Combatting Crawl Space Fungi

Q: I have enclosed some photographs showing a very serious fungus problem in a crawlspace. Our customer has asked us what could be done to solve this problem. Would you give us some ideas about how to proceed in helping our customer? (A.K.)

A: Unfortunately we can’t print the photographs showing the fungus infection in the crawlspace. I can point out to our readers that it is a very serious fungal problem. There are virtually no floor joists or portion of the wooden sub-flooring that is not affected by both brown-rot and white-rot fungi. There is also an abundance of surface-staining fungi. Clearly, the brown- and white-rot fungi are causing the bulk of the damage. In some cases, 2x10 floor joists have been totally destroyed and have fallen into the crawlspace area.

The photograph indicates the ventilation opening in the poured concrete stem wall is about 2 inches tall and 6 inches long. I don’t know how many of these openings exist around the foundation, but they are insufficient to properly ventilate this crawlspace area. Based on the information I have, I believe a fairly serious remedial approach is necessary. First, all of the affected wood, including the joists, sills, plates, headers and sub-flooring, will need replacement. There is no treatment that can be applied to these already heavily infected wooden components of the foundation that will cure this problem. When the repair process is underway, several things will need to be done simultaneously. Remove all wooden debris from the crawlspace and clean it thoroughly. It may be necessary to level the grade in the crawlspace so that you don’t have ponding of water. It may also be necessary to lay down a plastic moisture barrier within the crawl. If the water table is high and the soil remains wet most of the time, then a moisture barrier is necessary. You need to check the exterior perimeter grade around the outside of the crawlspace to determine whether or not rain or irrigation water is running into the crawlspace. If so, take action to divert water.

Ventilation for the crawlspace will also need to be increased. Current recommendations for crawlspace ventilation where no moisture barrier is in place call for approximately 2 square feet of ventilation for every 300 square feet of exposed soil. However, I have found this level of ventilation to be inadequate in some environments. In this case, I would double that. In other words, for every 300 square feet of exposed soil surface in the crawl, I would shoot for approximately 4 square feet of ventilation. The ventilation openings should be equally spaced around the perimeter of the crawl, however you must make certain that you ventilate any dead air spaces within the crawlspace. I have seen many perfectly ventilated crawls according to the government specifications that are full of decayed fungi because someone failed to ventilate a dead air corner that was not anticipated or allowed for in the building design. Finally, I would replace the damaged and infected lumber in this instance with treated lumber. Also, you may find it necessary to retreat the disturbed soil areas for subterranean termites, as this type of renovation often disrupts a previously existing barrier. And you may want to check the wood moisture level in the repaired crawl periodically for the first year after repairs are completed, to ensure that your efforts to reduce moisture in the area have been effective.

Not all fungus problems and moisture problems in crawlspaces will require this drastic approach. In many cases, simply improving the ventilation of the crawl or placing a soil moisture barrier will be sufficient.

NEW TERMITE BAIT

Q: I recently read about a new termite bait called Labyrinth. What is in this bait and how will it be used? (R.E.)

A: Labyrinth contains the active ingredient diflubenzuron. The most common trade name for this product in the past has been Dimilin. This material is a highly specific chitin synthesis inhibitor. As a result, it will interfere with the formation of an insect’s cuticle. Under the trade name Dimilin, this material has been used in agriculture on a wide range of foliage-feeding insects in forestry, ornamentals and fruit. The product has also been used on cotton, soybeans and vegetables. Some formulations have been used in the control of flies, mosquitoes and grasshoppers. It has even been used to control ectoparasites on some livestock.

Diflubenzuron has been around since the mid-1970s. Chemically speaking, diflubenzuron belongs to the class of insecticides known as the benzoylureas. This is the same class of compounds that hexaflumuron belongs to. As you are probably aware, hexaflumuron is the active ingredient in Recruit II termite bait. I’ve not seen any research or field trial data on this new termite bait so I am unable to comment on how effective it may or may not be against subterranean termites.

Questions for Jeff Tucker can be sent to Q&A, c/o Entomology Associates, P.O. Box 70375, Houston TX 77270.