Do Overwintering Red Mite Eggs 

 Portend Summer Mite Troubles? 



Jennifer Mason, Margaret Christie, and Ronald Prokopy 

 Department of Entomology^ University of Massachusetts 



Among foliar pests, European red mites 

 (ERM) remain a major problem for apple trees. 

 They can be particvdarly difGcvdt in second- level 

 IPM blocks, where growers are dependent on 

 predator mites to control summer ERM popula- 

 tions. In these blocks, current non-biological 

 control measures consist of one or two dormant 

 oil sprays in the spring prior to egg hatch. To 

 maintain control of ERM, predators build up to 

 levels capable of controlling the mites that 

 hatch. Unfortunately, it is difiicult to balance 

 spring oil control of ERM and encouragement of 

 a healthy population of predator mites. This 

 leads to the question: Can prebloom oil alone 

 effectively control summer ERM populations? 



During January of 1992, we collected 200 

 buds per orchard from 11 orchards that partici- 

 pate in the second-level IPM project. Six of these 

 were full second-level IPM blocks, and five were 

 transitional second-level blocks. The percentage 

 of buds with ERM eggs present was recorded for 

 each block, and orchards were placed into three 

 categories: low (0-33%), medium (34-66%), and 

 high (67-100% of buds with mite eggs). 



During late spring and summer months, 

 mite populations in each block were recorded as 

 part of normal IPM scouting procedures. ERM 

 presence or absence was counted on 200 fruit 

 cluster leaves beginning in May and continuing 

 through September. Examination of peak ERM 

 populations in the second-level IPM blocks in 

 May showed little or no apparent relationship 

 between winter ERM egg percentages and 

 spring mite numbers. Peak ERM populations in 

 June, however, were related to winter egg per- 

 centages (Table 1). The low and medium ERM 

 egg groups both had very low June ERM popula- 



tions, but all orchards in the high ERM egg 

 group had substantial numbers of Jxine mites. 

 In first-level blocks there appeared to be no 

 consistent relationship between overwintering 

 egg numbers and June mites, which were low in 

 all of these orchard blocks (Table 1). 



Of the second-level blocks, all received at 

 least one dormant oil spray prior to egg hatch in 

 the spring (Table 1). In the high group, two 

 blocks had received two sprays. In the low and 

 medium orchards, it appears that dormant oil 

 sprays were sufficient to control mite popula- 

 tions through June. In the orchards in the high 

 group, however, even those receiving two appli- 

 cations had thriving ERM populations by the 

 endof Jvme. 



Further work needs to be done on the rela- 

 tionship between dormant oil sprays, overwin- 

 tering ERM eggs and resulting early summer 

 ERM populations before any firm conclusions 

 can be drawn. If these results are estabhshed as 

 fact, then oil spray recommendations may need 

 to be revised for blocks where high numbers of 

 overwintering ERM eggs are foxuid in winter 

 coimts. Without a strong predator population, 

 these orchards may be subjected to large sum- 

 mer ERM populations if they depend on normal 

 amoimts of prebloom oil to be effective. Higher 

 rates of oil (e.g., three gallons of oil per 100 

 gallons of water) at green tip or half -inch green 

 may be necessary, with a second oil treatment at 

 a lower rate at tight cluster. It is p>ossible, 

 however, that the higher mite numbers in the 

 high blocks may be "attractive" to predator 

 populations, and that these orchards may even- 

 tually become areas of good biological control. 



Fruit Notes, Winter, 1993 



13 



