Hort Update for May 10, 2023

1. Compost & herbicide residualBe aware of potential herbicide residual problems in compost products

Manure or compost is a great soil amendment to loosen compacted soil, increase carbon in the soil, and reduce surface runoff and leaching all while providing nutrients that plants need. While this option is great, it is important to be aware of the potential carry over of herbicides in manure from grazing animals.

Recently, a group of herbicides has been identified as a concern for manure and compost. Often these chemicals are used for weed control on grazing land. When herbicides are sprayed onto forages, plants take up the chemicals. If these forages are then utilized as a carbon source in making compost, residues will be present in the finished compost product. The same is true when livestock eat treated forages and their manure is used to make compost.

Even though it may be completely safe for grazing livestock to consume treated plants, the resulting manure will contain herbicide residues. Use of manure or compost with these residues present can cause damage to plants or cause plant death. Additionally, the residues may remain in the soil for an extended period of time after application.

EPA Review of Pyridines
The EPA reviews all registered pesticides at least every 15 years to determine if the chemical is still able to function as intended without negatively affecting human health or the environment. As such, concerns with a product moving off target, not degrading, or causing harm to non-target organisms are often addressed during this review process. Currently, the EPA is reviewing a group of Pyridines for their persistence in organic matter such as plants, parts of plants, and manure from livestock that have grazed treated plants.

Registration Review of Pyridine and Pyrimidine Herbicides

The list of active ingredients being addressed by the EPA for residue concerns in manure and compost from herbicide's are as follows: Clopyralid, Triclopyr, Fluroxypyr, Aminopyralid, Aminocyclopyrachlor (ACP), Dithiopyr, and Picloram.

Triclopyr, dithiopyr and picloram are commonly found in products labeled for landscape use. Restrictions on the use of grass clippings following application should be fully communicated with your clientele.

There are no herbicides containing clopyralid labeled for use on residential turf, but Confront and Lontrel (both of which contain clopyralid) are labeled for use on golf courses and sod farms. Grass clippings from these sites, if treated with either product, should not be used to make compost. 

Clientele Landscapes
When planning to use compost or manure in client's landscapes, be sure to check with your compost supplier for any potential problems before using their product. Any compost source materials used within the last year could potentially include herbicide residue. Homeowners should also be aware of this issue and ask questions when purchasing bulk (not bagged) compost. 

You can find the active ingredient list for products on the first page of the herbicide label materials under the section title Active Ingredients. Ask questions about materials used to make the compost to ensure there is no potential for herbicide residue.

A list of products that may contain a form of aminopyralid is provided below. This list does not include any herbicides with the active ingredients Clopyralid, Triclopyr, Fluroxypyr, Aminocyclopyrachlor (ACP), Dithiopyr, and Picloram which are also under review for similar reasons. For more information on registered pesticides in Nebraska, visit Kelly Solutions. 

There are facilities that will test for pesticide residues, but the cost is high and doesn’t provide any recommendations for leftover compost or manure. It’s more important to keep records of what was used even if it’s a general use product and follow the label requirements to reduce the potential for damage of sensitive areas such as yards and gardens.

Image above - Example graphic from a pesticide label with grazing and composting restrictions. 

Authors

• Jennifer Weisbrod – Assistant Extension Educator
• Leslie Johnson - Animal Manure Management Extension Educator
• Sarah Browning - Extension Educator

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2. May 8th growing degree day(GDD)

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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. Bagworm controlMonitor for egg hatch and when to control

Monitor spruce, Juniper, Arborvitae and pine for the next generation of bagworms. In Nebraska, eggs typically hatch from mid-May into June at 600-900 GDD.. It's best to wait until the majority of eggs have hatched before making insecticide applications. It is also important to take the opportunity to pull and destroy left over bags from last year, as they may contain up to 1,000 eggs.

After hatching, larvae spin protective cases or "bags" around themselves using silk and fragments of needles or leaves. Bags are initially one-eighth inch long enlarging as larvae feed and grow. By summers end, bags are up to two inches long.

Bagworms move around trees feeding on needles until early September. Early signs of damage are brown or stressed needles at branch tips caused by tiny, first-stage caterpillars etching needle surfaces as they feed.

Bagworms are especially damaging to conifers because destroyed foliage is not regenerated. Feeding on conifers justifies control as bagworm populations can build up to levels that seriously damage or kill evergreens.

Insecticides are most effective when applied mid to late June targeting young caterpillars. Insecticidal spray applications require thorough coverage to penetrate the tree canopy. It's best to use ground equipment capable of delivering higher spray volumes and pressure. Insecticides containing Bacillus thuringiensis (Bt), spinosad, or neem oil (azadirachtin) and insecticidal soaps are effective against young larvae, but may require repeat applications. These products generally have minimal impact on beneficial insects.

For treating larger, more mature bagworms, other insecticide options control on conifers includes acephate, bifenthrin, chlorantraniliprole, cyfluthrin, dimethoate, esfenvalerate, fluvalinate, lambda-cyhalothrin, malathion, permethrin, and tebufenozide. When making an application, be certain the product is specifically labeled for both the target pest and plant species.

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5. Perennial weed grass control in turfBegin control with selective herbicide after greenup

Warm season perennial weedy grasses, like nimblewill and windmill grass, may still be dormant and appear as brown areas in cool season green turf. Herbicide control of these two difficult to control weeds needs to begin after they green up.

Nimblewill is a thin, wiry, pale green grass. The leaf blades are short and emerge at 45 degrees angles from the stems, which are slender, smooth and tend to lie flat on the ground. It spreads by short stolons, or above ground stems, that root at the nodes. Nimblewill forms circular patches as a result of its stoloniferous growth pattern, which grow larger each year.

Windmill grass is a bunchgrass that spreads primarily by seeds. Plants have coarse, light green leaves and produce seed heads at a short height, becoming unsightly in a mowed lawn. The seed heads consist of 6-20 spike-like branches attached to a central axis, which resemble small tumbleweeds and can roll across the lawn in fall dispersing seeds.

In spring, after these grasses break dormancy, they can be selectively controlled with Tenacity (mesotrione). Make 3 applications 7 to 10 days apart for the best control. Susceptible grasses will turn white following the application, as chlorophyll in their leaves breaks down. Tenacity is labeled for use on Kentucky bluegrass, tall fescue, fine fescue, perennial ryegrass, and buffalograss. It should not be used on zoysiagrass unless damage or grass death can be tolerated. Tenacity can be applied by commercial pesticide applicators or purchased online by homeowners.

Perennial Grassy Weed Control, UNL Turf iNfo

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6. Verticillium wiltSoil borne fungus; problem on stressed trees

Verticillium is a fungal pathogen found in soil. It is opportunistic, meaning it infects plants when they are stressed, such as by heat and drought. Verticillium wilt is most commonly seen in maple, catalpa and smoke trees although a number of shade trees and shrubs are susceptible.

After infecting plants through roots, the fungus moves into the vascular system and interferes with water transport. Symptoms include yellowing, wilting and drying of leaves in upper branches followed by branch dieback. When scraping away bark on dead branches, green to brown streaking might be visible.

There is no fungicide control for verticillium. Correctly water and mulch infected trees to reduce stress. Prune out infected or dead branches, being sure to disinfect (such as with a 10% household bleach solution) pruning tools between cuts. Since the pathogen is in the soil, trees and shrubs killed by Verticillium wilt are best replaced with plants listed as being resistant.

Verticillium Wilt, Iowa State University Extension

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7. Stem girdling roots (SGRs)Fix problems at planting

SGRs are a serious problem for trees. They lead to slow or stunted growth, increase a trees susceptibility to pests, and may lead to wind throw. SGRs develop when young trees are grown in smooth plastic containers. Young roots grow quickly and when a root touches the side of a smooth pot it begins to circle around the outside of the root ball. Even field grown trees are often started in pots, so investigate closely to find SGRs that developed when trees were young.

To help avoid SGRs, consumers should select smaller trees, those with a 2 inch or smaller trunk diameter. Trees purchased in grow bags, RootMaker® pots, or other containers designed to minimize circling roots are wise choices. Grow bags are made of fabric which traps the tip of a new root, preventing it from circling. Once the root tip stops growing, additional branching develops along the length of the root resulting in a denser, fuller root system overall. RootMaker® pots are design to air prune roots to prevent them from circling.

If a tree is purchased in a plastic pot, deal with girdling roots in one of two ways. The first option is to gently wash the root ball to remove all soil. Once roots are exposed, spread them out and prune away any that circle the trunk. Keep the roots moist during the process and until they are planted. The second option is to shear off one inch of the entire outer root ball with a sharp hand saw. This has been shown to be more effective than making several cuts or slices down the sides of the root ball.

Eliminate Stem Girdling Roots Before Plantings, Nebraska Extension

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8. Cytospora canker of spruceFungal bark infection, kills twigs/branches; can infect main trunk

Cytospora canker is a common fungal disease on larger, mature spruce trees stressed by drought, winter injury or other stress. Cankers girdle and kill scattered branches throughout the tree. On close inspection, a layer of hard, dry, bluish-white resin will coat the area of the branch over or near the canker. This disease usually does not kill spruce as the fungus does not grow into the trunk from infected branches. The disease does negatively affect the trees appearance. Fungicides will not control canker diseases. If feasible, prune out infected branches during dry weather. Reduce stress with correct irrigation and mulching. Replace deformed spruce with concolor or white fir, ponderosa pine, Norway or white spruce.

Cytospora Canker, University of Minnesota

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9. Roseslug sawflyPrimarily aesthetic damage; use least toxic product for control

Roseslugs have been damaging rose leaves during May and June for a number of years. While this pest rarely kills a healthy rose, feeding detracts from a plants appearance and can lead to stress. Roseslugs are the larvae of a small non-stinging wasp (sawfly). Light green roseslug larvae feed in large numbers on leaf undersides for about one month. They skeletonize leaves by feeding on green tissue and leaving irregular holes between veins. If control is wanted, leaf undersides need to be treated. Organic options include horticultural oil, insecticidal soap and spinosad. Synthetic options include carbaryl and pyrethroids. Larvae can also be handpicked or dislodged from the plant by a strong spray of water.

Roseslug Sawfly, Nebraska Extension

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10. Euonymus scaleLeaf yellowing, leaf drop; white waxy insects on stems

Euonymous leaves and stems covered with white, waxy spots are infested with Euonymous scale. Scale insects feed on sap beneath the protective white scale causing leaf yellowing, leaf dropping and stem dieback. Insecticidal control methods need to be used during egg hatch from late May into early June and again for the second generation in late July to August when crawlers are present. Manage by pruning out heavily infested branches and monitoring for crawlers using double-sided tape around infested stems. When present, organic insecticide options include horticultural oils, insecticidal soaps and neem products. Synthetic options are acephate, pyrethroid products and the systemic dinotefuran.

Euonymus Scale, Nebraska Extension

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11. Witches broomsDense proliferation of stunted twigs and/or leaves

Witches' broom is a proliferation of leaves or twigs at growing points on plants, often appearing as a clump of stunted twigs or leaves. The primary causal agent is usually a phytoplasma, a bacteria-like organism, that for the most part is poorly understood. There are also viral and fungal causes of witches' broom and feeding by Eriophyid mites lead to witches' broom. While these create concerns for clients, they rarely kill plants. They can be ignored or pruned out if feasible.

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13. Commercial/Non-commercial pesticide applicatorsObtaining a new license or updating an expired license

If you have a pesticide applicators license which expired in April 2023 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.)

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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14. 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 constitute endorsement by Nebraska Extension. Nor does it imply discrimination against other similar products.