Sunflowers planted near stone fruit orchards could help a parasite of the oriental fruit moth to survive the winter.
Planting sunflowers next to a peach or nectarine orchard may be a way to stop fruit damage by the oriental fruit moth, research in California suggests.
Early in the season, oriental fruit moth larvae bore into shoots. Later in the season, as the fruit matures, larvae bore through the flesh of the fruit to the pit.
Mating disruption has been successful for controlling oriental fruit moth, but is most effective on the first two generations of the pest, according to Dr. Walt Bentley, integrated pest management advisor at the University of California’s Kearney Agricultural Center. Insecticides are sometimes used in conjunction with mating disruption to prevent fruit damage in late-maturing peach and nectarine varieties.
Oriental fruit moth is attacked by a parasitic wasp called Macrocentrus ancylivorus. Female wasps lay eggs singly in orintal fruit moth larvae. The wasp larvae that hatch from the eggs develop through four larval stages. The first three develop inside the host, while the fourth feeds externally, consuming the host’s body contents.
Macrocentrus wasps can be released in the orchard to provide biological control, but they do not overwinter on oriental fruit moth. Bentley said oriental fruit moth overwinters as a prepupa. The prepupal stage triggers the parasite to emerge from the host, and the adult wasp does not survive the winter. However, the parasite has a number of other hosts, including the sunflower moth, which overwinters as a larva. Bentley’s research has shown that if beds of sunflowers are planted next to an orchard, the parasites will move between the trees and the sunflowers and overwinter inside sunflower moth larvae.
Sunflowers (Helianthus annuus) harbor huge numbers of sunflower moths, Bentley said. The larvae feed on tiny florets in the center of the sunflower before tunneling down to feed on the seeds.
Macrocentrus is attracted to the frass they leave behind. Mature sunflower moth larvae drop to the ground and pupate in the soil. The overwintering larvae emerge as adults over an extended period the following year.
The parasites emerge from their host larvae in the ground in early spring at about the time that oriental fruit moth is beginning to emerge in the orchard. At the time of their emergence, there are not yet any sunflowers in bloom. The new adult parasites, seeking hosts to continue their lifecycle, attack the oriental fruit moth larvae.
The sunflower planting needs to be maintained to ensure a continuing population of sunflower moths in order to sustain the parasite from year to year. Since sunflowers are annual plants, Bentley recommends planting seeds three times: in late April or early May, in early June, and in mid-July, to ensure flowers through the season into October.
It is easier to plant sunflowers adjacent to the orchard, where they can be conveniently watered, than at the end of tree rows, Bentley said. In trials, sunflowers were planted in a plot measuring about a third of an acre next to the orchard.
Sunflowers do not transplant well, so seeds should be planted in the soil at a depth of less than an inch. They require adequate moisture to germinate and full sun to thrive. They do not do well between trees in an orchard or in any area where they are shaded. Sunflower varieties with large heads provide more seeds as a food source for the sunflower moth larvae. Multibranched varieties will produce multiple flower heads over a longer period of time.
In his sunflower trials, he has seen increasing parasitism of oriental fruit moth over several years. Parasitism usually ranges from 40 to 80 percent.
In a test block of June-harvested peaches, where no mating disruption or insecticide was used, there’s been not a single fruit damaged in four seasons, he reported.
"It’s been working wonderfully. It’s beautiful."
This year, he’s beginning a trial in a block of late-harvested peaches.
There’s a lot of interest in planting sunflowers, he said, and some organic growers are already trying it.
Bentley said this has been a fun project because it uses a biological control agent in a sustainable way so that the grower doesn’t need to buy more parasites for release each year. It also solves issues of border damage from oriental fruit moths that fly into an orchard.
Another host of the Macrocentrus ancylivorus is the strawberry leafroller, which Dr. Tom Unruh, entomologist with the U.S. Department of Agriculture in Yakima, Washington, has been studying as a winter host of the leafroller parasite Colpoclypeus florus. The strawberry leafroller infests wild multiflora roses, and Unruh has been testing the idea of planting roses near orchards so the leafroller and the parasite can overwinter on them.
Unruh said he’s found only a very small number of Macrocentrus wasps parasitizing strawberry leafrollers and does not think the parasite is playing a role in control of oriental fruit moth in Washington. Generally, oriental fruit moth densities are quite low.