Mycocentrospora acerina in carrots; Effects of crop rotation on disease incidence

Four experimental sites located in different climatic regions in Norway were inoculated with Mycocentrospora acerina in 1985. In 1986, crop rotation experiments including carrot, barley, grass, red clover, onion and potato, were established at these sites. Incidence of M. acerina on the foliage and the roots of carrots after storage were recorded in 1989/90 and 1994/95. The 3 yr rotation only slightly reduced the inoculum of M. acerina in the soil. Red clover and grass were the most effective crops in reducing the inoculum, potato and barley were less effective, and onion had no effect on the inoculum. Differences in M. acerina infection on carrots between 3, 6 and 8 yr of rotation with barley and grass were not statistically significant.     

Weeds as hosts of Mycocentrospora acerina

Weeds were collected from carrot fields and some other sites at 27 localities in seven counties in Norway during August and September of 1986 and 1987. Leaf and petiole lesions were microscopically examined for Mycocentrospora acerina. Viola arvensis and Viola tricolor were commonly observed with the pathogen. The fungus was also registered on Fumaria officinalis, Galium aparine, Matricaria inodora, Matricaria matricarioides, Ranunculus repens, Senecio vulgaris and Stachys palustris. In inoculation experiments in the greenhouse, M. acerina infected carrot leaves and 13 of 16 species of weeds. The symptoms on the various susceptible plants showed some variation, but were essentially of the same pattern. The investigation indicates that weeds are common hosts of M. acerina. A list of 23 host weed species is given.     

Development of pythium ultimum in soil in relation to presence and germination of seeds of different crops

Summary A quantitative study was made to determine the effect of various crop seeds on the population ofPythium ultimum in naturally infested soil. Seeds of corn, peas, watermelon, wheat, barley, beet, and cabbage caused an increase inPythium population within 48 hours of planting. The extent of population rise varied with plant species sown, distance of soil from seed, and duration of stay of seeds in the soil. This rise in the population ofPythium in the soil has been attributed to non-specific stimulation provided by amino acids and sucrose in the seed exudates.The author wishes to express his grateful thanks to the United States Agency for International Development for giving him a traineeship during 1960 and to Dr. J. E.Mitchell of the Department of Plant Pathology, University of Wisconsin, U.S.A. for providing facilities, encouragement, and guidance.     

Effects of sowing date and volunteers on the infectivity of soil infested with Gaeumannomyces graminis var. tritici and on take-all disease in successive crops of winter wheat

In a field experiment on winter wheat, take‐all on plants and the infectivity of the soil were studied in crop sequences with different combinations of sowing dates. Take‐all was negligible in the first wheat crop, but thereafter the mean disease intensity (measured using a take‐all rating, TAR, with a maximum of 300) was 108, 190, 118 and 251 in the second to fifth successive crops. In each growing season, the disease differed amongst sequences and built up more rapidly and was more intense on plants sown in mid‐September than on plants sown in mid‐October. In late‐sown plots, where volunteers had been present during the mid‐September to mid‐October period, take‐all reached an intensity intermediate between that in early‐sown plots and that in late‐sown plots that had been kept free of volunteers. Volunteers, therefore, partially offset the expected beneficial effect of decreased disease with later sowing. Differences in take‐all amongst sequences were most pronounced in the second wheat crop and early sowing of the previous wheat increased intensity of disease. In the following (third) crop, differences in disease intensity amongst sequences were smaller. Soil infectivity (measured by seedling bioassay after harvest) built up progressively from a low level after the first crop to peak after the third crop. In this build‐up phase, soil infectivity estimates were always numerically greater after harvest of early‐sown treatments than after later‐sown treatments, although never significant at P= 0.05. The greatest difference (P= 0.06) was recorded in October before sowing of the third crop, where the comparison was between soil after two previous early sowings and soil after two previous later sowings and control of volunteers. In the same autumn, presence of green cover (i.e. volunteers) was associated with a smaller loss of soil infectivity between harvest and later sowing than occurred in an absence of green cover. In 2^nd–4^th crops, where comparisons were available and mean TARs indicated moderate levels of take‐all, sowing later had no yield benefit, despite more take‐all and greater soil infectivity associated with early sowing. Important considerations for the management of crops at risk of take‐all are 1) choosing appropriate sowing dates to minimize take‐all or to encourage take‐all decline and 2) controlling volunteers and weed hosts where crops are sown late to minimise take‐all.     

Occurrence of Didymella fabae,the Teleomorph of Ascochyta fabae,on Faba Bean Straw in Spain

Pseudothecia of Didymella fabae, the teleomorph of Ascochyta fabae, were first observed on faba bean (Vicia faba) debris in Spain during autumn 1995. Most pseudothecia were mature by December–February. The ascospores gave rise to typical cultures of A. fabae, and conidia from these cultures caused ascochyta blight symptoms on inoculated faba bean plants. Placing straw‐bearing pseudothecia over the plants to allow ascospore discharge also resulted in typical ascochyta blight symptoms. Pseudothecia maturity and discharge of ascospores from the infested faba bean straw overlapped with the vegetative stage of the faba bean crop, which occurs in southern Spain during winter as the crop is sown in autumn and harvested in spring. These observations indicate that ascospores may serve as primary inoculum for the disease.     

Post-harvest control of cassava tuber rot by Botryodiplodia acerina using extracts of plant origin

Abstract

Investigations were carried out on the pesticidal potentials of seed of Piper nigrum and Aframomum melegueta and leaves of P. nigrum and Ageratum conyzoides using water, ethanol and petroleum ether as extracting solvents. Leaf extracts of P. nigrum and A. conyzoides and seed extracts of A. melegueta and P. nigrum significantly inhibited the mycelial radial growth and mycelial biomass of Botryodiplodia acerina in vitro. Ethanol extracts recorded the highest growth inhibition followed by water and petroleum ether extracts. The extracts checked the rot development in unwounded cassava tubers especially when they were applied before spray-inoculating with B. acerina. Water leaf extracts of P. nigrum and A. conyzoides and seed extracts of A. melegueta and P. nigrum could be a potent source of natural pesticide for managing post-harvest rot of cassava tubers caused by B. acerina.     

Field evaluation of doubled haploid plants in the Apiaceae: dill (Anethum graveolens L.), caraway (Carum carvi L.), and fennel (Foeniculum vulgare Mill.)

The Apiaceae family includes vegetables, as well as herb and spice crops. Compared to major crops, there have been few breeding or genetic improvement programs for any of the Apiaceae, especially the herb and spice species. Haploidy technology can be used to develop uniform, true-breeding lines, as well as to accelerate breeding programs. Field trials of dill (Anethum graveolens L.), caraway (Carum carvi L.), and fennel (Foeniculum vulgare Mill.) doubled haploid (DH) lines were conducted over 2–5 cropping seasons. Several of the DH dill lines had desirable agronomic characteristics such as short uniform stature along with early maturity that would be useful for crop improvement. Seed yields and the essential oil content of the seed harvested from the best performing DH dill lines were either equal to or higher than the parental line. A DH annual caraway line was identified that produced higher seed yields than the industry standard. The main constituents of the essential oil for the DH lines of both dill and caraway were similar to the parental lines. Fennel DH lines exhibited differences in height but were too late in maturity for seed production under prairie conditions. The results indicate that not only were we able to generate DH lines that could be used in a crop improvement program, but we developed DH lines that could be used directly as cultivars as these lines performed better than the industry standard (parental line).     

Assessing long-term impacts of cover crops on soil organic carbon in the central US Midwestern agroecosystems

Cover crops have been reported as one of the most effective practices to increase soil organic carbon (SOC) for agroecosystems. Impacts of cover crops on SOC change vary depending on soil properties, climate, and management practices, but it remains unclear how these control factors affect SOC benefits from cover crops, as well as which management practices can maximize SOC benefits. To address these questions, we used an advanced process-based agroecosystem model, ecosys, to assess the impacts of winter cover cropping on SOC accumulation under different environmental and management conditions. We aimed to answer the following questions: (1) To what extent do cover crops benefit SOC accumulation, and how do SOC benefits from cover crops vary with different factors (i.e., initial soil properties, cover crop types, climate during the cover crop growth period, and cover crop planting and terminating time)? (2) How can we enhance SOC benefits from cover crops under different cover crop management options? Specifically, we first calibrated and validated the ecosys model at two long-term field experiment sites with SOC measurements in Illinois. We then applied the ecosys model to six cover crop field experiment sites spanning across Illinois to assess the impacts of different factors on SOC accumulation. Our modeling results revealed the following findings: (1) Growing cover crops can bring SOC benefits by 0.33 ± 0.06 MgC ha⁻¹ year⁻¹ in six cover crop field experiment sites across Illinois, and the SOC benefits are species specific to legume and non-legume cover crops. (2) Initial SOC stocks and clay contents had overall small influences on SOC benefits from cover crops. During the cover crop growth period (i.e., winter and spring in the US Midwest), high temperature increased SOC benefits from cover crops, while the impacts from larger precipitation on SOC benefits varied field by field. (3) The SOC benefits from cover crops can be maximized by optimizing cover crop management practices (e.g., selecting cover crop types and controlling cover crop growth period) for the US Midwestern maize–soybean rotation system. Finally, we discussed the economic and policy implications of adopting cover crops in the US Midwest, including that current economic incentives to grow cover crops may not be sufficient to cover costs. This study systematically assessed cover crop impacts for SOC change in the US Midwest context, while also demonstrating that the ecosys model, with rigorous validation using field experiment data, can be an effective tool to guide the adaptive management of cover crops and quantify SOC benefits from cover crops. The study thus provides practical tools and insights for practitioners and policy-makers to design cover crop related government agricultural policies and incentive programs for farmers and agri-food related industries.     

The use of cover crops in cereal-based cropping systems to control nitrate leaching in SE England

Field experiments were done to evaluate the extent to which cover crops can be used to help farmers comply with current legislation on nitrate leaching from arable land in nitrate vulnerable zones. Nitrate leaching was measured in sandy loam and chalky loam soils under a range of early sown (mid-August) cover crops at two sites in SE England, and in the subsequent winter following their incorporation. Cover crop species tested were forage rape, rye, white mustard, a rye/white mustard mixture, Phacelia and ryegrass. Additional treatments were weeds plus cereal volunteers, a bare fallow and a conventional winter barley crop sown one month later than the cover crops and grown to maturity. Cover crop and bare fallow treatments were followed by spring barley. This was followed by winter barley, as was the conventional winter barley crop. In the winter immediately after establishment, early sown cover crops decreased nitrate leaching by 29–91% compared to bare fallow. They were most effective in a wet winter on the sandy loam where nitrate leaching under bare fallow was greatest. There was little difference between cover crop species with respect to their capacity to decrease nitrate leaching, but losses were consistently smaller under forage rape. The growth of weeds plus cereal volunteers significantly decreased nitrate leaching on the sandy loam compared with a bare fallow, but was less effective on the chalky loam. Nitrate leaching under the later sown winter barley was often greater than under cover crops, but under dry conditions leaching losses were similar. In the longer-term, in most cases, the inclusion of cover crops in predominantly cereal-based cropping systems did not significantly decrease cumulative nitrate leaching compared with two successive winter cereals. In summary, early sown cover crops are most likely to be effective when grown on freely drained sandy soils where the risk of nitrate leaching is greatest. They are less likely to be effective on poorer drained, medium-heavy textured soils in the driest parts of SE England. In these areas the regeneration of weeds and cereal volunteers together with some additional broadcast seed may be sufficient to avoid excessive nitrate losses. In the short-term, mineralization of N derived from the relatively small cover crops grown once every 3–4years in cereal-based cropping systems is unlikely to contribute greatly to nitrate leaching in later years and adjustments to fertilizer N recommendations will not usually be necessary.     

The control of Aphis fabae Scop, on spring-sown field beans (Vicia faba L.)

Disulfoton or phorate granules or demeton-S-methyl, menazon and vamidothion sprays, applied once in early June as preventive treatments before heavy aphid colonies developed, gave good control of Aphis fabae Scop, on field beans. Phosalone gave relatively poor results and DDT was ineffective. Applications in June to crops sown in February and early March were made with minimal wheel damage to the crop and are known to be less harmful to bees than sprays at flowering time. Eradicant treatments with demeton-S-methyl and dimethoate sprays or with disulfoton or phorate granules on heavily infested plants during flowering were also effective, but menazon was less satisfactory. These eradicant sprays are likely to be harmful to bees, and wheel damage in late June reduced yield by 1–2 cwt/acre (125–250 kg/ha). Peak populations of 3000 aphids/plant in early July reduced yield by 6 cwt/acre (750 kg/ha) in one trial.     

Nitrogen fertilizer replacement indexes of legume cover crops in the derived savanna of West Africa

Legume cover crops are a potential means for overcoming N depletion in the derived savanna of West Africa. A 3-year trial was, therefore, conducted near Ibadan, southwestern Nigeria to measure the N contribution of 13 legume cover crops as compared to urea –N, using a N fertilizer replacement index for a maize test crop. Two series of trials involved the following legume cover crop species: Aeschynomene histrix, Centrosema brasilianum, Centrosema pascuorum, Chamaecrista rotundifolia, Cajanus cajan, Crotalaria verrucosa, Crotalaria ochroleuca, Lablab purpureus, Mucuna pruriens, Psophocarpus palustris, Pseudovigna argentea, Pueraria phaseoloides and Stylosanthes hamata. Trials were undertaken using a complete block design. Cover crops were planted in 1994 (Series 1) and 1995 (Series 2) in separate sites and each series was subsequently slashed and planted for one season with maize (Zea mays) in 1995 and 1996. At the 50% flowering stage, N concentration of above-ground vegetation of cover crops ranged from 21 to 38 g N kg^–1. Nitrogen accumulated by 4.5-month old cover crops ranged from 14 to 240 kg N ha^–1, depending on species and year. Cover crops increased grain yield of the subsequent maize crop by 25–136% over the control without N application. Nitrogen uptake by the maize crop was higher following cover crops than after maize or natural grass. The N fertilizer replacement index of cover crops for maize ranged from 11 (A. histrix) to 96 kg N ha^–1 (C. cajan) in Series 2. Perennial (C. brasilianum, S. hamata, C. cajan, P. phaseoloides and C. verrucosa) and annual (C. rotundifolia, M. pruriens, C. ochroleuca and L. purpureus) species could potentially save 50 to 100 kg N ha^–1 for maize crops. The cover crops accumulated more N in the wetter than in the drier year. However, the N fertilizer replacement index was higher for subsequent maize grown in the drier year. The cover crop-N recovery in maize was also higher than the urea-N uptake in the drier year. The N fertilizer replacement indexes can be predicted using the above-ground biomass amount of cover crops at 20 weeks after planting (drier year) or the N concentration at that stage (wetter year).     

Improving the Agronomy of Alyssum murale for Extensive Phytomining: A Five-Year Field Study

Large ultramafic areas exist in Albania, which could be suitable for phytomining with native Alyssum murale. We undertook a five-year field experiment on an ultramafic Vertisol, aimed at optimizing a low-cost Ni-phytoextraction crop of A. murale which is adapted to the Balkans. The following aspects were studied on 18-m² plots in natural conditions: the effect of (i) plant phenology and element distribution, (ii) plant nutrition and fertilization, (iii) plant cover and weed control and (iv), planting technique (natural cover vs. sown crop). The optimal harvest time was set at the mid-flowering stage when Ni concentration and biomass yield were highest. The application of N, P, and K fertilizers, and especially a split 100-kg ha^?1 N application, increased the density of A. murale against all other species. It significantly increased shoot yield, without reducing Ni concentration. In natural stands, the control of graminaceous weeds required the use of an anti-monocots herbicide. However, after the optimization of fertilization and harvest time, weed control procured little benefit. Finally, cropping sown A. murale was more efficient than enhancing native stands and gave higher biomass and phytoextraction yields; biomass yields progressively improved from 0.3 to 9.0 t ha^?1 and phytoextracted Ni increased from 1.7 to 105 kg ha^?1.     

Subsistence strategies of two Bronze Age hill-top settlements in the eastern Alps—Friaga/Bartholomäberg (Vorarlberg, Austria) and Ganglegg/Schluderns (South Tyrol, Italy)

Up to now, archaeobotanical investigations of prehistoric sites in the eastern Alpine region have been rare. Recent palaeoethnobotanical investigations of carbonised plant remains from two Bronze Age hill-top settlements, one located north and the other south of the main Alpine range, contribute essentially to the knowledge of subsistence strategies and husbandry regimes in the Alps in prehistoric periods. The principal cereals were Hordeum vulgare (hulled barley), Triticum dicoccon (emmer) and Panicum miliaceum (broomcorn millet). In general, hulled barley was the most important cereal crop in the eastern Alps. Legumes such as Vicia faba (horse bean) and Pisum sativum (pea) also occurred regularly in both hill-top settlements. In addition to these field crops, a large variety of wild plants was still gathered and contributed considerably to the daily diet. The arable weed flora suggests that crops were sown in spring and autumn and it indicates crop rotation in this period. The results of the plant macrofossils imply a complex pattern of plant resource utilisation in the Alpine area during the Bronze Age.     

Autecology of Bradyrhizobium japonicum in soybean-rice rotations

The effect of rice culture on changes in the number of a strain of soybean root-nodule bacteria, (Bradyrhizobium japonicum CB1809), already established in the soil by growing inoculated soybean crops, was investigated in transitional red-brown earth soils at two sites in south-western New South Wales. At the first site, 5.5 years elapsed between the harvest of the last of four successive crops of soybean and the sowing of the next. In this period three crops of rice and one crop of triticale were sown and in the intervals between these crops, and after the crop of triticale, the land was fallowed. Before sowing the first rice crop, the number of Bradyrhizobium japonicum was 1.32×10⁵ g^–1 soil. The respective numbers of bradyrhizobia after the first, second and third rice crops were 4.52 ×10⁴, 1.26×10⁴ and 6.40×10² g^–1 soil. In the following two years the population remained constant. Thus sufficient bradyrhizobia survived in soil to nodulate and allow N₂-fixation by the succeeding soybean crop. At the second site, numbers of bradyrhizobia declined during a rice crop, but the decline was less than when the soil was fallowed (400-fold cf. 2200-fold). Multiplication of bradyrhizobia was rapid in the rhizosphere of soybean seedlings sown without inoculation in the rice bays. At 16 days after sowing, their numbers were not significantly different (p<0.05) from those in plots where rice had not been sown. Nodulation of soybeans was greatest in plots where rice had not been grown, but yield and grain nitrogen were not significantly different (p<0.05). Our results indicate that flooding soil has a deleterious effect on the survival of bradyrhizobia but, under the conditions of the experiments, sufficient B. japonicum strain CB 1809 survived to provide good nodulation after three crops of rice covering a total period of 5.5 years between crops of soybean.     

Effect of fungicidal essential oils against Botrytis cinerea and Rhizopus stolonifer rot fungus in vitro conditions

The development of natural crop protection products as alternatives to the use of synthetic fungicides is currently popular. The aim of this study is to evaluate the antifungal effects of several essential oils against the fungal pathogens, Botrytis cinerea and Rhizopus stolonifer, under in vitro condition. Four essential oils (fennel, black caraway, peppermint and thyme) were each tested at five concentrations (0, 200, 400, 600 or 800 μl l^?1). In vitro results showed that the essential oil of black caraway and fennel had the highest fungicidal effect against B. cinerea and R. stolonifer, respectively. The growth of B. cinerea was completely inhibited by the essential oil of black caraway at 400 μl l^?1. Fennel oil perfectly inhibited growth of R. stolonifer fungus colonies at concentration higher than 600 μl L^?1 in potato dextrose agar medium. Percentage of spores germination was the lowest in medium of Fennel and black caraway essential oils, and was the highest in Thyme ones. These results show that plant essential oils can have a strong effect on reducing post-harvest decay. These plant essential oils could provide an alternative to synthetic chemicals to control post-harvest phytopathogenic fungi on fruit.     

Oat residue and soil compaction influences on common root rot (Aphanomyes euteiches) of peas in a fine-textured soil

Management of common root rot (Aphanomyces euteiches Drechs.) in peas (Pisum sativum L.) is sought primarily by host crop avoidance for several years. Soil compaction is known to aggravate A. euteiches disease in peas but effects on infection and subsequent symptom development are not sufficiently known to assist in cultural control. Several isolated observations have noted that oat crop residues may suppress A. euteiches infection and disease in pea roots. The individual and combined influence (a factorial combination of two factors each at two levels) of a prior oat crop and soil compaction were studied for their effects on common root rot severity in processing peas grown in an A. euteiches disease nursery on a fine-textured soil in the northern Corn Belt of the USA. A previous crop of summer oats relative to prior-year peas significantly suppressed common root rot and increased pea fresh vine weight 210% at peak bloom stage. Both fresh vine weight and green pea yield were reduced as much as 63% by soil compaction and increased as much as 48% by a prior oat crop. Greater soil bulk density at the 10 to 25-cm depth identified wheel traffic compaction patterns in each year. A 10-fold reduction of saturated hydraulic conductivity in the 10 to 25-cm compacted zone and high soil-water potentials within the upper 60 cm both confirmed an impaired water drainage, especially during infiltration events. These observations support the use of a previous full season or summer oat crop jointly with chisel plowing, plus the prevention of excessive traffic during secondary tillage and planting, to reduce common root rot in a field infested with A. euteiches. Shallow incorporation of oat shoot and root residue by chiseling could be a crucial component of the cultural control of the disease. R Rodriguez Kabana Section editor     

Studies on the etiology of black rot, Stemphylium radicinum (Meier, Drechsl. & Eddy) Neerg., and leaf blight, Alternaria dauci (Kühn) Groves & Skolko, on carrot crops; and on fungicide control of their seed-borne infection phases

Of nineteen commercial samples of carrot seed in use at Wellesbourne in 1963, eight were found to be infected with both Stemphylium radicinum and Alternaria dauci and five with S. radicinum alone. Both fungi caused damping-off of seedlings and when carrots were grown at high densities A. dauci caused severe foliar infection. Neither fungus gave rise to marked infection of ware crops at normal spacings but, when seed infected with S. radicinum was sown in the autumn, the resulting seed crop was heavily infected by the succeeding autumn. Spring-sown carrots grown in soil that had borne infected crops or contained debris infected with either fungus showed little or no infection in the autumn or after storage for 3 1/2 months; autumn-sown or spring-planted (steckling) carrots put into ground infected with S. radicinum showed severe infection in the following autumn. This suggested that ware-crop carrots were resistant to infection from the soil whereas the seed crop was not. Both fungi were eradicated from seed by a 24 hr. soak at 30d? C. in a 0.2% thiram suspension, but were not completely eliminated by seed dust treatments with a range of fungicides.     

Effects of potnetial trap crops and planting date on soil infestation with potato cyst nematodes and root-knot nematodes

In 1997 and 1998 the stimulation of hatch of potato cyst nematodes (PCN) by a trap crop was studied at various times during the growing season in a container and a field experiment. Solanum nigrum‘90‐4750‐188’was used as the trap crop in both experiments and was sown on 1 May, 16 June or 1 August in two successive years on different plots. Neither experiment revealed much seasonal variation in hatchability of PCN juveniles under a trap crop. In the container experiment, the hatch of the Globodera pallida Pa3 population was equally and strongly stimulated (89%) at all sowing dates in both years, except for the 1 August sowing in 1998 (when the hatch was 77% under extremely wet soil conditions). In the control treatment with non‐hosts (flax followed by barley) the total spontaneous hatch was 50% over 2 yr. In the field experiment, the hatch of PCN, averaged over the four populations, was also equally stimulated (71%) at all sowing dates in both years. In the control treatment with non‐hosts (flax‐barley) the total spontaneous hatch was 36% over 2 yr. Total hatch under the trap crop over 2 yr varied between the four PCN populations from 63% to 80%. In 1998 and 1999, control of potato cyst nematodes (PCN) by the potential trap crops Solanum sisymbriifolium and S. nigrum‘90‐4750‐188’was studied in the field. Potato was also included as a trap crop. In the 1998 experiment, potato, S. sisymbriifolium and S. nigrum strongly stimulated the hatch of PCN compared with the non‐host white mustard (Sinapis alba). Roots of potato and white mustard were mainly found in the top 10 cm of soil, whereas roots of S. sisymbriifolium and S. nigrum were also abundant at depths of 10–20 cm and 20–30 cm. In the 1999 experiment, soil infestation with PCN decreased markedly with potato and S. sisymbriifolium as trap crops. In plots moderately to severely infested with 2‐yr old cysts (2–29 juveniles ml^?1 air dried soil), potato reduced soil infestation by 87% and S. sisymbriifolium by 77%. In plots moderately to severely infested with 1‐yr old cysts the reductions were 74% and 60%, respectively. The reduction was least on plots very severely infested with PCN (110–242 juveniles ml^?1 soil): 69% and 52% for potato and S. sisymbriifolium, respectively. Soil infestations of plots that were initially slightly to severely infested with the root‐knot nematode Meloidogyne hapla were greatly reduced under fallow and S. sisymbriifolium but increased under potato. From these and previous experiments it was concluded that, for several reasons, S. sisymbriifolium is a promising trap crop.     

The effect of resistant cultivars of catch crops on the hatching of Heterodera schachtii

In laboratory tests with Heterodera schachtii, root leachates of nematode-resistant and susceptible cruciferous crops stimulated egg hatches of up to 77% and 95% respectively. In these tests very little hatch occurred at 5°C or 10°C, more at 15°C and most at 20°C. In field experiments in which these crops were sown in September 1982 and August 1983 into soil infested with H. schachtii, numbers of viable eggs had decreased only slightly under resistant crops 4–5 months later. This was possibly because the soil was too cold and dry to permit a large proportion to hatch.