ProHort Update for May 2025

1. Fire Smart Landscapes

Wildfires have been headline news not only in Nebraska but across the country. It’s comfortable to think devastating wildfire can’t happen in your area, but it’s better to be aware of the possibility and be prepared. Learn the aspects of Fire Smart Landscaping including creating a defensible space, planning for a fire event, and management of the surrounding landscapes to decrease potential fire damage.

Creating a Defensible Space Three factors determine wildfire behavior: fuels, weather, and topography. Fuel is the only one that humans can impact. Utilizing a defensible space can help to decrease the fuel load and potential for fire spread. 

There are three zones to a defensible space. 

Zone 0: The Ember Resistant Zone: 0-5 feet from the house. The objective of this zone is to create the most fire-resistant zone in the area immediately surrounding the home or structure to avoid ignition from blowing embers. The greatest hazard for this zone is plants against the house and near doors and windows. The recommendation for plants used in this zone are low growing, non-woody, herbaceous plants that are 18” tall or less. The plants should be planted sparsely with plenty of space between plantings. If mulches or walkways are used in this zone, only non-combustible materials are recommended, like concrete, brick pavers or gravel. Some of the aspects to avoid in this zone include climbing plants, branches within 10’ of chimney, litter in roof gutters, combustible items under the deck, combustible containers, mulch, fencing, furniture, firewood, combustible landscape items attached to the house like fences, arbors, trellises.

Zone 1: The Lean, Clean, and Green Zone: 5-30 feet from the house. The objective of this zone is to reduce the heat and movement of flame by creating a ‘lean and clean’ environment. Plants used in this zone should be low growing and well irrigated. Also allow for ample spacing between plants. Non-combustible materials should still be utilized for walkways. Organic mulches can be used in this zone if they are broken up and not a continuous mulch bed. Firewood, lumber, and other flammable items should be moved out of zone 1. Management of plant material is critical in this zone. Dead plant material and overgrown plants should be removed routinely. 

Zone 2: The Reduce Fuel Zone: 30-100 feet from the house to the property line. The objective of this zone is to decrease the energy and speed of the fire by eliminating continuous, dense vegetation both vertically and horizontally. This zone is often a transition zone between managed and outer fringe areas of the landscape. In this zone, plants may not need to be irrigated once established. Wood mulch can be used in larger expanses in this zone. Depending on the location, collaborating with neighbors would be a good idea. Woodpiles and lumber, gasoline generators, and propane tanks should be kept at least 30’ away from any structure and 10’ from plants.

Fire Smart Plant Selection: All plants burn, but some have traits that make them more flammable than others. High oil or resin content, low moisture content, tall growth, open growth form, fine twiggy stems and high-water needs all contribute to an increase in the plant’s flammability. Plants with low oil or resin content, high moisture content, compact growth form, green stems, drought tolerant, or plants that contain soap, latex or pectin have lower flammability.  Select plant material that is the right plant for the right place and that matches the landscape aesthetic. It is more important to consider where a plant is placed and how it is managed.

Management of a Fire Smart Landscape: The objective of managing a fire smart landscape is to reduce the amount of fuel. Before each fire season, the property needs to be reevaluated. Dead or dried plants, branches, and leaves need to be removed. Combustible plant debris on and under decks needs to be removed. Equipment needs to be used properly to avoid sparks, especially when conditions are dry. Routinely remove and dispose of overgrown plant material from the landscape.

Creating and maintaining a defensible space, following fire smart guidelines for plant spacing and selection and properly managing the landscape can all help to decrease the potential for a fire to spread through the landscape. For more resources go to https://go.unl.edu/firesmartlandscapes. With a few small changes your landscape can be fire ready and you can be more prepared.

Top

2. April 29th growing degree days (GDD)

Top

3. Pest update

For a more complete list, visit Michigan State University GGD of Landscape Insects or GGD of Conifer Insects.

Top

4. Arborvitaes. Why are some dying?, The Ohio State University

The number of arborvitae in the landscape that are showing stress symptoms has increased significantly in recent months.  Like many diagnostic situations, the cause(s) are many, overlapping and sometimes not well understood.  They range from lack of consistent watering, excessive winter winds, poorly drained/compacted soils, spider mites, needle blights and bagworms.  Monitoring soil moisture and keeping it moist, not soggy or dry from planting throughout the growing season is crucial to success.   

Top

5. Helping Trees Avoid Storm Damage Likelihood

Shade trees are long lived plants providing numerous environmental, economic and social benefits. Unfortunately, storm damage is becoming a common occurrence. While all storm damage cannot be prevented, there are steps to take to help reduce a trees likelihood of sustaining storm damage. Using the following practices and actively educating clients on these will help trees become community assets, not liabilities. 

• Select slower growing trees with stronger wood. Avoid fast growing trees that tend to have weak, brittle wood. These include silver, red and Freeman maples, poplar, willow, mulberry, tree-of-heaven and Siberian elm. 
• Plant at the correct depth. There is a pandemic of too deep planting leading to slower growth, stressed trees, girdling roots, and increased likelihood of wind throw in storms. Educate staff and clientele on correct planting depth. Wait to dig the hole until the first lateral root or the trunk flare is located. Soil may need to be scraped off the top of the root ball to find this. Only then dig the hole just deep enough so the root ball is set on firm, undisturbed soil and the first lateral root remains just below, at, or above the soil line after backfilling the hole. 
• Dig planting holes one to two times wider than the root ball to loosen surrounding soil and encourage root growth. Tree roots can grow outward up to two to three times a trees height with the majority in the upper 24 inches. It is this wide anchor of roots that supports trees during wind storms. 
• Avoid girdling roots by planting smaller trees and trees not grown in smooth, hard sided containers. Inspect root systems before purchasing and deal with encircling roots if needed.
• Only stake trees if needed, low on the trunk, not too tight and for one year only, in most cases. A tree develops strength and ability to bend in the wind by being able to move with wind as it grows. Trunk movement also stimulates root growth. Trees staked too tight and for too long are at greater risk of snapping in wind storms just above where staked. 
• Avoid wounding trees such as with lawn mowers, weed trimmers and improper pruning. Wounds are openings for decay organisms to infect and cause decay. Use a 4 to 6-foot diameter ring of organic mulch around the tree base to protect trunks. Keep this mulch ring at a uniform 2-3 inch depth.
• Co-dominant leaders or double trunks are major structural weaknesses in trees, especially as they grow larger and develop included bark. At planting or soon after, remove one of the double leaders. To help a tree develop strong structure as it grows over the next 10 to 15 years, hire an arborist with knowledge of structural pruning to check the tree every two to three years for pruning needs. Structural issues are easier to prevent than correct.

Top

6. Diplodia Tip Blight in Austrian Pine (Pinus nigra)

Diplodia tip blight is a significant fungal disease affecting Austrian pine, particularly in stressed or mature trees. The pathogen Diplodia sapinea infects newly emerging shoots during bud swell in spring, leading to distorted growth and shoot dieback. Infected shoots often develop short, straw-colored needles at the tips, which become especially noticeable during summer heat and drought stress. 

A key diagnostic feature is the presence of black fungal fruiting bodies (pycnidia) that produce conidia on second-year cones, needles, and twigs. These structures are often visible with a hand lens and are an important tool for confirming the disease in the field. 

Management relies heavily on prevention. Fungicide applications containing the active ingredients propiconazole, thiophanate-methyl, or azoxystrobin can help protect developing shoots. Applications should be timed to coincide with bud swell and repeated as directed on the label to ensure continued protection and reduce the risk of reinfection. Always follow label instructions for application rates and intervals. 

If diagnostic confirmation is needed, samples can be submitted to the UNL Plant & Pest Diagnostic Clinic. Visit plantpathology.unl.edu/extension-outreach/plant-pest-diagnostic-clinic for submission guidelines and additional information. 

Top

7. Spruce Needle Cast

Rhizosphaera needle cast is an increasingly common fungal disease affecting spruce trees. Symptoms typically begin in the lower canopy, where second-year needles turn purplish or straw brown in the spring before dying. Over time, the disease progresses upward through the tree, and repeated infections can lead to significant branch dieback. 

Colorado blue spruce (Picea pungens) is especially susceptible, though Black Hills spruce (P. glauca) and Norway spruce (P. abies) may also be affected. The fungus overwinters on recently killed but still attached needles, enabling it to re-infect the tree year after year. 

Management begins in spring as new needles start to expand. Fungicides containing chlorothalonil or mancozeb can protect emerging needles from infection. It’s important to note that these treatments are preventive—they will not cure already infected needles. As a result, it may appear the fungicide is ineffective, when in fact it's preventing new infections rather than reversing existing damage. 

If you suspect Rhizosphaera needle cast and would like confirmation, samples can be submitted to the University of Nebraska–Lincoln Plant & Pest Diagnostic Clinic. For submission details, visit: https://plantpathology.unl.edu/extension-outreach/plant-pest-diagnostic-clinic/ 

Top

8. Winter Desiccation in Evergreens

This winter was a tough season for evergreen conifers, and many homeowners are noticing the effects of winter desiccation now. Some may confuse or assume the signs with a fungal or other disease, but there is no spray for this. There are varying degrees of winter desiccation, but the common complaint is that "the tree looked fine all winter and then turned brown this spring." It does seem that way, because conifers — even though they are evergreen — do slow down their photosynthesis in the winter, delaying the effects of a tough winter until spring when photosynthesis speeds back up. Winters in Nebraska also tend to be droughty for trees; not only is soil moisture frozen for much of winter, but cold air is dry and wicks away moisture from tree leaves. This winter was especially dry as relatively little precipitation fell. All of this combined to be too much for many young conifer trees that responded by turning brown this spring. Unfortunately, once a tree is entirely brown, it is unlikely to recover. But don't give up hope if only some of the needles are off-color! The tree can push through new growth. Up the watering schedule to seasonal norms and do corrective pruning before bud break; otherwise, just watch and wait to see how tree responds. Next fall, though, check into anti-desiccant products and winter watering strategies to guard against another surprise browning of conifers next spring: https://water.unl.edu/article/lawns-gardens-landscapes/tree-care-during-winter/

Top

9. Commercial/Non-commercial pesticide applicators

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 and 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 are available at https://pested.unl.edu/. Help your employees be successful at getting a license by purchasing study materials. 

Top

10. Digital Diagnostic Network - Need help with diagnostics?

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.

Top

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 Nebraskas Extension. Nor does it imply discrimination against other similar products.