Question
How can I get the black sooty mold off of the deck next to my elm tree?  Power washing doesn't seem to do it.  I need something to dissolve the black substance.  Any idea?

Thanks,  Jim

Answer
First you will need to control the sucking insects that are causing the sooty mold.

The fall webworm, Hyphantria cunea (Drury), is most often discovered when the unsightly, light gray, silken webs on the trees in late summer and early fall are observed. Webworms enclose leaves and small branches in their nests,

This pest usually eats leaves late in the season and the nests are generally concentrated to limited areas. Because of this, little real damage is done to most trees. However, the nests can look very unsightly and multiple generations in long summers can lead to significant defoliation.

Because the nests are only found on the ends of tree branches they are easily noticed. Webworm feeding cause no health danger to the tree, it only lowers the overall beauty of the tree because their nests are ugly. Remember that tree leaves are most efficient at producing food during the first few weeks after emerging in spring. As the season progresses into fall the leaves produce less and lesser food but have already stored enough food for next years leaf production and other growth. Leaf loss is less important in late summer and fall.

Though the webs are very unsightly, damage to most trees is considered to be insignificant. However, in southern states where several generations of attack can severely defoliate trees, control measures are needed. This pest tends to go through periodic population explosions. Outbreaks every four to seven years may last for two to three years and then natural control agents greatly reduce the activity.

Mechanical Control - Removal of Nests - Small nests can be pruned out of small to medium trees. Monitor trees early to detect the nests when only several leaves are involved. These small nests can be easily crushed. Do not burn or torch the nests in trees as this may do additional damage to the tree.

Biological Control - Apply Bacillus thuringiensis (Bt) - The bacterial insecticide, Bt, is quite effective against fall webworms if it is applied when the larvae are small. Use formulations with UV protectants and thoroughly cover leaves next to nests. As these leaves are incorporated into the nest and eaten, the Bt will be ingested. Bt will work but the caterpillars will need to feed on the insecticide covered leaves to be killed.

Contact insecticides are sprayed on the adjacent foliage and when the caterpillars crawl on the leaves they are killed or if the spray gets on the insect it is killed. These work faster than Bt. Recommended insecticides are Orthene, bifenthrin (Talstar Lawn&Tree)and liquid carbaryl (Sevin). Check with your local nursery for these for control of fall webworm.

These products can be sprayed by the homeowner with pump up type hand sprayers if the trees are not too large. For tall trees either contract with a pesticide operator or do nothing realizing that the tree will not be killed but may look not too pleasing with the webs in the foliage.

If the power washer is not working try a cleaner. heree are two that seem to work.

DECK CLEANERS:
Household cleaners and bleaches can be effective to some extent but they have their limitations. Also, since they are not usually designed for deck cleaning applications they can present some handling problems. For cleaning wood decks and the exterior of your home I recommend either one of these two products...

Trisodium phosphate has been used by painters for years and years as a heavy duty degreaser and all purpose cleaner. TSP is formulated for removing Grease, soot,and lead paint dust cleanup. A washing of surfaces prior to painting helps insure a good clean "bite" for the finish coats of paint. TSP can be mixed with a small amount of laundry detergent to help keep it wet longer and penetrate deeper into the surface dirt.

Hy-Tech House Wash is a complete environmentally friendly powdered concentrate that is simply mixed with water. This product is formulated with oxygen bleach and other agents for deep penetration, long "wet time", ease of use and will not harm wood fibers, pets, grass, or most plants.

DECK BRIGHTENERS AND RESTORERS: After cleaning to remove dirt, grease and other foreign materials the next step is to remove the natural "graying" and lighten other stains. There are countless "old home recipes" for solutions to brighten wood.

XYGEN BLEACH: (Disodium Peroxydicarbonate, not to be confused with sodium bicarbonate)... is Biodegradable, Non-toxic, Color-safe and Fabric-safe. It is not harsh like chlorine bleach. It's mildly acidic and may be used to help neutralize previously-applied basic cleaners. Environmentally friendly, sodium percarbonate will react with water to form hydrogen peroxide, which acts as both cleaner and slightly acidic bleach/brightener. A great benefit is that the hydrogen peroxide will evaporate and leave behind no pockets of acidic solids. The hydrogen peroxide is unusually effective in lightening heavily darkened wood. Except for industrial-strength cleaning or stripping jobs, sodium percarbonate is our hands-down choice for most average wood preparation jobs.