Saturday, May 01, 2010

Codling Moth Season

The codling moth, (CM) (Fig. 1), is the most important pest on apples in most of the Midwest. This moth larva feeds on apple, pear, English walnut, quince, crab apple, hawthorn, and wild apple. Flowering quince and apple are prime host plants in the backyard. Codling moths occasionally attack stone fruits.


Fig. 2

The larva eats its way into the center of the apple and feeds on the seeds and core. Later it tunnels back out and leaves the fruit (Fig. 2). It most often enters through the calyx end. Sometimes it enters where two fruits touch or where a leaf touches a fruit.

Stings are shallow blemishes on the surface of the fruit, usually caused when a newly hatched larva takes a few bites and then dies from various causes, including the effects of an insecticide.
Female codling moths lay their eggs singly on the foliage or fruit. The egg is a pearly white oval. The newly hatched larva is semitransparent, white with a shiny black head, and about 1/16 inch long. The full-grown larva spins a silken cocoon under bark or other suitable shelter. The pupa is about 1/2 inch long and varies in color from yellow to brown, depending on age.
Adult mothes vary in size, with a wing expanse of 3/4 inch or less. The wings are brownish gray with dark bands. Near the tip of each forewing, there is a dark brown spot, which contains two irregular coppery lines.

Setting a Biofix

Initial trap catches for adult moth in the early spring are termed biofixes. This information will be used to predict when egg hatch will occur and synchronize insecticide sprays. The biofix for the codling moth is the starting date of the first sustained flight of male moths captured in pheromone traps. Generally, this is when the fifth moth has been captured in the trap. A few moths often emerge very early in the spring ahead of the rest. Using the fifth moth as the biofix better represents when the majority of the codling moths begin to emerge. This usually occurs just after petal fall. Codling moth traps need to be examined daily in order to know exactly when the biofix occurs. After the biofix has occurred, degree days are calculated on a daily basis and a running total is kept. The codling moth has a 50F threshold temperature. These degree day accumulations can be  compared with the target values in the CM GDD Model table.

Throughout the growing season in commercial IPM orchards, pheromone trap catches that exceed an average of five moths per trap per week can trip an insecticide application. Growers need to estimate the residual activity of previous insecticide sprays (generally 10 to 14 days of activity after each application) relative to the anticipated egg hatch predicted by the degree day accumulation to determine the need for additional sprays.

In the early stages of setting a biofix for CM, growers do need to be aware of the emergence in the Midwest of False Codling Moth.  False Codling Moth (FCM), (Fig. 3)can be confused with codling moth (CM)  because of similar appearance and damage, however, unlike codling moth its host range does not include apples, pears or quince (USDA 1984).


Fig. 3


FCM can be distinguished from CM by close examination of morphological characters.  Most notably is the variation in wing coloration.  CM have a definite copper color on the tip of their wing.  At Royal Oak Farm, we have not set biofix on CM as of yet, but have trapped many FCM.  Don’t confuse these FCM with the real CM.