Written by Alli Vincent, Nursery IPM (Integrated Pest Management) Specialist
As many of our customers know, we strive to meet the demand that our island community has for plants that we do not actively propagate, and we work closely with nurseries on other islands to source these plants. Inter-island shipments are inspected on both ends by the nurseries, and also by the Department of Agriculture, but pests do sometimes get through the first two lines of defense. Often these pests are common ones that exist on all the islands, but sometimes these shipments can be the source of an introduction of a new pest that was previously unseen on our island. We are committed to a rigorous inspection, quarantine, and pest treatment protocol on all our imports, prior to releasing them to the public.
A bulletin from the Dept. of Ag in early 2020 warned of a new pest that could be very detrimental to avocado trees on Kauai. The avocado lace bug is a recent introduction to the islands, and we did find this pest present in some of our stock after receiving the bulletin. We notified the Dept of Ag and followed their quarantine and treatment protocols, as well as notified all customers who had recently purchased avocado trees from us. We believe we contained the pest, but as we are not the only company who imports fruit trees it is most likely that this pest may be found elsewhere on the island by now. We want to share this information with the community so we all can keep a look-out for this new pest.
While the avocado lace bug does not directly attack the fruit, an infestation can seriously impact the health of the tree, especially ones that are not fully mature yet. The avocado lace bug attacks the underside of the leaves, by piercing the surface and sucking out chlorophyll and other plant fluids from the cells. This reduces the leaves’ ability to photosynthesize, therefore reducing the tree’s ability to make food for itself. If a leaf experiences enough damage, the tree will drop it. A few dropped leaves isn’t that bad under normal circumstances, but a major infestation will lead to defoliation of a tree. This can lower the overall health of the tree. Another issue is that the damage on the leaves can create openings for fungal or bacterial pathogens to enter. Avocados in Hawaii are susceptible to all sorts of fungal issues so reducing damage will also keep them healthier in the long run.
It’s important to check for signs on your avocado trees, especially young ones that have been recently planted in the last year. One of the main signs is scorched looking leaves. The top of the leaf will have brown spots that look dry or burnt. On the underside, you will most likely find nymphs (juveniles) and adults. These are very small bugs, the adults are only 2mm long! Another sign you can look for on the underside of the leaf is their shiny black frass (feces). Here are two photos to show you what the bugs look like up close, and also what the frass looks like on the underside. You will also see plenty of tiny black eggs as well. The eggs will be present around the area that the leaf is turning brown.
Though these pests can be very detrimental, they also can be controlled with some diligence. The first step you can take to reduce the infestation is to use a wet paper towel and wipe the bugs and eggs off the leaves. Then discard the waste in a sealed plastic bag. Once this has been done, the next step is to use an insecticidal soap or horticultural oil spray to kill off any remaining adults. These sprays do not work on the eggs, so it is important to check back a few times a week to continue wiping the leaves off with a paper towel and spraying soap or oil to smother the remaining bugs. Once this has been done many times over the course of a few weeks, you should see less bugs and residue on the leaves, and you can breathe a sigh of relief.
If you don’t want to buy a special product, you can make your own soap spray to combat these and other bugs. You can use dish soap, or Dr. Bronners, which is nice because it usually has a botanical aroma like peppermint or tea tree, that adds an added layer of repelling quality. We typically use 1 oz of soap per gallon of water. It’s best to add the soap after filling the container with water so that it doesn’t get too foamy.
If you have a particularly challenging infestation, I would recommend adding an oil to the mix to further smother the bugs. We sell two products that would work for this: Monterey brand Horticultural oil, or Monterey brand Neem concentrate. They are both oils that you dilute with water to create a spray. For added coverage, you can make a spray with both oil and soap. For this to be effective, you must spray the underside of the leaves where the bugs exist because this works on contact–it is not a systemic pesticide. If you are trying to treat a larger tree, you can use a hose attachment sprayer with the horticultural or neem oil in it, so that you can use the pressure of the hose to get the spray up high on the tree.
The arrival of a new avocado pest to Kauai was a reminder to inform the community about a pre-existing and common avocado pest, that you may be seeing on your leaves. Some identification details will help you to discern if you have avocado mites, avocado lace bug, or both! Avocado mites are very tiny, so you will likely not see the actual bugs, but you will see their damage on the leaves. It is pretty common for young avocado trees to arrive here with this type of damage on them–even after treatment, the damage will still be visible. Following any treatment, it is always important to observe your leaves to make sure mites have not returned to cause further damage. A regular pest management program will help you keep these types of issues in check, versus needing to scramble to get an infestation taken care of.
The avocado mite chews on both sides of the leaf and causes brown spots to occur, usually along the veins or the midrib. If you look very closely at the leaf or use a hand lens, you will see a webbing that is indicative of an active colony. The webbing creates silvery looking spots on the leaf. Like the avocado lace bug, if the chewing damage becomes serious enough, the tree will shed the leaf, so that a big infestation will lead to defoliation of the whole tree.
The treatment for this pest is similar to that of the avocado lace bug, though it is recommended that you use an oil-based treatment, not just a soap-based treatment. The oil is best for smothering these mites. If the infestation is particularly heavy, you can also use garden sulfur. This is a very potent element, so it must be used with care as it can cause all the leaves to fall off the tree. There are specially formulated oil and sulfur ready-to-use sprays that can be purchased at garden centers, as well as sulfur powder. We do not sell these at the nursery currently.
As a reminder, it is important for you to use personal protection equipment when spraying anything in your garden, even organic solutions. Long sleeves, gloves, eye protection, even a mask may be necessary.
It’s also critical that we point out that healthy trees are much less likely to develop a pest infestation. In almost all cases, there is an underlying physical stressor that contributes to a pest or disease becoming established. Physical stressors for trees can include drought, flooding, eroded or compacted soil, lack of nutrients, lack of sunlight, and wind or salt damage.
If you have a pest infestation, its important to also address these physical stressors as much as possible in order to holistically treat the pest and get your tree back to health. Think of it as treating the disease versus just treating the symptoms. Keeping up with a yearly routine of organic fertilizer and compost is one of the best ways to prevent physical stressors. If you’re not sure what might be stressing your tree, contact us for a consultation with an ISA Certified Arborist!
Our hope is that this pest information will help prevent damage and have you rolling in delicious avocados!