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Hort Update for January 4, 2023

Hort Update for January 2023
Serious ConcernsMajor Symptom:
1. Sunscald and tree wrap Use care to prevent unintentional tree damage
2. January 3rd growing degree days (GDD) Several Nebraska sites below, Understanding Growing Degree Days
Timely Tips
3. Pruning shade trees, fruit trees and shrubs Good pruning practices - timing and techniques - essential for plant health & productivity
4. Dormant oil applications Apply in late winter before budbreak
For Your Information
5. ProHort Lawn & Landscape Management Workshop series for nursery & green industry professionals
6. Commercial/Non-commercial pesticide applicator certification New license and recertification options
7. Digital Diagnostic Network - Need help with diagnostics? Submit pictures and questions for diagnosis by Nebraska Extension experts
8. Spanish for horticulture professionals Learn phrases and vocabulary related to plant and landscape maintenance at Metropolitan Community College

1. Sunscald and tree wrapUse care to prevent unintentional tree damage

The use of tree wraps is controversial. Some greenspace professionals promote their use and others are against them. In many cases, the use of tree wraps is now only recommended when a nursery guarantee requires it or while a tree is being transported.

Protecting young trees from sunscald during winter is a common reason for using tree wrap. Sunscald occurs on the south and southwest sides of trunks as a vertical area of cracked, discolored and/or sunken bark that sloughs off over time. The wound can cause tree stress and lead to trunk decay or insect/disease entry.

Sunscald injury occurs during winter due to sudden temperature changes in bark. The sun does not actually "scald" bark. On cold winter days, direct sun warms exposed bark to the point dormant tissue just beneath the outer bark (mostly phloem and cambium) becomes active. As temperatures suddenly drop at night or when the sun is blocked by clouds or a building, the active tissue is killed.

The trunks of young, tender barked trees are most prone to winter sunscald. When bark thickens on older trees, it better insulates dormant inner bark. Maple, honey locust, linden, crabapple, and cherry are some susceptible trees. Trees pruned to raise lower branches and those transplanted from shady to sunny locations are also more susceptible.

Sunscald is fairly common in Nebraska and so the use of tree wraps to prevent it has often been recommended. Here, in part, is where the subject becomes controversial. Some studies, according to Purdue University, indicate tree wraps do not prevent extreme fluctuations in bark temperature.

Downside of Tree Wrap
The use of tree wraps can also lead to trunk damage and other issues. Tree wraps can cause girdling damage to trunks if left on too long, photosynthetic tissue of young trees is covered, moisture is often trapped beneath the wrap, and wraps provide cover for insects. These are good reasons to reconsider the use of tree wraps.

Alternatives for sunscald prevention include making sure trees are watered correctly going into winter. Drought stressed trees are more susceptible to sunscald injury. On young trees, leave lower branches as long as possible to shade the trunk and provide photosynthetic tissue to increase tree vigor. Consider placing a light-colored, upright board on the southwest side of the tree near the trunk to provide shade during winter.

Careful Tree Wrap Use
If tree wrap is used on young trees, wait until November to apply. Remove tree wrap in April or after the last hard freeze to expose photosynthetic tissue, prevent girdling damage as the trunk expands, and avoid hiding places for insects or moisture buildup. Tree wrap or guards should not remain on a tree during the growing season.

If wrapping, use white or light-colored commercial tree wraps, white plastic tree spirals, or white corrugated tree guards. White is recommended as it reflects sunlight. Do not use dark colored tree wraps or guards. These absorb heat, warming tissue during the day and exposing it to cold temperature injury at night.

While wrapping, begin at the base of the trunk and wind the wrap up to the first major branch. Overlap the wrap so no trunk is exposed. If using plastic spirals around the trunk, take care not to injure tender bark while applying the spiral.

Care of Newly Planted Trees, Nebraska Forest Service


2. January 3rd growing degree day(GDD)

Location Accumulated Growing Degree Days
Grand Island, NE - Airport 0
Lincoln, NE - Airport 0
Omaha, NE - Airport 0
Norfolk, NE - Airport 0
North Platte, NE - Airport 0
Scottsbluff, NE - Airport 0


3. Pruning shade trees, fruit trees and shrubsGood pruning practices - timing and techniques - essential for plant health & productivity

Trees - New research shows the optimum time to prune living branches is late spring and early summer because pruning at this time promotes the quickest sealing of pruning wounds. Late spring and early summer is when tree cells are most active during the growing season, hence sealing occurs the quickest. However, professionals may not have a choice to limit pruning to this time frame, due to the total amount of tree work needed by clients, or when pruning is needed to repair tree damage after a wind or ice storm. Oaks are best pruned during winter - December, January or February - to avoid potential infection with oak wilt. 

Pruning Shade Trees In Landscapes, Edward Gilman, University of Florida
ANSI A300 Pruning Standard, International Society of Arboriculture
Best Management Practices - Utility Pruning of Trees, International Society of Arboriculture
Structure Pruning, Backyard Farmer

Fruit trees - Less winter hardy tree fruits like peach, apricot and sweet cherry should always be pruned in late winter, usually mid-March to early April, no matter how much warm mid-winter weather we experience. Pruning is done just before new growth starts. This is also the best practice for the more cold-hardy fruits, like pear, apple, plum tart cherry and shade trees.

Does late pruning, after blooming or growth has begun, have a detrimental effect on fruit trees? Pruning can be done after growth begins, but it becomes very important to prevent the spread of common diseases, like fireblight and brown rot, with each cut. That's one of the main reasons dormant pruning is preferred.

Pruning after blooming begins does not reduce fruit production more than normal dormant pruning. Some flower buds are removed, but fruit trees do require annual thinning of fruits. In particular, peaches normally set many more fruits than the tree can support physically or develop to a good size. Breaking of peach tree branches under excess fruit weight is a common occurrence. Only 10% of peach flowers are needed for full crop set.

Does pruning cause early leaf and flower bud development? No, pruning actually has a slight delaying effect on bud growth. After pruning, a plant has to adjust and begin sending growth hormones to new buds, since the preferred buds at the tips of branches removed are now gone. This process could take about 10 days, so bud development is slowed down a little. But it's risky for growers to use pruning to slow down and "protect" flower buds.

Fruit Tree Pruning - Basic Principles, PennState Extension

Shrubs - Prune summer-flowering deciduous shrubs during dormancy, typically late February or March; examples include spirea, potentilla, and smokebush. Spring-flowering shrubs should be pruned when blooming is finished; this includes forsythia, weigela, mock orange, lilacs and viburnums (Koreanspice, Arrowwood, European cranberrybush, etc.).

Pruning Ornamental Trees and Shrubs, Purdue Extension

Evergreen Shrubs like juniper or yew, often need pruning to control size/shape or because a client prefers a sheared form over a natural form. Late winter, just before new growth begins is a good time to start. When pruning most evergreens, do not prune beyond the green needles on a branch. Most evergreens will not generate new growth from bare wood.


4. Dormant oil applicationsApply in late winter before budbreak

Dormant oils are applied to dormant plants to help manage pests that overwinter on plants, like scales and mites. Dormant oils reduce a wide range of insects and mites, but not all. For example, they control spruce spider mite but not two-spotted spider mite which tend to overwinter in plant debris rather than on plants. Dormant oils are effective against some eggs, but less so on those that are stacked on top of one another. The risk of pests developing resistance to oils is low, however resistance has been found in pine needle scale. While oils can be applied any time during dormancy, they will likely be more effective in mid to late winter when pests are in a weakened state.

There is a risk of phytotoxicity from dormant oils. To avoid plant damage, read label directions for use, application timing, and a list of plants products should not be applied to. Always apply dormant oils to plants before bud break to avoid tender plant tissue being damaged. Make applications when temperatures will remain above freezing, ideally above 40 degrees F., for 24 hours and continually agitate the spray solution. Avoid applying dormant oils to stressed plants as these are at higher risk of phytotoxicity.

Dormant Oils, Kansas State University


5. ProHort Lawn & Landscape UpdateWorkshop series for nursery & green industry professionals

This year a series of seven workshops will be offered across Nebraska on the following dates. Register now!

  • February 8, Grand Island
  • February 9, Beatrice
  • February 14, Columbus
  • February 15, North Platte
  • February 21, Lincoln
  • March 9, Scottsbluff
  • March 15, Omaha

Cost varies by site. Lunch is included at some sites. At those sites, lunch is not guaranteed for registrations received after the site's registration deadline.

Topics include:

Japanese Beetles and More - Japanese beetles are an invasive species moving throughout Nebraska and leaving a wake of destruction in its path. These and a few other pests are causing a great deal of damage to many of our landscape ornamentals. Learn about these more problematic pests including magnolia scale, kermes scale, twig girdlers and more and find ways to manage your plants from these harmful pests.

What's Wrong with my Turf? - Solving turf problems can be challenging and complicated. Living and non-living factors are influential including seasonal changes of the environment; all must be taken into account in a step-by-step approach. Grow your diagnostic skills by learning how to distinguish damage symptoms between common insects, diseases and drought effects.

What's Wrong with this Spruce? - Spruces are an important evergreen tree for Nebraska landscapes and windbreaks. But even this tough, hardy tree can struggle due to soil, planting and management issues, along with several insect and disease pests. Learn how common management missteps can cause problems for spruce trees, current best management practices and how to identify and control common pest problems.

Evergreen Selection & Placement for Nebraska - Evergreens play an important role in our landscapes. Some struggle due to weather extremes, pest issues and overplanting. Diversity in evergreen plantings is needed. Hear about new and tried and true conifers for Nebraska, where best to site them, and some management tips to increase success.


6. Commercial/Non-commercial pesticide applicator certificationNew and recertification options

If you have a pesticide applicators license expiring April 2023 or you need to get a new license — classes begin soon. Make plans now to attend the training option that fits your needs.

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.

Commercial/noncommercial applicators have several options to recertify or get a new license.

Traditional In-person Classes
Classes begin in late January. Visit for dates, locations and registration. Preregistration is required; cost $95 per on-line registration.

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

On-line Self-Paced Option - Recertification ONLY
This is a 100% online training, which includes watching the General Standards recertification video, plus a video for each additional category to be renewed. Cost is $80.00 per on-line registration. Visit to register, beginning December 19, 2022. 

Conference Options - Recertification ONLY

  • Urban Pest Management Conference - For commercial/noncommercial applicators needing recertification only for General Standards (00), Structural Health (08), Wood Destroying Organismas (08w) and Fumigation (11) categories. Visit more information.

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 -
  • 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.)


7. 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.


8. Spanish for horticulure professionalsLearn phrases and vocabulary related to plant and landscape maintenance at Metropolitan Community College

Our instructors have developed a series of noncredit courses, Spanish for Horticulture Professionals. The first in the series will have a focus on the phrases and vocabulary related to maintenance of plants and landscapes. No base level of Spanish proficiency is needed; this class is for beginning learners.

Future series will focus on communication related to hardscaping, softscaping, and contracts/labor.

The class is aimed at individuals working in the horticulture industry, who would benefit from learning to communicate more effectively with their Spanish-speaking team members.

Class information: Spanish for Horticulture Professionals: Maintenance
Location: Metropolitan Community College, Fort Omaha Campus, 32nd and Sorensen Parkway
Dates: January 11, 18 & 25
Time: 5:30-7:00pm
Cost: $40 for all three classes in this first program series

Register now!


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.