Controlling pests of tropical legumes; current recommendations and future strategies

Legumes have evolved effective defences against many pests by accumulating high levels of poisonous or indigestible compounds, pubescence and vigorous growth. These defences are greatly reduced in many cultivars of cowpea and common bean, which are susceptible to a succession of pest complexes. Stem pests and defoliators may kill seedlings but well-established plants tolerate heavy insect damage to leaves, flowers and green pods before pod or grain yields are reduced; virus vectors and root-knot nematode may be of greater importance. Generally, pod-borers, pod-sucking bugs and seed beetles are the main key pests. Control programmes are based on post-flowering treatments with broad spectrum insecticides. Battery-powered, controlled-droplet application machines are ousting knapsack sprayers in small-scale farming and competing with tractors and aircraft in larger units; subsistence cropping is still predominant and most legume crops remain unsprayed. Consequently, current emphasis is placed on developing cultivars with high yield potential and multiple pest and disease resistance. Insect infestations are lower in most other major legume crops largely due to pubescence (e.g. soybean, blackgram, greengram), fruiting in the dry season (e.g. pigeonpea, chickpea) or geocarpy (e.g. groundnut). Future entomological research will presumably concentrate on assessing the status of pests on resistant cultivars and introducing integrated control methods for the key pests.     

Reverse modelling to estimate yield losses caused by crop diseases

Yield loss analysis is critical to inform tactical and strategic decisions in crop health management, and requires quantification of three elements: the levels of injury caused by disease or pest, the actual (injured) yield, and the attainable (uninjured) yield. Reverse modelling allows reconstruction of an object or a process from limited information combined with a mathematical model. This approach is applied to estimate yield losses caused by diseases in winter wheat using a process‐based simulation model (WHEATPEST), in combination with field data generated by a network of experiments across France, where multiple disease injuries and actual yields, but not attainable yields, were measured. The analysis covers 70 [year × region × variety × crop management] combinations encompassing five years (2004–2008), four French regions, two winter wheat varieties (one high‐yielding and one hardy variety), and two levels of crop management corresponding to two levels of chemical intensification. The analysis involved three main successive modelling steps where actual yield, attainable yield and yield losses associated with individual diseases were simulated. Overall, simulated yield losses to combined diseases ranged from 0 to 4.2 t ha^?1, and averaged 0.80 t ha^?1. Septoria tritici blotch caused the highest mean yield loss of 0.66 t ha^?1. The results highlight the contribution of varietal improvement to agricultural sustainability and performances. Reverse modelling can be applied to other crops and diseases or pests, in order to estimate individual and combined disease yield losses.     

Interception and persistence of parathion and fenvalerate on cotton plants as a function of application method

Parathion (O,O-diethyl O-4-nitrophenyl phosphorothioate) and fenvalerate [(RS)-α-cyano-3-phenoxybenzyl (RS)-2-(4-chlorophenyl)-3-methylbutyrate] were applied by controlled droplet applicators (CDAs) and conventional hydraulic nozzles in refined soybean oil, soybean oil + water, or water, to mature cotton plants (Gossypium hirsutum L.) as ULV (ultra-low volume, < 5 litre ha^?1), VLV(very low volume, 5-50 litre ha^?1), or LV(low volume, 50–200 litre ha^?1) carrier rates. The use of CDA or soybean oil applied as ULV and VLV sprays did not produce greater deposition or persistence for either insecticide during the 49-h test period following application. In general, insecticide persistence was greatest when applied with water or soybean oil + water as LV sprays using the conventional TX8 hydraulic nozzle.     

Biological characterization of sulfoxaflor, a novel insecticide

BACKGROUND: The commercialization of new insecticides is important for ensuring that multiple effective product choices are available. In particular, new insecticides that exhibit high potency and lack insecticidal cross‐resistance are particularly useful in insecticide resistance management (IRM) programs. Sulfoxaflor possesses these characteristics and is the first compound under development from the novel sulfoxamine class of insecticides. RESULTS: In the laboratory, sulfoxaflor demonstrated high levels of insecticidal potency against a broad range of sap‐feeding insect species. The potency of sulfoxaflor was comparable with that of commercial products, including neonicotinoids, for the control of a wide range of aphids, whiteflies (Homoptera) and true bugs (Heteroptera). Sulfoxaflor performed equally well in the laboratory against both insecticide‐susceptible and insecticide‐resistant populations of sweetpotato whitefly, Bemisia tabaci Gennadius, and brown planthopper, Nilaparvata lugens (Stål), including populations resistant to the neonicotinoid insecticide imidacloprid. These laboratory efficacy trends were confirmed in field trials from multiple geographies and crops, and in populations of insects with histories of repeated exposure to insecticides. In particular, a sulfoxaflor use rate of 25 g ha^?1 against cotton aphid (Aphis gossypii Glover) outperformed acetamiprid (25 g ha^?1) and dicrotophos (560 g ha^?1). Sulfoxaflor (50 g ha^?1) provided a control of sweetpotato whitefly equivalent to that of acetamiprid (75 g ha^?1) and imidacloprid (50 g ha^?1) and better than that of thiamethoxam (50 g ha^?1). CONCLUSION: The novel chemistry of sulfoxaflor, its unique biological spectrum of activity and its lack of cross‐resistance highlight the potential of sulfoxaflor as an important new tool for the control of sap‐feeding insect pests. Copyright © 2010 Society of Chemical Industry     

Investigations on Oecophylla longinoda (Latreille) (Hymenoptera: Formicidae) as a biocontrol agent in the protection of cashew plantations

BACKGROUND: Cashew (Anacardium occidentale L.) has become a very important non‐traditional tree crop in Ghana. The crop is, however, attacked by sap‐sucking insects, particularly the mosquito bug, Helopeltis schoutedeni Reuter, the leaf‐footed bug, Pseudotheraptus devastans (Dist.), and the coreid bug, Anoplocnemis curvipes (F.), which feed on shoots, panicles and fruits. Their damage is characterised by withering of the latter. In Ghana, Oecophylla longinoda Latr. occurs in large numbers on cashew and other native plants, but little is known about its relationship with insect pests. The relationship between O. longinoda and shoot and panicle damage by sap‐sucking bugs and the effectiveness of O. longinoda as a biocontrol agent in the protection of cashew as compared with two chemical insecticides, lambda‐cyhalothrin (Karate^®) and cypermethrin + dimethoate (Cyperdim^®), were therefore investigated at Bole in the northern region of Ghana. RESULTS: There was a negative correlation between numbers of O. longinoda nests and pest damage. Trees treated with cypermethrin + dimethoate (969 mg AI mL^?1 tree^?1) and lambda‐cyhalothrin (100 mg AI mL^?1 tree^?1) recorded the smallest bug numbers, followed by O. longinoda. Trees infested by Oecophylla longinoda and trees treated with cypermethrin + dimethoate and with lambda‐cyhalothrin had less than 6% pest damage to shoots, panicles and fruits, while water‐sprayed trees recorded damage as high as 36.8% (shoots) in February, 32.9% (panicles) in February and 37.8% (fruits) in March. Cypermethrin + dimethoate again recorded the highest (485.0 kg ha^?1) nut yield, followed by O. longinoda (431.0 kg ha^?1), with water recording the lowest (93.0 kg ha^?1) nut yield. CONCLUSION: The results indicate that O. longinoda can be used to control some sucking bugs as effectively as some insecticides. Copyright © 2008 Society of Chemical Industry     

Residualwirkung von Chlortriazin-Herbiziden im Boden an drei rumänischen Standorten. II. Prognose möglicher Folgekulturen bei Atrazinrükständen im Boden

Residual effects of chlorotriazine herbicides in soil at three Rumanian sites. II. Prediction of the phytotoxicity of atrazine residues to following crops Total and plant-available atrazine residues in the top 10 cm soil were measured 120 days after application of 3 kg ai ha^?1 to maize (Zea mays L.) at three sites in Rumania. At one site, similar measurements were made 3?5 years after application of 100 kg ai ha^?1. Plant-available atrazine residues were estimated by extraction of soil samples with water, and by bioassay using Brassica rapa as the test plant. It was calculated that between 30 and 120μg atrazine 1^?1 was potentially available to plants in the different soils. Dose-response relationships for atrazine and the most important rotational crops with maize in Rumania—sunflower, winter wheat, soybean and flax—were determined in hydroponic culture using herbicide concentrations corresponding with the plant-available fractions measured in the different soils. ED₅₀ values were determined by probit analysis and the results showed that sunflower (ED₅₀, 22μg 1^?1) was the most sensitive crop, and soybean (ED₅₀, 78μg 1^?1) was the least. The residual phytotoxicity of atrazine to succeeding crops in the different soils was predicted using the appropriate availability and phytotoxicity data, and the results showed good agreement with those observed. The results suggest that measurements of plant-available herbicide residues afford a rapid method of assessing possible phytotoxicity to following crops.     

Impact of foliar nickel application on urease activity,antioxidant metabolism and control of powdery mildew (Microsphaera diffusa) in soybean plants

Nickel (Ni) is a cofactor for urease, an enzyme that breaks down urea into ammonia and carbon dioxide. This study aimed to evaluate the physiological impact of Ni on urea, antioxidant metabolism and powdery mildew severity in soybean plants. Seven levels of Ni (0, 10, 20, 40, 60, 80 and 100 g ha^?1) alone or combined with the fungicides fluxapyroxad and pyraclostrobin were applied to soybean plants. The total Ni concentration ranged from 3.8 to 38.0 mg kg^?1 in leaves and 3.0 to 18.0 mg kg^?1 in seeds. A strong correlation was observed between Ni concentration in the leaves and seeds, indicating translocation of Ni from leaves to seeds. Application of Ni above 60 g ha^?1 increased lipid peroxidation in the leaf tissues, indicative of oxidative stress. Application of 40 g ha^?1 Ni combined with 300 mL ha^?1 of fungicide reduced powdery mildew severity by up to 99%. Superoxide dismutase, catalase, peroxidase and urease enzyme activity were greatest under these conditions. Urea concentration decreased in response to Ni application. Urease activity in soybean leaves showed a negative correlation with powdery mildew severity. The leaf Ni concentration showed a positive correlation with the urease and a negative correlation with powdery mildew severity. The results of this study suggest that urease is a key enzyme regulated by Ni and has a role in host defence against powdery mildew by stimulating antioxidant metabolism in soybean plants.     

Management of cardamom borer,Conogethes punctiferalis Guenee and thrips,Sciothrips cardamomi Ramk using diafenthiuron and its residues in fresh and cured cardamom capsules

Cardamom is an important spice crops used all over the world as a flavoring agent of food materials. The productivity is limited by insect pests and thus effective insecticide which does not leave residues in the produce is the need of the hour. Diafenthiuron 50 WP @ 300 g a.i ha^?1 was found effective in managing both the cardamom shoot and capsule borer, Conogethes punctiferalis Guenee and thrips, Sciothrips cardamomi Ramk and thus can be recommended for pest management. Cardamom capsules were collected from the plants that were sprayed with diafenthiuron at the recommended dose of 200 g a.i ha^?1 and double the dose (400 g a.i ha^?1), which were then analyzed under HPLC with a normal phase column. The diafenthiuron residue was below the detectable levels of 0.05 µg g^?1 in the harvested produce (both fresh and cured) after twelve and fourteen days of spray. So, capsules can be harvested safely without any risk of insecticide residues 12 days after spraying of diafenthiuron and thus can be recommended for usage in cardamom plantations.     

Residues in blackcurrants,fodder peas,spinach and potatoes treated with sublethal doses of 2,4,5-T to simulate wind drift damage

Blackcurrants, treated with 0.1 kg of 2,4,5-T ha^?1 (as esters of mixed C₄–C₆ alcohols; ‘Tormona 80’), contained 0.1 mg of 2,4,5-T residues kg^?1 in the berries at ripeness 29 days after treatment. Total residues in the berries were not reduced during growth and ripening, although the residue concentrations declined in the same period due to growth dilution. In spinach leaves from old plants, treated with 0.1 kg ha^?1, 0.05 mg of 2,4,5-T kg^?1 was found 14 days after treatment. Fodder peas showed no residues (< 0.002 mg kg^?1) at harvest 62 days after treatment with 2,4,5-T esters. After application of 0.1 kg ha^?1 on potato plants, the disappearance of 2,4,5-T was rapid during the first month, but residues were translocated into the tubers and reached a constant level of 0.02 mg kg^?1 after 1 month until harvest at 108 days after treatment. In all crops, visible effects were observed after treatment with 0.1 kg ha^?1. After the application at 0.01 kg ha^?1, phytotoxic effects were observed only in blackcurrants, but negligible residues were found in all the test crops.     

Studies on the development of a mating disruption system to control the tomato leafminer, Tuta absoluta Povolny (Lepidoptera: Gelechiidae)

BACKGROUND: The tomato leafminer (Tuta absoluta Povolny) has rapidly colonised the whole Mediterranean and South‐Atlantic coasts of Spain, and it has become a key problem in both outdoor and greenhouse crops. New control methods compatible with biological control are required, and mating disruption appears to be a perfect method in current agriculture, as it is an environmentally friendly and residue‐free technique. IPM packages tested have included the use of pheromones to detect populations, but there has not been much previous research on mating disruption of T. absoluta. In this work, pheromone doses varying from 10 to 40 g ha^?1, emitted at a constant rate over 4 months, were tested in greenhouses with different levels of containment in order to evaluate the efficacy of mating disruption on T. absoluta. RESULTS: Trials on containment level revealed that the flight of T. absoluta was satisfactorily disrupted with an initial pheromone dose of 30 g ha^?1, and levels of damage did not significantly differ from those in reference plots with insecticide treatments. Later efficacy trials confirmed previous experiences, and release studies showed that control of damage and flight disruption were taking place when releasing at least 85 mg pheromone per ha per day. CONCLUSION: Effective control using pheromone application against T. absoluta can be achieved, in greenhouses with high containment levels, for 4 months, with initial doses of 30 g ha^?1. Further research must be conducted in order to evaluate the prospect of outdoor application of mating disruption systems. Copyright © 2011 Society of Chemical Industry     

Abscisic acid as a protectant of Avena fatua L. against diclofop-methyl activity

The imposition of water stress before or al the time of spraying diclofop-methyl reduced efficacy against wild oat (Avena fatua L.). Similar reductions in herbicide performance were obtained by application of 20 μg of the methyl ester of abscisic acid (ABA) to plants with three to four leaves before spraying with I kg ha^?1 diclofop-methyl. Application of 40–100 μg ABA per plant effectively protected plants against damage from diclofop-methyl applied at 1 5–2 0 kg ha ^?1. The application of 20 μg ABA induced rapid stomatal closure and a reduction in leaf extension rate, which were sustained for 7–8 days after treatment. These changes were associated with an overall reduction in shoot growth. ABA-treated plants that were additionally sprayed with diclofop-methyl sustained ABA symptoms, but no additional weight loss or leaf chlorosis. The mechanism of the protective action of ABA on diclofop-methyl has not been determined.     

An approach to investigate the costs of herbicide‐resistant Alopecurus myosuroides

Herbicide resistance in Alopecurus myosuroides causes severe problems in Western European cropping systems. Costs of herbicide resistance were investigated in this study by analysing variable production costs and sales revenues. Three farms were selected for this study, with winter wheat as the dominating crop in all farms. Resistance in A. myosuroides populations was verified at all locations. Four farming approaches were simulated over a period of 20 years: (i) continuing the actual cropping system without increase of resistance, (ii) continuing the actual cropping system with increase of resistance, (iii) changing cropping practice to overcome resistance and (iv) changing cropping practice to prevent resistance. Contribution margins representing the proportion of sales revenue that is not consumed by variable costs were calculated for all approaches. Comparative static simulations showed that average contribution margins in a cropping system with more than 60% winter cereals and reduced tillage practice dropped from 807 € ha^?1 a^?1 without herbicide resistance to 307 € ha^?1 a^?1 with herbicide resistance. Alopecurus myosuroides population densities increased to more than 1000 plants m^?2. Diverse crop rotations, including spring crops, clover–grass leys and intensive tillage, suppressed A. myosuroides populations, and average contribution margin was 630 € ha^?1 a^?1. Preventive methods with rotations of winter cereals and spring crops with less clover–grass leys resulted in an average contribution margin of 691 € ha^?1 a^?1. In conclusion, rotations of winter cereals and spring crops combined with inversion tillage and herbicides provide stable yields and can prevent weed population increase.     

Relative importance of crop seed, manure and irrigation water as sources of weed infestation

Three possible sources of field contamination by weed seeds were studied during 1983–86 in two areas of Fars Province, Iran. These sources were crop seed, irrigation water and sheep manure. Manure was found to be the most important, adding almost 10 million seeds ha^?1 at each application. Farmer-saved seed of wheat, the main crop of the area, added an average of 182,000 weed seeds ha^?1. Irrigation water added no more than 120 seeds ha^?1, but was able to carry seeds over long distances without affecting viability.     

Effect of fluazifop-butyl on the chlorophyll content, fluorescence and chloroplast ultrastructure of Elymus repens (L.) Gould. leaves

Some aspects of the action of fluazifop-butyl on the chlorophyll content, chloroplast functioning and chloroplast ultrastructure of Elymus repens are reported. Over a period of 0–12 days after spraying with 0.25 or 1.0 kg ha^?1 of the herbicide, chlorophyll a and b contents of this susceptible plant decreased, progressing from the youngest to the more mature leaves. Newly formed tillers and the youngest expanding leaves exhibited a more severe type of chlorosis and were often found to be devoid of chlorophyll. A similar progressive decline of the chlorophyll content was observed in an experiment where leaf segments were floated in fluazifop-butyl. Evidence of a rapid and significant alteration of the normal chlorophyll fluorescence of E. repens leaves treated with fluazifopbutyl was obtained. The herbicide, at a concentration range of 0.25–1.0 μg μ1^?1, caused a significant loss of the fast fluorescence rise, fluorescence yield and, after 24 h, caused a total abolition of the fluorescence decay (PS decas). These results are discussed. Ultrastructural damage to chloroplasts was seen within 24 h after treatment with fluazifop-butyl. This damage ranged from a partial to total disruption of the outer chloroplast envelope and a disorganization of the internal thylakoid system. Such Ultrastructural effects on chloroplasts were found to intensify up to about 6–7 days after spraying, by which time nearly all chloroplasts in tissue sections were affected to some degree.     

Evaluation of entomopathogenic fungi and a nematode against the soil-dwelling stages of the crane fly Tipula paludosa

BACKGROUND: Larvae of the crane fly Tipula paludosa (Diptera: Nematocera) are economically important pests of grasslands, nurseries and organically grown crops. This study was conducted to evaluate several entomopathogenic fungal strains, the entomopathogenic nematode Heterorhabditis bacteriophora and the organophosphate insecticide Dursban WG (75% chlorpyrifos) against larval stages of T. paludosa under laboratory and greenhouse conditions. RESULTS: Metarhizium robertsii strain V1005 was the most virulent, causing 100% larval mortality 4 weeks post-inoculation. Eight other M. robertsii strains and M. brunneum (ARSEF 3297) caused mortality ranging between 0 and 60%, whereas strains of Beauveria bassiana, Isaria fumosorosea and Lecanicillium longisporum were non-pathogenic to T. paludosa. In greenhouse tests, medium (2 × 10¹⁴ conidia ha⁻¹) and high (2 × 10¹⁶ conidia ha⁻¹) concentrations of V1005 gave higher larval mortalities (90 and 100%) than lower (2 × 10¹³ conidia ha⁻¹) concentrations (52 and 78%) at 4 and 8 weeks after treatment respectively. Dursban WG gave 100% larval mortality 4 weeks after treatment; H. bacteriophora UWS1 caused 28 and 65% mortality 4 and 8 weeks after treatment respectively. CONCLUSIONS: This study shows that M. robertsii V1005 has considerable potential for the control of T. paludosa, thereby reducing the use of chemical insecticides. Copyright © 2012 Society of Chemical Industry     

Meta‐analytic modelling of the incidence–yield and incidence–sclerotial production relationships in soybean white mould epidemics

White mould (Sclerotinia sclerotiorum) is a destructive disease of soybean worldwide. However, little is known of its impact on soybean production in Brazil. A meta‐analytic approach was used to assess the relationship between disease incidence and soybean yield (35 trials) and between incidence and sclerotia production (29 trials) in experiments conducted in 14 locations across four seasons. Region, site elevation and season included as moderators in random‐effects and random‐coefficients models did not significantly explain the variability in the slopes of the incidence–yield relationship. The Pearson's r, obtained from back‐transforming the Fisher's Z estimated by an overall random‐effects model, showed that incidence of white mould was moderately and negatively correlated with yield (r = ?0.76, P < 0.0001). A random‐coefficients model estimated a slope of ?17.2 kg ha^?1%^?1, for a mean attainable yield of 3455 kg ha^?1, indicating that a 10% increase in white mould incidence would result in a mean yield reduction of 172 kg ha^?1. White mould incidence and production of sclerotia were strongly and positively correlated (r = 0.85, P < 0.0001). For every 10% increase in white mould incidence, 1 kg ha^?1 of sclerotia was produced. The relationship between disease incidence and production of sclerotia was stronger in southern regions and at higher elevation. In the absence of management, economic losses associated with white mould epidemics, assuming 43% incidence in 22% of the soybean area, were estimated at approximately US $1.47 billion annually within Brazil.     

Manipulating crop row orientation and crop density to suppress Lolium rigidum

Light is an important resource that crops and weeds compete for and so increased light interception by the crop can be used as a method of weed suppression in cereal crops. This research investigated the impact of altered availability of photosynthetically active radiation (PAR) (from crop row orientation or seeding rate) on the growth and fecundity of Lolium rigidum. Wheat and barley crops were sown in an east–west (EW) or north–south (NS) direction, at a high or low seeding rate, in three field trials in 2010 and 2011 (at Merredin, Wongan Hills and Katanning, Western Australia). The average PAR available to L. rigidum in the inter‐row space of EW crops compared with NS crops was 78% to 91% at crop tillering, 39% to 56% at stem elongation, 28% to 53% at boot/anthesis and 41% to 59% at grain fill. Reduced PAR in the EW crop rows resulted in reduced L. rigidum fecundity in five of the six trials (average of 2968 and 5705 L. rigidum seeds m^?2 in the EW and NS crops). Availability of PAR was not influenced by seeding rate, but the high seeding rate reduced fecundity in three of the six trials (average of 3354 and 5092 seeds m^?2 in the crops with high and low seeding rate). Increased competitive ability of crops (through increased interception of PAR or increased crop density) was highly effective in reducing L. rigidum fecundity and is an environmentally friendly and low cost method of weed suppression.     

Diseases and pests of pigeonpea in eastern Africa: A review

Pigeonpea is one of the major legume crops grown in eastern Africa but has been relatively neglected in terms of research and development. The peas are a rich source of protein and the crop is nitrogen-fixing and drought tolerant. It is an ideal crop for the semi-arid areas of Africa and there is great potential for it to be more widely grown. The large number of pests and diseases which attack pigeonpea in Africa (and elsewhere) is perhaps the main constraint to increased production. The most important pest worldwide is the pod borer, Helicoverpa armigera, but the flowers and pods are attractive to a wide range of insect pests. The most important disease in eastern Africa is Fusarium wilt (Fusarium udum) and considerable effort has been devoted by ICRISAT to developing wilt-resistant pigeonpeas, adapted to cultivation in the region. This paper reviews the literature on pests and diseases of pigeonpea with special reference to eastern Africa and presents some new information on distribution and damage levels for the key pests and diseases.     

Application timing of asulam for torpedograss (Panicum repens L.) control in sugarcane in Okinawa island

Field and glasshouse experiments were conducted from 1995 through 1996 to evaluate application timing of asulam (methyl sulfanilylcarbamate) for torpedograss (Panicum repens L.) control in relation to plant age in sugarcane. Above‐ground shoots of torpedograss were completely controlled with asulam at 2–4 kg active ingredient (a.i.) ha^?1 applied 60 or 80 days after planting (DAP) in artificially infested pots. But some newly developed rhizome buds survived after asulam application resulting in 1–25 and 76–100% or more regrowth in 60 and 80 DAP‐applied pots, respectively. Whereas the herbicide at 2–4 kg a.i. ha^?1 applied within 60 DAP completely controlled above‐ground shoots, applied 80 DAP at 2 kg a.i. ha^?1 it did not completely control the weed in the artificially infested field. Regrowth levels were 1–25 and 76–100% or more in 60 and 80 DAP‐applied plots, respectively. Asulam at 2–3 kg a.i. ha^?1 applied 20, 40, 60 or 80 DAP in a naturally infested field completely controlled above‐ground shoots and regrowth levels were 76–100 or more, 51–75, 1–25 and 26–50% in these same DAP applied plots, respectively. The herbicide applied at 4 kg a.i. ha^?1 caused chlorosis on younger sugarcane leaves (one‐leaf stage), but when applied at 2–3 kg a.i. ha^?1, no injury symptoms were shown. The herbicide at 2–4 kg a.i. ha^?1 applied within 60 DAP resulted in remarkably higher yield and shoot biomass of sugarcane than that applied 80 DAP. This study suggested that asulam at 2–3 kg a.i. ha^?1 should be applied 60 days after planting for the maximum control of torpedograss regrowth and better yield of sugarcane. This study also indicated that torpedograss cannot be completely controlled with a single application of asulam in a naturally infested field because of rhizome fragmentation by cross plowing and distribution of rhizomes into different soil layers that require different times to emerge. The shoots emerging after asulam application could not be controlled. Another study is required to determine the interval between sequential applications of asulam for better control of torpedograss in a naturally infested field.     

Sublethal effect of Beauveria bassiana on feeding and fecundity of the sunn pest,Eurygaster integriceps Puton (Hemiptera: Scutelleridae)

The sunn pest, Eurygaster integriceps Puton, is a major pest of wheat in West and Central Asia. Studies were conducted to investigate the effect of Beauveria bassiana (teleomorph; Cordyceps bassiana) isolates on the sunn pest. Bioassays were done with adult insects collected from overwintering sites at three different times. The effect of sublethal doses of fungi on the insects’ feeding and fecundity was determined. When the sunn pest adults were treated with 2 × 10⁷ conidia mL^?1, all isolates caused significant sunn pest mortality varying between 24 and 100% 12 days after inoculation. There were significant differences between mortality, depending on the date of fungal application. Adult sunn pests treated with B. bassiana at sublethal concentrations caused significantly less damage to wheat leaves than sunn pests in the control. The number of eggs laid by the sunn pest was significantly fewer when wheat plots in plastic greenhouse and field cages were infested with adult sunn pests treated at sublethal concentrations, compared with sunn pests in control plots. Results show that sublethal dosages of B. bassiana reduced sunn pest feeding and fecundity. Applying B. bassiana in sunn pest overwintering sites minimizes the pest populations, which would move to wheat fields in spring.