Factoren, welke van belang zijn bij de beoordeling van de mate der spintbestrijding door wintersproeimiddelen

Summary

In laboratory trials with ovicidal sprays on red spider winter eggs it was found that these sprays retarded the hatching of the eggs, that were not killed by the spray. In orchardspraying during wintertime the same phenomena was seen. A very poor acting oil emulsion was chosen so as to demonstrate the effect mentioned above more clearly. On the sprayed trees the hatching of the eggs was much delayed compared with the check trees; this was especially the case in the first period of hatching. If a count had been made only at this period the kill of the eggs by the winterspray would have been 80–90% compared with the checks. If the counts were made at a later date one would only find a kill of 30–40% compared with the check.

These facts demonstrate the absolute necessity of several countings if big mistakes will be avoided.

The delayed hatching of the winter eggs of red spider seems to be due to the stage of development of the eggs at the time of spraying. The further the development the more sensitive are the eggs.