Insects on
Aquatic Plants
by Dave Brigante
Oregon
Click images to enlarge

 
Dave Brigante

 
Aphid infestation on a taro leaf
Photo from taropest.sci.qut.edu.au

What is really bugging you? As far as aquatic plants are concerned anyone who has grown them has had some insect contact on one level or another. Nuisance pests are inherent in this plant group just as they are in all of the others. Over the many years that I have been growing aquatics I have certainly noticed some trends. I hope that by making pond plant growers and enthusiasts more aware of the potential for insect invasions on certain varieties, we can all cope with and possibly avoid some of the more typical insect damage issues that can come along.

In preparing to write this article I started by making a chart (I love charts) of most of the plants that I grow or that are somewhat common in the aquatic plant field. Then I determined which insects just can't seem to stay away from each of them. This information is geared for aquatic marginals, but floating aquatics are also prone to visits by an occasional pest or two. One example would be the special fondness that aphids have for waterlilies. The chart's main headings are aphids, spider mites and white flies, plus my personal favorite category, none.
Aphids are far and away the most prevalent problem of the "Big Three". It made me question whether there are any plants that they won't suck on. These versatile insects can be found in at least seven different colors. They can come into the world from unimpregnated females and they can transmit disease from one plant to the next. The earlier you can detect these guys (or girls) on your plants before the damage is done the better. Some of the various types typically show up on an annual basis on the same plants, green aphids on variegated cattails, black aphids on waterlilies and yellow aphids on Canna lilies. If any of these are allowed to go unchecked you can end up with some very sick looking plants. One good thing is that they are not too hard to get rid of if only a small population is found initially. 

Aphids on a baby Victoria leaf
Kit Knotts Photo

Aphids on a taro leaf
Photo from taropest.sci.qut.edu.au
More aphid information
More aphid photos

Spider mites on Eichhornia crassipes
Kit Knotts Photo

The other two, spider mites and white flies, are less common but still have the potential to explode onto the scene when you least expect it. Spider mites often go undetected until you notice the tiny white webbing that is usually associated with their colonies. The use of a magnifying hand lens comes in really handy when scouting for mites.

 
Spider mites
Photo from bio.scarletts.co.uk

Adults can be seen crawling around slowly and more than likely there will also be some spherical egg clusters close by getting ready to hatch. These little critters are more apt to create havoc during the warmer seasons, then down cycling to a less active demeanor as temperatures decrease below 60 degrees. Amazingly, as you'll see on "The Chart" they even cause grief for waterlilies. I've seen vast damage take place very quickly in high density growing conditions.
More spider mite information 

White flies
Photo by Dr. Martin Fregene
from africancrops.net

The last main player, white flies, can be equally as annoying as the other two previously mentioned. I know I have a problem when I first see them merrily fluttering about in all of their pure white glory. Once again prompt action is required to snuff them out before they can take hold. As a beginner grower I learned that these insects absolutely need repeated eradication treatments to stop their reproductive cycles. As with most insects it is best to eliminate the present day adults and also take some type of measures to suppress ensuing juvenile stage hatches.  
As a general rule good clean maintenance practices can go along ways towards reducing the potential for insect population explosions. Taking the extra time required to inspect your plants on a regular basis will also help. As "they" say, it's best to "nip it in the bud".
If any of these assassins do make their way into your personal jungle, there may be a few things that you may want to consider before taking your flame thrower out for a spin. How important are the plants to you? How bad is the infestation and what method of treatment are you going to pursue? Tossing the plants can be relatively easy, but you wouldn't want to make a habit of using that type of treatment too many times. If the colony of insects is so large that the plants have already suffered so much that a short term recovery is looking bleak, a grooming, hosing off and possible spray application could be a consideration.

White flies on a taro leaf
Photo from taropest.sci.qut.edu.au
More white fly information

The options for treatment are plentiful, always using pesticides only as a last resort. There are some garden-ready sprays that are much less toxic to the environment and the applier too. For the backyard pond, using something on that level or just hosing off your plants on a regular basis may be best. If the plant (or plants) can be submerged below the waters surface for a few days, that can also be a very effective alternative. Of course, if using a pesticide is necessary read the label completely to be aware of any safety precautions and to check to see if it is fish safe or not. On a commercial level using lower toxicity insecticides that are insect specific and have a longer residual prevention period should be considered.  
The incidence of insect discovery is more common in a greenhouse versus outside where mother nature is lending a hand. The greenhouse environment is so controlled and the plant diversity is such that it makes the prevalence of insect problems that much greater. Unfortunately the season for the right conditions is also extended indoors. This is usually from March to October; outdoors you can probably take a month off each end of that time period.
The chart below highlights the potential for what may come around for an unwelcome visit. With good plant spacing, keeping your plants clean and regular monitoring, a lot of this can be kept as just potential and not become a reality.

 Plant Name

 Spider Mites

 Aphids

 White Flies

 None or Other

 Acorus

 X

 X

 Anemopsis

 X

 Arundo

 X

 Bacopa

 X

 Baumea

 X

 Caltha

 X

 Canna

 X

 X

 X

 Carex

 X

 Colocasia

 X

 X

 X

 Cyperus

 X

 Cyperus haspan

 X

 Dichromena

 X

 Dulichium

 X

 Echinodorus

 X

 X

 Elettaria

 X

 Equisetum

 X

 Eriophorum

 X

 Glyceria

 X

 Gunnera

 X

 Hibiscus

 X

 X

 X

 Hippurus

 X

 Houttynia

 X

 Hydrocleys

 X

 Hydrocotyle

 X

 Iris

 X

 X

 Juncus

 X

 Lobelia

 X

 X

 Lysimachia

 X

 X

 Marsilea

 X

 Menyanthes

 X

 X

 Mimulus

 X

 X

 Myosotis

 X

 Nymphaea

 X

 X

 China mark moth

 Oenanthe

 X

 X

 X

 Peltandra

 X

 Pontederia

 X

 X

 X

 Ranunculus

 X

 X

 Ruellia

 X

 X

 Sagittaria

 X

 X

 Saururus

 X

 X

 Scirpus

 X

 Scirpus cernuus

 Wooly aphid

 Thalia

 X

 X

 Tulbaghia

 X

 Typha

 X

 X

 Vallisneria

 X

 Victoria

 X

 X

 Wedelia

 X

 X

 Zephyranthes

 X