Predicting Plum Curculio Immigration 

 into Apple Orchards in Massachusetts: 

 Degree Days versus Tree Phenology 



Jaime Pinero and Ronald Prokopy 



Department of Plant, Soil, and Insect Sciences, University of Massachusetts 



Determining need for and timing of insecticide 

 applications that will protect fruit from injury by plum 

 curculio (PC) based on presence of adults on host trees 

 has been a critical aspect for managing populations. In 

 concept, a reduction in amount of insecticide used 

 against PC, from the current norm in Massachusetts of 

 three spray applications during May and June to an 

 amount that is precise according to need should be 

 accompanied with an effective approach to monitoring 

 the course of PC immigration into apple orchards. Limb 

 jarring, an approach that involves tapping tree limbs 

 using a pole to dislodge PCs onto an underlying ground 

 cloth is one of the methods traditionally used to 

 determine the time of first appearance, location, and 

 relative abundance of PCs within an orchard. However, 

 limb jarring has several shortcomings: (1) it is labor 

 intensive; (2) it is not very accurate (its effectiveness 

 is highly dependent upon tree size, weather, and other 

 factors); (3) it carmot be used to study immigration, 

 because PCs that are able to overwinter beneath 

 perimeter-row trees will be confounded with true 

 immigrants that overwintered in the woods; and (4) it 

 cannot be performed at night, the time of day when 

 PCs are most active on trees. 



In the 2000 combined issue of Fruit Notes we 

 reported that panel and pyramid traps baited with 

 attractive odor and deployed in close proximity to the 

 forested areas that are the main overwintering sites of 

 adult PCs offered great potential for monitoring the 

 onset and extent of PC immigration into apple orchards. 

 Here, we investigated, over a five-year period, temporal 

 dynamics of PC immigration into an unsprayed section 

 of a commercial apple orchard using odor-baited traps. 

 In particular, our objectives were: (1) characterizing 

 the overall pattern of PC immigration; (2) determining 

 the relationships among trap captures, tree phenology, 



and weather; (3) estimating thermal constants, 

 expressed in Degree Days, for different stages (onset, 

 50* and SO"" percentiles of cumulative captures) of PC 

 immigration; and (4) determining the relative 

 predictability of different stages of PC immigration by 

 comparing tree phenology versus thermal constants. 



Materials & Methods 



Study site and trap deployment. We conducted 

 this study over a period of five years (2000-2004) at 

 the University of Massachusetts Cold Spring Orchard 

 Research & Education Center (Belchertown, MA) 

 utilizing a 1 .4-acre unsprayed block comprised of a 

 secfion having 2 1 6 small (M.9 rootstock) Mcintosh and 

 Delicious trees located on the eastern side, and two 

 smaller sections having 145 medium-sized (M.26 

 rootstock) trees of various disease-resistant varieties 

 located on the western side (Figure 1). The perimeter 

 of the entire block, bordered almost entirely by mixed 

 deciduous forest, was about 500 yards. 



Traps utilized for the study were of two different 

 types: (a) clear sticky Plexiglas panels (2x2 feet), 

 which capture PCs in flight, and (b) a trunk-mimicking 

 black pyramid ti-aps, which capture PCs approaching 

 host trees primarily by crawling. The woods-facing side 

 of each panel was coated with Tangletrap glue to 

 capture PCs that were presumably immigrating from 

 the woods into the orchard block. 



For each of the five years, traps were deployed in 

 pairs along the periphery of the orchard, in close 

 proximity to the woods. Each pair of traps was spaced 

 10 yards from other trap pairs on either side except in 

 2004, when the distance between each trap pair was 

 35 yards. For each of the five years, trap captures were 

 pooled across all traps of the same type deployed m 



Fruit Notes, Volume 69, Fall, 2004 



