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In a more years-lasting field trial the influence of a second crop cultivation of rye and rape in winter time on the incidence of Rhizoctonia solani Kühn on potato or mustard as indicator plants was studied. The second crops were ploughed in during spring time. On part of the trial was artificially infested by this causal agent. Three crop rotations with different proportions of host plants (potato) were compared. The results obtained demonstrate the following: 1. On the part of experimental area arficially infested the incidence rate was higher for 3 till 4 years than on the control plots, but later it became equally to the control one, which also was very high (approximately 50). 2. In the last very dry year (1969) the disease developed only a little. 3. The second crop cultivation decreased the incidence of R. solani in 7 (rye) or 8 (rape) of 10 cases, but mostly the rate of decreasing was low. 4. A high weed density induced by a diminished mechanical cultivation increased the incidence of R. solani at the end of the experiment (1969), specially in the rotation with 80% host plants. 5. The number of soil bacteria, the respiration rate, and partly also the activity of dehydrogenase and the soil acidity were increased by green manuring of the second crop, however, the number of the actinomycetes, and the cellulolytic activity didn't be influenced remarkably. 6. The second crop cultivation ist nounced as a measure stimulating the soil fertiligy and discussed in connection with the microbial processes taking place in soil.

1. In glass-house trials the influence of residues of clover, grass, and mixtures (1:1) of them added to natural and partially sterilized loam soil upon the parasitic activity of Rhizoctonia solani and the soil micro-organisms and their activity was analyzed. 2. Burying of plant residues (1%) increased the content of organic substance in soil for 8 weeks and longer. 3. The soil reaction (pH) was not noteworthy affected by application of clover or grass residues. 4. However, the populations of bacteria and actinomycetes were increased, especially by adding clover dried. In natural soil, the maximum of stimulation was reached later than in soil sterilized. Adding of grass and roots of grass enlarged the spectrum of fungi observed in the soil amended. Roots of grass stimulated the cellulose-decomposing organisms remarkably. 5. The activity of dehydrogenase (AD) was influenced in different manner: in natural soil fresh clover, grass, mixtures of them, and clover dried increased, and fresh roots of clover, grass, and mixtures of them diminished AD; in soil sterilized the most variants stimulated this activity. 6. All plants residues increased the cellulolytic activity of soil for a long time, but in sterilized soil this effect reached its maximum earlier than in natural soil amended and did not last so long, too. 7. The possible explanations for the inhibition of parasitic activity of Rhizoctonia solani caused by burying plant residues are discussed.

In a five-years field trial, the influence of two winter catchcrops, rye and rape, upon the incidence of Cercosporella herpotrichoides has been studied. The winter catch-crops had been repeated three times, followed either by stubble-crop or without in fall of the fourth year. The variants (blocks) had been completed by two variants without catch-crop, either carefully cultivated or overgrown with weeds. Each of the four blocks had been divided three times to be grown with three different crop sequences containing 80%, 60% (with the insusceptible corn), or 40% haulm fruit, respectively. Each of the 12 variants had been divided into two parts by continuous fallow stripe, one part being artificially infested with the pathogen in the beginning (1st winter wheat). In the 2nd, 3rd, and 4th year, only spring crops were grown, followed by winter wheat in the 5th year. The final exploration resulted in a medium to heavy degree of infection, being significantly higher in the 80% cereal crop sequence than in the 60% and 40% sequences. Concerning the catch-crops, infection in the rye variants was equal or significantly lower than in the carefully cultivated variants without catch-crop. On the other hand, infection of the rape variants had become significantly higher than that of the catch-crop-free ones, about as heavily as in the weed-infested variants. From fall 1966 to summer 1969, the development of the saprophytic soil microflora and several other edaphic parameters had been investigated. Remarkable differences in intensity of disintegration have been observed under the influence of the main crops, cereals or potatoes, respectively, but no differences could be stated resulting from the matter of disintegration--residues of rye or rape--, which might interpret the contrasting effects on the pathogen. Too, no indication for antagonistic activity of bacteria or actinomycetes has been noted. The results are compared with known facts of Cercosporella and of other soil borne pathogens. The difference in biology of Cercosporella on the one hand, and of root infecting fungi on the other hand seems to be most important to explain the results obtained.