Garden Talk: April 7, 2011

From NGA Editors

Devilishly Good Ninebark

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Plants with purple foliage are great for adding some drama to the garden. And dusky-leaved cultivars of ninebark (Physocarpus opulifolius) are some of the best choices for adding color throughout the season and serving as accents to all the garden's green. Ninebark is a tough, adaptable, easy care shrub that is resistant to most pests and diseases. Native to the eastern U.S., it is not fussy about soil and is hardy in zones 3-7.

Its only drawback is that many of the selections offered in nurseries mature into large shrubs. Now space-challenged gardeners can enjoy the benefits of ninebark with a new cultivar introduced by Bailey Nurseries. Little Devil™ ninebark (Physocarpus opulifolius 'Donna May') stays a compact 3 to 4 feet tall and wide. Easy to maintain with little or no pruning, it's a good choice for urban and low-maintenance gardens. The deep burgundy foliage is accented in June with pinkish-white, button-like flowers that entice butterflies to stop by. Drought tolerant once established, it grows best in full sun. Look for Little Devil™ in retail nurseries this spring.

For more information on Little Devil™ ninebark, go to: Bailey Nurseries.

Borers Get Burned with Fire Gel

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Among the most troublesome pests for peach growers are peachtree borers. These larvae of clearwing moths attack the roots of the trees or, in the case of the lesser peachtree borer, the aboveground portions, weakening and even killing trees. Researchers at the USDA Agricultural Research Service's Southeastern Fruit and Tree Nut Research Laboratory investigating biological controls of the borers have discovered a species of nematode that attacks these pests. Nematodes are microscopic, soil dwelling worms. While some species are pests themselves on crops we value, other species help us out by preying on pests.

This is the case with Steinernema carpocapsae, the nematode that attacks both kinds of peachtree borers. While the scientists showed that the nematodes were efficient at controlling the borer that feeds underground on the tree roots, the tiny worms lost their effectiveness in controlling the above-ground feeding lesser peachtree borer when exposure to heat and sunlight dried them out and killed them.

So the scientists tried a novel approach to protect the miniscule nematodes. Firefighters use what is called "fire gel" to help prevent the spread of fires between structures by creating a blanket of moisture. To see if the gel could also keep the nematodes from drying out, they sprayed peach trees with a non-toxic, environmentally friendly formulation along with an application of the beneficial nematodes. The first year of the trial only 30 percent of the borers survived on treated trees; by the second year, none survived.

The scientists are getting ready to test the nematode-gel combination in commercial orchards to come up with an efficient, economical, and environmentally safe way for growers to keep borers at bay. They also plan to investigate the potential for this technique to be used to protect other beneficial species of nematodes that are potential controls for a wide range of pests in trees and other crops.

For read more about this research, go to: ARS.

Defying Late Blight

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A couple of summers ago, many gardeners in the East were devastated to find their once healthy tomato plants dying within a matter of days. What started as a few water-soaked spots on the leaves and stems spread rapidly until the entire plant collapsed in a heap. The cause of all this devastation was late blight, a disease caused by the fungus-like pathogen Phytopthera infestans, which strikes potatoes as well. (Eggplant and peppers are related to tomatoes and potatoes, but don't show the same susceptibility to this disease.)

The first sign of trouble is the appearance of dark, water-soaked, irregularly shaped spots, about the size of a nickel or a quarter, on the leaves. These spots become covered with a fuzzy white mold on the undersides of the leaves. They enlarge quickly, turn black and kill the entire leaf. The infection then spreads to the leafstalks and main stem, eventually causing the entire plant to collapse and die. Tomato fruits and potato tubers can also be affected. Weather can have a lot to do with the severity of the disease in a particular season, and gardeners are eager for ways to help prevent a large scale outbreak when conditions are ripe for the spread of the disease.

While there is no tomato variety that is immune to this problem, Johnny's Selected Seeds has released a new variety that is highly resistant to late blight.'Defiant PhR' is a mid-sized slicer that not only resists late blight, it also shows intermediate resistance to the fungal disease early blight, as well high resistance to verticillium and fusarium wilts. The medium size, determinate plants produce high yields of 6-8 ounce, deep red, globe-shaped fruits that are smooth and medium firm, with a great taste and texture. These tomatoes are a good choice for container growing, as well as planting in the garden.

For more information on 'Defiant PhR' tomatoes, go to: Johnny's Selected Seeds.

Chiming in on Bellflowers

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Few groups of flowering plants show the diversity of the bellflower clan, or campanulas. With bell-shaped, tubular or star-shaped flowers in shades of blue, white, pink, and red, they have growth habits that range from low and creeping to tall and upright. Most of the garden-worthy choices are perennials, although there are some annuals and a biennial in the genus. And all are beautiful, even the few that are such vigorous spreaders and seeders that you may need to think twice about including them in your garden.

To help gardeners choose from among the many possibilities this genus offers, the Chicago Botanic Garden evaluated 89 different species and cultivars for eight years in their Zone 5 gardens. Plants were grown in full sun and given only minimal maintenance in an effort to duplicate the kind of care they would receive in most home gardens. Plants were evaluated for ornamental quality, vigor, resistance to pests and disease problems, and winter hardiness, receiving an overall rating of from one to five stars.

The sole five-star winner was the 22 inch tall hybrid cultivar 'Sarastro'. A cross between Campanula punctata and C. trachelium, 'Sarastro' has a compact, non-spreading habit and a profusion of large, tubular, violet-blue flowers over a long period.

Many other plants received a four-star rating, including the low-growing, spreading Serbian bellflower (C. poscharskyana) and several of its cultivars, and the petite, long-blooming hybrid 'Samantha'. Given the range of sizes, colors, and growth habits, there is no doubt a bellflower that is just right for a spot in your garden.

To read the entire bellflower performance appraisal, go to: Chicago Botanic Garden.

 
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