Post-dispersal seed predation of non-target weeds in arable crops

Field experiments were conducted to quantify the natural levels of post-dispersal seed predation of arable weed species in spring barley and to identify the main groups of seed predators. Four arable weed species were investigated that were of high biodiversity value, yet of low to moderate competitive ability with the crop. These were Chenopodium album, Sinapis arvensis, Stellaria media and Polygonum aviculare. Exclusion treatments were used to allow selective access to dishes of seeds by different predator groups. Seed predation was highest early in the season, followed by a gradual decline in predation over the summer for all species. All species were taken by invertebrates. The activity of two phytophagous carabid genera showed significant correlations with seed predation levels. However, in general carabid activity was not related to seed predation and this is discussed in terms of the mainly polyphagous nature of many Carabid species that utilized the seed resource early in the season, but then switched to carnivory as prey populations increased. The potential relevance of post-dispersal seed predation to the development of weed management systems that maximize biological control through conservation and optimize herbicide use, is discussed.     

Postdispersal seed predation by Teleogryllus emma (Orthoptera: Gryllidae) reduces the seedling emergence of a non‐native grass weed,Italian ryegrass (Lolium multiflorum)

The potential impact of postdispersal seed predation by the field cricket, Teleogryllus emma (Ohmachi et Matsuura), on the seedling emergence of Italian ryegrass (Lolium multiflorum Lam.), a non‐native grass weed in Japan, was determined. The relationship between cricket density and the proportion of seedling emergence was investigated by conducting manipulative experiments in duplicate, using enclosures. One‐thousand seeds of Italian ryegrass were exposed to adult crickets at different densities (zero, one, two, four and eight individuals per 2.25 m² enclosure) for 2 weeks. The proportion of seedling emergence decreased with increasing cricket density. The proportion of seedling emergence in the enclosures without the crickets was 90.9–97.2%, whereas the seedling emergence in the enclosures with eight crickets greatly decreased, to 0.5–2.5%. These results suggest that postdispersal seed predation by T. emma can substantially decrease the abundance of Italian ryegrass at an early life stage and reduce its population in environments with a high density of crickets.     

Over-winter predation of Abutilon theophrasti and Setaria faberi seeds in arable land

To improve understanding of over-winter weed seed predation in arable fields, we used data from winter exclosure trials to determine the amount of predation and the influence of crop habitats on predation of Abutilon theophrasti and Setaria faberi seed in 2-year (maize/soyabean) and 4-year (maize/soyabean/small grain+lucerne/lucerne) crop rotation systems between 2005 and 2008. Crop habitat influenced seed predation, and had similar impacts on the two weed species. Mean A. theophrasti predation ranged from 31% in the 2-year soyabean habitat to 99% in the 4-year lucerne habitat. Mean S. faberi predation ranged from 31% in the 2-year soyabean habitat to 97% in the 4-year lucerne habitat. Results suggest that a combination or interaction of cover and substrate may have affected crop habitat preference by seed predators. Future research should further examine the influence of physical habitat on seed predation to determine characteristics of cropping systems that encourage predation, particularly during over-winter periods, so as to routinely incorporate seed predators into long-term weed management strategies.     

Predispersal seed predation of Amaranthus retroflexus and Chenopodium album growing in soyabean fields

Field experiments were made in 1998 and 1999 to determine the influence of tillage and soyabean (Glycine max) row width on predispersal weed seed predation in Amaranthus retroflexus L. (redroot pigweed) and Chenopodium album L. (common lambsquarters). Soyabean was planted in wide (76 cm) and narrow (19 cm) rows with conventional or conservation tillage. Additional control plots without soyabean were also established. The two objectives were to determine (1) whether predispersal seed predation occurs in A. retroflexus or C. album, and (2) whether disturbance (soil tillage) or microclimate (planting pattern) influence predation level. Mean rates of seed predation were 26% and 4% in A. retroflexus and C. album, respectively. Although these levels were low at the population level, individual plants of both species had predation levels ranging from 0% to 80%, however, very few individuals of C. album had levels of predation above 10%. Differences among tillage and row width treatments occurred for A. retroflexus, but not for C. album. Amaranthus retroflexus and C. album growing within the soyabean crop received less light than those in the no‐crop plots, and produced less above‐ground biomass, smaller terminal inflorescences, and fewer seeds per inflorescence. Plant height, terminal inflorescence weight, and total seeds were correlated with predation in both weed species.     

Distribution of Megastigmus aculeatus (Hymenoptera: Torymidae) and the levels of seed predation of Rosa multiflora (Rosaceae)

Rosa multiflora Thunb. (Rosaceae), an invasive plant that currently infests millions of hectares in the eastern half of the USA, was planted initially in the 1940s as a “living fence”, cover for game animals and for erosion control. The larvae of Megastigmus aculeatus var. nigroflavus Hoffmeyer (Hymenoptera: Torymidae) feed on the developing R. multiflora seeds and have the potential to reduce the seed output of R. multiflora. Rosehips were collected from 49 sites across eastern and southern Iowa, USA, to determine the presence and distribution of M. aculeatus, the larvae of which were found in 266 of the 979 (27%) rosehips that were dissected and at 31 of the 49 sites (63%) that were sampled. The levels of M. aculeatus infestation over 2–3 years were determined at three selected sites and it was documented that more seeds were aborted than were viable or contained wasp larvae. A negative relationship was observed between the numbers of both the aborted and the viable seeds and the probability of a rosehip being attacked by M. aculeatus, indicating that M. aculeatus females are not preferentially selecting rosehips with higher numbers of viable or aborted seeds for oviposition. There is a significant reduction in both the viable seeds and the aborted seeds in hips that have been attacked by M. aculeatus. Detailed knowledge of R. multiflora demography is necessary to determine the level of seed predation that is required to reduce the recruitment of new individuals into the population.     

Reproductive traits,flowering phenology and seed bank dynamics in Retama raetam (Fabaceae) in a hyper-arid environment

This study explores the effects of year and location on reproductive traits and flowering phenology in Retama raetam populations growing in a hyper-arid environment. Besides year, season, and location, variations in the soil seed bank were also evaluated. Germination percentage of seeds buried in soil at two different depths for one year was determined. I hypothesized that changes in water availability between years and locations would lead to variations in reproductive traits, flowering phenology, and the seed bank of R. raetam. The study was conducted at a midstream and an upstream location during 2013 and 2014 in Wadi Rishrash in the Eastern Desert of Egypt. Flower, fruit, and seed production were significantly higher in the midstream location than the upstream location and in 2014 than in 2013. Flowering onset and duration did not differ significantly between locations. Flowering occurred earlier in 2014 than in 2013 at both locations, and the flowering period was longer in 2014 than in 2013. The size of the seed bank was greater at the midstream than at the upstream location, and in summer than in spring season. Germination of seeds decreased with burial depth, but increased with burial duration. Larger individuals produced more seeds and flowered earlier than smaller plants. The size of plant was also positively correlated with flowering duration. The location and temporal variations in all these traits may be related to environmental differences between locations and differences in annual precipitation.     

Differences in flowering phenology and seed production of four morning glory (Ipomoea) species in Japan

The spread of morning glory (Ipomoea spp.) in soybean fields in Japan has severely decreased soybean yield. Yet, current control measures do not control the proliferation of Ipomoea spp. As little is known about the flowering period and seed production among the different invading Ipomoea spp., it is challenging to create targeted control measures based on ecological characteristics. This study aimed to reveal the characteristics of the flowering phenology and seed production of four morning glory species, namely, Ipomoea coccinea L. (red morning glory), Ipomoea lacunosa L. (pitted morning glory), Ipomoea hederacea L. Jacq. var. integriuscula A. Gray (entireleaf morning glory), and Ipomoea triloba L. (three-lobe morning glory). Between 2017 and 2019, the four selected study species were grown under similar conditions of soil quality, irrigation, and environmental influences and their flowering phenology and seed data were recorded. The flowering period ranged from 36 to 40 days, and the initial flowering of I. triloba was approximately 2 weeks later than the others. I. coccinea had the highest flowering number and seed production, followed by I. lacunosa, I. triloba, and I. hederacea var. integriuscula. The fruit setting rate of I. triloba decreased later in the reproductive stage but tended to increase as the daily mean temperature increased on each flowering day. Thus, we report that the flowering phenology and seed production differed greatly among the Ipomoea spp. These findings can provide crucial insights into designing targeted species-specific control measures against the spread of Ipomoea spp. in Japan.     

Residual toxicity of two insecticides on three field populations of Lygus lineolaris (Hemiptera: Miridae) collected along the St Lawrence valley in eastern Canada

Insecticides are still the single main pest control method employed today by most growers to mitigate damage done by the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae). In eastern Canada, the complex agricultural ecosystem, which may be described as a mosaic of farmlands dispersed among natural habitats (forest, prairies), allows tarnished plant bug adults to fly and move from sprayed to non-sprayed areas. In 2004 (late August to early September), three populations of L. lineolaris were collected from three mixed vegetation strips adjacent to orchards and vineyards along the St Lawrence valley: the Niagara Peninsula (Ontario), Dunham (Quebec) and La Pocatière (Quebec). Assays were done in the laboratory by confining adults in glass vials coated with dried residues. The estimated LC(50) values for the three populations varied from 11.2 to 16.8 x 10(-5) g L(-1) for azinphos-methyl and from 0.8 to 1.4 x 10(-5) g L(-1) for cypermethrin. In contrast to the Mississippi delta, no tolerance to insecticides was found in the populations collected. Possible explanations for this non-tolerance to insecticides includes a very low selection pressure as a result of the reduced number of insecticide treatments done in the context of the diversified agricultural landscapes encountered in eastern Canada which allow movements of adults from treated to non-treated areas.     

Effects of harvesting and stubble management on abundance of pest rodents (Mus musculus) in a conservation agriculture system

BACKGROUND

The shift to more environmentally sensitive agricultural practices over the last several decades has changed farmland landscapes worldwide. Changes including no-till and retaining high biomass mulch has been coincident with an increase in rodent pests in South Africa, India, South America and Europe, indicating a possible conflict between conservation agriculture (CA) and rodent pest management. Research on effects of various crop management practices associated with CA on pest rodent population dynamics is needed to anticipate and develop CA-relevant management strategies.

RESULTS

During the Australian 2020–2021 mouse plague, farmers used postharvest stubble management practices, including flattening and/or cutting, to reduce stubble cover in paddocks to lessen habitat suitability for pest house mice. We used this opportunity to assess the effects of both harvest and stubble management on the movement and abundance of mice in paddocks using mouse trapping and radio tracking. We found that most tracked mice remained resident in paddocks throughout harvest, and that mouse population abundance was generally unaffected by stubble management.

CONCLUSION

Recent conversions to CA practices have changed how pest house mice use cropped land. Management practices that reduce postharvest habitat complexity do not appear to reduce the attractiveness of paddocks to mice, and further research into new management strategies in addition to toxic bait use is required as part of an integrated pest management approach. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Identification and properties of a deviant isolate of the broad bean yellow band serotype of pea early-browning virus from faba bean (Vicia faba) in Algeria

A virus, isolated from faba bean (Vicia faba) obtained from Algeria, was readily recognized as a tobravirus by its particle sizes and morphology. Pea (Pisum sativum) and French bean (Phaseolus vulgaris) characteristically reacted to the isolate like pea early-browning virus (PEBV), but faba bean,Antirrhinum majus, Nicotiana rustica, andN. tabacum reacted with line-pattern symptoms which were unusually brilliant on theNicotiana species. In electronmicroscope decoration tests, the isolate did not react with an antiserum to the Dutch type strain of PEBV, but with one to the broad bean yellow band (BBYB) serotype from Italy. It resembles this serotype in reaction on faba bean, but seems to differ appreciably onN. rustica, N. tabacum, andPetunia hybrida. It is described as a deviant isolate of the BBYB serotype of PEBV.All thirteen faba-bean genotypes tested were found to be susceptible to the Algerian isolate and two Dutch type strain isolates of the virus, and to react with erratic line-pattern symptoms to the Algerian isolate only. All ten genotypes of chickpea (Cicer arietinum) tested reacted hypersensitively, and four out of ten genotypes of lentil (Lens culinaris) were susceptible to the virus but reacted differentially to the three isolates. Seed transmission of PEBV, including the new isolate, in faba bean is confirmed (9% for the Algerian isolate, and over 45% for one of the Dutch type strain isolates), and seed transmission of the virus in a non-legume (N. rustica, 4%) is herewith first reported. This is the first report on the occurrence of the BBYB serotype of PEBV outside Italy, and of PEBV outside Morocco in North Africa.     

Effect of treating soybean with 2,6-dichloroisonicotinic acid (INA) and benzothiadiazole (BTH) on seed yields and the level of disease caused by Sclerotinia sclerotiorum in field and greenhouse studies

Field or greenhouse grown soybeans were treated with 2,6-dichloroisonicotinic acid or benzothiadiazole and subsequently assessed for severity of white mold disease caused by Sclerotinia sclerotiorum. Three or four applications of 2,6-dichloroisonicotinic acid to field plots in 1993–1995 reduced severity of white mold after natural infection by 20–70% compared with water-treated controls in soybean cultivars Elgin 87 and Williams 82, which are considered to be highly susceptible to the disease. The effect was not as large in the cultivars Corsoy 79 and NKS19-90 which are more resistant to white mold. Two or four applications of benzothiadiazole to field plots in 1995 and 1996 reduced white mold severity by 20–60%, with the greatest reductions again observed in the more susceptible cultivars. Corresponding yields were increased compared with controls, particularly for the susceptible cultivars under conditions of high disease pressure. In greenhouse trials multiple applications of either compound resulted in significantly smaller lesion diameters following subsequent leaf inoculations with the fungus. The compounds did not result in observable phytotoxicity or inhibit growth of Sclerotinia sp. in vitro. We hypothesize that the decrease in disease severity following treatment with INA or BTH is a result of resistance induction.     

茶园间作功能植物对茶小绿叶蝉的调控作用

为研究间作功能植物对茶园主要害虫茶小绿叶蝉的影响,于2017—2018年在福建省泉州市安溪县茶园间作白三叶Trifolium repens L.、金花菜Medicago hispida Gaertn.、金盏菊Calendula officinalis L.,以自然留养杂草茶园为对照,用网捕法采集茶小绿叶蝉并于室内计数,镜检剥查法调查其茶梢着卵量。结果表明,在4种不同生境管理茶园网捕茶小绿叶蝉总个体数及每月个体数均无显著差异;茶小绿叶蝉个体数分别在2017年8月与2018年6月达到高峰。茶梢各节间着卵量不同,主要产卵在顶芽之下第2～5节间,以第4节着卵量最多。间作金盏菊茶园茶小绿叶蝉在茶梢第1节着卵量显著高于间作白三叶和金花菜茶园。不同生境管理茶园茶小绿叶蝉在茶梢第4节着卵量从大到小依次为间作金盏菊(8.13)、间作金花菜(7.50)、自然留养杂草(7.17)和间作白三叶茶园(6.57)。不同时间段4种不同生境管理茶园茶小绿叶蝉在茶梢各节之间的着卵量存在差异,且均在9月上中旬着卵量达到高峰。在茶园间作功能植物,短期内未见其显著降低茶小绿叶蝉网捕量和茶梢着卵量的效应。     

Effect of the sowing date on the growth of hairy vetch (Vicia villosa) as a cover crop influenced the weed biomass and soil chemical properties in a subtropical region

Weeds emerge throughout the year in agricultural fields in subtropical regions. The weed suppression and improved soil fertility resulting from a living mulch of hairy vetch were investigated. Hairy vetch was sown in October and in December 2006. The fallow condition was without the sowing of hairy vetch, with the weeds allowed to grow naturally. The biomass of the top parts (BOT) of hairy vetch increased from February to April and then decreased in May on both sowing dates. The BOT of hairy vetch sown in October was significantly higher in February, March, and April than that sown in December. Hairy vetch sown in October and harvested from February to April varied from 372–403 × 10⁻³ kg m⁻², with weed suppression percentages of 62.8% in comparison with the fallow plots. The fixed C, N, P, and mineral uptake of hairy vetch showed similar patterns to its biomass. The nitrate (NO₃-N) content increased from February to May for the soils in the October and December plots, in contrast to the fallow plots. Moreover, the NO₃-N and available N of the October and December soils sampled from February to May were higher than that of the fallow soils. In subtropical agriculture, hairy vetch should be sown in October in order to achieve a higher biomass for suppressing weeds effectively and improving the soil fertility, mainly N.     

An Experiment to Assess Losses Caused by Frit-fly (Oscinella frit L) Shoot Attack and the Application of Phorate in a Crop of Sweet Corn (Zea mays L)

Wilt caused by the fungus Fusarium oxysporum f. sp. ciceris adversely affects the productivity of cultivated chickpea. For the management of this disease, seed and soil application formulations developed from another fungus, Trichoderma species, were evaluated. In pot experiments, T. harzianum-based formulations Pusa 5SD for seed dressing and Pusa Biopellet (PBP) 10G and Pusa Biogranule (PBG) 5 for soil application, and T. viride-based formulations Pusa 5SD for seed dressing and PBP 4G and PBG 4 for soil application, were found to be highly effective against the disease. A combination of PBP 4G (T. viride) for soil application and Pusa 5SD (T. harzianum) for seed treatment together with a fungicide, carboxin, provided the highest seed germination, shoot and root lengths and grain yield with the lowest incidence of wilt in chickpea under field conditions. Individually, soil application of PBP 4G, and seed treatment with Pusa 5SD were effective in reducing the incidence of wilt and increasing the grain yield of chickpea, but their effectiveness was greater when applied as a combination. Thus, combined application of the formulations of two different species of Trichoderma in two modes of application is recommended for the management of chickpea wilt.     

Genetics and mechanism of resistance to deltamethrin in a field population of Spodoptera litura (Lepidoptera: Noctuidae)

BACKGROUND: Spodoptera litura (F.) causes enormous losses in many economically important crops. The genetics of insecticide resistance has been extensively studied in several insect pests, but there is a lack of information on S. litura. Therefore, the genetics and mechanisms of the resistance of S. litura to deltamethrin were investigated. RESULTS: Bioassays at generation G1 gave resistance ratios of 9, 5, 41, 52 and 49 for deltamethrin, cypermethrin, profenofos, chlorpyrifos and triazofos respectively, when compared with the susceptible Lab-PK strain. Bioassays at G4 with a deltamethrin-selected population (Delta-SEL) showed that selection gave resistance ratios of 63 and 7 for deltamethrin when compared with the Lab-PK and UNSEL strains respectively. Cross-resistance to other insecticides tested was observed in the selected population. A notable feature of the Delta-SEL strain was that resistance to deltamethrin, cypermethrin, profenofos and chlorpyrifos did not decline over the course of five generations. Synergism tests with microsomal oxidase (MO) and esterase-specific inhibitors indicated that the deltamethrin resistance was associated with MO and, possibly, esterase activity. Reciprocal crosses between the Delta-SEL and Lab-PK strains indicated that resistance was autosomal and incompletely dominant. A direct test of monogenic inheritance suggested that resistance to deltamethrin was controlled by more than one locus. CONCLUSION: Stability and dominance of resistance and cross-resistance suggest that insecticides with different modes of action should be recommended to reduce pyrethroid selection pressure.     

Genetics and evidence for an esterase-associated mechanism of resistance to indoxacarb in a field population of diamondback moth (Lepidoptera: Plutellidae)

Bioassays (at generation G2) with a newly collected field population (designated CH3) of Plutella xylostella L. from farmers' fields in the Cameron Highlands, Malaysia, indicated resistance ratios of 813-, 79-, 171-, 498- and 1285-fold for indoxacarb, fipronil, spinosad, deltamethrin and Bacillus thuringiensis toxin Cry1Ac respectively compared with a laboratory susceptible population (Lab-UK). At G2 the field-derived population was divided into two subpopulations: one was selected (G2 to G7) with indoxacarb (indoxa-SEL), while the second was left unselected (UNSEL). A significant reduction in the resistance ratio for each compound was observed in UNSEL at G8. For indoxa-SEL, bioassays at G8 found that selection with indoxacarb gave a resistance ratio of 2594 compared with Lab-UK and of 90 compared with UNSEL. The toxicity of fipronil, spinosad and deltamethrin was not significantly different in indoxa-SEL at G8 compared with G2 but was significantly greater than UNSEL at G8. The toxicity of Cry1Ac was significantly reduced in indoxa-SEL at G8 compared with G2 but was also significantly greater than UNSEL at G8. This suggests that indoxacarb selection maintained resistance to these compounds in the indoxa-SEL population. Synergist studies indicated that resistance to indoxacarb in indoxa-SEL was esterase associated. Logit regression analysis of F1 reciprocal crosses between indoxa-SEL and Lab-UK indicated that resistance to indoxacarb was inherited as an autosomal, incompletely recessive (D(LC) = 0.35) trait. Tests of monogenic inheritance suggested that resistance to indoxacarb was controlled by a single locus.