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Fact Sheet on Powderpost Beetles and Wood-Inhabiting Fungi
Insect Note - ENT/rsc-19


Powderpost Beetles

Powderpost beetle emergence holesThe term "powderpost beetles" refers to several groups of small woodboring beetles. In North Carolina, our primary concern is with anobiid ("an-oh-be-id") powderpost beetles, which attack the softwood species (conifers), such as spruce, pine and fir that are commonly used to make floor joists, wall studs and other structural lumber. Lyctid ("lick-tid") powderpost beetles attack only hardwoods, such as oak, ash, hickory, and maple. They tend to be a problem with antique furniture, cabinets, wooden floors and some interior moldings/trim in houses. Infested wood may look fine on the outside with no real evidence of an underlying problem.

Powderpost beetles lay their eggs in cracks, crevices or wood pores, preferably in unseasoned and unfinished (no paint or stain coating). The hatching larvae (immatures) feed primarily in the sapwood (outer lighter-colored wood). The name "powderpost" refers to the type of damage caused by the beetles. As the larvae feed, they produce the characteristic flour-like fecal material or "frass". Anobiids usually take 2+ years to complete their life cycle. Lyctid beetles may complete their life cycle in as little as three months, but more typically 9-12 months (or longer). We rarely find the actual beetles and only months or years later do we discover the damage. Typically, the only indication of a powderpost beetle infestation are small round holes about 1/32 - 1/16 inch in diameter scattered over the wood surface (as seen in the accompanying picture). In some cases, only one or a few boards are infested. In other instances, several joists may show sign of powderpost beetle activity. At first sight, people often assume that these holes are made by insects boring into the wood. The holes are actually made by adult beetles exiting the wood after they complete their life cycle. As the beetle emerges from the hole, it pushes out frass (yellow arrows in image) that will be found streaming from these holes or on the ground beneath the infested boards or surrounding the holes on horizontal wood. The frass of the lyctid beetles looks and feels like talcum powder. The frass of anobiid beetles is powdery but has a gritty texture. Frass that is yellow and caked is usually considered to be "old" and likely an indication an infestation that is no longer active. You may find exit holes and frass almost any time of the year, particularly in heated buildings or in crawlspaces. However, the peak time to watch for emerging beetles occurs in May through August.

You cannot simply look at a piece of wood to determine if the damage is severe enough to require repair or replacement. Probing the wood may give you some indication of the extent of the damage. If you are concerned about the condition of structural wood, such as floor joists, you may need to contact a general contractor or structural engineer.


Powderpost Beetle Control
Many powderpost beetle problems are related to high moisture in the wood, particularly in crawlspaces. Wood moisture levels need to be closer to 13% to become less favorable to the beetles. In assessing problems in your home, the inspector needs to collect moisture readings on floor joists in several areas of the crawlspace. You can reduce moisture in the crawlspace by improving the ventilation and/or installing a 6-8 mil plastic moisture barrier covering 70-80% of the soil. In some instances, the crawlspace may be "closed" or encapsulated which is a more elaborate process that requires the installation of a dehumidifier. Spraying the wood with an insecticide is the most common method of chemical control for powderpost beetles. Pesticides available for control of powderpost beetles are listed in the NC Agricultural Chemicals Manual . Pesticides containing "borate" are particularly effective against powderpost beetle because they penetrate the wood and kill beetles feeding within wood, as well as killing adults entering or exiting the wood surface. If you are concerned that wood behind walls or in other inaccessible areas is infested, then it may be necessary to fumigate. If you find activity in late fall or in the winter, you might want to wait until spring before treating so you can tell if the problem is limited only to that area or is more extensive.

 

Fungi Associated with Wood

There are several types of fungi associated with wood, but not all of them actually cause damage.

Surface Mold and Mildew
Mold and mildew on floor joists may indicate excessive moisture in the crawlspace. However, mold and mildew do not cause wood to decay. In these instances, chemical control is not needed to protect the wood from decay, but you should take some steps to lower the moisture in the crawlspace (the same steps outlined for powderpost beetles). Since mold may be associated with indoor air quality and respiratory health issues, potentially severe problems should be evaluated by qualified individuals. For additional information, visit the EPA's Mold Resource Web Page.

Sapstain Fungi
These fungi are similar to surface molds, except that the discoloration goes deeper into the wood. The wood may have a blue, black or gray color; however, the staining fungi do not weaken the wood structurally. Sapstain fungi are an indication that the wood was wet at some time. However, once the wood dries, the fungus becomes dormant and stops growing. No chemical control measures are needed.

Brown Rot and White Rot
These fungi actually cause structural damage to wood. They often produce a white cottony growth on the surface of the wood. Brown rot is one of the most common types of wood-decaying fungi. As the wood decay, it darkens, shrinks, and twists, with cracks forming across the grain of the wood. Finally, the wood becomes dry and powdery. Wood decayed by white-rot fungi has a bleached appearance and is fibrous and soft (sponge-like). Wood that is saturated with water (30% moisture readings) will rot. If the wood moisture drops below 20%, then these fungi will not grow. Brown and white rot fungi can be controlled by removing the source of moisture that allows them to grow (e.g., by improving ventilation or drainage, repairing leaks, etc.). Treating the wood chemically will halt decay, but it is still important to address the sources of the moisture problems that caused the initial problem. If the moisture source cannot be eliminated, decayed wood should be replaced with pressure-treated wood.

Water-Conducting Fungi
Meruliporia incrassata fungus growing on wall and over soilMost wood-decaying fungi only grow on moist wood and do not attack nearby dry wood. However, there are some brown-rot fungi, sometimes called "water-conducting fungi" which can conduct water for several feet through root-like strands to moisten dry wood. The most common type of water-conducting fungus in North Carolina is Meruliporia incrassata (sometimes called by its former name "Poria"). These fungi are common in the southeastern U.S. and can cause extensive damage in 2-3 years. The damage is similar in appearance to brown rot. The problem is most common in new or remodeled houses. In order to control water-conducting fungi, you must find and eliminate the source of moisture that supports fungal growth. The top priority should be to get the wood moisture content below 20%. Untreated wood in contact with or near the soil is most vulnerable. Where the fungus grows from a porch, the soil should be removed from the porch next to the foundation wall to prevent continued growth of the fungus into the house. Untreated wood should be at least 8 inches from the soil. If this is not possible, then treatment with a borate pesticide can be used.



Prepared by
Michael Waldvogel, Extension Entomology Specialist and
Larry Jahn, Extension Wood Products Specialist (Ret.)


Pest information and control recommendations presented here were developed for North Carolina and may not be appropriate for other states or regions. Any recommendations for the use of chemicals are included solely as a convenience to the reader and do not imply that insecticides are necessarily the sole or most appropriate method of control. Any mention of brand names or listing of commercial products or services in the publication does not imply endorsements by North Carolina Cooperative Extension nor discrimination against similar products or services. All recommendations for pesticide use were legal at the time of publication, but the status of pesticide registrations and use patterns are subject to change by actions of state and federal regulatory agencies. Individuals who use chemicals are responsible for using these products according to the regulations in their state and to the guidelines on the product label. Before applying any chemical, always obtain current information about its use and read the product label carefully. For assistance, contact the Cooperative Extension Center in your county.

Distributed in furtherance of the acts of Congress of May 8 and June 30, 1914. North Carolina State University and North Carolina A&T State University commit themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age, or disability. In addition, the two Universities welcome all persons without regard to sexual orientation. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.



(Photograph of Poria damage courtesy of K. Spillman, Innovative Pest Solutions, Raleigh, NC)

Last updated - Sept. 2005

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