Natter’s Notes

Blister Mites: Grapes; Pears; Walnuts

Jean R. Natter, OSU Master Gardener

Erineum mite damage on home garden grape leaves: “Blisters” on the top; corresponding concave areas on reverse filled white fuzzy material (enlarged leaf hairs). (J.R. Natter; 2016-04)

Blister mites are running wild this season. It seems that the perfect conditions combined for population explosions of these tiny, elongated mites which noticeably disfigure the leaves of grapes, pears, walnuts, and more. Among pears, even newly planted trees are victims. The symptoms are similar on all three genera but the specific causal agents – also referred to as eriophyid mites or simply eriophyids – vary.

Blister or eriophyid mites reside on the undersides of the leaves, injecting fluids into the leaf tissue as they feed. Those fluids cause the blistering on the top surface with the associated white “fuzz” (enlarged plant hairs) in the concave areas on the reverse. (So, no, it’s not fungal growth.)

Blister mites are far different than the more common spider mites. Adults are microscopic, light in color, cylindrical, tapered at the posterior end, with two pairs of short legs just behind the head. Nymphs are the same but are smaller.

Microscopic image of an erineum mite, Aceria species, elongated, 2 pair legs, size about approximately 1/100-inch. (

Grape Erineum Mites (Colomerus vitis) are microscopic, wormlike, with 2 short pairs of legs at the head end, and white-yellow in color. They overwinter between the outer bud scales and bud tissue and feed on leaves during spring and summer. Feeding from the undersides of the leaves produces a blistered appearance on the top of the leaves. At the same time, the corresponding depressions on the underside are filled with enlarged light-colored leaf hairs which shelter the mites from natural enemies and pesticides. In spite of how extensive and nasty-looking the infestation is, blister mites seldom affect grape health or production.

As the season progresses, the enlarged leaf hairs progress from white to yellow and, finally, brown. Then, from mid-August until leaf drop, the mites return to their overwintering sites beneath the bud scales.

Home management for grape erineum mites: Sprays aren’t needed. Dormant-season oils and insecticides used for other pests and sulfur applications for powdery mildew usually control this pest.”

Pear Leaf Blister Mites (Eriophyes pyri) feeding causes reddish to yellowish green blisters on the top surface of the leaves, often in 2 lengthwise rows, one at each side of the main vein. With time, the blisters turn brown or black. Leaves may drop prematurely. Loss of excess foliage weakens trees, reduces shoot growth, and interferes with fruit maturation and fruit bud formation. Feeding on fruit causes irregular, russeted spots which feel rough and somewhat scaly. PNW Insect says “Eriophyid mites move from tree to tree, perhaps by wind or carried on birds or insects.”

Home Management for Pear Leaf Blister Mites: Lime sulfur applications in the fall can significantly reduce populations of these mites the following year. (The trick, though is to obtain it in small home-use packaging.) Applications before bud swell can also be effective. Or apply superior oil as buds begin to swell.

Walnut Blister Mites (Aceria erineus)

Just as do the previous two mites, walnut blister mites overwinter beneath bud scales. When springtime temperatures rise, the mites feed among the leaf hairs on the undersides of the leaves. Several generations occur during the summer, which attack new foliage as soon as it unfurls.

Home Management of Walnut Blister Mites: Naturally-occurring predator mites almost always keep mites under control if broad-spectrum insecticide applications are avoided. Heavy rain and cold weather also suppress mite numbers.

Broadleaf weeds like mallow, bindweed, white clover, and knotweed enhance mite numbers. Avoid excessive nitrogen applications, as this encourages mites.

Horticultural oil is the only spray suggested for home-use.


Eriophyid Mites:

Grape Erineum Mites:

Pear Leaf Blister Mites:

Walnut Blister Mites:

(Click the link below for PDF containing the above text and all the images.)

Blister Mites – PDF



We might think we are nurturing our garden, but of course it’s our garden that is really nurturing us.  – Jenny Uglow

July and August bring a profusion of fun and rewarding volunteer opportunities for Master Gardeners.  Phone hotlines, county and state fairs, farmer’s markets, the Oregon Zoo, Blue Lake Park, Cracked Pots Recycled Art Show and more! How do you learn about those great gigs?  Log-in to CERVIS to see new listings and recent openings as schedules change (don’t be discouraged if you find a full schedule – check back as openings always pop up).

The MG hotlines have been hopping with lots of intriguing questions. Sign-up to learn alongside your fellow MGs while answering client questions.  We have an increased need for volunteers in July at all 3 offices.  Please look at the schedule on CERVIS and consider signing up for a shift.  Special request:  Both the Clackamas and Washington Co. offices need volunteers the first week in July.  Can you help out?  That would be grand!

Pie Eating Contest!  Largest Watermelon!  Longest Bean!
Master Gardeners!  Oh my!

If you want a big dose of summer fun, sign-up for the MG Clinic table at one of the county fairs or, the ‘granddaddy of them all’, 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 largest homegrown fruits and veggies, or the best home brew or chocolate layer cake!  You get free-entry into the fair the day you volunteer!

Clackamas County Fair
Although only a few volunteer slots remain for the ever-popular Clackamas County Fair – grab a remaining slot or be sure to check back closer to the date (August 14 – 18th) as inevitably slots will open up.  Sign-up on CERVIS

Child proudly holds carrot - just pulled from the Washington County Master Gardener's Demonstration Garden
Capturing a carrot! Photo courtesy of Anna Stubbs

Washington County Fair
Sign-ups for this stellar community event just opened – so sign-up today for best selection!  Enjoy the fair (July 26th – 29th) hosting guests at the Washington County Master Gardener’s beautiful Demonstration Garden.  Sign-up for “Tours and Clinics” to guide visitors in the garden and answer their gardening questions at an MG Clinic table.  Or sign-up to serve in the “Kids Zone” sharing the wonder of the garden with children – assisting them on a scavenger hunt and earning the supreme prize, of “capturing” a carrot from the garden.  Sign-up on CERVIS

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-area MG program does the honors on Friday and Saturday, August 31st and September 1st. Don’t miss this festive state celebration!  Sign-up on CERVIS

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, to download the form, to log your volunteer hours.  All hours due by October 1, 2018.

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

2017 MG Advisory Meeting. Photo courtesy of Eddie Rosen

Master Gardener Advisory Meeting July 25th: You’re Invited!

10:00am – 12:00pm at the Food Innovation Center (1207 NW Naito Parkway, Suite   154, Portland).  A light lunch will be provided following the meeting!  Parking is free.  RSVP required.

Please join the conversation at a metro-wide Master Gardener advisory meeting to provide feedback and suggestions for the OSU Master Gardener program staff.  We value and appreciate your input as we look to the future.

RSVP to no later than Monday, July 16th   to confirm your participation.   Space limited to 50 participants.

Goal: Gain insight and inspiration from MGs about the Master Gardener program and our public outreach service.

Save the Date!  Saturday, November 10th – FALL RECERTIFICATION!

Gail Langellotto will be presenting ‘The Science of Ecological Gardening’ at the 2018 Fall Recertification

Our annual Master Gardener Fall Recertification Training is scheduled for Saturday, November 10th, 8:00am to 3:30pm, at Portland Community College – Rock Creek Campus.  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.  We are thrilled to announce that OSU’s Andony Melathopoulos, Gail Langellotto and Heather Stoven will be part of our line-up of guest presenters.




2018 Master Gardener Trainees to Receive OSU MG Badges

Robin Greenwood holding her OSU Master Gardener badge
Robin Greenwood proudly displays her newly awarded OSU MG badge at the 2017 Fall Recertification

Our November 10th, Fall Recertification event also gives us the opportunity to congratulate the new class of Master Gardener interns as they step-up to Veteran status after completing their volunteer requirements.

We will present 2018 Interns with their OSU Extension Service Master Gardener badges and a big shout-out for successfully completing the program.  2018 Interns are cordially invited to attend the full day of training – which will count toward your continuing education/recertification hours for 2019.






European Chafer. Photo: Washington State Unversity

Advanced Training Webinars Continue
Two more informative online Advanced MG Training Webinars from Brooke Edmunds, Oregon State Extension and the OSU Master Gardener Program remain for July and August.

These webinars each count for 1 hour continuing garden education/recertification credit.  A wonderful way to expand your gardening knowledge in the comfort of your own home or sitting in a lovely garden watching on the electronic device of your choice.

Can’t make the webinar date?  No worries!  A recording of each webinar is posted a few days after the live webinar.  See the link below.

Upcoming Live Webinars

7/26 at 11am PST Meet the New Neighbors: Emerging Pest Issues in Oregon presented by Robin Rosetta

8/30 at 11am PST The Latest Research on Bees in the Garden: Results from the OSU Garden Ecology Lab presented by Dr. Gail Langellotto

For more information or to watch recordings of past webinars:

Photo courtesy of Bob Dueltgen

In fond remembrance…
It is with deep sadness that we share the loss of a valued and dear, OSU Extension Service Master Gardener.  Ann Dueltgen passed away on May 22nd, 2018.  Since completing her training in 1999, Ann was dedicated in her service as a Master Gardener.  Ann served alongside, her husband, Bob Dueltgen (training class of 1998).

Bob shared with us that being Master Gardeners was part of their retirement plan.  What a generous plan it was!  Throughout the years you could find Ann and Bob serving their community at Farmer’s Markets (Hollywood was a favorite), garden shows, the Portland Nursery Apple Tasting and the Oregon State Fair.

Ann and Bob combined their volunteer service with the Master Wildlife Stewards program working with area schools, educating students via the creation of wildlife habitats.  Ann and Bob also initiated a partnership with Marysville School and the Multnomah Master Gardener’s Community Demonstration Garden where students learned about composting for the garden.  As Master Gardeners fondly remember Ann, the resounding memory was of her kind heart, and how welcoming and encouraging she was to all she met.  We will miss Ann and are grateful for her two decades of generous service.  On behalf of the OSU Master Gardeners, we extend our sincere sympathies to Bob and his family.

Here is a memorial remembrance of Ann on Oregonlive.

Photo: Dave Shaw, OSU

What is happening to so many Willamette Valley Trees?
Have you noticed diseased and dying trees as you navigate around the Metro-area and Willamette Valley?  Or have you needed to answer clients concerns about the dead and dying trees they observe?

Here are two great, “Tree Topic” blog posts from Brad Withrow-Robinson, Forestry & Natural Resources Extension Agent for Benton, Linn and Polk Counties.  Brad shares his thoughts and insight on what he sees happening.

Another Rough Year for Willamette Valley Trees Part 1 and Part 2







View Our Garden Checklist Video for June


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

July/August 2018

Should I tie or braid the daffodil leaves after the daffodils are done blooming?  The answer is…NO!  Not only is it a waste of time, it isn’t good for next year’s flowers.   Learn more about daffodil care. (Richard Jauron, Willy Klein, Iowa State Extension)

Moms are the best (in the insect world)!Insects are exceptionally skilled at developing adaptations to increase their evolutionary success. One way to promote a species’ survival is through effective parenting, and in some standout insect species mothers go the extra mile for their young.” (Adrienne Antonsen,

Home and garden use of treated wood.” Selecting the correct type of treated wood can reduce risks to people and the environment. Some preservatives can leach into soil or water and be taken up by plants. Touching treated wood may also leave residues on the skin. Consider that some treated wood may protect against both mold and insects, and some may only protect against molds.” (

Travel deep inside of a leaf in this cool video! Life Science Academy via Garden Professors/Facebook

Pollution is changing the mycorrhizal fungi that provide mineral nutrients to the roots of European trees.  This could explain malnutrition trends in Europe’s trees. (Imperial College London via

Aphid. Photo: OSU

How do insects, like aphids survive on a high sugary diet? There’s a reason parents tell their kids to lay off the sugar: too much isn’t good for you.  But small sap-sucking insects called aphids can survive quite nicely on a largely sugar-based diet, despite their inability to make important nutrients from scratch. The key to their success is symbiotic bacteria, which live inside aphid cells and make amino acids, the building blocks of proteins needed for growth.” (University of California, Riverside via

Is that bug really a bug? Learn about True Bugs. (Michelle Ross,

How does Rose of Jericho survive in the harsh climate of the desert?  “To survive in a desert, plants must eek out an existence in specific microclimates that provide conditions that are only slightly better than the surrounding landscape. Such is the case for the Rose of Jericho (Anastatica hierochuntica). This tenacious little mustard is found throughout arid regions of the Middle East and the Saharan Desert and it has been made famous the world over for its “resurrection” abilities (

Promising Yellow-jacket bait.   Researchers are studying an “…experimental synthetic alternative bait that, to paraphrase an old saying, looks like meat, tastes like meat, and, as far as western yellowjackets (Vespula pensylvanica) are concerned, must be meat. So, they feed on it and bring it back to their nest, along with the pesticide it contains.” (Ed Ricciuiti,

Galls, Galls, Galls!  Learn more about these natural beauties. (

Ants provide clues to why biodiversity is higher in the tropics. New global data of invertebrate distributions suggests time holds key to species diversity. (Okinawa Institute of Science and Technology (OIST) Graduate University via

Desert bees have a secret: how to survive a decade of drought. “Bees are most diverse in arid places. Will their strategies hold up in a changing climate — and can we learn enough about them before it’s too late?” (Sara Van Note,

Ladybugs, Aphids and the toxic combat that might be happening in your garden. “Aphids are a familiar sight in the garden, sucking the juices out of your rose bushes. Luckily, so are ladybugs, which prey on aphids and keep them in check.  But the relationship between predator and prey is more complex than you might think. Aphids may be important to the survival of some ladybug species we have come to know and love by warding off another predator that has been moving in and feasting on them.” (Veronique Greenwood,

Vintage photos of insects and spiders in vivid detail.  “In 1913, National Geographic magazine published a series of microscopic images revealing the “monsters in our own backyards.” (Christine Dell’Amore,

Stick insects expand territory after being eaten by birds. (Kobe University via

Honey Crisp apple podcast…”This is the story of that miracle apple and the innovation that made the business of better apples sustainable — all while hastening the downfall of the Red Delicious.” (

Watering newly planted tree. Photo: Kathy Zuzkek, UMN

Watering newly planted trees and shrubs.  Great information! (Kathy Zuzek, University of Minnesota Extension)

Bumblebees are confused by iridescent colors. (University of Bristol, via

The conclusion of a report from Newcastle University about the removal of neonicotinoid for use in seed treatment of oilseed rape… “Insecticidal control of CSFB in the past has relied on a combination of seed treatment and foliar sprays. The absence of neonicotinoid seed treatments is making CSFB control more challenging for farmers with significant losses of crop identified in the autumn of 2014. The estimated 33,957 kg of a.s. used in the autumn to combat the threat of CSFB represents a 2.5 fold increase in the use of autumn insecticides to WOSR in England and is likely to be a direct result of the ban on neonicotinoid seed dressings. The increased use and reliance on pyrethroids for CSFB control has significant future implications since resistance has now been identified in the UK. The loss of neonicotinoid seed treatments poses a significant challenge to growers at a time when significant price reductions have occurred in the value of this crop, together with an increased threat from the fungal pathogen light leaf spot raising the question for many farmers as to the true value of oilseed rape in the crop rotation.” Read the study:

15 Stunning Photos That Prove You Have No Clue How Food Is Grown! (D.G. Sciortino,

Container gardening: The rules to know, and the rules to break.
(Adrian Higgins,

Extrafloral Nectaries and Ants.Most of us learned in school that flowers produce nectar, which is then collected by bees, butterflies, bats and/or moths. Extrafloral nectaries are structures on a plant that produce nectar, but they are not inside flowers. They may be located on petioles, leaves, sepals, or stems.” (Roberta,

How to tell how much wasp stings will hurt. Short stinging organs tend to carry more-toxic venom — but inflict less pain — than long ones. (Peerj, Toxicology, via

New insights into the evolution of the fig.

Testing shows dry, red sticky traps improve Spotted-Wing Drosophila monitoring. (John P. Roche, Ph.D,

Coddling Moth. Photo: Ken Gray, OSU

Guide to Codling Moth damage identification from WSU.  Great info and photos. (Tree Fruit & Extension Center, WSU)

International research team finds ‘staggering’ number of fly species in small patch of tropical forest. (Mark Lowey, University of Calgary, via

It’s all about location, location, location. The location of your garden, environment, and even the microclimate in your yard is important to know when selecting plants. (

More than a living syringe: Mosquito saliva alone triggers unexpected immune response. (Baylor College of Medicine via

How to protect your local pollinators in ten easy ways. (Ryan P. Smith,

To deadhead or not? The final answer is…(Penn State Extension)

New species of Hot Pink Slug described in Australia (

Time-lapse video of molting Mexican Red-kneed Tarantula will haunt your dreams. (iflscience)

Watch videos on how to make an insect hotel. (Jefferson County, Colorado Extension)
Part 1:  Part 2:

Battling bubbles: How plants protect themselves from killer fungus.  UCR researchers show how plants fight against infections by delivering protective molecules into fungi using bubble-like exosomes. (University of California, Riverside)

The costs and benefits of pre-plant root manipulation. (

What to do with ornamental grasses in spring. (Mary Hockenberry Meyer, Gail Hudson, University of Minnesota Extension)