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MEETING REPORT: Thrips To Palm Weevils - Identifying & Managing SD County Horticultural Pests

Submitted by Lynn Langley (report 1) and Donna Mallen (report 2) for Let's Talk Plants! October 2023.

Dr. Eric Middleton is now the contributing author to The Bug Man column in our newsletter, Let's Talk Plants!.
Dr. Eric Middleton.

Thrips to Palm Weevils: Identifying and Managing Horticultural Pests of San Diego County

While San Diego offers ideal conditions to grow many different crops, it also allows a wide range of pests to flourish. Learn to identify and manage some of the most damaging insect pests found in San Diego, including South American Palm Weevil, Asian Citrus Psyllid, Black Fig Fly, and Thrips parvispinus.

Dr. Eric Middleton is the UCCE Integrated Pest Management advisor for San Diego, Orange, and Los Angeles Counties. Eric is passionate about sustainable agriculture and investigating practical pest management solutions. His goals are to conduct research that is directly applicable to the needs of growers, to promote practices that have less of an impact on the environment, and to share his findings in a way that is accessible to everyone.

 

Did you miss the meeting with Dr. Eric Middleton or wish to see it again? Here is the meeting recording:


 

Editor's note: Snafues happen. Every now and then two people submit meeting reports for the same meeting as has happened this month. This can only mean the meeting was particularly good! Which it was. Instead of combining the reports or only publishing one of the two, I have chosen to post both with big SDHS thanks to both reporters for some very good reporting. -Karen England


Meeting report one submitted by Lynn Langley:

Members attending the September monthly meeting had the pleasure of listening to an information packed presentation by Dr. Eric Middleton, Area Integrated Pest Management Advisor for the University of California Agriculture and Natural Resources Cooperative Extension. His presentation focused on Invasive Pests in San Diego.


Dr. Middleton began his presentation by discussing Integrated Pest Management (IPM) which focuses on knowledge-based pest management that utilizes many different techniques and tries to avoid the pitfalls of conventional (usually chemical) techniques. Of primary importance to IPM is a shift in perspective – that some damage is acceptable and expectations can and are adjusted based on that larger damage acceptance (call it a “Nature tax”). When using IPM the first and most important step is to monitor, scout and correctly identify the pest that is causing the problem. Without proper identification it isn’t possible to ensure any pest management techniques used will be effective. After identifying the pest, the next step should be using cultural control through prevention or sanitation, maybe keeping the pest issue small and easier to control. From there mechanical (physically removing the pest or cutting off the affected area of the plant) control and/or biological control should be attempted. Biological control can be passive or active using other insects that will feed on the pest and get rid of it. Some examples of this are ladybugs and green lacewings. Their larva will feast on aphids and are usually very effective in reducing that pest population. The last option to choose for pest management should be chemical. Indiscriminate applications of chemical pesticides can not only kill the pest but any other insects that come in contact with the plant. It is important to use as little as possible, take care in the application, and make sure that the pesticide used is specified for the target pest. There are pests for which the only management available is the use of pesticides. One example of this was Eric’s first pest he discussed.


The South American Palm Weevil has been in San Diego since 2011. It is problematic throughout San Diego County and is decimating the Canary Island Palm population. The females lay eggs in the tops of trees and the larvae consume the growing tissue of the palm. It is often not recognized until so much damage has been done that the tree can’t be saved. If left unchecked the infected tree will most likely die. The damage can occur rapidly so trees have to be monitored closely for symptoms. Traps are being used to monitor weevil populations. Management options are limited but include soil drenches, canopy sprays and trunk injections. Some palms can recover but the damage already done cannot be fixed. If the tree dies it is important to chip the remains of the tree to kill any surviving weevils.


The Asian Citrus Psyllid is another serious issue in San Diego. The psyllid is the vector (or carrier) of Huanglongbing (HLB) or Citrus Greening disease. This is an extremely serious disease of citrus. It first came to Florida in 1998 and has decimated the citrus industry there. The psyllid transmits the disease when feeding on new growth. There is no cure for HLB. The trees lose roots, dies back and the fruit stays green and bitter. It is being very closely monitored in San Diego County. Management may be possible with the psyllid. The best time to monitor for the psyllid is when the trees have their new flush of growth. Possible biological control of the psyllid are Syrphid flies and the Tamarixia radiate parasitoid wasp. Alyssum and yarrow attract Syrphid flies. It is important to contact the county if HLB is suspected.

If a tree is diagnosed with HLB, it will be removed by the county.


The Black Fig Fly was first detected in San Diego in 2021. It is rapidly becoming a serious pest of figs. The Fig fly lays its eggs inside unripe fruit. The larvae consume the fruit from inside, causing the unripe fruit to drop. That is generally the first sign of the presence of the fig fly. Very few good treatment options are available, and they are mostly sanitary. Dispose of any fallen fruit by double bagging and throwing in the trash (not greenery recycling!). Also plastic mulch under the trees helps prevent pupation of the larvae since they can’t get into the ground. If adults are detected then insecticidal baits (GF-120) can be used.


The final pest Eric discussed was thrips. There are several varieties in San Diego County. They are very small, so almost impossible to see. The best way to monitor for thrips is to use sticky cards near plants and to check for signs of damage. Thrips are vectors for several diseases like the Tomato Spotted Wilt virus or the Impatiens Necrotic Spot virus. Reflective mulch can be used to try and prevent them. It is important to use a variety of treatment options with thrips as they adapt very well. Mechanical control includes cutting off the affected areas of the plant (usually the new growth). Sanitary control involves removing any infested material not cut off. There are predatory mites, fungus (Beauveria bassiana) and nematodes available for biological control. It is important to apply early. Finally some type of chemical control (such as Spinosad) may be necessary. Once again, when using any chemicals it is important to ensure that is targets the specific pest.


Eric ended his presentation by discussing two pests to look out for and a research project. The first pest is yet another type of thrip (parrispinus) that has been in Hawaii for years. First found in Florida in 2020, they were recently discovered in an Ontario, Ca greenhouse. So far it isn’t known to be present anywhere else in California. The second pest is the Dotted Parospine Leaf beetle that is attacking Eucalyptus trees. It was found in Los Angeles in 2022. Eric’s research project involves the African Tulip tree. It is a common ornamental tree here in San Diego. The nectar has been found to be toxic to native bees in Brazil and Australia. He is in the process of trying to get the location of every African Tulip tree in Southern California. Master Gardeners in Los Angeles, Orange County and San Diego are assisting with this effort. Just in one tree he examined in Balboa Park he found 90 flowers and 84 dead bees as well as other dead insects. More information on this will be available as Eric’s research project progresses. The answer may well end up becoming a suggestion to plant other types of ornamental trees.


 

Meeting report two submitted by Donna Mallen:

Thrips to Palm Weevils – Identifying and Managing San Diego County Horticultural Pests

Our speaker, Dr. Eric Middleton, UCCE IPM Advisor for San Diego County, gave us a comprehensive overview of identification and management of some of the horticultural pests that are of current concern for us.


He noted that the San Diego area is particularly threatened by invasive pests originating from other regions, due to factors such as San Diego County’s proximity to the border, being a port city, the diversity of our potential host plants, the multiplicity of our microclimates, and our generally mild climate.


As a result, we need to be on the watch for new threats, as well as the more familiar ones that we may already recognize on sight. Some of these can be managed though careful monitoring and an “IPM” (Integrated Pest Management) approach. Refer to the end of this article, but some, such as the Goldspotted Oak Borer and the Palm Weevil, are beyond our likely control.


His presentation included some excellent photos of juvenile and adult insects and mites, and of the identifying damage on the targeted plants. Watch the YouTube replay of the program to see the close-up photos.


How to apply IPM principles to your garden:

Take the least harmful step before moving to the next intervention. Recognize that some damage is naturally going to occur and accept it.

Step 1: Identification - What signs do you observe on the plant? They may not be attributable to a pest infestation, but rather a nutrient deficiency, irrigation issues, physical damage by rodents, etc. Pest control is not what is needed.

Step 2: Prevention – Once you have identified a pest that is the cause of this damage, consider planting a resistant variety or move the plant to a healthier location, instead of having to fight the same battle every year, manually remove invasive competitors.

Step 3: Biological – Passive: Improve the site. Active: Beneficial insects or other organic control.

Step 4: Chemical: Find a chemical control that is not harmful to the health of the soil, the environment and other inhabitants.

Step 5: Shift Your Perspective: Consider the health of the environment and adjust your expectations to accept non-perfect plants.


Notes on particular pests:

South American Palm Weevil: In San Diego County since 2011. Mostly in the South County – Bonita, Chula Vista. Distinctive notched area in crown where juveniles have hatched and eaten fronds. of partial missing fronds in crown in tree, which eventually collapses. Rapid damage. Almost always kills trees. Primarily Canary Island Date Palm, but can spread to King and Queen Palms. Monitor trees closely and report sighting of damage. Current management steps by professionals: Traps are placed in shade at least 500 yards away from trees (attracts and captures weevils). Systemic soil drenches. Chip dead trees to prevent spread.


Asian Citrus Psyllid and Huanglongbing Disease (HLB): HLB is fatal. Very dangerous to citrus crops worldwide. Asian Citrus Psyllid damages new growth of citrus trees and carries HLB bacterium if it has fed on an HLB-infected tree. The only control for HLB is prevent spread by controlling psyllids and destroying infected trees. So far, damage is low in our area, due to quarantine and prevention by removal.


Black Fig Fly (Silba adipata): Tiny black fly with red head. First detected here in 2021. Causes premature fruit drop. Female deposits eggs in pinholes in fruit. Interior of fruit rots. Look for exit holes. 4-6 generations of flies per year. Control: Bag young fruits early and dispose. Plastic mulch under trees can confuse flies. Research ongoing.

Thrips: Several varieties. See UCIPM website for table of Thrips. Due to their tiny size, thrips are difficult to detect until their damage to the plants becomes apparent. Adults lay eggs on plants. Hatched larvae drop to the ground. Silvered stippling appears on leaves, distorted fruit can occur. Most damage is cosmetic, but thrips are vectors for other diseases. Manage with sticky cards, reflective plastic mulch below the plant, predatory mites.


Finally, some sad news:

The beautiful African Tulip Tree, Spathodea campanulata, has been implicated in the deaths of some of our local native bees! What is known so far is dead bees have been found inside some of the tree’s fallen blossoms. It appears that the nectar is toxic to the bees, and to ants and beetles. The details of this phenomenon are under study.

 

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