodes (EPN) as biological control agents. Different adjuvants can be added to suspensions of EPNs, to improve control as a foliar application. An aqueous suspension containing Heterorhabditis zealandica and 0.3% Zeba® significantly increased P.citri mortality by 22% at 80% relative humidity (RH) with a temperature cycle starting at 22°C for 14 h and 11°C for 11 h. The same polymer formulation was tested for Steinernema yirgalemense and mortality of P. citri increased by 21% at 60% RH and by 27% at 80% RH. The addition of Nu-Film-P® and Zeba® to H. zealandica suspensions did not significantly retard application run-off on citrus leaves. The combination of Nu-Film-P® and Zeba®, however, was able to significantly retard sedimentation, increasing the average number of nematodes deposited on 2-cm2 leaf discs by 10 nematodes. In an aqueous suspension, nematodes settle rapidly to the bottom, resulting in an uneven distribution of nematodes. Xanthan gum, at a concentration of 0.2%, was highly effective at retarding sedimentation, with 72% of the initial nematode number still in suspension after 1 h. Zeba®, at a concentration of 0.3%, despite not being as effective as Xanthan gum, nevertheless still retarded sedimentation significantly. This is the first report of the potential of Nu-Film-P® and Zeba® to improve EPN performance against P. citri when used above ground in citrus orchards.
The efficacy of soil amendment with fever tea (Lippia javanica) in suppressing the root-knot nematode, Meloidogyne incognita, and enhancing tomato productivity was investigated over four consecutive seasons between 2002 and 2003. Four treatments were compared, viz. pasteurised soil only, fever tea amendment of pasteurised soil, nematode-infested soil without fever tea amendment, and nematode-infested soil amended with fever tea. M. incognita was applied at 4600 - 6420 juveniles and fever tea at 5 g powdered leaves per 10 l soil in pots according to a complete randomised block design, with 15 replicates per treatment per season.Application of fever tea to M.incognita-infested soil reduced nematode numbers in tomato roots by 79 - 92 % and significantly increased fresh fruit yield, dry shoot mass, plant height and stem diameter of the tomato plants, as well as levels of potassium, nitrogen and manganese in leaf tissue. Fever tea amendment also significantly improved plant development in uninfested soil, albeit not to the same extent as in infested soil. This indicates that fever tea has both nematicidal and plant growth-promoting properties.
Alternaria blight (AB), caused by Alternaria bataticola, is a new disease report on sweet potato in South Africa. Although at present limited in distribution locally, the disease can be destructive under hot, humid conditions. Fourteen sweet potato cultivars and breeding lines were screened in the greenhouse for tolerance to AB. Monate, Khano, Impilo and Ndou showed the highest tolerance, whereas Ribbok, Serolane, Excel, Resisto, W-119 and Beauregard were the least tolerant. The level of AB infection was not related to the skin or flesh colour of storage roots.
A new stem and foliar disease of sweet potato appeared in the 2004/05 season on sweet potato plants in field trials at Roodeplaat Experimental Farm, ARC-VOPI, Pretoria, Gauteng province, and subsequently in a commercial field near Brits, North West province. An Alternaria species consistently isolated from infected stems, petioles and leaves was identified as A. bataticola. Pathogenicity was confirmed under greenhouse conditions on the sweet potato cultivars A15 and Excel. This is the first report of A. bataticola infecting sweet potato in South Africa.
Plant-parasitic nematodes are a constraint to sugarcane production on sandy soils in South Africa. Nematode management has, for many years, relied on the use of chemical nematicides. However, with the demise of many commercially available chemical nematicides and the increasing demand for more environmentally-friendly biological control products, research is needed to evaluate some of these formulations for nematode management in sugarcane under field conditions. Two field trials (a plant crop and a ratoon) were conducted to assess four biological control products (Biostart, Eco-T, EMand Pl-Plus) and a more recent, environmentally-friendly, chemical nematicide (CropGuard), at single (recommended) and double rates. These were compared with a chemical nematicide (aldicarb) at the recommended rate and an untreated control. The biological control products had a negligible and inconsistent effect on the levels of soil and leaf chemical elements (i.e. soil and plant health) and on the population densities of plant-parasitic nematode genera and nematode feeding groups. They also failed to improve growth and yield of the sugarcane plants. CropGuard at double the recommended rate (i.e. 100 l ha-1) and aldicarb, however, significantly increased sugarcane and sucrose yield in both trials.
A survey was conducted during 2001-2003 of sweet potato grown by small-scale farmers in the seven main sweet potato-producing provinces of South Africa to determine the incidence of viral diseases in the field. Based on symptoms observed, disease incidence was relatively low. The highest levels of infection observed were between 9-10 % in the Western Cape and Mpumalanga. Symptoms were less prevalent or absent in the Eastern Cape, Limpopo, Gauteng, KwaZulu-Natal and North West. However, grafting onto Ipomoea setosa and subsequent testing by ELISA indicated that 81%of the samples were infected by viruses. Nine viruses were identified. Sweet potato feathery mottle virus (SPFMV) was the most common and occurred in 73 % of the samples tested. Sweet potato mild mottle ipomovirus (SPMMV) and Sweet potato latent potyvirus (SPLV) were detected in 3 % and 5 % of the samples, respectively. Five viruses were found for the first time in South Africa, viz. Sweet potato chlorotic fleck virus (SPCFV), Sweet potato mild speckling virus (SPMSV), Sweet potato chlorotic stunt crinivirus (SPCSV-East and West African strains), Sweet potato virus Y (SPVY) and Sweet potato virus G (SPVG). The effect of viral infection on storage root yield of ten sweet potato varieties was also studied over two seasons. Total yield was on average reduced by between 12 and 22 %, and marketable yield by 21 to 38 %. Reduction in marketable yield was mainly due to increased cracking of the storage roots. The new Agricultural Research Council varieties Monate and Ndou, and the 1994-5-1 breeding line produced marketable yields of 34-48 tonnes ha-1 even when infected with viruses, whereas the established South African varieties Mafutha and Natal Red yielded only 4-16 tonnes ha-1.
Epigeic spider (Araneae) populations were studied in three commercial pistachio orchards (REM, GVN 1, GVN 19) and in a natural undisturbed Nama Karoo grassland site in the Prieska district of the Northern Cape Province, South Africa.A total of 2814 spiders was collected, representing 25 families and 80 species.The grassland site supported a significantly greater abundance and diversity of spiders (n = 1112, 56 spp.) than the three pistachio orchards, viz. REM (n = 704, 35 spp.), GVN 1 (n = 560, 26 spp.) and GVN 19 (n = 428, 25 spp.). Five families (Agelenidae, Ammoxenidae, Cyrtaucheniidae, Gnaphosidae and Philodromidae) dominated the epigeic fauna of the grassland, whereas the orchard stands were dominated by Linyphiidae, Lycosidae and Salticidae.Overall, species composition was more even in the grassland than in the orchards.
Epigeic spider (Araneae) populations were studied in three commercial pistachio orchards (REM, GVN 1, GVN 19) and in a natural undisturbed Nama Karoo grassland site in the Prieska district of the Northern Cape Province, South Africa. A total of 2814 spiders was collected, representing 25 families and 80 species. The grassland site supported a significantly greater abundance and diversity of spiders (n = 1112, 56 spp.) than the three pistachio orchards, viz. REM (n = 704, 35 spp.), GVN 1 (n = 560, 26 spp.) and GVN 19 (n = 428, 25 spp.). Five families (Agelenidae, Ammoxenidae, Cyrtaucheniidae, Gnaphosidae and Philodromidae) dominated the epigeic fauna of the grassland, whereas the orchard stands were dominated by Linyphiidae, Lycosidae and Salticidae.Overall, species composition was more even in the grassland than in the orchards. These results indicate that establishment of the pistachio orchards and subsequent management disturbances had a negative impact on the abundance and diversity of epigeic spider communities. Interestingly, the epigeic spider fauna of the orchards was quite similar to that in central and northern Europe, but the fauna of the grassland differed completely from that in undisturbed European habitats.
The search for safe and environmentally-friendly pest control options has led to the exploration of pesticidal plants for potential alternatives. Plants from several families have been reported to exhibit a wide range of biological activities against insect pests, some of which have been scientifically validated. Recently, attention has focused on the identification of the compounds present in plants that possess insecticidal properties. Although there is a wealth of information available on this field of science, the data are scattered in various journals and other publications.This paper presents a review of the literature on biological activities of pesticidal plant extracts, types of insecticidal phytochemicals, synergistic effects of pure compounds and crude extracts, role of botanical insecticides in integrated pest management, drawbacks of phytoinsecticides, and methods employed in the screening and validation of such products.
Different host and habitat preferences necessitate confident species determination for the successful release of trichogrammatid wasps as part of a biological control programme. Trichogrammatoidea lutea and Trichogrammatoidea cryptophlebiae are indigenous to South Africa and have considerable potential as biological control agents of various economically important agricultural pests in the country. Unfortunately, rapid, accurate means of identifying these species are not available. DNA sequence analysis of the internal transcribed spacer 2 (ITS 2) region of the ribosomal gene complex has previously been applied for identification and distinction of Trichogramma species, but not for members of the closely-related genus Trichogrammatoidea. In this study a protocol was developed that allows DNA sequence determination of the above region, following genomic DNA extraction from a single Trichogrammatoidea wasp. DNA sequence analysis of the ITS 2 region revealed both length and within-sequence variation, indicating that T. lutea and T. cryptophlebiae are distinct species. This information can be used for simple and rapid identification of the two species based on a PCR reaction of extracted DNA, avoiding time-consuming slide-mounting procedures and the availability of expert knowledge for morphological identification.
Plantain is an important staple food in West and Central Africa and the Congo Basin. The crop is largely grown in extensive 'slash and burn' systems, drawing heavily on the natural resource base, but is low-yielding due to its high susceptibility to a complex of root and corm pests and diseases. Farmers are unaware of nematodes, fungi and banana weevil eggs, and therefore practise virtually no pest or disease control. This study evaluated the effects on plantain bunch yield of factorial combinations of a simple physical sanitation method, paring, followed by five different treatments (control, ash-coating, hot-water treatment, boiling-water treatment and application of the nematicide carbofuran). Paring reduced plantain establishment. It had no effect on fresh bunch yield but reduced uprooting and improved root health status. Without prior paring, bunch yields after the traditional ash-coating (5.7 tonnes ha-1) and nematicide application (6.3 tonnes ha-1) were not significantly different from the control (4.6 tonnes ha-1). Hot-water treatment (12.0 tonnes ha-1) and boiling-water treatment (14.2 tonnes ha-1) increased yield significantly. Boiling-water-treated plantain attained 90 % of the total yield earlier than any other treatment. Yield losses were mainly caused by pseudostem break, whereas uprooting resulted in only minor losses. Yield losses in this study could not be attributed to a particular group of pests or diseases but to all factors contributing to water deficiency which lead to the low turgor that permitted pseudostem break. Root health parameters were positively related to bunch yield and to bunch mass per producing plant. Owing to its simplicity, flexibility, low cost, accelerated production, and absence of negative environmental effects, boiling-water treatment was the most labour-efficient and profitable sucker-sanitising method.
Plant nematodes recorded during surveys of the Goegap and Witsand Nature Reserves are listed. Eight families represented by 17 genera and 34 species were identified. The genus Tylenchorhynchus was the only genus found at more than 50 % of the localities, whereas Criconemoides, Ditylenchus, Hemicycliophora, Longidorus, Paratrichodorus, Pratylenchus, Rotylenchus and Scutellonema were present at fewer sites. The genera Criconema, Helicotylenchus, Hemicriconemoides, Histotylenchus, Hoplolaimus, Meloidogyne, Rotylenchulus and Xiphinema were each identified from a single locality. Pratylenchus fallax is herein reported as a first record for South Africa. A new species, Rotylenchus aqualamus, based only on female specimens, is described and characterised by having a rounded, slightly set-off lip region with four annuli; a 26-28 µm long stylet with grape-stone-like stylet knobs; metenchium shorter than telenchium (m = 43-48.5 %); dorsal oesophageal gland opening 7.5-12 µm posterior to base of stylet with an o-value of 27.3 to 42; lateral field regularly areolated opposite oesophageal area and irregularly areolated over whole length of body, mostly ending between phasmid and anus but in a few specimens continuing right up to end of lateral field; tail with a rounded, non-annulated, irregularly folded tip, 19.5-27 µm long with 12-17 ventral annuli; phasmid situated 11-27 annuli anterior to anus. No males were found. Scanning electron microscope photographs are provided.
Plant nematodes recorded during surveys in the Bizana, Lusikisiki and Port St Johns area in the Eastern Cape Province, South Africa, are listed. Eleven families represented by 27 genera and 105 species were identified. The genera Helicotylenchus, Scutellonema, Xiphinema and Meloidogyne were present in more than 30 % of the localities, whereas Criconema, Criconemoides, Discocriconemella, Dolichodorus, Hemicycliophora, Longidorus, Ogma, Paralongidorus, Paratrichodorus, Paratylenchus, Pratylenchus, Rotylenchulus, Rotylenchus, Trophotylenchulus and Tylenchorhynchus were found at fewer localities. The genera Aphelenchoides, Ditylenchus, Hemicriconemoides, Hoplolaimus, Radopholus, Trichodorus and Tylenchulus were each identified from a single locality. Discocriconemella degrisseiis herein reported as a first record for South Africa. Various nematode-plant associations are reported for the first time in South Africa.
Bt -cotton, containing and expressing genes from the soil bacterium, Bacillus thuringiensisl/Ig var. kurstaki , is toxic specifically to lepidopteran larvae, but little is known about the impact it could have on predators such as spiders. A survey to determine the effect of Bt -cotton and endosulfan application on spider populations was conducted over two cotton-growing seasons (2001/2002 and 2002/2003) on a farm near Marble Hall in South Africa. Plant-dwelling spiders (lIgnl/Ig = 227) were counted over the two seasons while scouting the plants, but were not identified. Ground-dwelling spiders ( n = 3777) were collected with pitfall traps in both seasons and identified to species level. The ground dwellers were represented by 21 families, 49 genera and 54 species. During the first season a total of 2431 spiders was collected from the pitfall traps, 945 from Bt -cotton and 1486 from non- Bt -cotton (control) fields. In the second season a total of 781 was collected, 416 from Bt -cotton and 365 from non- Bt -cotton fields. A total of 565 spiders was collected from a non- Bt -cotton field sprayed with endosulfan during the second season. The Lycosidae ( n = 2359) represented 62.5 % of all spiders collected in the pitfall traps, followed by the Theridiidae ( n = 757) with 20.0% and Linyphiidae ( n = 342) with 9.1 %. Steatoda erigoniformisl/Ig (Theridiidae) ( n = 744) was the most abundant species, representing 19.7%of all the spiders collected, followed by Pardosa clavipalpisl/Ig (Lycosidae) ( n = 624) with 16.5 %, an undetermined lIgTrabeal/Ig sp. (Lycosidae) ( n= 592) with 15.7 % and another lycosid, Pardosa crassipalpisl/Ig ( n = 543), with 14.4 %. Neither Bt -cotton nor the application of endosulfan had a marked or persistent negative impact on ground- or plant-dwelling spiders in the field.
Malan A P, Nguye nKB&A ddison M F 2006. Entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) from the southwestern parts of South Africa. African Plant Protection 12: 65–69. Soil samples were collected in the southwestern parts of South Africa to obtain entomopathogenic nematodes of the families Steinernematidae and Heterorhabditidae. In total, 498 samples were randomly taken from cultivated and uncultivated habitats, including deciduous fruit orchards, vineyards and natural vegetation. Entomopathogenic nematodes were isolated from 36 samples (7 %) by baiting with larvae of Galleria mellonella (greater wax moth). Heterorhabditis was the dominant genus isolated, while Steinernema was rare. The most common species was Heterorhabditis bacteriophora Other species identified were Heterorhabditis zealandica and Steinernema khoisanae. The isolation of H. zealandica represents a new record for South Africa, whereas S. khoisanae has thus far been recorded only from South Africa. Entomopathogenic nematodes (EPNs) of the genera Steinernema and Heterorhabditis occur naturally in soil, where they parasitise different life stages of various soil-inhabiting insects. The nematodes are synergistically associated with bacteria and together they kill and utilise their insect host. Infective juveniles (IJs) are the only free-living stage in soil and carry the bacteria in their intestines, releasing them once the haemocoel of the host is penetrated. The IJ is a special third stage of development, highly resistant to adverse conditions in the soil, with some species capable of surviving for several months or even years without feeding. They kill their hosts within 1–2 days, can be produced commercially and can be applied with standard spraying equipment or through certain types of irrigation systems. The main interest in these nematodes is their potential as biological control agents in integrated pest management systems. The first record of EPNs in South Africa was from the maize beetle Heteronychus arator (Fabricius) (Heteronychus sanctae-helenae Blanch.) in Grahamstown, Eastern Cape Province (Harington 1953). Three isolates of Steinernema and a Heterorhabditis were evaluated in KwaZulu-Natal against the African sugarcane stalk-borer, Eldana saccharina Walker, in laboratory and field tests (Spaull 1988, 1990).A further survey was conducted in 1991 to obtain isolates more virulent against E. saccharina, during which seven Heterorhabditis and 15 Steinernema isolates were found (Spaull 1991), but they were not identified to species level. A new species of Steinernema for South Africa,
