ProHort Update for November 2024

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Nebraska's drought status, 10/31/24 Map updated weekly.

1. AntitranspirantsPros and cons of antitranspirant use

Antitranspirants are products applied to plants to reduce moisture loss. The materials form a film over leaves which allows for oxygen and carbon dioxide exchange while reducing water movement out of leaves. To help reduce winter dessication, they are applied to some evergreen conifers and broadleaf plants during winter. Common examples are Wilt-Pruf®, Transfilm®, Vapor Gard® and Moistureloc®.

There are mixed reviews in scientific literature and Extension publications on whether or not these products work and if they can be harmful to plants; making it difficult to make recommendations. Concerns for plants is the increase in foliage water may increase the risk of freeze injury; and that residual products will stay on into the growing season and interfere with photosynthesis. 

Best Practices 
Based on literature, use the following points when applying anti-transpirants to evergreens for the purpose of reducing winter dessication.

• Read and follow label directions carefully for application, including reapplication, to avoid plant damage and maintain effectiveness throughout winter.
• Check the label for precautions to use with certain plants. Some plants are sensitive to some products. For example, the Vapor Gard® label says not to use on arborvitae.
• It is best not to use anti-transpirants on blue spruce or other plants with bluish, waxy coatings on their leaves. The waxy coating is the plant’s natural anti-transpirant. Anti-transpirant products wash away the wax and blue color.
• Wait until plants go fully dormant, usually after Thanksgiving, to make the first application and plan to make at least two. The product will wear off, possibly in as little as 5 weeks depending on the product, plant, and environmental conditions. It is during late winter when the most severe winter dessication injury can occur.  
• Temperatures need to be above freezing when applications are made with 3 to 4 hours of drying after. Use the winter application rate.
• Leaves lose moisture from upper and lower surfaces so cover both leaf surfaces to the point of runoff.
• An article in the International Society of Arborist recommends only applying the product to the sides of the plant exposed to sun and wind.
• Anti-transpirants are thick materials that can be hard to mix in cold water. To make mixing easier, premix them in warm water before adding them to the spray tank.
• It is important to flush and clean a sprayer immediately after applying an anti-transpirant to avoid clogging nozzles and screens. It will dry quickly.

Alternate Methods for Reducing Winter Desiccation
Practices to use in place of and/or along with anti-transpirants to reduce winter dessication including the following. 

• Correct watering during summer and well into fall. Moisten the soil of trees and shrubs 12” deep from near the trunk to beyond the trees drip line. Lawn irrigation systems often water too shallow to fully benefit trees in dry years.
• Use a 2 to 4- inch layer of organic mulch in at least a 4 to 6- foot diameter ring around trees. This conserves soil moisture, protects root hairs and roots may take up moisture longer into fall.
• Plant evergreens in the right locations. Yew, arborvitae and boxwood prefer the north side of homes. Avoid planting evergreens on the south or southwest sides of homes and near pavement or where root growth will be limited.
• Use burlap to protect plants from winter winds and sunlight. Put in stakes a few inches taller than the plant around the plant or on the south, southwest and windward side of trees.Wrap burlap around the stakes and secure it. Avoid burlap on top as it can sag with heavy snow and damage branches, and reduce air circulation.
• Avoid pruning after August as new tender growth may be induced.

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3. Fall or Late Winter Applications of Preemergence Herbicides Rarely Provide Season-long Control of Crabgrass in NebraskaStudy showed even at high rate of application not reliable for season-long control

When using single applications of PREs, applying at the high rate will improve control regardless of application timing. Fall or late winter applications only occasionally provided adequate season-long control, but applying a single PRE application in April or early May maximized crabgrass control through August. This is different from previous research in milder climates where fall or late winter applications often provided season-long control. Since crabgrass control rated in June was effective in over half of the herbicide × timing combinations, a sequential PRE application in early June should be considered if the initial application is applied in fall or late winter.

Full Article

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4. Layering the Landscape for WildlifeLandscapes increasing important for habitat

With hundreds of native plant species to choose from, deciding which to choose can seem overwhelming but don’t overthink it, as almost every native plant is beneficial to wildlife on some level. 

Full Article, Nebraska Statewide Arboretum

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5. Tree wrap pros and consDo not always protect tree trunk; correct use guidelines 

Plastic or paper tree wraps are often recommended to protect the trunk of young, thinned bark trees from sunscald injury and wildlife damage. However, tree wraps are a contentious issue causing disagreement over how helpful they actually are. There are studies that show they can help and studies that show they may cause harm. If recommended to homeowners, it is important to inform them on how to use tree wraps correctly.

Sunscald occurs when sunny, warm winter days heat the bark to relatively high temperatures. Research done in Georgia has shown the southwest side of the trunk of a peach tree can be 40 degrees warmer than shaded bark. This warming can cause a loss of cold hardiness of bark tissue resulting in cells becoming active. These cells are then susceptible to freezing when temperatures drop at night. The damaged (dead) bark tissue becomes sunken and discolored and eventually cracks and sloughs off.

According to Purdue University, studies of common tree wraps have shown they do not prevent extreme fluctuations in temperature on the bark. In some cases, the temperature extremes are worse. Tree wraps are also ineffective in preventing insect entry. In fact, some insects like to burrow under them. A tree wrap can also kill a tree if left on too long and girdles to tree.

If used, Purdue Extension states that flexible, light-colored, plastic wraps appear to be the safest for providing trunk protection. These loosely-fitting wraps allow air circulation to buffer temperature extremes and prevent excess moisture from accumulating between the wrap and the trunk tissue. Light colored corrugated wraps may be better than flat paper wraps as well. If used for protection from wildlife, plastic wraps or 1/4" mesh hardware cloth around tree trunks are better choices. 

When used, place them on young, smooth barked trees during winter only. In November, apply a light-colored plastic tree wrap or corrugated wrap from the ground up to the lowest branches. Remove tree wrap in spring. Usually, protecting the tree the year of planting is sufficient but some trees may need to be wrapped a second year.

Tree Support Systems, Purdue University

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6. Winter wildlife damage preventionReducing deer, rabbit and vole damage

It’s the time of year to prepare for protecting landscape plants from wildlife damage during winter. When green foliage is no longer present, wildlife often turn to other plant parts, such as tree bark and inner wood of young trees. This type of feeding causes damage that is more harmful to plants in the long run. This damage cannot be fixed once it happens, prevent the damage before it becomes a problem.

Managing Deer Damage in Nebraska, Nebraska Extension
Managing Rabbit Damage, Nebraska Extension
Excluding Rabbits, Backyard Farmer
Controlling Vole Damage, Nebraska Extension
Vole Control, Backyard Farmer

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7. Dormant lawn seedingPrepare site now; seed between late November and late March

The best time to seed cool season turfgrass is mid-August into mid-September, but dormant seeding can also be very successful. Dormant seeding is defined as such because seed lies dormant until soil temperatures warm in April or May. Dormant seeding can be done as early as Thanksgiving or as late as March in most locations. The key is to seed after the soil is cold enough that germination will not occur until after soils warm in spring. The benefit of dormant seeding is as soil heaves and cracks during winter, crevices are created for seed to fall into, providing ideal germination conditions in spring. Dormant seeding may be easier to schedule than spring seeding, because spring rains can make it difficult to seed after March.

There are risks with dormant seeding. It is most effective if temperatures remain cold enough to delay germination until spring. Occasionally, extended warm periods in winter could allow seed to germinate, and seedlings may then be killed by ensuing cold weather. As with any seeding, soil preparation needs to be done prior to seeding. For dormant seeding, this would be now, or in fall before the soil freezes. If using dormant seeding, monitor the area in mid spring for the need to do additional over-seeding.

Dormant Lawn Seeding, Nebraska Extension

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8. Clean up equipment before winter storageLengthen the life of equipment with good maintenance

With winter coming right around the corner, it is time to prepare landscape equipment for winter storage.

• Clean out all sprayers used during the growing season. Triple rinse for safety.
• Put all herbicides in a storage cabinet where they will not freeze. Be sure to store them with their original labels. Most herbicides can be stored and used for multiple years as long as they don’t freeze and thaw.
• When mowing has been completed for the year, clean mowers before winter storage. Remove all grass debris from under the deck. Change the oil, sharpen or replace blades. Check and change spark plugs as necessary.
• Finally, clean all other tools such as shovels, rakes and hoes. Remove debris, sharpen, remove rust with sandpaper or steel wool, and oil them to prevent rust from building up.

Winterize Garden Tools, GRO Big Red Blog

Lawn Mower Preparation, GRO Big Red Blog

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9. Preparing roses for winterBest practices for winter protection and pruning

Shrub Roses
Pruning is not needed during fall for shrub roses, such as Knock Out, Buck roses, or Nearly Wild. They are very winter hardy and do not need special protection. Prune in April, removing dead or damaged branches, and adjusting plant height.

Hybrid Tea, Grandiflora & Floribunda Roses
However, hybrid tea, grandiflora, floribunda and some cultivars of miniature roses need winter protection. Most roses are protected by covering them, either with a rose cone or mulch. These plants may need pruning to allow them to fit beneath a rose cone or to remove very tall laterals that may be damaged by winter winds. 

The key is to wait until the plant has hardened off and temperatures are cold. Do not put rose protection in place until soil has frozen or night temperatures are consistently dropping into the 20s at night.

Winter protection methods with mulch, include the following. 

• Encircle the rose with a chicken wire cage staked to hold it in place, then fill the cage with coarse leaves.
• Or, to protect the plant's crown and graft union, mound 8-inches of soil around the base. Use a well-drained soil for this purpose rather than one high in clay. After mounding, moisten the soil mound. After the soil is frozen, apply coarse mulch.

Spring Pruning
The majority of rose pruning should be done in April, right before or as new growth begins. Prune out any brown or black winter killed wood and shape the plants as needed. 

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10. Perennial garden clean upPros and cons of a spick & span fall landscape 

Fall sanitation or clean-up is beginning to be frowned upon due to pollinator conservation, winter interest and even drought concerns. Alternatively, it is promoted as a management practice in the landscape to help reduce overwintering pathogens and some insects. And some gardeners prefer a tidy winter landscape, thoroughly removing all dead plant material in the fall.

What is the best recommendation for clients?
There are good reasons for removing the tops of some plants after they are killed by a fall freeze; but equally good reasons for leaving the tops of some plants until spring. The trend is to leave the tops whenever possible. The ideal situation may be to do a little of both depending on the type of plant and other factors. Inform clientele of the pros and cons before they make the decision for their landscape.

Plant tops left until spring provide the following benefits:

• Catch snow to increase soil moisture as snow melts. After a dry year or drought, this would be especially important.
• Catch and trap plant debris, like leaves, which act as a mulch to protect plant crowns and roots from winter extremes.
• Provide nesting sites for pollinators. About 30% of native bees nest inside hollow plant stems over winter and emerge the next growing season.
• Provide seeds and protection for some overwintering birds.
• Avoids moisture reaching plant crowns through hollow cut stems which can lead to crown rots or freeze/thaw damage. This is a known problem for Chrysanthemum, Buddleia (butterfly bush) and Caryopteris (blue mist spirea).
• Provide winter interest in the landscape such as the tops of ornamental grasses.

When to Remove Plant Debris
Plant tops should be removed in the fall in situations where the plant material had many insects or diseases. Leaving the plant material can reduce the overwintering sites for these plant problems. Plants that have common disease issues, like peonies, are best cut back each fall. Other plants can be left most years and only cut back if they had a pest issue that season.

Plants are also removed from landscapes where clients prefer a cleaner appearance to their landscape, these clients prefer a tidy appearance. If removed for a cleaner landscape, opt to cut plants back by leaving at least 8-24 inches of stem to trap snow and leaf debris, and to minimize removal of pollinator nesting sites.

Plants are removed in cases to reduce the fire risk during an open, dry winter if ornamental grasses are planted right next to a building. With all the wildfires lately, it is best to be proactive and maintain a fire-ready landscape.

Because native bee emergence from hollow stems occurs throughout the growing season, the stems of perennials should not be cut back to the crown in spring. This ensures pollinator nesting sites are not destroyed. Pruning to vary the length of remaining stalks from 8-24 inches will give emerging pollinators a fighting chance to survive. By early summer, emerging new growth will hide the dead stalks.

If plant tops are to be cut back in fall, encourage clients to wait until after a hard freeze. If foliage is green, photosynthesis is taking place and the plant is storing carbohydrates in roots and the crown for next season’s growth. In some instances, there is no ideal situation but to do some pruning in the fall and some in the spring. While there may be mitigating factors, where feasible, the recommendation is to leave the tops in place for winter.

Fire Smart Landscaping, Nebraska Extension Water.unl.edu

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

If you have a pesticide applicators license which expired in April 2025 or you need to get a new license, testing options are listed below.

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.)

2025 Commercial/non-commercial training is held from January through April. Training schedules will be available soon at https://pested.unl.edu/. Help your employees be successful at getting a license by purchasing study materials. 

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

• TBA | Nebraska Extension Crop Production Clinics - 00 general standards, 01 ag plant, demonstration/research
• Jan. 7-9 | Nebraska Turf Conference - 00 general standards, 04 turf & ornamental 
• Feb. 19-21 | Nebraska State Pest Control Association Conference
• Feb. 24-26 | Nebraska Aviation Trades Association Convention

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12. 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.