Lauterbach: Look closely for onion thrips - they can harm other plants too.

Special to the Idaho StatesmanMay 2, 2014 

Onion thrips emerged in Canyon County in early April, so they're undoubtedly out in most of the Valley. Volunteer onions host onion thrips that might carry Iris yellow spot virus, then they might migrate and infect new crops or ornamental gardens.

Volunteer onions are quite common in home gardens. Thrips and their damage are not easily spotted on onions, because they tend to congregate near the bulb and do most of their damage in the narrow space between onion leaves. Volunteer onions will just go to seed anyway, so it's a good idea to pull them out and use them as scallions. If they were going to form bulbs, thrips might have already damaged the top of the future bulb.

Iris yellow spot virus doesn't kill plants, but it weakens them and affects bulb (or rhizome) development. It infects onions, garlic, iris and lisianthus. Weed hosts include Jimsonweed, Nicotiana species and redroot pigweed. Symptoms are round or diamond-shaped yellow lesions on leaves or seed stalk. There's no cure, but control of thrips carrying that disease, sanitation and destroying infected plants helps limit the spread.

Thrips are tiny insects, less than one-twentieth of an inch long. You can see them without magnification, but if you use a small hand lens, you'll see more than a tiny line. They have fringed wings, straight bodies (no waist), are yellow to brown in color, and they feed on plants by puncturing plant tissue and sucking out cell contents. They leave foliage appearing stippled or silvered, with tiny black dots of feces.

They're inefficient fliers, but may ride the wind for considerable distances. There are many species of thrips, even some beneficial thrips. Each species of destructive thrips feeds on specific plants.

Onion thrips feed on onions, garlic, leeks, peppers, cucumber, asparagus, cauliflower, cabbage, bean, tomato and many ornamental plants. Their feeding on ornamental plants distorts terminals as well as scarring petals and leaves. They can continue to feed on bulbs after harvest.

You can monitor their presence (and target their appearance) by setting up yellow sticky traps. Natural enemies include green lacewings and minute pirate bugs. You can bar their assault on your plants with covers. Anything that admits light and air but bars insects would work, protecting plants until they grow large enough that thrip attacks no longer threaten the life of the plant. Or blast them off with a jet of water.

Reflective mulch works as well, apparently because reflected light interferes with insects' ability to locate plants. Lightweight oil, Neem, spinosad or pyrethrins help control thrips, but you must carefully follow label directions and be sure to direct your spray to the right part of the plant for the insecticide to be effective.

GARDENING GRANTS

If you or your group is thinking of a project that would create, promote and "further the interest in horticulture, gardening, civic beautification and natural resource conservation" within the state of Idaho or Malheur County, Ore., you may apply for a grant from the Idaho Horticulture Society.

Grant application forms and guidelines are available at www.idhort.com. If you think your project is eligible, apply via email by Friday, May 30. The society has $7,500 available and expects to make several awards of money, from $200 to $1,200. Winners will be announced by July 1.

BRASSICAS

If you have some brassica winter survivors in your garden, but not enough of any one variety to save seeds from, let them continue to blossom and send out sprouts. Snap them off and steam or stir fry for supper. They're very nutritious and delicious, according to Stella Schneider, a resident of Boise's North End.

Those brassicas that may overwinter include kale, broccoli, cabbage, collards, Piracicaba, etc. Western Front kale, bred by Tim Peters of Oregon, is said to be one of the hardiest kales available. Some seed savers claim it might be treated as a perennial, harvestable during the "hunger gap" that occurs after nonhardy crops expire and before newly planted crops are ready to harvest.

Send garden questions to melauter@earthlink.net or Gardening, The Statesman, P.O. Box 40, Boise, ID 83707.

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