CSI: Pondville

What's killing the aquatic plants?

4_overspray_PBiles

Chemical overspray can even drift from next door, causing leaf damage. Luckily, new pads will be normal.

Nowadays, forensic science principles are
being applied in many fields. The good
news for those of us in the field of aquatic
flora is that careful examination of dead and dying
aquatics can lead to fewer deaths, happier customers
and occasionally, increased profits.
Water gardeners get spoiled because there are
far fewer pests to deal with in ponds than in any
other garden. Unfortunately, they are unprepared
when mayhem does strike. When plants start dying,
the result is customer dissatisfaction and numerous
complaints. Thankfully, this presents numerous
opportunities for knowledgeable businesses to solve
pond plant problems quickly and profitably.

Let’s begin with an examination of the evidence.

Mysterious Holes, Spots and Tracks

Different insects and small animals that prey on aquatic plants each leave a specific kind of damage. Most often the damage appears on leaves, which are the predominant and tastiest part of the plant. The distinctive holes, tracks and other visual clues are like fingerprints that can lead to the culprits.

 The most common villain is the China Mark moth larva. It cuts oval-shaped holes along the outer edges of lily and lotus pads. The cutout forms a cocoon on the back of the leaf, which explains its common name: Sandwich Man. The next most common killer is the dastardly aphid, a tiny black or green spot that can multiply faster than the speed of light.

Lower-ranking perpetrators on the most-wanted list are large snails and various caterpillars. Snail damage usually starts along leaf edges and quickly expands to huge swatches. Caterpillars are easy to spot since they move slowly and leave droppings. Some cause big holes all in a row (leafrollers) while others only eat the top leaf layer. Their destruction appears more irregular than most other leaf damage. Harmless small snails (like ramshorn) often appear on damaged leaves but are not at fault; they’re just cleaning up the debris.


The least common crimes are caused by a range of criminals. Random wiggly tracks in waterlily pads can be caused by leaf miners, midge larvae or weevils. Japanese beetles create holes in leaves and, occasionally, flowers. Spotty holes from fungi, bacteria and viruses seem to be declining. However, chemical overspray holes and bleached markings are becoming more common as everyone in the neighborhood uses sprays to enhance and control things.

Remember that not all unknown pond denizens are out to harm aquatic plants. Most of the tiny creatures are beneficial parts of the aquatic ecosystem and have always been there. It’s only when something goes wrong that we notice them for the first time. They’re just innocent bystanders.

Ugly, Contorted Limbs

A waterlily may have distorted pads in spring because of a nutrient deficiency that it will outgrow after repotting. Crispy and curled leaves (or flowers) are caused by excessive heat or drought. Luckily, new growth usually returns to normal when the extreme conditions pass. Rolled up leaves of cannas and other broad-leafed
aquatics are sure signs of leafroller caterpillars enjoying a salad in the pond. Mites cause a more subtle distortion in some leafy aquatics, usually in dry conditions or climates. These tiny insects literally suck the juices and color out of leaves, leaving faint webbing and tiny speckles. Severe aphid infestations cause enough
damage on new leaves to make them curl and become stunted.

Dangerous Shifty Behavior

dead lotus

Without enough water,
aquatics get crispy. This lotus pot was finally watered and it bounced back wih healthy new leaves and flowers.

The first symptom of something amiss with a pond plant is shifting leaf colors. This is not the normal yellowing of mature leaves as they fade and die. It is a color change from healthy deep green to sickly yellow and is a sure sign of nutrient deficiency. When left untreated this leads to plant starvation, which leads to reduced blooms, which leads to increased pests, which leads to unhappy customers, which leads to money out of your pocket to fix things. So … pay close attention to changing leaf colors! If you are colorblind, get help to recognize those starving yellow-green colors that indicate a lack of fertilizer or pest damage.

Dastardly plant killers almost always attack sick plants, since healthy specimens can defend themselves. So the first sign of invaders is likely to appear on plants that are stressed. Overcrowded and overgrown plants are constantly fighting for limited space and nutrients, which makes them highly stressed. These conditions are the most frequent causes of poorly performing plants (especially lilies and lotus).

Unhealthy plants are prime targets of opportunity for nefarious killers. The first signs of attack will appear on new growth or dying and dead leaves. Elaborate sleuthing is not required to prevent plants from becoming easy prey. Just watch for the first signs of aquatic overcrowding and nip them in the bud — pun intended. [The March/April 2014 aquatic propagation article covers this in more detail, with photos.] Regular repotting and dividing is easier than waiting until the overgrown plant mass is being circled by buzzards. Then it will need protection from the baddies and major surgery. Repotting is also an excellent opportunity for add-on sales — supplies, fertilizer, services and classes.

Case Histories

Just as in any criminal investigation, getting a detailed case history from the plant owner is necessary to obtain an accurate diagnosis of the problems. Ask the following questions to reconstruct conditions leading up to the crime:

– When was the plant bought, repotted, fertilized or divided, and what size is the pot?

– What are the symptoms, especially changes in leaf size and color or flower numbers and frequency?

Digital Sleuthing

If your investigation gets stuck, a bit of technology may help. Cut off the injured leaf or blossom — along with the culprit devouring it. Then, take a good, close-up photo of the perp in action and save it on your computer.

Next, go to Google image search, click on the camera icon in the search bar, drag and drop your image into the box and click “Search by image.” Google will search for similar images to match the one you provided — potentially with identifying data. Hopefully you will get lucky and your mystery killer will be identified!

After the Arrest

After the perp has been caught, the obvious step is treatment for the victim. This article doesn’t have room to provide all the options, but here are some strategies and resources. The most critical step is to act while the infestation is small and easily contained.

Use treatments in this order; it is the best way to go easy on affected plants, fish, water quality and environment.

The first level is the least invasive: treatment by hand. Remove as many damaged leaves as possible, then destroy or burn them. (Leave at least four or five pads on lilies.) This prevents spreading the problem
and makes the pond look better. Squish invaders when possible, like China Mark moth larvae, caterpillars and
snails. Spray aphids off with a hose blast, then overflow the pond or container garden
to wash them away. Repeat as needed.

Every aquatic plant is subject to starvation when nutrients run out or they become overcrowded. Take action as soon as yellowing leaves appear. This prevents weak plants getting attacked by pests. The next level of attack also avoids chemicals. Leave a layer of newspaper over aphid-infested leaves for an hour to drown the little buggers. Other steps to combat chewing insects are to sprinkle diatomaceous earth on leaves or use Bt (Bacillus thuringiensis), natural bacteria that only affect chewing insects and not fish, pets or people. It is the active ingredient in many biological controls used for terrestrial and aquatic plants.

The final level of treatment is chemical, starting with the least toxic. Whenever possible, remove the affected plant from the pond for treatment, rinse it off and then return it. In some cases it might be more cost- or time-effective to replace the diseased plant with a healthy one.

Wrapping Up the Case

The aquatics you sold, installed or maintain in clients’ ponds are counting on you to keep them healthy, thriving and beautiful. So stay tuned to slight changes in their appearance and conditions. Be vigilant for warning signs of danger to prevent needless plant crimes before they happen. The lotus will thank you. The lilies will reward you with blooms. The marginals will jump for joy. And most of all, your clients will think you can walk on water. Case closed.

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