Effect of glyphosate application time on yield parameters of South African glyphosate-resistant maize cultivars

Glyphosate is the most used herbicide in South Africa. Due to observations by some South African maize producers that the application of glyphosate to glyphosate-resistant (GR) maize cultivars resulted in reduced yield, we conducted an in-depth study under local conditions. Through field trials, over two seasons (2017/2018 and 2018/2019), we investigated whether the application time of glyphosate would impact maize yields negatively. Various yield parameters were measured subsequent to glyphosate application to the local GR maize cultivars DKC74-74BR, DKC78-79BR, KKS4581, KKS8408, BG5785BR, PAN6R-710BR, P1814R and P2880WBR. Four glyphosate products were included (Roundup PowerMax®; Slash Plus 540 SL; TouchdownForte® and MambaTM DMA 480 SL), resulting in 32 cultivar x glyphosate product combinations. Each product was applied at V4, V4+V6, V6 and V8 growth stages together with an untreated control. Yield parameters measured (ears per plant, rows per ear, kernels per row, thousand kernel mass and yield) were expressed as a percentage of the control. The trials were planted as randomised complete block designs with three replicates. Limited response was observed with all the parameters investigated, with a significant negative yield response, greater than the untreated control, observed in only 3.1% of the cultivar x glyphosate product combinations evaluated. No clear trends or discernible and consistent impacts on yield and yield parameters could be established based on the application time of glyphosate (within label recommendations) across seasons. The findings contribute significantly to the knowledge base and current understanding of the international community and local producers alike regarding the effective use of glyphosate and generic variations thereof in crops of diverse genetic backgrounds. Significance: Limited response in the yield parameters evaluated were obtained in response to the application time (V4, V4+V6, V6 and V8) of the four glyphosate products on eight GR maize cultivars tested (p=0.1). Inconsistent patterns or trends were detected in cases where significance was obtained, implying that it would not be possible to draw accurate conclusions or formulate recommendations. Application time of glyphosate did not result in a significant reduction in yield compared to the untreated control, in the majority of the cultivar x glyphosate product combinations investigated, confirming that glyphosate application conducted within label specifications would not reduce yield, irrespective of the glyphosate product or genetic background of maize

Assessment of the repellent effect of citronella and lemon eucalyptus oil against South African Culicoides species

The use of insect repellents to reduce the attack rate of Culicoides species (Diptera: Ceratopogonidae) should form part of an integrated control programme to combat African horse sickness and other diseases transmitted by these blood-feeding midges. In the present study the repellent effects of a commercially available mosquito repellent, a combination of citronella and lemon eucalyptus oils, on Culicoides midges was determined. The number of midges collected with two 220 V Onderstepoort traps fitted with 8 W 23 cm white light tubes and baited with peel-stick patches, each containing 40 mg of active ingredient, was compared with that of two unbaited traps. Two trials were conducted and in each trial the four traps were rotated in two replicates of a 4 x 4 randomised Latin square design. Although more midges were collected in the baited traps, the mean number in the baited and unbaited traps was not significantly different. This mosquito repellent did not influence either the species composition or the physiological groups of Culicoides imicola Kieffer. The higher mean numbers in the baited traps, although not statistically significant, may indicate that this mosquito repellent might even attract Culicoides midges under certain conditions.http://www.jsava.co.zaam201

The suitability of the Triple trap for the collection of South African livestock-associated Culicoides species

The relatively large number of Culicoides midges (Diptera: Ceratopogonidae) that can be collected with a light trap makes it the most widely used tool for this purpose. However, the majority of these traps were originally designed for collecting mosquitoes. The evaluation and improvement of traps to increase their effectiveness in collecting Culicoides midges will unavoidably form part of research on these insects. In the present study the efficiency of the Triple trap for collecting livestock-associated Culicoides midges was compared with that of the Onderstepoort 220 V, the BG-sentinel and the mini-CDC traps. A unique feature of the Triple trap is that selected surfaces are coated with TiO2 (titanium dioxide) which, in the presence of ultra violet light, acts as a photo-catalyser to produce CO2, which in turn may attract blood-feeding insects. Overall, the Onderstepoort trap collected significantly higher numbers of midges than the others. Relative efficiency varied between different occasions and under some conditions, for example periods with low midge abundance during the winter, the mean numbers collected with the Triple trap did not differ significantly from those of the Onderstepoort or BG-sentinel traps. By replacing the collection chamber of the Triple trap with a sock and beaker, similar to that of the Onderstepoort trap, it can effectively be used for the collection of Culicoides midges.The South African Equine Veterinary Association of the South African Veterinary Associationhttp://www.jsava.co.zaam2014ab201

Influence of carbon dioxide on numbers of Culicoides midges collected with suction light traps in South Africa

To implement risk management against diseases transmitted by Culicoides species Latreille, 1809 (Diptera: Ceratopogonidae) it will be essential to identify all potential vectors. Light traps are the most commonly used tool for the collection of Culicoides midges. Taking into account the indiscriminative artificial attraction of light, these traps will collect all night flying insects and not only livestock associated Culicoides midges. Factors that could increase the efficacy of these traps for especially livestock associated Culicoides midges need to be investigated. In the present study, results obtained with CDC- and Onderstepoort light traps baited with CO2 were compared to those of unbaited traps. Comparisons were done in two replicates of a 4 x 4 randomized Latin square design. With both traps, the mean numbers of Culicoides midges collected in 16 baited collections were higher than those in 16 un-baited collections. Despite exceptionally low numbers collected with the CDC traps, the increase in the numbers and frequency of collection of Culicoides imicola Kieffer, 1913 was more pronounced in the CDC compared to that in the Onderstepoort trap. These results indicate that the addition of CO2 could increase the efficiency of these traps for the collection of C. imicola, and other livestock associated Culicoides species.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-29152017-03-30hb201

Repellent effect of organic fatty acids on Culicoides midges as determined with suction light traps in South Africa

The efficacy of a 15% (w/w) mixture of octanoic, nonanoic and decanoic acids in light mineral oil to repel Culicoides biting midges (Diptera; Ceratopogonidae) was determined in three replicates of a 4 × 4 Latin square design under South African field conditions. The fatty acids were applied to ±0.07 m2 polyester meshes with a mesh size 2–3 mm fitted to 220 V 8 W Onderstepoort downdraught light traps. To reduce the relatively strong attraction of the light trap, the black light tubes in the Onderstepoort trap were replaced with 8 W 23 cm white light tubes. The traps were operating overnight next to cattle. Two traps treated with the mixture of fatty acids collected 1.7 times fewer midges than two untreated traps. Although this mixture of fatty acids had shown a repellent effect against a number of blood-feeding insects this is the first indication that it also has a significant repellent effect against Culicoides species and especially Culicoides (Avaritia) imicola Kieffer when applied to polyester mesh.Afrivet (Pty) Ltd.http://www.elsevier.com/locate/vetparab201

Attraction range of the Onderstepoort 220 V light trap for Culicoides biting midges as determined under South African field conditions

Despite some limitations suction lighttraps are the primary tools used for the collection of Culicoides species (Diptera: Ceratopogonidae). The range of attraction of the Onderstepoortlighttrap is not known but an insight into the range of a trap will determine where the trap must be positioned relative to the hosts present, possible breeding sites and environmental structures in the trapping vicinity. It will therefore contribute to a more meaningful interpretation and comparison of results between trapping events. In the present study the number of Culicoidesmidges collected in a single trap was compared to those of traps made with an additional trap respectively 1 m, 4 m and 8.5 m away from the first. Treatments between sites were rotated in three replicates of a 4 × 4 Latin square design. While interactions were found in traps 4 m apart no statistically significant interactions were found when they were 8.5 m apart. The range of attraction, indicated by the interaction between two traps, will be between 2 m and 4 m. In interpreting lighttrap results the limitations of this collection method needs to be taken into consideration.http://www.elsevier.com/locate/vetparab201

Critical periods of weed control for naked crabgrass (Digitaria nuda), a grass weed in corn in South Africa

Difficulties in chemically controlling large crabgrass in corn in South Africa have recently been attributed to the occurrence of naked crabgrass. In contrast to large crabgrass, naked crabgrass is not easily controlled with acetanilide herbicides. Critical periods of weed control (CPWC) for naked crabgrass in corn was determined in field studies during the 2009/2010 and 2010/2011 growing seasons at two separate localities for an early and late planting date of corn. Weed-free and weed–crop interference treatments of increasing duration were maintained at various crop growth stages in the presence of naked crabgrass. Biomass of naked crabgrass was determined as dry weight per square meter quadrant, which yielded 428 g m22 at Potchefstroom and 594 g m22 at Wesselsbron. An exponential regression model was used to determine the CPWC expressed as growing degree days after crop emergence, on the basis of an estimated 10% relative yield loss in corn. The onset and ending, as well as the duration of the CPWC, differed between seasons and localities. At 10% relative yield loss, the onset of the CPWC ranged between the two-leaf (V2) and six-leaf (V6) stages, and the ending between the 12-leaf (V12) stage and 2 wk after tasseling (T + 2). The duration of the CPWC ranged between 22 and 80 d for the respective planting dates, years, and localities. Yield losses ranged from 28 to 82% in the season-long weedy plots. The shifting of planting dates alone did not reduce yield losses since the effect of late infestations of naked crabgrass is significant. Naked crabgrass control from crop emergence is essential, followed by POST herbicide application during the critical period of weed control to lower the risk of corn yield losses.Maize Trust of South Africa and the Agricultural Research Council.http://www.wssajournals.org/loi/weeshb201

Risk Factors of Porcine Cysticercosis in the Eastern Cape Province, South Africa

There is a high prevalence of Taenia solium taeniosis/cysticercosis in humans and pigs in the Eastern Cape Province (ECP) of South Africa. The objective of this study was to identify risk factors of porcine cysticercosis in select districts of the ECP. Data were collected in 2003 by interviewing 217 pig producers from the area. Blood samples were collected from 261 of their pigs, which were tested using two enzyme-linked immunosorbent assays (ELISA) for the presence of antibodies to cysticercosis. Frequencies of both owner- and pig-level characteristics were determined. For pig-level analysis, all bivariable and multivariable associations were determined using the surveylogistic procedure of the SAS/STAT® software to accommodate for the intraclass correlation that exists for clusters of pigs within one owner and for clusters of owners within a district. All tests for significance were performed at the α = 0.05 level, and adjusted odds ratios (aOR) and 95% confidence intervals (CI) were determined. Among the respondents, 48% of their households lacked a latrine, 98% slaughtered pigs at home, and 99% indicated that meat inspection services were not available. On bivariable analysis, there was a significant association between porcine infection and district (p = 0.003), breed (p = 0.041) and the absence of a latrine (p = 0.006). On multivariable analysis, the absence of a latrine was the only variable significantly associated with porcine infection (aOR = 1.89; 95% CI = 1.07, 3.35) (p = 0.028). The increased odds of porcine infection with households lacking a latrine contributes to our understanding of the transmission of this parasite in the ECP. Determining and addressing the risk factors for T. solium infection can potentially lower the very high prevalence in humans and pigs in this endemic area

The effect of high frequency sound on <i>Culicoides</i> numbers collected with suction light traps

Culicoides midges (Diptera: Ceratopogonidae), are involved in the transmission of various pathogens that cause important diseases of livestock worldwide. The use of insect repellents to reduce the attack rate of these insects on livestock could play an important role as part of an integrated control programme against diseases transmitted by these midges. The objective of this study was to determine whether high frequency sound has any repellent effect on Culicoides midges. The number of midges collected with 220 V Onderstepoort white light traps fitted with electronic mosquito repellents (EMRs), emitting 5-20 KHz multi-frequency sound waves, was compared with that of two untreated traps. Treatments were rotated in two replicates of a 4 x 4 randomised Latin square design. Although fewer midges were collected in the two traps fitted with EMRs, the average number collected over eight consecutive nights was not significantly different. The EMRs also had no influence on any of the physiological groups of Culicoides imicola Kieffer or the species composition of the Culicoides population as determined with light traps. The results indicate that high frequency sound has no repellent effect on Culicoides midges. There is therefore no evidence to support their promotion or use in the protection of animals against pathogens transmitted by Culicoides midges

Effect of glyphosate application time on yield parameters of South African glyphosate-resistant maize cultivars

Glyphosate is the most used herbicide in South Africa. Due to observations by some South African maize producers that the application of glyphosate to glyphosate-resistant (GR) maize cultivars resulted in reduced yield, we conducted an in-depth study under local conditions. Through field trials, over two seasons (2017/2018 and 2018/2019), we investigated whether the application time of glyphosate would impact maize yields negatively. Various yield parameters were measured subsequent to glyphosate application to the local GR maize cultivars DKC74-74BR, DKC78-79BR, KKS4581, KKS8408, BG5785BR, PAN6R-710BR, P1814R and P2880WBR. Four glyphosate products were included (Roundup PowerMax®; Slash Plus 540 SL; TouchdownForte® and MambaTM&nbsp;DMA 480 SL), resulting in 32 cultivar x glyphosate product combinations. Each product was applied at V4, V4+V6, V6 and V8 growth stages together with an untreated control. Yield parameters measured (ears per plant, rows per ear, kernels per row, thousand kernel mass and yield) were expressed as a percentage of the control. The trials were planted as randomised complete block designs with three replicates. Limited response was observed with all the parameters investigated, with a significant negative yield response, greater than the untreated control, observed in only 3.1% of the cultivar x glyphosate product combinations evaluated. No clear trends or discernible and consistent impacts on yield and yield parameters could be established based on the application time of glyphosate (within label recommendations) across seasons. The findings contribute significantly to the knowledge base and current understanding of the international community and local producers alike regarding the effective use of glyphosate and generic variations thereof in crops of diverse genetic backgrounds.Significance: Limited response in the yield parameters evaluated were obtained in response to the application time (V4, V4+V6, V6 and V8) of the four glyphosate products on eight GR maize cultivars tested (p=0.1). Inconsistent patterns or trends were detected in cases where significance was obtained, implying that it would not be possible to draw accurate conclusions or formulate recommendations. Application time of glyphosate did not result in a significant reduction in yield compared to the untreated control, in the majority of the cultivar x glyphosate product combinations investigated, confirming that glyphosate application conducted within label specifications would not reduce yield, irrespective of the glyphosate product or genetic background of maize.&nbsp