Home and garden notes

May 17, 1992

Not too late to plant

This is a special time of year, when most azaleas are in full bloom, turning parks, roadsides and home gardens into a kaleidoscope of unmatchable color.

Although spring and early fall -- before October -- are the best planting seasons for azaleas, it's not too late to add some of the colorful shrubs to your yard, said Raymond Bosmans, a horticulturist with the Home & Garden Information Center of the Cooperative Extension Service, Maryland Institute for Agriculture and Natural Resources.

"Evergreen varieties can be planted any time, even when in full bloom," he said. "This makes them a popular spring gift."

He said azaleas should only be transplanted -- dug up and moved -- in the early spring before flowers and new foliage appear.

Azaleas, the common name for rhododendrons with small, thin leaves, grow throughout Maryland. They should be planted where they will have some protection from strong wind and where there is some shade for at least half a day.

Azaleas prefer loose, well-drained, acidic soil that contains an abundance of organic matter. A soil test, conducted by the Soil Testing Laboratory at the University of Maryland College Park, can tell you if your soil is sufficiently acidic for azaleas.

A test costs $5, and kits are available from county offices of the Cooperative Extension Service and the Home & Garden Information Center at 1-800-342-2507.

Based on the results, you'll know if you need to apply an acidifying material, such as iron sulfate, sulfur or aluminum sulfate.

To improve the organic matter of the soil, spade in a 3- to 6-inch layer of peat, leaf mold, well-rotted sawdust or shavings, old mulch (especially pine bark mulch) or well-rotted manure.

"Don't use manure that has lime added to it because lime decreases the acidity of the soil," said Bosmans.

Azaleas benefit from mulching at planting time and later on. Mulching materials include leaves, leaf mold, peat, pine needles and aged wood chips. As these materials decompose, they supply the soil with nutrients. They also help the soil keep a uniform moisture content and prevent rapid freezing and thawing.

If the soil is well-prepared at the time of planting, you do not need to add fertilizer to the azaleas the first year. Established plants, however, benefit from an annual application of a complete fertilizer -- one that supplies nitrogen, phosphorus and potassium.

Several of these fertilizers are made specifically for azaleas and other acid-loving plants.

During the summer, azaleas should be watered thoroughly, but infrequently. Established plantings will withstand considerable drought, but newly planted shrubs should not be allowed to get too dry.

To learn more about azaleas, contact the center for a copy of "Growing Azaleas" (EB 165). The publication, which costs $1, contains information on planting, pruning, fertilizing, propagation and management of diseases and insect pests.

Specialists at the center are available to handle calls between 8 a.m. and 1 p.m. weekdays. Prerecorded information is accessible via touch-tone phones 24 hours a day.

Aphids invade area

Cool weather this spring throughout the state has upset normal patterns in the world of plants, insects and plant disease.

Pest management and plant pathology specialists for the Cooperative Extension Service, Maryland Institute for Agriculture and Natural Resources, note that growth of most plants -- even in greenhouses -- is behind normal for this time of year.

Below-normal temperatures also have kept populations of many insect pests and plant disease organisms in check. For example, light-trap catches of flying insects during April by the state Department of Agriculture were at a record low for the month, said Galen P. Dively, Integrated Pest Management specialist for the service.

But aphids thrive during cool spring weather, he said, partly because many of their natural enemies need warm weather to multiply rapidly.

As a result, pea aphids are running rampant in some alfalfa fields and devastating young plants in both home gardens and commercial plantings. A Maryland outbreak of the blue alfalfa aphid -- common in the western United States -- has been found for the first time in the Northeast.

Another tiny insect pest, the flea beetle, is causing damage to susceptible varieties of early planted sweet corn. Flea beetle populations were at a record-high last year and mild weather last winter did little to cut back their survival rates.

Aphids weaken plants by sucking out nutrients, and flea beetles cause damage by chewing. Both insects are also notorious transmitters of certain plant diseases. Examples are Stewart's bacterial wilt of sweet corn, spread by flea beetles, and barley yellow dwarf virus, spread by aphids.

Planting resistant varieties of sweet corn is the best defense against Stewart's bacterial wilt. Yellow cultivars generally are more resistant than white varieties. A complete list is available from the service offices throughout the state as well as seed dealers.

The recommended threshold level for insecticide application to control aphids in alfalfa fields is reached when populations exceed five to 10 aphids per plant or 50 aphids per sweep with an insect net during plant growth from the 10th internode to first bloom. No spraying should be done within one week of harvest.

The threshold level for foliar application of chemicals to control flea beetles in corn is reached when five percent or more of the plants are infested. Repeat application every three to five days, if beetle activity remains high.

Threshold levels are considerably lower in situations where there is a danger of the insects spreading disease to susceptible plant varieties. Weeds in surrounding fields often are a reservoir from which flea beetles spread the wilt virus to susceptible sweet corn cultivars.

For recommendations on which pesticides to use, consult any office of the Cooperative Extension Service. In Carroll County, call 848-4611.

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