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Natter’s Notes: Heat Stress

Jean R. Natter, OSU Master Gardener

September 2017

This has been an interesting year as far as plant problems go. The past winter was colder than usual; this spring was wetter than usual; this summer hotter and drier than usual; and, oh yes, we had a total solar eclipse (2017-08-21) even as I was writing this. Then, too, in spite of the plentiful rainfall this past winter and spring, established trees in forests and landscapes are dying from consecutive years of drought.

For the most part, causal agents of plant problems are abiotic, caused by naturally-occurring adverse environmental factors, also the garden’s care-takers, John and/or Jane Doe. So, when clients ask which disease afflicts their plants, we have a lot to consider. We need a detailed history of what occurred and when, including pre-plant preparations as well as follow-up maintenance.

Just how plants react to high temperatures depends upon numerous factors, among them the extent and duration of the heat; the relative humidity; wind conditions; soil moisture content; the kind of plant, its age, site, and general status before the heat hit. (Phew! That’s a lot to consider.) Sometimes leaves are only damaged superficially.  Other times, tissues die. Tissue survival is most likely when the plant is fully hydrated well before the heat hits. If heat is predicted, water the night before or early morning, between 2 and 6 AM.

One good thing about the recent heat waves, the accompanying low humidity has helped limit common leaf diseases. Well, except for powdery mildew, the fungus that creates a whitish film on the leaf surface. If that’s the case, recall that most fungicides are preventive and must be applied at the very first sign of disease, long before the leaf is snowy white.

Accurately diagnosing heat damage relies, in part, upon how well you “read” the signs and symptoms. It’s a skill that requires time to develop. (You know the old saw: Practice, practice, practice.)

Let’s take a look at how heat damage may be expressed, especially on leaves, since that’s often the only thing a client submits for diagnosis.

Young dogwood (Cornus sp.), probably about 2 years old, in a commercial landscape. (Fig 1) Exposure to bright sunlight damaged superficial tissues, killed the chlorophyll (green), revealing the underlying anthocyanins (red pigments), resulting in a reddened sheen on only the most exposed leaves.  The somewhat shaded leaves retain excellent green color.

Signs of heat stress on dogwood leaves
Fig 1 – Superficial heat damage to dogwood leaves (Cornus sp.) which killed the green pigments near the leaf surface, thereby revealing the underlying red pigments. (J.R. Natter; 2017-08

Vine maple leaf with dry, brown edges, evidence of acute water shortage to the shrub. (Fig 2) Sudden heat exposure to a 19-year-old shrub damaged many leaves in a wide swath across the shrub. Affected leaves were tan and shriveled while others only had dry edges. Client wondered if the tree was at the end of its life span. The Ask an Expert response, said essentially this: It’s the recent heat. (Client image; 2017-08) Click image for larger view.

Vine maple leaves suffering from heat stress
Fig 2 – Vine maple leaves, damaged by heat and sunlight. Owner asked if the 19-year-old tree had a disease. Another vine maple, planted at the same time, was fine. (Client image submitted to Ask an Expert; 2017-08)

Hosta, exposed to sudden and extreme heat, accompanied by low humidity. (Fig 3) The most severely damaged tissue at the right edge of the leaf, outlined by a zone of white tissue, still retains normal color. This kind of damage can develop in susceptible plants even if they’re in full shade. (J.R. Natter; 2017-06-24)

Heat Stress on Hosta plant
Fig 3 – Hosta leaf, damaged in less than a day, by searing heat and low humidity that dried the tissue so rapidly it retained its normal color. The crisp, dry zone at the periphery is separated from healthy tissue by a narrow white zone. (J.R. Natter; 2017-06)

Click link below for PDF with additional information and images:

2017-09 Heat stress_Natter’s_Notes

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Horticultural Updates

By Margaret Bayne, OSU Extension Staff-retired, OSU Master Gardener

September 2017

Scientists uncover how bees choose to pollinate. A team of researchers at the University of Arizona have figured out how bees decide what method of pollination they use. They also captured some great high speed footage of the bees.

Do you want to learn about the zoo beneath your feet? Learn about the “…subterranean community that includes worms, insects, mites, other arthropods you’ve never heard of, amoebas, and fellow protozoa. The dominant organisms are bacteria and fungi. All these players work together, sometimes by eating one another…”(Adrian Higgins, Washington Post). 

Honey bee on flower
Honey bee. Photo: Michigan State University Extension

Bees Are the First Insects Found to Understand the Concept Of Zero.  When the insects were encouraged to fly towards a platform carrying fewer shapes than another one, they apparently recognised “no shapes” as a smaller value than “some shapes”, (Sam Wong, New Scientist).

Good news!  The US bee population has increased in 2017- the number of bees disappearing due to colony collapse disorder is significantly smaller than it was in 2016.” (IFLScience).

Elm Seed Bugs
Life stages of Elm Seed Bugs.  Photo: Ryan Davis, Utah State University

Managing Elm Seed Bugs around Your Home– Recent publication from University of Idaho:

Oh my! This plant murders bugs and decorates itself with dead bodies.
(Helen Thompson,

A forgotten treasure at the intersection of Science and Poetry. Long before she wrote her poems, she gathered, grew, classified, and pressed flowers. Harvard has digitized Emily Dickinson’s herbarium in its totality. (Maria Popova,

Mow before you spray- and other tips for protecting pollinators in grassy landscapes.  A new guide in the Journal of Integrated Pest Management shows how lawn care and pollinator protection can coexist. (Entomology Today))

Do you use a rain barrel?  Learn from an expert about potential contaminants.  (Linda Chalker-Scott, WSU Fact Sheet, FS280E; photo by William McCaleb)

Beetle art: ‘Sweet and curious’ drawing beetle wins hearts online.  A talented beetle named Spike is drawing attention with his mini masterpieces. (BBC news-Asia)

Foliar Diseases of Tomato!  Check out this informative publication.  Note: Only use OSU publications for treatment recommendations. (Steve Bost, U of Tennessee)

Need a soil test?  This publication has finally been updated!

An interesting read on the Neonic controversy: Do Neonics Hurt Bees? Researchers and the Media Say Yes. The Data Do Not.”  (John Entine,

Aphid galls
Aphid galls. Photo: Duke Elsner, Michigan State University Extension

Galls, galls and more galls! Learn about the many types of aphid galls.  (

There is an App or online tool for almost everything nowadays!  Check out the ITP (Identification Technology Program) pest identification page. ITP is part of the United States Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) Plant Protection and Quarantine (PPQ) division. They have an ant key, Lepidoptera larva key, aphid ID, bark beetle ID and more.  (Photo by David Cappaert, MSU)

Just for fun! Watch a lovely, short animated film on the Story of Flowers” (AMKK)

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Don’t judge each day by the harvest you reap but by the seeds that you plant. ~Robert Louis Stevenson

Pumpkin, tomatoes, zucchini, tomatillo, and pepper harvestSeptember greetings!

It’s harvest time in the garden and time for OSU MGs to “harvest”, compile and submit their volunteer hours! As Volunteer log sheets start rolling in, the Metro MG Team would like to express a hearty thanks for the generous, wide-ranging efforts to Metro-area MGs. Thank YOU for sharing your passion and knowledge, while guiding and educating home gardeners!  You are making a difference and sowing so many seeds!  Thank you!


MG News in a Brand New Format!

Welcome to the inaugural issue of our new Metro Master Gardeners newsletter.  This new format offers:

  • Easy streamlined view
  • Print option for those who prefer a printed newsletter
  • Ability to save in PDF form for those who prefer to save issues on their computer
  • Capacity to track and report on newsletter use by our volunteers

With this “blog” format styled, past issues are easily accessed.  We have assembled the blog with these main sections:

  • MG Program Monthly Newsletter
  • Natter’s Notes with MG Jean R. Natter
  • Horticulture Updates from MG Margaret Bayne
  • Study Group Diagnostics and Show-and-Tell from MG Elizabeth Price
  • Clackamas Chapter News
  • Multnomah Chapter News
  • Washington Chapter News

As before, you will receive email notification when the latest newsletter is posted. The email will contain a snippet of news features and easy “Read more” button links to the newsletter sections.

How to Print, email or save a PDF of your MG News
For those of you who prefer to save the newsletters in a PDF on your computer or to print the newsletter, the steps to do both are easy.  You can even easily share the newsletter via email.
Once you click on the newsletter issue of your choice.  Find and click the green “Print Friendly” button above the newsletter.  A pop-up will then appear with the issue of the newsletter you selected.  On the top left of the pop-up box you will see buttons for a “Print”, “PDF”, or “Email”.  Click on your desired option.  It is that easy!

Big Shout Out of Thanks!
As we move to this new format, we want to extend a big shout-out of thanks to OSU Extension staff member, Jean Bremer, who has skillfully assembled and polished our Metro MG Newsletter over the past several years.  We are truly grateful to Jean for her time, energy, skills, patience and kindness.  Thank you Jean!

Master Gardener Volunteer takes a break from volunteering
Robin Greenwood, 2017 Master Gardener Trainee, takes a well-deserved break from volunteering and filling our her Metro MG Volunteer Log Sheet. Photo courtesy of Robin Greenwood.

Harvest of Volunteer Hours Begins!

‘Tis the season to gather your volunteer hours and submit your volunteer log sheet, prior to the October 1st deadline.

Metro-area Master Gardeners, you are stellar in your contributions education and supporting the gardening public, and we want to share that fantastic fact!

The October 1st deadline allows the metro MG program office enough time to compile and share the great news of your tremendous contributions with the state Master Gardener program and OSU Extension Service.

Help us get those statistics to the state level by recording and submitting your hours this month!  We will share the grand totals at our Fall Recertification.

How to Report Your Volunteer Hours?

You can report volunteer hours on one of two volunteer hour log sheets provided in the Volunteer Portal, choose from a PDF or Excel spreadsheet.

Please email or snail mail your completed log sheet to or MG Hours, 200 Warner-Milne Road, Oregon City, OR 97045

Note:  Please do not submit your hours via the OSU MG online volunteer submission option, CERVIS or CANVAS.  We only process hours sent on the provided OSU Metro Master Gardener log sheets.

A special thank you to those who have already submitted your hours!  Great going early birds!

For those of you who are still seeking Recertification/continuing education or volunteer opportunities look for some great opportunities below

MG Nuts and Bolts
Need a refresher on how to maintain your Master Gardener certification?  All the nuts and bolts can be found here!  Whether you are a 2017 trainee or a Veteran MG, to continue to serve as a “current” OSU Master Gardener you must submit an annual, signed Conditions of Volunteer Service form.  A 2018 certification sticker will be given to all MGs who meet the criteria and submit their signed forms.

New Advanced Training Webinar Series for Master Gardeners

Pollinator on flower
Creative Commons

Check out the new webinar series which was specifically developed for OSU Extension Master Gardeners seeking recertification.  This year, the series provides advanced training in Integrated Pest Management (IPM).  Each session is approved for one hour of continuing education/recertification credit.

  • September 5, 1PM: Never doubt how a small, thoughtful and committed pollinator habitat (in your garden) can change the world.  Presented by: Andony Melathopoulos, OSU Department of Horticulture
  • September 19, 1PM: Japanese Beetles in Oregon.   Presented by Rachel Suits and Heather Stoven, OSU Extension
  • October 3, 1PM: Status of Boxwood Blight in Oregon. Presented by Cassie Bouska, OSU Extension and Jay Pscheidt, OSU Department of Botany & Plant Pathology

You must pre-register to participate in the webinar.  For details and a registration link go to:

Do not despair!  If you missed the first two webinars, they are now available for online viewing!  See individual links below:

Fun fall volunteer opportunities, sign-up on CERVIS!       

Apple hangin on tree branch
Creative Commons
  • Fall Home and Garden Show – one of the most popular garden shows and MG volunteer opportunities!  October 12 – 15th, various shifts.
  • Portland Nursery Apple Tasting – festive fun celebrating the apple!  October 14, 15, 21, 22, various shifts.
  • Farmers Markets – opportunities to volunteer at a Farmers Market remain for Beaverton, Gresham, Hillsdale, Lake Oswego, Lents, Oregon City, Sherwood and Tigard.  Grab an open slot on CERVIS

Guide home gardeners through the fall and winter season!   As the days shorten and the temperatures cool, a new host of gardening conundrums perplex the home gardener. You can assist and expand your own knowledge, collaborating with other MGs as you research and advise gardeners.  Sign-up on CERVIS or contact a phone coordinator.

Sam Chan
Photo courtesy of Sam Chan

Our annual Master Gardener Fall Recertification Training is scheduled for Saturday, October 28th, 8:00am to 3:30pm, at Clackamas Community College.  This annual event is a daylong continuing education opportunity.  Earn 6 hours of continuing education/recertification credit by attending.

We have a great line-up.  This year’s presenters all bring their wealth of experience from their work with OSU Extension Service.

  • Water to Sustain our Oregon Lifestyle with Sam Chan
  • Plant Diagnostics for MGs with Brooke Edwards
  • A Vital Partnership: OSU MG Program and OMGA Chapters with Joy Jones
  • Vegetable IPM with Weston Miller

The Fall Recertification day also gives us the opportunity to congratulate the new class of trainees as they step up to Veteran status after completing their volunteer requirements.  We will present trainees who have successfully completed MG training with their OSU Extension Service Master Gardener badges and a big cheer for successfully completing the program and joining the ranks!

Seeking Master Gardener Speakers

Are you interested in making presentation on gardening to community groups?  The Metro MG program receives dozens of requests every year for garden presentations.  We have a small but mighty group of MGs who answer the call and present throughout the 3 counties – but requests greatly exceed what these dedicated MGs can handle.  Thus, we are looking for even more MGs to share their research-based gardening know-how.  We will supply support materials and those interested can shadow experienced presenters.  Have fun making a few presentations a year!

Presentations are needed on a variety of subjects:

  • Beginning gardening
  • Vegetable gardening
  • Fruit trees
  • Pruning
  • Composting
  • Container Gardening
  • IPM for the Home Gardener
  • Small Fruits
  • Perennials
  • Planting
  • Soil
  • Beneficial insects
  • Pollinator gardens
  • Tomatoes
  • Small space gardening
  • Native plants
  • Seed starting
  • Propagation
  • What’s your garden passion that you are willing to share?

Would you like to be part of this vital community outreach?  If so, contact Marcia McIntyre,

2017 Trainees at Vegetable Clinic with Weston Miller
2017 Trainees at Vegetable Clinic with Weston Miller. Photo: Eddie Rosen
Weston, with MGs Corinne, and Eddie at Vegetable Clinic, Photo: Eddie Rosen
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Where but in a garden do summer hours pass so quickly?  – Anonymous

Summer greetings!  We hope your gardens are flourishing in these high summer months.  July and August are good months to sit back, enjoy your garden, and of course spend some time wearing your volunteer hat as an OSU Master Gardener!


Phones are ringing!  Questions are flying into the Master Gardener phone clinics via email, phone calls, and visitors to our offices.  This is a great time to expand your knowledge, collaborating with other MGs as you research and advise gardeners regarding their gardening conundrums.  Sign-up on CERVIS or contact a phone coordinator.

Clackamas County Phones, Jean Bremer, 503-655-8631
Multnomah County Phones, Susan Marcus, 503-703-4937
Washington County Phones, David Butt, 503-645-5769

Farmer’s Markets are busy and vibrant with a bounty of summer vegetables and fruits, plus lots of inquiring minds seeking answers to their garden questions.  Each market has its own special qualities.  Discover those unique traits by volunteering at a few farmers markets new to you.  Grab an open slot on CERVIS  Don’t despair if market schedules appear full.  Check back often as schedules change and openings arise throughout the summer.  Let a clinic coordinator know you if you are willing to serve as a substitute for last minute cancellations at your favorite market.

Summer Farmer’s Markets:  Beaverton – Gresham – Hillsdale – King – Lake Oswego – Lents – Milwaukie – Oregon City – Sherwood – Tigard



Oregon and County Fair FUN!

If you want a big dose of summer fun, sign-up for an MG Clinic table at one of the county fairs or the Oregon State Fair.  Give sage (OSU proven), garden advice to fair visitors and take a bit of time, before and after your shift, to grab some shaved ice and check out the fair competitions whether it is honey products, the biggest homegrown fruits and veggies, or the best home brew or chocolate layer cake!  Sign-up on CERVIS to grab a shift now!  Admission passes and instructions provided to all fair volunteers.

Clackamas County Fair, August 15 – 19 (Tuesday – Saturday). MGs are in a prime location at the Clackamas County Fair with our clinic table right by the entertainment stage, lovely display garden and plant sale. Join-in!   Sign-up on CERVIS or contact coordinator Jane Collier:, 503-266-1191.

Washington County Fair, July 27 – 30 (Thursday – Sunday). Nestled right next to the demonstration gardens is the perfect location for the MG clinic. This area of the fairgrounds owes its planning and attractive appearance to the Washington County Master Gardeners and is a popular stop for fairgoers.  Yes, MGs have bragging rights for this beautiful feature of the fair grounds.  Come see it!  Sign up on CERVIS or contact Margery Brunello: or 973-699-2304

Oregon State Fair, September 1-2. For the ultimate fair experience, take a quick jaunt to Salem for the Oregon State Fair.  Master Gardeners from around the state host the OSU Extension Master Gardener Clinic.  Our Metro MG program does the honors on Friday and Saturday, September 1st and 2nd. Don’t miss this festive state celebration! Sign-up on CERVIS or email Jordis Yost, and ask for a morning, afternoon, or evening shift on Friday, or Saturday.

Get Volunteering! CERVIS will get you there!

All of the OSU metro MG Program volunteer activities are available for sign-up on CERVIS, our online volunteer registration system (for Partner activities contact coordinators). Go to the “Volunteer Portal” link found on the right side of our main website page.  Then find the “CERVIS volunteer event registration” link.

When logging into CERVIS for the first time, enter your email and click on “Don’t Know password/ Reset password” to get a temporary password.

Please only sign up for events that you know that you can attend. If you need to cancel an event, please contact the clinic coordinator for a list of other volunteers interested in serving as substitutes. It is your responsibility to find a backup.

advisory group photo
MG program Manager Weston Miller providing instructions for lively group discussions about the MG program’s future outlook. Photo by: Marcia McIntyre

Moving Forward…
Master Gardeners Advise Program

An engaged and thoughtful group of 40 Master Gardeners convened on Tuesday, June 6th for a Metro Master Gardener Advisory meeting.  Using the 2014-2019 Metro Master Gardener Strategic Plan as a prompt, participants broke into three groups for a brainstorming session, offering suggestions and recommendations for the program moving toward the future.  Lively discussion ensued, with the compilation of many thoughtful and insightful suggestions.  Program staff greatly value the input and creative ideas.  These suggestions will be further explored via upcoming Master Gardener Liaison Meetings.

Master Gardener Liaison Meetings are open to all Metro Master Gardener volunteers.  Upcoming meetings:

  • Tuesday, August 8 10am to 12noon, Washington Co. (location TBA)
  • Tuesday, October 10 10am to 12noon, Clackamas Co. (location TBA)
  • Tuesday, December 12 10am to 12noon, Multnomah Co. (location TBA)

There will also be a special meeting to explore the use of technology in the Master Gardener Program following the August 8th Liaison Meeting. The technology meeting will be from 1:00pm to 3:00pm.  Look for an email invitation to the Liaison Meetings in the next couple of weeks (RSVPs required for all meetings), with details on specific locations which will rotate among the three counties.

Hands-on in Demonstration Gardens
Summer is a glorious time for hands-on learning in any of our ‘Partner’ demonstration gardens.  Each garden offers unique active, relevant, learning opportunities.  Contact a coordinator and dig in!

Hopkins Demonstration Forest
Frank Wille 503-342-6699

Grow-An-Extra-Row and Learning Garden’ at Clackamas Community College
Nancy Muir 503-789-697  

End of the Oregon Trail Pioneer Garden
Kathy Turner 503-630-5794

Community Demonstration Garden – SE Portland
Heidi Nichols at
Nancy Fine at

Washington County Fairplex Garden
Bob Campbell 503-691-6708

Learning Garden at Jenkins Estate
Sandy Japely 503-531-8482

International Rose Test Garden in Washington Park Photo credit:

Beautiful, historic gardens.
Consider spending time this summer in a beautiful, garden – dispensing reliable gardening information.

It is a very special year at Washington Park International Rose Test Garden.  Sign-up for a shift as the garden celebrates its Centennial year!

The Pittock Mansion is another lovely and historic setting in which to share your garden knowledge.

Sign-up for a shift via CERVIS or contact the clinic coordinators.

Log Your Hours
Thank you for your passion, energy and volunteer service educating the gardening public.  We want to be sure to have a record of all your efforts.  Here is the link you need for the forms to log your volunteer hours.  Choose from a PDF or Excel form.  All hours due by October 1, 2017.

MG Nuts and Bolts
Need a refresher on how to maintain your Master Gardener certification?  All the nuts and bolts can be found here!

Save the Date!  Saturday, October 28th FALL RECERTIFICATION!

Our annual Master Gardener Fall Recertification Training is scheduled for Saturday, October 28th, 8:00am to 3:30pm, at Clackamas Community College.  This annual event is a daylong continuing education opportunity.  Earn 6 hours of continuing education/recertification credit by attending.

A great line-up of speakers is forming.  This year’s presenters all bring their wealth of experience from their work with OSU Extension Service.  They will offer a wide range of topics to enrich the knowledge base of Master Gardeners.  They are Joy Jones, Sam Chan, Brooke Edwards and our very own Weston Miller.

The Fall Recertification day also gives us the opportunity to congratulate the new class of trainees as they step up to Veteran status after completing their volunteer requirements.  We will present trainees with their OSU Extension Service Master Gardener badges and a big shout out for successfully completing the program.