The apple maggot, Rhagoletis pomonella, is a serious pest that can quickly ruin an entire crop of apples and other fruit. Often called the “railroad worm” due to the winding trails it leaves inside the fruit, this insect is a major concern for home gardeners. The female fly deposits eggs just beneath the skin of the developing apple, and the resulting larvae feed internally, making the fruit unpalatable and often causing it to drop prematurely. Controlling this pest requires an understanding of its life cycle and a targeted, multi-step approach to prevent internal fruit damage.
Recognizing the Pest and Its Life Cycle
The adult apple maggot is a small, black fly, measuring about one-quarter inch long. It is easily identified by the distinct black, zigzagging “F-shaped” bands on its clear wings and a noticeable white spot where the thorax joins the abdomen. The female fly also has four white bands across her abdomen, while the male has three. The damage caused by the larvae, which are legless, white maggots up to a third of an inch long, is far more destructive than the adult fly.
The life cycle dictates the timing of effective control measures, as the adult stage is the only time the pest is vulnerable to sprays and traps. Apple maggots overwinter as pupae buried in the top few inches of soil beneath the host tree. Adult flies begin to emerge from the ground around late June or early July, continuing through August. Females require about seven to ten days of feeding on honeydew before they are ready to mate and lay eggs. They puncture the fruit skin with an ovipositor to deposit eggs singly, and these eggs hatch within five to ten days.
The larval stage feeds inside the apple for three to four weeks, creating the characteristic brown, tunneling trails and causing the fruit to rot. Once mature, the maggot drops to the soil, often inside prematurely fallen fruit, to pupate and begin the cycle again the following summer. Control efforts must be focused on eliminating the adult fly before it lays eggs to prevent internal fruit damage.
Non-Spray Methods for Prevention and Control
Sanitation is a foundational step in managing apple maggots. Since the mature larvae exit the fruit and burrow into the soil to pupate, all dropped or infested apples must be removed from the ground immediately. Collecting fallen fruit every two to three days prevents the larvae from completing their life cycle and significantly reduces the population for the following season. Destroying the collected fruit by deep burial or sealing it in bags for disposal is necessary to ensure the maggots do not escape.
Physical barriers offer a highly effective, non-chemical way to protect developing fruit. Fine mesh insect netting can be draped over entire small trees or individual branches to prevent the adult flies from reaching the fruit to lay eggs. For a more targeted approach, individual apples can be enclosed in small paper or plastic bags once the fruit has been thinned in early to mid-June. This exclusion technique provides a physical shield against the ovipositor of the female fly.
Trapping is an important tool for both monitoring the presence of the pest and for mass-capturing adult flies. The most effective traps are sticky red spheres, which mimic the color and shape of a ripe apple. These traps should be coated with a sticky substance and hung in the tree canopy by the end of June, positioned in the brightest, sunniest areas. Place one to two traps per small tree, or up to five or more for larger trees, and check them weekly to monitor fly activity and reapply the sticky coating as needed.
Targeted Insecticide and Organic Applications
Chemical control is most effective when timed precisely to the emergence of the adult flies. The goal of any spray application is to eliminate the adult fly before it has a chance to lay eggs in the apple. Traps should be used to confirm the first emergence of adult flies, and the initial spray should be applied within seven to ten days of that first detection.
Organic Options
Organic options provide a means of effective control without synthetic chemicals. Kaolin clay, applied as a spray, creates a white, powdery film on the leaves and fruit, which acts as a physical barrier and visual repellent. This material must be reapplied every seven to fourteen days, and immediately after heavy rain, to maintain complete coverage as the fruit expands.
Another organic choice is Spinosad, an insecticide derived from a naturally occurring soil bacterium. Spinosad products are often mixed with a bait attractant, such as GF-120, to increase their effectiveness as the flies are drawn to feed on the toxic droplets.
Conventional Management
For conventional management, synthetic insecticides like carbaryl or permethrin can be used, as they offer longer residual activity. Regardless of the product chosen, repeated applications every seven to ten days are necessary throughout the egg-laying period to ensure that newly emerging adults are controlled before they damage the fruit.