although by definition directly toxic to mites, still offer a 

 spectrum of safety to predator mites, ranging from 

 dormant oil that is relatively safe to A. fallacis, to 

 formetanate hydrochloride (Carzol^^) which is extremely 

 damaging to predator mites. Miticides in current use are 

 arranged in terms of relative safety toA. fallacis, the major 

 mite predator in Massachusetts, in Table 3. 



Second-stage IPM, currently being developed in 

 Massachusetts apple orchards, provides another approach 

 to pesticide management that aids in conserving mite 

 predators. Under this management strategy, regular cover 

 sprays are used only in the early portion of the growing 

 season (to approximately the end of May). After this 

 period only fungicide applications are made. Apple 

 maggot fly damage is prevented after termination of cover 

 sprays by intensive trapping (using red sticky spheres) and 

 removal of wild or abandoned apple and hawthornc trees. 

 Preliminary data on this strategy from 1987 tests show an 

 improvement of predator:prey mite ratios from 1:9 in 

 grower-sprayed control blocks to 1:5 in second-stage 1PM 

 blocks. At the 1:5 ratio predator mites can be relied on to 

 maintain spider mites under commercially acceptable 

 control in most cases. 



Nitrogen Management . Apple foliage with elevated 

 nitrogen levels is a more nutritious food for spider mites, 

 resulting in more rapid development and a larger number 

 of eggs laid per female mite (van DcVric & Boersma, 

 1970). This more rapid build up of spider mite populations 

 makes control by any existing level of predator mites more 

 difficult. Nitrogen levels thus should be kept at the lowest 

 levels consistent with healthy tree growth. Nitrogen may 

 become available to trees either directly, in the form of 



fertilizer applications, or indirectly from nutrients 

 released from groundcovers killed by herbicide 

 application or plowing. Growers should monitor actual 

 nitrogen levels in leaves and adjust their fertilization 

 practices accordingly. 



Groundcover Management . Over and above the 

 indirect effects of orchard floor vegetation management 

 through leaf nitrogen levels, groundcover management 

 directly influences predator numbers. Because A. fallacis 

 overwinters off the tree, groundcovers can influence the 

 numbers of predators that survive, and can affect the 

 timing in the following growing season of predator 

 movement back into the trees. The timing of predator re- 

 entry into trees depends in part on the availability of two- 

 spotted spider mites and other food sources in the 

 groundcover. The ideal groundcover species and 

 management practices are not known, but are currently 

 the subject of research in both Massachusetts and New 

 York. In addition, herbicides are sometimes used to kill 

 strips of orchard floor vegetation. Certain of these (e.g., 

 glyphosate, paraquat, and ammonium sulfamate, see 

 Table 2) are highly toxic to predator mites. 



Other actions that growers can take to promote 

 biological mite control include encouraging development 

 of apple rust mite populations. These mites make apple 

 leaves less favorable for spider mites and serve as food for 

 predator mites when spider mites are scarce. Alternate 

 food sources moderate predator mite population declines 

 when primary prey species are low in number with the 

 result that more predators remain in the orchard to 

 suppress spider mite populations when their numbers 

 begin to increase. 



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