predators should be released in each target tree. 



The fourth method of transferring T. pyri is 

 perhaps the easiest and does not carry the risks of 

 also moving unwanted pests that the three prior 

 methods have. Artificial overwintering sites for T. 

 pyri can be created by gluing burlap to the inside of 

 tree wrap. These composite bands, approximately 

 12 to 16 inches in length, are then placed on source 

 trees in early to mid-September by stapling them 

 around the tree bole and/or large scaffold 

 branches. In early December, these bands should 

 be collected, tightly rolled with a rubber band used 

 to hold them so, and placed in a sealed plastic bag 

 with a bit (ca. 1 in') of wet cotton. The bag should 

 be placed in an insulated storage container, which 

 in turn should be placed in a cold, though 

 protected, environment that will buffer large 

 temperature fluctuations. Ideally, temperatures 

 should be maintained right at the freezing point. 

 The following spring, the burlap bands should be 

 placed around recipient trees at around the half- 

 inch green bud growth stage. While the number of 

 predators that overwinter in bands is variable, as 

 many as 400 predators can be transferred in each 

 band. We suggest placing a single band on each 

 recipient tree if the bands were collected from trees 

 that harbored moderate to high numbers of T. pyri 

 (1-2 per leaf) the prior fall, and two bands in each 

 tree otherwise. 



After a receiver orchard is inoculated with T. 

 pyri, it often takes 2 to 3 years for the predator 

 population to become abundant enough to 

 regulate ERM without the need for any miticides. 

 During this time, additional control measures are 



often needed to keep ERM below damaging levels. 

 There are two key aspects to any strategy designed 

 to do so. First, early season dormant oil sprays 

 should be used to reduce ERM populations in the 

 spring. These oil applications have no deleterious 

 effect on T. pyri. Second, ERM numbers should be 

 monitored, and if densities exceed threshold levels, 

 a miticide that is not toxic to T. pyri should be used 

 to control the pest mites. Note that it is actually 

 desirable to have some pest mites in the trees after 

 inoculation with T. pyri because these plant- 

 feeding mites provide a food source for the 

 predators and foster faster predator population 

 growth. 



A commonly asked question is, "How do you 

 know when there are enough T. pyri to effect 

 biological control?" This question is difficult to 

 answer. While predators can be seen in the field, 

 they are easy to miss, especially at low densities, 

 and their impact on ERM is dependent on which 

 species they are. Guidelines have been provided 

 for the ratio of predators to ERM needed to 

 achieve biological control; however, estimating 

 these ratios is not practical. Fortunately, all that is 

 required to determine if biological control is 

 working is to note whether pest mites remain 

 below threshold levels. This can be determined 

 without regard to predator abundance. A 

 procedure for determining whether ERM exceed 

 threshold levels is described in the appendix. If 

 pesticide regimes for all orchard pests can be 

 followed that allow T. pyri to survive, these 

 predators will become abundant enough to make 

 miticide applications unnecessary. 



Appendix - Monitoring European Red Mite in Apple Orchards 



Damage by European red mites (ERM) to 

 apple leaves is best related to cumulative mite 

 density, which is measured as mite-days. Apple 

 trees with a normal crop load can tolerate 

 approximately 500 mite-days before reductions in 

 fruit yield or quality occur. Therefore, one goal of 

 any mite monitoring program is to ensure that 

 miticide treatments are recommended so as to 

 prevent 500 mite-days from occurring. Another 

 goal of a mite monitoring program is to allow 

 biological control to take its course when mite 



natural enemies (phytoseiid mites) are present. So, 

 a mite monitoring program should not recommend 

 intervention with pesticides when treatments are 

 not necessary. A final goal of a mite monitoring 

 program is to indicate when the pest population 

 should again be sampled to determine its status. If, 

 at the time of sampling, mite densities are very low, 

 then it is not necessary to sample the population 

 again in a short period of time. On the other hand, 

 if densities are currently close to but not greater 

 than a treatment threshold, the population should 



Fruit Notes, Volume 64 (Number 1), Winter, 1999 



