Giant whitefly on hibiscus with close up of heavily infested leaves.

We're now seeing the aftermath of this long rainy season. The heavier than normal rain has given us velvety green hills carpeted with an abundance of wildflowers. But we cannot overlook the other less pretty things that benefit from a wet winter – lots of weeds and insects.

For now, we'll focus on insects. They're already showing up in a news-worthy fashion. KSBY did a feature story on whiteflies and spoke with UC Master Gardener Cathryn Howarth.

https://ksby.com/news/2019/04/01/tiny-whiteflies-seem-to-be-bugging-people-across-the-central-coast-but-why-are-there-so-many-this-year

This story has been posted on various social media pages and people are wondering if this whitefly is a new pest, where it came from and what can be done about it. I wanted to follow up to fill in some of the gaps in information. So, I went to Cal Poly entomology professor, Dr. David Headrick who has done quite a bit of research on whiteflies over the course of his career.

Here's what he had to say after watching the news story.

"The whitefly pictured on hibiscus (in the news story) is giant whitefly which came to California from Mexico. It was first noticed in San Diego County in the early 1990s. Hibiscus is a favored host plant, but they also are seen on citrus, but more commonly on the landscape plant Xylosma. In the mid-1990s, a biological control program began with researchers at the University of California, Riverside. They successfully imported two beneficial species of tiny stingless wasps that feed exclusively on giant whitefly and achieved excellent control of giant whitefly."

Encarsiellla noyesi, a stingless wasp that exclusively targets giant whitefly.

Idioporus affinis, a stingless wasps that exclusively targets giant whitefly.

"Giant whitefly and the two beneficial wasps (pictured above) all occur in San Luis Obispo County and normally the populations are all under good control. When the giant whitefly first invaded SLO county in the early 2000s, the populations were enormous and made the news then also. But the wasps soon brought whitefly numbers under control. However, in some years since then, environmental conditions have favored the giant whitefly and allowed them to outpace their natural enemies. Eventually, the wasps will catch up and population balance will be restored."

"There are many species of whitefly, most are native species that cause no serious harm to their host plants. The whiteflies that you see on broccoli, citrus, oaks, and poinsettias are all different species. Some of the invasive species of whiteflies, like giant whitefly, can indeed kill their host plants."

"As for management, spraying plants with the garden hose is a good approach when numbers are low."

Thank you, Dr. Headrick, for your insights.

UC Master Gardeners always recommend monitoring your plants regularly to catch pest populations before they become a problem. Whiteflies can be observed any time of day. Remember to flip over the leaves to look for evidence of nymphs and the waxy coating as pictured below. Insecticides, such as horticultural oils may provide some relief. However, direct contact with the insect is necessary to smother and kill them which is difficult to achieve, particularly for whiteflies that congregate under the waxy coating on the underside of leaves.

Giant whitefly on underside of hibiscus leaf.

If you have questions about plant or pest issues, call the Master Gardener Helpline

Arroyo Grande: 805-473-7190

SLO Office: 805-781-5939

Templeton: 805-434-4105

Or email us at anrmgslo@ucanr.edu

Looking for more?

• Visit UC IPM for more photos and information: http://ipm.ucanr.edu/PMG/PESTNOTES/pn7401.html
• For more information about the early biological control program and findings -

UC Riverside research paper - http://www.nhm.ac.uk/resources/research-curation/projects/chalcidoids/pdf_X/BellowMe2000b.pdf

Cal AG article - http://calag.ucanr.edu/Archive/?article=ca.v051n06p5

• And if you really want o geek out, like I sometimes do, check out this catalog of introduced species - https://bugwoodcloud.org/resource/pdf/FHAAST-2018-09_Arthropod_Biological_Control.pdf

Beetle borers. They are very small and they cause a lot of damage to trees, including death.

These insects have not been found yet in our County but they are very close and we are especially concerned about the ISHB which can attack over 110 tree species. Many of these are native riparian species such as Sycamore, Cottonwood, Alder, Willows, Box Elders and this insect also attacks coast live oak and valley oaks.

Cal Fire, the City of San Luis Obispo and UC Ag and Natural Resources are offering a workshop to educate the public about these two serious pests. Early efforts and education are key in preventing an attack on a wide range of tree species in San Luis Obispo County.

SLO ISHB GSOB Workshop Flyer

Here is a message from Kim Corella of Cal Fire:

I am excited to announce that we are having an invasive shot hole borer (ISHB) and goldspotted oak borer (GSOB) workshop here in San Luis Obispo on May 9^th from 9:30-2:30.  

This workshop will address biology, identification, surveillance, and management of infested trees, downed wood, and firewood. We'll cover these topics in the classroom, then have a hands-on lab to learn how to identify signs of shot hole borer damage, set up a monitoring program, and sample trees. 

$30.00 registration fee includes lunch, a ISHB Field Guide, and ISHB Demonstration Kit. Pre-registration is required. Click here to register.

We have applied for CEU's from the Department of Pesticide Regulation and the International Society for Arboriculture. 

For more information on the training and to register, visit www.pshb.org.

Kim Corella, Forest Pest Specialist, Cal Fire

Thank you, Kim, for keeping us well-informed!

 Wrong Place to Plant Beautiful Tree

Wow, the Jacaranda's are beautiful right now (actually most may be on their downhill side).  As you drive around town they are easy to spot with their striking purple flowers covering the entire tree.  I have noticed that they do vary in how they bloom.  Some trees seem to flower before putting on any leaves, while others tend to flower and put on leaves simultaneously, those flowers occurring more in bunches.  They are both attractive, but I think those trees that just contain the flowers with no leaves are more striking. 

But, they do have their downside.  One thing that you don't want to do, is to plant them over a driveway or parking lot or a frequently walked pathway.  The constant dropping of flowers is a real nuisance and stains the drive or pathway.  Jacaranda flowers also drop large drops of nectar or honeydew on whatever is below them.  I speak from experience as I have a Jacaranda planted over my driveway (planted by my homeowners association so I am stuck with it).
My truck is constantly covered in dropped flowers or leaves at certain times of the year, and I don't think I will ever get the discoloration from crushed flowers and nectar out of my driveway pavers.

Jacarandas can also get insect problems.  This year, just as the flowers were beginning to push, my truck began to get covered with a fine mist of honeydew. After a few days it got so bad that I could not see out the front windshield, and wherever I touched my truck it was sticky.  This was different from the larger drops of nectar that the flowers produce.  This was due to aphids.  It took a while, but I did eventually find what was causing it - masses of aphids feeding on the flower stems of some of the bunches.  About this time, I began to see an increase in lady bugs around the tree, and of course Argentine Ants were thoroughly enjoying the bounty of honeydew.  Perhaps eventually, though not quickly enough for me, the lady bugs would have brought the aphids under control. But I think what did control them was the hot spell in the middle of June.  Those few days over 100 took their toll of the aphids and they weren't much trouble after that.  Oh yes, I do live in San Luis Obispo.

So, from a distance, Jacarandas are beautiful, and definitely have their place in our landscapes in San Luis Obispo County.  But plant them away from high traffic situations, either walking or driving, and you will likely be much happier with them.

Next time you're on Higuera St. in downtown SLO, look up.

Cal Poly entomology professor, Dr. David Headrick, is taking biological control to new heights!

Here's his story:

An invasive whitefly pest is attacking our giant fig trees in downtown SLO. I got a call to help out, so we started a proof of concept experiment to release microscopic stingless parasitoid wasps that lay eggs in whiteflies. Then, their young hatch out and eat them. If these wasps do the job, we can release lots more to get control. First step is to try them out in cages on the trees. I hope this raises some awareness. I like elevating people's knowledge about biological control. It's uplifting. Raising to the occasion. (Btw, can't lie, it's totally cool being in a bucket up in a tree.)

A big thank you to Dr. Headrick for keeping us informed and entertained. We'll be checking in with him again soon so stay tuned for updates! Also thank you to Crystal Kirkland for helping with photos and keeping track of all the findings. 

To see more photos of his downtown adventure, check out our Facebook page - SLO MGs