Issue link: https://read.dmtmag.com/i/705612
34 AUGUST 2016 Good Fruit Grower www.goodfruit.com C ontrol is so difficult for the black stem borer, researchers have been recommending that growers remove infested trees and burn them. Now, efforts are afoot in New York — again — to find a way to stop the borer. Researchers are making strides to better understand the beetle, and several biopesticides under review are showing promise. The bad news: Field trials run last year using Lorsban (chlorpyrifos) and a number of trunk sprays produced disappointing results. "None of the treatments were tremendously effective," said Art Agnello, a Cornell University Extension entomologist. Agnello is continuing to research effective controls, baiting borers with ethanol and testing, among other things, verbenone — currently used as an organic insect repellent in pine forests — in wooded areas just outside orchards. Meanwhile, Ithaca, New York-based USDA-ARS research entomologist John Vandenberg is investigating organic controls, and Kerik Cox, an asso- ciate professor in Cornell University's plant pathology and plant-microbe biology section, examined a possible connection to fire blight and blister bark. The insect, which hails from Asia, has been in this country since the 1930s. In the not-too-distant past, the black stem borer — a type of ambrosia beetle — limited its activities to forest hardwood and ornamental species like ash, black cherry, black walnut, cedar, dogwood, oak, pine, poplar, rhododendron and willow. Recently, it developed a taste for apple trees. "We're seeing them in all varieties of apples, although we see them more in young plantings, which tend to be newer varieties," Agnello said. The insects tend to attack smaller caliper trees suffer- ing from flood or cold injury, severe pruning or disease, which may be why they moved into orchards and nurs- eries. "There were enough stress-producing events to get them moving into nurseries and orchards," he said. Vandenberg suggests nearly all modern apple trees may be stressed to some extent, raising the stakes against the pest. "Pruning, the cutting, the shaping, it all causes trees some stress and may make them more vulnerable to insect attack," he said. Last month, the research was part of a scheduled field day held at the New York State Agricultural Experiment Station in Geneva, New York, which coincided with the International Fruit Tree Association's summer tour. Fungal solutions? Vandenberg and Louela Castrillo, a research scientist in Cornell University's entomology department, are evaluating biocontrols that may provide an alternative to uprooting and destroying infested trees. Working in concert with scientists in Tennessee, they have identified three biopesticides capable of either killing the insects or limiting their ability to reproduce. (Female borers hollow out galleries in the sapwood or heartwood of the tree in which to lay eggs.) The active ingredients in each of the products — Botanigard, Met52 and RootShield — are fungi. Beauveria bassiana is Botanigard's active ingredient. It is a fungal pathogen of insects occurring naturally in soils throughout the world and is not harmful to humans. The fungus requires contact to kill beetles, though it will not kill them when they ingest it. B. bassiana attacks both adults and larvae, producing spores called conidia, which produce enzymes that attack the beetle's cuticle, then later its organs, killing it within three to seven days. Met52's active ingredient is Metarhizium brunneum, and its action is similar to that of B. bassiana. "We found it killed about half the females and significantly reduced the remaining females' abilities to reproduce," Vandenberg said. Adults soon become infected, which, in turn, leads to infected larvae. "It creates an epidemic in the galleries," he said. The downside to this is that the female walks through Bearing down on black stem borers Courtesy of usDA-Ars Black stem borer females excavate galleries in apple tree trunks to lay eggs and hatch larvae. Later in the season, they move deeper into the trunk to overwinter. tJ MullinAx/GooD fruit Grower Art Agnello adjusts five potted apple trees in the middle of a hardwood forest that borders an apple orchard near Huron, New York, in early July. The young trees are part of a pest control trial to combat the spread of black stem borers. This location has 20 sets of five stressed trees each; 10 sets use ethanol lures, 10 use ethanol and the repellent verbenone. New York researchers working to stop one of the newest apple pests. by Dave Weinstock Art Agnello