Fruit Insect Focus for June, 1997

Tufted Apple Bud Moth, Platynota idaeusalis (Walker)

I. Introduction: Tufted apple bud moth (TABM) is probably the most serious direct pest of apples in the mid-Atlantic region. Although this pest can be found in most commercial orchards, those orchards located in intensive production areas are usually more seriously affected. This has been primarily due to the increased insecticide selection pressure which has resulted in the development of resistance to the organophosphate insecticides.

II. Hosts: The major hosts of TABM include: apple, pear, peach, nectarine, cherry and a wide range of herbaceous plants found in the ground cover.

III. Description: The adult female moth is approximately 1/2 inch (13 mm) long, with the males being slightly smaller. Moths are inconspicuous in color, varying from a mottled gray to brown (photo 1-13). The coloration of the wings is generally one-third grayish at the wing base, with gradual darkening to brown at the wing tips. There is usually a lighter colored margin along the leading edge of the wings. The moth is named after the tufted scales which can be seen as two or three groups on the top of the wings. First and second instar larvae are yellowish with a black head capsule, and are about 1/16 inch (1.5 mm) long. Older larvae are a light brown to grayish tan with a chestnut brown head capsule, a darker prothoracic shield (hardened collar between the head and the body), and a dark stripe down the back of the body. A full grown larva is approximately 3/4 inch (19 mm) long (photo 1-14). Pupae are brown and about 3/8 inch (10 mm) long. TABM deposit their eggs on the upper leaf surface in a flattened, ovoid, green mass (dime size) consisting of upwards of 150 eggs (photo 1-15). As the egg mass matures it changes from a green to a bronze color (photo 1-16), and finally to a black-head stage (photo 1-17), which occurs within 24 hours of hatch. A hatched egg mass resembles a fish scale (photo 1-18).

IV. Biology: TABM produces two generations a year, with larvae overwintering as second through fifth instars in larval shelters such as rolled leaves and decaying fruit on the ground beneath fruit trees. Larvae become active in early spring and complete development on a variety of host plants (e.g., root suckers, dandelion, dock, and wild strawberry). Larvae pupate and adults begin to emerge about the beginning of May. Egg-laying begins anywhere from mid- to late May. Egg masses usually hatch within 8-10 days, with peak egg hatch occurring about mid-June. First instar larvae disperse by crawling or ballooning (floating in the wind on a strand of silk). First and second instars then feed along a leaf midrib, and, beginning with the third instar, they create shelters by rolling leaves after notching petioles (photo 1-19), tying leaves to other leaves or fruit, and by building shelters within fruit clusters. Larvae generally pupate within these shelters, emerge as adults, and begin second brood egg-laying about the beginning of August. Peak second brood egg-laying and hatch occur in mid- to late August. Late season second brood larvae (second through fifth instars) drop to the ground during fruit harvest or with leaf fall to overwinter. Larvae are attacked by a number of parasitoids, the most common being an ichneumonid, Exochus atriceps Walsh, and a braconid, Meteorus trachynotus Viereck. They are also subject to virus infection (photo 1-20).

V. Injury: TABM belongs to a family of moths known as leafrollers, but the leafrolling activity has little economic impact on the fruit grower and little physiological impact on the tree. It is when this insect webs a leaf onto the apple fruit and feeds directly on the fruit that it becomes a pest. This damage appears as tiny holes (early instar feeding)(photo 1-21), as irregular scarring or channeling of the apple surface, or as an area of rot, generally around the stem. Rot or corking around the stem usually occurs after larvae have finished feeding and have pupated. Larvae occasionally enter the apple calyx and feed unnoticed within the seed cavity. Most injury to apples is caused by second brood feeding, although in some years first brood injury can exceed that caused by the following generation. Injury to fruits destined for fresh markets has a greater economic impact since their cash value is much higher compared to that of processing grade apples. Generally, TABM injury does not reduce the grade of processing apples, but it can affect the rate of fruit drop and storageability of those apples by promoting decay, both of which can have an economic impact on the grower and processor.

VI. Monitoring: Install a minimum of two pheromone traps for every ten acres (4 ha) at petal fall to monitor male moth emergence. Traps should be attached to a limb at five to six feet (1.5-1.8 m) above the ground in the outer third of the tree's canopy. Check traps every day until the first TABM adult male (photo 1-13) is caught, and record this date, after which the traps should be checked once a week. In order to time insecticide applications more efficiently when eggs hatch, begin monitoring and recording daily maximum and minimum temperatures from the first sustained trap catch. Accumulate degree days (DD) using a base temperature of 45 F and upper threshold of 91 F (use Appendix D in Mid-Atlantic Orchard Monitoring Guide). If degree days are not used to time insecticide applications, begin monitoring the upper leaf surface of sample trees for egg masses (photo 1-15, 1-16) approximately 3-4 weeks after first trap catch of spring brood moths or 1-2 weeks after first trap catch of summer brood moths. Careful observation is required to detect egg masses. Mark locations of egg masses with flagging ribbon so that development can be followed. Penn State University researchers have found a relation between the amount of fruit injury caused by larvae of the first brood and the amount of fruit injury caused by the second brood (Table 1). This relationship was developed from orchards treated with an average of four alternate-row-middle sprays for each brood (June and August). In order to estimate this relationship, select ten trees of a TABM sensitive cultivar (e.g., `Yorking', `Stayman', `Rome') which are representative of tree size and crop load in the orchard. Examine 100 apples per tree (50 top and 50 bottom) during late July or early August. Then calculate the percentage of apples having TABM injury (photo 1-21) and use Table 1 to determine the amount of injury to expect from the second brood. If the percentage of first brood injured apples does not equal one of the values in Table 1, it can be inserted into the equation at the bottom of Table 1 and the predicted amount of second brood injury can be calculated. For example, if first brood fruit injury is 3.5 percent, the amount of predicted second brood injury is 7.4 percent (7.4% = 2.22 + 1.47 X [3.5%]).

Table 1. Predicted TABM brood II fruit injury estimated from the percentage of brood I injury.

^a Regression equation for predicting Brood II fruit injury is y = 2.22 + 1.47x.
^b 95 percent confidence interval.

If the predicted second brood injury is too high for intended markets, then one or more of the following adjustments should be considered to improve the effectiveness of the control program: 1) improve spray coverage by increasing the volume of water applied per acre, 2) shorten the spray interval and increase the number of complete or alternate-row-middle (ARM) sprays (e.g., five rather than four ARM sprays/brood), or 3) increase insecticide rates. If the predicted second brood injury is considerably less than an acceptable level for intended markets, then decrease the number of complete or ARM sprays (e.g. three rather than four ARM sprays/brood) and/or insecticide rate.

VII. Management: Based on recent work by Penn State University researchers, applications of carbamate and/or organophosphate insecticides for first brood control should begin at about 10 percent egg hatch, which occurs at 525-550 DD from the first sustained trap capture. A second application should be made 300 DD after the first application. These recommendations are based on applying complete sprays. For alternate-row-middle (ARM) sprays, applications should commence 50-75 DD earlier, at about 475 DD after first trap capture and repeated every seven days for a total of up to four applications, depending upon insect density. If Confirm insecticide is used (Section 18 Emergency Exemption label granted on June 16 in West Virginia), a single application should be applied for first brood control at 600-650 DD after first trap catch, which coincides with approximately 20-30 percent egg hatch. For second brood control, initiate carbamate and/or organophosphate insecticide applications at an accumulation of 2280 DD after first trap catch of first brood moths, or at 530 DD after first trap catch of second brood moths. A second spray should be applied 300 DD after the first application. These recommendations are based on applying complete sprays. ARM applications should precede the above DD accumulation by 50-75 DD and repeated every seven days for a total of at least four applications. Additional insecticide applications may be needed for second brood control since the egg hatch period extends over a 650 DD period. For Confirm, time applications at 2350-2450 DD (20-30 percent egg hatch) and 2670-2740 DD (60-70 percent egg hatch) after first trap catch of first brood moths. If degree days are not used, begin insecticide applications when the first marked egg mass reaches the "black head" stage (photo1-17) or hatches (photo 1-18).