Tuesday, November 24, 2020

This fruitworm is the enemy of cranberry farmers

For cranberry farmers, autumn brings falling leaves and rising hopes. Family-owned operations, such as Deer River Cranberry Farm in Brasher Falls, cultivate their vines in meticulously manicured marshes. Droplets descended from irrigation spigots glisten atop entangled mats of waxy, evergreen vines, forming a coruscant carpet. Harvest season begins in mid-September, and is well underway by early November.

Most cranberry varieties produce fruit every other year. To harvest the crop, some farmers flood their typically well-drained bogs. The hollow, red berries rise above their short canopy. Collecting tools include buoyed nets, or water reels, which corral fruit for a mechanical harvester. Berries are then sent careening down a series of steps, with the roundest, plumpest, highest quality fruit tumbling the farthest.

The fierce, firetruck red aesthetic of a Demoranville berry contrasts sharply with the mottled, red-and-white complexion of a Mullica Queen, but both must pass the test. Wizened, infested, or misshapen products that aren’t firm enough to sufficiently bounce will be discarded, along with the farmer’s hope for an unblemished crop.

Insects pollinate cranberries, but they also represent the bane of the bog by damaging volumes of fruit. The sparganothis fruitworm, a yellow moth one centimeter in length, characterized by a brown “X” on its wings, bears an unassuming countenance. Despite its meek appearance, cranberry farmers in St. Lawrence County regard it as a sulfur specter.

Unlike the slow-growing cranberry, sparganothis fruitworm populations churn out two generations per year. They fly for the first time in July, laying eggs in either the canopy or on the fruit. The eggs hatch into small, green, vaguely translucent larvae. These rascals either burrow into hollow fruit or web the leaves together into tents. They pupate in the canopy, duff, or soil, taking flight again in late August through September.  Here in Essex county, adult sparganothis fruitworm have been observed as recently as September 30. The larvae that emerge from the second generation’s eggs are typically the overwintering stage, which takes place in the detritus beneath the cranberry vines. When temperatures begin to rise in the spring, so too do the larvae, which climb up into the canopy and resume the cycle.

One caveat of controlling sparganothis fruitworms in cranberry farms is that the moth and the crop are native to the northeast. Farmers do business in an agricultural paradigm where crops of international origin are staple items, with many invasive pests. Cultivating cranberries is a distinct agricultural challenge because the wild populations of cranberry plants provide habitat for both pests, predators, and pollinators that might move into the crop. Natural fruit grows under the protective camouflage and support of spongy, sage green Sphagnum moss hummocks. The ripe, red berries hanging precariously from uprights look more decorative than edible, but nonetheless are a meal for moths that move from the wilderness to farms. The sparganothis fruitworm can also use sunflower, goldenrod, wild celery, pines, and over a dozen additional plants as alternate hosts.

This pest can also infest blueberries, which are close relatives of cranberry plants. Like cranberries, blueberries thrive in acidic soils, but the acidity does little to deter the fruitworm. Another similarity is that both sport white flowers, which are pollinated by a variety of bees, and are also known to capture the attention of the fruitworm. A noteworthy difference is that the highbush blueberry can grow to a height of twelve feet, whereas cranberry plants reach about twelve inches off the ground. Nonetheless, moths can roost in both canopy architectures. Thankfully, there are control options for this polyphagous and adaptable pest.

Documented natural enemies of the sparganothis fruitworm include parasitoid wasps and flies. The fly known to scientists as Erynnia tortricis Coquillet (Diptera: Tachinidae) can parasitize the larval stage of the moth, by laying eggs inside the larva. Those eggs hatch into maggots, that kill the larva before it can reach adulthood. Furthermore, Trichogramma wasps lay their eggs inside the eggs of the moth, preventing the moth’s eggs from hatching. Both the fly and the wasp are native to upstate New York, and consume nectar as adults. By not spraying pesticides at times when the plant is flowering, it is possible to reduce damage to the beneficial insects that visit the flowers, such as the flies, wasps, and bees.

The sparganothis fruitworm is a serious pest of blueberries and cranberries. Nonetheless, it is a native member of the wetland ecosystem. Cranberry farmers are adept at balancing their roles as stewards of nature and producers of food. By balancing these goals, they cultivate a sustainable future along with their fruit crop.

Photo: A sparganothis fruitworm larva eating a cranberry, with the adult superimposed.  

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Shane Foye is an entomologist volunteering with the Cornell Cooperative Extension of Essex County Agriculture Program. Learn more about Shane and the on-farm projects he's working on at the CCE Essex Agriculture page: http://essex.cce.cornell.edu/agriculture/biocontrol-projects

One Response

  1. Vanessa says:

    Read this article with Fleetwood Mac in my head 🙂 – thanks internet

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