Slugs: Orchid Enemy #1

Slugs. We all have them. In the garden, on the steps, crawling up the glass. Big ones. Little ones. With and without spiral shells.

No orchid pests are more destructive. They are non-discriminating in their eating habits – devouring flowers, buds, leaves, and roots. Mature plants are set back by years and seedlings often succumb.

They are also cunning. They strike at night, without warning, and are gone by sunrise. Like a taunting villain, they leave their calling card – a slimy trail.

Autumn is the time when growers in this part of the country bring their orchids inside. Unwanted pests, including slugs, may come along for the ride.  

Mature slugs are typically 2” long and lay tiny clear eggs inside the pot. The emerging babies slither to the top and begin feeding immediately on tender plant parts such as root tips and new leaves. As the slugs get bigger, so does their appetite.

Snails, which have a shell and are close relatives of slugs, can be found in many sizes as well. The smallest, bush snails, are only 1/8” long but they chew off every root tip they can find. It’s hard for a plant to thrive when the roots are missing.

Luckily, we don’t have to deal with the dreaded Giant African Snail which has been spotted in a number of American states.  Inspectors from the U.S. Department of Agriculture have been visiting nurseries handing out leaflets warning about the mollusk which is thought to have migrated from east Africa in imported goods. The gigantic snail can reach eight inches in length and five inches in diameter, lay 500 eggs at a time, and has the distinction of being one of the world’s top 100 invasive species. 

Seasoned hobbyists always keep flashlights on hand for ‘midnight slug hunting’. Some of my fondest memories are of searching the benches late at night with a cup of soapy water in one hand and a flashlight in the other. It’s surprisingly quick and easy to pick up a gooey mollusk and drop it in the cup. It’s like Easter egg hunting, only a little less colorful.

For decades, the commercial orchid industry used a chemical called metaldehyde to control slugs. However, the formulations were toxic to pets and wildlife so many growers sought an alternative.

In recent years, a new product has become available in the fight against slugs. The active ingredient is a non-toxic material called iron phosphate which acts as an eating suppressant for mollusks. Sold under the brand name of Sluggo, the pellets are sprinkled on top of the potting media. Slugs can’t resist the taste and never harm another orchid again.

No treatment regime would be complete with repotting. Since slugs, snails, and their eggs live inside the pot, it only makes sense to periodically change the media. Look closely for the clear eggs which can be hidden in the bottom.

When possible, it’s always best to prevent problems before they occur. Not long ago, scientists discovered that the metal, copper, repels mollusks with a tiny electrical charge. Eco-minded growers now wrap their bench legs with copper flashings, tape, wire, or strips so that slugs will not crawl up the legs. Liquid copper, as found in the common fungicide, copper sulfate, can also be sprayed on the plants.

The old wives tale of using fermenting beer traps to attract slugs doesn’t seem to work as slugs still prefer mouthwatering orchids. The tried and true method of traipsing around at night with a flashlight and hand picking the offenders never fails. 

Thursday, October 1, 2015 - 03:15