What's eating my plant!?! Common Garden Pests of Hawaii
What's eating my plant!?!
A common question brought into the nursery by gardeners plagued with plants that look like they’re sporting Halloween costumes beyond Oct. 31st (faux pas). Thankfully we don’t have to keep those skeletons in the closet! I started this article in October focusing on Rose Beetles and spun it for the Halloween festivities, but we decided to expand it to include more garden pests. I am leaving the original Halloween spin for your enjoyment, or annoyance, I mean come on, it’s December…
Besides leaf munchers, we see a lot of other garden pests. We'll get into more of those lower in the article, but will start with your three main suspects for holey leaves:
1) Rose Beetles
The Chinese Rose Beetle, Adoretus sinicus—nothing to adore about this critter! —is a reddish brown hard shelled invasive beetle from eastern Asia. It will eat anything that tastes good at dusk, leaving you with a haunting surprise to find the next day. Your plants might only be left with the veins in their leaves, resembling skeletons. Or maybe he wasn’t too hungry last night, and your plants leaves look like the most beautiful piece of lace (are you kidding me?!) Either way, the damage is distinguishable from slugs as they will eat the leaf with no artistic expression.
Yay! We know what’s eating our plants! Now what?! I really hate to break it to you, there’s not much you can do about Rose Beetles but wait for them to get full or sick of that flavor plant and move on to your neighbors.
There are some methods to attempt, including shining bright lights on your plants at dusk, they dislike bright light and sleep at night. You will be attempting to trick them into thinking it’s midday (who’s celebrating Halloween now?). Alternatively, you can spray your plants with something that tastes bad and train your rose beetles not to eat your plants (I’ll take chocolate over stale bread any day).
I train critters using a simple recipe of garlic and hot peppers. A couple cautions when spraying: spray early morning or evening, the hot sun combined with hot oils can burn the plants. Secondly, some plants will not be happy with the spray. My perpetual spinach plant didn’t like it and decided to go limp. He pushed through and I’m happy to report a vibrant pest free plant.
Now you can play around with training rose beetles! Isn’t that what you always wanted? Wait—there’s more…
2) Slugs
Veronicella cubensis, the Cuban slug. One of our most commonly seen garden pests, and my least favorite. Soft, slimy, disgusting creatures, vectors of rat lungworm disease (wash your produce!) As they move along our soil and plants they leave a slimy trail leading us to their unsightly blotches of holes in our plants. I get furious when I see they have devoured an entire leaf!
Early morning or late evening I’ll go out and collect them with a spoon into a bucket and toss them far away. After regular collections, the population decreases, and one may only need bait for the occasional straggler, if so desired. Even with larger infestations—which I have filled a 5gal bucket half full (snails and slugs)—I have found collecting and disposing the most effective.
But for those of us with less time or larger areas to cover, regular applications of organic Sluggo when it’s dry or other creative methods like beer traps can help. Keep your garden clean of debris and standing water as best you can, no food for them means they’ll move on.
3) Caterpillars
If you read our previous blog on Native Butterflies, Hawaii is home to 17 species of butterflys (2 native) and also 955 species of native moths (as well as many other non-native moths.) Each of these winged creatures has host plant(s) that support their juvenile caterpillar form. While butterflies are delightful creatures to see, their caterpillar forms can do destructive damage to your garden plants.
With caterpillars, we pick our battles at the nursery. We purposely grow Crownflower to support the Monarch Butterfly, but on very young plants we do have to monitor the caterpillar population or they will literally eat the plant to death. Same for the Citrus Swallowtail Butterfly which lays it's eggs on citrus leaves. If you have a young citrus tree with minimal leaves, you'll want to monitor it for caterpillars, as one caterpillar can demolish all the new growth on the tree in a matter of days!
Watching for eggs and gently smoosh or scrapping them off is easiest, or smooshing or removing the young caterpillars once they've hatched. (FYI relocating a young caterpillar off of it's host plant to another species of plant is still effectively killing it, unless you relocate it to a larger host tree where it can continue eating.)
Now I Know the Culprit...What Do I Do?
Rose beetles, slugs, and caterpillars are attracted to your plants because they’re hungry. Not necessarily because there’s something wrong with your plant.If, however, a plant is stressed, they send out stress hormones which can attract a whole host annoying pests like mealy bugs, whitefly, scale, or gall mites.
Two key principles when you notice pests:
1. Relieve the stress.
2. Treat the pest.
Determine sunlight, watering, and fertilizer needs of your plant and adjust appropriately. Maybe your Areca palms are shading out something that needs more sun, cut the tall ones, or we’ve had a dry spell and you need to increase water.
When’s the last time you fertilized? If you can’t remember, make notifications in your phone calendar, read your fertilizer instructions for application rates and frequency and stay on it!
There may be many things stressing your plant. If you can figure out what’s stressing between sunlight, water and fertilizer, you will have more success treating the problem than the symptoms (pests) alone. I will also mention, as part of your regular plant health check, prune appropriately! They like it!
Sometimes we put a good plant in the wrong place.
Sometimes the weedwhacker or the mower damages the plant (how plants deal with damage is a whole other issue we will get into in a future articlce) and the injury can compromise the rest of the plant’s life. We all make mistakes and sometimes we must start over, which sucks, I feel ya.
Bottom line—Relieve the stress, sunlight, water, fertilize, prune appropriately. Then when you’ve got that going, determine your pest and its appropriate insecticide.
Common garden pests in Hawaii:
Mealybugs:
Mealybugs are white cotton looking creatures that suck plant sap and ooze yellow guts when squished.They live on the underside of leaves, stems and occasionally roots. Individuals are distinct.
Whitefly:
Whitefly is another white cotton looking cluster of creatures, but different from mealybugs. The adult stage of whiteflies flies, mealybugs do not.You can see different stages of development on the undersides of leaves: eggs and nymph stages form a white frosty dusting, like “Jack Frost” if you’re familiar with those cold midwestern mornings where I’m from.As they mature, they form a "lovely" thick blanket of snow, and the tiny snowflakes (adults) dance around the plant.
Scale:
Scale are interesting creatures, immovable by itself, sucks sap, and are farmed by ants who enjoy the sticky residue produced by the scale.Scale comes in a wide variety of shapes, colors, and sizes. They live on tops and bottoms of the leaves, stems and apices.
Gall mites:
Gall mites (Aceria hibisci) are the most hideous intrusion on a beautiful hibiscus. You will see ugly, bumpy, warty protrusions inside the newer leaves.
Luckily their life cycle is only 3 weeks. Remove infected foliage as soon as you see it, to prevent further spread.
Sooty Mold:
Sooty Mold is a black fungal disease that grows on the secretions (aka 'Honeydew') of pest insects, usually aphids, scale, or whitefly. Sooty mold is not an infection of the plant, but rather grows on the surface of your plant. However severely coated leaves cannot photosynthesis and the plant's growth can become stunted.Treating the insect pest responsible for feeding the sooty mold is your first step, followed by an organic fungicide treatment for the mold. Once the mold is treated for and losses it's food source, it will slowly flake off or can be gentry scrubbed from the plant. In sever cases, it may be best to lightly prune back the infected areas to encourage new clean growth.
Let's Talk About Ants:
Many of the above pests go hand in hand with ants (who "farm" the pests for their secretions), so while you’re treating pests, don’t forego the ants. Let’s talk about ants for a sec. They work on two substances: sugar and protein.
Sugar is the most likely food to get picked up and taken back to the nest, but may not get passed to the queen.
Protein is the most likely to get passed to the queen. You need both sugar and protein in the same crumb to ensure it’s taken back to her.
Here at the nursery we do a combination of Mrs. Buttersworth syrup and peanut butter with borox. A combo of sugar and protein, certain to get poison to the queen.
Keep in mind, when you kill a nest of ants, you now have a vacant ant home for sale to which new ants can take up residence. Be prepared to repeat applications. If you’re looking for conventional ant bait, MaxForce has the combination of sugar and protein, which not all ant baits work on.
Garden Pest Treatments:
Remember, to manage pests on your garden plants:
1st) Release The Stress
& 2nd) Treat The Pest.
Most of these pests can be treated with eco-friendly options such as Neem Oil, Insecticidal Soaps, Horticultural Oil, and Copper Sulfate. Read labels on any product you purchase to verify it will work on the pest you are treating, and also how to correctly apply the product.
At the nursery, we have found it is also best to vary your treatment on repeat offenders. We rely on Neem Oil and a few other concoctions of organic pesticide products, and are able to treat all our pest problems at the nursery organically.
Here's a simple Homemade Insecticidal Soap Recipe for minor pest issues:
The simplest insecticidal soap is nothing more than a 2% soap solution. To make this at home, you will need:
Sprayer: Any clean spray bottle or garden sprayer will work fine for spraying insecticidal soap. Make sure the sprayer or bottle hasn’t been used for herbicides.
Pure Soap: Use a pure liquid soap, such as Castile, or all-natural soap. The active ingredient in insecticidal soap comes from the fatty acids in animal fat or vegetable oil, so it’s important to use the real thing. Don’t use detergents (which aren’t actually soaps), dish soaps, or any products with degreasers, skin moisturizers, or synthetic chemicals. Dr. Bronner’s Pure Castile Soap is usually pretty easy to find in stores, or check your local natural-foods store for other options.
Pure Water: Tap water is fine for making insecticidal soap. If you have hard water, you may want to use bottled water to prevent soap scum from building up on your plants.
To make homemade 2% insecticidal soap, mix together: 5 tablespoons soap to 1 gallon of water
Like any other home remedy, there are as many variations on this recipe as there are gardeners! You can also try:
Cooking Oil: To help the solution stick a little longer, add two tablespoons of light cooking oil (such as corn, canola, olive, or safflower) per gallon of water to the mix.
Vinegar: To make a spray that also targets powdery mildew, add a teaspoon of cider vinegar per gallon of water to the mix.
Garlic or Pepper: To help repel chewing insects, add a teaspoon of ground red pepper and/or garlic per gallon of water to the mix.
Aloha, and Happy Gardening!
This article was written by Holly, Senior Sales Associate at Seascapes Nursery.
Edited by Serina Marchi, General Manager.