Scaffolds 00 index

(Art Agnello ama4@nysaes.cornell.edu, Entomology, Geneva)

It is once again nearly time to expect the first appearance of apple maggot (AM) flies in abandoned orchards, particularly in eastern N.Y. (western N.Y. should be about a week later if all goes normally, which has never been known to happen). Crop scouts and consultants have been using traps to monitor AM populations for a long time, but as useful a tactic as this is, it is nevertheless not recommended in all cases. Some orchards have such high or such low AM populations that monitoring for them is a waste of time; that is, sprays are needed predictably every season in some blocks, and on a calendar basis, and they are rarely needed at all in other blocks. However, most commercial N.Y. orchards have moderate or variable pressure from this pest, and monitoring to determine when damaging numbers of them are present can reduce the number of sprays used in the summer with no decrease in fruit quality.

AM BOARD TRAP

Sticky yellow panels have been in use for over 25 years, and can be very helpful in determining when AM flies are present. These insects emerge from their hibernation sites in the soil from mid-June to early July in New York, and spend the first 7—10 days of their adult life feeding on substances such as aphid honeydew until they are sexually mature. Because honeydew is most likely to be found on foliage, and because the flies see the yellow panel as a "super leaf", they are naturally attracted to it during this early adult stage. A few of these panels hung in an orchard can serve as an early-warning device for growers if there is a likely AM emergence site nearby.

Apple Maggot Adult

Many flies pass this period outside of the orchard, however, and then begin searching for fruit only when they are ready to mate and lay eggs. That means this advance warning doesn't always have a chance to take place – the catch of a single (sexually mature) fly then means that a spray is necessary immediately to adequately protect the fruit. This can translate into an undesirable risk if the traps are not being checked daily, something that is not always possible during a busy summer.

AM VBS TRAP

To regain this time advantage, researchers have developed newer traps that have the form of a "super apple" – large, round, deep red, and sometimes with the smell of a ripe apple -- in an attempt to catch that first AM fly in the orchard. Because this kind of trap is so much more efficient at detecting AM flies when they are still at relatively low levels in the orchard, the traps can usually be checked twice a week to allow a one- or two-day response period (before spraying) after a catch is recorded, without incurring any risk to the fruit. In fact, research done in Geneva over a number of years indicates that some of these traps work so well, it is possible to use a higher threshold than the old "one fly and spray" guidelines recommended for the panel traps. Specifically, it has been found that sphere-type traps baited with a lure that emits apple volatiles attract AM flies so efficiently that an insecticide cover spray is not required until a threshold of 5 flies per trap is reached.

The recommended practice is to hang three volatile-baited sphere traps in a 10- to 15-acre orchard, on the outside row facing the most probable direction of AM migration (south, or else toward woods or abandoned apple trees). Then, periodically check the traps to get a total number of flies caught; divide this by 3 to get the average catch per trap, and spray when the result is 5 or more. Be sure you know how to distinguish AM flies from others that will be collected by the inviting-looking sphere. There are good photos for identifying the adults on the Apple Maggot IPM Fact Sheet.

In home apple plantings, these traps can be used to "trap out" local populations of AM flies by attracting any adult female in the tree's vicinity to the sticky surface of the red sphere before it can lay eggs in the fruit. Research done in Massachusetts suggests that this strategy will protect the fruit if one trap is used for every 100-150 apples normally produced by the tree (i.e., a maximum of three to four traps per tree in most cases).

A variety of traps and lures are currently available from commercial suppliers; among them: permanent sphere traps made of wood or stiff plastic, disposable sphere traps made of flexible plastic, and sphere-plus-panel ("Ladd") traps. The disposable traps are cheaper than the others, of course, but only last one season. Ladd traps are very effective at catching flies, but are harder to keep clean, and performed no better than any other sphere trap in field tests. Brush-on stickum is available to facilitate trap setup in the orchard. Apple volatile lures are available for use in combination with any of these traps. These tools are available from a number of orchard pest monitoring suppliers, among them:

• Consep Inc., 213 SW Columbia St., Bend, OR 97702; 800-367-8727, Fax 541-388-3705

• Gempler's Inc., 100 Countryside Dr., PO Box 328, Belleville, WI 53508; 608-424-1544, Fax, 608-424-1555

• Great Lakes IPM, 10220 Church Rd. NE, Vestaburg, MI 48891; 800/235-0285, Fax 517/268-5311

• Harmony Farm Supply, 3244 Gravenstein Hwy, No. B, Sebastopol, CA 95472; 707/823-9125, Fax 707/823-1734

• Ladd Research Industries Inc., 13 Dorset Lane, Williston, VT 05495; 800-451-3406, Fax 802-878-8074

• Olson Products Inc., PO Box 1043, Medina, OH 44258; 330-723-3210, Fax 330-723-9977

By preparing now for the apple maggot season, you can simplify the decisions required to get your apples through the summer in good shape for harvest.

As reflected in current pheromone trap counts, the 1st brood spotted tentiform leafminer flight has subsided in both Geneva and the Hudson Valley, and the 2nd brood is getting under way statewide. Because the season at least started out being relatively advanced, this flight might peak and the eggs hatch by as early as the last week in June. That is the time at which time we recommend sampling leaves for the young (sap-feeding) mines of the second generation, to determine the need for a spray. Sampling should be conducted when the first of the mines reach the tissue-feeding stage.

Tissue feeding mines caused by later spotted tentiform leafminer instars, visible from both sides of leaf

This is when most of the population is in the sap-feeding stage, and it usually occurs about 500-700 degree-days (base 43°F) after the start of the second moth flight. The larvae can be found easily, but at that stage they have not yet caused much damage to the leaf. You may wish to make a note of the 2nd flight's start date in your region, or use the Geneva date, when we publish it, for accumulating degree-days in your locality if you don't happen to document this event in local traps.

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