摘要:

SUMMARYThe distribution of the egg stage of the cabbage root fly around brassica plants was studied at Wellesbourne on 0.05–0.4 ha plots during 1970 and 1971.The three generations of flies occurred at similar times in both years and the numbers of eggs collected generally decreased from the first to the third generation. Differences between generations demonstrated that each generation should be treated separately. The number of plant samples required for a given level of precision increased from the first to the third generation, indicating that experiments relying on egg counts should be planned to coincide with the first generation whenever possible. A sampling plan for the range of oviposition normally encountered during the three generations is illustrated for both one‐ and five‐plant samples. For the same level of precision, estimates of the populations from five‐plant samples required only 50% to 80% of the time of those from one‐plant samples. When aestivation occurs the peak of oviposition in the second generation is difficult to determine, and designed experiments should not be undertaken. The negative binomial distribution failed to describe the clumping of the eggs for a complete generation, since a commonkcould not be fitted to the data. The distribution of the eggs was best described by Taylor's power law which showed that although sampling factors changed with generation, the value of the power did not. A value of 1.4 appears to be the index of aggregation characteristic of the egg stage of thi

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1975.tb01516.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYSurveys of pest incidence on oil‐seed rape in the south of England in 6 yr have shown thatMeligethes aeneuscan cause a considerable loss of pods on some fields. There is some evidence that control measures are often applied too late to obtain the best results; preliminary observations on the probable effect on yield are also presented.Ceuthorhynchus assimiliswas recorded on the majority of fields with an average of 19% pods infested on spring‐sown rape. Very heavy pod infestations were found on farms where rape had been grown regularly for some years.Dasyneura brassicaeis at present not an important pest with an average of less than 1% pods infested. However, in each year infestations of up to 11% pod attack were recorded on a few fie

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1975.tb01517.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYField‐caged, post‐anthesis populations of the aphidsSitobion avenaeandMetopolophium dirhodumreduced grain weight of wheat by 14 and 7% respectively and induced changes in the senescence of the flag leaf. Spikelet number and grain number were unaffected as they are normally determined by pre‐anthesis factors. Percentage grain protein was significantly reduced by both aphid species.The pattern of grain weight reduction within the ear was consistent with known limitations on the distribution of flag leaf assimilates among the grains. The relative effects of the two aphid species apparently resulted from the degree of nutrient drain imposed at particular feeding sites and the reduction in the leaf area duration of the flag

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1975.tb01518.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYIn experiments on the control ofMycogone perniciosathere was a good relationship between yield, disease incidence and the rate of benomyl applied to the casing. Casing treatment controlled the disease irrespective of time of inoculation. Benomyl controlled the disease in all experiments and good results were also achieved with thiophanate methyl and to a lesser extent with thiabendazole. Bioassay of sporophores showed the presence of an inhibitory substance from benomyl and thiophanate methyl treatments even after 6 wk of cropping.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1975.tb01519.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYIn glasshouse experiments, isolates ofFusarium nivale, applied as mycelial macerates, caused marked reductions in the number and length of roots, and in the height and fresh weight of S. 321 perennial ryegrass seedlings. Spore inocula failed to cause infection.Damage byF. nivalewas increased when inoculation was immediately followed by four alternate 12 h periods in a growth cabinet at 0°C and in a warm glasshouse atc.17°C, succeeded by a further 11 days in the same glasshouse.Although inoculated seedlings receiving no cold treatments initially showed damage, regrowth of roots and some recovery of the shoots occurred in a fortnight. Exposure of the plants after that time to four intermittent 12 h periods at 0°C, however, arrested their recovery and caused further root damage.The implication of these results in the importance of low temperature in the winterkill syndrome is discuss

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1975.tb01520.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYSoil from twelve of twenty‐six sites on ten nurseries growing ornamental trees and shrubs contained viruliferous nematodes, transmitting arabis mosaic virus (AMV) at eight sites, tomato black ring virus at three and tobacco rattle virus at one site. Tobacco necrosis virus was detected at two sites.Xiphinemaspp. were found at nine sites,Longidorusspp. at sixteen andTrichodorusspp. at thirteen sites. Thirty‐one ornamental species of Rosaceae were tested for virus infections and AMV was found inSpiraea bumalda, Spiraea japonica albaandKerria japon

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1975.tb01521.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYDefoliation reduced the dry weight of stems, pods, grains and size of individual grains in all four of the legume crops studied and the dry weight of flowering inflorescence stalk in the case of cowpeas and green gram only. The adverse effect of defoliation was more pronounced when defoliation was complete than when half of the number of leaves were removed. The greatest reduction in grain yield occurred when the plants were defoliated during the early podding stage, the percentage reduction being 59.7, 79.0, 86.4 and 95.3 in groundnut, cowpeas, soyabeans and green gram respectively when completely defoliated at this stage and 43.3, 14.0, 42.4 and 46.1 respectively when only half defoliated. The results show that assimilates produced by the leaves during the early stages of growth are used in the growth of stems and leaves, but the assimilates produced during the reproductive stage are used mainly for the growth of the pods. In groundnut, pod number and grain weight were positively correlated with stem weight. It appears that defoliation reduced pod number by depressing the growth of stems and this in turn reduced the number of flowering nodes.The reasons for the differences between the crops in their response to the defoliation treatments and the practical implications of the findings in relation to pest and disease control and plucking of leaves for human consumption are discussed.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1975.tb01522.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYLolium perenneselection lines with high calculated stomatal resistances to diffusion (rs) as a result of either few or short stomata, maintained leaf extension rates and photosynthetic rates longer than selection lines with low resistances when deprived of water. There were no significant differences between high and lowrsplants in light saturated CO2uptake of turgid attached leaves.When grown in soil drying to 21% moisture, plants with lowcalculated rsexhibited lower minimum leaf resistances (rl) than those with high, measured with a diffusion porometer, on all except the last day. The daily maximumrl(1.5 h after the start of the light period) became greater among low than highrsplants as the difference in rate of leaf extension between the two groups of plants increased with drying soil. Rate of leaf extension was negatively correlated with daily maximumrland started to decline when relative leaf water content (RLWC), at 5 h after the start of the light period, fell below about 88%. Transpiration rate of plants grown in different soil moisture regimes was correlated (r=+ 0.83,P<0.01) with mean maximum adaxial leaf conductance (reciprocal of resistance). There was a highly significant correlation (r=+ 0.62,P<0.01) betweencalculatedadaxialrsand mean minimum measuredrlamong plants growing at high or intermediate soil moisture, but not at low. Therefore, some random variation in minimumrl, even with adequate moisture, seemed to be unaccounted for by variation in stomatal numbers or size. Selection for increased numbers of adaxial stomata also resulted in more on the abaxial surface, but mean adaxial/abaxial ratio in the ‘frequent’ stomata plants was still only about

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1975.tb01523.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYGroups ofLolium perenneplants selected for either deep or shallow adaxial epidermal ridging were grown in a 16 h day of 70 W m‐2at 25°C, and either watered daily to 33% or allowed to dry to and then watered daily to 21% or to 16% soil moisture. During a 9 day experimental period, adaxial leaf resistances (r1) were measured with a diffusion porometer four times daily, transpiration was estimated gravimetrically, and daily rates of leaf extension were recorded.Measurements were also made of minimum abaxial resistances, stomatal frequencies and lengths, and relative leaf water content (RLWC). At 33%, 21% or 16% soil moisture, leaf extension rates of deep ridged leaves were, respectively, slower, the same, and more rapid than those with shallow ridges. At 21% or 16% soil moisture, the adaxialrlof deep‐ridged was much lower than that of shallow‐ridged leaves at all four sampling times. This difference was most marked on leaves below the youngest fully expanded, and was observed among older leaves even when plants were well watered. At low RLWC (<85%), leaf resistance was greatest in leaves with shallow ridges. There was no significant difference between the leaf types in the calculated contributions of stomatal frequency or of morphology at any one pore opening, torlbut deep‐ridged leaves had more stomataonthe abaxial surface. Daily rate of plant water loss was directly correlated (r=+ 0.86,P<0.01) with mean daily maximum stomatal conductance (1/rl), and rate of leaf extension negatively with maximumrl. It is suggested that stomata operating in the concavity formed by deep ridges open wider and are less responsive to internal changes in, for example, leaf water status, than those on shallow‐ridged leaves because of a more humid microenvironment at the epidermal surface. The results are discussed in relation to the concept of ‘water‐savers’ and ‘water‐spenders’ and its application to breed

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1975.tb01524.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYIn field experiments on a sandy loam at Wellesbourne, England in 1972 and on a silt loam at Agassiz, British Columbia in 1973, combinations of herbicides and insecticides were applied at sowing to determine their effects on weeds and invertebrate populations and on the growth and yield of cauliflowers grown at high densityThere was good agreement between the results from the two locations. The two combinations of herbicides, 0.6 kg trifluralin/ha incorporated pre‐drilling plus 2.2 kg propachlor/ha pre‐emergence and 2.2 kg nitrofen/ha plus 2.2 kg propachlor/ha both applied pre‐emergence, gave good weed control, their relative effectiveness depending on the species composition of the weed population. The insecticides isophenphos, carbofuran, chlorfenvinphos and fensulfothion were applied as bow‐wave treatments. None of them, whether in combination with herbicides or not, adversely affected crop stand or yield. Yield was reduced when either weeds or root‐fly maggots (Hylemya brassicae(Bouché)) were not controlled.Only in one experiment was there any evidence of any herbicide‐insecticide interactions. Where trifluralin and carbofuran were applied together at Agassiz, the control of both weeds and maggots was less than that with the other combinations. None of the treatments affected the populations of predatory beetles, but the numbers of earthworms were greatly reduced by carbofuran and to a lesser extent by chlorfenvinphos. Except for carbofuran in one experiment, the treatments had no effects on the numbers of aphids, lepidopterous larvae or leaf miners presen

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1975.tb01525.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY