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Ask an expert: Rhodies and rhubarb don’t make good neighbors. Here’s why


Ask an expert: Rhodies and rhubarb don’t make good neighbors. Here’s why


We’re well into gardening season and you may have some questions. For answers, turn to Ask an Expert, an online question-and-answer tool from Oregon State University’s Extension Service. OSU Extension faculty and Master Gardeners reply to queries within two business days, usually less. To ask a question, simply go to the OSU Extension website, type it in and include the county where you live. Here are some questions asked by other gardeners. What’s yours?

Q: We have some rhubarb plants that are doing very poorly. We planted them in the spring of 2018 and they seemed to be doing OK, but this year have failed.

What is odd is that we planted 1, 3, 4 and 5 at the same time. Rhubarb 1 is doing well (far left), but the 3, 4 and 5 are very poor. Plant 2 is a different variety planted earlier – it is doing well; 3, 4 and 5 are near a rhododendron.

Could that be a cause of problems? We also had some mole activity last year in the area, but none lately. Any ideas on what may be happening? All plants have received same watering and fertilizer. Thanks. – Washington County

Ask an Expert

Rhubarb and rhododendron compete for nutrients.OSU Extension Service

A: There are probably several factors at play here:

  1. Rhubarb needs full sun six to eight hours a day; rhododendrons are shade plants.
  2. Rhubarb needs additional nutrients; rhododendrons rarely need supplemental fertilizer.
  3. Rhubarb need the soil pH to be in the 6.0 to 6.8 range; rhododendrons need an acidic soil with a pH between 5.0 and 5.5. 

I cannot tell from the photo or the information you gave me which of these are operative, but they clearly are not plants that need similar environments. I suggest you get a soil test for soil pH and nutrient content through one of these testing labs: Analytical Laboratories Serving Oregon | OSU Extension Catalog | Oregon State University  When submitting the soil samples, ask the lab for recommendations relevant to these specific plants. However, I suspect you may need to plant the rhubarb in a different place in your garden to maximize their health and production. Here are two articles on these two plant species:

Grow Your Own Rhubarb | OSU Extension Catalog | Oregon State University

Azalea and Rhododendron Care and Culture | OSU Extension Catalog | Oregon State University – Kris LaMar, OSU Extension Master Gardener

Ask an Expert

What’s eating this leaf?OSU Extension Service

Q: Please see photo of leaf from snow pea plant. The leaf is 12-plus inches above ground. Any suggestions as to source of the damage and preventative measures? – Tillamook County

A: Your snow pea leaf was probably chewed by a caterpillar of some type (possibly cutworm) or by slugs. Check out the plants at night (use a flashlight if needed) and look for any caterpillars and/or slugs/snails. In the daylight you can scratch the soil surface to look for larvae. Slugs/snails leave a telltale slime trail. If they are there, you can hand pick them and put in a container of soapy water.

You could also try spraying with a Btk (Bacillus thuringiensis var. kurstaki) or spinosad to treat caterpillars. Btk and spinosad must be ingested by the caterpillar to work so spray top and underside of leaves. Slugs/snails can be treated with slug/snail bait.

You can also remove plant debris and any weeds around the beans that might provide cover for these pests. – Bill Hutmacher, OSU Extension Master Gardener

Ask an Expert

Box elder bugsOSU Extension Service

Q: I have a major beetle issue in my backyard. I have a very large maple of some kind and I think they live in its bark, as well as in my mulch and all over the outside my house. The tree appears to still be healthy. I’m wondering: Do I need to be concerned? And how I might get rid of them?

– Deschutes County

A: These are box elder bugs in various stages of development. They are particularly fond of maple trees and feed off the fluids in the leaves by inserting a needle like projection into the leaf and sucking it out. If the infestation is bad enough the leaves will turn brown.

They also may come into structures in the winter and stay there until the weather warms in the spring.

They are considered nuisance pests and generally there is no chemical treatment recommended to homeowners.

Here are a couple of links with more information: Box Elder Bug and Pestnotes. – Toni Stephan, OSU Extension instructor

Ask an Expert

Bell pepper plantOSU Extension Service

Q: I have a few bell pepper plants that are having a problem. The newer leaves are showing a strange “water drop” pattern and the growing tips are drying up and flowers are dropping. I water with a soaker hose, so there’s no soil splash. One plant will show it but the one right next to it is fine, so far. – Union County

A: From the photos, it would appear that your pepper plants have a bacterial leaf infection described here:  Pepper (Capsicum spp.)-Bacterial Spot | Pacific Northwest Pest Management Handbooks (pnwhandbooks.org)  Your plants may be of different varieties, or from different seed or transplant sources, which accounts for some being infected and others not.  You can apply any of the chemicals marked “H” (homeowner) or “O” (organic, if available to you), to see if you can control it.  However, this infection may spread to the fruit. – Kris LaMar, OSU Extension Master Gardener

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