What Is Artillery Fungus, And Does It Hurt Plants?

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You may have been puzzled by unsightly, tar-like dots on your yard’s plants, vehicles, and other surfaces. Where do these mystery spots come from?

You may be surprised to know that these spots are the peridioles (glebal masses) of Artillery Fungus (Sphaerobolus spp.).

Artillery FungusPin

This wood-decaying fungus has the alarming and annoying habit of forcibly ejecting these hard-to-remove dots as far as twenty feet in all directions. 

How is this possible?

This type of fungus is equipped with a powerful firing mechanism that delivers about 1/10,000 horsepower of built-up osmotic pressure.

When the fungus releases its artillery, you can actually hear a loud popping sound. 

When the fruiting body discharges the spores, it tends to do so toward a strong source of light, so you are likely to see dots of spores on the sunny side of a building or reflective surfaces, such as the surface of an automobile.

The fruiting body is so sensitive to the presence of light that it will actually throw more spores toward light-colored objects than dark ones.

As a result, removing the glebal masses from surfaces is extremely difficult. Attempting to scrape them off may spread the spores, which can survive for over a decade. 

How Can You Tell If The Problem Is Artillery Fungus?

You can recognize Artillery Fungus by carefully examining the dark spots it produces. As mentioned, they are about a tenth of an inch across and may appear rounded or a bit raised.

The outside of the spot is shiny and becomes darker the longer the area is in place.

If you scrape off the top of the site, you’ll find a gummy, granular, tan filling. This is a mass of mature spores. 

The spots will mature and swell into a fruiting body which will split open to form a cup-like structure with the masses of spores resting in liquid at the bottom.

After about 5 hours, the highly phototropic fruiting body will discharge the spores into the air and toward the brightest surfaces in the surrounding area. 

People often mistake these spores for insect frass, scale insects, tar spots, or the spore of its relative, bird’s nest fungus.

One way to hone in on a diagnosis is to consider the weather. You will most likely see Sphaerobolus damage on cooler days in the spring and fall.

This is because the fungus cannot produce fruiting bodies unless the temperature is below 77° degrees Fahrenheit. 

Additionally, when temperatures are high, surfaces tend to be dry. This means that any glebal masses that might be released would probably be unable to stick.

Moist surfaces make it easier for the cup-shaped spores to get a hold so that their sticky coating can adhere. 

You will usually find Artillery fungi growing in damp and sunny areas. For example, this fungus thrives on piles of rotting wood and unturned dung heaps. 

It is rare to find the spores indoors, but if the fungus has been brought inside on the mulch of houseplants, the ripe, fruiting body will do its best to shoot spores into a well-lighted area when the time comes. 

What Can You Do About Artillery Fungus?

Unfortunately, no fungicides have been found to be effective against Artillery Fungus, but prevention can work quite well to keep it under control. 

It’s important to avoid using old mulch to give the fungus a good surface to grow and thrive to prevent the growth and spread of this fungus.

Rather than leaving old mulch undisturbed on the surface of the soil where it will receive ample sunlight, either remove and replace it or till it into the soil and cover it with fresh mulch. 

Several types of mulch are known to suppress the growth of Sphaerobolus.

These are: 

  • Atlantic White Cedar
  • Cypress 
  • Pine

Using inorganic mulch, such as pebbles or rubber mulch, also helps prevent the growth of Artillery Fungus. 

Remove Artillery Fungus Spots Promptly

When the global masses hit a surface, they stick thanks to a tough, glue-like coating.

As a result, removing these cup-shaped spores (about a tenth of an inch) is extremely hard without damaging their adhered surfaces. 

It’s important to catch them early to eliminate the spores on walls, vehicles, and other surfaces.

When you see them, scrub and treat the surface with soap and water and follow up with a bleach rinse. Then employ a power sprayer (unless it would destroy the surface) to blow them off. 

Even these steps may not be effective.

You may end up having to sand them off. In any event, protect yourself against inhaling released spores, and lay some protective covering over the ground below the infestation to prevent having released spores take hold and grow. 

Will Artillery Fungus Hurt Plants?

If Artillery Fungus spores appear on plant leaves, examine the plant carefully and simply prune away affected leaves and stems.

The fungus will not hurt the plant, but the spores are unattractive. Leaving them in place will only allow them to multiply. 

Dispose of pruned stems and foliage by burning or placing them in black plastic bags in the sun to be picked up by sanitation. The heat will kill the spores.

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