Nymphaea Fidelity » Caterpillar Invasion

We begin by identifying the party responsible. Most of the time, it will be the larvae of the infamous ‘China Mark Moth’ (a). We see the larvae as identified as (b). Damaged caused includes sections of foliage cut out and patches of foliage missing (c and d). The larvae are also known as “sandwich men” because when they have consumed enough water lily foliage they will “sandwich” two cut pieces of a water lily pad and form a cocoon.

You’ll notice that these pests show up when its warm rather than cold. Also, they will likely attack young foliage first. This means that smaller water lilies will see more damage than a water lily planted in a large container. This is because the foliage is more tender on a small water lily.

Once an invasion occurs, action must be taken immediately they may wreak havoc across all water lilies in your pond.

The first thing you should do is acquire the proper items for treatment. The generic product will be BT (Bacillus thuringensis). The specific form that targets caterpillars is Bacillus thuringensis kurstaki. This organism works by stopping the larvae from being able to eat and therefore they starve and perish a few days later. There are two forms of BT–a liquid and a powder. There are also several brands that market BT. We make no preference for brands other than what is available locally but we highly recommend getting both a powder and a liquid form. As for the specific brands that we use: liquid (Thuricide) & powder (Dipel). We have been able to get Thuricide from The Home Depot. Dipel was purchased from a hydroponic gardening store. If all fails, you may acquire BT products via the internet. Be sure to store products in a cool location.

The next step is to locate all of the sandwiched pieces and remove them. Search everywhere including underneath water lily pads. We suggest lightly spraying the foliage of a water lily with a garden hose to dislodge the pests (spray away from plant so they are easy to round up and remove). Then you will want to remove a couple lily pads with the most damage (this will trigger growth of new lily pads quicker).

It is now time to apply the BT. Note that BT is a living organism so its best to apply in the early morning or late evening at the heat of the midday sun will drastically reduce its effectiveness. If using the powder, you will want to lightly dust the foliage of all water lilies. If using a liquid, you will need a sprayer. We use a 1 gallon sprayer and mix it with about two tablespoons (we use pond water in the mix). Then you will want to spray all water lilies. Keep in mind that this is not a quick fix. You will need to apply the BT over a period of a few days until you can find no traces of the China Mark Moth larvae. At that point you may reduce application to just once a week or so. You may store unused mixes in a cool location.

At Utopia Aquatic there is a constant battle with these pests because of our year round warm weather. We typically see them ease off in winter. We are proactive in alternating our application of both the powder and liquid form.