I’ve had these ferns for years and had never had this problem before. The caterpillars probably showed up to give me something to write about. I showed my appreciation by smashing as many as I could find.
I was surprised to find them on my ferns because this is normally a problem with eggs laid on newly bought ferns that are grown in Florida. The culprit – the Florida fern caterpillar – is a tropical insect. So how they showed up in Augusta I am not sure! The mild winter may have had something to do with it.
The Florida fern caterpillar adult is a moth – a brownish insect with variegated wings.
The female lays eggs that are slightly flattened spheres covered with tiny longitudinal and transvers ribs.
They are pale green with a yellow tint and are .02 inch wide, so very small. The eggs are laid singly under fern leaflets near the tips. They hatch in five to seven days and the tiny new caterpillars feed on the tender new leaflets mostly at night, but larger caterpillars will feed on the tougher leaves and tender stems.
As the caterpillars mature, they usually hide on the stems at the base of the plants or in the soil during the day.
The caterpillars have five color forms. The ones on my ferns have a white line down each side. The caterpillars eventually grow to about 1.25 to 1.5 inches long when mature.
The fern caterpillars are active feeders, and several can damage a plant severely. They often chew off more plant material than they consume.
These caterpillars have been reported to feed primarily on ferns (at least 14 species) including maidenhair fern, Boston fern and other varieties of sword fern, holly fern, table fern, silver fern, rabbit’s foot fern, and asparagus fern.
Be sure to check your ferns for possible eggs or for caterpillars.
A sure sign caterpillars are feeding is finding the droppings on the ground beneath.
You might be able to remove all the caterpillars by hand.
Either smash them on the ground or have a small container to put them in. Picking them off might prove difficult if they are numerous.
At least by removing them you will prevent the laying of eggs once they have grown into moths.
There are several insecticides you can use. Organically, you can treat with Bacillus thuringiensis, (B.t.). The powder is Dipel while the liquid is Thuricide. You can also treat with Spinosad.
Other insecticides would include carbaryl (Sevin) bifenthrin, lambda-cyhalothrin, or permethrin.
Use the insecticides with caution as the leaves of ferns can be delicate. Make sure your fern is well hydrated prior to spraying and don’t spray them in direct sunlight.
Excess rain affects plants
A problem associated with our excess rain in June and July is that oxygen was prevented from reaching the plant roots, especially in compacted soils.
Certainly, some plants are more tolerant of wet conditions, but the longer the lack of aeration, the greater the chance of root death.
Lack of oxygen will result in root dieback, with above-ground symptoms appearing as leaf yellowing, droopy foliage, leaf drop, and eventually branch dieback. It can take a while after the damage to the roots for the top to start showing problems which is why much of this is appearing now.
Water-logged root systems are more susceptible to attack by root-rot organisms. In addition to the obvious damage to plants, there are more long-term effects to the soil.
Soil micro-organisms that require oxygen may be killed and those that survive without oxygen take over, which in turn affects availability of nutrients for plant use.
The soil structure might be physically harmed because of compaction of soil particles.
There isn’t much you can do other than wait to see how your plants respond in the long run to the drier conditions we’ve had the last month.
Watch for signs of dieback, but don’t be too hasty to cut limbs. Branches that have lost leaves aren’t necessary dead, even though leaves might drop.
There might be buds that will be able to leaf out again next summer.
Live stems and buds will have some green tissue visible.
A light fertilization can be helpful to replace nutrients that were lost and to encourage regrowth.