EFFECTS OF COVER CROPS, WEEDS AND PLANT DEBRIS ON DEVELOPMENT OF MYCOCENTROSPORA-ACERINA IN CARAWAY

This paper reports on the search for inoculum sources of Mycocentrospo ra acerina on caraway (Carum carvi L.). Obvious suspects are cover cro ps of biennial caraway and preceding crops of annual caraway. Other su spects are weeds in or alongside the field. Finally, survival structur es of the fungus, chlamydospore chains, packed in plant debris or nake d, are suspected. M. acerina is able to infect many plant species, inc luding cover crops of caraway such as spinach for seed production and peas. However, the agronomical suitability of a crop to serve as a cov er crop of biennial caraway proved to be a more important factor in de termining caraway yield than the susceptibility of the cover crop to M . acerina. This finding was corroborated by the fact that spinach and peas as preceding crops had no significant effects on M. acerina devel opment in spring caraway sown the next year. Dill, barley and four wee d species were found as new hosts of M. acerina. The role of weed host s, susceptible crops and plant debris in the survival of the fungus in years without caraway is discussed. Caraway sown on soil containing i nfested caraway straw, infested debris of other plant species or chlam ydospores grown in pure culture, became infected by M. acerina. Only h igh inoculum densities of chlamydospores in the soil caused severe dam ping-off of caraway seedlings. The opportunity for disease management by agronomical means is quite limited.