Economic damage by Limothrips denticornis in rye, triticale and winter barley

Abstract:  Limothrips denticornis is a common thrips infesting rye, triticale and winter barley in Sweden. Field experiments with insecticides were carried out 1983–1996 in farmers' fields to investigate the damage to the plant and to evaluate the relationship between thrips density and crop yield losses. The total number of experiments was 99 in rye, 41 in triticale and nine in winter barley. The mean number of thrips per leaf sheath was around 8 in all three crops. The highest number found was 27 thrips per leaf sheath. The population density in the leaf sheath was correlated with the damage observed on the leaf sheath as percentage damaged surface. The effect on the leaf sheath alone contributed to a significant proportion of the yield loss. Thrips in the ear and aphids also contributed to the damage but with multiple regression methods it was possible to estimate the damage done solely by L. denticornis . The yield loss caused by L. denticornis was about the same in all three crops, with a variation between 21 and 26 kg per thrips per leaf sheath and hectare. Compared with the yield loss for aphids, which is about 40 kg per aphid per tiller and hectare, this is considerably lower. The economic injury level was found to be about 14 thrips per straw. The economic threshold for L. denticornis has to be decided when the females are flying into the crop and it was found to be 0.5 females per straw at earing. Economic damage by L. denticornis alone was estimated to be 20% of the total number of experiments for all three crops but economic damage for the three pests together was estimated at 40% of the total number of experiments.     

Nutrient levels in corn and competing weed species in a first year milpa,Indian church,Belize, C.A.

Summary Grain production in two 1/4 hectare plots gave 2971 and 1380 kg/ha for an average yield of 2175 kg/ha. Average yield for local farmers was 1700 kg/ha. Weed biomass accounted for 50% of total bioomass in the hydric Site 4, but held 64–83% of the total nutrients. In the mesic Site 1, values were 5% and 3–29% respectively.Canna edulis was the most abundant weed species. Soil nutrient levels neither increased or decreased significantly between clearing and harvesting. Any decline in future crop production would be due to increased weed competition and not a decline in soil fertility. Weevil (Sitophilus zeamais) infestation is a serious problem in hybrid corn not encountered with local varieties.     

Response of eight sugarcane cultivars to glyphosine and glyphosate ripeners

Studies were conducted on eight sugarcane (Saccharum spp. hydrid) cultivars during the 1982–83 (plant crop) and 1983–84 (ratoon crop) growing seasons to determine the effects of glyphosine (Polaris) (N,N-bis (phosphonomethyl) glycine) and glyphosate (Polado) (sodium-N-(phosphonomethyl) glycine) on stalk sucrose content and yield. Difference due to crops (plant vs. ratoon) for sugarcane quality, kilograms of sugar per ton of cane (S/T), sugarcane yield, tons of cane per hectare (TCH), and sugar yield, tons of sugar per hectare (TSH) were significant. Significant differences were found in quality for the ratoon crop and cane and sugar yield in both crops due to ripener treatment. Cultivars in both crops differed significantly in quality and yield. Harvest dates were significantly different for all plant characteristics. Interactions of cultivar by treatment for the plant crop, harvest date by treatment for the ratoon crop, and cultivar by harvest date for both crops for cane quality also were significant. Time from ripener application to achievement of maximum sugar concentration also depended on cultivar. This is important in determining the economic benefits of a ripener treatment. Climatic conditions may also affect the benefits of such applications.Mention of trade name or proprietary product does not imply or constitute an endorsement or recommendation by the USDA or the University of Florida.     

Effect of Brassica carinata (L.) biofumigants (seed meal) on chickpea wilt (Fusarium oxysporum f.sp. ciceris), growth,yield and yield component in Ethiopia

Pot experiments were carried out in the green house at Amhara Regional Agriculture Research Institute (ARARI) Bahirdar, Ethiopia to evaluate the potential of Brassica carinata cultivars namely; Holleta-l, S-67 and Yellow Dodola in 2007 and 2008. The treatment effects of B. carinata (L.) cultivars Holleta–1, S-67 and Yellow Dodola seed meals on chickpea fusarium wilt (Fusarium oxysporum f.sp. ciceris) were studied. Six rates of seed (0, 5, 10, 15, 20 and 25 g/kg of infested soil) were used. Infested soil without B.carinata cultivars amendments as a control and susceptible check variety JG-62 also without amendments were used in all the experiments. For each seed meal experiment, the treatments were arranged in factorial randomised complete block design in three replications. Data on seedling emergence, wilt incidence, fresh weight, dry weight, pod per plant, seed per pod, hundred seed weight and yield per hectare were collected. The amendments of infested soil with B.carinata cultivars seed meal reduced the incidence of chickpea fusarium wilt and increased yield per hectare. The interaction of the seed meal Holleta-1, S-67 and Yellow Dodola at 10–25 g/kg infested soil were effective in reducing wilt incidences on chickpea. However, the interaction of Yellow Dodola with 20 and 25 g seed meal per kg infested soil were the best combination in reducing significantly wilt incidence. The three cultivars incorporated at different level of doses significantly affected the influence of Fusarium wilt on the fresh weight, dry weight, pod per plant, seed per pod, hundred seed weight and yield per hectare. The highest yield kg/ha was recorded in combination of Yellow Dodola seed meal at 20 and 25 g followed by S-67 and Holleta-1 at 25 g /kg infested soil, respectively. The interaction of Holleta-1 at 5–25 infested soil significantly reduced disease incidence up to 16.7–43.3% and increased yield per hectare with mean by (30%) over the control. Seed meal amendment S-67 significantly reduce disease incidence 26.7–46.7% and increased yield kg/ha with mean by (36.7%) from the unamended control. Yellow dodola reduces disease incidence with 26.7–63.3% and increased yield kg/ha with mean by (45%) from the unamended control. The result indicates the potential of using Brassica crop seed meal amendment as useful component of integrated chickpea wilt management.     

Stinkbug complex of soybean glycine max (l.) Merrill and the importance of insecticidal control in the northern guinea savanna area of Nigeria

Field experiments were conducted in Samara for a two year period (1996 and 1997) to identify the major pod sucking bugs of soybean and to determine the effect of insecticides and frequency of application on the bugs and soybean yield. Nezara viridula L. Halydicoris ventralis Dall. Sphaerocoris annulus Fab. and Agonoscelis versicolor Fab. were the major bugs and their population were less than two bugs per plot. Also, insecticides and frequency of spray application had no significant effect on the pod sucking bugs population, percentage damage pods, seed damage index, 100 seed weight and seed yield per hectare. Hence, except the status of the pod sucking bugs population in this area of study changes significantly (possibly due to the influence of environmental factors and cropping patterns) soybean may be grown in this area with no insecticidal protection.     

How does plant population density affect the biomass of Ravenna grass?

Ravenna grass, Tripidium ravennae (L.) H. Scholz, is known to produce an abundance of biomass, but how plant density affects its biomass potential remains unknown. The objectives were to determine the effects of plant density on biomass yield; plant growth traits; biomass?carbon, nitrogen, and ash concentrations; heating value; nitrogen removal; and sucrose concentration in leaves and culms. The treatments consisted of five plant densities (1,250; 2,500; 5,000; 10,000; and 20,000 plants per hectare) in a randomized complete block design with four blocks. Plots were nonirrigated, unfertilized, and harvested once during the dormant season each year. Data were collected from 2015?2019. Dependent variables that varied with plant population density (p < .05) were biomass yield, number of reproductive culms per plant, reproductive culm diameter, reproductive culm sucrose concentration, and nitrogen removal with biomass. Biomass yield ranged from 5.6 to 16.3 Mg/ha for plant densities of 1,250–20,000 plants per hectare, respectively. Combined over years, nonlinear regression of the data showed the equation for biomass yield to plateau at 16.2 Mg/ha at a plant density of 10,640 plants per hectare. As plant density increased, the number of reproductive culms per plant, culm diameter, and culm sucrose concentration significantly decreased. At 1,250 plants per hectare, the number of reproductive culms per plant, culm diameter, and culm sucrose averaged 70, 10.2 mm, and 63.2 g/kg, respectively. Nitrogen removed with biomass significantly increased as biomass yield increased with plant density. At a density of 10,000 and 20,000 plants per hectare, the amount of nitrogen removed annually in the harvested biomass averaged 88 kg/ha. The data suggest that 10,000 plants per hectare would produce the greatest annual biomass yields; however, research is needed to determine the nutrient requirement for Ravenna grass to sustain biomass production at that density.     

China's success in increasing per capita food production

China has to feed 20% of the global population with only about 5% of the planet's water resources and 7% of its arable land. With such limited natural conditions, however, China's grain production has increased from about 200 kg per capita in 1949 to about 400 kg in the early 1990s. Hunger as a social problem has largely disappeared after being prevalent in China for several thousand years with the rise and decline of dynasties. This achievement has been accompanied by a 2.5-fold increase in the population and a 4.5-fold increase in total grain production. Although total cropped land has increased slightly in some areas, land used for cropping has decreased from 0.18 hectare per capita in the 1950s to less than 0.1 hectare per capita today. Apparently, yield increase or improved land productivity is the major contributor to the increase of food production per capita. What are the major reasons for the unprecedented achievement in China's food production? Political decisions, good or bad, on land distribution and ownership changes, have caused unusual fluctuation in grain production. Technical progress, however, has maintained a long-term increasing trend. The semi-dwarf cultivars of rice and wheat, the use of heterosis in rice and maize, and the alleviation of salinized soil stress in the major grain-producing areas have all played significant roles in increasing China's food production capability.     

Sampling and distribution pattern of Trioza erytreae Del Guercio, 1918 (Hemiptera: Triozidae) in citrus orchard

Developing efficient sampling protocols is essential to monitor crop pests. One vector of the citrus disease HLB, the African citrus psyllid Trioza erytreae Del Guercio, 1918 (Hemiptera: Triozidae), currently threatens the lemon industry throughout the Mediterranean region. In this work, a pool of sampling methods devoted to monitoring the population of T. erytreae was compared, its spatial distribution in the orchard was assessed, and the minimum sampling effort for the best sampling method was estimated. Three lemon orchards in North-western Portugal were sampled for one year using two types of yellow sticky traps (standard yellow and fluorescent Saturn yellow), B-vac sampling and sweep net sampling. The method that best performed, in terms of cost-efficiency, was the yellow sticky traps. The two colours of the sticky traps tested did not yield a significantly different number of catches. The spatial distribution throughout the orchards was found to be aggregated towards the borders. A minimum of three sticky traps per hectare was found to be enough to estimate the population at 90% accuracy for the mean during the outbreak. These results should help to monitor and anticipate outbreaks that may even colonize neighbour orchards. Studies on the local dispersion patterns of T. erytreae throughout the orchard are mandatory to further refine and optimize efficient monitoring protocols.     

Methane yield from switchgrass and reed canarygrass grown in Eastern Canada

Methane yields from silage made from switchgrass- and reed canarygrass-seeded plots with two N application rates and three harvest dates were assessed in Eastern Canada. The average specific methane yield from reed canarygrass-seeded plots (0.187 NL CH4 g VS(-1)) was less than from switchgrass-seeded plots (0.212 NL CH4 g VS(-1)). Switchgrass did not establish well and made up only a small proportion of the DM yield. As a consequence, the average methane yield per hectare from reed canarygrass-seeded plots (1.37 GL CH4 ha(-1)) was significantly greater than switchgrass-seeded plots (0.91 GL CH4 ha(-1)). Increased N fertilization reduced specific methane yields but increased methane yield per hectare, primarily because of increased DM yield. Delaying harvest resulted in decreased methane yields per hectare and specific methane yields, particularly for reed canarygrass. Further long-term research could help identify important factors influencing methane yields from crops during a complete stand life cycle.     

Rotylenchulus reniformis Management in Cotton with Crop Rotation

One-year crop rotations with corn or highly resistant soybean were evaluated at four locations for their effect on Rotylenchulus reniformis population levels and yield of a subsequent cotton crop. Four nematicide (aldicarb) regimes were included at two of the locations, and rotation with reniform-susceptible soybean was included at the other two locations. One-year rotations to corn or resistant soybean resulted in lower R. reniformis population levels (P ≤ 0.05) than those found in cotton at three test sites. However, the effect of rotation on nematode populations was undetectable by mid-season when cotton was grown the following year. Cotton yield following a one-year rotation to resistant soybean increased at all test locations compared to continuous cotton, and yield following corn increased at three locations. The optimum application rate for aldicarb in this study was 0.84 kg a.i./ha in furrow. Side-dress applications of aldicarb resulted in yield increases that were insufficient to cover the cost of application in 3 of the 4 years.     

Impact of density of Aphis craccivora (Aphididae) on growth and yield of susceptible and resistant cowpea cultivars

Impact of initial density of cowpea aphid Aphis craccivora Koch (Aphididae) at infestation on the growth and yield of aphid-susceptible cowpea cultivar ICV-1 and aphid-resistant cultivar ICV-12, was investigated. Plants at the seedling, flowering and podding stages of development were infested with five aphid densities consisting of 0, 2, 5, 10 and. 20 aphids per plant and maintained for 22 days. Extended leaf heights of plants and aphid counts were recorded at 7, 12, 17 and 22 days after infestation. Two crop growth parameters (biomass duration and leaf area duration), and two plant yield parameters (number of pods per plant and number of seeds per pod) were recorded. Due to the occurrence of parthenogenesis and changes in population dynamics during infestations, aphid densities were converted into cumulative cowpea aphid-days, to facilitate data analyses and interpretation. ANOVA indicated that there was significant (P=s 0.05) difference in aphid-day accumulations between the two cultivars when infested at the seedling stage. Accumulations on cv. ICV-1 were greater than on cv. ICV-12. However, no such differences between the cultivars were detected when plants were infested at flowering and podding stages. Therefore, the seedling stage was used for comparisons of the impact of cowpea aphid-days on the growth and yield parameters of the two cultivars. At the 95% confidence intervals, ICV-12 plants were consistently taller than ICV-1 plants. Infested ICV-1 seedlings showed stunting and other growth deformities which were not observed on ICV-12 plants. Regression analyses revealed substantial reductions in the growth and yield parameters of ICV-1 relative to ICV-12. Overall, cowpea aphid-days provided a convenient and reliable method for studying the aphid population dynamics and the subsequent impact on plant growth and yield performance.     

Development of mating disruption for control of pine sawfly populations

Mating disruption of the pine sawflyNeodiprion sertifer (Geoffroy) (Hymenoptera: Diprionidae) was strongly indicated by reduced male trap catches in pine plantations permeated with the sex phermone, (2S, 3S, 7S)-diprionly acetate. The trap catch reduction was 95 to near 100% when dispensers every 10 m were used, giving a total release of about 3 mg per hectare and day. Two mg of pheromone per cotton roll dispenser maintained low catches for the whole season (about 2 months) without any renewal of disruption dispensers. Anerythro-mixture was as effective as the pure pheromone isomer. The effects of the experiments on population density and sex ratio were not possible to investigate, due to a general collapse of the population, also outside experimental plots, the year after the experiments.     

Response of eight sugarcane cultivars to glyphosine and glyphosate ripeners

Studies were conducted on eight sugarcane (Saccharum spp. hydrid) cultivars during the 1982–83 (plant crop) and 1983–84 (ratoon crop) growing seasons to determine the effects of glyphosine (Polaris) (N,N-bis (phosphonomethyl) glycine) and glyphosate (Polado) (sodium-N-(phosphonomethyl) glycine) on stalk sucrose content and yield. Difference due to crops (plant vs. ratoon) for sugarcane quality, kilograms of sugar per ton of cane (S/T), sugarcane yield, tons of cane per hectare (TCH), and sugar yield, tons of sugar per hectare (TSH) were significant. Significant differences were found in quality for the ratoon crop and cane and sugar yield in both crops due to ripener treatment. Cultivars in both crops differed significantly in quality and yield. Harvest dates were significantly different for all plant characteristics. Interactions of cultivar by treatment for the plant crop, harvest date by treatment for the ratoon crop, and cultivar by harvest date for both crops for cane quality also were significant. Time from ripener application to achievement of maximum sugar concentration also depended on cultivar. This is important in determining the economic benefits of a ripener treatment. Climatic conditions may also affect the benefits of such applications.     

Effect of tobacco budworm (Lepidoptera: Noctuidae) infestation level on budworm-resistant and -susceptible varieties of flue-cured tobacco in North Carolina

Field experiments were conducted from 1972 to 1978 and from 1998 to 1999 to evaluate tobacco budworm, Heliothis virescens (F.) (Lepidoptera: Noctuidae), larval feeding on flue-cured tobacco, Nicotiana tabacum (L.), yield in eastern North Carolina. In the earlier studies, using variety Coker 319, treatment plots were evaluated when either 0 or 100% of plants in a plot were infested with H. virescens larvae. Treatment differences based on actual yield loss (kilograms per hectare) were compared with estimations of yield loss based on leaf consumption and leaf loss. Results indicate actual yield loss when 100% of plants were infested was less than the corresponding estimates of yield loss. In the later experiments, two tobacco budworm-resistant lines, 'CU 263' and 'CU 370', were compared with a commercial susceptible variety, K 326, when 0, 10, 20, or 40% of plants were infested (1998) and 0, 10, 40, 75, or 100% of plants were infested (1999). Although significant increases in leaf equivalents consumed were associated with infestations exceeding the recommended threshold, differences were not detected for yield (kilograms per hectare), quality (dollars per kilogram), and value (dollars per hectare) within each tobacco line. Additionally, there was not a significant correlation between value and infestations level for any of the tobacco lines. These results provide economic support for tolerance of a higher treatment threshold. Although K 326 sustained more leaf equivalent loss than CU 263 and CU 370, the value of K 326 harvested was higher than that of CU 263 and CU 370. To justify use of resistant varieties, the combination of pest pressure and the benefit of host plant resistance must be greater than the capacity of a susceptible variety to produce competitive yields, despite sustaining significantly higher loss.     

The effect of Banana streak virus on the growth and yield of dessert bananas in tropical Australia

We have examined the effect of a strain of Banana streak virus (BSV‐Cav) on the growth and yield of dessert bananas (Musa AAA group, Cavendish subgroup cv. Williams) in north Queensland, Australia. Healthy and infected plants were compared in a replicated field experiment over plant and first ratoon crops. In both crops, symptom expression followed a similar pattern, increasing to a maximum near the estimated time of bunch initiation, then decreasing in the period prior to bunch emergence. There was no evidence of plant‐to‐plant spread of virus, but the rate of transmission through suckers was 100%. In the plant crop, the mean bunch weights of healthy and infected plants were not significantly different. However, BSV‐Cav infection resulted in an 18 day delay in harvest, causing a 6% reduction in yield per annum. In the ratoon crop, the mean bunch weight of infected plants was 7% less than that of healthy plants, and the interval between the harvest of plant and ratoon crops was delayed by 9 days, resulting in a 11% reduction in yield per annum. Also, the mean length of fruit from infected plants was 5% less than that of healthy plants, resulting in a smaller percentage of fruit in the extra large size category. We conclude that in horticulturally favourable conditions typical of the tropical Australian banana industry, the effects of BSV‐Cav infection on the growth and yield of Cavendish bananas are small.     

Foliar boron applications increase the final number of branches and pods on branches of field-grown soybeans

Our previous work demonstrated that boron (B) supplied to soybeans (Glycine max [L.] Merrill cv `Williams 82') by a stem infusion technique increased the number of pods on branches and led to a significant yield increase. Therefore, research was continued to determine whether soil or foliar applications of B could be used to achieve the same results. Field experiments were completed with both soil and foliar applications of B. Only the foliar applications of B resulted in a significant increase in the number of pods/branch. When split foliar treatments were applied twice during flowering, the total application of 0.56 kilograms of B per hectare was the optimal treatment for increasing pods/branch. In a second field experiment in 1987, soybeans were treated weekly from flowering through podfill with six split foliar applications of aqueous H₃BO₃ solutions so that total applications were either 0, 1.1, or 2.24 kilograms of B per hectare. Foliar applications increased the number of branches/plant at the end of the season and significantly stimulated the formation of pods on branches, with 1.12 kilograms of B per hectare being the optimal treatment for these variables. This rate also tended to increase the number of seeds/plant and seed yield/plant. A duplicate experiment with minor modifications was conducted during the summer of 1988, and again the 1.12 kilograms of B per hectare application rate resulted in significant increases in number of branches at harvest as well as number of pods on branches. The 2.24 kilograms of B per hectare application rate also significantly increased these parameters. Foliar B applications induced increases in leaf B concentration far above the 60 micrograms per gram level that was previously accepted as the upper level of tolerance for soybeans. Since optimal branching and per plant yield parameters were achieved by plants with B leaf concentrations greater than 160 micrograms per gram, the accepted range of soybean tolerance for B must be reconsidered when B is foliarly applied.     

Effects of preplant inoculation of apple (Malus domestica Borkh.) with arbuscular mycorrhizal fungi on population growth of the root-lesion nematode,Pratylenchus penetrans

Six species of arbuscular mycorrhizal (AM) fungi (Glomus aggregatum, G. clarum, G. etunicatum, G. intraradices, G. mosseae and G. versiforme) were evaluated, in three greenhouse experiments, for their effects on reproduction of the root-lesion nematode, Pratylenchus penetrans, and growth of Ottawa 3 apple rootstock. Glomus mosseae increased total dry weights of nematode-inoculated and non-inoculated rootstock in all three greenhouse experiments, and G. intraradices increased dry weights in two of three greenhouse experiments. Plants inoculated with G. mosseae generally supported fewer P. penetrans per gram of root than plants inoculated with other AM fungi, but did not differ significantly from the controls in any greenhouse experiment. Colonization of roots by AM fungi was reduced by P. penetrans at initial inoculum densities greater than 250 nematodes/L soil. In field trials, preplant inoculation with either G. intraradices or G. mosseae increased rootstock growth and leaf concentrations of P, Mg, Zn and Cu in fumigated plots but not in non-fumigated plots, indicating that colonization by native AM fungi in non-fumigated plots may have been sufficient for adequate nutrient acquisition. The abundance of vesicles and arbuscules was greater in roots of plants inoculated with AM fungi before planting than in roots of non-inoculated plants, in both fumigated and non-fumigated plots. P. penetrans per gram of root and per 50 ml soil were significantly lower for G. mosseae- inoculated plants than for non-inoculated plants in fumigated soil but not in non-fumigated soil.     

Genetic analysis of physiological components of salt tolerance conferred by Solanum rootstocks. What is the rootstock doing for the scion?

Grafting desirable crop varieties on stress-tolerant rootstocks provides an opportunity to increase crop salt tolerance. Here, a commercial hybrid tomato variety was grafted on two populations of recombinant inbred lines developed from a salt-sensitive genotype of Solanum lycopersicum var. cerasiforme, as female parent, and two salt-tolerant lines, as male parents, from S. pimpinellifolium, the P population, and S. cheesmaniae, the C population, to identify an easy screening method for identifying rootstocks conferring salt tolerance in terms of fruit yield. Potential physiological components of salt tolerance were assessed in the scion: leaf biomass, [Na⁺], nutrition, water relations and xylem ABA concentration. A significant correlation between scion fruit yield and scion leaf fresh weight, water potential or the ABA concentration was found in the C population under salinity, but the only detected QTL did not support this relationship. The rootstocks of the P population clearly affected seven traits related to the sodium, phosphorous and copper concentrations and water content of the scion leaf, showing heritability estimates around 0.4 or higher. According to heritability estimates in the P population, up to five QTLs were detected per trait. QTLs contributing over 15% to the total variance were found for P and Cu concentrations and water content of the scion leaf, and the proportion of fresh root weight. Correlation and QTL analysis suggests that rootstock-mediated improvement of fruit yield in the P population under salinity is mainly explained by the rootstock’s ability to minimise perturbations in scion water status.     

Intra-specific mechanisms in relation to the natural regulation of numbers of Aphis fabae Scop

Parthenogenetic virginoparous apterae of Aphis fabae Scop. on field beans (Vicia faba) reproduced faster initially in populations of eight colonizing apterae than in those with 2–4 or 16–32 per plant. The aphids were at first mutually benefited but were quickly affected by competition as numbers rose above the critical density represented by about eight apterae and their first progeny. This is because the aphids remained densely aggregated and seemingly created a local shortage despite abundant food and space elsewhere on the plant. Such self-induced competition provides the basis for self-regulation of numbers of A. fabae in relation to (1) food and space provided by the growing plant and (2) mortality from natural enemies and from other causes including insecticides. As competition increased, the multiplication of A. fabae populations slowed, newly formed adult apterae emigrated and increasing numbers of alatae were formed. The mean weights of apterae decreased from about 1·8 mg. to 0·3 mg. and of alatae from 0·9 to 0·2 mg. Such decrease probably favours production of many adults that might otherwise fail to mature. Experiments in a glasshouse and in field cages indicated the success with which an A. fabae population adapts to and exploits a growing plant. Field bean plants sown in mid-March and infested as in the field produced an average of 15,000–17,000 A. fabae emigrants per plant of which 78–84% were adults (mostly alatae). This is equivalent to about 1600 million alate emigrants from 1 acre (0·4 hectare) of an infested field bean crop.     

The invertebrate population and response to pesticide treatment of two permanent and two temporary pastures

During 1979 and 1980 the herbage yields of two permanent pastures and two temporary swards were compared. All four swards received 250 kg N/ha per yr. The invertebrate population of all four swards was studied. Pot-worms (Enchytraeidae) and some species with long life cycles, e.g. wireworms (Agriotes spp.) were more numerous in the permanent swards, but aerial species were more numerous in the temporary swards. A range of pesticide treatments was applied. At one temporary sward site, application of the broad-spectrum pesticide aldicarb increased total annual yield of herbage by 16% in 1979 and 33% in 1980. Insecticide application at the same site resulted in no increase in herbage yield in 1979 and 12% yield increase in 1980. At the other three sites no significant increases in total annual yield were recorded in either year, but there were significant responses at one harvest or more at every site.