Natter’s Notes

A New Spider; Trellis Rust

Jean R. Natter, OSU Master Gardener

A new spider in Oregon: The Brown Widow Spider

The Brown Widow Spider (Latrodectus geometricus) recently identified (October 2018) in Oregon City, OR, is a tropical species unlikely to survive outdoors in the northwest. The hourglass mark on the ventral abdomen is orange instead of red as on the Black Widow (L. hesperus). (http://cisr.ucr.edu/brown_widow_spider.html)

Almost everybody loves to hate spiders. Especially during the late summer and fall, when the males are dashing around the house searching for females.

Well, let me introduce the Brown Widow Spider, Latrodectus geometricus, a relative of the black widow. Now, people have another spider to worry about. (The western black widow, L. hesperus, is scarce in western Oregon, more abundant in the south and east sections.)

A first-ever record for Oregon, the brown widow was found in Oregon City earlier this year. It resembles an adult-sized version of an immature black widow, a variable combination of off-white, brown, tan and black. It can be challenging to differentiate between the 2 species until they’re more than half-grown. Finding an egg sac makes it easier; the brown widow’s is “spiky” whereas the black widow’s is smooth.

Resources: Spiders

– Oregon Spider Facts, a livestream video, with the main topic the recently identified Brown Widow Spider (ODA 2018-10-01; Entomologists Jim LaBonte and Josh Vlach, ODA Insect Pest Prevention and Management Program; https://www.facebook.com/ORAgriculture/videos/1704791909648978/)

– “How to Identify the Brown Widow Spider” (R. Vetter; UC Riverside) –https://cisr.ucr.edu/identifying_brown_widow_spiders.html.

– “Brown Widow Spider: Facts from Entomologist Josh Vlach” (video; 2 min 35 sec; https://www.facebook.com/ORAgriculture/videos/2151585361748105/)

– “Oregon Spiders” contains basic information and numerous links –  https://www.oregon.gov/ODA/programs/IPPM/Pages/OregonSpiders.aspx.

– Overview of potentially venomous spiders in Washington (and Oregon): https://www.doh.wa.gov/CommunityandEnvironment/Pests/Spiders.

– “How to Identify the Hobo Spider” and the giant house spider (Eratigena atrica) – https://s3.wp.wsu.edu/uploads/sites/408/2015/02/PLS-116-How-to-Identify-or-Misidentify-the-Hobo-Spider.pdf. The final verification step: Examine the male palps (p.7) or the female epigyne (p.9).

Trellis Rust on Pear

Trellis Rust on pear was submitted to the Clackamas County MG office last month (October 2018). To date, reported cases in the metro counties have been mild, with the unusual eruptions (“acorns”) on the leaf reverse of only a few leaves on each infected tree. (Client image)

An alert client submitted images of Trellis Rust on 3 y.o. pear trees to the Clackamas County MG office last month (October 2018), a disease first identified in Oregon during 2016. Signs, symptoms, and the alternate host (juniper) are quite different from those of the more common Pacific Coast Pear Rust (alternate host incense cedar).

The MGs reported the infection to Jay Pscheidt, the OSU Plant Pathologist. Here’s his response:

Looks like we have this disease on pear in Benton, Marion, Clackamas and Multnomah counties. I have not heard of any other places. No one has made mention of it on Juniper which is interesting in itself.

From our experience this year in the Corvallis area it has not been too severe on pear. A few leaves on a few trees. In the home landscape, leaf removal seems a viable option for the moment.

I suspect chemical management may help but timing is everything. Bonide Fruit Tree and Plant Guard RTS is registered for pear but also contains an insecticide in addition to a group 7 + 11 fungicide. It should have some activity on both scab and rust. But we don’t need to be spraying pear trees now as the spores are heading to the juniper alternate host. Infuse Systemic Disease Control is registered for juniper and may have some activity to prevent infection of rust. In other words, spray pears in the spring and junipers in the fall if you want to use chemical protection.

Separation of the hosts will be the best method.

Resources: Trellis Rust on Pear

– Trellis Rust (PNW Handbook; – https://pnwhandbooks.org/plantdisease/host-disease/pear-pyrus-spp-trellis-rust-european-pear-rust)

– Pacific Coast Pear Rust (PNW Handbook – https://pnwhandbooks.org/plantdisease/host-disease/pear-pyrus-spp-pacific-coast-pear-rust)

– “Pear Trellis rust, a new disease” (Natters Notes; 2017-10 – http://blogs.oregonstate.edu/mgmetro/index.php?cat=1179565&paged=2.)

– “Pear Trees: Rust, times 2” (Natters Notes; 2018-06 – http://blogs.oregonstate.edu/mgmetro/2018/06/01/pear-trees-rust-times-2/)

PDF Version:

Natter’s Notes Spiders and Trellis Rust PDF

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