Q&A WITH BOB POLOMSKI 24

Extension Consumer Horticulturist Clemson University

My heavenly bamboo has all of its leaves concentrated at the top. How can I prune it to make it look fuller?

–B.W., Galveston

, TX

Answer: I Ieavenly or sacred bamboo (Nan–dina domestica) is a durable, drought–tolerant, long–lived evergreen shrub hardy to USDA Zone 7. It can reach a height ol six to eight feet and grows slightly less wide. Native to India and China, heavenly bamboo is prized for its bronze to rose, lacy bamboo–like leaves, which emerge in the spring and eventually age to a bluish green.

This foliage turns bronze or purplish in fall, then fiery red in winter, especially in full sun. Panicles of white flowers appear in May and June and give rise to bright red berries that persist in fall and winter. Although tolerant of shade, heavenly bamboo looks best in full sun. Gardeners in the southeastern United States, however, should be aware that the plant is currently listed as a forest invasive.

Left to its own devices, heavenly bamboo develops a flattened, umbrella–like crown of branches atop leggy, leafless stems. To maintain a fuller shape, prune shoots periodically—ideally, before new growth emerges in the spring. There are two options to renovating this shrub. The simplest approach is to cut back all of the stems at an arbitrary height (making the cuts just above a node) and wait for new shoots to appear. The alternative is to cut back just a few of the stems. When these cut ends leaf out, the foliage will hide the tallest stems that were left uncut. The following year, these remaining stems can be cut back. Occasionally it may be necessary to altogether remove a few of the thickest, oldest stems at the base to improve sunlight penetration and to encourage the production of new shoots, which emerge from underground stems or rhizomes.

Some cultivars of heavenly bamboo are naturally denser and more compact. These include ‘Fire Power’, ‘Atropurpurea Nana’, ‘Gulf Stream’, ‘Wood's Dwarf, and ’San Gabriel' (sometimes listed as ‘Orhime’).

Can you tell me about orchard mason bees? I hear they are an alternative where honeybees are in short supply.

–T.A., Yuma. AZ

Answer: The blue orchard bee (Osmia tig–naria), also known as the orchard mason bee because it uses mud to build its nest, is a species of solitary bee that is being tried as a pollinator for such early–blooming fruits as apples, cherries, and blueberries. Blue orchard bees are native to most of North America. They are slightly smaller than a honeybee and are shiny bluish black in color. The short adult life of these bees and their nonaggrcssive nature make them an attractive pollinator for home fruit–growers.

There is only one generation of blue orchard bee each year. Adults emerge about the lime redbud (Ccrcis spp.) blooms. They will forage and pollinate crops when temperatures go as low as 55oF and during overcast days, conditions which ground other bees.

After mating, the females search for narrow cavities to use as nests. In nature the nests are constructed in hollow stems and small holes in the trunks of trees. The bees will also occupy wooden blocks that have been drilled with holes one–quarter to three–eighths inches in diameter and at least three inches deep, cardboard tubes or paper straws, and commercially available nest blocks. The . female collects pollen and nectar and then lays an egg in each of five to ten cells within each cavity, provisioning each cell with food before capping the finished nest with mud. The period of foraging and nest provisioning lasts only four to six weeks, after which the adult bees die. The larvae develop over the summer inside the nest, feeding on the pollen and nectar. They make cocoons, pupate, and become adults while remaining in the cells. In the fall the adults go dormant and hibernate. Some cold temperatures are required in order for them to come out of dormancy and emerge from the nests in the spring.

For more information about blue orchard bees, refer to the book How to Manage the Blue Orchard Bee by Jordi Bosche and W. Kemp (Sustainable Agriculture Network, 2001).

How can I protect my peach trees from peach leaf curl?

–F.P., Morgantown, WV

Answer: Peach leaf curl is a spring fungal disease that infects the young leaves of peaches and nectarines. The pathogen (Taphrina deformans) overwinters in the bark and around the buds. Infection begins at bud swell and continues until the young leaves emerge. Favorable temperatures for infection are 50–70oF. Rainfall and cool temperatures that delay unfolding and maturation of the leaf increase the severity of the disease. Once they are fully expanded, mature leaves are resistant to infection.

The fungus attacks the meristcm region of the leaf, resulting in foliage that is curled and wrinkled. Thick fleshy portions of the leaf 5 may be flushed with shades of red, yellow, or purple. When the fungus sporulates on infected leaves, it produces a powdery gray dust. In–fected leaves then turn brown, shrivel, and fall from the tree. The spores are carried by wind and rain to infect the tree again the following spring. Repeated annual infections will lead to branch dieback and a shorter life for the peach tree.

The best way to control peach leaf curl is with applications of fungicide in the fall after the leaves have dropped or in the early spring before bud swell. Bordeaux mix (copper sulfate plus hydrated lime), chlorothalonil (Da–conil 2787), ferbam, and lime sulfur will all provide control. Very light infections can be addressed by simply pruning out and disposing of the shoots that exhibit deformed leaves. Keeping your trees vigorous through regular pruning, fertilizing, and watering will also provide some protection.

Finally, there are a few cultivars with genetic resistance to peach leaf curl. These include the heirloom varieties ‘Blood Free’ (occasionally called ‘Indian Blood Freestone’) and ‘Muir’. Newer resistant varieties include ‘Candor’, ‘Clayton’, ‘Five Star Curlless’, ‘Frost’, and ‘Q 1–8’.

Is there any way to get rid of nipple gall on a vernal witch hazel? It is terribly unsightly.

–E.K., Manteo, NC

Answer: While unsightly, nipple galls pose no harm to the health of your witch hazels. The half–inch–high conical green swellings, sometimes tipped with red, are the handiwork of the witch hazel gall aphid (Hormaphis hamamelidis). This insect occurs in the northeast United States, west to Illinois, and south to North Carolina.

In early spring, aphid eggs that overwintered on the twigs of witch hazel hatch. The young nymphs feed on the surfaces of the unfolding leaves with their piercing mouth–parts. The leaf responds to the injury by growing to create a pocket around the insect. Females produce winged young within these galls. The young aphids then escape through a small opening on the underside of the leaf, and by midsummer the galls are empty.

These winged young fly to the leaves of birch trees and produce several generations of wingless aphids during the summer. These, however, do not cause gall formation as they feed on the birch leaves. With the arrival of fall a winged generation of aphids is created and these migrate back to witch hazels. They lay eggs on the witch hazel twigs, completing the cycle. This alternation of hosts is common for a number of aphids—for example, the woolly apple aphid that alternates between apple and elm, or the woolly alder aphid that docs the same between alder and maple. Because the galls have no effect on the health of the witch hazel, the best solution is tolerance. You can, however, try spraying your witch hazel with horticultural oil before the buds leaf out in the spring.

I just removed an asphalt driveway and want to plant shrubs and flowers in this area. Should I be worried about the soil beneath the asphalt?

–KM., Mamaroneck, NY

Answer: The soil beneath your driveway is probably not contaminated, but it almost certainly needs improvement. In the construction of your driveway, the topsoil was moved and sand or gravel may have been added as a base. To improve the growing conditions of this nutrient–poor, compacted soil, you will need to loosen and amend it. This can be done with a pick and a shovel. After breaking up the planting area, add several inches of compost, leaf mold, or rotted manure and mix it into the top eight inches of the soil. If you live in an area with acid soil you should probably add five pounds of limestone per 100 square feet, although a soil test will give you a more detailed recommendation. Barring that, you should also add about two pounds of a balanced fertilizer, such as 5–10–10 or the equivalent. After you have mixed in all the amendments, you can rake the bed smooth, plant it, and congratulate yourself for growing something, while not actually in asphalt, at least where asphalt once was. H