The seasonal response of Italian and hybrid ryegrasses to the control of frit fly, Oscinella frit

In years of relatively high frit fly activity the control of all generations produced increases averaging 0×44 t d.m. ha^-1 in annual yield of Italian and hybrid ryegrass. A cutting programme designed to make the sward especially vulnerable to frit fly attack did not increase the total annual effect of pesticide treatment but accentuated the periods at which damage occurred. The annual yield increase was almost entirely obtainable by controlling the second and third frit fly generations, but even one treatment for this purpose was of doubtful economic justification. The prospect of augmenting the response to control of later-occurring pests, such as leatherjackets or eriophyid mites, by including the part of the frit fly response which is recoverable by the same treatment, was a more probable justification for pesticide usage. There was some evidence that a Westerwold and a hybrid cultivar suffered more damage than an Italian ryegrass cultivar, but pesticide treatment did not improve the persistence of any cultivar.     

The effect of frit fly Oscinella frit on the yield and persistence of Italian and hybrid ryegrasses in the laboratory

Three cultivars of Italian or hybrid ryegrass were exposed to frit fly attack at varying frequency in the laboratory. Initially a Westerwolds and a hybrid cultivar showed greater yield reductions than an Italian ryegrass cultivar, although they did not usually suffer a higher proportion of damaged tillers. The differing effect on yield appeared to be due mainly to greater impact of first or infrequent attacks on cultivars producing fewer tillers. After two to six attacks in approximately 7 months the Westerwolds and hybrid cultivars appeared to become tolerant to attack and were subsequently the least affected, although continuing to suffer tiller damage at a rate at least as high as the Italian ryegrass. All cultivars recovered fully when attack ceased, and their exclusion from attack did not improve their persistence.     

A comparison of the effects of sward improvement on invertebrates, sward establishment and herbage yield

Field experiments were done at two widely separated sites in England (Tadcaster, North Yorkshire and North Wyke, Devon). In each case an old permanent sward was re-seeded after ploughing or by direct drilling, or was left intact and fertilised. The carbamate pesticide aldicarb was applied to half of each experimental plot. The effects of sward improvement and pesticide on various soil invertebrate groups were assessed. Soil-dwelling macrofauna arthropods were scarce at both sites. Stem-boring dipterous larvae, however, were numerous at both sites. At Tadcaster, Oscinella vastator was the only species present in the original sward, but 0. frit was by far the most prevalent species in re-seeded areas. These can only have arisen from direct oviposition of eggs by adults on or near the emerging seedlings and not by migration of larvae from buried turf or the desiccated old pasture.
Mites and Collembola were abundant. Their numbers were reduced initially by cultivation and pesticide usage, but the effects of these practices were transient and their numbers recovered to previous levels usually within 10 wk.
Earthworms were present at both sites. Deep burrowing species, e.g. Lumbricus terrestris and Allolobophora longa were less affected by the treatments imposed than species such as A. chlorotica and L. rubelius which usually live close to the soil surface. Effects on their numbers were in any case, short-lived.
No improvement method consistently provided the greatest herbage dry matter yield. Pesticide application, however, greatly increased seedling stand and/or herbage yield at both sites and showed the benefits of using crop protectants, especially on direct-drilled re-seeds.     

Chemical control of frit fly on winter cereals sown after grass

From 1978 - 1985, 14 trials were conducted, mainly in Northern England, to assess the efficacy of different insecticides, formulations and application times for the control of frit fly (Oscinella frit) on winter cereals (13 on winter wheat and one on winter barley). Treatments were compared by assessing shoot damage in December-January, numbers of healthy tillers in April and harvested yield. A chlorpyrifos spray to the grass before ploughing or at crop emergence gave the most consistently good results, significantly reducing damage and increasing yield by 0·61 and 0·31 t/ha respectively when taken over all trials. Sprays or granules of other insecticides applied from before drilling to 8 wk after emergence gave variable but sometimes good control and enhanced yield. Chlorpyrifos applied from crop emergence to 8 wk after emergence was generally more effective than other insecticides. Cypermethrin at emergence or 2wk later gave promising results in the two trials where it was used. Of the seed treatments fonofos was the most effective though it did not match the spray treatments. In additional trials, where insecticides were applied after damage occurred, sprays of chlorpyrifos and pirimphos-methyl reduced damage and increased yield.     

The effect of pesticides on establishment of grass swards in England and Wales

Pesticide applications made at the time of sowing significantly improved seedling stand and/or herbage dry matter yield at 20 of 45 sites studied during 1977-79 in England and Wales. More autumn-sown swards responded to pesticide treatment than spring-sown ones and re-seeded grass was attacked more often than grass sown after arable crops. Pest damage was seldom obvious although some noticeable attacks by frit fly occurred. Slugs and leatherjackets appeared to be unimportant. The effect of nematodes was unresolved.     

EXPERIMENTS ON THE MODE OF ACTION OF DIELDRIN SEED-DRESSINGS AGAINST SEEDLING ATTACK BY THE LARVAL FRIT FLY, OSCINELLA FRIT L

Experiments with dieldrin seed-dressings were done to see whether the conditions favouring their action against wheat bulb fly larvae apply also to frit fly.
Experiments with oats and wheat in boxes and a small field trial with oats showed that fewer newly hatched larvae were killed when dieldrin-treated seed was sown deeply than when sown 1/4 - 1/2 in. deep; shallow sowing probably puts the insecticide where the larvae are likely to meet it before they attack the plant. Kill was never complete even with dieldrin applied at almost forty times more than the highest rate normally used. This is partly because some larvae hatch from eggs on the plant and these, unlike those from soil eggs, can enter the shoot without touching the seed dressing.
Even in the most favourable circumstances (large doses of dieldrin applied to the shallow-sown seed and the plant at the one-leaf stage at the time of attack) there was little evidence that frit fly larvae are killed inside the shoot by systemic action of dieldrin translocated from the seed. This is not because the pales which normally surround the oat seed impair the uptake of insecticide, or because of any other factor specific to oats. Frit fly larvae also survived in wheat from seed dressed with doses of dieldrin that can kill almost all wheat bulb fly larvae by systemic action. Possible reasons for this difference are discussed.     

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.     

Distribution of frit flies (Chloropidae: Meromyza Mg.) in Vologda oblast and East Poland

Species diversity and abundance of frit flies from the genus Meromyza have been assessed in coastal biotopes, grasslands, and agro-ecosystems of Vologda oblast (Russia) and Warsaw province (Poland). The Jaccard quotient of similarity (IG) of frit fly abundance has shown a uniformity between coastal banks and grasslands along these banks, as well as between cultivated cereals (except for oats) and field boundaries, cultivated fields, and some reach-in-herbs grasslands, including hayfields. Considerable heterogeneity of species composition of the flies has been revealed in similar biotopes. The biotopes studied have been found to be dominated by one species of frit flies. It has been discovered that cereal rotation in agro-ecosystem results in change in the dominant species of frit fly. The cereal height has been found to influence the abundance and diversity of frit flies. No regularities have been observed in the correlation between the abundances of frit flies in different biotopes. It has been pointed out that M. nigriseta Fed. and M. variegata Mg. can feed on cultivated cereals.     

Population persistence of the parasitoid fly Zaira cinerea (Fallén) (Diptera: Tachinidae) utilizing multiple host carabid beetles with different seasonality and quality

Zaira cinerea (Fallén) is a parasitoid fly (Diptera: Tachinidae) that attacks adult carabid beetles. To better understand mechanisms of population persistence in this species, we examined seasonality of host beetle abundance, the frequency of parasitism, and the timing of fly eclosion. In addition, we evaluated host quality using numbers of larvae or puparia per individual beetle as a measure of quality. The fly parasitized only large carabids (≥15 mm body length); the lengths of fly puparia reached 7.4–10.8 mm during development in beetle abdomens, and larger hosts are likely essential. Of the 18 large carabid species collected in this study, we chose two, Carabus maiyasanus Bates and Leptocarabus procerulus (Bates), because they were large and abundant (87% of total catch). The two carabids had different phonologies; C. maiyasanus was abundant from spring to summer, and its abundance dropped sharply in autumn, while L. procerulus was abundant in autumn and rare from spring to summer except July. Parasitism was observed in all the months from May to November except June, and adult flies eclosed more than once a year (in early summer, late summer, and mid‐autumn), indicating that the species is multivoltine. Host quality of L. procerulus was higher than that of C. maiyasanus. Carabus maiyasanus was mainly used as a host from spring to summer, and L. procerulus was used in autumn. Thus, adult beetles of one or both species are available over most of spring, summer, and autumn, allowing population persistence of this fly species over time.     

Damage to the oat panicle by the frit fly

About 2,000 panicles (60,000 spikelets) of known bursting date from small plots of oats were dissected in detail. It is noted that spraying young oat plants with DDT against first generation attack also reduces panicle attack. The spraying causes physical differences between the sprayed and the unsprayed areas — namely spraying gives a higher plant density and uniformity of panicle bursting date. The liability of main grain rather than a bosom grain to be attacked is noted at different levels of overall attack.Blindness of oats is discussed, and data are given to support the theory that one type of blindness is due to early frit fly attack on the immature grain.

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Zusammenfassung Ungefähr 2000 Rispen (60000 Ährchen) von kleinen Haferparzellen bekannter Blühdaten wurden genau seziert. Es wurde festgestellt, daß DDT-Spritzungen junger Haferpflanzen gegen die erste Generation der Fritfliege auch den Rispenbefall vermindert. Die Spritzung verursacht physikalische Unterschiede zwischen gespritzten und unbehandelten Flächen—Spritzen ergibt nämlich eine höhere Bestandsdichte und Gleichförmigkeit der Daten des Ährenschiebens. Die größere Befallsgefährdung der Hauptkörner gegenüber den Innenkörner wird auf erschiedenen Stufen des Gesamtbefalls festgestellt.Die Taubheit des Hafers wird diskutiert und es werden Befunde mitgeteilt, welche die Theorie stützen, daß eine Art der Taubheit auf frühem Fritfliegenbefall der unreifen Körner beruht.

     

The complementary effects of plant resistance and the choice of sowing and harvest times in reducing carrot fly (Psila rosae) damage to carrots

The benefits of combining a partially-resistant carrot cultivar with different sowing and lifting dates to reduce carrot fly, Psila rosae, damage were investigated at Wellesbourne in 1983 and 1984-85. The partially-resistant cv. Sytan was less damaged and supported fewer insects than the susceptible cv. Danvers on all lifting dates. The estimated reduction of carrot fly larvae on Sytan compared with Danvers ranged from 33 to 95%. Nine combinations of sowing and lifting dates provided more than 75% marketable roots of Sytan compared with only three combinations of dates for Danvers. An early June sowing of both cultivars provided roots of a marketable size with the least attack. More than 90% of Sytan roots were still marketable in December and fewer insects were produced by the end of the season on these roots than on those sown earlier. In addition, sowing in June decreased the number of pupae produced on cv. Danvers by 10 times compared with earlier sowings. Combining partial resistance with specific sowing and lifting times enabled satisfactory yields of marketable carrots to be obtained in a field infested by high populations of carrot fly.     

Differences in the relative resistance of two carrot cultivars to carrot fly attack over five seasons

A comparison was made over five seasons of carrot fly (Psila rosae) damage on two carrot cultivars, Sytan and Danvers, which represented the extremes of resistance discovered in screening trials at Wellesbourne. Plants were harvested regularly during the seasons and at each harvest the number and weight of roots was recorded and carrot fly damage was assessed using various techniques; in 1979-80 the numbers of carrot fly larvae and pupae in and around root samples were counted. The experiments confirmed repeatedly the relative resistance of cv. Sytan compared with Danvers. The estimated reduction in carrot fly larvae on Sytan relative to Danvers in early November in four seasons ranged from 40% to 67%. When tested against first generation carrot fly attack the reduction in larvae on Sytan was 54%. There were 45% fewer mines per root on Sytan resulting in less damage at each harvest in all seasons. Larvae took longer to develop on Sytan than Danvers and 18% more plants of Sytan survived carrot fly attack. Differences in seedstock, season, sowing time, generation of carrot fly, plant size and density did not account for observed differences in damage between the two cultivars. The studies indicated satisfactory practical techniques for assessing carrot fly damage in cultivar screening trials.     

Investigations on the gout fly (Chlorops pumilionis Bjerk.) in Devon and Cornwall

Field observations from 1943 to 1946 on attacks by gout fly on wheat in south-west England show that there are two generations of the fly during the year, the first emerging in May from October-laid eggs and the second emerging in late July and early August. The first generation severely damages spring wheat and may also attack very late sown and backward autumn wheat; wheat not above ground before 20 October escapes attack by the second generation. In south-west England, the optimum period for drilling wheat to escape gout-fly damage is mid-October. In this area, both generations of gout fly show a marked preference for wheat; attacks on barley are negligible.     

Factors affecting winter survival of the florally determinate white lupin cv. Lucyane

In a series of three field experiments with factorial design, on sites that had not grown lupins previously, sowing date was the main factor affecting over-winter survival of autumn-sown white lupin. In 1993, the sowing dates (23 September and 20 October) were too late to prevent much plant death in autumn and early winter, with the onset of frosts. In 1994, the sowing dates (30 August and 22 September) were early enough to prevent severe frost damage, but infestations of bean seed fly (Delia platura) occurred, more in the later than in the earlier sown crops, causing wilting and plant death. Losses were decreased where furothiocarb seed treatment was applied. In 1995, losses were greater in early-sown (12 September) than in later sown (28 September) crops; plant death was gradual, occurring into the spring, and was apparently associated with over-development of young shoots before an unusually long, cold winter. A chlorpyrifos spray (13 or 29 September for early or late sown plots, respectively) slightly increased survival, possibly by controlling Thrips angusticeps. Fungicides applied to seed or as sprays in late autumn had little or no effect in these experiments. In another series of experiments to test fungicides, in 1992-93 and 1993-94, survival was poor following late sowing (in October), but was increased by application of prochloraz in December or January, or, in 1994, by seed treatment with thiram.     

Effects of Sward Height, Gap Size, and Slug Grazing on Emergence and Establishment of Trollius europaeus (Globeflower)

Abstract To determine the effects of sward height and gap size on the emergence and subsequent development of Trollius europaeus, seeds were introduced into artificially created gaps in mown and unmown wet meadow grassland in Ayr, Scotland. Emergence and establishment of nondormant seed (previously leached in running tap water and soaked in gibberellic acid) placed in a range of circular gaps (25 mm, 50 mm with and without root barrier, 100 and 200 mm diameter) were monitored over 305 days. Trollius demonstrated high field emergence (mean, 46% of viable seed sown) in this experiment. Emergence was not significantly affected by either sward height or gap size, although emergence was greater in mown swards. The critical factor determining subsequent survival of seedlings was slug predation rather than sward height or gap size. However, losses due to slug predation were significantly greater in unmown swards, resulting in more seedlings in mown swards. One hundred eleven days after sowing (September) seedling numbers had declined substantially in both unmown and mown swards, and by day 305 (April) seedlings were extinct in both sward types. The implications of the research for the restoration and management of T. europaeus are discussed.     

Reduction of shoot fly damage in irrigated post-rainy season sorghum by manipulating irrigation

Soil moisture was manipulated in an attempt to control shoot fly (Atherigona soccata Rondani) incidence in irrigated post-rainy season sorghum grown under a rainout shelter (ROS) and in field conditions. After uniform irrigation at sowing, the plants were subjected to water stress at young seedling stage (7–28 days after emergence, DAE) for different lengths of time. Soil water had profound effects on the production of water droplets on the surface of the central whorl leaf of seedlings (leaf surface wetness, LSW) of sorghum genotypes. LSW, which facilitates movement of the larvae, was more drastically affected in susceptible (CSH 5) than in moderately resistant (IS 1054) sorghum genotypes. Shoot fly oviposition (infestation) and deadhearts (crop damage) were much higher in treatments with full irrigation (control) than in treatments to which less water was applied during the first 3 wk after seedling emergence. This resulted in higher plant biomass and overall grain yield in the latter treatments than in the control. Using insecticides to control shoot fly infestation, it was shown that a simple cultural practice of inducing plant stress by reduced soil moisture content during early plant growth gave the same or better control of shoot fly damage and the same or higher grain yield than insecticide-protected plots with full irrigation. Thus the costs associated with irrigation requirement and insecticide can be greatly reduced in the former management option compared with the latter. It is suggested that manipulation of soil water content during the vulnerable early stages of crop growth can reduce shoot fly damage in irrigated post-rainy season sorghum.     

The effect of rabbit (Oryctolagus cuniculus) grazing damage on the growth, botanical composition and yield of a ryegrass re-seed

A perennial ryegrass sward was established in the autumn of 1989 in an enclosed 0.3 ha site and was exposed to captive wild rabbit (Oryctolagus cuniculus) grazing. Rabbit numbers were varied from 16 rabbits ha^-1 in winter to 55 rabbits ha^-1 corresponding to natural fluctuations in the field. The original sward was grown for three seasons (1989/1990 to 1990/1991) and a range of grazing regimes imposed. In 1989/1990 four grazing regimes were arranged in a replicated split block design in the experimental area. These were ungrazed, winter grazed, spring grazed and totally grazed. In the second year of the experiment all plots were exposed to grazing with the exception of the originally protected plots. This was to examine the effects of longer-term grazing damage on a ryegrass sward. In the final year half of all treatments were protected to study recovery of a sward which had been damaged previously. The remainder of the plots were exposed to grazing. Three cuts were harvested in each year and the productivity assessed in terms of yield and botanical composition. There was a significant reduction in ryegrass proportion in grazed swards following the first winter of grazing, while clover, other grasses and weeds were enhanced. The promotion of clover content in grazed swards was a feature throughout the 3 yr of the study. In the second year, protection of grazed swards led to a restoration of yields, although the botanical composition remained altered. The exposure of previously ungrazed plots in the final year of the experiment showed that these swards were particularly attractive to rabbits and they suffered the greatest yield losses relative to the protected plots at the first cut in 1991. In this year dry weather conditions were experienced following the first cut and demonstrated that yield losses are exacerbated when rabbit grazing is compounded with adverse growing conditions. The results overall indicate that protection of ryegrass swards at the establishment phase is important, but that a degree of recovery is possible by providing protection at a later stage, although the ryegrass component is still impaired in swards which suffer early damage.     

Establishment and yield of three ryegrasses following aldicarb use, and changes in abundance of plant parasitic nematodes

Pure swards of Lolium multiflorum, L. multiflorum var. westerwoldicum and L. perenne sown in August had greater yields than autumn on areas treated with either 5 or 10 kg a.i./ha aldicarb than on untreated areas. Total annual dry matter yields increased by larger amounts where the greater rate of aldicarb was applied; throughout the trial, L. perenne was usually less affected by treatment than the other two grasses. Plant-parasitic nematodes were more numerous on untreated than treated plots and were fewest in areas receiving the larger application (except in the second harvest year). Numbers of Tylenchorhynchus and Helicotylenchus were affected most by treatments; abundance of Paratylenchus and Criconemella were little altered. Stem-boring Diptera invaded tillers of all three grasses but infection was least in L. perenne. Invasion occurred only on untreated plots in the establishment year and some yield benefit probably resulted from their control. In subsequent years invasion was similar on treated and untreated areas. Effects on other, non-target organisms were not assessed. Ectoparasitic nematodes multiplied more in L. multiflorum plots than in others during the first full-harvest year. The next year numbers of Paratylenchus only were greater in plots of L. perenne than in other plots. Sward persistence of L. multiflorum var. westerwoldicum was better on treated than untreated areas. It was concluded a) that aldicarb use greatly decreased nematode numbers and yields from treated areas were larger than from those untreated; b) that sward persistence was similarly improved following aldicarb use and c) that ryegrasses differed in their suitability as hosts to ectoparasitic nematodes.     

The effects of time of sowing and harvest on carrot biochemistry and the resistance of carrots to carrot fly

Two carrot cultivars which represented contrasting levels of resistance to carrot fly, Psila rosae, were grown in a replicated field experiment at Wellesbourne in 1984–85. Seed was sown on five occasions between April and August 1984 and the crop harvested after a minimum growth in the field of 16 wk on seven occasions between August 1984 and February 1985. A highly significant correlation (r = -0.78; P > 0.001) between the levels of carrot fly damage and the concentration of chlorogenic acid in the roots enabled a model to be formulated to predict the relative predisposition to carrot fly larval damage; high levels of chlorogenic acid early in the season predisposed roots to severe attack when they were older.     

Reintroduction of rare arable plants by seed transfer. What are the optimal sowing rates?

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