ProHort Update - October 2024

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Nebraska's drought status, 9/26/24 Map updated weekly.

1. Emerald ash borer updateLocation update; understanding the tree "death curve"

Emerald ash borer (EAB) has now been in Nebraska since 2016. The first confirmation was June 2016 in Omaha, followed by additional confirmation as follows.

• 2016 - Pulaski Park Omaha, Zorinsky Lake and Greenwood, NE. Sarpy county
• 2018 - Mahoney State Park and Lincoln, NE. Cass and Otoe counties. Evidence of infestations found in Fremont, NE late in the year, but no living insects could be found for confirmation. 
• 2019 - Fremont, NE and Dodge county
• 2020- Kearney, NE. Seward and Washington counties
• 2021 - Hall and Platte counties
• 2023 - Lincoln and Nemaha counties

The state's oldest areas of infestation have been active for 6-8 years and it's becoming easy to see dying untreated trees. In areas where the insects have been present for just a fewer years - such as Hall, Lincoln, Nemaha and Platte counites - effects of EAB activity are still largely unseen, but that doesn't mean it's not coming. The graph above shows the gradual increase in tree mortality as EAB populations grow in each new area it invades, AKA the tree death curve.

White and green ash, Fraxinus americana and F. pennsylvanica, are both highly susceptible to EAB and even healthy vigorous trees are easily invaded. The first symptom to look for - dieback of smaller branches, usually in the top 1/3 of the tree. As the infestation progresses, larger branches lower in the canopy die too.

Drought in 2022 and 2023 has been hard on Nebraska trees, resulting in increased stress and making them more susceptible by our native borers. For our ash trees, this means attack by redheaded and banded ash borers, and ash-lilac borer.  It certainly is possible for trees to be declining from drought, as well as native borer attack, and/or EAB at the same time.

More information: EAB Tree Care Professionals, Nebraska Forest Service

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2. September 30th growing degree days (GGD)

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4. Influence of Phosphorous in Starter Fertilizer on the Establishment of Tall FescueStudy showed no difference between Nitrogen alone, vs. Nitrogen + Phosporus

Phosphorus (P)-containing starter fertilizers are often recommended for establishing new turf, regardless of P levels indicated by the soil test. However, few field studies have been conducted to determine the effects of P in starter fertilizer on the rate of turf establishment. The primary objective of this study was to determine if P in starter fertilizer enhances tall fescue groundcover and growth during establishment on silt loam soil. This 2-year field study was conducted during fall on silt loam soil tilled with a rototiller or core-aerated and vertically sliced. At the conclusion of the experiment, comparisons indicated no differences between the 49 kg·ha⁻¹ N treatment and 49 kg·ha⁻¹ N + P treatments regarding visual and digital groundcover.

Influence of Phosphorous in Starter Fertilizer on the Establishment of Tall Fescue, HortScience

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5. Soil test to determine phosphorus needs of turfgrassPhosphorus is an essential nutrient for plant growth, but use of excess phosphorus is linked to declining water quality of ponds, lakes and streams.

Phosphorus is an essential nutrient all plants need to grow and survive. Several environmental studies, however, have documented excess phosphorus and nitrogen are partly responsible for declining surface water quality. These nutrients have been linked to eutrophication, a biological process in ponds, lakes, and streams where excessive seasonal algal growth occurs. These blooms can make the water smell and taste bad and decrease its recreational value. In severe cases, algae deplete oxygen levels, which may kill fish.

Phosphorous tends to bind to soil and is therefore less mobile in soil than nitrogen. If a lawn has received regular fertilization containing phosphorous, there is a good chance phosphorous may not be needed. Soil testing is the best way to determine phosphorous needs of turfgrass. In mature lawns, unless a soil test indicates the turf needs supplemental phosphorus, it is best to apply lawn maintenance fertilizers. These products contain low (such as < 3%) phosphate levels. An example of a low-phosphate fertilizer analysis is 27-3-10. If a soil test indicates sufficient to high phosphorus levels, which is commonly seen on Nebraska soil tests from turf, then a zero phosphorus analysis such as 27-0-10 is appropriate.

When applying fertilizers, do not apply unneeded nutrients. Do not apply to drought stressed, dormant or frozen turf or run-off of nutrients is a high risk. Keep fertilizer on the turf. If granules, or grass clippings, land on hard surfaces like sidewalks and driveways, sweep or blow them onto the turf, not just to the turf's edge.

For more in-depth information, see Facts About Phosphorous and Lawns from Purdue Extension. 

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6. Avoid pruning spring flowering shrubsSpring's flower buds have already formed and will be removed by fall pruning

Shrubs that bloom in spring have already developed their flower buds during this past summer. For this reason, general management pruning, such as thinning or heading back, is best done in spring within a few weeks following bloom to avoid removing flower buds and reducing or preventing spring blooms.

If a shrub needs renovation pruning, such as cutting it near to ground level, this is best done while it is dormant in late winter or early spring. The shrub will not bloom that year but blooming will return in future springs.

Common spring blooming shrubs include lilac, forsythia, some Spirea like Bridal wreath, Weigela, some dogwoods, oakleaf and bigleaf Hydrangea, mockorange and spring blooming Viburnums.

How and When to Prune Flowering Shrubs, Penn State Extension

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7. Utilizing tree leavesMow into turf or use as mulch in landscapes and gardens

Many professional turf managers mulch fallen tree leaves by mowing them into the turf. Mulch mowing can be easier than raking and returns complex organic matter and nutrients to the soil. According to research at Kansas State Extension, fallen leaves to a depth of 6-inches or more can be chopped by the mower and returned to the soil without causing damage, if done properly.

However, it is best to mow a thin layer, 1- to 2-inches or so of leaves, each time they accumulate on the turf. Do not wait until six inches have piled up and then mow them all at once. This process of frequent mowing can continue as long as the shredded leaves do not start to pile up on top of the turf and shade out the grass.

Ground tree leaves will not increase thatch, which is mainly a layer of dead roots and rhizomes. Tree leaves can fall fast and quickly pile over the lawn. If needed, rake and bag excess leaves, then compost them or use as garden mulch.

Do not blow leaves into the street or onto other concrete surfaces. Leaves leach nutrients which pollute waterways or can be carried to surface water through storm drains where they release nutrients leading to algal problems.

Mulch Mowing Fall Leaves, K-State Research and Extension

Leaves can also be utilized as mulch in landscapes and garden spaces. Winter mulch provides extra protection for sensitive plants or those prone to frost heaving. Apply mulch up to 4-6 inches deep. For many years Extension recommended not applying mulch in early fall. The theory originated from the knowledge that mulch moderates large temperature swings in the soil, thus it was predicted early fall mulch applications would keep soil warm longer and delay development of winter hardiness in landscape plants. However, research has shown this theory is not true - mulch does not delay development of winter hardiness. Mulch provides several benefits to landscape plants during winter, most notably holding moisture in the soil and moderating soil from extreme temperature swings which could kill roots. But landscape managers do not have to wait until late fall or early winter to refresh landscape mulch.

Finally, leaves can be used to cover a vegetable garden space through the winter to ensure good topsoil doesn't blow off site during the winter and adds nutrients into the soil as the leaves breakdown for improved garden produce. Or they can be incorporated during fall bed preparation as a soil amendment.  

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8. Natural needle drop in evergreensYellowing of older, inner needles

Evergreen conifers do not keep their needles forever. Older needles on the interior of trees are shed each fall after they turn yellow, brown or reddish tan in color. This natural process is usually subtle and goes unnoticed, but some years it is very evident, especially in white pine trees. However, natural needle drop is a natural process and is not harmful to trees. The fallen needles will also not make the soil too acid. It will provide a good natural mulch around the trees.

Fall needle drop is a natural condition and is not a sign of disease or insect infestation, however, any factor that increases stress on evergreen trees will intensify the autumn needle drop causing more needles to drop. Severely stressed trees, or those with underlying factors reducing their health and vigor long term, will lose more needles and may develop a thin canopy of foliage. Stress factors include drought, herbicide injury, root damage and insect or disease damage.

Natural needle drop occurs only on the inner needles; if entire branches or needles at the tips of branches are dying, then something else is happening. A sample of the affected branches should be submitted to your local Cooperative Extension office for diagnosis. A close inspection of any brown foliage should also be done to eliminate the presence of fungal leaf spots, spider mites, aphids or other potential pest problems.

• Pine trees hold needles for 2-5 or more years, depending on the species.

• Spruce trees generally hold needles longer than pine trees, approximately 5-7 years, which serves to hide the browning inner needles on very health, full trees.
• Firs and Douglas-fir needles last 3-4 years.
• Yew needles last about 3 years and tend to yellow and drop in spring rather than fall.
• Branchlets of Arborvitae turn brown and drop off, rather than individual needles. The brown branchlets remain on the tree for some time before falling.

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9. Fall weed control and timingFall best time to control perennial, biennial and winter annual weeds

Identification of problem weeds is critical before attempting control. Annual weeds, such as crabgrass, foxtail, knotweed, oxalis and spurge, will naturally die in just a few weeks. Applying herbicide to kill them now is a waste of time and chemicals. Preemergent herbicide should be applied next spring to kill germinating summer annual weeds.

However, perennial and winter annual weeds are best controlled right now for the following reasons.

1. Winter annual weeds germinate in late summer/early fall and can be controlled with preemergent herbicide applied at that time.
2. Winter annual weeds that have already germinated now are small and easier to control than when they mature in spring.
3. Perennial broadleaf weeds are translocating stored energy (and properly applied herbicide) below ground better at this time of year than they do in summer.
4. Cooler temperatures reduce the likelihood of injuring turf or ornamental plants through herbicide volatilization and drift. 

Winter Annuals - Preemergence herbicide should be applied now for control of winter annuals like little barley, henbit and speedwell. Winter annuals are or will soon be germinating. Common landscape preemergent herbicides include bensulide (Bensumec), dithiopyr (Dimension), oxadiazon (Ronstar G), pendimethalin (Pendulum) and prodiamine (Barricade). Other management options for winter annual control include maintaining a healthy and vigorously growing lawn or landscape bed plant cover to crowd out weed invaders. A good layer of organic mulch 2-3 inches thick will also minimize weed germination.

Perennials and germinated winter annuals - Apply herbicide now and again in 4 to 5 weeks if any new growth emerges or green tissue remains. If weeds are not killed completely, weakening them with fall herbicide applications makes them more susceptible to winterkill. Weeds are killed more slowly as daytime temperatures drops. Ideally daytime temperatures should be between 65-85º when applications are made. Selective broadleaf weed control products include triclopyr, quinclorac, carfentrazone, sulfentrazone, dicamba and 2, 4-D.

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10. Minute pirate bugsTiny nuisance insects; painful, itchy bite 

These tiny bugs, 1/8-inch long, can cause painful bites that seem out of proportion with their size. They are oval to triangular in shape, flattened and black with whitish markings on the back. Normally, they are predators and feed on insect eggs and small insects. They feed by impaling their prey with their short blunt beak and sucking the juices.

Minute pirate bugs are found throughout the summer in fields, woodlands, gardens and landscapes. In the late summer, they begin the unpleasant behavior of biting humans. They do not feed on blood or inject a venom or saliva.

People differ in their response to pirate bug bites. Some people have no reaction to the bite, but others have bites that swell like a mosquito bite or turn red. Because the bite is noticeable and the pirate bug doesn't fly quickly, the victim is usually able to successfully smash the offending insect.

Preventing lace bugs and minute pirate bugs bites is not easy. Repellents are generally not 100% effective, but may repel insects somewhat. Some people have found applying baby oil or suntan oil liberally to the skin is another way to repel insects. Wearing dark clothing, long sleeves & pants may help, too. 

Minute Pirate Bugs: Little Bugs, Big Bite, Nebraska Extension

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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 2024 or you need to get a new license, commercial/noncommercial applicators have several options to recertify or get a new license.

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?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.