Most phalaenopsis growers have encountered the problem of root damage caused by larval Lyprauta gnats, commonly referred to in the industry as ‘pot worms’. Arne Steelandt, Quality Control and R&D Coordinator at Microflor, has solid expertise in dealing with this pest and shares some useful tips.

Pot worm infestations have been around for many years in the phalaenopsis cultivation industry. However, they used to be managed quite easily in the past through the use of chemical pesticides. These days, more stringent regulations have been imposed on the use of such agents, which has made controlling the pest much more difficult.

Pot worms: unknown and unloved

As pot worm outbreaks were quite easily managed in the past, little is known today about the life cycle, feeding pattern and natural predators of this persistent pest. To promote sustainable production practices, detailed knowledge is required about how these infestations develop and spread among the plants and their surroundings—in this case the greenhouse.

Results from studies indicate that it will not be an easy task for growers to eradicate pot worms without the use of chemical agents.

In recent years, many studies have been conducted to pinpoint the exact species of gnats that are the cause of this problem. The search for natural predators is ongoing, and initial results have revealed that it will not be an easy task for growers to eradicate pot worms without the use of chemical pesticides.

Nematodes: from lab to greenhouse

Does this mean the battle against pot worms is a lost cause? Not at all. Some techniques that are effective in controlling a certain type of pest have shown to be somewhat effective in combating pot worms as well. The Sciara gnat, for instance, is similar in many ways to the Lyprauta gnat.

Not all pest control methods work equally well for both organisms, but some of the principles work in an analogous way, as examined by a number of research centres. It appears that in a lab environment, Steinernema nematodes are effective to some extent. However, obtaining similar results in a greenhouse setting is not as simple as it may sound.    

Light traps and glue-based traps: not a fix-all solution

Some phalaenopsis growers have started experimenting with colours. They use sticky traps or blue lights to attract adult gnats and trap them before they can lay their eggs. This pest control method is effective to a certain degree but the results are inconsistent. What is certain, however, is that this method is not a fix-all solution to eradicate pot worms. Light traps do not deal with the root cause of the problem, which means they are not a sustainable solution.   

The importance of a clean greenhouse environment

The experiments with light traps did reveal that a lot of pot worms are found underneath the tables used for tissue culture propagation. This is an important discovery, because an efficient, sustainable cultivation system begins with a clean greenhouse. Many growers disregard the importance of maintaining proper care of the surfaces underneath the tables, as well as the paths and any other areas in the greenhouse that aren’t used for growing plants.

Many growers disregard the importance of a clean greenhouse in the battle against pot worm, but I challenge them to give it a try.

Mosses, algae, weeds, substrate residue and puddles containing stagnant water are perfect breeding grounds for flies and other insects, including pot worms. It is therefore crucial that greenhouses are kept neat and tidy—a task that requires time and effort. Many growers disregard the importance of a clean greenhouse, but I challenge them to give it a try.

Dry cultivation: safe but expensive

Many growers are currently trying to control their pot worm problem by implementing dry cultivation methods. These methods are safe but they do extend the time required to produce the final product, which is an important factor to consider in an expensive phalaenopsis greenhouse setup.