ProHort Update for March 2025

1. Plant roots and soil oxygen

We often recommend not to overwater, mulch too deep, add soil over established roots, or compact soil because it reduces oxygen available to plant roots. But how does a lack of soil oxygen impact plant health and growth?

The components of soil are mineral (clay, silt, sand), water, oxygen and organic matter. Oxygen enters soil from the atmosphere and is found in soil pore spaces, along with water. Soil oxygen and soil water are equally important in plant growth processes. 

Plant Uses of Soil Oxygen

During photosynthesis, plant leaves use carbon dioxide from the air along with water taken up by roots to produce sugars (glucose). Plants use sugars as fuel to function and grow. Many of these sugars are moved into and stored in roots. 

During respiration, plant roots require oxygen to be able to use glucose as fuel to take up water and nutrients. Without adequate soil oxygen, roots are limited in the amount of sugar they can burn and therefore how much water and nutrients are absorbed. Reducing a plant’s water and nutrient uptake restricts its overall growth rate and leads to stress. Weak plants are more susceptible to diseases and less tolerant of environmental stress, like heat and drought.

Soil oxygen is also critical for the health of soil macro and microorganisms like earthworms and beneficial bacteria and fungi such as mycorrhizae. These organisms play a role in soil aggregation for good soil structure which increases macropores in soil for increased soil oxygen. 

Improving Soil Health and Oxygen Content

As we move into the growing season and begin managing green spaces or guiding clients in managing their landscapes, focus on practices that improve soil health and increase soil oxygen levels. It would also be beneficial to increase understanding of the role soil oxygen plays in plant health. 

Practices that increase soil oxygen include: 

• Preventing and relieving soil compaction. Depending on the situation, this may include core aeration, tillage, radial trenching for trees planted on new construction sites, and reducing foot/equipment traffic, especially on wet soil.
• Avoiding excessive tillage of soil. While tillage initially increases soil oxygen and helps relieve compaction, excess tillage over time will break down soil structure to decrease soil macropores and lower soil oxygen. 
• Not “setting automatic irrigation systems and forgetting them”. Irrigate only when soil is becoming dry and plants need moisture. When soil it too wet or waterlogged, oxygen content is reduced as water displaces oxygen in pore spaces. 
• Using a 2- to 4- inch layer of organic mulch, like arborist wood chips, placed on bare soil. 
• Limiting the use of landscape fabrics for weed control. These limit gas exchange between soil and the atmosphere lowering oxygen levels in soil. This is increasingly true as pores in landscape fabric become clogged with sediment. 

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2. March 3rd growing degree days (GGD)

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3. Pest update

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4. Abiotic Urban Tree Stressors, PennState Extension

Trees only have so much energy to expend, especially in the spring. If they are stressed from abiotic factors including drought, late frost, extreme heat, or more, they will have to use more of their stored energy than in normal growing seasons. They also will have reduced energy production due to these stressors, which compound the effects on the tree. With inadequate water for the tree, it will shift from growth mode to survival mode, which makes the tree less able to defend itself against insect or disease pests. Trees can be stressed from many other things that can cause a similar shift in energy use and production. This includes planting site such as poor or compacted soil, like construction soil. Compacted soils from where sidewalks are added are more stress to the tree because there is poor drainage and low airflow for the roots. This will cause the roots to grow in the gravel subbase below the sidewalk because it has the best growing condition which will cause the sidewalk to lift over time. There are also many human-induced stressors that can damage the tree including improper fertilization, mulching, pruning, planting, staking, and more. These practices cause stress to the tree that can also weaken its defenses and shorten the overall life cycle.  

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5. Evaluation of Turfgrass Clippings from Mulching vs. Side Discharge Mower Operation, Applied Turfgrass Science

It has been reported that recycling lawn clippings promotes retention of plant nutrients and enhances turfgrass quality. Mower design and operation have been based on reducing clipping size to enhance filtering into the turfgrass canopy away from the surface. From a consumer's perspective, fewer clippings visible on the turfgrass surface results in a more uniform, attractive turfgrass canopy. This study was conducted to determine the effectiveness of mulching mowers to reduce clipping particle size compared with traditional side-discharge mowers. The test hypothesis was that mulching would reduce clipping size.

Outcome - The turfgrass species and mower size had a greater impact on clipping length and specific projected area (clipping surface area) than mode of mowing.

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6. Spruce spider mite

Stippling of needles becomes evident on older foliage in early spring. By early summer, infested portions turn yellow or brown and appear dried out. Dirty, fine webbing is evident. Occasionally heavily infested trees suffer severe damage. 

Monitor regularly for early damage in April. Treat infestations with vigorous sprays of an insecticidal soap or an insecticide/miticide. Thorough coverage is important, and re-treatment is often necessary. By mid summer, infestations naturally decline; do not treat.

Spruce Spider Mite, Penn State University Extension

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7. Kermes oak scale

Pale brown, hemispherical scales appear as large growths attached to leaf midribs and twigs. Mature scales are very tough and gall-like. Leaves become stressed, yellow, or withered, and honeydew secretions are evident. Infested trees can suffer serious branch dieback, but infestations are usually isolated to specific trees and are rarely widespread.

This scale produces a profuse amount of honeydew that covers leaves and becomes blackened by sooty mold. Ants and many other insects feed on the honeydew, and there are a number of natural enemies that help restrain populations.

Nebraska records have confirmed the presence of Kermes Scale since 1921. Hosts affected have been red, pin, and bur oaks, but a wide range of oaks can be infested. Counties involved in the records include Gage, Otoe, Richardson, Pawnee, Lancaster, Douglas, Dodge, Saline, Sarpy, Platte, and Buffalo counties, but this pest is undoubtedly widespread across the state wherever oaks occur. 

There is one generation per season, with females reaching maturity in June. Crawlers emerge in September then migrate to buds being formed for the following year where they spend the winter.  A dormant-season spray oil from March through mid-April is an opportunity to treat. Crawlers are also susceptible to control in September with a topical insecticidal spray.

Kermes Oak Scale, Kansas State Research and Extension

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8. Still time for dormant seeding

The best time to seed cool season turfgrass is late summer, however spring seeding may be needed. If spring-seeding is necessary, consider seeding before the ground thaws. Dormant seeding can be done as early as Thanksgiving and as late as March in most locations. The benefit of dormant seeding is that as soil heaves and cracks during winter, crevices are created providing ideal germination conditions in spring. Additionally, dormant-seeding is easier to schedule than spring seeding, because spring rains make it difficult to seed after March in much of the Great Plains states.

Dormant seeding is more effective when weather remains cold enough to delay germination until spring. Occasionally, extended warm periods in winter could allow for germination and seedling death with ensuing cold weather. Thus a fast-germinating species like perennial ryegrass is rarely used for dormant seeding. If late summer or dormant-seeding are not possible, seed cool-season grasses as early in the spring as possible to take advantage of spring rains and cool temperatures.

Establishing Lawns from Seed, Nebraska Extension

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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 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 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.