Thiram residues on glasshouse lettuce.

Thiram dust was applied at different concentrations and dates to lettuce crops and residue levels were analysed at harvest or at weekly intervals. The growth of the plant was the major factor influencing residue levels. The later the application the greater was the residue. The use of irrigation, either by spray lines or trickle equipment, appeared to have only a small effect on residue levels. Some of the fungicide could be washed off, but only if irrigation was applied in the early stages of crop development. (Abstract retrieved from CAB Abstracts by CABI’s permission

Methodiek voor de beproeving van bestrijdingsmiddelen tegen Cladosporium cucumerinum bij komkommers

Ook verschenen als: Publicatie / Proefstation voor de Groenten- en Fruitteelt onder Glas te Naaldwijk, No. 4

De chemische en biologische bestrijding van de spintmijt Tetranychus urticae Koch

Glasshouses have a favourable climate for greenhouse red spider mite, which can rapidly proliferate. Up to 1959 its practical control has been by chemicals only. Bravenboer studied whether biological control was also possible.Chemical treatment acted as a density-independent factor and was unable to regulate the population. It must frequently be repeated and would certainly lead eventually to resistance of the mite, so causing a failure of chemical control in the future.The predators Stethorus punctillum and Typhlodromus longipilus could act as density-dependent factors and regulate the population of Tetranychus urticae. Although the conditions for biological control were favourable in greenhouses, the predators alone were seldom able to give economic control of T.urticae. A single application of a selective acaricide per year gave adequate control.The first chapters deal also with taxonomic problems over Tetranychus urticae, with the influence of temperature on the development of both T. urticae and its mentioned predators, their egg production, their diapause (not for Typhlodromus longipilus), the influence of the host plant on the reproduction of T. urticae and many observations on the behaviour of predators in the presence of their prey