American Nurseryman Magazine - Horticulture Magazine and Horticulture Books - European Invasion - August, 2014 - FEATURES

American Nurseryman Magazine - Horticulture Magazine and Horticulture Books - August, 2014

FEATURES

European Invasion

European pepper moth is beginning to make its way into greenhouse production areas, as well as propagation greenhouses for woody plants. Here's how to identify the invasive pest, plus what to do if you discover an infestation.
By Stanton Gill


The larvae of European pepper moth can girdle stems at the soil line, as seen here on a greenhouse-grown poinsettia plant.
Photo courtesy of Suzanne Klick

If you are a woody plant propagator, then you need to be alert to a new pest that is cropping up in greenhouses - and now propagation greenhouses - in North America. This pest is an unexpected gift from Europe that is adapting to the greenhouse environment in several states in the U.S. The caterpillar that is of concern is called the European pepper moth (EPM), Duponchelia fovealis (Zeller), which is native to several countries in Europe. This caterpillar has a wide range of plant material that it will feed upon, including woody plant material that is being propagated in greenhouses.

In the summer of 2013, a Maryland grower submitted for identification a caterpillar that was damaging several species of greenhouse plants in Maryland. This caterpillar was feeding on herbaceous plants in the commercial greenhouses. The caterpillar was the European pepper moth. Subsequently, we found the European pepper moth in four additional greenhouse operations in Maryland, but always in herbaceous plant material.

Our team published an article on this pest in a national greenhouse magazine, after which I received emails from growers in several states reporting this pest on greenhouse bedding plants and herbaceous perennial plants. An alert nursery owner in New Jersey, who propagates woody plants, realized a caterpillar that showed up in their woody plant propagation greenhouse might be the European pepper moth. Larvae and adults were collected and keyed out by Rutgers University Extension agent Joseph Imgerson-Mahar for initial identification. Samples were submitted to USDA's Animal and Plant Health Inspection Service (APHIS), and the pest's identity was confirmed as EPM.

The woody plants were being propagated in a greenhouse, under a mist system, over a six-month period. The grower noticed that the woody plants would suddenly collapse. On examination of the plants, she discovered that the root systems were developing well but the bases of the plants were girdled. The larvae were difficult to spot because they are photophobic (avoid light) and will hide under leaf litter. The larvae will often produce silk and cover the base of the stem in the silk as they feed on the crown of the plant. The grower found it was easier to spot the silken webbing at the base of the plant, then spot the larvae: When the silk was pulled back, the larvae were revealed. Often the larvae will thrash around when exposed to light.



European pepper moth larvae feed at the base of host plants.

The woody plant propagator placed out baited European pepper moth pheromone traps for capturing adult male moths. The traps filled rapidly, and this confirmed that the pest was established in their propagation house. She remarked that she first noticed moths showing up in five-gallon buckets of water that were left standing overnight in the greenhouse. She found this curious, but this was before she realized the moths were related to the larvae that were actively girdling the bases of the plants under mist in the propagation area. The bucket the grower inadvertently left out was a natural trap for the adult moths: One of the trapping methods for the adult moth is to place pheromone-baited wet trap with a container of water on the bottom half. This makes a natural trap, as the moth is native of wetland areas - both freshwater and saltwater - of southern Europe, the eastern Mediterranean region, the Canary Islands, Syria and Algeria. The larvae of this moth have been recorded on more than 70 host species in a wide range of plants families.

On the move

European pepper moth is being spread from state to state, first showing up in key greenhouse states such as Florida and California, and now has been confirmed in four Maryland greenhouse operations. Nurseries that propagate woody plants, greenhouse managers and Extension people working with greenhouse growers should be alert and monitor for this new pest. How much economic damage the European pepper moth might cause in the United States is still unknown, but we do know that this pest is being detected in many states in greenhouse operations. In Maryland, we know it damages geraniums and girdles the stems of poinsettias.

Because this pest has spread rapidly across the United States and Canada, traditional containment through quarantine has been discarded as impractical. Extensive monitoring was conducted in 2011 in several counties in Georgia and Florida; European pepper moth was found infesting lantana plants in a greenhouse in Georgia. While EPM was found in greenhouses in those states, it has not been found in field production of fruits or vegetables.



The pupal case of European pepper moth is visible beneath a propagation tray of Syringa.
Photos courtesy of Stanton Gill

It might be that the insect is adapted to the close growing conditions in a greenhouse environment and is not suited for most field production situations. In greenhouse environments, the foliage touching the substrate surface may make ideal conditions for this moisture-loving pest. The high moisture levels maintained in woody plant propagation greenhouses also may be ideal for the European pepper moth.

In the United States, the moth was first detected on begonia in San Diego County, California, in 2004. This population was eradicated. In 2010, it showed up again in San Diego County. By September 2011 it had been detected in 17 counties in California. Information from an entomologist in California suggests that the EPM has spread to several additional counties in the state. It has also been detected in Alabama, Arizona, Colorado, Florida, Georgia, Kentucky, Mississippi, New York (including Long Island), North Carolina, Oklahoma, Oregon, South Carolina, Tennessee, Texas and Washington State.

European pepper moth has also been recorded as a problem in greenhouse-grown chrysanthemums and other cut flower species in Ontario. At this time, it is not known whether this pest is mainly a greenhouse problem or whether it could cause damage in field and landscape plantings.

In June 2013, European pepper moth larvae were found infesting zonal geraniums and petunias in a commercial greenhouse in Central Maryland. Two alert greenhouse managers found the caterpillars boring in the base stems of plants and submitted samples to our University of Maryland Central Maryland Research and Education lab. We identified the caterpillars with help from Lance Osborne, an entomologist at University of Florida and USDA-ARS (Agricultural Research Service). A Maryland Department of Agriculture taxonomist, Gaye Williams, has subsequently confirmed our identification of this pest.

Damage

In Maryland we have found the caterpillars boring into geranium stems at the base of the plant. On petunias they were mainly feeding on leaves close to the substrate surface, but there was some girdling damage at the base of the plant. We have detected them feeding on foliage of chrysanthemums, but none was found girdling the stems. On poinsettia crops we found the larvae will use partially decomposed leaves to cover their bodies while they feed on the stems of poinsettias. This makes detection difficult, and growers will have to probe away the foliage to expose the larvae.

Plants hosts for the European pepper moth

European pepper moth has a wide host range; the list of plant hosts included here is not all-inclusive. It focuses on plants most likely to be found in nurseries, greenhouses and home gardens in Maryland.

In the case of the Southern New Jersey woody plant propagator, the stems of the woody plants were girdled, but the larvae did not bore into the stems. The grower did note that she found larvae pupating under the plant trays and on the bottom of the plastic rooting tray tubes.

Monitoring for EPM

Adult European pepper moths fly at night, but if you disturb plants during the day they will take flight, moving in evasive patterns and traveling a short distance before they alight again. At night the moths have been reported to travel greater distances. The adults are small moths with bodies half the length of a penny. When sitting on surfaces, moths typically project their abdomens up in the air, displaying C-shaped bodies. The wings have distinct white, wavy patterns.

Pheromone traps are available from biological supply houses: We found pheromone for baiting traps available from Koppert Biological Systems (http://www.koppert.com) and Syngenta (http://www.syngenta.com). In spring, hang the traps over woody plants under mist systems. The traps will not trap-out a population, but are an effective monitoring tool.

Most nursery and greenhouse operations have a discard-plant pile somewhere behind the greenhouse. In Maryland we discovered that the discard pile served as the epicenter for the EPM. The insect may also overwinter in these discard-plant piles, because the decomposing plant material creates a little warmer micro-environment. Be sure to monitor the discard pile at the greenhouse operation.

When examining for EPM, look for wilting plants and for silk located on the stems near the soil line. The larvae camouflage their body with decomposing leaves as they feed on the stems; the decomposing leaves may need to be probed off to expose the larvae.

What damage is caused by the larvae?

The eggs are laid on foliage, and hatching larvae of EPM initially feed on lower leaves near the soil level, making round or crescent-shaped holes. This is damage that can be monitored visually in an IPM scouting program. Older larvae consume whole leaves, or they can feed on roots or at the base of the plant at soil level. In some cases they girdle the base of a plant. With some vegetables and fruits the larvae bore into the fruit. Later instar larvae burrow into soft woody or herbaceous stems, causing damage in which fungi can enter.



Compost piles have proved to be breeding grounds for the European pepper moth, but with good composting practices the plant material will reach temperatures of 150° to 170° F, killing any larvae and adults.
Photo courtesy of Stanton Gill

In the zonal geranium brought into our lab, the stems had visible holes; this is what workers first detected. The larvae are reported to girdle stems, but none has been reported to bore into the stems of woody plant material. On poinsettia crops we found them girdling the stems at the soil level. As the larvae prepare to pupate, they web silk together, usually on foliage close to the soil.

Life cycle

The moth is active at night and lays white eggs in small clusters on the undersides of foliage, usually close to a main vein. Eggs have been recorded on stems and on the tops of leaves but usually are found on undersides of foliage. The egg clusters are in groups of three to 10 and are usually laid in overlapping patterns. The eggs turn pink, then red as the embryo develops and end up brown just before hatching.

The larvae have a dark-colored head capsule and a dark-colored, hardened dorsal plate just behind the head.On segments just behind the head there are two rows of transverse spots. There is at least one stout hair sticking out of each spot. The larvae feed mainly at night and avoid light. When we placed live larvae under a dissecting microscope with a light source, they were actively trying to move out of the lit area.

As the larvae grow their body color changes from a creamy white to a dirty brown. The larvae lose their spots just before pupation. The length of development depends on temperature, but in a greenhouse at 68°F the egg stage is four to nine days; the larval stage is three to four weeks; one to two weeks for pupation; and adults live for one to two weeks. Females mate soon after emerging. The males and females are strong fliers and have been recorded to fly several miles. Strong flight is at night. In the day adults fly up and travel short distances.

Controlling an infestation

Cultural control:

Removing debris and lower leaves will reduce habitat for the larvae.The problem is that most greenhouse plants are grown to have leaves all of the way down to the soil level. The foliage is often close to the substrate, especially with woody plant propagation. If this moth becomes established in the greenhouse, then making the effort to remove lower foliage will help reduce larval populations.

Plant discard piles should be turned regularly so the other plant material is turned into the center of the pile to improve the composting process. With good composting practices the plant material will reach temperatures of 150° to 170° F, killing any larvae and adults.

Some growers have used black light electric zappers to kill adults flying at night.

Chemical and biological control:

Fortunately this caterpillar is susceptible to several classes of pesticides. Young larvae feeding on foliage are fairly easy to hit with pesticides. Older larvae are less accessible to insecticides if they cover themselves with silk or move to the underside of the pot or plant tray; they are therefore more difficult to control. Repeated sprays of Bacillus thuringiensis can be directed to foliage to kill larvae feeding on the foliage. At least three applications at seven-day intervals are suggested.

Spinosad materials should also be effective in controlling the caterpillars, but making contact on the undersides of foliage where larvae feed will be challenging. Acephate was effective in our Maryland trials, but it may cause phototoxicity on some plant plants such as poinsettia.

In propagation greenhouses where mist systems turn on often during the day, the pesticide may be washed off the foliage or plant part before the larvae consume enough to be impacted.

The rove beetle, Atheta coriaria, is a good predator to release in a propagation greenhouse. This beetle adapts well in greenhouse environments and is a general predator that will feed on caterpillars.

Beneficial nematodes

It would be wise to combine the release of rove beetles with an application of entomopathogenic nematodes such as Steinernema carpocapsae. This nematode species is good at searching out caterpillar larvae in the order Lepidoptera. Check on the web for the several brands of S. carpocapsae that are available.

Apply nematodes with a sprayer (remove screens and filters), injector or a hose-end sprayer. If using an injector, set the dilution to 1:100. Remove all filters or screens (50 mesh or finer) in any spray lines so that the nematodes can pass through unimpeded and undamaged; spray pressure should be kept below 300 psi. Although nematodes are applied in water, they are not aquatic animals and therefore they need extra care while in stock and tank solutions, so adequate aeration of the nematode suspension during application is important. This can be done using a small, battery-powered submersible pump. You can also mechanically stir the solution to keep the nematode solution agitated. The small pump will also keep them from settling on the bottom.

Unlike many traditional pesticides, there is no REI or possibility that the target pest will develop resistance. No adverse effects have been shown against nontarget organisms in many different field studies. But, beneficial nematodes are living organisms, so there are a number of precautions you need to follow for their successful use.

It's critical to check their viability before application. To do this, place a small amount of the product in a small clear container or petri dish. Add a couple of drops of room temperature water; wait a few minutes and look for actively moving or swimming nematodes. They have a slight "J"curvature at the ends of their bodies. Use a black background and a hand lens or field microscope to see the small nematodes. Dead nematodes will be straight and still. Nematodes are very sensitive to UV light and desiccation, so applying during a cloud cover period is an excellent idea. Nematodes are compatible with a number of different pesticides.

We are interested in hearing if other nursery operations are having problems with this pest. Please contact me at Sgill@umd.edu.

Stanton Gill is Extension Specialist in IPM for Greenhouses and Nurseries, University of Maryland Extension in Ellicott City. He can be reached at sgill@umd.edu.

References

Feature Creatures: European Pepper Moth, Stephanie D. Stocks and Amanda Hodges, University of Florida, http://entnemdept.ufl.edu/creatures/veg/leps/european_pepper_moth.htm

Greenhouse Pest Alert: The European Pepper Moth, Duponchelia fovealis

Jen White, Extension Entomologist, University of Kentucky Cooperative Extension Service
http://www.ca.uky.edu/entomology/entfacts/entfactpdf/ef324.pdf