Regional Gardening Reports :: National Gardening Association

In the Garden:
Western Mountains and High Plains
July, 2008
Regional Report

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Leaf cutter bees visit the rose garden in summer, but their activity is a mere annoyance.

Coping with Rose Pests in Summer

The extreme high temperatures can be relentless in the garden and make it a bigger challenge to grow roses with bountiful blossoms. Heat makes the blooms fade faster, and pests can become more prevalent with low humidity.

Spider Mites
I'm already finding spider mites attacking a wide variety of plants in the vegetable garden, including cucumbers, squash, and beans, and they are on some of the rose bushes, too. Roses with more delicate foliage seem to be attacked first, and if the mites are not controlled they will move to other plants nearby. When the leaves on my roses take on a bronzy coloration and stippled look, it's a good bet that mites are active.

Spider mites are not true insects but members of the spider family. They are very hard to detect since they are the size of a pinhead. But if you turn over a leaf, you might be able to see the pepper-like dusting that is the insects crawling about. Less than one-sixteenth of an inch, spider mites are visible to the unaided eye, but a magnifying glass or hand lens makes them easier to see up close and personal. When abundant, they will network from leaf to leaf, and stem to stem with fine webbing. Prevention is the best defense against these troublesome pests.

Luckily, spider mites are rather wimpy and can be overcome with a forceful spray of water directed to the undersides of the leaves. Of course, you should employ this treatment during the early morning or early afternoon so the foliage can dry before nightfall. This reduces the incidence of leaf diseases that thrive with moisture, such as powdery mildew.

One of my favorite organic controls is insecticidal soap sprays or summer horticultural oils. The soap sprays kill mites on contact. Just be sure to get the spray on the undersides of the leaves where the mites are most numerous. One important caveat: During hot weather it's best to use soap sprays during the coolest part of the day, either in early morning or evening. Horticultural oils should be used at the same rate as summer oils -- usually a 2 percent solution -- and applied to the undersides of the leaves.

Keeping your roses well watered during the summer when the temperature is high and conditions are dry will help to suppress spider mite outbreaks.

Leaf Cutter Bees
Leaf cutter bees are another summer annoyance. They methodically cut half-circles in the leaves, not to use the leaf tissue as food but to take it back to the nesting site to create chambers for egg laying. The damage they inflict on the foliage is certainly not appealing, but there is no point in trying to control the bees since they are too fast to capture. Bees are much needed pollinators for our fruit and vegetable crops. So we should learn to accept a little cosmetic damage in the garden; it's all part of the garden ecosystem.

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