Farming Magazine - December, 2012
New Pests Galore
The brown marmorated stinkbug.
Photo from Wikipedia, User:Lildobe.
The 2012 fruit and vegetable growing season may well be remembered as the year of the pest. In addition to significant pressure from insects (flea beetles, leafhoppers) and diseases (late blight, downy mildew) we're already familiar with, a remarkable number of new threats to vegetable and fruit production have become cause for concern. These include the brown marmorated stinkbug, garlic bloat nematode, leek moth, spotted wing drosophila and swede midge.
These new pests started to show up in our region over the past few years, and they appear to be spreading, some faster than others. If you grow crops susceptible to any of these pests, then I suggest you spend some time this winter studying up on their appearance, behavior, life cycle and management options so you can plan ahead to deal with them and won't be taken by surprise.
The brown marmorated stinkbug (Halyomorpha halys) was first identified in the U.S. in Pennsylvania in 2001. It's native to Southeast Asia, and probably arrived here via shipping crates. It's since been found in many states across the country, and has become a serious pest in some locations.
Known as BMSB, this pest attacks a wide range of plants and crops, including many tree fruits, vegetables, woody ornamentals and legumes, especially soybeans. It causes damage by sucking plant juices, leaving small, necrotic lesions. Although BMSB can fly, their rapid spread is likely due to their ability to move around on vehicles and via other forms of human activity. They are expected to keep spreading to new locations.
Researchers are hard at work studying BMSB biology, behavior and ecology in order to develop effective and sustainable management tactics. However, the almost unrestricted movement of BMSB adults from one field to another poses a significant challenge. In addition to monitoring and timely use of insecticides, alternative management options may eventually include border sprays, ground cover applications, biological controls, and the use of pheromones, other attractants or repellents. For more information, visit www.stopbmsb.org.
Garlic bloat nematode (Ditylenchus dipsaci) is a microscopic worm that is also known as a bulb and stem nematode. Though it has been found in the U.S. in the past, it only recently became a significant threat, probably after it was imported from Canada on garlic intended for food use that was planted as seed garlic. The problem then spread through the sale of garlic seed, because there is no certification program for seed garlic.
This pest causes bloated, twisted, swollen leaves, as well as distorted, cracked bulbs. Infestation can weaken plants, causing them to be susceptible to infection by secondary diseases and insects. The nematode can attack other Allium species, such as leeks, onions and chives, as well as flower bulb crops like iris and gladiolus. It can overwinter in the soil, and can be moved through a field or farm on equipment, shoes, etc.
Management recommendations include destruction of plant debris, which can harbor the nematode; management of nightshades near crops; a four-year crop rotation out of alliums; good seed sanitation practices; and use of biofumigant cover crops. Hot water treatment of seed may need to be explored if the problem increases.
This garlic bulb shows symptoms of nematode infestation.
Photo by Vern Grubinger.
Growers who have not purchased any new garlic seed in a while should be at less risk of infestation. If you have garlic bulbs that look discolored or diseased in any way, you should not plant or sell them. Any garlic to be sold for seed should have samples sent to a nematode laboratory for testing beforehand. For more information, visit http://extension.umaine.edu/publications/1205e
Leek moth (Acrolepiopsis assectella) is native to Europe, where it's a serious pest of onions and leeks. It is also an established pest in Hawaii. It was first discovered in North America near Ottawa, Ont., in 1993, and then confirmed in the continental U.S. in Plattsburgh, N.Y., in 2009. It has since spread a little from that area into northern New York and Vermont. It is not clear how far it will go.
The larvae of this moth feed on a variety of alliums, including onions, leeks, garlic, shallots and chives. Adult moths emerge in the spring and lay eggs on the lower surfaces of leaves. The hatched larvae mine through the leaves inward toward the heart of the plant, occasionally attacking the bulb and the stem.
Symptoms include mining and pinhole damage on inner leaves. Plants may look distorted because of this damage, and rotting may occur. If you think you have leek moth damage, report it immediately to your cooperative extension vegetable or IPM specialist.
A male Drosophila suzukii, or spotted wing drosophila.
Photo by M. Francisco.
In Ontario, pheromone traps are used to properly time insecticide applications to manage this pest. Cultural controls include crop rotation; delayed planting; removal of old and infested leaves; early harvesting to avoid damage by last generation larvae; and destruction of plant debris after harvest. For more details, go to http://web.entomology.cornell.edu/shelton/leek-moth
Spotted wing drosophila (Drosophila suzukii), or SWD, is a small fruit fly with the potential to damage many fruit crops. It was first discovered in the U.S. in California in 2008 and moved quickly through the Pacific Northwest, into Canada and Michigan, and then into Florida and the Carolinas. It showed up in the Northeast in 2011, and this past year it has been widespread in the region.
Unlike other fruit flies, SWD can damage intact ripe fruit because the females have a saw-like egg-laying appendage (called a serrated ovipositor). This insect is a pest of most berry crops, cherries, grapes and other tree fruits, with a preference for softer-fleshed fruit. After egg laying, the larvae hatch rapidly and can be present in large numbers as a crop ripens. Since females cut a slit in the fruit to lay their eggs, this can lead to introduction of bacterial and fungal diseases, further damaging fruit. So far, damage has been greatest on crops that mature in late summer and fall.
SWD management recommendations include both cultural and chemical options. Harvest to remove as much ripe and cull fruit as possible. Harvest frequently and pick fruit as soon as possible. Trapping may be useful for early detection of the pest, and work continues to develop the best possible traps. Traps may also be used to "mop up" SWD that could otherwise overwinter. Fine-mesh screening may protect small areas of crops if the mesh openings are less than 1 millimeter wide. Biocontrols may eventually offer some hope for reducing populations of this pest, but much more research is needed. Insecticide recommendations have been targeted at adults to minimize the number of eggs laid and thus larvae in fruit. Given the nature of this pest, it can be a challenge to find materials that do not interfere with harvest or pollinator activities. For more information, go to www.ipm.msu.edu/swd.htm.
Swede midge (Contarinia nasturtii) is a gall midge that is native to Europe and southwestern Asia. It was first discovered in North America in 2000 in Ontario. In 2004 it was detected in Niagara County, N.Y. It attacks cruciferous vegetable crops, including broccoli, cabbage, cauliflower, Brussels sprouts, kale and radishes. It can cause severe losses to these crops. Adult midges emerge from overwintering pupae in late spring and lay clusters of eggs on young plants near the growth point. Then larvae hatch and begin to feed on plant tissue, often damaging the growing point.
All stages of the swede midge are very small, so this may easily go undetected at first. Symptoms of an infestation can be difficult to diagnose because they can look similar to other common problems of crucifers. Some things to look for are swollen and distorted leaf stalks, blind heads, brown scarring in the growing tips, crumpled heart leaves and multiheaded plants.
Combining several management practices should allow growers to keep the population of this pest low enough to avoid significant damage. These practices include use of clean transplants; a two to three-year rotation out of crucifers; plowing crop residue after harvest; monitoring for the pest; and timely application of insecticides as needed. For more information, visit http://web.entomology.cornell.edu/shelton/swede-midge.
The author is a vegetable and berry specialist with University of Vermont Extension based at the Brattleboro office. He can be reached at firstname.lastname@example.org.