ProHort Update for September 2026

1. Some Trees are Big Weeds

What’s the definition of a weed?  The most common one is “a plant growing out of place in the landscape”.   The most familiar weed in a landscape is a dandelion in the lawn, but just about any plant can be a weed if it’s inappropriately located or in poor condition.   So, if a tree is too close to the foundation of a house, encroaching on the driveway, casting too much shade and competing with an important part of the lawn or continually infested or infected with various pests, perhaps it’s time for removal.  Here’s how to go through a systematic approach to determining if a tree is a boon or bane.

Purpose

Determining if a particular tree is to be considered a weed begins with recalling its purpose.  Is it to produce shade for a patio?  To frame the house?  For fall color/spring blooms?  Or is it the all-too-often “front yard ornament”…a lollipop that is planted when the house was built?  Knowing the answer to this basic question really helps in that it’s the foundation that all future maintenance or new plantings are based on. 

Once the original purpose is known, it should be re-examined to determine if it is still valid.  For example, if the tree’s purpose was for shade on the deck and the deck is no longer there, or the current residents never go out on the deck due to being faced with too many mosquitos or a lack of interest, then perhaps the tree is no longer needed, or at least not worthy of its presence in light of the problems that it may be causing (moss, surface roots, thin turf, disruption of the turf sprinkler pattern, etc.).  If, however, the owners of the property really enjoy the deck and use it frequently, then it should be viewed as an asset, not a detriment.

Location

Next, consider the location.  What part of the landscape is it sited in?  Commonly, when planted by do it yourselfer’s, the location is an afterthought.  The result is trees under power lines, next to the foundation, adjacent to a vegetable garden or driveway and maybe the worst of all, at least visually, smack dab in the middle of the front yard and in front of the front door.

One of the ways to ensure proper placement is to embrace the concept of Separation of Turf and Ornamentals.  With the guiding influence of purpose in mind, trees can be placed in the landscape either in groups or singly, without the co-location of turfgrass.  The key to success is starting or a revisit to a bubble diagram, where each plant type (vegetables, fruits, turf, shrubs, trees, groundcovers, perennials) are designated as planting masses in relation to each other.  This approach limits problems with competition, excessive maintenance needs, shade and pests.

Size

The current and future size of a tree is an important consideration.  Again, a couple of questions help with classifying a specimen as a weed or valued plant.  Is it too big for the location?  Too small to do the job/accomplish the purpose?  Commonly, the older neighborhoods of a city can take on the well-deserved reputation of “shade havens”, where the trees are large and the tree canopy is strong.  This is a good thing in general, with the benefits of atmospheric cooling and carbon dioxide sequestration being realized; however, just the very nature of the size of the specimens carry with them potential for being too large for the landscape.

When a tree is too large or too dense, we often see problems with excessive moss growth on roofs, droppage of small twigs and branches, high costs for tree maintenance and the lack of the option to grow sun-loving plants such as coneflowers, sedums, lilac, roses and yarrow underneath.  As well, in heavily treed sites, sun adapted turf species such as Bermuda grass, zoysia grass, buffalo grass and Kentucky bluegrass simply won’t thrive, let alone survive.  Even shade tolerant turfs such as centipede grass and tall fescue can struggle if they receive less than 3 hours of sun each day.

The flip side of the size issue is equally as important.  If the purpose is to frame the house, newly planted deciduous trees simply aren’t going to fit the bill, especially if the property owners are impatient or if slow growing species such as paperbark maple or ginkgo were planted.    

Condition of Tree

The health and vigor of the tree in question is a crucial step in the process of whether a particular specimen is a weed.  The list of possible defects is a long one (decay, co-dominant leaders, cracks, basal/bole issues, previously cabled operations, leaning, root detachment from soil, stem girdling roots, deeply planted, hanging branches, dead wood and heavy duty/probably forever maladies such as chlorosis and emerald ash borers).  In addition to the actual flaw, the consideration of “target” or what the tree could fall on if it failed is important.  People and valued property are the most common targets.  If the site is one where frequent human activity takes place such as a day care center, school or home residence, and/or the structure underneath or nearby the tree (new fence, house, neighbor’s pool) is highly valued, then the need for immediate action increases dramatically.

 An thorough and honest assessment for each specimen should be conducted to determine if any of these concerns are present, and if so, to what degree or extent.  For most lawn care operators and landscape contractors, the best approach is to identify each potential problem and then consult with an ISA Certified Arborist to validate the concern and assist with communicating the importance of action to the property owner.  Finding one in your area is easy; simply visit https://www.treesaregood.org/findanarborist.

Post Evaluation Options

Once an expert opinion has been provided, a decision for appropriate tree care must be made.  This usually falls into one of four categories – monitoring aka “watch and wait”, pruning, pest control and removal.  

• Monitoring - Best suited for issues that are just starting or where no target is present.  
• Pruning – Good choice where only one tree in a specific area is being treated, for species that close wounds readily and for specimens that are well sited and in good overall health.  
• Pest Control – It’s wise to choose this option for diseases and insects that can be controlled in a 1-3 year timeframe, then put on a regular inspection regimen to detect re-infestation/reinfection.
• Removal – When the risks and concerns greatly outweigh the rewards and benefits, it’s time to remove a tree.  Age, condition and location greatly influence this choice of action.

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2. August 31st 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. Oak Wilt

Oak wilt is a potentially devastating fungal pathogen that will infect all species of oaks (Quercus sp.). The red-black oak group is most susceptible and includes: (northern and southern) red, (northern) pin, black, blackjack, scarlet, shingle, and shumard. The red-black oak groups is easily identified because they have the bristle/pointed leaf tips. White oak group is also susceptible but to a lesser degree and the symptom look different. The white oak group has the rounded/lobed leaf ends.

A sample was recently brought into Extension from a red oak tree in Omaha. An arborist reached out concerned about possible oak wilt. It was sent to the Nebraska Forest Service for help. They collected samples sent them to Iowa State and the tree tested positive for the pathogen.

Oak wilt is vectored by bark and sap/picnic beetles. It can also move through root grafts. When doing work on any oak tree pruning should be done between Halloween up to Valentine's Day (maybe St. Patrick's Day) to avoid times when the beetles are active. Different literature suggests different time frames. However, humans like set dates. If pruning needs to be done outside those dates the arborist should use a pruning sealant after making the cut.

Further readings:

USDA Forest Service

Iowa State University

Ohio State University

University of Minnesota

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5. What to do with Fall Leaves, University of Illinois

As we move into the fall, leaves will be falling from our trees. These leaves should not be left on the turf over the winter months to avoid problems with snow mold that can develop under thick mats of leaves, but are there other uses for the leaves? There are many great ways to utilize these leaves rather than just throwing them in the garbage, the University of Illinois describes many great uses for those leaves to suggest to your clientele this fall.  

Full Article

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6. Aerify, Aerify, Aerify

Now is a great time to aerify your customer’s lawns.  Follow up with 5 pounds of turf type tall fescue or 2 pounds of Kentucky bluegrass per 1,000 sq. ft and an instruction to keep the soil moist, not soggy or dry.

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7. Fall Lawn Fertilizer

Early September is a great time to apply a mix of slow and quick release N to lawns to help them recover from summer stressors.

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8. Fall Broadleaf Weed Control in Turf

Mid September starts the optimal time for broadleaf weed control.  Scout for violets, clover, dandelions, wild strawberries and plantain.  Read and follow all label instructions.

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9. Fall Planting

If you find “gaps and holes” in your clients landscapes, suggest a shrub that is suited with Right Plant, Right Place in mind.  Consider sun/shade, wind exposure and soil draingage when choosing.

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10. Wait to Prune Trees

Avoid pruning for most trees unless correcting storm damage and broken or crossing/rubbing limbs. Wait until after full dormancy to prune trees for best success. If pruned this late in the summer/early fall, it can cause new growth to start that wouldn't be fully hardened off when winter sets in. This late in the season it is best to wait until trees are fully dormant, in November-March to do extensive pruning. 

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11. Commercial/Non-commercial pesticide applicators

If you have a pesticide applicators license which expired in April 2026 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.)

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.

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12. 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.