Over den smaak van stoppelknollen in verband met den weerstand tegen knolvoet

Summary The method to determine the mustard oil content in turnips, by means of silver-ammonio nitrate (blackcolouring) is not reliable under dutch conditions. Nor does blackcolouring give any indication as to the sharpness of taste. A difference must be made between sharpness (probably localized in the shell) and the typical taste of turnips.The relation often suggested between sharpness of taste, resulting bij high mustard oil content and resistance against Club Root a relation unfavourable for selection, does apparently not exist.     

Proeven over de zaadbehandeling tegen de bonenvlieg,Delia (Chortophila) cilicrura Rond.

Summary Good results in control of the seed-corn maggot in beans were obtained in a field trial in 1952, by treating the seed with lindane. At present the recommended dosage is 5 grms, 20% lindane per kg seed. Soil treatment with lindane, BHC and parathion gave no beneficial results.     

Plantenziektenkundige vraagstukken in verband met de vlascultuur

Voordracht gehouden op de Landbouwweek, Juni'32, Wageningen     

Het voorkomen van resistentie tegen organische fosforverbindingen bij de bonespintmijt (Tetranychus urticae) in Aalsmeer

Samenvatting Bij een onderzoek naar de gevoeligheid voor acariciden van spintpopulaties, afkomstig van verschillende bedrijven in Aalsmeer, bleek in 20 van de 22 onderzochte gevallen een resistentie te bestaan tegen organische fosforverbindingen. Deze resistentie bleek ook te bestaan ten opzichte van organische fosforverbindingen, die nooit eerder tegen de onderzochte spintpopulaties gebruikt waren. De resistentie tegen demeton (Systox) bleek bij enkele populaties niet even groot.Tegen acariciden op basis van gechloreerde koolwaterstoffen zoals kelthane en chloorbenzilaat, werd nog geen resistentie bij de onderzochte populaties aangetroffen.Een onderzoek naar de gevoeligheid voor acariciden van spintpopulaties, welke in de directe omgeving buiten de kassen op onkruiden e.d. voorkomen, leidde tot de conclusie dat resistente spintmijten niet buiten de kas voorkomen. De resistentie van spintpopulaties is op de verschillende bedrijven in Aalsmeer zelfstandig spontaan opgetreden. Er bleek geen correlatie te bestaan tussen de verschillende waardplanten (roos, anjer enGerbera) en het optreden van resistentie.Summary During the year 1958 the susceptibility to acaricides of a number of populations of the two-spotted spider mite (Teranychus urticae Auct.) occurring in several nurseries in Aalsmeer (fig. 5) was studied at the Experimental Station for Floriculture at Aalsmeer, The Netherlands.The susceptibility of a population was examined by placing 50 adult female mites on a bean plant, treated with an acaricide. The percentage mortality was determined after four days.In these experiments both spider mite populations in the greenhouses (on roses, carnations andGerbera) and those in the open air near the greenhouses (on weeds) were studied. Fig. 1 gives the susceptibility of the different populations for water, parathion, diazinon, demeton (Systox) and kelthane. Of the 22 populations from glasshouses 20 proved to be resistant to organic P-compounds. Of those collected from weeds growing outside the greenhouses, not a single one proved to be resistant, so that it may be taken for granted that the resistant red spider mite, found in the greenhouse, does not survive outside.A number of populations were examined for their susceptibility to some other acaricides (fig. 2). In this experiment the resistance to those organic P-compounds with which the populations had never been treated before, such as phosdrin, thiometon and phenkapton was observed. It clearly illustrates that there is no question of resistance to a definite acaricide, but to the group of organic P-compounds. Resistance to demeton did not prove to be equally strong for every population.In all cases examined chlorinated hydro-carbons, such as kelthane and chlorobenzilate, proved to be normally active. Resistance to this group of acaricides has not yet been found in Aalsmeer.A special case is stated in fig. 3, where the spider mite population in a cucumberhouse, in which no chemical control had been applied, is compared with a population on nettles outside the glasshouse and a resistant population in a rosehouse of the same nursery.An experiment, repeated on several dates over a period of 13 months (fig. 4), shows that there was no important shift in the susceptibility of the population studied. It is clear that the resistance of two-spotted spider mites to organic P-compounds has been developed in Aalsmeer independently in more than twenty separate glasshouses.In no case the host plant (carnation, rose,Gerbera) proved to have an appreciable influence on the appearence of resistance.     

Bescherming van jonge plantsoenen tegen wildschade

Naar:Protection contre les dégáts du gibier, note du service spécial de recherches et consultations en matière forestière du Ministère de l’Agriculture.