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1.
A gas chromatographic method, using electrolytic conductivity detection, is presented for the determination of 2,4-0 as its methyl ester in triticale (X Triticosecale Wittmack). The method was used to monitor the dissipation of 2,4-0 residues in triticale over a growing season at two sites following post-emergence application of the dimethylamine salt of 2,4-D at 0.56 kkg ha?1. Initial residues, in the order of30 mg kg?1. on the day afer application (3- to 4-leaf stage of the crop), decreased to non-detectable levels in the mature straw and seed. Recoveries of 2,4-D were greater than 90% fiom green tissue fortified at 0.1 mg k?1., and in the order of 75% from seed fortified at 0.05 mg kg?1.  相似文献   

2.
Phalaris minor, the most serious weed in wheat in north‐western India, has developed extensive isoproturon resistance due to continuous isoproturon use. For its control, alternative herbicides (flufenacet, metribuzin and sulfosulfuron) at different application rates and timing were evaluated in wheat. In addition, herbicide carryover risk onto rotational crops (sorghum; maize and green gram, Vigina radiata) was also assessed. Isoproturon at 1 and 2 kg a.i. ha?1 provided only 10.5% and 51.8%P. minor control respectively. Of the other herbicides, early post‐emergent [15–21 days after sowing (DAS)] flufenacet at 180–480 g a.i. ha?1 provided acceptable control of P. minor, but failed to control broad‐leaved weeds and was phytotoxic to the wheat crop. Metribuzin at 210 g a.i. ha?1 was effective in controlling both Phalaris and dicotyledonous weeds. Mixtures of both flufenacet and metribuzin at reduced rates were better than flufenacet for weed control and grain yield. The efficacy of flufenacet and metribuzin was drastically reduced with later growth stages of P. minor (four to five leaf). Whereas sulfosulfuron at 25–30 g a.i. ha?1, applied either early post‐emergence (19 DAS) or post‐emergence (30–42 DAS), was quite effective. Overall, sulfosulfuron was the most effective treatment with regard to weed control and crop yield. However, maize and sorghum grown in rotation after harvest of sulfosulfuron‐treated wheat plots showed 65–73% crop biomass inhibition. The residual effect of sulfosulfuron was also noticed on Trianthema portulacastrum (Horse purslane), causing 73.5% dry matter reduction. By contrast, no carryover damage with flufenacet was observed on maize, sorghum and green gram. Glasshouse pot experiments and field trials investigating crop sensitivity to pre‐plant applications of sulfosulfuron found the decreasing order: sorghum > maize > green gram. The risk of carryover onto rotational crops should be considered when choosing alternative herbicides for P. minor control in wheat.  相似文献   

3.
Correspondence     
Abstract

Twenty-seven different herbicides were tested at the AUB Agricultural Research and Education Center in the Beqa'a, Lebanon, to determine their effects on weeds in wheat, barley, maize, onion and sugar beet. Each herbicide was tested at three different rates as pre-emergence and post-emergence applications. Unweeded and hand-weeded check plots were included. Data on yield, quality and other agronomic characteristics of the crops tested were recorded.

Concentrations of 1,000 and 10,000 ppm of 2, 4–D caused a significant decrease in the height and grain yield of wheat and barley when sprayed at the 3-leaf stage. At the 5-leaf stage, injury to wheat and barley occurred only when sprayed at 10,000 ppm, whereas an increase in the grain yield was obtained at 1,000 ppm of 2, 4–D acid equivalent (1 kg a.i./ha).

Pre-emergence treatments of atrazine and simazine at 2.5 kg a.i./ha caused a significant increase in the forage and grain yields of maize as compared to unweeded check plots. Wheat, oats, vetch and sugar beet were injured when planted after triazine-treated maize, whereas onions and soyabeans were tolerant. Other promising herbicides tested on maize were C 3095 (N–3–trifluoromethylphenyl–N'–methyl–N'–methoxyurea) and BV– 201 (1–(3′, 4′–dichlorophenyl)–3–methylpyrrolidin–2–one) applied as a pre-emergence spray at 1 and 2 kg/ha respectively.

Pre-planting treatment of EPTC and pre-emergence treatment of pebulate at 2 kg/ha gave a slight increase in the yield of roots of sugar beet. BV–201 and BV–207 (1–(3–chloro–4–methylphenyl)–3–methylpyrrolidin–2–one) were phytotoxic to beet.

In onions, nitrofen, BV–201 and BV–207 at 1–2 kg/ha were promising as pre-emergence and post-emergence sprays. DNOC and dinoseb at 1.5 kg/ha and ioxynil at 0.5 kg/ha sprayed post-emergence increased the yield of onions significantly over the check. No significant effects of these herbicides were observed on the bulb index, moisture content and total soluble solids of onions.  相似文献   

4.
Broomrapes (Orobanche spp.) are parasitic weeds that cause significant losses of crop yield. Experiments were conducted to investigate the seed response to the artificial germination stimulant GR24 in three species of Orobanche subjected to preconditioning under various temperatures, water potentials and with plant growth regulators. The highest germination percentages were observed in Orobanche ramosa, Orobanche aegyptiaca and Orobanche minor seeds conditioned at 18°C for 7 days followed by germination stimulation at 18°C. With the increase of the conditioning period (7, 14, 21 and 28 days), the germination percentage of O. ramosa and O. aegyptiaca progressively decreased. When conditioned at −2 MPa, the germination percentage was lower than at 0 and −1 MPa, especially at 13 and 28°C. Orobanche minor seeds could retain relatively high germination if conditioned at 18, 23 or 28°C, even after significantly extended conditioning periods (up to 84 days). GA3 (30–100 mg L−1), norflurazon and fluridone (10–100 mg L−1), and brassinolide (0.5–1.0 mg L−1) increased seed germination, while 0.01 mg L−1 uniconazole significantly reduced germination rates of all three Orobanche spp. The promotional effects of GA3 and norflurazon and the inhibitory effect of uniconazole were evident, even when they were treated for 3 days. Germination of Orobanche seeds was much lower when the unconditioned seeds were directly exposed to GR24 at 10−6 m . This early GR24-induced inhibition was however alleviated or even eliminated by the inclusion of GA3 or norflurazon (10–50 mg L−1) in the conditioning medium. On the contrary, the inclusion of uniconazole increased the inhibitory effect of GR24, particularly in the case of O. ramosa.  相似文献   

5.
Ultraviolet-B radiation effects on intra- and interspecific competition in broccoli (Brassica oleracea) and Chenopodium album were studied using bivariate factorial experiments. A randomized block design was used in which three monoculture densities for each species [144 (low), 256 (medium), and 400 (high) plants m−2] and all binary combinations were grown in a glasshouse at two (4 and 7 kJ m−2 day−1) UV-BBE radiation levels for 4 weeks in 1999 and 5 weeks in 2000. Inverse yield–density relationships were more discernible at 4, compared with 7 kJ m−2 day−1 UV-BBE radiation. Substitution rates, indicating the balance of intra- to interspecific competitive effects, declined for broccoli at 7, compared with 4 kJ m−2 day−1 UV-BBE radiation, largely because of reduced interspecific competitive influences. Conversely, substitution rates increased for C. album grown at 7 kJ m−2 day−1 UV-BBE radiation, as a result of both decreased intraspecific and increased interspecific competition. Interspecific competitive effects were influenced more than intraspecific competitive effects by UV-B radiation. Based on relative magnitude of substitution rates, C. album was a stronger competitor than broccoli at 4 kJ m−2 day−1 UV-BBE radiation in both years, and at 7 kJ m−2 day−1 UV-BBE radiation in 1999. In 2000, broccoli was the stronger competitor at 7 kJ m−2 day−1 UV-BBE radiation. Overall, the relative competitiveness of broccoli was enhanced, while that of C. album diminished at 7, compared with 4 kJ m−2 day−1 UV-BBE radiation. These findings indicate that above-ambient UV-B radiation has the potential to alter crop–weed competitive interactions, which could change acceptable weed threshold levels.  相似文献   

6.
Tri-allate degraded faster in soil from a site (T1) that had received 1·7 kg ha?1 of tri-allate annually for 23 years than in soil from an adjacent site (TO) that had received no pesticide application. Soil from the untreated site, which had been removed to a glasshouse and treated three times per annum with tri-allate at 1·7 kg ha?1 for 7 years (T2), also showed faster degradation. Soil previously treated with tri-allate showed an increased degradation rate for carbofuran and EPTC but not for aldicarb. A further experiment, 2 years after the last treatment with tri-allate, showed that the enhanced degradation effect was still present. Degradation rates were always in the order T1 > T2 > T0 for tri-allate, EPTC and carbofuran. Half-life for degradation was reduced for tri-allate and carbofuran by approximately 40% in the previously treated soils and for EPTC by approximately 80% when compared with the previously untreated soil.  相似文献   

7.
Soil weed seed bank is an important factor determining above-ground floristic composition and weed density in agricultural systems. The quantitative and qualitative measures of weed seed bank can help growers to predict the extent to which they are facing weed problems. Along with tillage, crop residues can affect the fate of weeds in the upcoming crops. To investigate such effects, we compared the effects of tillage systems [conventional tillage (CT), reduced tillage (RT), and no tillage (NT)], wheat residue retention, and nitrogen (N) rates (0, 69, 138, and 207 kg N ha−1) on depth-related characteristics of the weed seed bank under a sweet corn-wheat sequence during 2014–2015 growing seasons in Shiraz, Iran. Soil bank was not affected by tillage systems but tended to be slightly higher under RT. The highest (898 seeds m−2) and lowest (322 seeds m−2) weed population at 0–10 cm depth were found when 138 kg N ha−1 in 2015 and 207 kg N ha−1 in 2014 were applied. Species richness and diversity were higher under NT and RT practices at the top layer, but CT system was more diversified at deeper depths. They were higher when crop residues were retained as well. Barnyard grass (Echinochloa crus-galli [L.] Beauv), common lambsquarter (Chenopodium album L.), common purslane (Portulaca oleracea L.), field bindweed (Convolvulus arvensis L.), flixweed (Descoreinia sofia [L.] Webb. & Berth.), henbit (Lamium amplexicaule L.), pigweeds (Amaranthus spp.), and stinking goosefoot (Chenopodium vulvaria L.) were the most common weeds found in all tillage systems and soil depths. Grasses were relatively lower than broadleaves regardless of treatments. Weed seed bank was mostly affected by weather conditions than treatments in this short-term experiment.  相似文献   

8.
The feasibility of achieving selective wild oat (Avena fatua L.) control in a stand of the Australian oat (Avena sativa L.) cv. Savena I was examined. Diclofop-methyl was applied at rates of 0·4–0·7 kg a.i. ha?1 at the three- and five-leaf stages of A. fatua (84–132 culms m2). Although all rates of diclofop-methyl caused initial chlorosis and necrosis to the crop, the subsequent control of A. fatua permitted increased crop tillering. Avena fatua control and crop yield response were maximized when diclofop-methyl was applied at the three-leaf stage. Crop grain yield was increased by as much as 32% and 22% during 1984 and 1985, respectively. In the absence of A. fatua competition, crop shoot dry weight at ear emergence was reduced only where diclofop-methyl was applied at 0·6 or 0·7 kg ha?1. However, final grain yield was not reduced by any treatment. Only 11 of 240 cultivars or lines tolerated diclofop-methyl, and none reached the level attained by Savena I and a closely related Australian line [(Irwin × (West × New Zealand Cape/42)) × West]/24. The nature of the inheritance of diclofop-methyl tolerance was examined (1983–1985) by crossing and backcrossing (BC) Savena I with four diclofop-methyl susceptible, but agronomically superior, lines. Inheritance of diclofop-methyl tolerance appeared to be controlled by two genes, with susceptibility being dominant to tolerance in F3, BCIF2 and BCIF3 lines.  相似文献   

9.
The phytotoxicity of 10% w/w tri-allate granules to emerged plants of Avena fatua L. and wheat was investigated in the glasshouse, and to A. fatua alone under outdoor conditions. Tri-allate was applied at 1.68 and 3.36 kg a.i./ha using two patterns of granule distribution (1) the granules uniformly distributed over the soil surface and (2) the same weight of granules as in (1) but applied only to a central area of the soil surface. Wheat was very tolerant of high concentrations of tri-allate. Under optimum conditions of temperature and soil moisture in the glasshouse phytotoxic effects on wild oats were visible within 6 h and coleoptile or primary leaf entrapment was observed within 3 to 4 days of treatment. Phytotoxic effects of tri-allate were detectable at distances up to 12 cm from the site of restricted-granule application, although beyond 8 cm the effect was sub-lethal. On a sloping soil surface (1:8 gradient) the dispersal of tri-allate was approximately the same upwards or downwards from the site of herbicide application. Under outside conditions where the mean temperature was about 5 C tri-allate dispersal was sub-lethal beyond 3 cm although it evidently occurred primarily as vapour.  相似文献   

10.
Effects of density and period of competition by Solanum nigrum L. on direct seeded tomatoes in relation to weed control The effects of density and period of competition from Solanum nigrum L. were measured in direct seeded tomatoes given weed control treatments currently used in south-east France. S. nigrum emerging after a diquat treatment at the 2–3 leaf stage of the crop and thinned to low densities (<12.8 plants ha?1) at the 5–6 leaf stage of the crop caused significant yield loss if left to compete with the crop until harvest. Yield reduction was smaller if the same weed densities were present only until the onset of flowering. The regression curves of yield on weed density differed as annual climatic variations affected sowing date and plant growth; a comparison between years was made using the relation ‘crop yield × weed biomass/crop biomass’. Significant interactions between weed density and period of competition were found with yield of both green and red fruit. For late sown crops with low densities of S. nigrum two weed control treatments at the 5–6 leaf stage and at the onset of flowering were sufficient to prevent yield loss.  相似文献   

11.
Cinidon-ethyl (BAS 615H) is a new herbicide of isoindoldione structure which selectively controls a wide spectrum of broadleaf weeds in cereals. The uptake, translocation, metabolism and mode of action of cinidon-ethyl were investigated in Galium aparine L, Solanum nigrum L and the tolerant crop species wheat (Triticum aestivum L). When plants at the second-leaf stage were foliarly treated with cinidon-ethyl equivalent to a field rate of 50 g ha−1 for 48 h, the light requirement for phytotoxicity and the symptoms of plant damage in the weed species, including rapid chlorophyll bleaching, desiccation and necrosis of the green tissues, were identical to those of inhibitors of porphyrin synthesis, such as acifluorfen-methyl. The selectivity of cinidon-ethyl between wheat and the weed species has been quantified as approximately 500-fold. Cinidon-ethyl strongly inhibited protoporphyrinogen oxidase (Protox) activity in vitro, with I50 values of approximately 1 nM for the enzyme isolated from the weed species and from wheat. However, subsequent effects of herbicide action, with accumulation of protoporphyrin IX, light-dependent formation of 1-aminocyclopropane-1-carboxylic acid-derived ethylene, ethane evolution and desiccation of the green tissue, were induced by cinidon-ethyl only in the weed species. After foliar application of [14C] cinidon-ethyl, the herbicide, due to its lipophilic nature, was rapidly adsorbed by the epicuticular wax layer of the leaf surface before it penetrated into the leaf tissue more slowly. No significant differences between foliar and root absorption and translocation of the herbicide by S nigrum, G aparine and wheat were found. After foliar or root application of [14C]- cinidon-ethyl, translocation of 14C into untreated plant parts was minimal, as demonstrated by combustion analysis and autoradiography. Metabolism of [14C]cinidon-ethyl via its E-isomer and acid to further metabolites was more rapid in wheat than in S nigrum and G aparine. After 32 h of foliar treatment with 50 g ha−1 of the [14C]-herbicide, approximately 47%, 36%, and 12% of the absorbed radioactivity, respectively, were found as unchanged parent or its biologically low active E-isomer and acid in the leaf tissue of G aparine, S nigrum and wheat. In conclusion, cinidon-ethyl is a Protox-inhibiting, peroxidizing herbicide which is effective through contact action in the green tissue of sensitive weed species. It is suggested that a more rapid metabolism, coupled with moderate leaf absorption, contribute to the tolerance of wheat to cinidon-ethyl. © 1999 Society of Chemical Industry  相似文献   

12.
It has been hypothesized that increased crop density and spatial uniformity can increase weed suppression and thereby play a role in weed management. Field experiments were performed over 2 years to investigate the effects of the density and spatial arrangement of spring wheat (Triticum aestivum) on weed biomass and wheat yield in weed-infested fields. We used three crop spatial patterns (normal rows, random and uniform) and three densities (204, 449 and 721 seeds m−2), plus a fourth density (1000 seeds m−2) in the random pattern. Increased crop density reduced weed biomass in all three patterns. Weed biomass was lower and crop biomass higher in wheat sown in the random and uniform patterns than in normal rows in both years. At 449 seeds m−2, weed biomass was 38% lower in the uniform and 27% lower in the random pattern than in rows. There was evidence of decreasing grain yield due to intraspecific competition only at 1000 seeds m−2. The results not only confirm that increasing density and increasing crop spatial uniformity increase the suppression of weeds, but also suggest that a very high degree of spatial uniformity may not be necessary to achieve a major increase in weed suppression by cereal crops. Rows represent a very high degree of spatial aggregation. Decreasing this aggregation increased weed suppression almost as much as sowing the crop in a highly uniform spatial pattern. While the random pattern produced as much crop biomass and suppressed weeds almost as well as the uniform pattern, the uniform pattern gave the highest yield.  相似文献   

13.
The dissipation of mecoprop in wheat (Triticum aestivum L.) and oat (Avena sativa L.) was monitored over a growing season following post-emergence application of the dimethylamine salt of mecoprop to each crop at 1·1 kg ha?1. Residues of mecoprop, as its methyl ester, were determined gas chromatographically using electrolytic conductivity detection. Initial residues in wheat (119 (±20) mg kg?1) and oat (95·3 (± 10·0) mg kg?1) on the day of application (four-leaf stage of wheat and four- to five-leaf stage of oat) decreased to 0·1 to 0·2 mg kg?1, respectively, within six weeks. Residues were non-detectable in the mature seed of both crops. Recoveries of mecoprop were in the order of 90% from the green tissue and seed of both crops fortified at 0·05 mg kg?1.  相似文献   

14.
  相似文献   

15.
Abstract

The tolerance of wheat and barley to 2, 4-D sprayed at six stages of growth, ranging from the 3-leaf stage up to the ripe grain stage, was studied. Five concentrations ranging from 500 to 8000 ppm (a.e.) of 2, 4-D were tested.

All the concentrations sprayed at the 3-leaf stage were phytotoxic to wheat and barley, whereas at the 5-leaf, jointing, and booting-to-heading stages, only 4000 and 8000 ppm were phytotoxic and caused lodging in the two crops. Reductions in plant height were significant at all concentrations used in the case of barley, and at 1000 ppm and above in the case of wheat.

The 8000 ppm treatment, applied at the jointing and anthesis stages, caused significant reductions in the grain yield of wheat; in the case of barley, significant reductions in the grain yield were observed at concentrations ranging from 2000 to 8000 ppm, sprayed at the 3-leaf, booting-to-heading, arid anthesis stages. At the 5-leaf stage, the 1000 ppm treatment gave a highly significant increase of 18.7% in the grain yield over the unweeded check. Significant reductions in the 1000-kernel weight and test weight of the two crops were observed only at the higher concentrations used.

The protein percentages of wheat and barley seeds were significantly increased as a result of the application of 2, 4-D at 2000 to 8000 ppm, sprayed at the 3-leaf, jointing, booting-to-heading, and anthesis stages of growth. However, significant reductions in the protein yield of the two crops were observed at these treatments. No significant effects were observed on the straw yield and germination percentages of wheat and barley as a result of 2, 4-D applications at the various stages of growth.  相似文献   

16.
The growth and competition of wild oats (Avena fatua L.) emerging at different times, and the time of onset of competition by them were studied using natural populations in spring barley. In one experiment in 1972, wild oats emerging in the 0–0?5, 0?5–2?5, 2?5–4 crop leaf stages at densities of 54, 46, 15 m ?2 respectively were allowed to compete all season with the crcp. These gave rise to 82, 17 and l% of all seed shed and caused 16%, and two non-significant yield losses respectively. In two other experiments in 1973, nearly all the wild oats that caused yield losses had emerged by the crop 2˙45 leaf stage. Where wild oats emerging up to the crop 2?5 leaf stage were removed, the later ones did not compensate by making extra growth. In one of these experiments in which densities of crop and weed were 416 and 414 m 2, and in the other where they were 295 and 294 m 2 respectively, grain yield losses were significant if the wild oats remained in the crop until the crop had 2?5–4?5 leaves and 4?5–6?5 leaves respectively. In a third experiment in 1973 with initial densities of 464 wild oats and 336 barley plants m ?2, and where a top dressing of nitrogen was given at the crop 3–4 leaf stage, unlike the other two experiments in 1973 where all nitrogen was applied at sowing, no yield losses resulted unless the wild oats remained in the crop until after the crop 6 leaf stage.  相似文献   

17.
Summary. Factors investigated included the susceptibility of Avena fatua L. at various stages of growth, the amount of moisture needed to activate di-allate in Regina heavy clay, the vapour action of di-allate in soil, the effect of organic matter on the availability of di-allate, and the persistence of di-allate and tri-allate in Regina heavy clay.
A. fatua sown at depths of 5–15 cm was killed by di-allate or tri-allate. as were seedlings treated at the 15–2-leaf stage. Seedlings of spring wheat ( Triticum aestivum L.) survived rates of 24 oz/ac if the shoots were 1–3 cm long prior to exposure.
When di-allate at 16 oz/ac was mixed with a 5 cm layer of Regina heavy clay (wilting point 19–6%) slightly less than 15% soil moisture was required to give complete control of A.fatua. Further experiments indicated that a large percentage of A. fatua seedlings were killed by the action of di-allate vapour in the soil.
In other tests the activity of di-allate and tri-allate was reduced when the percentage of organic matter in the soil was increased by adding peat. This could explain why there is little damage to wheat sown in treated soil of high organic content while similar rates can cause extensive damage in soils of low organic content.
Under comparable conditions tri-allate persisted for a longer period in the soil than di-allate. Both chemicals exhibited a lag period after which their breakdown appeared to follow a first-order reaction. Differences in the period of persistence were attributed to a much longer lag period and a slightly slower rate of biological breakdown for tri-allate as compared to di-allate.
Facteurs affectant l'activité du di-allate et du tri-allate  相似文献   

18.
A method is presented to quantify the net effect of disease management on greenhouse gas (GHG) emissions per hectare of crop and per tonne of crop produce (grain, animal feed, flour or bioethanol). Calculations were based on experimental and survey data representative of UK wheat production during the period 2004–06. Elite wheat cultivars, with contrasting yields and levels of disease resistance, were compared. Across cultivars, fungicides increased yields by an average of 1·78 t ha?1 and GHG emissions were reduced from 386 to 327 kg CO2 eq. t?1 grain. The amount by which fungicides increased yield – and hence reduced emissions per tonne – was negatively correlated with cultivar resistance to septoria leaf blotch (Mycosphaerella graminicola, anamorph Septoria tritici). GHG emissions of treated cultivars were always less than those of untreated cultivars. Without fungicide use, an additional 0·93 Mt CO2 eq. would be emitted to maintain annual UK grain production at 15 Mt, if the additional land required for wheat production displaced other UK arable crops/set aside. The GHG cost would be much greater if grassland or natural vegetation were displaced. These additional emissions would be reduced substantially if cultivars had more effective septoria leaf blotch resistance. The GHGs associated with UK fungicide use were calculated to be 0·06 Mt CO2 eq. per annum. It was estimated that if it were possible to eliminate diseases completely by increasing disease resistance without any yield penalty and/or developing better fungicides, emissions could theoretically be reduced further to 313 kg CO2 eq. t?1 grain.  相似文献   

19.
Isolates of Penicillium spp. were collected regularly from 2001 to 2003 from the surfaces of apple fruit pre- and postharvest, and from the atmosphere of orchards and storage rooms in France. Penicillium spp. were not detected from the atmosphere of conventional orchards, while their density did not exceed 50 spores m−3 in the atmosphere of organically managed orchards. Penicillium spp. were seldom detected on apple surfaces in the orchard. The density of Penicillium on apples increased from 10 to 50 spores cm−2 after 1 month in storage to 300–400 spores cm−2 after 6 months. The level of airborne Penicillium increased by up to 2 × 104 and 2·5 × 103 spores m−3 within nondisinfected and previously disinfected warehouses, respectively. Penicillium expansum (30–62%) and P. solitum (6–45%) were the most prevalent species on apple or in storage rooms. Other species of Penicillium isolated included P. commune, P. verrucosum, P. chrysogenum, P. rugulosum and P. digitatum. Apple fruit were also surveyed for wounds and the number of open lenticels using the sulphur dioxide test. The incidence of wounding at harvest varied from 12 to 36%, depending on cultivar and locality. When apples were inoculated at harvest by either aqueous or aerial inoculum of P. expansum, the decay incidence was constantly higher than the incidence of wounding. The number of open lenticels per cm2 of apple surface varied from 0·5 on cv. Boskoop to 4·4 on cv. Golden Delicious. An average of 13 and 2·1% of lenticels, respectively, were infected when they were inoculated by P. expansum and P. verrucosum. Cultivars of apple fruit that showed a greater number of open lenticels, combined with a large diameter varying from 100 to 200 µm, were more susceptible to P. expansum.  相似文献   

20.
A field experiment was carried out on bulk sorghum stored for 26 weeks in concrete silos in South Queensland. No natural infestation occurred. Laboratory bioassays of treated grain, in which malathion-resistant strains of insects were added to grain samples, indicated that all the treatments were generally effective. Deltamethrin (2mg kg−1)+piperonyl butoxide (8mg kg−1), fenitrothion (12mg kg−1)+fenvalerate (1 mg kg−1)+piperonyl butoxide (8mg kg−1), and fenitrothion (12mg kg−1)+phenothrin (2mg kg−1)+piperonyl butoxide (8mg kg−1) controlled typical malathion-resistant strains of Sitophilus oryzae (L.), Rhyzopertha dominica (F.), Tribolium castaneum (Herbst) and Ephestia cautella (Walker). Pirimiphos-methyl (6mg kg−1)+permethrin (1mg kg−1)+piperonyl butoxide (8mg kg−1) allowed some survival of adults and progeny production by S. oryzae after 12 weeks, and by one strain of R. dominica throughout. Chemical assays established that the residues and rates of breakdown of these grain protectants on sorghum conformed to the general pattern on other cereal grains. Residues at the conclusion of the experiment were below the individual Maximum Residue Limits recommended by the Codex Alimentarius Commission.  相似文献   

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