Gardening on the Garden Isle: The evil web of an avocado lace bug

I was stretched out on my favorite chaise lounge, admiring the grass that needed mowing. I leaned back and casually looked up at the fluttering leaves of my avocado tree. Then I saw it. It wasn’t big. It wasn’t glaring. It was hardly noticeable, but I knew it was trouble. I leapt to my feet, shuffled over to a low-hanging branch, and turned over a new leaf. There they were — a convention of bugs sucking the life out of an innocent leaf.

Time for action. After years of “all speed no direction,” I have finally learned to take the time to identify the problem first. I retrieved my pruning shears. I clipped a couple of leaves and took them to my workbench in the garage. 

The first thing I noticed was little yellow patches in the middle of the upper surface of the leaf. In a few places the yellow patches surrounded a rust color as if that part of the leaf had died. I flipped the leaf over. Aha! There was the resident culprit, a bug. I wasn’t surprised; there is no shortage of bugs on Kauaʻi and the Big Island. 

I grabbed my trusty magnifying glass so that I could go eye-to-eye with the critters on the leaf. It was like a poster from a science fiction horror film. If I were an avocado tree, I would be shaking in fear, having something that looked like that crawling on me.

I recognized that creepy-crawly from a class on pest identification and management. It was an avocado lace bug. They are small. The adult is only about a sixteenth of an inch long. To the naked eye, they may look like course ground pepper. If you look carefully through a magnifying lens, you will notice the edge of the wings have a lacy appearance. Hence the name, lace bug.

Depending on the avocado cultivar, the lace bugs may do little harm to the tree. Treat the infestation as soon as you notice it. Lace bugs are prolific, and unsightly. If allowed to go unchecked, the avocado tree will start dropping leaves faster than this old man can rake them up.

The lace bug is a soft bodied insect, which are not difficult to treat if you can reach them. Hopefully, your avocado tree isn’t 25 feet tall. The second issue is that they live on the underside of the leaf, which can be an advantage. Third, you should spray every leaf that is infected. How many leaves are on an avocado tree? Aaargh!

Attack Method 1: Take the garden hose with a high-pressure spray nozzle and wash them off. This doesn’t kill them, but it does remove them from doing more damage while you prepare an arsenal that will knock the little varmints dead. Don’t forget to bring a towel! From bitter experience I have learned that there are two things my wife doesn’t like in her kitchen: a wet dog and a wet husband.

Attack Method 2: Insecticidal soap is effective on all soft-bodied insects (aphids, scales, thrips). It kills the bug without harming the tree. Be assured that if your cat, dog or kids come in contact with the leaves after you have sprayed, it should not harm them. 

There are several name brands of insecticidal soap, which generally sell for about $10 for a 16-ounce bottle. They all seem to perform equally well. I prefer to make my own. It is easy, inexpensive, and you should have enough to treat an avocado tree swarming with lace bugs. Be certain that you read and follow the directions on the bottle before applying.

Insecticidal soaps kill by suffocation. The soap can also disrupt the cellular membranes of the insect, and removes waxes that cover the insect, which results in dehydration. Note that insecticidal soap is only effective while wet. 

Insecticidal soap must coat the insect’s body to be effective. You should apply it generously, but not so heavily that it is cascading off the leaves. Spray the underside of the leaves where the lace bug lives. Insecticidal soap doesn’t kill immediately upon contact. Rather, the soap causes the bug to suffocate and/or dehydrate and die. 

Not all soaps are created equal when it comes to making an effective insecticidal soap. The safest, and in my opinion, the best option, is to use real soap from your great grandmother’s time. These traditional soaps have three basic ingredients: animal fat, water and lye. There are many of these available. However, don’t use one that has perfumes or moisturizers added. Pure Castile soaps are a generic liquid soap that does not have additives, perfumes and they don’t foam. One quart will make 24 gallons of insecticidal soap. You should be able to find at least one brand of Castile soap on Kauaʻi or the Big Island. 

You want water that is clean. Lace bugs don’t know the difference between Perrier and tap water. So, use tap water, and let it warm in the sunshine before continuing. Soap mixes better when the water is warm. Of course, you already knew that.

A quart bottle with a spray attachment works quite well if you can reach the infected leaves. If upper leaves are infected, you need a safe way to treat them. A pump sprayer works nicely. However, if your tree is tall, it may not get the topmost leaves. A word of caution: don’t use a sprayer that you have used with herbicides. Also, don’t spray late in the day or during the hottest time of the day.

Mix one tablespoon of soap per one quart of water. I like to add a teaspoon of canola or olive oil per quart into my mixture. However, you will see those that advise against this. The reason I add the oil is to help the soapy mix cling to the underside of the leaves a little better. 

You may also wonder if you can use commercial dish soap? It depends on who you ask. Generally, I say be very careful about the soap you use. You will find many Internet recipes that recommend dish detergent.  The components in dish detergents that remove crusty food from plates and burnt-on gunk from cooking pans may be too strong and potentially harmful to the tree. If you use a commercial dish detergent, spray it on a few leaves that are infected. Wait a day and check to see if the insects are dead and the tree has not been damaged. 

Caveat: Home-made insecticidal soaps do not meet the EPA pesticide criteria. However, it is being used as such, and must be treated with the same care as any pesticide. It is important that you never exceed a concentration level of 1% to 2%, or approximately 2 tablespoons per quart. More is not better. You risk damaging the plant if you don’t measure carefully.

Attack Method 3. Neem oil is an effective insecticide. It is also safe. It won’t hurt you, pets or birds if ingested. Before you begin applying Neem oil, read the directions carefully. It is a pesticide and must be applied so as not to harm the plant or beneficial insects. When you spray Neem oil, do it early in the day when the bad bugs are feeding, and the good bugs are waiting for the late-morning wakeup call.

Neem oil acts as a repellent. Bugs apparently don’t like the taste of leaves that have been sprayed with Neem oil and won’t eat them. It also interferes with the bug’s ability to lay eggs and grow. It is an ideal oil to use in your insecticidal soaps. Caveat: I think it is stinky and tastes awful if the wind is blowing it back in my face.

Neem oil is most effective when it covers the lace bug. However, because it is an oil, its effectiveness lasts much longer than insecticidal soap. You can use the same sprayer that you used for the insecticidal soap. With either insecticidal soap or Neem oil, use protective eye wear. It irritates the eyes, and stings like the dickens.

As we learned in fifth grade, oil and water don’t mix. Preparing Neem oil for use requires an emulsifier. Soap is an effective emulsifying agent, especially when the Neem oil is added to warm water. There is no exact ratio of Neem oil to soap and water because Neem oils come in different strengths. The container should tell you how much Neem oil to add to 1 gallon of water. I then add an identical amount of soap and mix until everybody gets to know everybody else.

A last bit of wisdom about Neem oil: clean the sprayer thoroughly when you finish. If you fail to do this, says the voice of experience, you may be going to the garden shop for a new sprayer.

Water, insecticidal soap, and Neem oil are the three effective and inexpensive ways to treat Lace bug infections. They are not the only ways, of course. However, I am confident that the three attack strategies I have provided will solve the problem.

It is time to get rid of my avocado lace bugs. My wife is pressurizing the sprayer and is about ready to spray the avocado tree. I better move my chaise lounge under the mango tree to avoid an unfortunate encounter with a mean stream of Neem.

References

• Bond, C.; Buhl, K.; Stone, D. 2012. “Neem Oil General Fact Sheet” National Pesticide Information Center, Oregon State University Extension Services.
• Borden, Matthew A. and Dale, Adam G. 2019. “Managing Plant Pests with Soaps” University of Florida, Institute of Food and Agricultural Sciences.
• Hahn, Jeffrey. 2019. “Lace Bugs” University of Minnesota Extension.
• Master Class. 2023. “How to Mix Neem Oil for Plants: DIY Natural Insecticide Spray”
• Williamson, Joey. 2021. “Less Tox Insecticides”. Clemson University Cooperative Extension Service.
• Wright, Mark. 2020. “Avocado Lace Bugs in Hawaiʻi” University of Hawaii. CTAHR.

Editor’s Note: Every other week, Big Island Now will feature a guest gardening column by Tom Timmons. He is a certified Master Gardener respected for his gardening experience, but his views are not necessarily those of the University of Hawai‘i.

Other gardening columns by Tom Timmons:

• Getting under the skin of bulb onions
• Choosing a fertilizer of your lawn and plants
• The KISS method of composting
• Why should you play in the dirt?
• Basil – the royal herb