Ask Extension expert: Fatty acid salts, insecticidal soaps can be good choice against leafhoppers

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Gardening season is underway, and you may have questions. To ask one, simply go to the OSU Extension website, type it in and include the county where you live. A photo is very helpful.

Q: I have had these bugs every year and they eat grape and squash leaves from the bottom side. They leave white dots all over the leaves and eventually kill them. Looking online I’m guessing they are variegated leafhoppers. I am attaching a picture and would really appreciate knowing for sure what this pest is and how to eliminate them. – Baker County

A: This is likely caused by leafhoppers. Leafhoppers are diminutive insects measuring less than 1/10 inch in length that attack the leaves of sage and other plants. Leafhoppers actually suck out the sap from leaves, which leaves pale spots that turn brown or bronze over time. Unlike caterpillars, leafhoppers don’t actually make holes in the plant’s leaves, just spots.

The damage these pests cause initially appears as a collection of small white or yellowish spots that grow larger and merge together as the damage progresses. The leafhopper lays eggs inside the veins and petioles of plant leaves, making them extremely difficult to locate. The insect in the nymph stage has coloring similar to that in the adult stage. Nymph leafhoppers are often found on the underside of leaves near a leaf vein; they are less active than adults and thus easier to spot. Adult specimens are agile and often jump from the plant when disturbed.

Fatty acid salts or insecticidal soaps can be a good choice against leafhoppers. They weaken the outer shell of leafhoppers but are safe to use on your plants and they don’t leave much of a residue that could kill beneficial bugs in your garden.

With soaps, coverage is very important as it does not stay on your plant for long, so follow-up applications may be necessary.

Another option is neem oil. This will leave an unpleasant taste/smell on the leaves. There’s also some evidence neem oil may be harmful to humans so use with care. That being said, neem oil is an all-natural remedy that is very effective against many different types of bugs and mold, including leafhoppers. You will need a mister (also called a one-hand pressure sprayer) to spray all the leaves evenly, since neem oil and water can separate easily. – Chris Rusch, OSU Extension Master Gardener

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AzaleaOSU Extension Service

Q: I have some very mature azaleas that are not in great health. They have had lace leaf bugs for several years and I wasn’t sure the plants were going to make it this year. They did go on to bloom but now have what I believe to be leaf gall. I have cut some of it off but there is so much. I wonder if I should do a hard prune and hope for the best or is it time for removal? – Multnomah County

A: Yes, you pegged it. Here is an article about it but basically what you need to do is remove all the leaves affected right away and put them in the trash. The only spray listed for home use is Monterey Liqui-Cop at 3 Tbsp/gal water. Some references say this is unsuccessful and the recurrence will depend on what kind of spring we have. This one was so wet, we were bound to get lots of fungi!

I like your idea of a hard prune after they are done flowering, but you will still want to pick off as many of the white leaves as you can, so the spores don’t go into the soil. – Rhonda Frick-Wright, OSU Extension Master Gardener

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Fruit treeOSU Extension Service

Q: Our young apple and pear trees have curled up leaves or barely emerged leaves. The plums have been somewhat affected. Older trees seem OK, but the blooms maybe look off to me. I believe I have a potted maple in front of the house with similar curled leaves. I have had sawfly the last couple years that I treated with neem oil. – Coos County

A: You have multiple plants of different genera with similar injuries. Your images show in some cases where buds did not break and in other cases where buds grew but the leaves were strap shaped and bunched rather than normal. These are classic symptoms of herbicide injury. One of the images shows these symptoms more toward the base of the canopy and much less toward the top. I know you have only put oil and soap on these trees, but the herbicide can come from nearby applications. For example, some will volatilize and drift with the breeze in warm weather. So, it could come from applications to the ground or from a neighboring field. It can also be a problem from year to year with only one exposure.

The best place to look for this information is under grape or rose in the PNW Disease Management Handbook. There is not one included as I do not have one for pome fruit yet. There was a canker or two you mentioned and that were in the images. Those can simply be pruned out since it was so limited. – Jay Pscheidt, OSU Extension plant pathologist

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WeevilOSU Extension Service

Q: My lettuce plants have a lot of what I think may be root weevils. Do you have any suggestions for treating them? I’d rather avoid pesticides if possible. I saw some suggestions to pick them off by hand but it’s difficult to do when they are deep between the lettuce leaves. – Lincoln City

A: Definitely looks like a root weevil. Here are some non-pesticide controls beyond hand picking that you may want to try:

– Apply beneficial nematodes, e.g., Steinernema or Heterorhabditis, as a soil drench as long as soil temperature is over 42 degrees. Follow label instructions. Many nurseries carry them or check online.  – Dust vegetable grade diatomaceous earth at base of plants (may not work as well as lettuce leaves usually touch the ground).  – Set up pitfall traps – sink cups into the soil with the lip even with the soil surface, partially fill the cups with water and soap.  Keep in mind that this trap is not exclusive to root weevils and may trap beneficials as well. – Bill Hutmacher, OSU Extension Master Gardener



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