Hort Update for December 5, 2023

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Nebraska's drought status, 11/30/23 Map updated weekly.

1. Salt damage in turf & ornamentalsChoose products and strategies for managing ice and minimize landscape damage

Salt damage to turf or landscape plants growing near pavement where deicing agents are used is common. High salt levels change the structure of soil, causing it to become compacted and restricting the availability of nutrients, water and oxygen to plants.  In summer, high salt levels decrease a plant's ability to absorb sufficient water, even when water is available. Symptoms of salt damage include stunting, leaf burn, root damage, and plant death.

Diagnosing Salt Damage
Salt damage of turf, trees and shrubs occurs in three ways: 1) Salt sprayed directly on the plant makes the plant lose cold hardiness and become susceptible to freezing; 2) Salt accumulation in the soil absorbs water, making it unavailable to plants; and 3) Chloride ions are absorbed by the roots, transported to the leaves, and accumulate there to toxic levels - it is these toxic levels that cause the characteristic marginal leaf scorch.

To determine if salt is playing a role in damaging client plants, note where the worst damage occurs. Salt-damage symptoms will be more severe on sides facing the road or sidewalk. In evergreens, damage usually appears in late winter as browning, starting at the needle tips. Keep in mind that snow-covered branches will be less affected than those exposed to salt spray, and that as you move away from the spray zone, the symptoms should abate.

It is more difficult to diagnose spray damage on deciduous plants. Usually, leaf buds facing the road are killed or are very slow to break dormancy and bud and leaf out in spring. Flower buds facing the road often fail, but the unaffected side of the tree or shrub flowers normally. Repeated salt damage over several winters may produce a witch's broom effect, which is a tufted and stunted appearance of the plants on the side facing the road.

Prevention
The easiest way to prevent salt damage is to avoid it.

• Erect barriers with plastic fencing, burlap, or snow fencing to protect sensitive plants from salt spray.
• Avoid piling snow containing salt on turfgrass or around salt sensitive plants, such as redbud, hackberry, hawthorn, crabapple, pin and red oak, littleleaf linden, barberry, boxwood, dogwood, spirea, Viburnum, Balsam Fir, White Spruce, White Pine, Scotch Pine, Yew, Arborvitae and Hemlock.
• Use non-sodium de-icing agents known to cause less soil & plant damge.
• Use products to improve client footing on slick surfaces, like sand, sawdust, or cat litter instead of deicer. Or blend it into a deicer product to provide traction while reducing product use.
• If traditional salt products are the only option, then use the smallest amount needed to manage ice.

Although salt is applied throughout the winter, most salt damage occurs in late winter and early spring when plants are beginning active growth and excess salts are pulled into the plant.  So, it is particularly important to protect plants during this time, and limit salt use in late winter.

Reducing Salt in the Soil
In years when large amounts of salt are used, minimize plant damage by irrigating soils to leach out the sodium and chloride prior to spring growth. Since most salts are water-soluble, thorough and repeated applications of water can effectively leach salts out of the root zones.

In areas affected by high salt levels, flushing the soil with 2" of water over a 2-3 hour period in early spring may help leach salt from soil. Repeat this procedure 3 days later. However, if the soil is not well drained in the area, leaching will not work well.

In cases with repeated and heavy deicing salt use, removing the top four to six inches of soil may be needed.

Choosing Ice Melt Products
Another way to protect turf and landscape plants is to use chemical de-icing products with lower potential for damage. These products may be used alone or blended, to improve performance or reduce damage to concrete or landscapes.

The de-icing products listed below are in order of potential plant damage, with the most damaging first.

• Sodium chloride is the least expensive product and commonly used on roadways.  It has a high burn potential for landscape plants.
• Urea can harm landscape plants and cause runoff pollution in ponds and waterways.
• Potassium chloride, also known as muriate of potash, is less damaging than sodium chloride.
• Calcium chloride is the most effective deicing product at low temperatures, down to -25°F. Will not damage vegetation if used as directed.
• Magnesium chloride is sprayed on roadways before a snowstorm to prevent ice bonds from forming, making ice and snow removal easier. It causes very little damage to concrete or metal. It's gentle on landscape plants and pet safe if used as directed.  It also doesn't track into the house.
• Acetates can be found in three forms- calcium magnesium acetate (CMA), sodium acetate and potassium acetate.  CMA is a salt-free product and is the safest product for use around pets and landscape plants.  CMA is made from dolomitic limestone and acetic acid (the principal component of vinegar). Studies have shown the material has little impact on plants. It also has a very low level of damage to concrete or metal.

More information on managing salt damage in landscapes and lawns.

• Salt Damage in Landscape Plants, Purdue Extension
• Growing Turf on Salt-Affected Sites, Colorado State University Extension

Reference to commercial products is made with the understanding that no discrimination is intended and no endorsement by Nebraska Extension is implied. Mention does not imply approval or constitute endorsement by Nebraska Extension. Nor does it imply discrimination against other similar products.

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2. Peeling barkShedding bark is characteristic of sycamore, redbud, silver maple, shagbark hickory, birch

Tree owners may be concerned if they notice bark peeling off of a tree. For some trees, this is normal. The bark of young trees is smooth and thin. As a tree grows, the bark layer thickens with the outer tissue dying. Continued growth pushes bark outward, causing outer layers to crack. On some trees, these dead layers peel and drop off.

Shedding bark is characteristic of sycamore, redbud, silver maple, shagbark hickory, and birch. Sycamore tends to peel in blotches revealing a cream or green inner bark. On redbuds, outer bark may fall off exposing an orangish inner bark. Silver maple tends to peel long, thin bark strips. Peeling is of no concern on these trees.

However, cracking and bark peeling only on the south sides of fruit trees, red maples, and lindens indicates sunscald and can lead to issues. Unfortunately, not much can be done for trees with damaged bark. Wound dressings or tree paints are of no benefit. Correctly wrapping the trunks of young trees with paper wraps in late fall may reduce sunscald.

Shedding, Peeling and Splitting Bark on Shade Trees, Iowa State University Extension

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3. Slime fluxSmelly slime; patches/streaks of discolored bark

If a smelly slime is noticed oozing out of a tree or patches/streaks of bark appear bleached, this is likely a bacterial disease known as wetwood or slime flux. It is most common on elms, cottonwood and willow. The flow of ooze is what bleaches the bark a lighter color. This ooze is toxic to the cambium layer of the tree and can retard the formation of callus tissue that covers pruning wounds. Though the strength of wood may be affected, the effect is minor as this disease also inhibits wood-rotting organisms.

The bacteria causing wetwood are common in soil and water, and likely enter the tree through wounds in roots. Wetwood cannot be cured. Since this disease rarely affects the overall health of a tree, no treatment is needed other than preventing stress through timely watering. Drain tubes were once recommended to help relieve pressure, but they no longer are as they create an additional wound that can make the disease worse.

Bacterial Wetwood, Colorado State University Extension

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4. MulchBenefits of soil temperature moderation

Trees and landscape plants are often mulched. While we know mulch conserves soil moisture and controls weeds during summer, a benefit we may not think about is how mulch protects soil from temperature extremes and how this benefits plants. Mulch keeps soil cooler in summer and warmer in winter. This benefits plants because temperature extremes can kill very fine roots which are responsible for most water and nutrient absorption.

While soil temperature extremes rarely kill established plants, they can cause a chronic stress as plants expend energy to generate new fine roots. This may allow opportunistic pests, like root rots, to infect.

Modifying soil temperature is especially important near the soil surface, where fine roots can be killed by hot soils in summer and by freezing and frost heaving during winter. The correct use of organic landscape mulch benefits plants year-round. Coarse mulches, like wood chips, tree leaves or recycled greenery, make great mulches.  

Apply mulch in an even layer, 2 to 4 inches deep, around woody plants and 1 to 2 inches thick around annual and perennial flowers. Mulch should be kept an inch or two away from plant stems, even tree trunks. Watering organic mulches after installation will increase their ability to hold together and minimize movement during heavy rains or gusty winds.

Impact of Mulches on Landscape Plants and the Environment: A Review, Journal of Environmental Horticulture

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5. Pruning evergreensBe cautions when pruning into the "dead zone"

Evergreen shrubs like junipers, yews, Arborvitae and Mugho pine are often planted where they become too large; blocking views or hanging over sidewalks. When this happens, clients may ask for the plants to be pruned.

This is fine, but be aware when an evergreen branch is pruned back into the bare zone or "dead zone", where there are no green needles, that branch will not develop new growth to cover a now bare spot. While these evergreen shrubs can be pruned a little each year, to minimize their yearly growth and keep them somewhat in bounds, if they are ignored and become 1-2 feet or more larger than desired, it is difficult to successfully prune them back to the size needed.

If the only way to reduce the size of an evergreen shrub is to prune into the bare zone where there are no green needles, the shrub may need to be removed and replaced with a new shrub that is the right size for the location.

Pruning Evergreens, Morton Arboretum

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6. Don't stake trees too long!Remove staking after 1 year

Thigmomorphogenesis is a long word, but we witness it happening just about every day in the windy state of Nebraska. When trees are swaying in the wind, or bending under the weight of snow and ice, thigmomorphogenesis is happening. Basically, thigmomorphogenesis is a plant's growth response to external mechanical influences, such as wind. Trees respond to mechanical loading with growth responses that add strength to loaded components (roots, trunk, branches) and reduce the likelihood of failure. 

Bottom line - If a tree was planted a year or more ago, and still has staking materials supporting it, it is time to remove the stakes. Allowing the tree to sway and bend in the wind, and under the weight of ice and snow, results in growth responses which ultimately reduce the tree's risk of breakage. If trees are staked tightly and not allowed to sway in the wind, these growth responses will not readily occur which increases the tree's risk of failure in a storm. Stake young trees as low as possible on the trunk and stake new trees for one year only.

Staking and Guying Trees, University of Minnesota Extension

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8. Commercial/Non-commercial pesticide applicatorsObtaining a new license or updating an expired license

If you have a pesticide applicators license which expired in April 2024 or you need to get a new license, commercial/noncommercial applicators have several options to recertify or get a new license.

2024 Traditional Classroom Training
Commercial/non-commercial in-person training classes are held from January through April. Training schedules will be available soon at https://pested.unl.edu/. In-person trainings are a supplemental learning opportunity; they DO NOT replace pre-class studying of category manuals or flipcharts for test preparation. Study materials for all commercial categories must be purchased online https://pested.unl.edu/

Testing-only Options

• Closed-book exams are given by the Nebraska Department of Agriculture (NDA). Preregistration is not required an there is no cost. Visit the link below for a list of available test-only dates, times and locations - https://pested.unl.edu/.
• NDA computer-based testing is provided through the Pearson-Vue company. Click here for a list of testing sites, categories available, dates, and registration information. Cost $55 per exam. (For applicators with multiple categories on their license, each category is charged the full testing fee.)

2024 Conference Options
Extension and industry-sponsored events also offer opportunities to renew a license. Recertification only.

• Jan. 3-23 | Nebraska Extension Crop Production Clinics - 00 general standards, 01 ag plant, demonstration/research
• Jan. 9-11 | Nebraska Turf Conference - 00 general standards, 04 turf & ornamental 
• Feb. 19-21 | Nebraska Aviation Trades Association Convention - 00 general standards, 01 ag plant, 07 right-of-way, 09 public health, 12 aerial
• Feb. 21-23 | Nebraska State Pest Control Association Conference - 00 general standards, 08 structural/health related, 08w wood destroying organisms, 11 fumigation, 14 wildlife damage control

Commercial/noncommercial applicators are professionals who apply restricted-use pesticides for hire or compensation. Anyone who applies pesticides to the property of another person, either restricted- or general-use products, for control of pests in lawns, landscapes, buildings or homes must also have a commercial pesticide applicators license. Public employees (those employed by a town, county, state) applying mosquito control pesticides whether restricted- or general-use, must also hold a commercial or noncommercial certification.

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9. Digital Diagnostic Network - Need help with diagnostics?Submit pictures and questions for diagnosis by Nebraska Extension experts

Do you or your clients have questions you need help answering? Maybe you are a lawn care person and they're asking about trees, shrubs, or flowers? While you can refer them to their local Extension office, another option is Digital Diagnostic Network. Homeowners, lawn care professionals, pest control operators and others are invited to submit questions and photos through this website or with the assistance from an Extension professional at any Nebraska Extension office. All offices are equipped with high-resolution digital image capturing technology. Whether the question is about a lawn weed, insects on a plant, diseases in a shrub border or other, an expert panel of Extension professionals will review and respond to the question. To get started, create an account so the question can be reviewed and responded to via email. For more information and to create an account, go to Digital Diagnostic Network.

Bugging Out With Your Camera Phone - Tips on how to get a good picture.

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Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by Nebraska Extension is implied. Use of commercial and trade names does not imply approval or constitue endorsement by Nebraskas Extension. Nor does it imply discrimination against other similar products.