Chemical control of beet cyst-nematode, Heterodera schachtii, in some peaty loam soils

In peaty loam soils, aldicarb or oxamyl mixed with the top 15 cm of the soil in spring before sugar beet seeds were sown, minimised invasion of the roots by larvae of the beet cyst-nematode, Heterodera schachtii, so preventing injury to the seedlings, and greatly increased sugar yields in heavily infested soil. Small amounts of both compounds were often as effective as larger amounts. Nematode increase on sugar beet roots was slow. Aldicarb or oxamyl lessened nematode increase in four years out of five. Fumigating predetermined row positions with dichloropropene mixtures (D-D, Telone) or incorporating aldicarb or methomyl shallowly in soil, later occupied by the roots of sugar beet seedlings, did not control the nematode, although sugar yields were sometimes increased.     

Vertical distribution of Pratylenchus neglectus, P. crenatus and Tylenchorynchus dubius associated with maize roots and the effect of aldicarb residues

Depth samples on a field trial on forage maize revealed consistent differences in the numbers of Pratylenchus neglectus, P. crenatus and Tylenchorynchus dubius at different depths after treatment with aldicarb the previous year. Pratylenchus was more numerous lower down in residual-treated soils but more evenly distributed in untreated soils. T. dubius, although less numerous after aldicarb, was more numerous in the upper layers of the soil. Aldicarb and benomyl applied the previous year had no residual effects on yields.     

Does a warmer climate with frequent mild water shortages protect grassland communities against a prolonged drought?

While irrigation of farm dairy effluent (FDE) to land is becoming popular in New Zealand, it can lead to increased emissions of the greenhouse gas nitrous oxide (N₂O). This paper reports the results from trials on N₂O emissions from irrigation of FDE to two dairy-grazed pastures on two poorly drained silt-loam soils located at Waikato and Manawatu, New Zealand. These pasture soils were periodically irrigated with FDE under contrasting soil moisture conditions with water-filled pore-space (WFPS) ranging between 26% and 94%. Nitrous oxide emissions were measured from the FDE irrigated and unirrigated sites using large numbers of static chambers (12–20). Irrigation of FDE generally increased N₂O emissions compared to the control. N₂O emissions varied with changes in climatic conditions and soil WFPS. Overall N₂O emissions from effluent-derived N ranged between 0.01% and 4.93% depending on irrigation time and soil WFPS. Lower N₂O emissions from FDE were attributable to very low soil WFPS conditions during the dry seasons. Higher N₂O emissions were measured from application of FDE to a recently grazed pasture on wet soil. Our results suggest strategic application of FDE during dry summer and autumn seasons can reduce N₂O emissions from application of FDE. Delaying effluent-irrigation after grazing events could further reduce N₂O emissions by reducing the levels of surplus mineral-N.     

Populations in Saskatchewan soils of spore-perforating amoebae and an amoeba (Thecamoeba granifera s.sp.minor) which feeds on hyphae ofCochliobolus sativus

Summary Thecamoeba granifera s.sp.minor was the predominant species of hyphal feeding amoeba in Saskatchewan soils. The average number per gram dry weight in soil was 66.2 in 1983 and 76.2 in 1984 with a range of 2 to 429 individuals. This population was 10 times greater than that of spore perforating amoebae which occurred in average numbers of 5.9 in 1983 to 4.5 in 1984. The populations of both the hyphal-feeding amoeba and the sporeperforating type, varied over the growing season with low numbers in summer and a peak population in fall. The data suggest that the number ofT. granifera s.sp.minor remains similar in a field from year to year regardless of cropping practice. Contribution no. 895.     

Use of Chitin for Controlling Heterodera avenae and Tylenchulus semipenetrans

The nematicidal effect of chitin, relative to other pesticides, was evaluated against two plant-parasitic nematodes, Heterodera avenae and Tylenchulus semipenetrans. Wheat seedlings, grown in soils artificially or naturally infested with H. avenae, were treated with 0.4% (w/w) ClandoSan (CLA) prepared from crustacean chitin, aldicarb (Temik 15G), or ethylene dibromide (EDB 90EC). The CLA treatment significantly increased wheat straw, ear, and average grain dry weights of nematode-infected plants, compared with the other two treatments. In an experiment covering two consecutive seasons, all three treatments reduced the number of cysts in the soil by 60%. In a one-season experiment, CLA reduced the number of cysts by 51% and aldicarb or EDB reduced cyst number by about 40%. A reduction of 50-90% in T. semipenetrans population densities on roots of two citrus rootstocks was recorded following an application of 0.2% (w/w) CLA to the soil.     

Control of beet cyst-nematode, Heterodera schachtii, by aldicarb applied to the soil by a vertical band-reciprocating harrow technique or by rotary cultivation

As little as 0.8 kg aldicarb ha^-1 applied to bands of soil 15 cm wide × 15 cm deep, in which sugar beet seeds were sown, increased beet yields as much as did 2.6 or 5.0 kg ha^-1 rotary cultivated into the top 15 cm of soil lightly or moderately infested with beet cyst-nematode, Heterodera schachtii. In a very heavily infested soil, 1.7 kg ha^-1 applied to the bands of soil increased beet yields as much as 2.6 kg ha^-1 rotavated into the top 15 cm of the soil; yields were further increased by 5.0 and 9.9 kg ha^-1 rotavated in but not by 3.5 kg ha^-1 in the bands of soil. Soil populations of the nematode increased little or not at all whether the soil was treated with aldicarb or not. The band treatment was achieved by a vertical band- reciprocating harrow technique, which is described. The advantages of this new technique for the control of beet cyst-nematode and other soil pests of widely spaced row crops are safer application of less pesticide, thereby minimising cost of treatment and any risk to the environment, faster seedbed preparation and adequate control of pest population increase on the susceptible crop, especially if coupled with biological control.     

Field Interrelationships among Heterodera glycines,Pratylenchus scribneri,and Three Other Nematode Species Associated with Soybean

Field experiments were conducted in 1982 and 1983 to assess interactions between Heterodera glycines and Pratylenchus scribneri on soybean in southern Illinois. Soybean cyst nematode susceptible cultivar Williams 79 and resistant cultivar Fayette were treated or not treated with aldicarb 15G. Initial population densities were 35 H. glycines cysts containing eggs, 100 P. scribneri, 30 Helicotylenchus pseudorobustus, 225 Paratylenchus projectus, and 85 Tylenchorhynchus martini per 250 cm³ soil in 1982, whereas in 1983 populations were 11 H. glycines cysts, 330 P. scribneri, and 620 H. pseudorobustus. In both years H. glycines populations increased on nontreated Williams 79, decreased on both treated and nontreated Fayette, and remained at initial levels on treated Williams 79. Recovery of P. scribneri per gram dry root was different between nontreated cultivars in 1982 but not in 1983. Aldicarb treatment suppressed soil and root populations of P. scribneri on both cultivars in both years. Populations of H. pseudorobustus, P. projectus, and T. martini at harvest indicated little population increase on either nontreated cultivar. In 1982 H. glycines caused yield suppression but P. scribneri did not, as differences in yield occurred between cultivars but not between aldicarb treatments. In 1983, however, there were no yield differences between cultivars, but aldicarb application resulted in yield increase in both cultivars. In 1983 the yield increase resulting from P. scribneri control was approximately 25%. No synergistic effect on yield was observed between H. glycines and P. scribneri.     

Seasonal variation in enzyme activities and temperature sensitivities in Arctic tundra soils

Arctic soils contain large amounts of organic matter due to very slow rates of detritus decomposition. The first step in decomposition results from the activity of extracellular enzymes produced by soil microbes. We hypothesized that potential enzyme activities are low relative to the large stocks of organic matter in Arctic tundra soils, and that enzyme activity is low at in situ temperatures. We measured the potential activity of six hydrolytic enzymes at 4 and 20 °C on four sampling dates in tussock, intertussock, shrub organic, and shrub mineral soils at Toolik Lake, Alaska. Potential activities of N‐acetyl glucosaminidase, β‐glucosidase, and peptidase tended to be greatest at the end of winter, suggesting that microbes produced enzymes while soils were frozen. In general, enzyme activities did not increase during the Arctic summer, suggesting that enzyme production is N‐limited during the period when temperatures would otherwise drive higher enzyme activity in situ. We also detected seasonal variations in the temperature sensitivity (Q₁₀) of soil enzymes. In general, soil enzyme pools were more sensitive to temperature at the end of the winter than during the summer. We modeled potential in situβ‐glucosidase activities for tussock and shrub organic soils based on measured enzyme activities, temperature sensitivities, and daily soil temperature data. Modeled in situ enzyme activity in tussock soils increased briefly during the spring, then declined through the summer. In shrub soils, modeled enzyme activities increased through the spring thaw into early August, and then declined through the late summer and into winter. Overall, temperature is the strongest factor driving low in situ enzyme activities in the Arctic. However, enzyme activity was low during the summer, possibly due to N‐limitation of enzyme production, which would constrain enzyme activity during the brief period when temperatures would otherwise drive higher rates of decomposition.     

Helicotylenchus vulgaris and its association with damage to sugar beet

Severe and irregular stunting of sugar beet has been associated with Helicotylenchus vulgaris but little is known of the pathogenicity of this nematode. A survey was made at 10 sites in East Anglia on calcareous soils (Wantage series) on which the original damage was reported. Numbers were usually maintained under a variety of crops, despite fluctuations during the period. In field trials, aldicarb treatment did not improve the yield of either sugar beet or winter wheat on land infested with H. vulgaris. In pot tests growth of sugar beet was stimulated by low nematode inocula; this effect diminished as numbers inoculated increased. Sugar beet grown at 10 °C and 15 °C with H. vulgaris grew markedly better in sterilised soil than in untreated field soil, especially at the higher temperature early in the experiment. It is concluded that though H. vulgaris may damage sugar beet it requires an atypical combination of external conditions to cause significant yield loss.     

Needle nematodes (Longidorus spp.) and stubby-root nematodes (Trichodorus spp.) harmful to sugar beet and other field crops in England

Longidorus attenuatus produces galls at the tips of roots of field crops, including sugar beet, growing in alkaline, sandy soils in eastern England. L. elongatus produces similar, but often larger, galls on the roots of sugar beet and other crops in sandy soils in the W. Midlands and in Fen peats. Trichodorus spp. cause ‘stubby root’ of sugar beet and can feed on many field crops. Seven species of Trichodorus were found in sandy soils in eastern England. L. attenuatus, L. elongatus and Trichodorus spp. aggregate around roots and stunt sugar beet and other crop plants. L. attenuatus is commoner below plough depth than in the topsoil, whereas T. cylindricus, T. pachy-dermus and T. anemones are more abundant in the topsoil. These nematodes cause some forms of ‘Docking disorder’.     

Seasonal variation in nitrogen uptake and turnover in two high-elevation soils: mineralization responses are site-dependent

In arctic and alpine ecosystems, soil nitrogen (N) dynamics can differ markedly between winter and summer months, and nitrogen losses can be measurable during the spring and fall transitions. To explore the effect of seasonality on biogeochemical processes in a temperate alpine environment, we used a combination of field incubations (year-round) and ¹⁵N tracer additions (late fall, early spring, summer) to characterize soil N dynamics in a wet and dry meadow in the Sierra Nevada, California. The snowmelt to early summer season marked a period of high ¹⁵N uptake and turnover in the two soils, coincident with the increase in microbial N pools at the start of snowmelt (wet and dry meadow); an increase in net N mineralization and net nitrification as snowmelt progressed (wet meadow only); and measureable net production of ¹⁵N-NH₄ ⁺ in mid-summer (wet and dry meadow). Whereas fluctuations in microbial biomass were generally synchronous between the wet and dry meadow soils, only wet meadow soils appeared to mineralize N in response to declines in the microbial N pool. Net N mineralization and net nitrification rates in the dry meadow soil were negligible on all but one sampling date, in spite of periodic decreases in biomass of up to 60%. Across both sites, high ¹⁵N recoveries in microbial biomass N, rapid ¹⁵N-NH₄ ⁺ turnover, and low or negative net ¹⁵N-NH₄ ⁺ fluxes suggested tight cycling of N, particularly in the late fall and early spring.     

Modelling partitioning between structure and storage in sugar beet: Effects of drought and soil nitrogen

In the UK sugar beet is grown on contrasting soils that vary both in their nutritional status and water-holding capacities. Water shortage and low nitrogen reduce canopy growth and dry matter production, which is compensated in part by an increase in the fraction of assimilates partitioned to storage. Conversely, high nitrogen and ample water encourage growth of the canopy, increase assimilation of carbon dioxide but reduce the proportion of assimilates stored as sugar. This paper sets out to examine simple relationships between sugar yield, total dry matter and soil nitrogen in rain-fed and irrigated sugar beet crops (Beta vulgaris L.) from 46 field experiments spanning 12 years and a range of soil types, in order to improve prediction of sugar yields. Two partitioning functions were fitted to the data. The first represents a useful alternative formulation of the allometric growth function that overcomes some of the difficulties in the interpretation of the parameters. This model adequately described the seasonal progress of sugar yield (Y) in relation to total dry matter (W), but it was difficult to postulate biological mechanisms as to how the parameters should vary in relation to varying soil nitrogen or to drought. The second partitioning function, given by Y = W − (1/k) log(1 + kW), also described the data well, but had the more useful parameter, k, the decay rate of the fraction of assimilates partitioned to structural matter. This was shown to be greater in crops which had experienced significant drought and was inversely proportional to the amount of nitrogen taken up by the crops. Relationships between k and amounts of nitrogen fertilizer applied and/or amounts of residual nitrogen in the soil at sowing, however, were more variable. These could be improved by additionally taking account of soil type and rainfall following nitrogen fertilizer application in late spring. The models are a useful extension to yield forecasting models because they provide a simple means of estimating sugar yield from total dry matter in relation to factors that affect partitioning of assimilates such as drought and soil nitrogen availability. This revised version was published online in June 2006 with corrections to the Cover Date.     

Toxicity of 1,3-dichloropropene and fosthiazate to wireworms (Agriotes spp.)

Wireworms (Agriotes spp.) are sporadic but increasingly important pests of potatoes, sugar beet and cereals. Whilst effective chemical control is possible, the granular organophosphates normally require high rates of application and the seed dressings containing lindane (gamma‐HCH) have been withdrawn from use. The soil fumigant 1,3‐dichloropropene (1,3‐D as Telone II) and the granular nematicide fosthiazate (Nemathorin 10G) are currently used for the control of potato cyst nematodes. We investigated the effects of both of these chemicals on wireworms. Air‐vapour phase toxicities for 1,3‐D against wireworm were LD₅₀ 2.74 mg.litre.day and LD₉₉ 5.05 mg.litre.day. The in vitro soil phase toxicity was LD₉₉ 8.15 mg.litre.day. 1,3‐D soil phase activity against wireworm may be associated more with air‐vapour phase than a soil‐water phase activity. In glasshouse experiments 16.0 mg.litre.day of 1,3‐D gave 75% control. Fosthiazate, which is applied at approximately 2 μg g^?1 of soil for potato cyst nematode control, achieved an LC₅₀ at 3.20 μg g^?1. In both in vitro and glasshouse studies 1,3‐dichloropropene showed high toxicity to wireworm at dosages below the current commercial application rate for potato cyst nematode control and fosthiazate also showed useful efficacy. These chemicals may therefore prove to be valuable additional tools for limiting initial wireworm plant damage or reducing wireworm populations.     

Efficacy of Aldicarb to Rotylenchulus reniformis and Biodegradation in Cotton Field Soils

The microbial degradation of aldicarb was examined in the greenhouse using soil from four cotton fields with a history of aldicarb use. The addition of aldicarb at 0.59 kg a.i./ha to natural soil increased Rotylenchulus reniformis numbers 6.6% in one soil and decreased R. reniformis numbers only 25.8% in another soil as compared to the corresponding natural soil without aldicarb. The use of increasing rates of aldicarb did not increase the efficacy of aldicarb in these soils. Rotylenchulus reniformis numbers were reduced 39.8, 22.6, and 6.8%, and increased 5.7% for aldicarb applied at 0.29, 0.59, 0.85, and 1.19 kg a.i./ha, respectively, in one natural soil. In another natural soil, R. reniformis numbers were reduced 42.5 and 21.9% for aldicarb applied at 0.29 and 1.19 kg a.i./ha, respectively, but increased 19.1 and 10.6% for aldicarb applied at 0.59 and 0.85 kg a.i./ha, respectively. Autoclaving the soils restored aldicarb toxicity in both soils, and R. reniformis numbers were reduced 96 and 99%, respectively, as compared to autoclaved soil without aldicarb. Bacterial populations were greater in the natural soils where aldicarb did not reduce R. reniformis numbers relative to the same soils that were autoclaved. However, no bacterial species was consistently associated with aldicarb degradation.     

Effects of soil treatments and cultivars on 'early dying' disease of potatoes caused by Globodera rostochiensis and Verticilliurn dahliae

Plots in a field infested with Globodera rostochiensis and Verticillium dahliae were treated in 1971 with methyl bromide, dazomet, aldicarb, benomyl or aldicarb + benomyl and potatoes (cv. Pentland Dell) were grown in four consecutive years. In 1971, all treatments delayed the development of haulm symptoms, decreased soil populations of G. rostochiensis and increased yields. In the second year yields were increased by all treatments except dazomet whereas in the third and fourth years only benomyl or aldicarb + benomyl increased yields. Soil populations of V. dahliae were decreased by methyl bromide in 1971 but not by other treatments or in later years. In 1976, Pentland Dell and Pentland Crown were grown on an infested field in plots fumigated with methyl bromide. Fumigation slightly delayed shoot emergence but increased plant height, ground cover and the size and persistence of the leaves; development of haulm symptoms was delayed and yield increased. Fumigating with methyl bromide at five times the normal rate was more beneficial to Pentland Dell than to Pentland Crown. In a comparison of 10 cultivars in 1975, symptoms developed sooner and yields were smaller on a field infested with G. rostochiensis and V. dahliae than on a non-infested field and on both sites Maris Peer plants died soonest and yielded least. Pentland Crown yielded most on the non-infested field and Maris Piper on the infested field.     

Control of potato cyst-nematodes, Heterodera rostochiensis and H. pallida, in sandy, peaty and silt loam soils by oximecarbamate and organophosphate nematicides

Small amounts (5.6 or n-2 kg a.i./ha) of aldicarb or oxamyl, incorporated in the soil before potatoes were planted in spring, controlled potato cyst-nematodes (Heterodera rostochiensis and H. pallida) on susceptible cultivars equally well in sandy, peaty and silt loam soils. In soils treated with either nematicide, nematode numbers increased little or decreased; in untreated soils nematode numbers increased greatly. In contrast organophosphate nematicides, similarly applied, fenamiphos (proposed BSI common name for O-ethyl-O-(3-methyl-4-methylthiophenyI)-isopropylamido-phosphate), ethoprophos (proposed BSI common name for (O-ethyl S, 5-dipropyl phos-phorodithioate), CGA 12223 (O, O-diethyl O-[i-isopropyl-5-chloro-i,2,4-triazoIyl-(3)] phosphorothioate) and Dowco 275 (O, O-diethyl O-(6-fluoro-2 pyridyl) phosphorothioate), were ineffective at one or more of the experimental sites. Potato yields were greatly increased by oximecarbamate or organophosphate nematicides only in soils heavily infested with the nematodes.     

Granular Nematicides for Control of the Yam Nematode,Scutellonema bradys, and Relevant Residues in Raw Tubers

Four granular nentaticides were evaluated for control of the yam nematode, Scutellonema bradys (Steiner &LeHew) Andrassy, on Guinea yam, Dioscorea rotundata Poir, under field conditions prevelant in the tropics. A single application of nematicides (sidedressing) at the rate of 2 kg ai/ha as postplanting treatment at the onset of the rainy season depressed numbers of S. bradys attacking yams during the growing season and significantly increased tuber yields over untreated. The efficacy, based on the regression coefficient values of evaluated nematicides, was in the order of miral, carbofuran, aldicarb, and oxamyl (b = -75.9, -75.5, -72.1, and -65.9, respectively). Yam tuber yields increased by 136.9, 90.6, 87.9, and 85.3% over untreated (P = 0.05) in aldicarb, carbofuran, oxamyl, and miral treated plots, respectively. Residues in raw tubers pretreated with aldicarb, carbofuran, or miral were negligible (front less than 0.02 to 0.3 ppm) and far below the established tolerance levels (l.0 and 1.3 ppm for aldicarb and carbofuran, respectively) of a related crop in the United States. This is the first report on residues of systemic pesticides in yams.     

The effects of nematode resistant and susceptible spring oat cultivars and aldicarb on the cereal cyst nematode Heterodera avenae and yields in contrasting soil types

The effects of the cereal cyst-nematode, Heterodera auenae Woll. on resistant and susceptible oat cultivars, with and without aldicarb treatment, were compared on a clay-with-flints soil at Rothamsted and a loamy sand at Woburn. At both sites, when H. auenae was extremely scarce, yields were not further enhanced by aldicarb. At Rothamsted aldicarb increased yields by 48–72% when H. auenae averaged 10 eggs/g soil. At Woburn, aldicarb increased yields of both susceptible and resistant varieties by 80–90% with 20 eggs/g. The resistant varieties conferred yield benefits in the following oat crop equal to the residual effects of aldicarb applied before the previous crop, demonstrating that H. auenae was wholly responsible for the yield losses. Nematode resistant oats suffered as much or more damage from root invasion by H. auenae juveniles as the susceptible varieties but the resulting decrease in nematode numbers led to considerable yield improvements in the following year. At Woburn in 1977, when formalin was an added treatment, fewer females were infected by parasitic fungi and post-crop egg numbers were greater.     

Effects of aldicarb and benomyl on nematodes, vesicular arbuscular mycorrhizas and the growth and yield of forage maize

The effects of aldicarb and benomyl on plant-parasitic nematodes, vesicular arbuscular mycorrhiza and the growth of forage maize were measured in 1980—1982 in two field experiments at Woburn, Bedfordshire and in a pot experiment using loamy sand soil from the field site. The most numerous migratory nematode, Tylenchorhynchus dubius increased three to four-fold during each season in untreated soil and was effectively controlled by aldicarb. Pratylenchus species were fewer but equally well controlled. The cereal cyst-nematode (Heterodera avenae), a serious maize pathogen in Northern France, was relatively scarce in untreated roots and was further decreased by aldicarb treatment; post-harvest H. avenae egg numbers were not affected by treatments; they declined equally because maize is such a poor host. Significant yield benefits (up to 37%) followed aldicarb treatment and were ascribed to nematode control in the absence of attribution to insect or other pests. Benomyl did not increase yields nor did it significantly affect the incidence of mycorrhiza. The results confirm that considerable losses of forage maize can be caused by nematodes in light soil and that aldicarb is an effective nematicide even at the rate of 1·7 kg a.i./ha.     

Anhydrobiosis in Pratylenchus penetrans and Tylenchorhynchus n. sp. in Cultivated Soils Cropped to Winter Rye

Anhydrobiotes of Pratylenchus penetrans were found in two cultivated soils sown to rye in southern Ontario during the growing season. Anhydrobiotes at the 0-2.5-cm depth were recovered from 9 and 6 of 11 samplings, respectively, of a Vineland silt loam and a Fox loamy sand during the dry summer of 1983. At the 2.5-15.0-cm depth, anhydrobiotes were recovered less frequently. In the summer of 1984, anhydrobiotes of P. penetrans were recovered once and anhydrobiotes of Tylenchorhynchus n. sp. twice in 11 samplings. The percentages of P. penetrans populations that were anhydrobiotes in 1983 and 1984 were closely related to soil moisture content and corresponding moisture tensions. Populations of P. penetrans were greatest in October in the lower soil depth, 2.5-15.0 cm; those of Tylenchorhynchus n. sp. were greater in the surface layer of soil, 0-2.5 cm, and peaked in August.