Blueberry growers focus on raising marketable fruit each year. A management plan for controlling pests such as the blueberry maggot and cranberry fruitworm is necessary.
1. Blueberry maggot
If there is one insect that pesters southeastern growers to no end, it is the blueberry maggot.
The larva looks creamy white, is legless and measures about 5 mm, according to the Entomology Department at the University of Florida. Its anterior end is tapered with small, black mouthhooks. The larva’s posterior end is truncate and tubercular. It has two fine, flat, brown-colored spiracles.
According to the University of Florida, the adult has a black-colored thorax with a white spot at its tip and a white stripe on each side of its body, which measures about 3 mm. The adult’s wing spreads out about 4 mm and sports black bands.
The blueberry maggot overwinters as pupae in the soil, according to entomologists at the University of Florida. Growers in Florida and Georgia can spot adult flies in late May. They continue to appear until about late July, when its native host plant – deerberry – is fruiting.
Entomologists note that the adult blueberry maggot goes through a pre-reproductive period for about one to two weeks. During this time, the maggot will search and feast on nutrients of different host plants. Once the pest matures, the adult flies mate as females start to ovipost, and the females tend to lay 25 to 100 eggs over 15 to 30 days. Once the eggs incubate during a three- to 10-day period, they produce their first instar maggot, according to the University of Florida. Larvae begin feeding for 17 to 22 days when they pass through two additional molts. They may eat the entire fruit pulp. Once they’ve finished, larvae fall to the ground, make their way into the dirt and pupate.
Growers can track the blueberry maggot’s movements by trapping adult flies on yellow sticky boards, entomologists advise. They indicate that growers can bait the boards with ammonium carbonate and place several traps in growers’ fields.
Growers are advised to place the traps near the plant’s fruit, perhaps in a shady area. They can aim for a threshold of about three adults per trap per week or five adults per field. That should give growers time to apply insecticides, if necessary, before infestations grow. It is only if necessary, because the adult maggots could simply be laying eggs. To determine if it is just laying eggs or is actually feeding, entomologists suggest cutting open some ripening fruit and checking for maggots. A word of caution: apply insecticides only in orchards with a history of blueberry maggot damage that was present the year before.
2. Cranberry fruitworm
Larva of the cranberry fruitworm is green in color with some brownish-red coloration, according to entomologists at the University of Massachusetts. This pest is only about 1/2 inch or slightly more once it matures. When the larva hatches, it crawls out of the eggshell to the berry’s stem end. There, they tend to burrow into the berry, where they will spread silk over the hole entrance. They immediately begin to feed, and growers will notice the green fruit turns blue in color. That is a strong sign that cranberry fruitworm is present.
Typically, in the Northeast, the cranberry fruitworm larva feeds from early June through harvest, according to the University of Massachusetts, and the larva will go from one berry to another, hollowing its way along. Each larva molts about five times and goes through six instar stages. It will eat from three to six berries while filling them with brown frass.
The end result of this feeding tendency is poor marketability of berries. In its last instar stage, the larva drops to the ground and spins silk along with leaf litter and soil. This starts the hibernaculum or dormant stage, according to entomologists, and the larva begins to overwinter.
Once spring arrives, the hibernacula begin to pupate. In about five weeks, they emerge as adult moths between late May and late July. Shortly after, females start to mate and lay eggs in the calyx end of the fruit.
Adult moths appear from June through early August, report entomologists at the University of Massachusetts. Their wings are a gray-brown color, sporting two small dots on their front. Two white markings are present on the base of the front wings and around the middle of the front. Their hindwings are gray-brown, too. These pests are active at night, as they remain hidden in the plants or nearby weeds during the day.
Adult females lay eggs in the blossom end of the blueberries. Before breaking open and within three to five days after being laid, the eggs appear with an irregular, orange streak.
Growers can scout for cranberry fruitworm using pheromone traps. These traps include a lure that is impregnated with a synthetic replication of the female sex pheromone, according to entomologists at the University of Massachusetts. These traps are intended to attract male moths.
They advise to check the traps at least once a week, noting the moths spotted and removed to compare with the week ahead. These lures are sound for about two to three weeks, and entomologists suggest replacing them in about five to eight weeks. Time insecticide applications one week after a peak in moths trapped.
Apply a second application in seven to 10 days. Also, apply another application if necessary.
Monitor traps after spraying to see if applications are effective, entomologists advise. On the other hand, growers can time applications based on the plant’s stage of growth, usually about three to five days before seeing the berries touching each other or when peaks in trap catches are seen. For another means to time second or third sprayings, growers can examine berries for eggs.
Entomologists advise using a magnifying lens. If they spot one or more eggs per 100 berries, growers may spray about 10 days after the previous spraying. Entomologists indicate that if growers follow a regular management program, they can reduce cranberry fruitworm losses to about 3 percent.