EFFECTS OF PREVIOUS WHEAT CROPS, SEED-RATE AND NITROGEN ON EYESPOT, TAKE-ALL, WEEDS AND YIELDS OF TWO VARIETIES OF WINTER WHEAT: FIELD EXPERIMENT 1954-56

In a replicated field experiment mean yields of wheat from plots that, in the preceding 2 years, had carried oats, beans or potatoes were 39.2 and 42.6 cwt. per acre in 1954 for Holdfast and Cappelle, respectively; 42.8 and 55.8 in 1955 and 34.9 and 49.6 in 1956. Previous wheat crops had more effect than any other treatment in increasing the incidence of eyespot, take-all and weeds and in decreasing the number of ears per unit area and the yield of grain. In 1956 on plots carrying the first, second and third successive wheat crops the percentages of straws with eyespot were respectively 12, 54 and 42 and with take-all 0.1, 1 and 16. Cappelle was less severely infected by eyespot than Holdfast. The second and third successive wheat crops yielded an average of 23.3 cwt./acre less than the first wheat crop. Cappelle consistently yielded more than Holdfast, the mean difference being 13.8 cwt./acre after potatoes but only 3.8 cwt./acre after two wheat crops. The higher seed-rate gave an average increase in grain yield of 3.3 cwt./acre; but where eyespot and take-all were both severe the lower seed-rate yielded as much total and more dressed grain than the higher. Wheat given a spring top dressing of 6 cwt./acre Nitro-Chalk yielded an average of 4 cwt./acre more grain than wheat given 3 cwt./acre.     

EFFECT OF NITROGENOUS FERTILIZER APPLIED AT DIFFERENT DATES ON TAKE-ALL, EYESPOT AND YIELD OF WINTER WHEAT GROWN ON LIGHT SANDY LOAM

In a replicated field experiment on light sandy loam at Woburn, where winter wheat is a very uncertain crop, Cappelle and Holdfast, grown after potatoes with dung, yielded 50 and 41 cwt./acre of grain, respectively, when given 6 cwt./acre of Nitro-Chalk in April, compared with 19 and 20 cwt./acre when unfertilized. The same fertilized plots yielded 29 and 19 cwt., respectively, in the second, and 25 and 17 cwt./acre, respectively, in the third year on the same land, whereas unfertilized plots of both varieties yielded only 9 and 5 cwt./acre. The decrease in mean yield from 27 cwt. in the first, to 15 and 10 cwt./acre in the second and third crops was associated with a decrease in ear number from 16.7 to 14.6 and 12.2, respectively, and with a striking decrease in weight of grain per ear, caused partly by a large increase in the proportion of small grains. Eyespot ( Cercosporella herpotrichoides Fron.) although present each year did not become prevalent; an increase in the percentage straws affected by take-all ( Ophiobolus graminis Sacc.) from 9 to 15 and 26%, respectively, and a severe increase in weed infestation ( Agrostis gigantea ) appeared to be the main factors reducing yield.
Nitro-Chalk applied in April yielded most grain every year, and wheat fertilized at this time had less eyespot and take-all than that fertilized in March. Fertilizer applied in May increased weed growth, failed to decrease take-all and yielded fewer ears, less grain, and a higher proportion of tailcorn than did earlier applications.     

THE EFFECT OF DATE OF SOWING ON THE INCIDENCE OF POWDERY MILDEW ON SPRING-SOWN CEREALS

Delaying the date of sowing of spring-sown barley in 1953 and wheat in 1954 from February to April increased the incidence of powdery mildew, Erysiphe graminis DC., from May onwards. Before then, conditions did not favour the rapid spread of mildew.
From mid-June, infected barley produced necrotic lesions. These developed sooner on the early- than on the late-sown crops, and on the lower than upper leaves. Perithecia were first seen on 29 June. They were abundant on the wheat by 20 July.
Mildew reduced the yield of barley sown on 30 March and 28 April 1955 by 8 cwt./acre. The percentage loss was greater in the late- than in the early-sown crops. The number of ears per metre of row, the weight of 100 ears and the 1000-grain weights were reduced. Altering the seed rate from 1 ½ to 2½ bushels/acre did not affect the incidence, or the effect, of mildew on grain yield.     

Grain yield and incidence of take-all (Ophiobolus graminis Sacc.) in wheat grown in different crop sequences

The yield of wheat and the incidence of take-all were measured in crops grown in six different 4-year sequences, repeated in 3 successive years. The first crop of winter wheat grown after oats or beans yielded 13–23 cwt/acre (1632–2887 kg/ha) more grain than wheat after wheat or barley. Spring wheat after oats yielded 2–5 cwt/acre (250–625 kg/ha) more than spring wheat after wheat. The smaller yields of wheat after wheat or barley were caused mostly by greater prevalence of take-all. Regression analysis indicates that each 1 % increase in straws with take-all decreased yield of winter wheat by 0·6%. Take-all was more prevalent in the second and third successive wheat crops after oats than in the fourth crop.     

Fungal Communities and Disease Symptoms on Stem Bases of Wheat and Barley and Effects of Seed Treatments Containing Fluquinconazole and Prochloraz

Three successive crops of winter wheat or barley were grown as second, third and fourth cereals. Communities of fungi on shoot bases, identified after isolation on agar media, were more diverse (determined by number of taxa identified) on wheat than on barley, and their diversity increased from year to year. Diversity was not affected by seed treatments containing fluquinconazole or prochloraz. Eyespot (caused by Tapesia spp.) and brown foot rot (caused by Fusarium spp. or Microdochium nivale ) increased from year to year. Eyespot, brown foot rot (after the first year) and sharp eyespot (which remained infrequent), assessed in summer (June), affected wheat more than barley. Eyespot severity was increased slightly on barley by treatments containing fluquinconazole, formulated with or without prochloraz, in the second year (third cereal), when it was also decreased slightly on wheat by fluquinconazole plus prochloraz, except in plots where the treatment had been applied for two successive years. The increases or decreases in eyespot in the second year were accompanied by, respectively, decreases or increases in the frequency of Idriella bolleyi where fluquinconazole was applied alone. Although the eyespot pathogen Tapesia yallundae (but not Tapesia acuformis ) is sensitive to fluquinconazole in vitro , seed treatment, applied principally to control take-all disease, is likely to have only a small effect against eyespot (or other stem-base diseases), and then only on wheat and when formulated with prochloraz.     

Experiments with CCC on wheat: effects of spacing, nitrogen and irrigation

In experiments with spring and winter wheat at Rothamsted and Woburn during 4 years CCC increased yield at close spacing (4 in) (10 cm) more than at usual spacing (8 in) (20 cm), but there was no interaction between spacing and yield. Some experiments tested up to 2·4 cwt/acre (300 kg/ha) N to see whether yields continued to increase with more than usual amounts of N, when CCC prevented lodging. There was no evidence of this. When a short dry spell occurred at ear emergence, yield of spring wheat was increased by 6 cwt/acre (750 kg/ha) by CCC and 10 cwt (1250 kg) by irrigation. CCC probably improves yield in these conditions because the larger root system it causes enables more ear-bearing shoots to survive. CCC increases yield in two ways, either by increasing ears or grain per ear. In an unlodged crop CCC usually makes the grains smaller, but by preventing lodging it can also increase size. Usually CCC decreases the leaf area per shoot. The flag leaf may be smaller, unchanged or larger than those of untreated plants. There was no obvious connexion between flag-leaf area and grain yield; when CCC decreased flag-leaf area duration by 25 %, grain yield was unchanged. The results suggest that using CCC gives a more than even chance of a profitable yield increase.     

A COMPARISON OF HIGH AND LOW VOLUME SPRAYS FOR CONTROL OF THE BEAN APHID, APHIS FABAE SCOP. ON FIELD BEANS

Insecticides were sprayed in different amounts of water to control Aphis fabae Scop. attacking spring-sown field beans. The single application of each insecticide was timed to coincide with the end of aphid migration from the winter host to the crop. A tractor-mounted row-crop hydraulic sprayer was used.
In one experiment seven different insecticide sprays were compared at high volume (in 140 gal. of water per acre); the most effective were nicotine at 22.4 oz. of active constituent per acre, demeton at 5.6 oz. and demeton-methyl at 11.2 oz.
A further comparison was made of five insecticides for each of which a selected dose of active ingredient was applied in 60 gal. (medium volume) and in 10 gal. of water per acre (low volume). The amount of insecticide retained on the plant following the low-volume application was not less than that from the medium-volume spray; the efficiency of A. fabae control was not affected by the volume sprayed except with malathion which did better at the medium volume. The systemic insecticides demeton-methyl at 6 oz. of active constituents per acre, the related compound 4741 at 3 oz. and fluoroacetamide at 3 oz. stopped the aphid numbers from rising above a peak of eight per plant compared with 230 per plant for malathion (low volume) at 12 oz. 2400 per plant for lindane at 6 oz. and 3550 per plant for check treatments sprayed with wetter only. Grain yields ranged from around 4 cwt. per acre on check treatments to around 27 cwt. per acre on plots sprayed once with the systemic insecticides. There was a curvilinear relationship between grain yield and log number of A. fabae per plant.     

Pesticides and the soil fauna: effects of aldrin and DDT in an arable field

Aldrin dust (3 cwt. of 1¼% per acre) or DDT dust (2 cwt. of 5 % per acre) was applied to small plots replicated four times and four plots were untreated. All plots were kept fallow for one year. Soil samples were taken at 2 to 3-monthly intervals and the fauna extracted by a notation method. The insecticides did not affect Lumbricidae, Enchytraeidae or Nematoda. Nearly 100 species of arthropods were found, and the greatest effects were those of DDT on mesostigmatid mites and of aldrin on entomobryid or isotomid Collembola and on Pauropoda. Most species of Collembola increased in DDT-treated plots, apparently because mesostigmatid mites were reduced. In terms of biomass Coleoptera and Diptera were most affected. Both insecticides killed more pests than predators or beneficial animals. The effects of the insecticides were greatest during late summer or autumn.     

Dependence of Yields of Wheat Varieties on their Leaf Area Durations

In a field experiment three wheat varieties: autumn-sown CappelleDesprez, Prestige, both autumn-sown and spring-sown, and spring-sownJufy I, each supplied with 0.5 or 1.0 cwt nitrogen/acre (6₃or 126 kg/ha), had grain yields nearly proportional to theirLeaf Area Durations (D) during grain development. Squarehead'sMaster had a smaller grain yield relative to its total D, butwith 0.5 cwt N/acre the ratio of its grain yield to D of partsabove the flag leaf node (D_F) was similar to the other varieties.The difference in this ratio between varieties was less whenD_Fwas calculated from anthesis than from ear emergence to ripening.Squarehead’s Master with 1.0 cwt N/acre had a smallerratio of grain yield to D_F than other treatments, implying lessgrain per ear relative to D_Y per shoot, perhaps because of lodging,or because factors limiting size of ears restricted their abilityto accept all the assimilate the shoots could produce with thisamount of N.     

The effect of three or five years of set-aside on the husbandry and grain yield of subsequent cereal crops in the UK

During the period 1993–1997, at six contrasting sites located throughout England, two successive cereal test crops were grown both with and without nitrogen fertiliser after three or five years of set-aside or after continuous arable cropping. Vegetation during set-aside included natural regeneration and perennial rye-grass (Lolium perenne) with or without white clover (Trifolium repens), managed by mowing on one or more occasions per year. Establishment of the successive cereal test crops after destruction of the set-aside was generally not a problem. Fertile tiller numbers were increased by inclusion of clover in the set-aside cover or application of inorganic nitrogen. The presence of couch grass (Elytrigia repens) or volunteer cereals in the set-aside covers provided alternative hosts for take-all (Gaeumanomyces graminis) and eyespot (Pseudocercosporella herpotrichoides) and take-all caused some yield reductions in following cereal crops. Management during the set-aside period significantly affected grain yields of the subsequent cereal crops in the majority of the site-year combinations. However, these effects were not as large as would be expected after traditional break crops and were frequently masked by the application of nitrogen fertiliser. Mean yields increased by 80% due to the application nitrogen at the optimum rate compared to nil nitrogen. Most of the effects of set-aside treatment on grain yield were shown to be attributable to soil mineral nitrogen content, but at some sites, infections by take-all or eyespot also accounted for some of the variation. There were no effects of pests that could be related to treatment. The presence of sown clover during the set-aside period had the most consistent effect across sites, affecting tiller populations, grain yield and grain quality of cereal crops. At some sites, establishing a sown cover during the set-aside period, or cutting the cover more than once a year, improved grain yield and quality, and reduced the incidence of some specific weeds and disease. This revised version was published online in June 2006 with corrections to the Cover Date.     

FIELD STUDIES ON WHEAT-BULB FLY INFESTATIONS

An account is given of two experiments done on commercial farms in Essex to study the effect of tilth, cultivation and seed rate on wheat-bulb fly infestation and the effect of infestation on yield. Heavier infestations developed on rough fallows and those cultivated during the oviposition period, than on smooth fallows and those not cultivated during the oviposition period. These results confirmed those of an earlier experiment done at Rothamsted. At each level of infestation, more larvae survived on plots sown at 3 bus./acre than on plots sown at 2/3 or 1 bus./acre. Although some plots had a high larval population no effect of infestation on yield was observed even at the lower seed rates. This is attributed to early sowing. The extent to which the cultural treatments studied can be used to control wheat-bulb fly infestations is discussed.     

The effects of lodging and a paclobutrazol — chlormequat chloride mixture on the yield and quality of oilseed rape

The effects of lodging and a plant growth regulator mixture on oilseed rape cv. Ariana were studied in three field experiments. Natural and artificially induced lodging treatments varying in time of imposition and severity were compared to a supported control. A mixture of paclobutrazol and chlormequat chloride was applied either as a spray or as paclobutrazol granules followed immediately by a chlormequat chloride spray.
In 1987, severe lodging treatments reduced yield by up to 52%. Yield penalties varied with the time at which lodging was imposed. Yield was inversely correlated with the ground cover of volunteers growing from shed seed under lodged crops.
In 1988, two experiments showed increased incidence of disease and decreases in seed yield and quality in lodged crops. Yield reductions were related to the severity of lodging. Lodging decreased oil contents and increased glucosinolate levels. PGR treatments reduced lodging and maintained yield at a level not significantly different to a supported control treatment. Oil contents were also similar in seed from PGR treated and control plots. Glucosinolate levels in PGR treated seed were similar to control levels in one experiment and intermediate to those from control and artificially lodged plots in another experiment.
The results are discussed in relation to the use of PGRs to prevent lodging in 'double zero' varieties of oilseed rape, and the potential losses from using ground vehicles to apply pesticides after flowering.     

An experimental design and procedures for testing putative controls against naturally-occurring take-all in the field

In experiments during 1983–86 take-all was more severe and eyespot and sharp eyespot less frequent in 2nd-4th crops of winter wheat at Woburn (Beds.) than at Rothamsted (Herts.). Third crops had most take-all and yielded least grain. Against this background, small plots, 37 cm × 31 cm, in which all plants were sampled, were tried as a means of increasing experimental precision. They were arranged in fours in incomplete blocks and blocks with complementary treatments (putative controls of take-all) were paired. Thirty of these block-pairs were distributed throughout each experimental site in each year to provide one replicate of the design for each of three sampling times: April, June and August. Unattributed variation in disease and plant growth for plots within blocks was compared to that in other strata (block-pairs and blocks within block-pairs) of the experiment. The variability amongst block-pairs scattered throughout the site was nearly always greater than that for blocks within block-pairs (98% of take-all assessments, 71% of soil infectivity estimates, 94% of eyespot and sharp eyespot assessments and 86% of all plant measurements). The variability of blocks within block-pairs exceeded that of plots much less frequently (56% and 69% of take-all assessments, 33% and 25% of soil infectivity measurements, 63% and 56% of eyespot and sharp eyespot assessments and 50% and 63% of plant measurements; Rothamsted and Woburn, respectively). Small plots were judged mostly on this last comparison, where a variance ratio in excess of 1 indicated that the small plots had decreased variability and increased precision. Variance ratios for different assessments of take-all indicates that small plots: i) most consistently decreased disease variability during the years of maximum disease, ii) were slightly less effective at Rothamsted than at Woburn, and iii) were usually less effective in fourth crops than in previous crops. Soil infectivity was most uniform after crops with most disease and blocks were rarely more variable than plots. hxcept when disease was severe, soil infectivity in August tended to be positively associated with the yield of the crop just harvested. These findings reveal changes in the scale of disease patterns, both during the crop sequence and within individual crops, and suggest more than one scale of pattern in take-all-infested fields. This is discussed in relation to field experimentation and take-all decline.     

THE PHYTOTOXIC EFFECTS OF D.D.T., B.H.C., PARATHION AND TOXAPHENE ON TOBACCO

No phytotoxic effect was seen following a pre-sowing spray of tobacco seed-beds with 27 lb./acre technical D.D.T. or after an application of the same material at 75.6 lb./acre to 3-week-old tobacco seedlings.
A pre-sowing application of parathion (diethyl para nitrophenyl thiophosphate) (2 % dust) at 1–8 lb. parathion per acre had no harmful effect. Used on 3-week-old tobacco seedlings at the excessive rate of 22.7 lb./acre it caused serious stunting and many deaths.
Toxaphene (chlorinated camphene: empirical formula C₁₀H₁₀Cl₈), applied as a 25 % wettable powder in a pre-sowing spray at 6-4 lb. toxaphene per acre, did not injure tobacco seedlings.
No residual phytotoxic effects appeared in beds re-sown 4 months after being treated with parathion or toxaphene at the pre-sowing doses given above.
Benzene hexachloride, applied before sowing at doses above 1.6 lb. technical B.H.C. per acre, suppressed root development in newly germinated tobacco seedlings. B.H.C. dusts used on n-day-old seedlings at 2–25 lb. technical B.H.C. per acre caused temporary distortion and stunting. Up to 11 lb./acre these symptoms were transitory: at 37.5 lb./acre many plants were killed and the remainder severely stunted. Resistance to these phytotoxic effects increased with age of plant, but 3-week-old tobacco seedlings showed considerable mortality after the application of 75.6 lb./acre of technical B.H.C.
Beds re-sown 4 months after the application of 6-4 and 12.8 lb. respectively of technical B.H.C. per acre showed no phytotoxic effect, but, as tobacco seed is sown on the soil surface, the effect of the B.H.C. may have been merely masked, and it is not safe to assume that there was no residual effect. The actual persistence of B.H.C. in the soil was not determined.
The possible mechanism of action of the B.H.C. effect is discussed.     

CALCIUM CHLOROACETATE AS A SOIL DRESSING AGAINST BEET EELWORM: HETERODERA SCHACHTH SCHMIDT, WITH CERTAIN ADDITIONAL OBSERVATIONS

Calcium chloroacetate at 3 and 6 cwt./acre produced significant increases in the yields of sugar beet (both washed beet and total sugar) in a trial on fen soil of the 'skirt' type infested with beet eelworm, Heterodera schachtii Schmidt. However, the material had no effect on the eelworm content of the soil whether measured by cysts, viable cysts or eggs and larvae. An instance is recorded of a significant drop in the level of the beet eelworm infestation in the presence of sugar beet.     

Surveys of diseases of winter wheat in England and Wales, 1976–1988

Samples from 300 – 400 randomly selected winter wheat crops were taken annually at growth stage 73 – 75 from 1976 to 1988 with the exception of 1983 and 1984. The number of samples from each region was proportional to the area of wheat grown in each region. The percentage of the area of the top two leaves affected by diseases, the severity of ear and stem base diseases and, in 6 years, the severity of take-all were recorded. Septoria tritici and Septoria nodorum were, on average, the most severe of the foliar diseases and eyespot (Pseudocercosporella herpotrichoides) was the most severe of the stem base diseases. Regional differences in levels of S. tritici, brown rust, sharp eyespot and nodal fusarium were significant. Cultivar resistance affected disease severity, and previous cropping patterns particularly affected take-all and eyespot. Eyespot and sharp eyespot were less severe in late- than in early-sown crops. The percentage of crops treated with a fungicidal spray increased from 14% in 1976 to over 90% between 1983 and 1985. Use of benzimidazole fungicides applied at growth stage 31 declined, while use of morpholines from flag leaf emergence onwards increased between 1985 and 1988.     

The effects on soil fauna of insecticides tested against wireworms (Agriotes spp.) in wheat

The organophosphorus insecticides Bayer 38156 (O-ethyl S-p-tolyl ethyl phosphonodithioate), trichloronate, Stauffer N 2790 (O-ethyl S-phenyl ethyl phosphonodithioate), thionazin and fenitrothion were compared with aldrin, dieldrin and γ-BHC for their effects on soil fauna, particularly wire-worms, and on crop yields in 1964 and 1965. At 1·5 lb active ingredient/acre, none of the organophosphates had as great an effect on wireworms as an aldrin spray at 2·25 lb a.i./acre or a dieldrin seed dressing at 2·25 lb a.i./acre. Some treatments significantly increased and some significantly decreased numbers of mites and Collembola. Except for Allolobophora chlorotica in plots treated with Bayer 38156, earthworm numbers were greater in plots sprayed with Bayer 38156 or aldrin, or sown with dieldrin-dressed seeds, than in untreated plots. In May 1964, one month after sowing, untreated plots had significantly fewer plants than plots sprayed with aldrin, trichloronate or Bayer 38156, or sown with γ-BHC or dieldrin-dressed seeds, but yields from untreated plots at harvest were high for such a large wireworm population and did not differ significantly from yields of treated plots in either year. The persistence of thionazin and Bayer 38156 in treated plots was measured by a bioassay using Collembola. Bayer 38156 was detected in plots 1 month after spraying but not after 6 months. Thionazin left detectable residues 1 month after spraying in the two acid plots but not in the two alkaline plots. More frequent samples taken from thionazin-treated plots in 1965 showed a similar pattern of persistence, and laboratory tests, using soil mixed with various amounts of powdered calcium carbonate, confirmed that thionazin persisted longer in more acid soils.     

Interactions of crop density of field beans, abundance of Aphis fabae Scop., virus incidence and aphid control by chemicals

The number of Aphis fabae Scop. per plant and per acre developing on field beans (Vicia faba L.) was inversely related to seeding rate (i.e. plant density) except sometimes at very low rates; with equal numbers of plants per acre, fewer aphids developed on plants in rows 11 in. than 22 in. apart. Plots sown in mid-March with more than about 150,000 plants per acre were more attractive than less dense stands to colonizing alate A. fabae, but established colonies multiplied most on the sparsest and least on the densest plots. The number of plants per acre infected by pea leaf-roll virus was inversely related to planting density. There were more virus-infected plants on II in. than on 22 in. spaced rows-in contrast to the numbers of A. fabae. A single spray with demeton-methyl, timed to control A. fabae, did not significantly decrease virus incidence. Grain yields of sprayed plots were little altered by increasing the seed rate above a critical minimum, except in one year when the densest crops lodged. Increased yields from spraying were closely related to the numbers of A. fabae on unsprayed plots. Dense planting (more than 400,000 plants per acre) prevented or greatly decreased losses caused by A. fabae in unsprayed plots except in one year when the aphids were exceptionally abundant.     

Root-knot Nematode Management and Yield of Soybean as Affected by Winter Cover Crops,Tillage Systems,and Nematicides

Management of Meloidogyne incognita on soybean as affected by winter small grain crops or fallow, two tillage systems, and nematicides was studied. Numbers of M. incognita did not differ in plots planted to wheat and rye. Yields of soybean planted after these crops also did not differ. Numbers of M. incognita were greater in fallow than in rye plots, but soybean yield was not affected by the two treatments. Soybean yields were greater in subsoil-plant than in moldboard plowed plots. Ethylene dibromide reduced nematode population densities more consistently than aldicarb and phenamiphos. Also, ethylene dibromide increased yields the most and phenamiphos the least. There was a positive correlation (P = 0.001) of seed size (weight of 100 seeds) with yield (r = 0.79), indicating that factors affecting yield also affected seed size.     

The use of menazon seed dressing to decrease spread of virus yellows in sugar-beet root crops

Menazon, an organophosphorus insecticide (only slightly toxic to mammals), applied to sugar-beet seed, decreased the proportion of seedlings infested with aphids during May and early June and the number of aphids per plant during June and early July to one-third of that in the control plots. It also checked the spread of virus yellows. Of eight field trials in 1965, 1966 and 1967 in which more than 10% of the plants in plots not treated with insecticide had yellows, menazon seed dressing increased sugar yield by about 8 cwt per acre. Spraying with demeton-methyl when ‘a spray warning’ was issued in the area gave a similar increase, and had no further effect on plots sown with menazon-treated seed. Menazon-dressed sugar-beet seed is recommended in regions where yellows is usually prevalent, or where there is reason to expect a large aphid infestation.