Hort Update for August 4, 2023

1. Weedy vine controlWild cucumber, burcucumber, Japanese hops and honeyvine milkweed- recommendations for clientele

Weedy vines growing in trees or shrubbery is one of the most difficult weed situations to deal with in property management. Common culprits include wild cucumber, burcucumber and honeyvine milkweed. Less common are dodder and Japanese hops. All of these weeds shade the foliage of the host plant, and interfere with their ability to photosynthesis. This is especially damaging to evergreen trees, which don't tolerate shading well. Find pictures of all these plants in the resources linked below. 

Note: Poison ivy vines are also a problem, although they don't grow to cover plants in the way the above-mentioned weeds do. More information on poison ivy control.

Annual Weeds
Native to the United States, wild cucumber, burcucumber and dodder are annual vines, found in the same plant family as cucumber and muskmelon, although neither produces edible fruits. Both grow from seed each year, and can be found growing wild in prairie ravines, fence rows, creek and stream banks, and ditches.

Wild cucumber (Echinocystis lobata), also known as balsamapple or mockcucumber, can grow 15 to 25 feet long. It has smooth stems and alternately placed, star-shaped leaves, each with 5 to 7 pointed lobes. Greenish white flowers grow on short stems arising from the leaf axils. The twining vines are aided in climbing by forked tendrils. It has oval fruits, up to two inches long, that are covered with sharp spines.

Burcucumber (Sicyos angulatus) vines can grow up to 10 feet tall. The alternate leaves are broad with three to five pointed lobes. The stems are slightly fuzzy and develop clasping forked tendrils, similar to grapevines. Both wild cucumber and burcucumber produce separate male and female flowers. In burcucumber, the male flowers are greenish-white to pale yellow growing on short stems, the female flowers are found in round clusters at the ends of short stems. Green to yellow fruits are covered with prickly bristles, and ½ to ¾ inches long.

The name "Dodder" (Cuscuta sp.) encompasses a group of parasitic plants in the morning glory family. Dodder species are variable in the host plants they can infect, but a wide range of plants can be parasitized by one or more species. Plants produce very thin, string-like twining stems with tiny scale-like leaves. Host plants are buried in a strangled mass of intertwined stems. Dodder infection can weaken or kill plants. In Nebraska, dodder is an annual growing from seed each season and a prolific seed producer.

The final annual vine, Japanese hops (Humulus japonicas) is not a Nebraska native. It originates from eastern Asia and was introduced in North America in the mid-to-late 1880s as a garden ornamental. It is established throughout Nebraska and is officially considered an invasive weed. Unlike common hops, Japanese hops are not useful in beer production. 

Japanese hops plants grow as annual vines, often reaching 35 feet in a single growing season. Vines climb nearby trees, shrubs, buildings or other structures, or sprawl across the ground forming dense mats of foliage. Their oppositely-arranged leaves are palmate, with 5-7 lobes with toothed edges. Leaves are up to 6" long and 6" across. Stems and leaves have hooked hairs. Japanese hops grows as separate male and female plants (pictures right, image by Leslie J. Mehrhoff, University of Connecticut, Bugwood.org.) Both types of flowers are greenish and produced in mid to late summer. Female flowers are small arranged on short branched spikes. Male flowers develop into an aggregate cone, up to 1-inch long, appearing to be made up of green leafy bracts.

Perennial Weed
Honeyvine milkweed (Cynanchum laeve or Ampelamus albidus) is another native plant and a vining member of the milkweed family that can grow 6 feet or more long. It differs from wild cucumber and burcucumber, in that it is a perennial plant, growing back from the crown each year. Plants spread through underground rhizomes, and can regenerate if all the root system is not killed or removed.

Honeyvine milkweed has triangular, or elongated heart-shaped leaves located opposite each other on long, smooth stems. It may be confused with bindweeds or morning glories, but they have alternate leaves. Clusters of small white flowers are found in the leaf axils and develop into smooth, slender, elongated milkweed pods. When the pods mature and open, they release brown flattened seeds with silky white hairs.

Control
Wild cucumber and burcucumber - seeds germinate throughout the summer especially after rain, which makes periodic scouting and removal crucial for control. Plants are growing strongly by July so scout areas with a history of problems, and pull or hoe weeds before they have a chance to grow up into hedge or windbreak plantings. In large areas, mowing can be effective. Repeated mechanical removal prevents plants from producing additional seed and reduces weed pressure over time.

Japanese hops -  can also be controlled by handpulling or hoeing new seedlings as they appear. Plants are easiest to pull when young. Repeated cutting with a string trimmer or mower is another option, although plants will have to be recut often since they grow back quickly. Flowering stems and seedheads should be bagged or burned. Plants on the ground or not growing on a desirable plant can be sprayed with a systemic herbicide like glyphosate.

The control goal is to prevent further seed development; the soil seedbank is usually exhausted after 3-years of consistent control. Prevent seed from moving to new areas on clothing, vehicles, mowers and other equipment. Where protective clothing - long sleeve shirt, long pants, gloves, socks and shoes - to protect the skin when working around Japanese hops.

Honeyvine milkweed - Expect only partial control with preemergent herbicide products. Periodically scout areas with a history of infestation and hand pull or hoe out plants as they appear. Spot spray post emergent products, listed below, to kill young plants after they germinate.

Dodder is unique; as a parasitic plant it develops structures that grow within the host plant's branches. Physical removal of the existing dodder vines will not eliminate it; new vines will grow back from structures inside the branches. Young plants can be pulled or hoed out in spring before they reach their host plants; preemergent herbicides are also helpful in killing seeds as they germinate. If only a few branches of a plant are infested, those branches can be pruned out to minimize dodder regrowth. If the infestation is severe, removal of the dodder and host plants, followed by replanting with non-host plants is the best option.

• Pre-emergent herbicide- Oryzalin (Monterey Weed Impede) is labeled for preemergent control beneath trees to kill weed seeds as they germinate.
• Post emergent herbicide- Glyphosate (RoundUp) can be sprayed or painted on small plants under trees to kill seedlings; it has practically no soil residual and if used carefully according to label directions will not damage desirable plants. DO NOT use Tordon or any product containing Dicamba, which have a period of soil residual activity and can move deeper in the soil to be absorbed by trees roots.

If weedy vines escape notice early in spring and grow up into trees, cut larger plant stems near the ground before plants begin to flower. DO NOT spray herbicides on vines in trees or hedges.

Resources

• Burcucumber, University of Missouri 
• Dodder, University of California
• Honeyvine milkweed, University of Missouri
• Japanese hops, Minnesota Department of Agriculture
• Wild Cucumber, University of Wisconsin - Madison Extension

Reference to commercial products is made with the understanding that no discrimination is intended and no endorsement by Nebraska Extension is implied. Mention does not imply approval or constitute endorsement by Nebraska Extension. Nor does it imply discrimination against other similar products.

Top

2. August 3rd growing degree day(GDD)

Top

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.

Top

4. Summer patchMost prevalent in older Kentucky bluegrass; dead turf with healthy tuft of grass in center

Summer Patch disease is showing up in older Kentucky Bluegrass lawns. Key symptoms are circular patches of dead turf with a healthy tuft of grass in the center and brown to black roots. Symptoms are typically observed in full sun exposure areas or high stress areas near sidewalks and driveways. Summer patch is caused by the fungus Magnaporthe poae which infects turfgrass roots during spring. Symptoms appear during the hot, dry parts of summer after the fungus has caused roots to decline.

Newer KBG cultivars and tall fescue are resistant to summer patch. The long-term solution is to overseed with newer cultivars of KBG or convert lawns to tall fescue. Cultural practices to help reduce summer patch include core aeration to improve soil conditions for root health and correct irrigation, especially not overwatering, and proper fertilization. If fungicides are used, they need to be applied during the spring infection period of May.

Summer Patch, Turf iNfo

Top

5. Bagworms on evergreensInsects appearing in low numbers; but monitoring is still important

It appears 2023 could be a low population year for bagworm; however, due to the serious damage they cause on evergreens, monitoring for bagworms remains important. At this time of year, bagworms are larger making them easier to see. In early August, they can still be controlled fairly easily to help reduce damage. Most bagworms are now at least one inch or longer, making them more noticeable on trees than when they were one-eighth to one-half inch long in June. They will continue to feed until late August or early September. Bagworms are easiest to kill in June when small and susceptible. At this time of year, larger bagworms can be treated with synthetic pyrethroids.

Bagworms, Nebraska Extension

Top

6. New emerald ash borer (EAB) confirmationsLincoln & Nemaha counties; spring best time for treatment

Two new EAB confirmations were made this summer by Nebraska Department of Agriculture and USDA APHIS in North Platte (Lincoln County) and in the Shubert area in Nemaha County. Homeowners in these locations should begin assessing their ash trees for health and whether or not they are good candidates for treatment. Encourage them to make plans to begin treatment next spring or begin planning for tree removal. Fall treatments are not recommended.

For trunk injections, mid-May through June is the ideal application timing for good control. For soil treatment, products containing imidacloprid are best applied in April just before trees leaf. Products containing dinotefuran are best applied mid-May to early June. Continuing treatment will be required for the life of the tree.

For ash trees homeowners do not plan to treat, plans for removal should be considered once EAB has been found within 15 miles of that tree, rather than waiting for the tree to become infested and die. At that time, ash trees become brittle (more so than other species of trees that die from other causes) and they become a risk as well as more challenging to remove.

In December 2021, the USDA officially deregulated EAB and lifted federal quarantine regulations. Nebraska no longer has quarantine restrictions for EAB, but NDA inspectors continue to check nursery stock for diseases and insects, including EAB.

If you are in a non-infested county and think you have located an EAB infestation, please report it to the Nebraska Department of Agriculture at 402-471-2351, the Nebraska Forest Service at 402-472-2944, or your local Nebraska Extension office.

EAB Detections Map in Nebraska (7.26.23), Nebraska Department of Agriculture
Selecting Trees for EAB Treatment, Nebraska Forest Service
EAB Resource Center, Nebraska Forest Service

Top

7. Ascochyta leaf blightLeaf tips bleached; dieback from leaf tip to lower blade

Ascochyta leaf blight has shown up in some turf areas. It most frequently affects Kentucky bluegrass, but can occur on tall fescue and perennial ryegrass. It tends to show up suddenly and appear severe, affecting large areas of turf but seldom causes permanent damage. Key symptoms are large areas of turf taking on either a uniformly blighted or patchy appearance. The tips of leaf blades appear bleached and die from the tip down. Affected leaf blades may shrivel, forming a needle-point appearance at the tip. Aschochyta is associated with stress from drought, low fertility or other factors. Fungicides are not typically used to control this disease as turfgrass generally grows out of it and recovers fairly quickly without treatment.

Ascochyta Leaf Blight, Nebraska Extension

Top

8. Leaf scorch - trees, shrubs and ornamentalsBrowning from leaf edges into area between leaf veins

Excessive heat led to leaf scorch in a variety of plants, especially trees and shrubs. Leaf scorch is the browning of leaf edges and sometimes between leaf veins. It occurs when plants transpire water faster than roots can replace it. Larger leaved plants in full sun or windy locations and young plants with under established root systems are more likely to scorch. However, plants don’t have to be in full sun. Hosta, which prefers a shady location, can develop scorch in high temperatures. Plants with weakened root systems, such as from overwatering; or plants with damaged trunks or stems, such as from lawn mower or weed trimmer damage, are also more likely to scorch.

It is important not to confuse leaf scorch with a disease or insect issue and make unnecessary pesticide applications. It’s also important for homeowners not to water plants unless needed. It’s instinctive to water more when leaves scorch. However, it is not a lack of water but the roots’ inability to take in water at the same rate leaves are losing it that is the problem. While it is important to maintain a uniformly moist soil, watering when not needed can lead to saturated soils and root decline which further compounds the issue.

It’s normal for plants to respond to high temperatures by wilting or rolling leaves to reduce water loss, or allowing some foliage to die so water uptake by roots equals the amount of water lost from leaves. Again, it’s important to maintain a uniformly moist soil, but adding water when roots are already moist puts plants at risk for root and crown fungal diseases.

Top

9. WaspsTips to minimize stings

Wasp sightings increase in late summer when stinging insects are most abundant. Generally, these insects will not sting unless stepped on, touched, or annoyed. Most stinging wasps and bees are beneficial and should be preserved unless they pose a direct hazard to humans. Despite their many benefits, stinging insects may pose a hazard and control may become necessary.

Stings from yellowjackets are most common. Yellowjackets are social, meaning they live in a colony they will defend. They are medium-sized, stout-bodied, and black with bright yellow bands. Yellowjackets construct globular paper nests, usually in underground cavities. Favorite nesting sites include rodent burrows, compost piles, wood piles, and wall voids. Occasionally, these wasps build aerial nests in garages, crawl spaces, or other enclosed areas. Yellowjackets are scavengers and frequently found foraging in compost piles and garbage receptacles.

When yellowjackets are disturbed, they are capable of inflicting painful, multiple stings. If yellowjackets become excited and appear about to attack, do not panic. Do not make any sudden movements and retreat slowly and calmly from the area.

Control strategies for yellowjacket colonies depends on nest locations

1. Aerial nests: From a safe distance and after dark, treat the nest with liquid or aerosol jet spray insecticide. Remove the nest a day or two later.
2. Ground nests: Treat the nest with dust or liquid insecticide formulations after dark. Approach the nest very carefully, since a number of yellowjackets will typically guard the entrance. Apply the insecticide, then quickly seal the nest opening with a shovelful of dirt, a sheet of plywood, or a flat rock. Insecticide dust formulations are generally preferred because workers attempting to use the nest opening will track dust and contaminate brood and other colony members. Retreatment may be necessary after a few days if yellowjacket activity continues.
3. Nests within cavities: Yellowjackets occasionally build their nests in wall voids, cracks in stone walls, or other cavities associated with buildings. In such cases, do not seal the entrance hole following the insecticide treatment because yellowjackets attempting to leave the nest may enter the building through inside openings. Insecticide dust formulations are preferred since the workers entering or leaving the nest will tend to be contaminated.

Stinging Wasps and Bees, Nebraska Extension

Top

10. Wildlife damage to vegetables & fruitsAdditional water source may minimize damage

Some wildlife feed on fruits and vegetables for moisture during drought or high heat. Providing a nearby source of water may deter feeding. When temperatures soar, provide as many sources of water as possible, such as bird baths or setting out shallow basins of water near ground level. Keep all water sources topped up and clean. Avoid stagnant water that can be harmful to wildlife or lead to mosquitoes.

Top

11. Winter annual weed control in turfUse fall-applied preemergence herbicide to kill seedlings

Preemergence herbicide should be applied by early September for control of winter annuals like annual bluegrass, downy brome, henbit, little barley and speedwell. Winter annuals will soon be germinating and preemergence herbicides should be in place before germination begins as they kill seedlings after they germinate. Common landscape preemergent herbicides include bensulide (Bensumec), dithiopyr (Dimension), oxadiazon (Ronstar G), pendimethalin (Pendulum) and prodiamine (Barricade). Other management options for winter annual weed control includes maintaining a healthy and vigorou growing lawn or landscape bed plant cover to crowd out weed invaders. A layer of organic mulch 2-3 inches thick will also minimize weed germination.

Top

12. Overseeding lawnsTime to repair drought damaged or thin lawns

Overseeding is used to increase density of thinned lawns, introduce disease resistant cultivars, and convert Kentucky bluegrass lawns to turf-type tall fescue. The optimum time to seed cool-season grasses is between August 15 and September 15. Keys to success include using quality seed, obtaining seed to soil contact, and uniform irrigation following seeding.

Quality Seed
Purchasing quality seed is essential for long-term performance of a turf area. Seed cost is insignificant compared to long-term maintenance costs (you get what you pay for with seed). Poor quality seed can lead to problems like introducing rough bluegrass, Poa trivialis, to the site. If good quality seed is used, a lawn may last for twenty years or more with no reseeding if maintained properly.

Purchase seed from local, high quality seed wholesalers or retailers and purchase their more expensive seed; which virtually insures quality seed and dependable cultivars. Pay attention to label details on the seed bag such as purity, germination, and other crop seed. Know what the preferred ranges are for these details.

Improving Turf in Fall. Turf iNfo

Site Preparation
When seeding into an existing turf stand, it is important to ensure good seed to soil contact. Seeds that get hung up in thatch or other foliage can dry out and not establish properly. To achieve seed to soil contact while overseeding, mow the area to 1.5 inches or as low as feasible to reduce competition from established grass. Aerify the area, punching 20 to 40 holes/sq. ft. with the largest tines available, making at least 2 to 3 passes over the lawn. Power raking prior to aerating will also help increase seed-soil contact. Apply a starter fertilizer over the entire lawn at 1.0 - 1.25 lbs. P2O5/1000 sq. ft.

Seeding
Seed with a drop seeder or a power overseeder (also called a slit seeder or slicer-seeder) which is a machine that drops seed into small grooves cut into the soil. Make 2 to 4 passes over the lawn in different directions with either type of seeder to insure uniform seeding. Use recommended seeding rates for the type of turfgrass being planted. For Kentucky bluegrass, seed at a rate of 1.5 to 2.0 pounds per 1000 sq. ft. and for turf-type tall fescue, seed at 6.0 to 9.0 pounds per 1000 sq. ft.

After Seeding Care
After seeding, lightly water the newly-seeded area as much as 3 to 4 times daily to keep the soil surface moist. Light, frequent irrigation is the rule until seedlings are rooted. Once rooted, irrigation frequency can be reduced and irrigation depth increased.

Mow frequently to limit the competition from the established turf. Mow at 1.5 to two inches until new seedlings have been cut at least two times, probably 4 to 6 weeks after seeding. After that, gradually raise the mowing height back to 3.0 to 3.5 inches where it should remain. Four weeks after germination, apply a starter fertilizer again at 1.0-1.25 lbs P2O5/1000 sq. ft. unless a soil test indicates this is not needed.

Most broadleaf herbicides should not be applied until after the second mowing of the seedlings, which may be 4 to 6 weeks after seeding. However, some broadleaf herbicides like carfentrazone (QuickSilver from FMC) can be used sooner after seeding. Purchase herbicide products accordingly and be sure to follow label instructions for your specific herbicide.

When converting KBG to tall fescue, multiple years of overseeding may be required to increase the percent of tall fescue in the lawn.

Top

13. ProHort Lawn & Landscape Update- Lunch & LearnAugust 25 & September 22

Lunch and Learn zooms are something new. It is an informal opportunity for Extension staff and greenspace professionals to share what’s happening in landscapes, management recommendations and helpful resources. Mark your calendars for August 25 and September 22 from noon to one and please join us. Be ready to share! Program is free and open to all green industry professionals. Register now to receive the free zoom link.

Top

16. 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.

Top

17. 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.

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 Nebraska Extension. Nor does it imply discrimination against other similar products.