Multiresistentie van de bonespintmijt (Tetranychus urticae) in Aalsmeer

Samenvatting Een populatie van kasspint (T. urticae Auct.), die werd verzameld in een rozekas, werd onder laboratoriumcondities gekweekt en onderzocht op gevoeligheid voor kelthane. Het bleek, dat deze populatie resistent was tegen dit middel. Deze resistentie heeft zich binnen de tijd van twee jaar ontwikkeld. In deze twee jaar is van de groep van gechloreerde koolwaterstoffen kelthane slechts in hoogstens tien bespuitingen toegepast. Dat deze resistentie een cross-resistance is, wordt waarschijnlijk gemaakt door het feit dat ook voor chloorbenzilaat resistentie was opgetreden.Summary A spider mite population from an Aalsmeer rose-house was cultivated under laboratory conditions and its susceptibility to kelthane examined. It was found to be resistant to kelthane (figs. 1 and 2) and as it was also resistant to chlorobenzilate it must be assumed that this is a case of cross-resistance to the group of chlorinated hydrocarbons. This resistance developed within two years and after no more than ten applications. As the population was resistant to organophosphorous compounds, also, this is the first case of multi-resistance at Aalsmeer.     

Het uitwendig steriliseren van planten bij fytopathologisch onderzoek

Summary To demonstrate the presence of a fungus in plant tissue, parts of plants are often placed on agar plates. In this case it is necessary to be certain that the fungus does not occur on the outside of the plant.In the present study it is demonstrated that some common methods of disinfection are not sufficient to kill all conidia ofFusarium oxysporum which are present on the outside of plants. We give the results of experiments with the following disinfectants: 0,2% corrosive sublimate — 2 min., 50% to 96% ethanol — 2 tot, 10 min., and 4% sodium hypochlorite — 2 min. It is probable that these results also hold true for other fungi.     

Het vaststellen van de door de erwteknopmade (Contarinia pisi) veroorzaakte schade en de bestrijding van dit insekt

Summary The preceding paper deals with the damage caused byContarinia pisi. The technique used to determine the losses of yield is discussed. Heuver (1960) is of the opinion, that the cutting of flowerbuds (in fact flowers and young pods) of the pea plant is comparable to an infestation byContarinia pisi. However, according to the present authors' investigations these injuries are not comparable. It is also impossible to investigate the exact damage by treating small plots in larger untreated pea fields because reinfestation of the treated plots will occur.The most feasible method to determine crop losses is by comparing average yields in a well treated area with the yields obtained in untreated fields in the same area.The accuracy of this method is greatest in years when damage is heavy.The damage to both canning peas and harvesting peas may be serious.     

Het toezicht op de constantheid van samenstelling van vruchtboomcarbolineum

Voordracht gehouden tijdens de Landbouwweek te Wageningen 3 t/m 7 5uli 1933