Weed Mortality Research Articles

Effect of pre and post emergence herbicides for weed management in bermuda grass (Cynodon dactylon) var. Tif dwarf 419

Turf grasses are the plants which form a continuous ground cover and is the assurance of a lush, high-quality lawn but the presence of weeds during green establishment can reduce growth and turf quality. Field experiment was conducted to investigate efficacy of Pendimethalin (1.0 kg a.i./ha) – pre emergence, Atrazine (1.0 kg a.i./ha) - pre emergence, Carfentrazone (30 g/ha)- post emergence (40 DAS), Metribuzin (300 g/ha) - pre emergence, Pendimethalin (0.75 kg/ha) + Metribuzin- pre emergence, Pendimethalin (Pre emergence) + Carfentrazone- (Post emergence), Pendimethalin (Pre emergence) + Metribuzin (Post emergence), Atrazine (Pre emergence) + Carfentrazone (Post emergence), Atrazine (Pre emergence) + Metribuzin (Post emergence), manual weeding (four hand weeding) on the establishment of Tif dwarf 419 Bermuda grass from sprigs. The results suggest that application of Pendimethalin @ 0.75 l/ha (pre-emergence) + Carfentrazone @ 0.0225 kg/ha (post-mergence) at 40 days after sowing was effective for controlling the weeds followed by Atrazine @ 0.75 l/ha (pre-emergence) + Carfentrazone @ 0.0225 kg/ha (postemergence) at 40 days after sowing. Carfentrazone (30g/ha) alone as post emergence herbicide recorded about 75% weed mortality.

Evidence of synergy with ‘stacked’ intrarow cultivation tools

SummaryIntrarow cultivation efficacy is often low and highly variable. As the mechanisms affecting weed mortality likely vary by tool, several companies have developed cultivators with the ability to use several different intrarow tools at once. We evaluated the potential for such ‘stacking’ of cultivation tools to increase efficacy. We used different sequences of torsion weeders, finger weeders and row harrows in a test crop of maize with surrogate weeds, Sinapis alba and Panicum miliaceum. Most tool combinations resulted in an additive increase in efficacy compared with the individual tools, but the combination of torsion–finger–row harrow demonstrated a synergistic increase in efficacy. In separate experiments, forward speed, soil moisture and weed size were negatively correlated with efficacy, but the torsion–finger–row harrow combination continued to demonstrate a synergistic increase in efficacy compared with the individual tools in 7 of 11 cases. The drawback was high crop mortality (16.0 ± 1.16%); further mechanistic research is needed to reduce crop mortality while maintaining high mean efficacy, through tool design, adjustment and cultural factors.

Hot Water Treatment Enhances the Bioherbicidal Efficacy of a Fungus

Hemp sesbania (Sesbania exaltata) plants (>30 cm tall) sprayed with hot water (45°C – 95°C), followed by spray applications of fungal spores of Colletotrichum truncatum (CT) at 1.0 × 107 spores/ml-1 and 22°C – 25°C, suspended either in: 0.2% Silwet L-77 surfactant (SW); unrefined corn oil (CO)/distilled water (1:1, v:v); or 0.2% SW in CO were controlled by 80% - 95%, 12 days after treatment (DAT) under greenhouse conditions. These treatments also reduced dry weight accumulation of this weed. Plants treated with hot water without CT were also injured at temperatures ≥35°C (5% mortality), and 60% mortality at 95°C. Artificial dew treatments (25°C, 12 h), imposed on plants after the treatment protocols above, had little or no effect on weed mortality or dry weight reduction compared to treated plants without dew. Under field conditions, 85% control of hemp sesbania was achieved 12 - 15 DAT when a pre-treatment with hot water (65°C) was followed immediately with a CT application at the spore concentration as described above. Plants in field tests treated with CT without a hot water treatment were visually unaffected, with no mortality or plant biomass reductions recorded 15 DAT. These results suggest that use of hot water may be an important tool for improving the infectivity and bioherbicidal potential of some plant pathogens.

Weed Mortality Caused by Row-Crop Cultivation in Organic Corn–Soybean–Spelt Cropping Systems

To assess the effectiveness of interrow cultivation, counts were taken before and after cultivation of corn and soybean during the first two crop rotations in a corn–soybean–spelt organic grain cropping systems experiment. Overall control per cultivation event in soybean was 73%, about equal to the 67% of the interrow area actually covered by cultivator tools. Weed control per cultivation event in corn was higher, and exceeded 91% at later cultivations. The greater weed control in corn relative to soybean, particularly at later cultivations, was probably due to more soil being thrown into the corn row, burying a greater proportion of the weeds. Perennial weeds emerging from roots and rhizomes were less controlled by cultivation events than weeds emerging from seeds. Relatively poor control of perennials was due both to rapid resprouting during the few days between cultivation and assessment and to a lower probability of death in the zone indirectly disturbed by cultivator tools. Seedlings of perennial species suffered greater mortality from cultivation than annual weeds, probably because the low relative growth rate of perennials resulted in small seedlings that were susceptible to cultivation. Common ragweed was less controlled by cultivation than other annual weeds, probably because its heavier seeds produced larger seedlings at the time of cultivation. These larger seedlings were less likely to be buried during hilling-up operations at later cultivations. Counts of weeds before and after individual cultivation events provide insight into the processes affecting weed mortality during mechanical management.

Peatland Fire Danger Rating According to Weeds Characteristic Under Jelutung (Dyera Polyphylla) Plantation

<p>Besides to be a competitor plant, weeds could act as the potential fuel under plantation forest in peatland. Characteristic of weeds in relation to peat swamp forest fire danger was studied under jelutung plantation in Central Kalimantan. The research was aimed at exploring the potency of weed to become one of the fire danger rating indicators. By using vegetation analyses method in sampling unit of weeds population, results showed that three plantation area have different dominance weed species. The weeds species that could be the indicator of height fire risk according to water content and percentage of weed mortality during the drought, height potency of greenhouse gas emmision, culm height, and chemical material content that easy burned in this study were <em>Imperata cylindrica</em>, <em>Stenochlaena polustris</em>, <em>Cyclosorus aridus</em>, and <em>Nephrolepis exaltata</em>. While, the presence of <em>Glichenia linearis, Melastoma malabatracum, Ficus grossulariodes, Saurophus androginus, Spatoglathis plicata,Himenocalis littoralis, Leptaspis urcheolata, Cyperus rotundus,</em> and <em>Amaranthus spinosa</em> were not indicated high fire risk.</p>

Efficacy Improvement of a Bioherbicidal Fungus Using a Formulation-Based Approach

Greenhouse experiments were conducted to determine the effects of an invert (water-in-oil) emulsion (IE) on dew period duration and dew delay of Colletotrichum coccodes for biocontrol of the problematic weed, eastern black nightshade (Solanum ptycanthum). Dew periods of 4, 8, or 12 h provided 10%, 25%, and 40% control of eastern black nightshade plants, respectively, when C. coccodes (Strain NRRL 15,547) spores were applied in water + Tween 80 surfactant 12 days after inoculation, but a minimum of 16 h of dew was required to achieve ~95% plant mortality. In contrast, at these same intervals of dew, 95%, 100% and 100% mortality occurred, respectively, when fungal spores were formulated in the IE. Even in the absence of dew, 60% mortality and 70% dry weight reductions of plants was achieved with the fungus/IE formulation Delaying dew by 2 h after inoculation did not significantly reduce weed control or plant dry weight reductions when plants were inoculated with the fungus either in the aqueous or in the IE formulation. However, when dew was delayed for 4, 8, or 12 h, only 60%, 50%, and 25% mortality, respectively, of plants receiving the aqueous spore treatment occurred. In contrast, 95%, 90%, and 90% weed mortality occurred after the same dew delays of plants receiving the fungus/ IE treatments. These results demonstrate that formulating C. coccodes spores in an invert emulsion greatly improves the bioherbicidal potential of this fungus. Furthermore, results suggest that this formulation may render pathogens previously rejected for development as bioherbicides due to restrictive dew requirements more efficacious for use in controlling their target weeds.

Habitat and Time Are More Important Predictors of Weed Seed Predation than Space on a Diversified Vegetable Farm in Maine, USA

Postdispersal weed seed predation is a significant source of weed mortality in agroecosystems. The magnitude of seed predation, however, is variable. Understanding the relative importance of factors driving variability in seed predation rates will increase the potential utility of seed predation to farmers. We conducted landscape-scale field experiments to quantify and compare the effects of space, time of sampling, and habitat on weed seed predation. Seed predation assays, with and without vertebrate exclosures, measured seed predation rates at spatially explicit sample sites across 8.5 ha of crop and noncrop habitats on a diversified organic vegetable farm in Maine. Total and invertebrate seed predation averaged 8% and 3% d−1, respectively. Vertebrate seed predators detected by motion-sensing cameras included small mammals and birds. A ground beetle,Harpalus rufipes, was highly dominant in pitfall traps, comprising 66% of invertebrate seed predators captured within crop fields. Seed predation was randomly distributed in space. However, time of sampling and habitat were highly significant predictors of seed predation. Variance partitioning indicated that habitat factors explained more variation than did time of sampling. Total seed predation was greater in crop and riparian forest habitats than in mowed grass, meadow, or softwood forest. Generally, invertebrate seed predation was greatest at sites with an intermediate degree of vegetative cover, whereas habitat type was the chief biotic determinant of vertebrate seed predation rates. These results suggest cover cropping and wetland conservation as practices that may bolster seed predation rates.

Weed seedling herbivory by field cricket Teleogryllus emma (Orthoptera: Gryllidae) in relation to the depth of seedling emergence

This study aimed to determine whether seedling herbivory by the field cricket, Teleogryllus emma (Ohmachi et Matsuura), promoted the mortality of Italian ryegrass (Lolium multiflorum Lam.), a non‐native grass weed in Japan, whether the impact of seedling herbivory differed depending on the depth of seedling emergence and the influence of cricket density on seedling mortality. First, the seedlings at emergence depths of 0, 1 and 2 cm were exposed to the cricket for 2 days in plastic cups and the amount of seedling mortality by herbivory was calculated. The level of mortality of 60 seedlings that emerged from seeds on the soil surface was 92.4%, significantly higher than that of the seedlings that emerged from seeds at depths of 1 cm (10.8%) and 2 cm (9.6%). Second, the seedlings at the emergence depths of 0 and 1 cm were exposed to the crickets at four different densities (zero, one, two and three individuals per 5700 cm2) for 5 days in plastic containers and the amount of seedling mortality by herbivory was calculated. The level of mortality by herbivory of the seedlings that emerged from 100 seeds on the soil surface was higher (33.3–61.3%) than that of the seedlings that emerged from seeds at a depth of 1 cm (4.7–13.1%) in the containers with one‐to‐three crickets. The level of seedling mortality tended to increase with an increasing cricket density. These results suggest that seedling herbivory by crickets is an important factor in weed mortality, particularly in no‐till fields and in field margins, where the seeds are more prevalent near the soil surface.

Effect of urea and common salt (NaCl) treated glyphosate on parthenium weed (Parthenium hysterophorus L.) at Western Hararghe zone, Ethiopia

Field experiments were conducted from 2008 to 2011, at western Hararghe zone, Eastern Ethiopia to evaluate the effect of urea and common salt treated glyphosate on parthenium weed (Parthenium hysterophorus). The experiments were arranged in randomized complete block design with five replications. Glyphosate herbicide at 3 L/ha was applied with different rates (0, 50, 100 and 150 ml) of urea and common salt. From the pooled analysis of variance over years it was observed that there existed a significant difference among treatments (p<0.05) in which the total population of parthenium weed mortality was noted at 25 days after applications across years for 3000 ml of glyphosate treated with 150 ml of urea and 150 ml of common salt. Results from this experiment showed that treating 3000 ml of glyphosate with 150 ml of urea and 150 ml of common salt solutions and spraying at 6 to 8 leaves stages resulted in complete mortality of parthenium weed in short period of time by increasing the phytotoxicity of this herbicide. While spraying this solution at 50 and 75% flowering stages showed poor mortality rates on this weed. This study also elucidated the complete change of parthenium infested plots into soft weed species that suppresses the re-emergency of this noxious weed. This helps in reducing the soil seed bank of parthenium weed, thus its population declines over successive years. This finding helps in reducing the rate and frequency of glyphosate application in conservation tillage and plantation crops like coffee and fruit farms, thus managing cost of parthenium weed can be significantly reduced. Key words: Parthenium hysterophorus, glyphosate, mortality rate, phytotoxicity, soil seed bank.

Rapid Evolution of Herbicide Resistance by Low Herbicide Dosages

Herbicide rate cutting is an example of poor use of agrochemicals that can have potential adverse implications due to rapid herbicide resistance evolution. Recent laboratory-level studies have revealed that herbicides at lower-than-recommended rates can result in rapid herbicide resistance evolution in rigid ryegrass populations. However, crop-field-level studies have until now been lacking. In this study, we examined the impact of low rates of diclofop on the evolution of herbicide resistance in a herbicide-susceptible rigid ryegrass population grown either in a field wheat crop or in potted plants maintained in the field. Subsequent dose–response profiles indicated rapid evolution of diclofop resistance in the selected rigid ryegrass lines from both the crop-field and field pot studies. In addition, there was moderate level of resistance in the selected lines against other tested herbicides to which the population has never been exposed. This resistance evolution was possible because low rates of diclofop allowed substantial rigid ryegrass survivors due to the potential in this cross-pollinated species to accumulate all minor herbicide resistance traits present in the population. The practical lesson from this research is that herbicides should be used at the recommended rates that ensure high weed mortality to minimize the likelihood of minor herbicide resistance traits leading to rapid herbicide resistance evolution.

Corn–Velvetleaf (Abutilon theophrasti) Interference Is Affected by Sublethal Doses of Postemergence Herbicides

Injury to weeds from sublethal doses of POST herbicides may reduce the effect of weed interference on crop yield. Information on how herbicide dose influences weed mortality, growth, and seed production is needed to assess the potential benefit of applying reduced herbicide doses. Field experiments were conducted at Mead, NE, in 2001 and 2002 to quantify velvetleaf mortality, growth, and corn–velvetleaf interference in response to varying doses of three POST herbicides. Untreated velvetleaf at six densities (0, 1, 3, 6, 12, and 20 plants m−1corn row) was grown in mixture with corn to establish a baseline corn–velvetleaf interference relationship. Treated velvetleaf at a density of 20 plants m−1row received one of five doses of dicamba, halosulfuron, or flumiclorac. Untreated velvetleaf height, biomass, and seed capsule production were greater in 2002 than 2001 and declined with increasing velvetleaf density in both years. Corn yield was not affected by untreated velvetleaf in 2001, but yield loss increased with increasing velvetleaf density in 2002. Mortality of herbicide-treated velvetleaf was 56% greater in 2001 than 2002 and increased with increasing herbicide dose. Maximum height of treated velvetleaf was similar for all treatments in 2001 but declined with increasing herbicide dose in 2002. Biomass and seed production of treated velvetleaf varied among herbicides in 2002 and decreased with increasing dose. Corn yield was not influenced by velvetleaf in 2001, but yield loss in response to herbicide-treated velvetleaf declined with increasing herbicide dose in 2002. Results show that the assumption that weeds surviving herbicide application are as competitive as untreated weeds is incorrect. Reduction in growth and resource consumption by herbicide-damaged weeds reduced the negative effects of weeds on corn.

Relating Weed Size, Crop Soil Cover and Soil Moisture with Weed Harrowing Efficacy on Papaver rhoeas and Other Dicotyledoneous Weeds in Mediterranean Conditions

ABSTRACT Twelve field trials were conducted in Catalonia (North-Eastern Spain) between 1998 and 2003 on different winter cereal fields highly-infested with Papaver rhoeas L. or, in two cases, with mixed dicotyledoneous weeds. Trials were conducted in semi-arid conditions in order to find out which are the real limitations of harrowing in those circumstances. A tine harrow was used in a single pass as the only weed control method at 4–6 km h−1 and on four occasions again later in post-emergence. Weed size, crop soil cover and climatic conditions were significantly correlated with initial efficacy so that small weeds, low crop soil cover allowing good harrowing and dry conditions enhanced weed control. Despite soil moisture not being significantly correlated with initial efficacy, it was significantly related to other factors like weed size, thus having an indirect influence on initial control. Initial efficacy ranged between 18 and 93% and was not correlated with final weed control at crop elongation, which was highly related to natural weed mortality. Efficacy increases in time were significant in four cases but decreases due to new germination flushes were not significant. Repeating harrowing later in post-emergence does not seem to be generally convenient as efficacy did in fact not decrease but increased only in one out of four cases. The results show how initial efficacy is highly dependent on small weeds, which are at the same time related to dry soils, dry climatic conditions and low crop soil cover. As harrowing was conducted as soon as possible in the trials, the real main limitation was thus climatic, i.e. having dry soils. Later natural weed mortality can increase significantly initial weed control but this did not occur in all cases. Thus, in Mediterranean conditions, harrowing should be conducted as early as possible as wet winter periods can also impede correct timing.

Evaluation of Fungal Pathogens as Biological Control Agents for Cogongrass (Imperata cylindrica)1

Based on field surveys and evaluations in the greenhouse, two fungal pathogens,Bipolaris sacchari and Drechslera gigantea, were identified as promising biological control agents for cogon- grass. In greenhouse trials, the application of spore suspensions of these fungi containing 10 5 spores/ ml in a 1% aqueous gelatin solution to cogongrass plants and their incubation in a dew chamber for 24 h resulted in disease symptoms that ranged from discrete lesions to complete blighting of leaves. Disease severity (DS), based on a rating scale for southern corn leaf blight with 50% as the maximum DS rating, ranged from 42 to 49%. In greenhouse experiments, the application of spores formulated in an oil emulsion composed of 4% horticultural oil, 10% light mineral oil, and 86% water resulted in higher levels of foliar blight with no dew exposure or shorter periods of dew exposure (4, 8, or 12 h) as compared with the application of spores formulated in 1% gelatin. Field trials demonstrated that under natural conditions, the application of a spore and an oil emulsion mixture containing 10 5 spores/ml of either fungus could cause foliar injury from disease and phytotoxic damage from the oil emulsion. Depending on the application rate (100 or 200 ml/plot), the level of foliar injury ranged from 40 to 86% (based on a field assessment scale of 0 to 100% foliar injury) with B. sacchari as the test fungus. However, with D. gigantea as the test fungus, foliar injury ranged from 9 to 70% depending on the application volume and the oil concentration used. Although B. sacchari and D. gigantea were capable of causing foliar blight on cogongrass, the regenerative ability of the rhizomes allowed cogongrass to recover from the damage caused by these fungi. However, the level of injury caused by these fungi is sufficient to support their use as components for integrated management of cogongrass. Nomenclature: Cogongrass, Imperata cylindrica (L.) Beauv. # 3 IMPCY; corn, Zea mays L. Additional index words: Bioherbicide, biological control, Bipolaris sacchari (E.J. Butler) Shoe- maker, Drechslera gigantea (Heald & F.A. Wolf) Ito. Abbreviations: CRD, completely randomized design; DAI, days after inoculation; DS, disease se- verity; RH, relative humidity; SOE, spore and oil emulsion mixture; WAI, weeks after inoculation; WM, weed mortality.

Effect of soybean spatial arrangement and glyphosate dose on Anoda cristata demography

The annual weed Anoda cristata is recognised as a problem of increasing importance in soybean crops and can significantly reduce crop yields. The effect of soybean density, row spacings and glyphosate doses in reduced and no-tillage systems on demography and phenology of A. cristata was examined.The seedbank of A. cristata did not differ between tillage systems and was initially similar for all treatments. In the fourth year, it was higher in plots without glyphosate application than in plots treated with the recommended and half the recommended glyphosate dose. The highest seedbank was observed in wide-row soybean without glyphosate. Total emergence was not affected by the planting pattern with any glyphosate dose, but emergence was higher in the untreated plots than in those sprayed with the recommended glyphosate dose. Total weed mortality without glyphosate was independent of the planting pattern in 2001 but was lower in wide-row soybean in 2002. The application of half of the recommended dose killed almost all A. cristata plants in narrow-row soybean. Mortality was 100% with the recommended glyphosate dose in all years and in all planting patterns.Without herbicides, biomass and seed production per unit area was lower in narrow-row compared to wide-row soybean but no differences in biomass production of the weed were observed between narrow spacings with high and low densities. In all planting patterns, weed biomass and seed production decreased progressively from the first to the third weed emergence. The use of half of the recommended glyphosate dose relative to treatments without glyphosate application reduced biomass and seed production in all planting patterns, but this reduction was greatest in narrow-row soybean. Without glyphosate, in both the row spacings, flowering and seed production occurred earlier for the first relative to the second weed emergence. With the application of half of the recommended dose, flowering occurred only in the first weed emergence and both flowering and seed production were observed first in wide-row relative to narrow-row soybean. The recommended glyphosate dose controlled both the first and the second emergence, but the third emergence was not affected and remained in the vegetative stage till crop harvest. Without glyphosate and using half of the recommended glyphosate dose, reducing soybean row spacing is a more important factor than increasing crop density in reducing A. cristata populations.

Synergistic interaction of soilborne plant pathogens and root-attacking insects in classical biological control of an exotic rangeland weed

Abstract This investigation of the possible role of pathogen–insect interactions on the mortality of Euphorbia esula/virgata plants was prompted by repeated observations of an apparent association in the field between damage to the roots of this plant caused by root-attacking insects and disease occurrence. In studies using microcosms in a greenhouse consisting of potted, caged plants of E. esula/virgata , combinations of Fusarium oxysporum , Rhizoctonia solani , or both fungi with adults and larvae of the flea beetle Aphthona spp. caused significantly greater rates of injury to E. esula/virgata than any single agent. Kaplan–Meier survival curves were used to examine the effects on time to mortality of combinations of various inoculum densities of R. solani per gram of air-dried soil with 0, 5, and 15 Aphthona per plant. At each insect level per plant, increasing inoculum density increased the rate of mortality of E. esula/virgata ; the effect was significant at 5 and 15 beetles per plant using log rank tests. Additionally, at 5 flea beetles per plant, the rates of weed mortality in association with the second highest fungal inoculum concentration were similar to the mortality at the highest inoculum level, indicating that a minimum effective concentration is needed for effective synergism to exist. Cox regression analysis of proportional hazards was used to examine the relative contribution of plant pathogens and insects to weed mortality in the microcosms. The results indicated that plant pathogens are more than twice as likely to cause mortality of the target weed than insects under typical conditions and, under optimum conditions, are over four times more likely to do so. The results support the idea that supplementing flea beetle establishments with plant pathogens can be an effective means of both causing higher rates of successfully impacted release sites and greater biocontrol impact at individual release sites. Based on these findings it is recommended that a test of propensity for insect–plant pathogen synergisms should be a selection criterion for candidate agents. Additionally, it is recommended that survival analysis be applied to the target weed exposed to appropriate combinations of insects and pathogens as a means to assess the potential effectiveness of candidate agents. Application of one or both of these recommendations could increase success in classical biocontrol of weeds and reduce associated costs and environmental risks.

Weed seed production, crop planting pattern, and mechanical weeding in wheat

Experiments were carried out to investigate weed seed production in widely spaced spring wheat crops that received aggressive mechanical weed control (hoeing and harrowing) compared with that in narrowly spaced crops receiving less aggressive mechanical control (harrowing only). Three species (wild buckwheat [Polygonum convolvulus], ladysthumb [Polygonum persicaria], and common chickweed [Stellaria media]) were studied in three row-spacing treatments (10, 20, and 30 cm) and two sowing densities (140 and 180 kg ha−1). Average seed production per surviving plant was up to three times higher in the 30-cm treatments compared with the 10-cm treatments. Taking into account the 40–50% weed mortality resulting from control in the 30-cm treatments, seed production per seedling was still higher in the 30-cm treatments than in the 10-cm treatments. Differences in wheat yield were not found among treatments. From the perspective of long-term weed population management, using a narrow row spacing would be more effective in spring wheat on the basis of experiments with the weed species considered here.

Herbicidal control of water hyacinth (Eichhornia crassipes) and its impact on aquatic environment

A research programme was taken up to study the impact of herbicides on the control of water hyacinth [Eichhornia crassipes (Mart.) Solms-laubach], optimize dose and time of application, and to trace the impact on aquatic environment through a series of greenhouse and pond studies. The study was undertaken at Veeranum Lake which has a command area of 18,000 ha connected through 27 distributary channels, and infested heavily with water hyacinth. Among the different herbicides tried, viz. glyphosate, 2,4-D Na salt and paraquat, glyphosate proved more efficient with higher magnitude of plant height reduction, weed mortality and reduction in biomass compared with 2,4-D and paraquat. The optimum dose of glyphosate, 2,4-D Na salt and paraquat was 2.5 kg/ha, 1.5 kg/ha and 1.5 kg/ha respectively. Different seasons did not influence the efficacy of herbicides. Glyphosate caused least fish mortality of 23.3% after 32 days. Different organs like gills, brain, liver and kidney of the fishes were studied, for histology and the observations showed tissue distractions in herbicides- treated fish. Glyphosate also proved more efficient and safe on water quality in terms of pH, electrical conductivity, dissolved oxygen, chemical oxygen demand and mineral content of treated water. The glyphosate-treated water was found safe for irrigating crops with 87, 58 and 62% germination of rice, cotton and okra respectively.

Potential Biocontrol Agents on Nutsedges

PurpIe and yellow nutsedges are agriculturally important weeds. They have an adverse effect against a large number of cultivated crops under both protected and open field conditions. In this research, one phytophagous insect (Bactra sp., Tortricidae Lepidopterra) and two phytopathogenic fungi (Alternaria gloeosporioides) were found to be naturally infecting these weeds. After a successful rearing of the insect and isolation of the fungi, certain studies on the efficacy of both insect and fungi against the purple nutsedge were conducted. Detailed description of adult insect and its immature stages was provided for the first time. Results obtained on mean duration of different immature stages of the insect were: 3.5, 14.3, and 8.7 days for egg, larval and pupal stages, respectively. Therefore, duration of life cycle averaged 26.5 days at 20±tlCo. Longevity of adult insect was 12.3 days, and femal fecundity was 72.8 eggs per female during the life span. Biological effect of insect moth against the weed was shown by following the insect development inside the plan until reaching the rhizome and penetrating it. Results obtained on efficacy assessement procedures indicated that the percent of plant weed mortality was 73.1 % due to the insect attack, 25.69% and 36.84% due to inoculation with culture discs and conidial suspension of Colletotrichum gloeosporioides, respectively. This mortality occured in the above cases after penetration of the bioagent in plant rhizome. Infection of detach weed leaf pieces or rhizomes with three fungal strains of Alternaria alternata. or with one fungal strain of Colletotrichum gloeosporioides resulted in the following mean length of disease lesion: 8.1, 6.6, 5.6, and 15.8 mm, respectively for the above strains. Significant differences between these mean lengths were obtained. Further studies especially under field conditions, are recommended to be conducted to assure the efficacy of the insect and the fungal strains against the weed since their effectiveness under controlled conditions was clearly proved in this study.

Mechanical damage to annual weeds and carrots by in‐row brush weeding

Field experiments were carried out in order to assess the selectivity of in‐row brush weeding in carrots with a natural flora of annual weeds, represented by Urtica urens L., Stellaria media (L.) Vill., Chenopodium album L., Senecio vulgaris L., Capsella bursa‐pastoris (L.) Med., Chamomilla suaveolens (L.) Pursh Buch. and Matricaria inodora L. The mechanisms by which the weeds and carrots were controlled (uprooting vs. soil covering) were studied using a portable vacuum‐cleaner. Weeds at the two‐ to four‐true‐leaf stage proved to be more sensitive to brushing than carrots with two to four true leaves but, for later development stages of the weeds, there were no differences. Weeds at the six‐ to eight‐leaf stage were only killed to an extent of 20–50%. Uprooting generally accounted for 45–90% of the weed mortality at the two‐ to four‐leaf stage, whereas most of the mortality in carrots was the result of soil covering. The vacuum‐cleaning method proved to be a simple and rapid way of determining whether plants had been killed by uprooting or soil covering. It was concluded that the major mechanism of weed control obtained by brush weeding is uprooting.

Effect ofAlternaria cassiae, Pseudocercospora nigricans, and Soybean (Glycine max) Planting Density on the Biological Control of Sicklepod (Senna obtusifolia)

The interactions of two fungal biocontrol agents,Alternaria cassiaeandPseudocercospora nigricans, and soybean planting density on sicklepod mortality and dry weight were studied in the field over 2 yr. The experimental field was divided into three equal areas: one without soybean and two where the soybean was sown in densities of 20 and 36 seeds per meter row with a 0.95-m row spacing. The fungi were sprayed alone or in a mixture at three growth stages of sicklepod plants grown at three levels of crop interference resulting from the three soybean planting densities. The fungal treatments were: an untreated control,A. cassiae(105spores/m2),P. nigricans(3.3 g mycelium/m2), and the mixture of these two fungi. Sicklepod was at the cotyledonary leaf, two-leaf, and four-leaf stages when treated.Alternaria cassiaewas most effective in reducing both sicklepod survival and dry weight. The mixture ofP. nigricansandA. cassiaewas generally comparable to but not better thanA. cassiaealone in killing the weed (mortality) and reducing its growth (dry weight). Soybean density did not have significant effects on the mortality or the dry weight of sicklepod. Thus, there is no advantage to combining the highly effective biocontrol agentA. cassiaewith the less effectiveP. nigricansor with soybean interference to control sicklepod. However, the results validate the efficacy ofA. cassiaeby itself as a bioherbicide.