Artillery fungus answer?

June 11th, 2009

   A wood-rotting organism known as “artillery fungus” is the culprit behind those little black tarry dots showing up on light-colored house siding and fencing.

   The dots are spore masses. Once dry, they’re nearly impossible to remove.

 Where’s it coming from?

   Usually from wood mulch. Sometimes the fungus rides in on new mulch, but it’s also widely found on any rotting wood, including fallen branches. Rabbit droppings, decaying leaves, wind and even spore-infested new plants are other sources.

 How do I avoid it?

   Penn State researchers tested 27 kinds of mulch and found the fungus grew best in what people use most — shredded hardwood and wood/bark blends.

   It barely grew at all in cypress mulch, pine bark nuggets (large chunks) and mushroom compost — a blend of manure and straw that’s a byproduct of mushroom growing.

   Non-wood mulches such as stone or rubber sidestep the problem, as does planting low spreading groundcovers instead of mulching at all.

   Topping old mulch with a new layer each year also seems to keep a lid on outbreaks.

 A promising solution…

   Intrigued by the non-growth in mushroom compost, researchers mixed 40 percent fresh mushroom compost with 60 percent wood mulch and found nearly zero artillery-fungal action.

   Gloria Day, owner of Chester County’s Pretty Dirty Ladies, was the first to field-test that blend at a client’s home last summer and came away highly impressed.

   “I loved the look of it,” she says. “It gives that nice, dark color people like. The compost feeds the soil and aerates the mulch so you don’t get that matted-down spongy feel. It’s excellent for weed suppression. And I didn’t see any artillery fungus at all.”

   Other benefits: it uses a Pennsylvania-produced waste product and actually costs less.

 So where can I get it?

   Nowhere yet. No one is mixing and selling the blend. Aged mushroom compost and mulch are both available here, so you could mix your own. Aged mushroom compost may have some weed seeds, though. Compost fresh from the mushroom house is steamed and virtually weed-free.

How do I get the dots off my house?

   “The spore masses stick like Super-Glue,” says Dr. Don Davis, a Penn State plant pathologist researching the fungus. “We have not found a way to get them off without leaving a stain or damaging the siding.”

   RV cleaners, steel wool, ink erasers and a lot of elbow grease are options. Davis’s web site at www.personal.psu.edu/faculty/d/d/ddd2 lists two dozen other things homeowners have tried.