De Invloed van de Uitwendige Omstandigheden Bij Het Optreden van Boonenziekten

Summary

The influence of environmental conditions on diseases of the bean (Phaseolus) were studied last summer on the field and at the laboratory.

The diseases due to deficiencies of anorganic matter were accompanied by distinct symptoms during June and July, but later on could scarcely be recognized. The dry and warm conditions during both these months were the cause of great damage due to red spider and plant lice. The virus diseases which are transmitted by lastnamed insects, were very much spread, in particular„curlmosaic” (Phaseolus virus 1), „yellow mosaic” or „steengrauw” (Phaseolus virus 2?).

„Stipple-streak” (Nicotiana virus 11?) was partly masked during the heat season, but showed in August characteristic redbrown „ringspot” on the pods. This virus disease has wrongly been taken for a bacterial blight.

The haloblight, however, is seedborne and gave rise to a heavy attack e.g. on „Ceka” beans in August. In June and July the disease could hardly be discovered in the fields.

Further some „rust”- and „foot” diseases have been studied, which are often troubled withUromyces appendiculatus andColletotrichum Lindemuthianum. It was shown thatAscochyta Boltshauseri andAscochyta phaseolorum, both seedborne diseases, caused at first a foot- and stem-anthracnose, which was of little importance in midsummer; but in August the disease spread over the leaves and pods, causing brownish spots that flow together and give a reduction of quality and in yield.

The footrots due to Fusarium sp., Sclerotinia sclerotiorum and Botrytis cinerea eem also to increase during cool moist weather.