Effect of plant age and turfgrass competition on the efficacy of the Sclerotinia minor granular bioherbicide on broadleaf plantain and prostrate knotweed

Broadleaf plantain and prostrate knotweed are important weeds of turfgrass systems. The fungus Sclerotinia minor Jagger (IMI 344141) has been registered as a biological herbicide (Sarritor?) for dandelion (Taraxacum officinale) in Canadian turfgrass habitats. The objective of this study was to evaluate the effect of plant age and turfgrass environment on the efficacy of S. minor against two additional weeds; broadleaf plantain and prostrate knotweed. The turfgrass environment alone exerted significant reduction of above and below ground biomass of broadleaf plantain, to the same magnitude as the S. minor treatment in a grass-free environment. Prostrate knotweed biomass, however, was not reduced to this extent by competition with turfgrass. In the presence of grass, S. minor caused a significant biocontrol effect on all studied variables with more than 90% above ground damage on both weed species. Severe damage occurred on 3–6-week-old plantains with 100% above and below ground reduction, although smaller dry weight reductions were observed on older plantains. Treatment with S. minor reduced the dry matter of 3–5-week-old prostrate knotweed by 65–85%, but less damage occurred on older prostrate knotweed. The bioherbicide fungus is destructive for both species, but variation in area of contact due to different growth forms, growth rates and resource allocation patterns due to different life forms resulted in different biocontrol efficacy on the two species. Control of broadleaf plantain was effective – similar to that previously reported for dandelion – but control of prostrate knotweed was only partial.     

Effect of turfgrass mowing height on biocontrol of dandelion with Sclerotinia minor

The fungus, Sclerotinia minor Jagger is under development as a bioherbicide for control of dandelion and many broadleaf weeds in turfgrass environments. The effect of S. minor on dandelion survival was evaluated under different mowing heights and compared with a commonly used herbicide Killex™. In the greenhouse, the onset of symptoms was more rapid, foliar damage was more severe, and the reduction of aboveground biomass and root biomass was greater for the bioherbicide than the herbicide. The bioherbicide reduced root biomass ≥10-fold compared with untreated plants. Under high weed infestation levels in the field, S. minor caused a greater initial reduction of dandelion density than did the herbicide during the 2-week post-application period, although reductions were greater in herbicide treated plots by 6 weeks after application. Over the growing season, S. minor and the herbicide had similar suppressive effects on dandelion density except under the closest mowing height (3-5 cm). After treatment, close mowing favored dandelion seedling recruitment and the biocontrol had no residual activity. Survival of dandelion roots was significantly less after spring than fall treatment of S. minor and season long mowing at the close height significantly reduce root survival. Close mowing may be detrimental for S. minor applications on heavily infested domestic lawns and amenity grassland areas.     

阔叶丰花草对荔枝园杂草群落特征及物种多样性的影响

【目的】明确阔叶丰花草在荔枝园定植对杂草群落特征及物种多样性的影响,为阔叶丰花草在果园应用提供参考依据。【方法】通过调查广东茂名高州荔枝国家现代农业产业园的荔枝园中90个有、无阔叶丰花草样方中杂草群落组成、群落高度以及物种多样性,探究阔叶丰花草定植对荔枝园杂草群落结构及物种多样性的影响。【结果】阔叶丰花草在荔枝园定植后,杂草种类减少,由对照样方的42种减少到试验样方的30种;杂草群落结构显著改变,牛筋草、白花鬼针草等恶性杂草重要值降低,薇甘菊、香附子、火炭母等杂草消失;阔叶丰花草的重要值与杂草群落高度和物种多样性指数为显著性负相关(P0.001),且均呈显著三项式回归关系。阔叶花草在荔枝园定植后可建立结构较为单一,且低矮的杂草群落。【结论】阔叶丰花草有望成为荔枝园生草的有益草种。     

Two heteropteran predators in relation to weed management in herbicide-tolerant corn

Deployment of genetically modified (GM), herbicide-tolerant corn may alter weed flora abundance and composition and may affect pests and their natural enemies. Among on-plant predators, Orius spp. are the prevalent group in Spain and were selected to study the impact of glyphosate use on predators. We also studied Nabis sp. which is commonly recorded on corn in the study area. For this, a 4-year study was conducted in NE Spain. Three different herbicide regimes were compared: two glyphosate (a broad-spectrum herbicide) treatments per season, no herbicide treatment, and one pre-emergence conventional treatment with selective herbicides against broadleaf and grassy weeds. Density of main arthropod herbivores and the above two predatory groups was recorded on plants. Differences between herbicide regimes were observed in the two functional groups studied, herbivores and heteropteran predators. The comparison of glyphosate-treated and untreated plots showed significant differences for both functional groups, but the differences between glyphosate-treated and conventionally treated plots for the two functional groups were lower. For Orius spp., annual density per plot was significantly correlated with annual density of leafhoppers and to a lesser extent, with aphids. Nabis sp. densities were never different between glyphosate-treated and conventionally treated plots, and Nabis sp. density showed no relation to any of the herbivores tested. We concluded that no significant changes in heteropteran predator densities may be expected from moderate alterations in weeds arising from the deployment of herbicide-tolerant corn varieties and that leafhoppers are probably the herbivore prey that most influences Orius spp. densities in corn in our study area.     

Physiological characterization of the dandelion bioherbicide,Sclerotinia minor IMI 344141

The fungus Sclerotinia minor (IMI 344141) is being developed as a biological control for dandelion and other broadleaf weeds in turfgrass environments. Being a microbial pest control agent (MPCA), the S. minor strain must be characterized to show relatedness to like organisms and to distinguish the MPCA from related microorganisms. Phenotypic variation among 30 isolates of S. minor, collected from different regions and hosts, was studied on potato dextrose agar (PDA) and oatmeal agar (OMA). Isolates varied significantly in sclerotia shape (length/width ratio) and number, but did not vary in colony morphology or growth rates. There was high diversity (0.6) among the mycelial compatibility groups (MCG) as seven multi-member and 11 single member groups were recognized. Isolates were categorized into highly virulent, virulent, moderately virulent, and hypo virulent based on 48 h post mycelial growth on detached dandelion leaves. When assessed on dandelion plants in the greenhouse, isolate IMI 344141 ranked the highest in biocontrol efficacy, reduction of above- and below-ground biomass, and reduction in dandelion survival. Oxalic acid production was not correlated with isolate aggressiveness or growth rate and did not vary among isolates of the same MCG. IMI 344141 can be phenotypically distinguished from the other tested S. minor isolates by performing vegetative compatibility testing and counting sclerotia produced on standard 9-cm diameter PDA plates. IMI 344141 produces <100 sclerotia/plate.     

The impact of plant associations on Macrosteles quadrilineatus management in carrots

Habitat diversification can influence the interactions of insects with plants and this can be used in agroecosystems for the management of pest populations. Plant diversification can be achieved through planting crops, such as trap crops, or by adjusting weed management. Aster leafhopper, Macrosteles quadrilineatus Forbes (Hemiptera: Cicadellidae), is a polyphagous species that uses cereals, vegetables, and weeds as host plants. The influence of weeds on M. quadrilineatus abundance was investigated experimentally in carrot [Daucus carota L. cv. Canada (Apiaceae)] field plots by adjusting the level of management of two groups of weeds (broadleaf and grass) and by comparing it to weed‐free plots. The preference of M. quadrilineatus for different cereal and weed species relative to carrots was tested in choice test assays. Habitat context influenced the abundance of M. quadrilineatus in the field experiments. The presence of border crops such as oat, rye, barley, wheat, and triticale did not significantly attract or repel this insect to carrot plots compared to the no‐border treatment. However, spelt‐bordered plots had 42% fewer M. quadrilineatus than three treatments, triticale, wheat, and barley, that had the highest insect abundance. The type of weed management affected M. quadrilineatus abundance in carrot plots, but not the frequency of herbicide application. Plots that had carrot growing with broadleaf‐weeds had about 59% fewer M. quadrilineatus compared with those growing with crabgrass or carrot alone. In the greenhouse choice tests, grasses (e.g., cereals) attracted and broadleaf‐weeds repelled M. quadrilineatus relative to carrots. In summary, carrot growers may be able to manage this pest by reducing the interaction of cereal cover crops with carrots and eliminating grassy weeds in commercial production fields.     

Development of strain specific molecular markers for the Sclerotinia minor bioherbicide strain IMI 344141

The plant pathogenic fungus, Sclerotinia minor IMI 344141, has been developed as a bioherbicide for broadleaf weed control in turfgrass and a means to differentiate this biocontrol agent from like organisms is required. A strain specific molecular marker was developed to detect and monitor the Sclerotinia minor IMI 344141 bioherbicide strain. The method was based on polymerase chain reaction (PCR) amplification of two sequence-characterized amplified regions (SCAR) primer pairs for a first round PCR, and another two sets of nested primers was used for a second round PCR if higher sensitivity was needed. Sclerotinia minor IMI 344141 was successfully traced from both pure cultures and environmental samples originating from bioherbicide-released field trials. DNA of the S. minor bioherbicide isolate IMI 344141 was detected in the soil 2 months after application, but was not detected in the 3- and 9-month samples after application. When applied as a bioherbicide, S. minor (IMI 344141) did not persist into the following spring season in turf environments. This molecular detection method provides a mechanism to distinguish this isolate from related organisms and a tool to monitor behavior of the biocontrol agent S. minor IMI 344141 in nature, particularly in soil.     

油菜类型和品种对外来入侵杂草小子虉草的替代控制作用

外来入侵植物小子虉草（Phalaris minor Retz.）是世界公认的冬季农田恶性杂草,掌握农作物对其替代控制作用具有重要的研究价值。前期研究表明,油菜是替代控制小子虉草的优良农作物,然而,目前尚不清楚油菜类型与品种对其控制能力的影响。为此选取与小子虉草同域发生的不同类型（白菜型油菜、芥菜型油菜和甘蓝型油菜）油菜品种各3种,通过田间小区实验和室内化感作用测定,对比研究其对小子虉草的生长、繁殖、表型以及化感作用的影响。田间实验显示：竞争方式（种内或种间竞争）和油菜类型对小子虉草的地上生物量、种子数、株高、分枝数、叶面积和比叶面积存在极显著（P=0.0001）影响;而油菜品种对小子虉草的地上生物量（P=0.6064）、种子数（P=0.3577）、株高（P=0.4279）、分枝数（P=0.6357）、叶面积（P=0.8839）和比叶面积（P=0.3424）均无显著影响。3种类型油菜对小子虉草生长、繁殖以及表型的影响存在明显差异,其中芥菜型油菜对小子虉草的上述指标的影响最强,而白菜型油菜的影响最弱。室内生物测定显示,油菜对小子虉草具有化感抑制作用,当供试油菜叶片水提液浓度为0.1 g/mL时,小子虉草种子的萌发和幼苗的株高、根长、生物量均被显著抑制;研究也表明不同类型油菜对小子虉草的化感作用显著不同,同等条件下,芥菜型油菜对小子虉草的化感抑制作用最强。综上所述,油菜类型对外来入侵小子虉草的控制作用存在显著差异,其中芥菜型油菜对植物小子虉草的替代控制作用明显优于白菜型油菜和甘蓝型油菜,而其强的化感抑草特性或许是其强控草能力的原因之一。另外,本研究也为进一步利用油菜替代控制入侵植物小子虉草提供了参考。     

Mefluidide-chlorsulfuron-2,4-D surfactant combinations for roadside vegetation management

Using a combination of a primary growth retardant, mefluidide, a synergistic additive, chlorsulfuron, a detergent to enhance penetration (X-77), and a herbicide, 2,4-D, to provide for control of broadleaf weeds, full-season management of bluegrass (Poa pratensis L.)—tall fescue (Festuca arundinaceae Schreb.) mixtures along roadsides has been achieved. A single spray application is made in the spring, and no additional herbicide applications or mechanical mowing are needed. The treatment is effective with greater than 90% control of fescue seed heads. Those few seed heads that do form remain short. It is economical. The costs of materials and application are equal to or less than the cost of a single mowing cycle. The treatment is environmentally safe when applied in early spring before most agricultural crops have been planted. The effectiveness and low cost of the combination derive from laboratory and greenhouse observations that various materials, herein referred to as additives, often only weakly effective as growth retardants themselves, will interact synergistically with mefluidide to provide overall treatment effectiveness at application rates that are economical. Using this principle, a combination suitable for roadside vegetation management was devised, field-tested for 2 years under actual use conditions, and found to be effective for full-season vegetation management of mixed bluegrass—tall fescue turf to permit considerable cost savings when compared to three-cycle mechanical mowing.     

Riparian Forest Restoration: Increasing Success by Reducing Plant Competition and Herbivory

The reestablishment of riparian forest is often viewed as “best management practice” for restoring stream ecosystems to a quasi‐natural state and preventing non‐point source contaminants from entering them. We experimentally assessed seedling survivorship and growth of Quercus palustris (pin oak), Q. rubra (red oak), Q. alba (white oak), Betula nigra (river birch), and Acer rubrum (red maple) in response to root‐stock type (bare root vs. containerized), herbivore protection (tree shelters), and weed control (herbicide, mowing, tree mats) over a 4‐year period at two riparian sites near the Chester River in Maryland, U.S.A. We started with tree‐stocking densities of 988/ha (400/ac) in the experimental plots and considered 50% survivorship (i.e., a density of 494/ha [200/ac] at crown closure) to be an “acceptable or minimum” target for riparian restoration. Results after four growing seasons show no significant difference in survivorship and growth between bare‐root and containerized seedlings when averaged across all species and treatments. Overall survivorship and growth was significantly higher for sheltered versus unsheltered seedlings (49% and 77.6 cm vs. 12.1% and 3.6 cm, respectively) when averaged across all species and weed control treatments. Each of the five test species exhibited significantly higher 4‐year growth with shelter protection when averaged across all other treatments, and all species but river birch had significantly higher survivorship in shelters during the period. Seedlings protected from weeds by herbicide exhibited significantly higher survivorship and growth than seedlings in all other weed‐control treatments when averaged across all species and shelter treatments. The highest 4‐year levels of survivorship/growth, when averaged across all species, was associated with seedlings protected by shelters and herbicide (88.8%/125.7cm) and by shelters and weed mats (57.5%/73.5 cm). Thus, only plots where seedlings were assisted by a combination of tree shelters and either herbicide or tree mats exhibited an “acceptable or minimum” rate of survivorship (i.e.,>50%) for riparian forest restoration in the region. Moreover, the combined growth and survivorship data suggest that crown closure over most small streams in need of restoration in the region can be achieved most rapidly (i.e., 15 years or less) by protecting seedlings with tree shelters and controlling competing vegetation with herbicides.     

Dynamics of canopy-dwelling arthropods under different weed management options,including glyphosate,in conventional and genetically modified insect-resistant maize

The use of genetically modified varieties tolerant to herbicides (HT varieties) and resistant to insects (Bt varieties) in combination with application of a broad-spectrum herbicide such as glyphosate could be an effective option for the simultaneous control of weeds and pests in maize. Nevertheless, the possible impact of these tools on nontarget arthropods still needs to be evaluated. In a field study in central Spain, potential changes in populations of canopy-dwelling arthropods in Bt maize under different weed management options, including glyphosate application, were investigated. Canopy-dwelling arthropods were sampled by visual inspection and yellow sticky traps. The Bt variety had no effect on any group of studied arthropods, except for the expected case of corn borers—the target pests of Bt maize. Regarding the effects of herbicide regimes, the only observed difference was a lower abundance of Cicadellidae and Mymaridae on yellow sticky traps in plots not treated with pre-emergence herbicides. This effect was especially pronounced in a treatment involving two glyphosate applications. The decrease in Cicadellidae and Mymaridae populations was associated with a higher density of weeds in plots, which may have hindered colonization of the crop by leafhoppers. These differences, however, were only significant in the last year of the study. The low likelihood of the use of glyphosate- and herbicide-tolerant varieties for weed control triggering important effects on the nontarget arthropod fauna of the maize canopy is discussed.     

Assessing Insecticide Hazard to Bumble Bees Foraging on Flowering Weeds in Treated Lawns

Maintaining bee-friendly habitats in cities and suburbs can help conserve the vital pollination services of declining bee populations. Despite label precautions not to apply them to blooming plants, neonicotinoids and other residual systemic insecticides may be applied for preventive control of lawn insect pests when spring-flowering weeds are present. Dietary exposure to neonicotinoids adversely affects bees, but the extent of hazard from field usage is controversial. We exposed colonies of the bumble bee Bombus impatiens to turf with blooming white clover that had been treated with clothianidin, a neonicotinoid, or with chlorantraniliprole, the first anthranilic diamide labeled for use on lawns. The sprays were applied at label rate and lightly irrigated. After residues had dried, colonies were confined to forage for six days, and then moved to a non-treated rural site to openly forage and develop. Colonies exposed to clothianidin-treated weedy turf had delayed weight gain and produced no new queens whereas those exposed to chlorantraniliprole-treated plots developed normally compared with controls. Neither bumble bees nor honey bees avoided foraging on treated white clover in open plots. Nectar from clover blooms directly contaminated by spray residues contained 171±44 ppb clothianidin. Notably, neither insecticide adversely impacted bee colonies confined on the treated turf after it had been mown to remove clover blooms present at the time of treatment, and new blooms had formed. Our results validate EPA label precautionary statements not to apply neonicotinoids to blooming nectar-producing plants if bees may visit the treatment area. Whatever systemic hazard through lawn weeds they may pose appears transitory, however, and direct hazard can be mitigated by adhering to label precautions, or if blooms inadvertently are contaminated, by mowing to remove them. Chlorantraniliprole usage on lawns appears non-hazardous to bumble bees.     

Phenological observations on shrubs to predict weed emergence in turf

Phenology is the study of periodic biological events. If we can find easily recognizable events in common plants that precede or coincide with weed emergences, these plants could be used as indicators. Weed seedlings are usually difficult to detect in turf, so the use of phenological indicators may provide an alternative approach to predict the time when a weed appears and consequently guide management decisions. A study was undertaken to determine whether the phenological phases of some plants could serve as reliable indicators of time of weed emergence in turf. The phenology of six shrubs (Crataegus monogyna Jacq., Forsythia viridissima Lindl., Sambucus nigra L., Syringa vulgaris L., Rosa multiflora Thunb., Ziziphus jujuba Miller) and a perennial herbaceous plant [Cynodon dactylon (L.) Pers.] was observed and the emergence dynamics of four annual weed species [Digitaria sanguinalis (L.) Scop., Eleusine indica (L.) Gaertner, Setaria glauca (L.) Beauv., Setaria viridis (L.) Beauv.] were studied from 1999 to 2004 in northern Italy. A correlation between certain events and weed emergence was verified. S. vulgaris and F. viridissima appear to be the best indicators: there is a quite close correspondence between the appearance of D. sanguinalis and lilac flowering and between the beginning of emergence of E. indica and the end of lilac flowering; emergences of S. glauca and S. viridis were predicted well in relation to the end of forsythia flowering. Base temperatures and starting dates required to calculate the heat unit sums to reach and complete the flowering phase of the indicators were calculated using two different methods and the resultant cumulative growing degree days were compared.     

The effect of targeted high‐threat weed control on wet forest understorey vegetation in the Central Highlands region,Victoria

The effective control of highly invasive weeds in Australia is an important conservation management action. In this study, we monitored the outcome of herbicide control on high‐threat weeds in the wet forests of the Central Highlands of Victoria. Twenty‐two control (no weed control) and 32 treatment (weed control) plots were surveyed annually over 24 months. Initial results show that weed cover and frequency decreased substantially in response to weed control; however, it is too early to determine the response of native species. We recommend that herbicide control and the associated monitoring programme be continued, and depending on the outcomes, data should be used to develop a more integrated management strategy.     

Early establishment of planted Retama sphaerocarpa seedlings under different levels of light,water and weed competition

Large amounts of former cropland are being abandoned in developedregions. To formulate guidelines for land reclamation programmes, we exploredthe effects of artificial shading, irrigation, and removal of weed competitionon the performance of Retama sphaerocarpa (L.) Boiss.seedlings in a factorial experiment located in an abandoned cropland in CentralSpain. R. sphaerocarpa is of interest for revegetationbecause it is a drought tolerant leguminous shrub that is a major structuralcomponent of the native plant community. Seedling performance was evaluated inthree ways: seedling survivorship, growth, and photochemical efficiency. Wealsomeasured soil moisture and weed biomass production and found that bothincreasedunder artificial shading conditions. Soil moisture increased very slightlywhereweeds were removed. Thus, increased transpiration from weeds outweighed reducedevaporation from soils due to shading by weeds. Artificial shading was the mosteffective treatment for seedling survivorship, followed by removal ofcompetition by weeds. After summer, 34 % of the seedlings survived in the mostfavourable conditions (artificially shaded plots where weeds were removed),compared to ca. 1 % in full-light plots with no removal of weed competition. Apositive effect of irrigation was found for growth of seedling cover and heightin shaded plots. The analysis of photochemical efficiency pointed out therelevance of weed competition removal, and confirmed the usefulness of fastfluorescence transient techniques for the quantification of seedlingperformance. The data suggest that competition between seedlings and weeds wasprimarily for water rather than for light. We conclude that i) artificialshading improved seedling performance, but this is a little practical techniquebecause of its cost; ii) as weeds compete with, rather than facilitate, plantedseedlings, weed clipping around the seedlings is a feasible technique thatwouldimprove seedling survival; and iii) seedling performance could alsoconsiderablyimprove with a higher irrigation than was used in this experiment(75lm^–2 per growth period), provided that weedsare removed.     

草坪杂草生态位研究

调查研究草坪杂草的重要值、生态位宽度、以及不同种类杂草之间的生态位重叠值 ,能够揭示杂草种间生态相似关系 ,能够预测杂草之间相互影响的趋势。利用杂草种间的相互制约关系 ,可以指导合理地使用除草剂 ,从而达到降低草坪养护成本 ,保护环境的双重效果。以武汉市区多种不同种类草坪为研究对象 ,对该地区草坪主要杂草进行了系统调查 ,通过七级目测法 ,计算了草坪 2 0种主要杂草的重要值 ,并计测了它们的生态位宽度和生态位重叠值。结果表明 ,看麦娘 (Alopecurusaequalis) ,牛蘩缕(Stellaria media) ,野燕麦 (Avena fatua) ,猪殃殃 (Galium aparine) ,一年蓬 (Erigeron annuus) ,鼠麴草 (Gnaphalium multiceps) ,毛茛 (Ranunculus arevensis) ,通泉草 (Mazus japonicus)等杂草的实际生态位比较宽 ,它们是本地区草坪的主要杂草。而猪殃殃(Galium aparine) ,婆婆纳 (Veronica persica) ,野燕麦 (Avena fatua)等杂草间的生态位重叠值大。杂草生态位宽度大小反映了杂草利用资源的多样化水平或特化水平 ,通常生态位宽度大的杂草以牺牲对局域范围内资源的利用效率来换取对大范围内资源的利用能力     

Effects of weed harrowing frequency on beneficial arthropods,plants and crop yield

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Mefluidide-chlorsulfuron-2,4-D surfactant combinations for roadside vegetation management

Using a combination of a primary growth retardant, mefluidide, a synergistic additive, chlorsulfuron, a detergent to enhance penetration (X-77), and a herbicide, 2,4-D, to provide for control of broadleaf weeds, full-season management of bluegrass (Poa pratensis L.)—tall fescue (Festuca arundinaceae Schreb.) mixtures along roadsides has been achieved. A single spray application is made in the spring, and no additional herbicide applications or mechanical mowing are needed. The treatment is effective with greater than 90% control of fescue seed heads. Those few seed heads that do form remain short. It is economical. The costs of materials and application are equal to or less than the cost of a single mowing cycle. The treatment is environmentally safe when applied in early spring before most agricultural crops have been planted. The effectiveness and low cost of the combination derive from laboratory and greenhouse observations that various materials, herein referred to as additives, often only weakly effective as growth retardants themselves, will interact synergistically with mefluidide to provide overall treatment effectiveness at application rates that are economical. Using this principle, a combination suitable for roadside vegetation management was devised, field-tested for 2 years under actual use conditions, and found to be effective for full-season vegetation management of mixed bluegrass—tall fescue turf to permit considerable cost savings when compared to three-cycle mechanical mowing.     

Evaluation of Pre-Emergence and Post-Emergence Herbicides for Weed Management in <i>Miscanthus sacchariflorus</i> and <i>Miscanthus sinensis</i>

Miscanthus, is a promising bioenergy crop, considered superior to other bioenergy crops because of its higher water and nutrient use efficiency, cold tolerance, and higher production of biomass. Broadleaf weeds and grass weeds, cause major problems in the Miscanthus field. A field experiment was conducted in 2018 and 2019, to assess the effects of pre-emergence (alachlor and napropamide) and post-emergence herbicides (nicosulfuron, dicamba, bentazon, and glufosinate ammonium) on broadleaf and grass weeds in M. sinensis and M. sacchariflorus fields. The weed control efficiency and phytotoxicity of pre- and post-emergence herbicides were evaluated at 30 days after treatment (DAT) and compared to those of the control plots. The results showed wide variations in the susceptibility of the weed species to the treated herbicides. Treatment with nicosulfuron 40 g.a.i.ha⁻¹ provided the most effective overall weed control (with 10% visual injury), without affecting the height and biomass of neither Miscanthus species in the field. Post-emergence herbicides such as glufosinate ammonium 400 g.a.i.ha⁻¹ and dicamba 482 g.a.i.ha⁻¹ were effective and inhibited the growth and density of the majority of weeds to a 100%; however, they showed significant phytotoxicity (toxicity scale of 1–10) to both species of Miscanthus. The application of glufosinate ammonium caused severe injuries to the foliar region (90% visual injury) of both Miscanthus sps. Comparatively, M. sinensis showed a slightly higher tolerance to the herbicides nicosulfuron, bentazon and napropamide with 10% visual injury at the recommended dose than M. sacchariflorus. The present study clearly showed that infestation of broadleaf and grass weeds in Miscanthus fields can cause significant damage to the growth and biomass of Miscanthus and applying pre-emergence and post-emergence herbicides effectively controls the high infestation of these weeds.     

Effects of simulated insect damage and weed interference on cotton growth and reproduction

Early-season insect pests of cotton (Gossypium hirsutum L.) crops, including Lepidoptera larvae and mirids, feed on vegetative buds. The loss of vegetative buds transiently delays the plant's development and growth and has the potential to reduce its competitive ability. Yield reductions due to weed interference and insect damage, therefore, could be greater than expected from the additive effects of weeds and damage acting separately. Three varieties, two levels of weed infestation, and two levels of simulated damage were combined in a factorial experiment designed to assess the responses of cotton plants to the combined effects of damage and weeds. Weed treatments were: with (+W) and without weeds (-W), and damage treatments included: undamaged control (-D) and damaged plants (+D) which had their active vegetative buds removed at 30 and 49 days after sowing. Variety and interactions between variety and other factors were normally nonsignificant for all the response variables measured in this experiment. Cotton height, width, production of flowerbuds and production of fruit were all affected by both damage and weeds. While the effects of damage on these growth variables were transient, the effects of weeds normally increased with time throughout the season. Non-additive effects of weeds and damage were minor for plant height and width, and large for flowerbud and fruit production. At maturity, weed dry matter ranged from about 20 g m^-2 (-W treatments) to 300 gm^-2 (+W), cotton dry matter from 144 gm (+W+D) to 945 gm^-2 (-W-D), and seed cotton production from 54gm^-2 (+W+D) to 417 gnT^-2 (-W+D). Damage did not affect vegetative dry matter and marginally increased seed production in -W plots. Non-additive effects of weeds and damage were negligible for vegetative dry matter but highly significant for seed production (P < 0.0001). These contrasting responses of vegetative and reproductive growth are in agreement with neighbouring models of plant competitive interactions that emphasise the effects of neighbour interference on the fecundity of target plants that are not mediated by changes in target-plant size.