In addition, growers whose orchards have few 

 predator mites (due to factors such as past pesticide use 

 practices) can "re-seed" their orchards by purchasing 

 predators, such asA.fallacis, from commercial sources 

 and releasing them on orchard trees to induce a more rapid 

 increase in predator numbers, which must then be 

 conserved by altered (i.e. reduced pesticide) management. 

 In some cases such purchased predators may possess 

 higher levels of pesticide resistance than is common in 

 native predator mite populations. Such resistance will 

 promote better predator mite survival and reproduction 

 for populations subjected to pesticide use. 



State Programs to Enhance Biological Mite 

 Control 



Most of the decisions that influence biological mite 

 control in apples are made by growers. Two areas exist 

 however where state (or University) programs could 

 contribute to this process: introduction to Massachusetts 

 of more highly pesticide-resistant strains of existing 

 predator mite species and introduction of new species of 

 predator mites not currently found in Massachusetts. 

 Higher levels of pesticide-resistance than exist in field 

 populations have been induced in A. fallacis and other 

 species of phytoseiid predator mites. Such a pesticide- 

 resistant strain of A. fallacis has been released and 

 established in apples in Quebec with good results 

 (Bostanian & Coulombe, 1986). 



Existing native species of mite predators in 

 Massachusetts {A. fallacis etc.) are not necessarily the 

 most effective possible predator species. Some success has 

 occurred in establishing exotic predator mites in other 

 regions. For example, T.pyri has been moved successfully 

 to Austraha for control of European red mite (Thwaite & 

 Bower, 1980). Examples listed by McMurlry (1982) of 

 species that are of value against spider mites in apples in 

 other regions of the world \nc\\\de, Amblyscius potcntillae 

 (Garman) from Europe and Typhlodroimis arboreus 

 (Chant) from Oregon, among others. Attempts to 

 establish exotic mite predators on outdoor crops generally 

 have been inhibited by the widespread belief among 

 research acarologists that locally existing native species 

 likely are to be superior due to better adaptation to the 

 local conditions. However, given that apples, European 

 red mite and two-spotted spider mites all are recent 

 introductions in Massachusetts (i.e. a few hundred years at 

 most), there is little reason to hold this view. Successes in 

 other areas argue for trials of exotic species to test whether 

 or not more effective mite predators might not be 

 obtainable. 



Assessing Predator Levels in Your Orchard 



Decisions to apply or not apply miticides are made 



based on evaluations of numbers of prey mites (not 

 counting eggs) per leaf in light of numbers of predators 

 (either per leaf or per prey mite) and the point in the 

 growing season. The simplest assessment system is a fixed 

 predatorrprey ratio. For example if on 50 leaves 50 

 predators and 500 prey are found, you have a 1:10 

 predator: prey ratio, or 10 prey per leaf and only 1 predator 

 per leaf. Massachusetts makes miticide recommendations 

 based on a threshold than varies with the season (i.e. spray 

 if there are 2 to 3 mites/leaf in June, but 3 to 5/leaf in July 

 and 5 to 15/lcaf in August). New York recommends 

 miticide applications if there are more than 5 prey mites/ 

 leaf unless predators are numerous (1 or more per leaf). In 

 general a 1:5 predator:prey ratio seems to indicate good 

 prospects for biological mite control. A 1 : 10 ratio indicates 

 less prospect for control (but still possible). Ratios smaller 

 than 1:10 indicate biological mite control is unlikely to 

 occur. 



Actually counting all the mites on each of 40 or so 

 leaves can be a difficult task. To simplify the process. New 

 York has developed a sequential sampling scheme in 

 which leaves are picked one after another and then each 

 leaf is classified as cither having or lacking spider mites and 

 having or lacking predators. A chart with curves then 

 allows the sampler to determine if predator:prey ratios are 

 such that biocontrol is likely to occur, if miticide 

 applications arc needed, or if more leaves should be 

 examined (Nyrop, 1987). This scheme has been developed 

 for T. pyri in New York. No similar scheme has been 

 developed yet (or A. fallacis in Massachusetts. 



In Pennsylvania, a more elaborate decision making 

 process in the form of a question and answer "expert 

 system" has been developed that growers can use on home 

 computers. No similar system exists in Massachusetts. 



Regardless of the exact thresholds used, growers who 

 wish to monitor predator:prey ratios in their orchards 

 must learn to recognize predator mites as distinct from 

 prey mites (i.e. spider mites). A hand lens is sufficient for 

 this task and training can be requested from the regional 

 fruit extension agents. 



How to Convert From a Pesticide Mite Control 

 Program to a Biological Control Program 



Growers who wish to change management strategies 

 from chemical to biological mite control should begin by 

 requesting an evaluation of their mite control situation 

 from an IPM specialist or extension representative. 

 Factors to consider include past and current pesticide use 

 (both amounts and specific types), orchard floor 

 vegetation management, nitrogen management, and 

 current spider mite and predator densities. IPM scouts 

 can as.sess probable influences of various actions on mite 

 populations and recommend specific actions to promote 

 mite biological control. Regular monitoring for the first 



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