ProHort Update - September 2024

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The ProHort Update team strives to provide horticulture professionals with timely, relevant information from research-based sources. Complete a short survey and let us know how we can make Hort Update even better. Your feedback is greatly appreciated!  Survey

Nebraska's drought status, 8/29/24 Map updated weekly.

1. Herbicide issues in soilLong-term soil residual products frequently cause landscape damage

Unintentional damage to landscape plants from herbicides is an ongoing problem. But not all herbicide damage is caused by airborne drift, soil applied herbicides and long-term soil residual products frequently cause problems, too. When using pesticides it is very important to read the product label and fully understand: 

1. active ingredient(s),
2. possible long-term effects such as mobility and length of activity in soil,
3. sites where the product is labeled for use, and
4. prohibited sites.

When diagnosing client problems, consider or rule out pesticide damage. This may help determine the cause of problems when no obvious disease, insect, or other issue is present. Determine what, if any, pesticides have been applied in the last year by a professional or the client. If the client applied a product, ask if they have the label to identify active ingredients. Ask when and how the product was applied. If a professional applied a pesticide, determine what was used and when.

Examples of pesticide related issues through soil exposure:

1. A fairly common example is when a pesticide containing picloram (i.e. Tordon RTU, Pathway) causes nearby trees or shrubs to die back. A recent scenario occured from an individual who cut down a landscape tree and treated the cut stump with a product containing picloram. A short time later, a nearby lilac died back. Similar situations have occured when picloram was used as s stump treatment on weedy trees in windbreaks.
   
   Tordon 22K is labled for use on the following sites: rangeland, permanent grass pastures, fallow cropland, Conservation Reserve Program (CRP) acres, and non-crop areas such as forest planting sites (not windbreaks), industrial manufacturing sites and rights-of-way (electrical power lines, communication lines, pipelines, roadsides, railroads, and wildlife openings). It is NOT labeled for use in residential or commercial landscapes. 
   
   Picloram should not be used in residential landscapes. It is mobile in soil and long lived so damage/death of nearby desirable trees and shrubs can occur. Under "use precautions" on the Tordon RTU label, it states "...picloram can remain phytotoxic for a year or more if it gets in soil...". It also states "Untreated trees can occasionally be affected by root uptake of herbicide through movement into the top soil or by excretion of the product from the roots of nearby treated trees. Do not apply Tordon RTU within the root zone of desirable trees unless such injury can be tolerated". Note: Shade tree roots can extend outward two to three times the tree's height making tree root zones quite extensive.
2. Another example: A client told a landscaper, just prior to new plants being installed in a bed, they had applied an herbicide to the site. The landscaper asked to see the label and the active ingredient was imazypyr. Like picloram, imazypyr is mobile and active in soil and can remain phytotoxic for a year or longer. This was stated on the label. In this case, the landscaper did not plant and damage was prevented. It was wise of the client to share this information.
3. A third example also involved an imazypr product (Groundclear). Prior to turf establishment, the product was applied to an area which was then seeded to turfgrass. There was zero seed germination. The herbicide had been applied four times in 6 weeks which was off label as well.

Herbicide nomenclature:

Understanding herbicide nomenclature can help prevent pesticide injury. Each herbicide is classified by 3 names: trade name, common name and chemical name.

• Trade name - a unique name assigned by the chemical company. This is the name frequently used by professionals and other users. Examples are Roundup, Tordon RTU, Pathway
• Common name - a general name given to a specific active ingredient. Blended products may contain several active ingredients. It is important to know what active ingredient(s) are in a product and not just the trade name. There are many different products sold under different trade names that contain the same active ingredient. Also, some products have more than one active ingredient, but similar trade names.
• Chemical name - describes the product's chemistry.

For example:

• Trade name – Dimension
• Common name – dithiopyr
• Chemical name – S, S-dimethyl 2-(difluoromethyl)-4-(2-methylpropyl)-6-(trifluoromethyl)-3,5-pyridinedicarbothioate

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2. September 2nd growing degree days (GGD)

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3. Pest updatePests to watch for based on Growing Degree Days (GDD)

For a more complete list, visit Michigan State University GGD of Landscape Insects or GGD of Conifer Insects.

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4. Strategies for Reducing Inputs and Emissions in Turfgrass SystemsA review of research up to 2021 on 1) reducing fertilizer, irrigation, mowing and pesticide inputs, 2) reducing carbon and nitrous oxide emissions, 3) increasing carbon sequestration, 4) protecting pollinators.

Turfgrass systems (e.g., home lawns, commercial properties, golf courses, athletic fields, roadsides, sod farms, parks, and other green spaces) in the US employ 820,000 individuals, have a $60 billion economic impact, and cover nearly 2% (∼63,250 mi2; 163,800 km2) of the US. Turfgrass systems provide ecosystem services such as carbon sequestration, oxygen production, water and air purification, improved soil health, pollinator habitat, and evaporative cooling. Associated disservices with turfgrass systems include nutrient and pesticide leaching, greenhouse gas and particulate matter emissions, low plant diversity, and site-specific, high water consumption. The goal of recent research efforts is to maximize the services and minimize the disservices by focusing on sustainability initiatives to develop best management practices such reducing management inputs (e.g., mowing, irrigation, fertilizer, and pesticides), incorporating pollinator-friendly spaces, adopting new technologies, quantitatively assessing ecosystem services provided, minimizing energy inputs and greenhouse gas emissions, and increasing carbon sequestration. This part-review, part-management guide summarizes these efforts, identifies knowledge gaps, and outlines how turfgrass systems can adapt to and mitigate climate change.

Strategies for Reducing Inputs and Emissions in Turfgrass Sytems - American Society of Agronomy, Crop Science Society of America

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6. 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.

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7. Trees, fall watering & drought5 common questions clientele have about trees, drought and fall watering

Whew, has it been hot! Scorching temperatures and dry conditions in the last few weeks have made it difficult for both people and plants. Our trees are still recovering from the last two years of severe drought and are not fully recovered yet. Fall watering is one of the best things homeowners can do to prevent further stress and help their trees continue to recover. Here are a few common questions landscape managers may get from clientele this time of year. 

But the drought's over, why are trees still stressed?
During severe drought, as we experienced in 2022-2023, trees are damaged in several ways as listed below.

• Reduction in photosynthesis and, consequently, production of energy for growth, defense and storage.
• Reduction in stored energy reserves.
• Death of mycorrhizal fungi. This symbiotic tree root-fungal root association greatly expands a tree's root system and the tree's ability to take in nutrients and water from the soil.
• Death of tree root hairs and eventually progressively larger roots.
• Leaf loss.
• Loss of functional xylem, the water moving conductive tissues within a tree's roots, trunk and branches.

Trees must regrow xylem, roots, mycorrhizal fungi and replace stored energy reserves to fully recover. For this reason, woody plants often experience a 2-5 year period of biological lag time in their recovery from drought.

Yes, many parts of Nebraska have had good amounts of rain this year, but those rains have been followed by some long dry periods and hot weather which causes plants to need large amounts of water for normal growth and function. According to the U.S. Drought Monitor, Lancaster county has normal to abnormally dry levels of soil moisture. But that's not too bad, right?

Additional stress can slow down a tree's recovery or may be enough to push it over the edge into a downward spiral. As the proverb goes - that final straw which broke the camel's back.

Aren't tree roots really deep?
"Trees have roots as deep as the tree is tall" – this is a common misconception related to trees and watering. For those operating under this misconception, it's easy to think trees can draw moisture from very deep layers of the soil - but it's not true. Yes, some tree species do have tap roots or anchoring roots which grow deeply into the soil, but these are not water-absorbing roots.

Research has demonstrated 90% of tree water-absorbing roots are in the top 24-inches of the soil. In fact, 50% of water-absorbing roots are in the top 12-inches of the soil. If these relatively shallow layers of soil are dry, the tree is very limited in its ability to pull up water.

How can I tell if my trees are drought stressed?

• Symptoms of drought stress often include the following.
• Thin canopy of foliage. Few leaves or smaller than normal leaves.
• Browning or scorching around leaf edges. Evergreen needles turn brown from the tip, resulting in half brown-half green needles.
• Development of early fall coloration, reddening or yellowing of leaves.
• Early leaf drop.
• Smaller amounts of new growth.
• Twig or branch dieback.

Of course, these symptoms can be caused by other problems, too. If you need help determining the cause of problems in your tree, contact your local Nebraska Extension office.

How often should I water?
For mature established trees when conditions are dry, deep soaking every 2 weeks in August and September is usually adequate.  Apply water deeply, moistening the soil to a depth of about 12-18 inches. Use a long-bladed screwdriver or piece of rebar to check the depth of water penetration.  Once you've reached dry soil, it will be much harder to push the probe into the ground. Water the entire area underneath the tree's dripline if possible.

If using a sprinkler, let it run in a low pattern in one area until the top 12-18 inches of soil is moistened then move it as needed to water the entire area underneath the tree's canopy or over a shrub's root zone. Or coil a soaker hose several times around the tree from the trunk to the dripline, and let it run until the soil is moistened.

If dry conditions continue into late fall, irrigation can continue monthly from October through December or until the ground freezes.

What else can I do to help my tree?
Apply a 3 to 6-foot diameter ring of mulch around the base of your trees and shrubs, using 3-4 inches of an organic material, like coarse wood chips. Make sure the mulch is applied in a flat layer, like a pancake, not piled up like a volcano against the plant's bark. Keep it far enough away that it doesn't touch the tree's trunk.

Research has shown trees grow roots significantly better under wood chip mulch than they do under grass. Giving the tree a small area where it doesn't have to compete with grass roots for moisture and nutrients can help the tree more quickly regrow roots lost during the drought.

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8. Nuisance home invadersInsects, spiders, mice - exclusion provides best control

These pests may enter homes in fall as temperatures cool and they begin to look for overwintering sites. Pests like boxelder bugs, millipedes and Asian lady beetles are common. Most are harmless but still a nuisance.

Exclusion is the best means of reducing nuisance pests and mice indoors. Caulk cracks, crevices and conduits of the home. Repair window screens and check that doors are tight fitting. If needed, insecticides can be applied to building foundations according to label direction. Ideally, apply the insecticide from the foundation out to five to 10 feet.

Insects That Overwinter in Your Home, Nebraska Extension
Keeping Occasional Invaders Out, Nebraska Extension
Boxelder Bugs, Nebraska Extension
Controlling House Mice, Nebraska Extension
Identification Guide to Common Spiders in Nebraska, Nebraska Extension
Millipedes, Nebraska Extension
Multi-colored Asian Ladybird Beetles, Nebraska Extension

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9. Timing landscape weed controlFall best time to control perennial, biennial and winter annual weeds

While fall is the preferred time for herbicide control of perennial broadleaf weeds, it is not a good time to control many weeds. Identification of weeds, and knowing if they are annual or perennial, warm season or cool season, is key to knowing when and how to effectively manage weeds. Below is the preferred timing to apply labeled herbicides for some of our more common turf weeds in lawns. Be sure to alternate herbicides with different modes of action to help reduce herbicide resistance in weeds.

• Perennial broadleaf weeds, i.e. dandelion, ground ivy, violet: September into October
• Winter annual broadleaf weeds, i.e. henbit, chickweed, speedwell: preemergence herbicides applied in September.
• Warm season annual weeds, i.e. crabgrass, spurge, purslane: preemergence herbicides applied in spring; post emergence herbicides applied when plants are young if necessary.
• Warm season perennial grasses, i.e. tumble windmill grass, nimblewill: summer beginning when plants are fairly small. Repeat applications are needed.
• Cool season perennial grasses, i.e. tall fescue, orchardgrass, roughstalk bluegrass: dig out or apply glyphosate at a time when the area can be reseeded/sodded fairly soon.

Turfgrass Weed Control for Professionals publication to purchase, Purdue University

Perennial Weedy Grass Control, Nebraska Extension

Broadleaf Weed Control in Home Lawns, Nebraska Extension

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10. ProHort Lawn & Landscape - Lunch & LearnSeptember 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. This year's final discussion will be Tuesday, September 17. 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.

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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.