ProHort Update for June 2025

1. Fungal Lawn Diseases

Lawns can face injury through the summer. The environment can be difficult for lawns with drought, floods, heat stress, and cold injury, but lawns can also have problems with disease organisms through the season. 

Some of the common diseases seen in lawns include: 

• Dollar Spot – occurs in spring or fall but can linger through summer causing brown patches in the lawn. Leaf lesions occur on grass blades that are tan with a reddish-brown border. It is favored by warm, moist weather with heavy dew periods. If turf is lacking sufficient nitrogen, it can intensify the problem. 
• Summer Patch – occurs in the summer months. The pathogen infects roots when soil temperatures reach 65 degrees or warmer. This may be active all summer but shows up in our lawns during the hot, dry parts of the summer. Summer patch develops as tan colored turf with no lesions on the leaf blade, but when pulled up the roots are brown to black, slimy and wilted, which limits the capacity to absorb water.
• Brown Patch – occurs in the summer months. It is favored by hot, wet weather in lawns with excess fertilization and excess irrigation, especially when hot, wet conditions occur overnight. Due to this, it can be managed by avoiding high nitrogen fertilization in the summer months. Choose a low nitrogen fertilizer or opt out of a summer fertilization to help manage brown patch. Brown patch develops as tan lesions on grass blades with a gray edge to the irregularly-shaped spots. 
• Ascochyta – occurs in early summer when the weather shifts from cold and wet to hot and dry. It appears as tip dieback on leaf blades with the tips appearing bleached white. Red-brown spots may appear lower down on affected blades. You might also notice a dark brown/black band between green growth and the brown tip of the blade. After the initial disease moves through, a general brown appearance will show up in the lawn, often following lawn mower tire patterns. Mowing worsens the symptoms of this disease, it does not spread it. The physical traffic of the equipment weakens turf. This disease is made worse by plant stress, often due to a rapid shift in environmental conditions early in the season. 

These turf diseases primarily affect leaf blades and don’t damage the crown or growing point of turfgrass. They can be managed through the use of fungicides, but it isn’t always necessary in a home lawn because they show up in different locations and not usually every year. Changing the growing conditions for grass helps reduce these diseases. Proper management through correct mowing, proper irrigation, and fertilization practices will all improve turfgrass growth and reduce incidence of these diseases. 

Top

2. May 30th 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. Should I Fertilize My Trees, Nebraska Statewide Arboretum

As a human species, we’re “hard-wired” to care for things that are important to us.  The most common are our family members, pets and plants.  Perhaps the most impactful plants in the landscape are trees; as such, we often feel a deep need to care for them somehow.  That feeling often translates into extra watering, pest control and fertilization.  Are these practices needed for Nebraska trees?  Forester Sarah Browning breaks it down for us.

Top

5. Excess Nitrogen is Not Good

Nitrogen is an essential plant nutrient. Like most things, too much of a good thing is not good. I recently visited with a gentleman who told me when he purchased his shade tree he was told to fertilize it once a week through the growing season. I’m also asked if trees need to be fertilized. The client is often asking because their lawn service is offering to fertilize their trees at the same time they fertilize the lawn. These are both cases of excess or unneeded nitrogen use that can harm plants. 

Excess nitrogen is harmful to plants and soil health. It increases a plants water needs and susceptibility to insects, especially sap sucking insects. It burns fine root hairs responsible for water and nutrient uptake. It can lead to deficiencies of other nutrients like iron or manganese. It increases thatch in turf. In soil, excess nitrogen is harmful to beneficial microorganisms needed for a healthy soil and vigorous plants. In flowering and fruiting plants, excess nitrogen can decrease flowering and fruiting and lower fruit quality. Excess nitrogen leads to water pollution by leaching into ground water or running off into surface water. These are some of the negatives tied to excess nitrogen applied to soil and plants. 

Most established landscape trees and shrubs do not require nitrogen fertilization. They are supplied with nitrogen from decomposing organic matter in soil and from irrigation and rain water. On top of this, if they are growing in a fertilized lawn, they are receiving plenty if not more than needed when the turf is fertilized. Nitrogen fertilization is most warranted on turfgrass where the clippings are routinely removed.  Of all landscape plants, turfgrass requires the greatest amount of nitrogen fertilization compared to fruit, flowers, groundcovers and trees/shrubs.  See: Cool Season Lawn Calendar - Eastern Nebraska (G2356) for more information on turfgrass fertilization.]

Fruit and nut trees, vegetables, roses and other heavily flowering plants often require nitrogen fertilization. Young plants growing in sandy soils or new construction sites where the top soil was removed and not replaced may require nitrogen fertilization. When applying nitrogen, encourage clientele to read and follow label rates and remind them too much of a good thing is not good in the case of nitrogen and plants.

Fertilizer Use in Home Landscapes

Top

6. Honeylocust Plant Bug

The honeylocust plant bug (Diaphnocoris chlorionis) is a small, pale green insect pest of honeylocust trees that often goes unnoticed because it blends in with new foliage. It overwinters as eggs under bark and has one generation per year; eggs hatch in early spring around the time of bud break, and the young nymphs feed on newly unfolding leaves, maturing into adults by early summer. Feeding by nymphs injects a toxin into the leaf tissue, causing tiny yellow spots that later turn brown and lead to leaf curling, distortion, and stunted growth; heavy infestations can even defoliate trees (though rarely kill them), and damage is often more severe on yellow-leaved honeylocust cultivars (like ‘Sunburst’) than on green-leaved types (such as ‘Shademaster’ or ‘Skyline’). For management, non-chemical tactics include monitoring newly emerging leaves in spring for stippling or distortion and spraying the foliage with a strong jet of water to knock off nymphs; if needed, chemical controls such as insecticidal soaps, horticultural oils, or other insecticides should be applied shortly after bud break, targeting the young nymphs on new growth for best results. Original article from Penn State Extension 

Top

7. Chlorosis in Trees

Yellowing leaves with green veins—that’s the classic symptom of chlorosis. This condition usually signals a deficiency in metal nutrients like iron, manganese, or zinc. But it’s not always about what’s missing in the soil.

Chlorosis can result from several factors including root damage, waterlogged soils, high soil pH, or even an overabundance of certain nutrients. For example, iron is often present in the soil but becomes unavailable to plants when phosphorus levels are too high—a common issue in clay-based soils.

In most cases, iron, manganese, and zinc are not truly absent; the plant simply can’t access them. Addressing the soil pH and improving overall plant health are key steps to unlocking these nutrients and helping plants green up again.

Chlorosis of Trees in Eastern Nebraska

Top

8. Yellow Nutsedge Control

June 1-21 is the prime time to manage Yellow Nutsedge. This perennial sedge typically emerges from underground tubers in late May in Nebraska. The best time for herbicide control applications are from the first week of June to June 21 - before plants develop new tubers. To reduce nutsedge, mow tall and avoid overwatering. Hand-pulling is effective where there are fewer plants.  When herbicides are used, sulfentrazone (Dismiss), imazosulfuron (Celero), halosulfuron (SedgeHammer), and mesotrione (Tenacity) are labeled for postemergence control in cool-season turfgrasses and buffalograss.

Yellow Nutsedge Control (homeowners), Purdue Extension
Yellow Nutsedge (professionals), PennState Extension

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 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. 

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.