Q&A with Bob Polomski 5

Extension Consumer Horticulturist, Clemson University

My ‘Latham’ raspberry plants aren’t yielding much fruit. The fruit they do yield is small and crumbly. Is there something I can add to the soil to make the patch more productive? —S.J., Fairhaven, MA

Answer: I suspect that your raspberry plants are infected with one or more viruses. Viruses exact a higher toll on raspberries than on any other fruit crop. Any of several different viruses may be involved, but all can lead to a reduced harvest and fruit that readily breaks into individual drupelets. Raspberry mosaic, raspberry leaf curl, and crumbly berry, caused by tomato ringspot virus, are the most likely culprits in the Northeast. All these viruses deform the foliage or stunt the canes, but it is the poor yield—up to a 70 percent reduction—that is most conspicuous.

Tomato ringspot virus is transmitted by dagger nematodes, but the other raspberry viruses are transmitted by raspberry aphids. Amophorophora agathonica is the North American aphid vector of the raspberry mosaic virus complex.

Once a plant is infected, nothing can be done to save it. Do not establish new plantings next to old, infected ones. In the best of circumstances, new plantings should be located at least 600 feet from any wild or neglected brambles that may be a source of viruses. It is a poor idea to begin a new patch with sucker plants taken from someone else’s garden. Instead, new plantings should be of certified virus-indexed stock from a reputable nursery.

Over time, any planting of raspberries can become virus infected, but there are ways of prolonging the productive life of a planting, beyond spraying for aphids. While ‘Latham’ raspberry has been a reliable standard since 1920, it is not as resistant to aphid feeding as ‘Algonquin’, ‘Canby’, and ‘Titan’, three other midseason varieties you may consider as a substitute. As for the dagger nematodes, they are best controlled by maintaining ample organic matter in the soil, which encourages natural predators of nematodes. Also, keep your raspberry planting mulched and weed free, since dandelion, chickweed, and other weeds serve as hosts for the tomato ringspot virus.

I heard about some special azaleas that bloom in the summer. Can you tell me what they are and where I can find them? —C.B., Hicksville, NY

Answer: In the eastern woodlands of the United States, several species of deciduous azaleas bloom in mid- to late summer. They include the white- to light pink-flowered sweet azaleas (Rhododendron arborescens); Cumberland or Baker’s azalea (R. bakeri), which has red-orange flowers; white-flowered swamp azalea (R. viscosum); and plumleaf azalea (R. prunifolium), the last to bloom, with brilliant orange to red flowers. Many of these also have fragrant flowers.

The hybridizing of these native azaleas has produced a number of choice cultivars. Weston Nurseries (www.westonnurseries.com) in Hopkinton, Massachusetts, has developed a collection of summer azaleas, expanding the color range and hardiness of native azaleas. Some are hardy to -25°F and have attractive fall foliage.

The ones that bloom in mid-June in Hopkinton include ‘Lollipop’ (pink), ‘Pink and Sweet’ (pink), ‘Weston’s Innocence’ (pure white), ‘Popcorn’ (white with a yellow throat), and ‘Ribbon Candy’ (pink-and-white bicolor). They grow to a height and spread of five feet or more.

The July-flowering azaleas include the pink ‘Framingham’, ‘Pennsylvania’, ‘Weston’s Parade’, and ‘Weston’s Sparkler’. ‘Millennium’ has darker pink flowers. ‘Weston’s Lemon Drop’ and ‘Golden Showers’ have pastel yellow and peach-yellow flowers, respectively.

I like groundcovers, but because I don’t use chemical herbicides, I have to weed them by hand throughout the spring and summer. Do you know of any groundcovers that will naturally keep weeds at bay? —L.M., Temperance, MI

Answer: You should consult the Cornell Allstar Groundcover Web site: www.ento mology.cornell.edu/Extension/Woodys/C UGroundCoverSite/GroundcoverMain.ht ml. It reports groundcover trials conducted in Ithaca and Riverhead, New York, by Cornell University and Cornell Cooperative Extension researchers. The authors provide detailed information, such as habit, hardiness, height and spread, origin, aesthetics, sun requirement, water and soil preferences, salt tolerance, and roadside performance. They identify aggressive species that have the potential for becoming invasive. Moreover, the researchers assign the groundcovers a weed suppressive rating (WSR) of good, fair, or poor.

According to the study, good groundcovers include lady’s mantle (Alchemilla mollis), coral bells (Heuchera americana ‘Chocolate Veil’), creeping lily turf (Liriope spicata ‘Majestic’), Walker’s low catmint (Nepeta x faassenii ‘Walker’s Low’), moss phlox (Phlox subulata ‘Emerald Blue’), little bluestem (Schizachyrium scoparium), and northern dropseed (Sporobolus heterolepsis.

Groundcovers that received a poor rating include bearberry (Arctostaphylos uva-ursi ‘Point Reyes’), perennial candytuft (Iberis saxatilis), variegated yellow archangel (Lamium galeobdolon ‘Herman’s Pride’), creeping Jenny (Lysimachia nummularia ‘Aurea’), American cranberry (Vaccinium macrocarpon), and common periwinkle (Vinca minor).

When choosing groundcovers with a good WSR, be mindful that they can create a dense mat that suppresses not just weeds but companion plantings of desirable annuals, bulbs, or perennials, too.

I am getting tired of having Japanese beetles ravage my landscape. Are there any plants that Japanese beetles won’t eat? —E.W., Bartlett, TN

Answer: First found in the eastern United States in 1916, the Japanese beetle (Popillia japonica) has become established in all the states east of the Mississippi River except Florida. The Japanese beetle lives for one year, spending most of its life underground as a grub feeding on turf grass roots. The adults are active from June through August. They feed on the leaves and flowers of more than 300 species of woody and herbaceous plants, in at least 79 plant families.

There are, however, many plants that are resistant to Japanese beetles. In general, Japanese beetles rarely feed on plants with hairy leaves, such as the heavily pubescent leaves of Tilia platyphyllos ‘Parade’, T. tomentosa ‘Sterling’, and Ulmus lamellosa. The waxy or glossy leaves of holly (Ilex spp.) and rhododendron are also less preferred by them.

David W. Held, an entomologist at Mississippi State University Coastal Research and Extension Center in Biloxi, Mississippi, recently published an article titled “Relative Susceptibility of Woody Landscape Plants to Japanese Beetles” in the Journal of Arboriculture (November 2004). Dr. Held compiles a comprehensive list of woody plants and rates them according to their susceptibility to Japanese beetle infestations. Plants are rated from resistant (little, if any, feeding damage) to highly susceptible (serious defoliation). An abbreviated version of this list appears in an MSU publication called “Guide to Selecting Landscape and Garden Plants Based on Susceptibility to Adult Japanese Beetles.” It can be found online at www.msu cares.com/pubs/publications/p2333.pdf

How do I control sandspur in my lawn? —E.M., Dallas, TX

Answer: Southern sandspur or sandbur (Cenchrus echinatus) is an upright, tufted summer annual. Over time, its stems bend and root at nodes along their length. Often, the lower stems turn red to maroon. Southern sandspur can be found in sunny, well-drained sandy soils throughout the southern United States, from North Carolina to California. Coast or field sandspur (C. incertus) occasionally occurs as a short-lived perennial. It is commonly found in coastal areas from Virginia west to Arizona and California. It is also found in the Midwest and Great Lakes region of the U.S.

Sandspur produces spikes of spiny burs from midsummer to fall. The burs cling to skin, clothing, socks, and shoes, and they can be carried by water. Each bur holds one to three seeds, each a quarter inch long. Although southern sandspur is killed by a heavy frost, the burs can persist during the winter months and into the following summer. In small infestations, this shallow-rooted weed can be pulled by hand. Alternatively, apply a preemergence herbicide early next spring when the soil temperature reaches 50°F (which should be late March to early April in your area). Select a herbicide containing oxadiazon, oryzalin, or pendimethalin. Check the label to see when a repeat application needs to be made to provide season-long control.

Emerged weeds can be treated with a postemergence herbicide. Apply this when the weeds are young for the best control. Spot-treat with a nonselective herbicide containing glyphosate, pelargonic acid, or glufosinate-ammonium. Selective postemergence herbicides include MSMA or DSMA (for Bermuda grass and zoysia grass), sethoxydim (for centipede grass only), imazaquin (sold as Image), or combinations of MSMA, 24-D, MCPP, and dicamba (sold as Bayer Advanced All-in-One Weed Killer for Lawns Concentrate).

Improving the health and density of your lawn by fertilizing, maintaining an appropriate soil pH, mowing at the recommended height,.and watering deeply and infrequently will also reduce your sandspur population.H

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