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May 19, 2013

Answers to summer’s most common garden questions

No matter what the weather, every summer brings some perennial garden questions.

No matter what the weather, every summer brings some perennial garden questions.

But they’re usually not about perennials.

Segdwick County extension agents Bob Neier and Rebecca McMahon report that these are among the most-often-asked-about problems in the Wichita area. The Sedgwick County Extension master gardeners answer a hotline for garden questions Monday through Friday, 9 a.m. to noon and 1 to 4 p.m., at 316-660-0190.

I think I have spider mites on my tomatoes. How do I know for sure, and what should I do?

Plants with spider mites often look like they have pale white or yellow speckles on the leaves. Put a white piece of paper under the leaves and gently tap them. Specks may fall on the paper. After a few seconds, some of those specks may begin to move around. Those are spider mites.

Knock the mites off by spraying the entire plant, including the undersides of the leaves, with a hard stream of water. You can also spray the plants with a horticultural oil or soap or neem oil. You will probably have to repeat every three to five days until you do not see any new damage.

My tomatoes are flowering, but I don’t see any tomatoes setting. What can I do?

When the weather gets hot in midsummer, especially when daytime temperatures are about 95 and overnight temperatures above 75, most tomato varieties will not set fruit. We just have to wait until the weather cools a bit. Blossom-set products do not consistently help. Small-fruiting varieties such as cherry tomatoes and heat-set varieties may have more fruit during the hot part of the summer.

How can I tell if my grass is dead from heat and drought or has just gone dormant?

Get down on your hands and knees and find the crowns of a couple of grass plants. The crown is usually right at the soil level. A grass plant that is completely dead will be brown and crispy all the way through the crown. If you try to bend or break it, it will probably snap or crumble. A grass plant that is just dormant will still be flexible and supple. You should also probably be able to find some hint of green on the stem or crown.

I have grub problems in my lawn every year. When should I treat that and what should I use?

The best time to put down a pesticide that will prevent white grub problems is in late June to early July. The best products to use contain the active ingredient imidacloprid. Most of these products should be watered in after application; be sure to read the label and follow the instructions.

How do I get the nutsedge out of my lawn?

It’s hard to do, because it stores energy in small nutlets underground that will grow into new plants when a plant is pulled out or killed. The best herbicide to use is halosulfuron-methyl, often seen under the brand name Sedgehammer. The first application should be applied before June 21. You may need to make multiple applications to get complete control.

How can I get rid of bagworms?

On small infestations, pick off all the worms that you can and toss them in the trash – don’t just drop them on the ground or they will crawl back into the trees. For every bag you remove, you’ve kept 750 eggs inside from hatching. Hatching begins when catalpa trees are in bloom around Memorial Day. Wait about two weeks after that to treat affected plants if necessary. For organic options, Spinosad is effective on both young and older larvae, Bacillus thuringiensis only on young larvae. Permethrin also can be used on young larvae through mid-July. By mid-August the worms have stopped feeding, and hand-picking will reduce damage the next year.

Is there any control for pine wilt disease?

There is no control for this deadly disease once a pine tree is infected. An injection of abamectin can be done by professional licensed applicators to prevent the disease. This needs to be done every other year for as long as you have the tree. Once a pine has died, remove the tree and either burn, bury or chip the tree before the next April 1 to prevent the pine sawyer beetle from transmitting the pine wilt nematode to healthy pines.

Is it really necessary to water trees in the drought?

All trees that have been planted fewer than three years need a deep soaking every one to two weeks. Well-established older trees will benefit from a thorough watering to a depth of 18 inches out to the dripline of the branches. Do this every two to three weeks during drought conditions. A soaker hose laid around a tree is an effective way to water.

What are the most drought-tolerant trees?

Here are some of the most drought-tolerant that we can grow, once they’ve been established for a few years, on natural rainfall: amur maple, hedge maple, Chinese pistache, chinkapin oak, bur oak, English oak, Escarpment live oak, shingle oak, Shumard oak, lacebark elm, Emerald Prairie elm, western soapberry, chitalpa, smoketree, goldenrain tree, Osage orange, mulberry.

How can I get rid of the budworms that attack geraniums and petunias in midsummer?

Those that are heavily infested will respond well to a good shearing followed by treatment with Bt or Dipel at two-week intervals on new growth. Vigorous petunia varieties such as Vista Bubble Gum or Pretty Much Picasso are back to blooming within two and a half weeks after the budworm damage has been sheared off.

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