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Hort Update for November 16, 2020

Hort Update for November 16, 2020, Nebraska Extension, http://communityenvironment.unl.edu/update11162020
Avoid foot and vehicle traffic on frosted turf.
Serious ConcernsMajor Symptom:
1. Emerald Ash Borer - new confirmation Newest confirmation in Hall County; USDA quarantine regulations now in force
Minor Issues
2. Deicing salts Choose products carefully to avoid plant damage
Timely Topics
3. Minimizing snow & ice damage after the storm Advise clients how to remove snow & ice without causing additional damage; use good pruning practices with damaged branches
4. Mowing tree leaves into lawns Up to three inches of leaves can be mowed into turf at one time
5. Don't scalp turf going into winter Scalped turf more susceptible to winter kill
6. Avoid foot or vehicle traffic on frozen turf Trafficked turf more susceptible to winter kill
7. Preparing roses for winter Fall pruning can increase winter injury
8. The myth of "winter" mulch Applying mulch in early fall does not delay development of winter hardiness
9. Potential for limited plant & seed availability in 2021 Plant and seed shortages likely


1. Emerald ash borer - new confirmationNewest confirmation in Hall County; USDA quarantine regulations now in force

On October 29, 2020 the Nebraska Department of Agriculture (NDA), in partnership with the U.S. Department of Agriculture and the Nebraska Forest Service (NFS), confirmed the first discovery of emerald ash borer (EAB) in Hall County. Current EAB confirmation map, 10/29/2020

As of January 2020, an NDA quarantine was in force for several Nebraska counties - Washington, Dodge, Saunders, Douglas, Sarpy, Otoe and Lancaster. Since EAB was confirmed in several new Nebraska locations in 2020 - Seward, Hall and Buffalo counties - the NDA quarantine has been rescinded, now federal USDA quarantine regulations must be followed. Regulated materials are listed below. 

  • ash nursery stock
  • green ash lumber
  • other ash material living, dead, cut or fallen, including logs, limbs, stumps, roots and branches
  • all hardwood composted and uncomposted chips, bark or mulch
  • all hardwood firewood or fuelwood
  • any other product a federal USDA inspector determines is a risk of spreading EAB

In order to move any firewood or ash material to another state, contact NDA for certification requirements. Current EAB Federal Quarantine Map, 11/2/2020. The USDA quarantine may be extended to additional Nebraska counties, where confirmations have occurred, after the active beetle flight season has ended. 

NFS recommends the following practices to prevent human-assisted spread of the insect. 

  • Since EAB can easily be moved in firewood, always use locally-sourced firewood and burn it in the same county where you purchased it. 
  • Consider treating healthy, high-value ash tress located within a 15-mile radius of a known infestation. Treatment will need to be continually reapplied and will only prolong the tree’s life, not save it. Trees that are experiencing declining health should be considered for removal. 

If you are in a non-infested county and think you have found an EAB infestation, please report it to the Nebraska Department of Agriculture at 402-471-2351, the Nebraska Forest Service at 402-472-2944 or your local Extension office. 

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2. Deicing saltsChoose products carefully to avoid plant damage

De-icing agents are sometimes needed for safety but can be harmful to plants. Common deicing compounds are listed below in order of potential plant damage, with the most damaging first. These may be used alone or blended together to improve performance or reduce damage to concrete or landscapes.

  • 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, working down to ­‐25°F. It 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 also gentle on landscape plants and pet safe if used as directed.
  • 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.
  • Beet juice deicers - A newer organic option are products derived from beet juice. They contain only 12% sodium chloride (salt), much less than traditional sodium chloride. Beet juice products are fully biodegradable, however some research has shown potential problems with aquatic insects. So ideally it should not be applied where melt runoff will move to aquatic areas. Available to homeowners as Green Gobbler Pet Safe Ice Melt, Snow Joe Beet It Snow & Ice Melter, Organic Melt Premium Granular Ice Melter and others.  

Also keep on hand products that improve your footing on slick surfaces, like sand, sawdust, or cat litter. They can be used instead of traditional deicing products, or blended with them to improve traction and limit deicer use.

Winter De-icing Agents for Homeowners, Nebraska Extension
Salt Damage in Landscape Plants, Purdue Extension

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3. Minimizing snow & ice damage after the stormAdvise clients how to remove snow & ice without causing additional damage; use good pruning practices with damaged branches

Snow and ice loads on trees and shrubs can result in breakage. However, improper removal of ice or snow by homeowners from a tree or shrub can increase damage, and be a safety hazard.

Advise clients to allow snow and ice to melt naturally. Homeowners should never break ice off trees or shrubs by beating the ice covered branches. If it is safe to do so, snow loads can be gently brushed off of trees with a broom. If not broken, most evergreens branches will return to their natural form.

When heavy ice or snow loads have caused tree damage, homeowners should turn to professional arborists for assistance, especially with large trees. Damaged trees require immediate attention to remove broken branches that pose the greatest hazard. Broken but firmly attached branches posing no immediate danger can be pruned after more hazardous branches are removed.

Correct pruning cuts are important for tree recovery and it's ongoing health. Do not make flush cuts on the trunk and don't leave branch stubs. If hazardous branches are removed in a hurry for safety purposes, and correct pruning cuts are not made at the time (such as leaving branch stubs) it is important these stubs be removed in early spring or early summer.

Pruning wounds should not be treated with any kind of paint or wound dressing. 

The Nebraska Forest Service has a series of publications with information on dealing with storm damaged trees, such as leaning trees, trees with split trunks and more. The storm damaged tree series can be found at Storm Damaged Trees.

Resource to help clientele understand this issue:

  • Ice, Nebraska Extension

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4. Mowing tree leaves into lawnsUp to three inches of leaves can be mowed into turf at one time

While many homeowners bag tree leaves each fall, most professional turf managers mulch mow leaves. Mulch mowing can be easier and returns complex organic matter and nutrients to the soil. Some research suggests mulch mowing can even help control weeds. While this weed control benefit can be sporadic, it can help improve the health of your lawn and soil. Mulching leaves is also easier and less time consuming than bagging. Sometimes a double mowing at a slightly higher cutting height will help shred those leaves and bury them in the lawn. The ground tree leaves won’t add to thatch.  Sometimes tree leaves come fast and quickly pile over the lawn. If you need to rake and bag, compost those leaves and don’t put them on the street or other concrete surfaces. Leaves can leach nutrients that pollute waterways; or be carried to surface water through storm drains where they release nutrients leading to algal problems.

Mow Tree Leaves and Other Fall Lawn Care Tips, Nebraska Extension Turf iNfo

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5. Don't scalp turf going into winterScalped turf more susceptible to winter kill

Scalping occurs when more than one-third of the turf's foliage is removed at one time, often exposing the stems of the grass plants, resulting in stress and even plant death. Removal of 50% or more of the turf canopy at one mowing results in severe defoliation.

Some homeowners still like to lower their mowing height in fall as a way to "clean up" the turf at the end of the season. Lowering the mowing height from a 3.5" standard summer mowing height to 2" fall "clean up" height would result in scalping. Turf, which may already be drought-stressed due to ongoing dry fall conditions, could ultimately suffer grass thinning or death during winter. Advise clientele not to lower their mowing height for an end-of-season clean up mowing. It is better to maintain the same mowing height all season.   

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6. Avoid foot or vehicle traffic on frozen turfTrafficked turf more susceptible to winter kill

Minimize winter traffic on any turf area and especially when frost is present on green turf. If ice crystals (frost) have formed and foot or vehicle traffic occurs, the physical abrasion can damage turfgrass. Winter traffic can cause cosmetic damage, physical abrasion, and/or soil damage depending on the situation. Too much traffic on turfgrass at a time when it cannot recover also leads to winter injury. Winter golf or over-using soccer fields during winter are examples.

Winter Turf Damage, Nebraska Extenion Turf iNfo

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7. Preparing roses for winterFall pruning can increase winter injury

Research has shown roses sustain less winter injury if they are not pruned in fall, but instead in spring the following year right before new growth begins. Pruning earlier, including fall pruning, can increase winter injury.

To prepare roses for winter, now is the time to clean up old leaves to reduce overwintering organisms. For hybrid tea roses, or others particularly susceptible to winter injury - thus requiring extra winter protection - don't put rose cones in place too early. Wait until after two or three hard freezes before applying winter protection to insure the rose is fully dormant. This is a plant's best protection against cold temperature. When putting the rose cone in place prune only as needed to get the cone in place. Leave additional pruning for next spring. 

Shrub roses can also be pruned in early spring to remove any dead stems. 

Pruning Roses in the Spring, Iowa State University Extension and Outreach

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8. The "myth" of winter mulchApplying mulch in early fall does not delay development of winter hardiness

For many years Extension recommended not applying mulch in early fall. The theory originated from the knowledge that mulch moderates large temperature swings in the soil, thus it was predicted early fall mulch applications would keep soil warm longer and delay development of winter hardiness in landscape plants. However, research has shown this theory is not true - mulch does not delay development of winter hardiness. Dr. Linda Chalker-Scott, Washington State University, outlines this and many other properties of landscape mulch in the publication below in which she reviews research from multiple universities over the last 20+ years. 

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

Mulch provides several benefits to landscape plants during winter, most notably holding moisture in the soil and moderating soil from extreme temperature swings which could kill roots. But landscape managers do not have to wait until late fall or early winter to refresh landscape mulch. 

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9. Potential for limited plant & seed availability in 2021Plant and seed shortages likely

This year we've seen shortages in many commodities, from toilet paper, bread, meat and many more. Spring 2020 found plant shortages already occurring at nurseries and garden centers, and the same will likely be true in spring 2021. Plan ahead. Order plant and seed supplies early. Be prepared to choose alternate cultivars or varieties, if necessary.  

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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 constitute endorsement by Nebraska Extension. Nor does it imply discrimination against other similar products.