3
 Monitoring Spider Mite Densities
 The comprehensive est services of an adequately trained and experienced field
 scout are important to the success of pest management even when biological
 control is not a pa t of the system. However, these services are critical
 when biological con rol is used. A scout can be of enormous value in
 determining the cor ect timing of a predator release, assessing the success of
 the release, and gi ing early identification of problems (insects, diseases,
 etc.) that may have hearing on the success of biological control and
 ultimately the succe s of the crop.

 To manage spider mit populations successfully, an appropriate monitoring
 system is essential. Weekly monitoring usually will give sufficient
 information, but during critical periods, for instance close to decision
 making for the release increase the frequency to every 3 to 4 days. A hand
 lens, with a magnific tion of 6X to 14X, is indispensable for recognition of
 the various stages of mites. Always take a random, 100 leaflet (one of the
 three blades of a who e strawberry leaf) sample and keep records of results.
 Continue weekly monit ring for 6 to 8 weeks once the predators have been
 released.

 Counting spider mites nd their eggs on leaves in the field is difficult and
 time consuming. A rel tionship exists between the number of leaves infested
 with spider mites and he average mite density per leaf, so that a simple
 "absence/presence" sys em has been developed. The relationship between the
 number of infested lea es and the average mite density per leaflet in a sample
 of 100 leaflets is shove in Table 1.

 Table 1. Relationship between the percentage infested leaves and the average
 mite density n strawberry leaves.


 Average mite
 % infe ted leaves density per leaflet

 -5 2- 4
 -10 5- 9
 11 15 10 -13
 16 20 13 -15

There are three periods d ring which assessment of spider mite populations is
critical. These are:

1. Before planting. S rawberry plants from nurseries often arrive
 infested with spider mites. Careful examination of the plants is
 essential to determi e their presence. Each plant shipment should be
 inspected as differ t shipments from one nursery may have a different
 history; records sho ld be kept of plant sources, cultivars and planting
 locations. Fifty 1 0 plants from each shipment should be inspected;
 if 10 or more plants re infested, a miticide should be applied as soon