Photographs of Fresh and 

 Older Egglaying Scars of 

 Plum Curculio on Apples 



Jon Clements 



Department of Plant and Soil Sciences, University of Massachusetts Amherst 



Jaime Pinero and Ronald Prokopy 



Department of Entomology, University of Massachusetts Amherst 



The use of odor-baited trap trees to aggregate plum 

 curculio (PC) adults should simplify monitoring for PC 

 by confining sampling to just a few odor-baited trees in 

 an entire orchard. Under this approach, sampling would 

 involve examination of about 50 fruit on a trap tree for 

 signs of fresh PC egglaying scars. As discussed in a 

 previous article in this issue, application of a perimeter- 

 row spray would occur when one fruit out of 50 sampled 

 fruit shows fresh injury. The question then becomes: 

 how to tell a fresh injury from an older injury. Here, we 

 present photographs of fresh and older PC injury from 

 a study conducted m 2003. 



Materials & Methods 



At petal fall, cloth bags were placed over several 

 terminals of unsprayed Mcintosh and Delicious trees 

 at the University of Massachusetts Cold Spring Orchard 

 Research & Education Center in Belchertown. Each 

 Monday beginning when king fruit averaged 6 mm 

 diameter, two mated PC females were introduced into 

 each bag and allowed to remain until Tuesday, when 

 they were removed. On Wednesday, Friday, and the 

 following Monday, a digital camera (Nikon CoolPix 990) 

 was used to photograph some of the egglaying scars. 

 Each scar shown here was therefore 1 , 3, or 6 days old 

 when photographed. 



Results 



Figures 1 -4 show, respectively, egglaying scars that 

 were photographed over 6-day periods for the weeks 

 of May 28, June 4, June 1 1 and June 1 8. For Mcintosh, 

 fruit size averaged 6, 8, 14, and 19 mm diameter, 

 respectively, when injury was initiated, whereas for 

 Delicious fruit size averaged 6, 7, 10, and 14 mm 

 diameter, respectively. 



Regardless of the week when injury was initiated, 

 photographs show that 1 -day-old scars appear as 

 narrow crescents (from top to bottom) similar to an 

 eighth moon. Reflecting fruit growth, 3-day-old scars 

 appear as somewhat broader crescents, with 6-day- 

 old scars appearing as crescents that are broader still 

 (much like a half moon) or as scars that have begun to 

 lose their crescent shape. 



Scars initiated on 6 mm fruit (week of May 28) 

 show little sign of a stem and have little resemblance 

 to a mushroom (Figure 1). Scars initiated on 10-14 mm 

 fruit (week of June 1 1 ) show a distinct stem and strongly 

 resemble a mushroom (or the cloud of an atomic bomb) 

 (Figure 3). By 6 days after egglaying, even the most 

 pronounced mushroom shape of a 1 -day-old scar (as 

 m Figure 3) has begun to fade. 



It should be noted that the change in appearance 

 from fresh to older PC egg-laying scars as described 

 above is most accurate for Mcintosh. With Delicious, 

 the change in appearance is not quite as distinct - some 

 caution is advised when looking at different cultivars 

 as the age of PC egg-laying scars may be more difficult 

 to judge than it is on Mcintosh. More observations of 

 other cultivars (such as Gala) are needed. 



Conclusions 



Once a grower or consultant has firmly in mind the 

 image of a fresh (e.g., 1-day) versus an older (e.g., 6- 

 day) scar, that mental image can be carried to the field 

 to aid in interpretation of the age of PC scars on odor- 

 baited trap trees. 



Ackno wledgem en ts 



This study was supported by USDA Hatch funds. 



18 



Fruit Notes, Volume 69, Winter, 2004 



