Ag column: How to deal with unwelcome invaders

October 07, 2008

Unwelcome invaders come in all shapes and sizes, and the most annoying are what are known as nonnatives. If you look at most of these nonnatives, they were introduced by humans. As Pogo said, "We have met the enemy and he is us."

Established ecosystems have developed their own natural balance and controls over time. Plants and animals within those systems find this balance suitable for survival or they have been able to adapt in order to survive within those conditions. When nonnative species from other ecosystems are introduced, they can upset that balance and bring harm to the established plants and animals and the whole ecosystem. Nonnative species come from somewhere else and they are not natural to the ecosystem to which they have been introduced. They might be harmless and beneficial in their natural surroundings, but they can totally devastate different environments. When alien species enter an ecosystem, they can disrupt the natural balance, reduce biodiversity, degrade habitats, alter native genetic diversity, transmit exotic diseases to native species and further jeopardize endangered plants and animals. When there are no established natural controls, such as predators to keep the nonnative harmful species in check, there can be a population explosion of the invasive nonnative species, causing an ecological catastrophe.


Catastrophe might be an overstatement most of the time but unintended consequences almost always occur.

I will just name a few of these unwelcome guests and you decide what you think of them: Dutch elm disease, chestnut blight, gypsy moth, English starling. You are getting the picture now. The latest invader is the pinnacle of annoyance: the brown marmorated stink bug (Halyomorpha halys).

Our phones here have been ringing off the hook with questions about these most annoying creatures. Feeding damage appears as small dead or discolored spots on leaves and fruit. These stink bugs can also be a nuisance in homes and buildings as they seek shelter in the fall, much like Asian lady bird beetles and boxelder bugs.

Extension specialists tell us even though these insects do not harm humans and do not reproduce inside structures such as houses, they cause concern when they become active and conspicuous in fall and spring. If many of them are squashed or pulled into a vacuum cleaner, their smell can be quite apparent.

Mechanical exclusion is the best method to keep stink bugs from entering homes and buildings. Cracks around windows, doors, siding, utility pipes, behind chimneys and underneath wood fascia and other openings should be sealed with silicone or silicone-latex caulk. Damaged screens on doors and windows should be repaired or replaced.

Exterior applications of insecticides might offer some relief from infestations where the task of completely sealing the exterior is difficult or impossible. Applications should consist of a synthetic pyrethroid and should be applied by a licensed pest control operator in the fall just prior to bug congregation (it might be too late this year).

Unfortunately, because insecticides are broken down by sunlight, the residual effect of the material will be greatly decreased and might not kill the insects much beyond several days or a week.

Another option is using soapy water. Simply mix your choice of dish-washing liquid soap with warm water and douse away. Again, there is no residual effect, but you might get some exterior cleaning done, which may prove to be a side benefit.

If numerous bugs are entering the living areas of the home, attempt to locate the openings where the insects gain access. Typically, stink bugs will emerge from cracks under or behind baseboards, around window and door trim, and around exhaust fans or lights in ceilings. Seal these openings with caulk or other suitable materials to prevent the insects from crawling out.

Live and dead stink bugs can be removed from interior areas with the aid of a vacuum cleaner.

It is not advisable to use an insecticide inside after the insects have gained access to wall voids or attic areas. Spray insecticides directed into cracks and crevices will not prevent the bugs from emerging, and is not a viable or recommended treatment.

As mentioned by my colleague Annette Ipsan in her article on this subject dated Feb. 6, 2007, "they aren't harmful, just pesky, the perfect test of our ability to take the good with the bad."

Jeff Semler is an Extension educator, specializing in agriculture and natural resources, for the University of Maryland Cooperative Extension. He is based in Washington County. He can be reached weekdays by telephone at 301-791-1404, ext. 25, or by e-mail at

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