Growing Magazine - May, 2014

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Learning About Leek Moth

By Kara Lynn Dunn


Adult leek moths are speckled brown, white and black with a white spot halfway down the outer wings and measure about 3/8 inch long. They are nocturnal and have approximately a 23-day life span.
Photo by Dan Olmstead, Cornell University.

Northern New York (NNY) agricultural leaders are undertaking outreach and research to inform growers about a pest that likes onions, garlic, chives, shallots, leeks and other allium crops.

Leek moth was discovered in the continental U.S. in a home garden in Plattsburgh, N.Y., in 2009. Since then, the pest has been found in other pockets of the NNY region: St. Lawrence County in 2010; additional sites in Clinton and St. Lawrence counties in 2011; and by growers in Essex and Jefferson counties in 2012.

Native to Europe, leek moth was first identified in North America in Ontario, Canada, in 1993, and is now known to be in Quebec and on Prince Edward Island.

The 3/8-inch-long adult leek moth (Acrolepiopsis assectella) has a 0.5-inch wingspan and is speckled brown, black and white with a white spot halfway down the outer pair of wings. It overwinters as an adult or pupa, emerging in the spring.

Adult activity can be monitored by commercially available pheromone trap systems. First flight generally occurs from April to May; a second follows from June to July, with a third taking place from July to August.

Females lay 100 to 200 eggs on foliage three to four weeks after mating. The larvae feed on plant tissue, tunneling through the folded leaves of leeks and garlic and burrowing into the hollow leaves of onions, chives and shallots. Damage increases in severity as the generation progresses, stunting plant growth, introducing rot, compromising onion and garlic storage life, and negatively impacting allium crop marketability.

Researchers say leek moth damage is often overlooked at its early establishment because it resembles damage caused by thrips, snails, salt-marsh caterpillars and botrytis leaf blight.

In 2013, the Northern New York Agricultural Development Program (NNYADP) awarded Cornell University researchers a grant that includes trapping to identify leek moth's range in NNY. A nocturnal flyer, the leek moth adult is rarely seen unless trapped.

Dr. Masanori Seto, working under the auspices of Cornell entomologist Dr. Anthony Shelton, is partnering with growers with assistance from Cornell Cooperative Extension (CCE) educators. They hope to develop and deploy control strategies before leek moth becomes established in New York's major onion-producing areas. A leek moth infestation could cause significant economic damage to the state's $54 million onion industry.



Look for windowpaning on the hollow leaves of onion, shallot and chive crops. This photo shows a larva inside an onion leaf.
Photo by Amy Ivy, CCE Clinton County.

"The NNYADP grant is helping determine where leek moth is and how fast it is spreading. This and other data will help growers properly time control measures," says Amy Ivy, project co-leader and CCE Clinton County horticulture specialist. "Eradication is not realistic, so we are learning to properly time treatments to reduce leek moth populations and the associated crop damage."

Seto is developing a phenological model to predict leek moth growth and emergence to facilitate the timing of management strategies, including cultural practices, biological controls and pesticide applications.

Shelton is investigating opportunities to use biological control agents, evaluating insecticidal treatments, and developing a growing degree-day model to help target optimal insecticide application timing.

Two insecticidal products, Entrust and DiPel DF, are currently approved for use on organic crops. Those and three others - Warrior II, Radiant SC and Lannate LV - are approved for conventional production.

"Insecticide applications made seven to 10 days following a peak flight can greatly reduce leek moth populations. Applications of organic insecticides must be precisely applied to have an effect. Thorough coverage of a plant is essential to control young larvae, especially with DiPel," Shelton says.



Dr. Masanori Seto shows summer intern Catherine May (left) and Master Gardener Nora Teter the leek moth traps he's using in Teter's garden in Clinton County, N.Y.
Photo by Amy Ivy, CCE Clinton County.

What can growers do now?

To prevent leek moth infestation, Ivy encourages growers to implement cultural practices, such as crop rotation, delayed planting, good field and harvest hygiene, scouting and destruction of pupae or larvae, and early harvesting before the final seasonal flight occurs.

The use of row covers immediately after planting to prevent adults from laying eggs is proving helpful.

"In 2013, we used row covers, and our garlic was fabulous," says Dani Baker, an organic grower who operates Cross Island Farms on Wellesley Island. "You have to be diligent about covering the crop well and not having any holes in the netting."

Baker worked with Seto to trap leek moths and try different control methods.

"2012 was the worst for leek moth here. It damaged the garlic before we even knew it was there. It destroyed the garlic and leeks and was in the onions, but had not done as much damage there," she explains.



Dr. Masanori Seto checks a trap at Rehoboth Homestead in Peru, N.Y., for leek moth.
Photo by Amy Ivy, CCE Clinton County.

She salvaged some of the garlic crop that year by selling it to a processor who separated the usable cloves.

In Peru, N.Y., Seto set traps and deployed row covers at Beth Spaugh's Rehoboth Homestead, where alliums are an important part of the crop mix.

"Our CSA members, and the general population, like onions and garlic. Fresh onions - scallions, pearl and sweet onions - and garlic are most important to us. Leeks and winter onions are secondary," Spaugh says.

"In 2013, we grew about 3,600 feet of onions and leeks ... and 1,200 feet of garlic," Spaugh notes. She says their major garlic variety had a lot of fusarium, but she wonders now if it was really secondary leek moth damage.

"If we are going to have to deal with this pest, we might as well find out about it, and I am supportive of the folks researching challenges to organic vegetable growing. Having Dr. Seto available to answer questions about timing and prevention will save me much effort this year," Spaugh says.

"I had a fear of raising the cover once it was on the alliums [in 2013]. The onions were protected from leek moth, but negatively impacted by weed competition. While there were not many weeds, the ones we had were huge and poking through the cover," she explains. "I thought the garlic might need to be under cover through the summer, but Dr. Seto explained that a short window in very early spring is enough to keep the moths from laying eggs in the scapes and helps minimize first hatch."

At Kent Family Growers in Lisbon, N.Y., Dan and Megan Kent have grown 3 to 5 acres of garlic, red and white onions, shallots and leeks in past seasons. They have dealt with leek moth for the past three years.

"We may be out of the allium business in 2014," says Dan. "The fabric covers we experimented with in 2013 trap too much heat in the crop. The netting allows better heat transfer and the crops grow well, but the added expense is an issue, and we only got two years' use out of the netting."

Trapping at the Kent farm is designed to find the leek moth concentrations.

"We know it overwinters under leaf litter and in the hedgerows. When the NNYADP project became available, we wanted to partner with the researchers to be progressive, first in line for information, and part of the step-by-step development of what we can do as organic growers," Megan says.

They have considered other measures - for example, using tomatoes as a trap crop for the insect - but Dan says it is "only a 10 percent solution, and that is not enough protection."



This garlic plant shows leek moth damage to leaf and scape.
Photo courtesy of Shelton Lab, Cornell University.

Vermont on leek moth watch

Ann Hazelrigg with the University of Vermont (UVM) Plant Diagnostic Clinic has found leek moth larvae and damage in plant samples without larvae present.

"Onion, leek and garlic samples with leek moth damage have been increasing in the UVM Plant Diagnostic Clinic over the past few years. The pest's range also appears to be expanding in Vermont, since the insect seems to be showing up on farms a little farther north and south each year," Hazelrigg notes.

She says early impact has been mostly along Lake Champlain and to a lesser extent in interior Vermont.

In 2012, Vern Grubinger, UVM vegetable and berry specialist, reported leek moth in onions grown in Burlington in July, in garlic in South Hero in August, and in September in Fairfax.

"The good news is it seems to be moving slowly in Vermont; the bad news is it probably will keep moving. We need to get farmers to know what leek moth looks like, its life cycle, and the damage it can do so they do not get surprised by it," Grubinger says.

"Right now leek moth has been overshadowed in growers' minds by spotted wing drosophila and swede midge. There are so many well-known insect pests that farmers already have to deal with that it can be a challenge to put something new on the radar. However, keeping an eye out for early infestations is important. By the time a pest is widespread in a crop it's easy to identify, but harder to manage," Grubinger adds.



Check the newest leaves on leek plants for damage.
Photo courtesy of Shelton Lab, Cornell University.

In addition to netting and crop rotation, Grubinger suggests using multiple locations or off-farm locations for allium crop production, and he says, "Basic IPM practices become more important than ever."

Vermont CSA pioneer Andy Jones attended the fall 2013 Northern New York Allium School to talk with Seto about using leek moth traps at Intervale Community Farm (ICF) in Burlington, Vt., in 2014. ICF serves 550 summer and 200 winter CSA member-owners with 25 acres of organically grown vegetables, herbs, flowers and berries.

"We saw substantial loss in 2012 in our leeks and more signs of leek moth in 2013. We don't grow a ton of leeks, but approximately a third was affected, making some unmarketable. We stripped layers from some of the crop but lost yield. It definitely hampered crop growth," Jones says.

More Tips for Managing Leek Moth

  • Use crop rotation.
  • Delay allium plantings.
  • Destroy pupae or larvae; some growers have tried flooding crops for two days to suffocate them by drowning.
  • Some growers cut back leeks and regrow to smaller harvest size.
  • Tomatoes have been suggested as a sacrifice crop at field edges.
  • Harvest early to avoid damage by the last generation of larvae and to reduce population buildup.
  • Practice good field hygiene; destroy plant debris following harvest.
  • Look closely when trapping, as leek moth damage is sometimes confused with that from thrips, salt-marsh caterpillars or botrytis leaf blight.
  • Visually scout for damage: windowpaning on hollow leaves of onion, shallot and chive crops; split leaves open to look for frass and feeding debris; check garlic and leek leaf surfaces and look for tunneling through leaves; in June, hardneck garlic will show damage to scapes.
  • Report suspicious findings to local agriculture officials. Leek moth is considered problematic when more than one moth is identified in an area of less than 6 square miles.

"We need research and trapping to get a better sense of leek moth. We are a long way from understanding it, and management is yet far away," he says. "In 2014, we will spend more time getting a handle on timing coping strategies for leek moth."

In August 2013, a group of diversified organic growers from Quebec shared their management tips.

"They told us they scout their crops and have seen good results with the use of one to two organically acceptable insecticidal applications. The trick is knowing just the right time for application," Jones says.



Dan Kent of Kent Family Growers says his diversified farm may not produce allium crops in 2014 to avoid the expense of dealing with leek moth.
Photo courtesy of Kent Family Growers.

Literature for Quebec suggests scouting 25 plants, and if more than one plant is damaged (5 percent threshold), spraying is recommended.

Ivy and Seto have met with UVM horticulturists to develop a New York-Vermont information exchange to keep educators and growers in both states current with leek moth sightings.

Learning from long-term experience

"In certain areas of Ontario, some allium growers have been dealing with leek moth for more than a decade. However, the overall economic impact has not been quantified," says Marion Paibomesai, a specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs.

"Leek moth seems to be a larger issue for market gardeners and organic growers. Allium growers with leek moth infestations have been using a variety of techniques to minimize damage. An integrated pest management approach is suggested for both conventional and organic growers here, involving a combination of techniques to manage this pest," she adds.

Those techniques include:

  • Monitoring leek moth flights using pheromone traps in combination with the degree-day model.
  • Recording daily temperatures to determine development time according to a degree-day model.
  • Scouting crops for leek moth larvae, pupae and damage; some crops, crop stages and parts of the crop can tolerate more damage.
  • Using floating row covers with secured edges and without frames or other types of supports. Row covers may be removed during the day for weeding, but should be replaced before dusk.
  • If warranted, applying registered pest control products seven to 10 days after the peak of moth flights.
  • Burning, burying or bagging infested plant waste. Leave bags in the hot sun for several days.
  • Promoting biological control. Generalist native predators and native parasitoids may feed on leek moth as prey.Diadromus pulchellus is a parasitic wasp of European origin that attacks leek moth.

For More Information

Cornell University Leek Moth Information Center: http://bit.ly/1pabj7S

Leek Moth - A Pest of Allium Crops: http://bit.ly/Rp5tk8

Northern New York Agricultural Development Program: http://bit.ly/Rp5eWi

The author is a freelance writer with a 100-acre farm in Mannsville, N.Y.