For this, the insects are allowed to escape very slowly, as the base of the net is gradually opened. It is useful to carry small vials to collect insects requiring further identification. The only tool needed for this method is a carton or bucket in which to place the stems, or a tray onto which to shake the aphids or larvae from the stems. Sampling in still air is preferable to sampling in a light breeze, but is not often possible. Sampling in winds of more than 10 mph is not advised.
Insects are more active, and hence more visible and catchable, in warm weather.
Consequently, only second and third cuttings or recently established stands should be monitored. Monitoring for PLH may be concluded 7-10 days before harvest, since PLH cause little injury to more mature growth. First growth of spring planted seedling alfalfa should be checked closely for PLH, as it is much more sensitive to PLH injury. PLH Sequential Sampling Plan Crop ht. In very early regrowth, in which it is difficult to standardize sweeping efficiency, at least four 10-sweep samples should be taken per field.