Journal of Medical Systems

Abstract In 2016, Dematophora necatrix, the causal agent of white root rot (WRR), was identified in an avocado orchard in South Africa. Since then, this pathogen has spread to all avocado-growing regions in the country. This study aimed to evaluate the in-field efficacy of the biological control product EXTRASOL (Bacillus subtilis and Bacillus amyloquefaciens subsp. plantarum) and the fungicide fluazinam against WRR in two commercial avocado orchards in Tzaneen, Limpopo, South Africa. Over two growing seasons (2022 and 2023), disease severity, the number of D. necatrix-positive baits, and leaf area index (LAI) were monitored. Results showed that fluazinam significantly improved the health of WRR-symptomatic trees. At the start of the trial, symptomatic trees exhibited an average disease severity score of 4, which significantly declined to near 0 after two years, with symptoms largely absent. LAI of symptomatic trees treated with Fluazinam was significantly higher (> 4) in both orchards after two years. The combination of fluazinam and EXTRASOL performed similarly to fluazinam alone, while EXTRASOL alone provided minor benefits. Fluazinam residues also fell below detectable limits in the fruit of treated trees as soon as 2 weeks following treatment. These findings support fluazinam as a safe and effective treatment for WRR in South African avocado orchards.

Abstract Fall armyworm (Spodoptera frugiperda (J.E. Smith)) has become a significant pest to maize production, causing huge yield losses in sub-Saharan Africa. This study evaluated three non-Bt maize hybrids with tolerance to fall armyworm (FAW) along with a commercial hybrid check for yield and agronomic performance under natural FAW infestation and chemical control conditions in both on-station and on-farm trials. Significant differences were observed among the hybrids with the FAW tolerant hybrids showing reduced leaf and ear damage compared to the commercial hybrid. These hybrids also exhibited high grain yield performance, outyielding the commercial check by 197–252%. Mean grain yield under FAW infestation ranged from 6009.88 to 7117.30 kg ha−1 without chemical control, and even higher (8441.24 kg ha−1) under limited chemical control. Stepwise multiple regression analyses identified ear aspect, husk cover and ear damage as key traits accounting for 98% of the total variation in grain yield under FAW infestation. Participatory variety selection showed high farmer preference for these hybrids. The availability of these hybrids to farmers promises to enhance food security, reduce the environmental impact of insecticides, alleviate cost burdens on farmers, and increase household income.

Weeds pose a significant threat to agricultural productivity and food security, necessitating the use of herbicides for proper management. However, reliance on herbicides can lead to environmental degradation and the development of herbicide-resistant weeds. There is a growing trend towards employing natural weed control methods to reduce dependence on chemical herbicides and promote sustainable farming. This study aims to evaluate the effectiveness of maize hybrid mixture in integrated weed management practices. The research was conducted at the University of Agriculture, Faisalabad, Pakistan. The treatments were organized in a split-plot arrangement in a randomized complete block design with three replications. The experimental factors included a combination of maize hybrids (YH-5427 short-statured and DK-6714 tall-statured) with incremental doses of mesotrione and atrazine. A significant decrease in weed biomass of up to 81.7% was recorded in the hybrid mixture at the 25% reduced dose (mesotrione and atrazine), which was statistically at par with an 82.7% reduction in single hybrids. Similarly, the grain yield of the mixture at reduced herbicide dose was 11,127 kg ha−1 and 10,590 kg ha−1 having no statistical difference with the short-statured and tall-statured hybrid yields. Furthermore, the cultivar mixture consistently provided higher net return (up to $1412) and benefit-to-cost ratio (up to 2.21) across all treatments. However, careful selection of hybrids that are strong competitors with high yields and less dependence on herbicides can help achieve both environmental and economic objectives in weed control and crop production. These results suggest that proper combinations of hybrid mixtures can efficiently control weeds while reducing the need for herbicides, thus promoting sustainable agriculture.

Nymphs and adults of the spittlebug, Poophilus costalis Walker (Hemiptera: Aphrophoridae) are highly polyphagous and feed on xylem. Moreover, the host-plant association and preference of P. costalis is imperative. Therefore, this study aimed to record its nymphal abundance among the various plants, food plant preference, foam size, nymphal stage present in the foam, and temperature variation between the environment and within the foam. Results Observations revealed that spittlebugs preferred to construct their nests in 33 plant species belong to 14 families. Spittlebug constructed its nests in Peristrophe bicalyculata (Retz.) Nees. (Acanthaceae) (12.16%), followed by Cenchrus setigerus Vahl (Poaceae) (11.35%) and Tephrosia purpurea (L.) Pers. (Fabaceae) (10.86%). The recorded foams in T. purpurea is ranged from 1 to 13 foams. One or more individuals of different nymphal instars were recorded in foams. Most of the spittlebugs preferred to construct their nests either in nodes (45.45%) or internodes (48.48%) regions. Length, breadth and area of P. costalis foam also varied among plants. Temperature variation between immediate surrounding and foam reveals that spittlebugs maintained lower temperature (26.3 ± 0.17 °C) when compared to environmental temperature (31.4 ± 0.19 °C). This study showed that P. costalis prefers specific plants and parts for foam construction and to establish its population. Therefore, it is preferable to not cultivate these plants in the same field, which reduces the abundance of this pest where the foam covers surface area of host plants and maybe reduce the photosynthetic areas as well as plant growth.

Hypovirulence-mediated biological control has proven to be one of the most effective measures against Cryphonectria parasitica, the causal agent of chestnut blight. However, the success of this approach is constrained by the vegetative incompatibility (vic) system, which regulates the transmission of hypoviruses. The vic system is governed by six unlinked loci that determine vegetative compatibility (vc) groups. While 64 vc types (EU1-EU64) have been characterized in European C. parasitica populations, the emergence of new genetic variants in certain regions and their incompatibility with European vc testers suggests that the vic system’s complexity is not fully understood. In this study, we investigated the variability in the vic genes of C. parasitica isolates from Türkiye, where genetic divergence has been observed, particularly near the Georgian border. We analyzed the allelic patterns of six vic loci in Turkish isolates with undefined vc groups and compared them to European vc testers. PCR-based genotyping revealed that Turkish isolates belonged to previously known European vc types, including EU3, EU4, EU21, EU29, EU35, EU45, EU51, and EU60. However, significant vegetative incompatibility reactions were observed in co-culturing assays, indicating the presence of intra-group incompatibility even between isolates with identical vic genotypes. Our findings reveal a more complex genetic structure underlying vegetative incompatibility in Turkish C. parasitica populations, challenging the six-locus vic model. The identification of distinct vegetative incompatibility subgroups suggests additional genetic factors at play. This study highlights the need for a deeper understanding of the vic system to improve biological control strategies in Türkiye and beyond.

Silicon (Si) supplementation is known to cause the resistance of plants to insect herbivores. There is a lack of clarity regarding the methods by which silicon influences herbivore performance. We assessed different silicon concentrations (0, 125, 250 & 500 mg L−1) on Si accumulation, development and mandibular wear of insect herbivore, Mythimna separata on wheat. Higher Si concentrations decreased oviposition rates, weight gain, larval biomass and consumption rates in M. separata. On comparing with control, increased Si levels resulted in higher percent mortality, longer development and greater mandibular wear. Higher Si concentrations lead to abrasiveness and hardness of leaves and poor nutritional quality of the leaves which in turn affect the performance of herbivore. Thus, Si supplementation could be an alternative to insecticides and one of the potential ways of controlling insect pests in Integrated Pest Management Programs.

Tetranychus urticae Koch (Acari: Tetranychidae) is a key pest in various crops. Biological control with Neoseiulus californicus (McGregor) and Phytoseiulus macropilis Banks (Acari: Phytoseiidae) is promising, but predator–prey interactions need to be better understood. The present study was designed to compare the consumption rate and functional responses (FRs) of N. californicus and P. macropilis at low densities of T. urticae. To compare the FRs of N. californicus vs. P. macropilis on T. urticae, five densities (3, 5, 10, 15, 20 individuals per trial) of this prey were offered at adult stage. The prey was added to the experimental arena containing a single predatory mite that was allowed four days (i.e., 96 h) to consume prey without replacement of consumed individuals. Observations were carried out once a day (24 h, 48 h, 72 h and 96 h). The numbers of prey consumed, and eggs laid were counted every 24 h. Results indicate that both predator curves align with a Type II FR. P. macropilis was faster at attacking T. urticae but slower at handling it. Lower egg production by T. urticae indicates that P. macropilis seems to be more effective in controlling this prey compared to N. californicus. Conversely, N. californicus was faster at handling prey and performed comparably to P. macropilis at higher prey densities. Therefore, depending on the specific circumstances of pest infestation, both predators present viable options for the biological control of T. urticae, with P. macropilis excelling in low-density scenarios and N. californicus offering effectiveness at slightly higher densities.

The leafhopper, Yamatotettix flavovittatus Matsumura is a phytoplasma vector that causes white-leaf disease in sugarcane. The prevalence of Wolbachia infections and their impact on vector biology have been reported; however, their effect on phytoplasma in leafhoppers remains unknown. This research aims to examine the phytoplasma acquisition and retention abilities of Wolbachia-positive and -negative leafhoppers. Phytoplasma infection and titers were evaluated in the vectors after acquisition access periods of 6, 12, 24, and 48 h and latent periods of 7, 14, 21, and 28 days. A significant difference was observed in phytoplasma infection frequency, with a low infection rate in Wolbachia-positive leafhoppers from 6- and 12-h acquisition. Moreover, the phytoplasma titers were reduced in Wolbachia-positive leafhoppers from all acquisition time points (< 7.00 × 106 copies), whereas it increased for Wolbachia-negative leafhoppers (ranged from 6.50 to 26.86 × 106 copies). At the latent periods, the proportion of phytoplasma infection was 47.06–100% and 83.33–100% for Wolbachia-positive and -negative leafhoppers, respectively. The Wolbachia-positive leafhoppers retained a low phytoplasma titer (< 5 × 106 copies) throughout the latent periods, with the titers of Wolbachia and phytoplasma being inversely correlated. By contrast, increased levels, ranging from 12.19 to 30.87 × 106 copies were observed in Wolbachia-negative leafhoppers. These results indicate that Wolbachia prevalence negatively affects the phytoplasma acquisition and retention ability of the leafhopper vector. These findings provide useful information that may be utilized in developing new control strategies for vector and phytoplasma diseases.

New developing regulations of chemical-use on fruit calls for an integrated disease management approach using softer chemicals to reduce decay of fresh produce. The aim of this study was to evaluate the potential use of essential oil volatiles to manage postharvest citrus decay. Fifteen essential oils were tested in vitro for its fungicidal properties against growth- and spore-germination of two postharvest citrus pathogens. Cinnamon bark and oregano oils were fungicidal to fresh mycelial-growth of Penicillium digitatum (cinnamon: ≥ 212; oregano: ≥ 106 µl/L headspace) and Galactomyces citri-aurantii (cinnamon: ≥ 106; oregano: ≥ 212 µl/L headspace). Oregano inhibited sporulation of P. digitatum (≥ 53 µl/L headspace). When spores of these pathogens were exposed to cinnamon bark essential oil (≥ 106 µl/L headspace) for 72 h, spore germination was inhibited by 100% (P. digitatum) and 99% (G. citri-aurantii). Combining cinnamon with oregano (both at 53 µl/L headspace) inhibited spore germination, whilst inhibiting the sporulation of P. digitatum. Cinnamon (168 µl/L headspace) and oregano (84 µl/L headspace) tested in the absence of growth media were fungicidal to 100% of P. digitatum spores after 24 h exposure. Cinnamon (133 µl/L headspace) reduced green mould (43% control) when tested on sterile-wounded ‘Valencia’ oranges in the presence of a fruit sporulating with P. digitatum. Oregano (106 µl/L headspace) inhibited the sporulation on fruit injected with P. digitatum. These essential oils did not significantly affect degreening of ‘Eureka’ lemons when treated together with ethylene. This study demonstrates the potential use of cinnamon bark and oregano actives to manage postharvest decay of citrus during degreening.

Cocklebur (Xanthium strumarium L.) is one of the most widespread and abundant invasive plants in East Africa, including Ethiopia. It rapidly forms large stands that displace other plant species. Thus, the current study was conducted to assess the effect of X. strumarium on the herbaceous plant species composition and diversity of rangelands in eastern Ethiopia. The study was conducted in six districts, purposefully selected based on the level of X. strumarium invasion in the rangelands of eastern Ethiopia. A total of 72 sample plots consisting of 36 invaded and 36 uninvaded sites were selected using random sampling methods. Plant species composition and abundance were recorded using a 4 m2 quadrat. The collected data were subjected to univariate and multivariate analyses using R version 4.4.1. A total of 85 plant species were found in the uninvaded sites, whereas the invaded sites contained 57 plant species, reflecting a decline of 32.9%. Species richness, Shannon–Wiener diversity index, Simpson diversity index, and Pielou's evenness indicated that the uninvaded sites were more diverse than the invaded sites. A higher Sorensen and Jaccard similarity index of herbaceous plant species was observed at Haramaya (0.75, 0.60), whereas Sofi exhibited the lowest values (0.29, 0.17). The rank abundance curve also demonstrated that species abundance, richness, diversity, and evenness were greater in the uninvaded sites than in the invaded sites. The results of the NMDS and PERMANOVA also revealed that plant species composition and structure were significantly different between the invaded and uninvaded sites. Consequently, X. strumarium is one of the most dominant invasive alien plant species, and poses a severe threat to species diversity, composition, and structure in the rangelands of eastern Ethiopia. Therefore, effective policy planning, strategic intervention, and the adoption of appropriate control and management practices in the rangeland environment are crucial for mitigating the current impact and preventing potential future challenges.

Temperature is a key factor regulating the survival, reproduction and population growth of insects. We studied performance traits of Chilo infuscatellus Snellen (Lepidoptera: Crambidae), a serious sugarcane borer in Asia, at constant rearing temperatures (19, 23, 27, 31, and 35℃). Our results revealed that the developmental time of immature stages and adult lifespans decreased and fecundity increased at higher temperatures. Extreme temperature treatments (19 and 35 °C) reduced the survival rate of C. infuscatellus. The survival rate and fecundity of C. infuscatellus were high at 27 °C, suggesting it being a favourable temperature, at which we further explored their reproductive traits. We found that eclosion, mating, and oviposition all occurred during the scotophase, and the duration of the mating behaviour of most pairs lasted for 20–50 min. The results will provide important information of this sugarcane borer in relation to seasonal and global climate changes.