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| Going In-Depth | Major Symptom: |
|---|---|
| 1. Long term effects of drought stress on trees | Common disease and insect problems of drought-stressed trees |
| 2. July 30th growing degree days (GDD) | Several Nebraska sites below, Understanding Growing Degree Days. |
| 3. Pest update | Pests to watch for based on growing degree days (GDD). |
| Research You Can Use | |
|
New this year, we'll be sharing practical research articles on topics of relevance to professional landscape managers. |
Keywords: |
| 4. The Role of Trees in Urban Stormwater Management | Using trees for stormwater control. |
| Greener Landscapes - Conservation & Climate Change Mitigation in Action | |
| Also new this year, practical information on improving your client landscapes' impact on climate change, habitat for native insects and other ecosystem services. | Application: |
| 5. Stormwater runoff benefits of trees | Slow the rain, reduce runoff and more. |
| Serious Concerns | |
| 6. Lindens and stem girdling roots (SGRs) | Symptoms of SGR root-related issues include leaf yellowing, leaf scorch, early leaf drop, branch dieback, frost cracks, or other symptoms not explained by pests. |
| 7. Scout for bagworms | Look for signs of damage, particularly on evergreens, and insect bags. |
| 8. White grub curative, rescue treatments | Scattered patches of brown grass; easily rolled back due to root damage. |
| Timely Topics | |
| 9. Strawberry root weevils | Summer nuisance insect; no pesticides recommended. |
| 10. Japanese beetles | Expanding their range in central Nebraska. |
| 11. Green June beetles | Minor feeding on fruits and vegetables. |
| 12. Tick identification | Visit Nebraska Tick Surveillance for statewide maps of tick occurrence. |
| 13. Fungal foliar diseases | Brown, yellow, orange, red or black leaf spots. Infections usually not serious enough to warrant chemical control. |
| Heads Up: For Your Information | |
| 14. ProHort Lawn & Landscape - Lunch & Learn | August 20 and September 17. |
| 15. Commercial/Non-commercial pesticide applicator certification | Obtaining a new license or updating an expired license. |
| 16. Digital Diagnostic Network - Need help with diagnostics? | Submit pictures and questions for diagnosis by Nebraska Extension experts. |
Nebraska's drought status, 8/1/24 Map updated weekly.
1. Long term effects of drought stress on treesCommon disease and insect problems of drought-stressed trees.
Climate change is making periods of extreme weather, including drought, more frequent. Symptoms of a water deficit in plants during dry conditions are familiar to landscape professionals, including wilting, yellowing or marginal leaf scorch of deciduous leaves, purpling of spruce needles and premature leaf drop.
The long-term effects of drought to woody plants are often less recognizable, especially since they may occur long after the drought has ended - weeks, months or even years. Further decline will often continue as the tree repairs the root system, xylem and other structural changes caused by drought and which may take 3-5 years to be fully completed.
What are the underlying changes caused by drought?
- Death of fungal mycorrhizae, growing in associate with tree roots, and which greatly expand its ability to uptake soil moisture.
- Death of root hairs, which are responsible for a majority of water uptake.
- Leaf loss.
- Reduction in the plant's ability to photosynthesis, resulting in decreased amounts of growth and defensive chemicals.
- Death of small roots, then larger roots.
- Reduction in functioning xylem cells, which move water upward from the roots to leaves.
- Death of smaller, then larger branches.
What are the results of all these changes? Watch for these changes now, indicating which trees may need additional care to recover.
- Reduced growth and vigor.
- Smaller leaves and thinner canopies.
- Direct branch or plant death due to dry conditions.
Long-term Impact of Drought Damage
If plants experienced drought stress but survived, one important long-term effect is an increased susceptibility to insect and disease invasion, which may be the final death blow. Drought stressed trees and shrubs commonly affected by the following diseases and insect pests.
Root rots, such as Armillaria spp. This fungus is very commonly present in the soil, but is kept at bay by healthy roots with good defensive structures and chemicals. In drought stressed trees, the fungus is able to invade root cambium tissue and spread unchecked. Armillaria can kill a small tree in just a few years, while larger trees may take several years after the initial drought and infection, to die.
The publication below provides diagnostic information and pictures.
- Armillaria Root Rot, University of Minnesota Extension
Cankers are fungal or bacterial infections of bark, which kill the bark and cambium, eliminating water movement through the dead tissues. They can occur anywhere on the plant and be very destructive and difficult to control. The following canker diseases are often found on stressed trees in the years following the drought.
- Botryosphaeria
- Cytospora
- Hypoxylon
- Nectria
- Phomopsis
- Thyronectria
- Sphaeropsis
For pictures and more information, visit Fungal Cankers of Trees, Iowa State University.
Wood rot diseases are caused by a wide variety of fungi which enter the plant through wounds. Healthy vigorous trees can often wall-off or seal off small areas of infection minimizing it's spread. But drought stressed trees, which are producing fewer defensive chemicals, may fail in this defensive compartmentalization allowing wood rot to spread. There are no fungicidal controls for wood rot, so prevention is the best strategy, including the prevention of drought stress.
- Wood Decay Fungi in Landscape Trees, University of California IPM
Needle diseases, such as Diplodia tip blight and Rhizosphaera needle blight, are more common on trees weakened by drought.
- Rhizosphaera needle cast, University of Minnesota Extension
- Diplodia shoot blight and canker, University of Minnesota Extension
Verticillium wilt is caused by a common soil-borne fungi, which invade the roots of susceptible tree species. As with canker infections, drought stressed trees may not be able to resist the entry of verticillium fungi into their roots.
If a tree was already infected with verticillium wilt before the drought occurred, faster advancement and greater expression of disease symptoms (leaf yellowing, wilting and branch dieback) would be expected once drought stress had further reduced the tree's vigor.
- Verticillium Wilt of Woody Plants, Purdue University
Wood boring insects, such as bronze birch borer and bark beetles, are attracted to drought stressed, weakened trees. More emerald ash borer larvae will survive in drought-stressed ash trees, causing a faster tree decline. Even our native wood boring insects, which are not a serious problem on healthy vigorous trees, will attack and survive on drought stressed trees. And wood boring insects are often the final straw which kills the tree.
- Shade Tree Borers, Colorado State University Extension
Many - I would even go so far as to say, most - of our trees in Nebraska are still experiencing the effects of drought stress. Landscaper managers need to recognize this underlying factor, how long it takes for trees to fully recover from drought and provide stressed trees the care needed for recovery. Watch for signs of these secondary disease and insect problems and, when possible, provide control.
References
Kujawski, Ron. (2016, October 26). Long-term drought effects on trees and shrubs. Center for Agriculture, Food, and the Environment. https://ag.umass.edu/landscape/fact-sheets/long-term-drought-effects-on-trees-shrubs
2. August 1st growing degree days (GGD)
| Location | Accumulated Growing Degree Days |
|---|---|
| Grand Island, NE - Airport | 2123 |
| Lincoln, NE - Airport | 2234 |
| Omaha, NE - Airport | 2282 |
| Norfolk, NE - Airport | 2019 |
| North Platte, NE - Airport | 1868 |
| Scottsbluff, NE - Airport | 1902 |
3. Pest updatePests to watch for based on Growing Degree Days (GDD)
| GGD (base 50) | Insect | Lifestage present at this GGD |
|---|---|---|
| 950-2150 | Japanese beetle | Adult emergence |
| 1000-2000 | Emerald ash borer | Peak adult emergence |
| 1200-1800 | Fall webworm | Caterpillars feeding |
| 1250 | Codling moth | 2nd generation control stage |
| 1375 | American plum borer | 2nd generation |
| 1500 | Pine needle scale | 2nd generation control stage |
| 1700 | Zimmerman pine moth | adult flight |
| 1800-2200 | Banded ash clearwing | adult emergence |
| 1850-2025 | Fall webworm | Tents become apparent |
| 1925-1950 | Magnolia scale | Egg hatch |
For a more complete list, visit Michigan State University GGD of Landscape Insects or GGD of Conifer Insects.
4. The Role of Trees in Urban Stormwater ManagementUsing trees for stormwater control
Urban impervious surfaces convert precipitation to stormwater runoff, which causes water quality and quantity problems. While traditional stormwater management has relied on gray infrastructure such as piped conveyances to collect and convey stormwater to wastewater treatment facilities or into surface waters, cities are exploring green infrastructure to manage stormwater at its source.
To date, green infrastructure science and practice have largely focused on infiltration-based technologies that include rain gardens, bioswales, and permeable pavements. In this article, researchers propose that arboriculture, the cultivation of trees and other woody plants, deserves additional consideration as a stormwater control measure.
The Role of Trees in Urban Stormwater Management. Berland, A., Shiflett, S. A., Shuster, W. D., Garmestani, A. S., Goddard, H. C., Herrmann, D. L., & Hopton, M. E. (2017). Landscape and Urban Planning, 162, 167–177.
5. Stormwater runoff benefits of treesSlowing rain, reducing runoff and more
With the fall tree planting season coming up, help clients select the right tree and plant it right. The benefits trees provide, from energy conservation to improving air quality, mitigating heat islands, and increasing property values are well known. They also provide benefits by slowing rainwater and reducing run off.
- Stormwater is runoff produced during rainfall and snow melt. As stormwater flows over surfaces, it picks up pollutants in its path and carries these to surface water. This is nonpoint source pollution and is considered the number one cause of surface water pollution.
- The benefits of trees for stormwater management include canopy interception, absorption of rainwater in soil, evapotranspiration, and increased soil infiltration. Trees also filter pollutants such as sediment and nutrients from stormwater.
- Canopy interception is when rainfall is caught by leaves and evaporated back into the atmosphere so less runs off. Interception also slows rain drops to increase infiltration into soil. Interception is affected by intensity and duration of rain events and tree species. Estimates for the amount of water a typical street tree can intercept ranges from 760 gallons per tree per year to 4000 gallons per tree per year.
- Tree roots absorb rainwater so it is returned to the atmosphere via transpiration, after the tree has filtered potential pollutants. When trees use soil moisture, more rainwater can infiltrate into soil during the next rainfall.
- The roots of trees hold soil in place to reduce soil erosion and sediment pollution. Tree roots take up nutrients, a common stormwater pollutant, to help reduce the amount in stormwater runoff. Trees and other plants are nature's filters.
How to Plant a Tree, Nebraska Forest Service
6. Lindens and stem girdling roots (SGRs)Symptoms of SGR root-related issues include leaf yellowing, leaf scorch, early leaf drop, branch dieback, frost cracks, or other symptoms not explained by pests.
SGRs are roots that encircle and compress against a tree's trunk. While any tree can develop girdling roots, especially those grown in smooth sided plastic containers or planted too deep, SGRs are a common problem in lindens as well as maples and elms. Symptoms of root issues related to SGRs are leaf yellowing, leaf scorch, early leaf drop, branch dieback, frost cracks, or other symptoms not explained by a pest.
When symptoms occur, inspect the base of the trunk. Is a root circling or growing against one or more sides of the trunk? Does the trunk appear compressed near the base, especially on one side? Is the trunk flare absent so the tree looks like a telephone pole at the ground line? Are there suckers growing near the tree's base? Any or all can be signs of SGRs even if one is not visible above ground.
Once a tree is established, SGRs cannot be removed without further weakening or killing the tree. Prevention is key. Remind clients to purchase trees in containers designed to help prevent SGRs where available. If not, planting smaller, quality trees at the correct depth and dealing with SGRs by cutting them and spreading roots out at planting is important. Encourage clients to dig wide holes but no deeper than needed for the trunk taper to be visible above ground after planting. Soil should not be loosened beneath a tree's root ball.
All About Stem Girdling Roots, Iowa State University Extension and Outreach
7. Scout for bagwormsLook for signs of damage, particularly on evergreens, and insect bags.
While questions to Extension offices concerning bagworms have been low so far this year, it is important to monitor evergreens for bagworms. Bagworms will feed on shade trees, but are most damaging to evergreen trees and shrubs since these plants cannot replace foliage eaten by insects. After overwintering as eggs inside female bags, a new generation of insects typically begins hatching in late May and early June, GGD 600-900.
The exact hatching period is determined by temperature, so our spring's cooler temperatures may have delayed egg hatch this year. Scout evergreens for bagworm when on-site and/or teach clients what to look for on their trees.
Time to Scout for Bagworms, Nebraska Extension
8. White grub curative, rescue treatmentsScattered patches of brown grass; easily rolled back due to root damage.
Preventive grub insecticides are recommended on lawns that had white grub damage the previous season. Annual application is not recommended by Extension or pesticide labels. When this recommendation is followed, there may be years where a curative or rescue treatment is needed.
White grub eggs typically hatch from July into August. If preventive insecticide treatments were not applied by mid-July, there are curative or rescue insecticides available if white grub populations reach the threshold needed for treatment. For masked chafer grubs, our most common white grub, the threshold is 8 to 10 grubs per square foot. For Japanese beetle grubs, the threshold is 10 or more grubs per square foot. If only a few grubs can be found, treatment is not needed.
Trichlorfon (BioAdvanced Grub and Insect Control or Dylox) is the recommended rescue product. Be sure to water-in grub control products after application with one-half inch of water to increase control. Do not use products that contain ONLY bifenthrin, deltamethrin, cyfluthrin, permethrin, lambda-cyhalothrin or gamma-cyhalothrin for soil-applied grub control. These chemicals bind with organic matter at the soil surface and will not move down into the soil to provide effective grub control.
9. Strawberry root weevilsSummer nuisance insect; no pesticides recommended.
If clients ask about small black beetles in their home during summer, these may be strawberry root weevils. While not a common pest, there have been more calls related to them this year. Strawberry root weevils are harmless but become a nuisance when they invade homes during summer, sometimes in very large numbers.
The adult weevil is about one-fourth inch long, dark in color, and has a snout. Larvae feed on small roots of strawberries, brambles, and some ornamental plants, but damage is minimal. Adult weevils are wingless and enter homes through loose fitting doors, windows, screens, and other openings. They crawl everywhere in the home but don't bite, eat stored food, damage structures, infest pets, or transmit diseases. The best control of strawberry root weevil is to caulk and seal the outside of the house to prevent entry, and make sure doors and windows are tight fitting. The best control indoors is to vacuum the weevils and discard the bag.
Image left - strawberry root weevil adult by Whitney Cranshaw, Colorado State University, Bugwood.org.
10. Japanese beetlesExpanding their range in central Nebraska.
While Japanese beetle numbers appear to be lower in eastern Nebraska this year, they are appearing in more landscape in central counties, including Adams, Bulter, Hall, Howard and Johnson counties. Growing degree day (GGD) models target adult emergence from 950 to 2150 GGD (base 50). Emergence timing varies across the state based on location and yearly weather variations, but an emergence estimate for several locations are below. Adult feeding damage will occur during this entire period and for several weeks afterward, as the last adults complete their lifecycle. More details on control strategies for professionals.
Image right - Japanese beetle adults from Karla Salp, Washington State Department of Agriculture, Bugwood.org.
11. Green June beetlesMinor feeding on fruits and vegetables.
Green June beetles are large, ¾ to 1” long, greenish beetles with bronze, irregular stripes. They can emerge from soil in large numbers and sound like bumble bees. Adult will feed on corn ears, ripened fruit, and tree sap. While concerning to homeowners due to their size and damage to fruit, populations are rarely large enough to warrant control. Prompt harvest of ripe fruit is the best management practice.
Image left - green June beetle adult, from Kansas Department of Agriculture, Bugwood.org.
Green June Beetle, Nebraska Extension
12. Tick identificationVisit Nebraska Tick Surveillance.
When ticks are active in Nebraska (April-October), staff from the Nebraska Department of Health and Human Services vector-borne disease program and local health departments search for ticks at various sites throughout the state in a process called "tick dragging or flagging." Using a white flannel cloth, ticks are collected and identified to species under a microscope. This information is used to understand when and where ticks are active in Nebraska and what pathogens these ticks might be carrying.
When people are aware of the types of ticks and tick-borne diseases potentially circulating in their area, they can better protect themselves and healthcare providers can target appropriate testing and treatment.
For information about the common ticks in your area and the disease they can cause, visit Nebraska Tick Surveillance.
13. Foliar fungal leaf diseasesBrown, yellow, orange, red or black leaf spots. Infections usually not serious enough to warrant chemical control.
Fungi require moisture on a leaf’s surface for a certain period of time to infect a leaf. With the rainy spring we've had, we’re seeing more foliar diseases now than in the past few drought years. Fortunately, most of these diseases are minor on otherwise healthy, established plants, and fungicide use is not recommended.
While they concern homeowners, especially when leaves drop, remind clients to pay attention to the amount of healthy, green leafy tissue on the tree or plant. Photosynthesis is still occurring and most woody plants have already developed leaf buds for next year. If fungicides are applied, they need to be applied in spring or during rainy periods to be effective.
Common diseases in trees and ornamentals are
- cedar apple rust,
- apple scab,
- shade tree anthracnose,
- pear rust,
- hollyhock rust,
- cercospora leaf spots,
- bacterial blights and others.
In turf, we are seeing 1) brown patch, 2) dollar spot, 3) ascochyta leaf blight and 4) Helminthosporium leaf spot. On cool season turf, fall fertilization is almost as beneficial as applying a fungicide and this is often our main recommendation for managing foliar diseases on home lawns.
14. ProHort Lawn & Landscape - Lunch & LearnAugust 20 and September 17
Back for the 2nd year, Lunch and Learn zooms are an informal opportunity for Extension staff and greenspace professionals to share what’s happening in landscapes, management recommendations and helpful resources. Mark your calendars and plan to join us from Noon to 1 p.m. CDT for a fun discussion. Be ready to share questions or problems you are currently finding in client landscapes. Program is free and open to all green industry professionals. Register now to receive the free zoom link.
15. 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.
16. 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.
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.
