ProHort Update for September 2025

1. Emerald Ash Borer: Continued Threat Requires Ongoing Management 

Since its initial detection in the Omaha metro area in 2016, the emerald ash borer (EAB), Agrilus planipennis, has continued to advance across Nebraska, causing extensive mortality among ash trees (Fraxinus spp.). This non-native wood-boring beetle infests all ash species and cultivars and remains a serious concern for urban forestry and managed landscapes statewide.

EAB adults typically emerge in early summer, laying eggs on the bark surface. After hatching, the larvae tunnel beneath the bark and feed on the phloem and outer xylem, disrupting the tree's vascular system. Early signs of infestation include canopy thinning in the upper crown, vertical bark splitting, and increased woodpecker activity. As the infestation progresses, epicormic shoots may develop along the trunk, and dieback becomes more pronounced.

Once EAB becomes established in an area, it persists. Unprotected ash trees will continue to decline and ultimately die. Preventive systemic insecticide treatments remain the most effective management strategy and should be initiated before visible symptoms develop. Delayed treatment significantly reduces efficacy and increases the risk of failure.

Dead ash trees pose significant safety hazards due to rapid structural degradation and unpredictable limb failure, particularly under storm or wind stress. Prompt removal of non-treated, declining ash trees is recommended to mitigate risk in both residential and public spaces.

Although EAB’s primary host is ash, it has also been documented—albeit infrequently—infesting white fringetree (Chionanthus virginicus) and cultivated olive (Olea europaea), indicating a potential for a broader host range under certain conditions.

Treatment decisions should prioritize trees of high landscape or ecological value. Emamectin benzoate, delivered via trunk injection, continues to be the most reliable active ingredient for long-term protection, typically providing two to three years of control. Applications should be made during the active growing season, ideally between May and September, depending on local conditions.

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2. August 26th growing degree days (GDD)

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3. Pest update

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

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4. Investigating Tree-Caused Power Outages in Virginia, West Virginia University

One of the most important endeavors that green industry professionals can engage in is to regularly assess tree health and stability to prevent loss of life and damage to structures.  In some cases, there are definite tell-tale symptoms and signs of impending risk, and unfortunately, in others, there aren’t.  What’s more, in terms of learning and adding to an arborist’s experience and knowledge base, examining the interior heartwood, bole, branch attachments and other tissues after a branch or whole tree failure is vital to help solidify and learn from these limitations and consequences.   

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5. Blooms for All Seasons

Somewhat related to having diversity in the landscape, having native plants that bloom at different parts of the season is important to maintaining a functional ecosystem that can have multiple benefits for a landscape.

Early spring blooms provide nectar resources for emerging adults needing energy to get started laying eggs for the season’s new generations. Pollen from these flowers helps feed those new eggs – some native bees are done laying eggs before spring even ends! Summer blooms sustain adult insects and other bugs with nectar and provide plenty of pollen for eggs and developing larvae. Fall blooms provide these resources as the season nears the end and the last eggs are being laid and adults are preparing for overwintering.

Supporting habitat for adults means you can support a local population of beneficial pollinators and predatory bugs. Just like a diverse landscape, diverse bugs can minimize landscape-wide or plant-fatal pest issues. Common examples include adult and larval lady beetles and lacewings, but spiders, assassin bugs, adult wasps and parasitoid wasps are all present in a healthy landscape. The samurai wasp parasitizes eggs of brown marmorated stink bug, and adult wasps use caterpillars as baby food.

Landscapes with a lot of evergreens and ornamental grasses or those with beds that get planted up with only annuals each year won’t have the same beneficial activity as one that has blooms from the start of the season through the first freeze. There is plenty of space for annual beds and integration with annuals, but benefits tend to increase with native plants that support native bugs.

Some commonly available plants for…

• Spring
  • Columbine (Aquilegia spp.)
  • Anemone (Anemone canadensis)
  • Beardtongue (Penstemon spp.)
  • Phlox (Phlox spp.)
  • Bluestar (Amsonia spp.)
• Summer
  • Bee balm (Monarda spp.)
  • Butterfly milkweed (Asclepias tuberosa)
  • Ratibida spp.
  • Purple poppy mallow (Callirhoe involucrata)
  • Blazing star (Liatris spp.)
• Fall
  • Anise hyssop (Agastache foeniculum)
  • Helenium spp.
  • Goldenrod (Solidago spp.)
  • Aster (Symphyotrichum spp.)

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6. Welcome New Nebraska Extension Experts

We have had two new experts join the Nebraska Extension Horticulture, Landscapes, and Environmental Systems Team over the past year that we would like to introduce to you. 

Julia Cambridge is the Extension Assistant at the Douglas-Sarpy County Offices in Omaha. 
"I come from a background in landscape design and have spent time working in nurseries, managing landscapes, and designing annual displays. I’ve always loved the creative side of plants—how they move, change, and surprise us throughout the seasons—and I like to think I bring that appreciation of the landscape into my work with Extension. Since stepping into this role, I’ve become more of a horticulture generalist, helping people with everything from pest management to plant selection. I’m especially interested in underused and overlooked plant species, encouraging more sustainable and thoughtful choices, and helping folks notice the incredible details hiding in plain sight. Over the past year, I’ve contributed to a garden column in a local newspaper, taught several classes, and am learning the ropes of co-coordinating our Master Gardener program, where I get to support over 300 amazing volunteers." 

Rachel Anderson is the Extension Educator in Lancaster County in Lincoln
Rachel Anderson recently joined the Lancaster County Extension office as a Horticulture, Landscape, and Environmental Systems Extension Educator and will serve Lancaster, York, Seward, Otoe, and Cass Counties. Her focus will be working with residents and green industry professionals to find answers to their lawn, tree, and garden questions. Her areas of interest include landscape care, plant selection, waterwise gardening, and building healthy soil.

Rachel grew up in Omaha, Nebraska and practiced as a licensed landscape architect before joining Extension. She studied Horticulture at the University of Nebraska and went on to receive a Master of Landscape Architecture from Iowa State University. Rachel has a diverse background working with plants and people across the Midwest at design studios, garden centers, nurseries and greenhouses, arboreta, state and federal agencies, and in higher education.

Rachel’s favorite tree is the eastern cottonwood—what’s yours? Send Rachel a note at 402-441-7180 or randerson28@unl.edu.

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7. Fall Lawn Fertilizer

On older lawns (20-25 or more years), the first fall application should be made very soon if it has not yet been done. A fertilizer with a slow release nitrogen source can be used. Older lawns may only need one fertilizer application in the fall, depending on the overall health and green color by mid-October. On younger lawns, two fertilizer applications during fall are recommended; one in late August/ early September and one in mid-October. For the first one, use a slow release nitrogen source. For the last one, use a fast release nitrogen source. Applications much past November 1 are less efficient because plant uptake is low. This causes nutrients to leach away during winter or linger in soil until spring; resulting in too early succulent growth.  A specific winterizer-type fertilizer is not needed, but have homeowners buy a fertilizer with their particular fertilizer spreader settings listed on the label.

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8. Fall Tree Planting

Fall is a great time to plant a tree! For tree health and longevity, proper planting is vital. Start by removing any burlap and wire that may be around the soil ball or take the tree out of the pot it was bought in. Make the hole no deeper than the root ball and 2-3 times as wide as the root ball. When determining depth, dig around on the root ball for the roots, the first lateral roots should be just below the soil surface. If staking is used, only leave the stakes on the tree for one growing season and leave the staking material loose to allow the tree to move in wind. Use a wide material around the tree for the staking, something made of rubber, denim, burlap, or other fabric, avoid wire. Be sure to make a mulch ring to the dripline and beyond. The mulch should only be 2-4 inches deep and level across the ring. If a tree wrap is used, be sure to remove it in the spring. Tree wraps should not be left on through the growing season. 

How to Plant a Tree, Nebraska Forest Service - For more information on Proper Tree Planting and Care after planting

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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 was 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. 

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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.

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