Junipers Hardy, But Have Common Woes 05/30/01

MANHATTAN, Kan. – Junipers, including the native eastern redcedar, are common across the Midwest, because they’ll grow where many plants fail. They aren’t too fussy about planting site, temperature change or summertime drought.

"They’re generally thought of as low-maintenance ornamentals and windbreak plantings," said Ward Upham, horticulturist at Kansas State University. "But that doesn’t mean they are problem-free – as many homeowners are discovering this year."

Mid-May to early August is bagworm time for junipers. [See box for other host plants.]

"The hatch typically lasts from mid-May to mid-June. Each bag can contain up to 1,000 eggs. And each new larvae will begin eating and rapidly growing, building its own protective bag as it goes. So, the earlier you can catch them, the less protected and easier to control they’ll be," Upham said. "We generally recommend spraying soon after the hatch begins and respraying two to three weeks later, to get the larvae that hatched after the first treatment."

Several good natural and synthetic control formulas are available in garden stores and other retail outlets. All require thorough coverage of the infested plant’s inside, outside, upper and lower surfaces. For junipers, that generally means using a handheld tank sprayer at its highest pressure setting.

"Waving a spray wand over a juniper only kills the bagworms that are eating on the plant’s outer needles. You can miss a lot of larvae that way, each of which could produce 1,000 more bagworms to infest the shrub or tree next year," the horticulturist warned.

With light infestations, junipers can recover from bagworm damage in as little as three to four months, Upham said. Recovering from a heavy infestation can take several years. Repeated heavy infestations can strip and kill a shrub – inspiring the larvae to migrate elsewhere to look for food.

Several versions of four different types of disease can also affect juniper looks and/or health in Kansas, said Ned Tisserat, K-State Research and Extension plant pathologist.

"Unfortunately, they can produce similar symptoms. In turn, some of those symptoms can look a lot like the winterburn that’s emerged in unusual amounts across the state this spring. Beyond that, a winter-injured juniper can be an open door or disease organisms," he added. "So, you need to know how these conditions differ in appearance, timing and results, to know how to respond."

For example, juniper diseases and winter injury both can kill an entire plant, kill a few branches or just "scorch" the branch tips.

"Evergreens keep their needles during fall, so continue to transpire some water throughout winter. They can’t replace that water if their soil is dry or frozen. So, they simply dry up," Tisserat explained. "Unfortunately, junipers also can suffer from extreme cold or unfiltered sunlight.

"All of these problems tend to show up more often in horizontal than in upright juniper varieties."

The result is a gradual browning. No obvious "zone" separates the injured and healthy tissue – as often is the case with juniper diseases.

Wintertime injury also tends to affect a plant on one side (the northwest to southwest), while diseases do not. Dry winter winds can worsen the effect, increasing the risk for junipers in raised planting boxes, on a building’s southern exposure or at a windbreak corner.

"Disease injury sometimes starts with the inner needles and works out. It sometimes progresses from the bottom to the top of the plant. But it rarely affects just one side of a shrub – unless, of course, winter injury has led to the initial disease infection," Tisserat said.

All Kansas county Extension offices can provide information about ornamental plant problems, as well as forward samples to K-State’s network of diagnostic labs, which now are working together to identify and provide recommendations for landscape plants.

Tisserat’s publication on juniper diseases – with photographs – also is available on the World Wide Web at www.oznet.ksu.edu (enter "juniper diseases" in the "search" blank).

[NOTE TO EDITOR: If you’d like to provide a different ending that includes a summary of Tisserat’s publication, you’ll find a chart ready to download by clicking here.]

But those evergreens share worm-hosting duties each year with a broad range of ornamentals. Those hosts can include spruce, pine, willow, maple, oak, boxelder, sycamore, poplar, locust, rose, barberry, pyracanthia, clematis, sumac, cherry, quince pear, peach and blackberry plants.

Homeowners have reported the larvae will feed freely on clover, ragweed, parsley and nightshade if the worms’ preferred food isn’t available.

Common Juniper Diseases in Kansas
Disease	Kabatina Tip Blight	Phomopsis Tip Blight	Cereospora Needle Blight	Cedar Rusts	Botryosphaeria, Seiridium Canker	Root Diseases
Initial Symptoms	Feb.-March; tip dieback; gray lesion at base of infection; small, black, spore-carrying "fruit" in lesion; no lasting injury after tips drop in May-June.	April-Sept.; tip dieback; gray lesion at base of diseased tissue; small black "fruit" in lesion; on-going infection of any new tissue in humid weather.	Aug.-May; die-back and drop of inner, lower needles; fuzzy, spore - carrying "fruit" on dead needles; over time, moving out and up on shrub.	April-May; active orange, gelatinous, tendril-like or cigar - shaped galls; infection of nearby crabapples, hawthornes.	Year-round; long, sunken, often resinous cankers on woody stems, often at branch crotch; general decline in health.	Year-round; stunting; vigor loss; branch dieback and yellowing; in some cases, a rapid death.
Worst Outcome	No excessive branch loss or shrub death.	Repeat/severe cases; witches' broom, off-color foliage, stunting, and sometimes plant death.	Repeat/severe cases, foliage loss, causing open, spindly, scorched look; plant death.	Colorful, but ugly galls; on nearby apple tree relatives, however, both early leaf loss and distorted fruit.	Hard to see and diagnose; over time, restricted water and food movement can cause branch, top one-third, or shrub death.	Damage and/or death more common on prostrate forms; once started root rot usually hard to stop.
Diagnosis Aids*	10x hand lens	10x hand lens	10x hand lens	Not needed	May require lab	May require lab
Cultural Controls	Plant resistant varieties; prune out, dispose of dead tips on a hot/dry summer day; provide proper plant spacing; avoid night watering, excess pruning.	Plant resistant varieties; prune out, dispose of dead tips on a hot/dry summer day; provide proper plant spacing; avoid night watering, excess pruning.	Don't plant Rocky Mountain juniper; provide proper spacing to promote air circulation.	Use resistant varieties; remove and dispose of galls; get rid of other rust hosts.	Don't plant Rocky Mountain juniper; remove and dispose of sick branches; never prune in May-June.	Do not overwater; only plant in well - drained soils; don't use nonporous black plastic mulch.
Chemical Controls	None	Mancozeb, thiophanate-methyl or Bordeaux at 7- to 21-day intervals, as needed	Mancozeb, or Bordeaux mixture in early June and July.	Ferbam or triadimefon at 7- to 21-day intervals in July-August.	None	None

K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus, Manhattan.