Birgitta Rämert

Influence of soil fauna on fungal plant pathogens in agricultural and horticultural systems

Abstract An understanding of the ecology of plant pathogens is crucial for the development of agricultural and horticultural growing systems that enhance plant health. One important group of organisms that influences plant pathogen survival and dispersal is the soil fauna. This review deals with known and possible interactions between soil animals and different groups of fungal plant pathogens. It is suggested that facultative saprophytes may be affected considerably by mycelial grazing by soil animals, while obligate pathogens may be more influenced by animals that ingest spores and other types of propagules. Both types of pathogens can also be influenced by indirect interactions with the soil fauna. Manipulating the soil environment for enhancement of beneficial soil animals that consume pathogens seems to be a realistic possibility for sustainable agriculture and horticulture.

Effect of Intercropping on Oviposition and Emigration Behavior of the Leek Moth (Lepidoptera: Acrolepiidae) and the Diamondback Moth (Lepidoptera: Plutellidae)

Abstract We compared the effect of intercropping on oviposition and emigration behavior of two related specialist moth species. The effect of height of the intercrop species (red clover) on oviposition was studied in field cages, using the leek moth, a specialist on Allium species, and the diamondback moth, a specialist on Brassica species. The moths were also evaluated in an open field experiment. Emigration of both moths was studied in the laboratory and in the field in cages with host plants, red clover (nonhost), host plant and red clover, and bare soil. The possible influence of noncontact stimuli was also studied in the laboratory. The leek moth laid the same amount of eggs in monoculture as in intercroppings with high and low clover. White cabbage intercropped with high clover received fewer eggs of the diamondback moth compared with a cabbage monoculture. Intercropping with low clover did not reduce the amount of eggs laid. Intercropping did not appear to affect the emigration of either the leek moth or the diamondback moth. Leek moths were less likely to emigrate than diamondback moths during the first 4 h of the study. We conclude that diamondback moth may be more likely to be controlled by intercropping than leek moths.

Evaluation of Growing Media Containing Farmyard Manure Compost, Household Waste Compost or Chicken Manure for the Propagation of Lettuce (Lactuca sativa L.) Transplants

ABSTRACT Organic substrates, based on sphagnum peat and farmyard manure compost, household waste compost or chicken manure were tested for their suitability for plant propagation of lettuce. Net N mineralization in the substrates was followed, as well as uptake of plant nutrients and heavy metals in lettuce transplants. Net N mineralization from the compost-based substrates was not significantly secured and very low, about 1 % of initial organic N content during the 28-day period from the time of sowing the lettuce to the end of the propagation period. In the two chicken manure substrates, net N mineralization was higher, 9 and 28%, respectively, during a period of 50 days, which included the 3 weeks from mixing of substrates until the start of the propagation period. However, it was not only the total amount of net N mineralized that differed considerably between the two chicken manure substrates but also the rate of nitrification. There was a strong negative correlation between pH in the substrates and Cd concentrations in transplants, resulting in unacceptably high Cd levels in transplants grown in substrates with very low pH. Of the tested organic substrates, the one with the lowest concentration of farmyard manure was the most suitable for plant propagation of lettuce.

Germination of Plasmodiophora brassicae resting spores stimulated by a non-host plant

Plant-induced germination of Plasmodiophora brassicae resting spores was studied in a laboratory experiment. Spore reaction was analysed in nutrient solution with exudates from growing roots of different plant species – one host plant (Brassica rapa var. pekinensis) and four non-host plants (Lolium perenne, Allium porrum, Secale cereale and Trifolium pratense) – and in controls with distilled water and nutrient solution. It was found that root exudates from L. perenne stimulated spore germination more than exudates from the other plants, including those from the host plant. The effect could not be explained by differences in the nutritional composition of the solutions due to differential uptake of the plant species, or by differences in root activity, measured as exudation of soluble sugars. This is the first time such a separation of factors has been done in analysing the influence of plants on P. brassicae germination. Although stimulation of P. brassicae resting spore germination is not restricted to the presence of host plants, it seems to vary depending on the plant species.

Evaluating the enemies hypothesis in a clover-cabbage intercrop: effects of generalist and specialist natural enemies on the turnip root fly (Delia floralis).

1 The relative importance of the resource concentration hypothesis and the enemies hypothesis was investigated for the turnip root fly Delia floralis in a cabbage–red clover intercropping system compared with a cabbage monoculture. 2 Delia floralis egg densities were measured as well as the activity‐densities of generalist predators in a field experiment during two growing seasons. In the second year, a study of egg predation with artificially placed eggs was conducted, in addition to a predator exclusion experiment, to estimate total predation during the season. Parasitization rates were estimated from samples of pupae. 3 Delia floralis oviposition was greater in the monoculture during both years. The predator activity‐densities differed between treatments and study years. The known natural enemies of Delia spp., Bembidion spp. and Aleochara bipustulata showed a strong response to a cultivation system with higher activity‐densities in the monoculture. The response, however, appeared to be caused primarily by habitat preferences and not by D. floralis egg densities. 4 The reduction in the number of D. floralis pupae in the intercropping may be explained by a disruption in oviposition behaviour caused by the presence of clover because neither predation, nor parasitization rates differed between cultivation systems.

Use of Herbage Compost as Horticultural Substrate and Source of Plant Nutrients

ABSTRACTThe potential of herbage composts as horticultural substrate and source of nutrients was investigated. The effect of botanical composition of the herbage, as well as the effect of different kinds and amounts of carbon sources, on nitrogen losses during composting and growth properties of the compost were studied. Growth tests with different plant species as well as chemical analyses of total- and easily-soluble plant nutrients were used to evaluate compost quality. Seven herbage composts were studied and used in growth tests with seven different test plants. The results were evaluated by conventional and multivariate statistical methods.Accumulated nitrogen losses tended to vary with carbon source added, and were 2–25% of the initial N content over a 130-day composting period. Plant growth and seed germination were largely explained by the electrical conductivity of the compost mixes. Potassium concentrations were very high in the composts. The results showed the possibility of using herbage compo...

Organic household wastes as a nitrogen source in leek production.

Composted and anaerobically digested organic household wastes were evaluated as N sources in leek (Allium porrum L.) production in an incubation experiment without plants and in an outdoor frame with plants. Their N-fertilizing values were compared with that of chicken manure. Both experiments were conducted on four soil types (sand, two loams and a clay). After 168 days of incubation the percentage of inorganic N of total N applied was 40-60% for slurry, 15% for compost and 20-30% for chicken manure. Only in treatments with chicken manure was net N mineralization achieved in all four soils at the end of incubation. In the frame experiment, between 5 and 20% of the slurry N, 1% of the compost N and 6% of the chicken manure N was utilized by the above-ground leek crop. Slurry gave 1-20 Mg ha

Mortality risk from entomopathogenic fungi affects oviposition behavior in the parasitoid wasp Trybliographa rapae

Biological control of pests in agroecosystems could be enhanced by combining multiple natural enemies. However, this approach might also compromise the control efficacy through intraguild predation (IGP) among the natural enemies. Parasitoids may be able to avoid the risk of unidirectional IGP posed by entomopathogenic fungi through selective oviposition behavior during host foraging. Trybliographa rapae is a larval parasitoid of the cabbage root fly, Delia radicum. Here we evaluated the susceptibility of D. radicum and T. rapae to two species of generalist entomopathogenic fungi, Metarhizium brunneum isolate KVL 04-57 and Beauveria bassiana isolate KVL 03-90. Furthermore, T. rapae oviposition behavior was assessed in the presence of these entomopathogenic fungi either as infected hosts or as infective propagules in the environment. Both fungi were pathogenic to D. radicum larvae and T. rapae adults, but with variable virulence. When host patches were inoculated with M. brunneum conidia in a no-choice situation, more eggs were laid by T. rapae in hosts of those patches compared to control and B. bassiana treated patches. Females that later succumbed to mycosis from either fungus laid significantly more eggs than non-mycosed females, indicating that resources were allocated to increased oviposition due to perceived decreased life expectancy. When presented with a choice between healthy and fungal infected hosts, T. rapae females laid more eggs in healthy larvae than in M. brunneum infected larvae. This was less pronounced for B. bassiana. Based on our results we propose that T. rapae can perceive and react towards IGP risk posed by M. brunneum but not B. bassiana to the foraging female herself and her offspring. Thus, M. brunneum has the potential to be used for biological control against D. radicum with a limited risk to T. rapae populations.

The influence of intercropping and mulches on the occurrence of polyphagous predators in carrot fields in relation to carrot fly (Psila rosae (F.)) (Dipt., Psilidae) damage

Abstract: During 1989 and 1990 an inventory was made of beetles (Coleoptera), in the families Carabidae and Staphylinidae and spiders in carrot fields with a ley clipping mulch, a bark mulch, or lucerne (Medicago littoralis) as an intercrop. Two sites in central Sweden were included in the study. The most common carabid species at Uppsala were Bembidion quadrimaculatum, B. lampros, and Trechus quadristriatus. At Torslunda, B. lampros, Calathus melanocephalus, T. quadristriatus, Amara bifrons, and Harpalus rufipes were the most abundant. The most abundant staphylinid genera at Uppsala were Anotylus, Arpedium, Philonthus, and Aleochara, while at Torslunda Philonthus, Aleochara, and Anotylus were the most abundant. Differences in occurrence, measured as trap catch or numbers per soil sample, between treatments and over the season are presented and discussed. Emphasis was placed on assessing the potential importance of these predators in suppressing carrot fly populations.

Neighbouring monocultures enhance the effect of intercropping on the turnip root fly (Delia floralis)

Knowledge of insect behaviour is essential for accurately interpreting studies of diversification and to develop diversified agroecosystems that have a reliable pest‐suppressive effect. In this study, we investigated the egg‐laying behaviour of the turnip root fly, Delia floralis (Fall.) (Diptera: Anthomyiidae), in an intercrop‐monoculture system. We examined both the main effect of intercropping and the effect on oviposition in the border zone between a cabbage monoculture [Brassica oleracea L. var. capitata (Brassicaceae)] and a cabbage‐red clover intercropping system [Trifolium pratense L. (Fabaceae)]. To investigate the border‐effect, oviposition was measured along a transect from the border between the treatments to the centre of experimental plots. Intercropping reduced the total egg‐laying of D. floralis with 42% in 2003 and 55% in 2004. In 2004, it was also found that the spatial distribution of eggs within the experimental plots was affected by distance from the adjoining treatment. The difference in egg‐laying between monoculture and intercropping was most pronounced close to the border, where egg‐laying was 68% lower on intercropped plants. This difference in egg numbers decreased gradually up to a distance of 3.5 m from the border, where intercropped plants had 43% fewer eggs than the corresponding monocultured plants. The reason behind this oviposition pattern is most likely that flies in intercropped plots have a higher probability of entering the monoculture if they are close to the border than if they are in the centre of a plot. When entering the monoculture, flies can pursue their egg‐laying behaviour without being disrupted by the clover. As the final decision to land is visually stimulated, flies could also be attracted to fly from the intercropped plots into the monoculture, where host plants are more visually apparent. Visual cues could also hinder flies in a monoculture from entering an intercropped plot. Other possible patterns of insect attack due to differences in insect behaviour are discussed, as well as the practical application of the results of this study.