Snowbush Spanworm is a small yellow and green caterpillar and it is eating the leaves off Snowbush plants in Pinellas County. One distinctive is the Snowbush Spanworm moves in an inchworm manner.
Complete Defoliation Leaving Nothing But Twigs
Snowbush Spanworm will completely defoliate a Snowbush leaving nothing but sticks where a colorful bush once grew. When the foliage is all gone the Spanworm will turn to munching on the bark. The defoliating is often sub-lethal and mostly a cosmetic problem, however, the “girdling” effect of the bark eating will kill terminal branches and sometimes the entire plant.
How to Know You Have Snowbush Spanworm
If you wake up one day and find nothing but sticks where your Snowbush once stood, you most likely have Snowbush Spanworms. Look for the 1 - 1.5" worms clinging to twigs during the day. A vigorous shake of the Snowbush will send most them tumbling to the ground.
The spanworm is easily controlled with available insecticides. The adult – the White Tip Black Moth is of no harm (other than laying eggs) and in a swarm can be attractive. Repeat application will be required to control multiple generations.
There Can Be Years Between Outbreaks
All of this is a cyclic phenomenon - there were outbreaks in 2008 and 2017. Prior to 2006, it was rare to have any problems with Snowbush in Pinellas County. The cyclic pattern could be a natural population “bloom” of the spanworm and that there may be "quiet" periods of 8 to 10 years between outbreaks.
Pragmatic Approach to Snowbush Spanworm
The Snowbush Spanworm is often detected after the plant has been defoliated. Damage done and treatment will only kill the lingering spanworms. The plant may recover. There are years between outbreaks and not all Snowbushes come under attack. All this makes prevention more expensive than the replacement cost of the plant. If you can't stand to have your Snowbushes defoliated once every eight years, you should consider replacing it with an alternative plant.