Horticulture 2025 Newsletter No. 10

1712 Claflin, 2021 Throckmorton Plant Science Center
Manhattan, KS 66506 (785) 532-6173
Access Online: https://hnr.k-state.edu/extension/horticulture-resource-center/horticulture-newsletter/

Video of the Week: Native and Ornamental Grasses of Kansas
(June 2025 K-State Garden Hour Webinar Recording)
Explore native and ornamental grasses and learn species that thrive in the KS climate.
ANNOUNCEMENTS
Kansas Turf & Ornamentals Field Day
The Kansas Turf & Ornamentals Field Day will be held on Thursday, August 7, 2025 at the Rocky Ford Turfgrass Research Center in Manhattan.

This Field Day program is designed for all segments of the turf & ornamentals industry — lawn care, athletic fields, golf courses, sod farms, landscape, nursery, and grounds maintenance. Included on the program are research presentations, problem diagnosis, commercial exhibits, and equipment displays. There will be time to see current research, talk to the experts, and get the answers to your questions.

For more information and to register online, go to: www.kansasturfgrassfoundation.com

• • We hope to see you on August 7 in Manhattan!

    Commemorating Dr. Chuck Marr
    Dr. Chuck Marr served as a Vegetable Crop Specialist for K-State Research and Extension for 36 years. He was an active member of the community and supported gardeners in many capacities throughout his retirement as well.

    Chuck passed away in December of 2024. To honor the legacy of Chuck, many of his friends are coming together to designate a special area in the Kansas State University Gardens in his name. The Riley County Extension Master Gardeners and the Manhattan Watercolor Group are leading this meaningful tribute and warmly invite others to participate.
    Chuck was a strong advocate for the Gardens on campus. We envision dedicating the main vegetable growing bed in the Gardens in Chuck’s honor. This space, where he spent so much time nurturing plants and educating others, would be a fitting tribute.
    The sponsorship level for this area is $15,000. We hope to raise the total amount collected by July 15 to ensure recognition in the Gardens. If you would like to contribute, donations can be made to Kansas State University Foundation in the following ways:
    Online: Donation · Kansas State University · GiveCampus
    By phone: 785-775-2400
    By mail: Send checks payable to:
    Kansas State University Foundation
    1800 Kimball Ave., Suite 200
    Manhattan, KS 66502 Please include Fund # M47497 (Chuck Marr) in the memo
    Thank you for considering this request in memory of Dr. Chuck Marr. If you have any questions or would like additional information, please feel free to reach out to Riley County Extension Agent, Gregg Eyestone at 785-410-5336 or [email protected].

    GARDEN TO-DO

  • Remove sucker growth from fruit trees
  • Stop harvesting asparagus so plant can store energy for next year
  • Remove dead foliage from spring flowering bulbs
  • Remove tree stakes that have been in place for at least one year
  • Turn compost pile after it cools
  • flowers
  • Remove flower stalks from peonies and iris
  • Fertilize warm-season lawns such as zoysia, Bermuda and buffalo
  • Monitor plants regularly for signs of pests

    GARDEN SPOTLIGHT
    With 50 years of gardening experience, Mark shares his best practices for success including how to preserve a surplus of crops to eliminate waste.

    Read Mark’s garden story here. Advice from a Lifelong Gardener

    VEGETABLES
    New Potatoes
    New potatoes are harvested about 6-8 weeks after planting while they are still small and immature. Gently remove the soil from the base of the plant to check the size. When the potatoes reach the size of a walnut, carefully dig the entire plant without damaging the tubers. Allow them to dry, out of the sun, for a day or more to toughen the skin. Next, move the potatoes to a cold (below 40 degrees F), dark location for storage. Check on the potatoes occasionally for signs of rotting.

    Fertilizing Tomatoes
    Too much nitrogen for tomato plants may result in vigorous plant growth without much fruit. Plants should be side-dressed with nitrogen three times during the growing season.

    The first application should be applied one to two weeks prior to fruit ripening. Two weeks after ripening, it’s time for the second application. The third round of fertilizer should be applied one month after the second. Basically, there should be one month of time between each application.

    Common sources of nitrogen-only fertilizers include nitrate of soda, urea and ammonium sulfate. Blood meal contains primarily nitrogen but has other elements as well.

    Apply one of the following fertilizers at the rate provided:

  • Nitrate of soda (16-0-0): 2/3-pound (1.5 cups) fertilizer per 30 feet of row
  • Blood meal (12-1.5-.6): 14 ounces (1.75 cups) fertilizer per 30 feet of row
  • Urea (46-0-0): 4 ounces (1/2 cup) fertilizer per 30 feet of row
  • Ammonium Sulfate (21-0-0): 0.5 pounds (1 cup) fertilizer per 30 feet of row
  • Alternatively, lawn fertilizer, free of weed killer/preventer, can be used at a rate of 1/3 pound (3/4 cup) fertilizer per 30 feet of row. Choose a fertilizer that is about 30% nitrogen (the first number in the set of three).

    FRUIT
    Fruit Reminders

For the best harvest this year here is some fruit tree maintenance to complete.

• • Thin fruit on apple and peach trees. Fruit should be 6-8 inches apart.
    Remove suckers from the base of fruit trees and grape vines.
  • Water as needed. During hot weather, 1-inch of water per week is the recommendation.
  • Comb (position) grapevine shoots to prevent tangling and promote more uniform sun exposure.
  • Follow disease and pest management protocol. For more information about fruit sprays see our KSRE Publication: Spray Guide for Growing Stone Fruit at Home.
  • FLOWERS
    Rust on Hollyhock Flowers
    Description: Hollyhock rust is a fungal disease that is most prevalent on hollyhocks, but other members of the mallow family are also susceptible. The fungus is introduced by infected plants. Fungal spores can travel by wind and splashing water as well. Warm, humid weather supports the fungal growth. The fungus can overwinter on infected plant debris and spread to new plants in the spring.

    Symptoms: Orange-yellow spots develop on the lower leaves and sometimes brown spots will appear on stems. Raised bumps that are reddish-brown later develop on the undersides of leaves beneath the orange-yellow spots. These are the reproductive structures of the fungus. The infected leaves may develop holes and eventually die back.

    Control: Prevention is the best approach against hollyhock rust. Begin with healthy plants each year and remove all plant debris from the previous growing season. Allow adequate spacing between plants so the fungus is less likely to spread if one plant is infected. Water at the soil level and avoid splashing on the plant.

    If a plant develops rust, remove the infected leaves immediately and dispose of them. Plants that have a history of infection may benefit from a preventative fungicide when the weather is warm and humid. Spray every two weeks until the weather is dry. Sulfur and myclobutanil (Immunox, Monterey Fungi-Max, F-Stop Lawn & Garden Fungicide) are recommended. If the temperature rises above 85 degrees F within 24 hours of application the sulfur treatment may cause damage to treated leaves.

    Rose Trouble
    Several counties are reporting problems with their roses. One of those problems is rose rosette virus. The classic symptoms that may appear include:
    Rapid elongation of a new shoot
    “Witches’ broom” (clustering of small branches)
    Branches develop excessive thorns
    Small, deformed, reddish-purple leaves
    Certain varieties may develop streaks or blotches of reddish-purple on stems and petioles

Plant death
Infected plants, including the roots, should be removed and destroyed. Garden tools that come in contact with the plant need to be sterilized to avoid spreading the virus.

Rose blackspot has also been reported. Blackspot is a fungal disease that can cause these symptoms:
Dark, circular lesions with feathery edges on top surface of leaves (usually lower leaves are infected first)
Raised, purple spots on young canes
Yellowing between spots on infected leaves
Leaf drop
Prevention is the best approach for controlling blackspot. Purchase resistant cultivars of roses. Use drip irrigation to avoid splashing water on the leaves. Ensure roses are planted in the sun with good air movement. Don’t crowd plants together in a planting. Diseased leaves should be removed from the ground and infected plant parts should be pruned out of the plant.

If you choose to apply fungicide you can treat on a 10–14-day schedule. Some recommended fungicides include tebuconazole (Bayer Disease Control for Roses, Flowers and Shrubs), myclobutanil (Immunox, Immunox Plus), triticonazole (Ortho Rose & Flower Disease Control) and chlorothalonil (Broad Spectrum Fungicide, Garden Disease Control). As always, follow all label instructions carefully.

Deadheading Flowers
Deadheading is a method of pruning out old flowers. This practice allows plants to direct their energy to new growth and producing new flowers rather than creating seed. The frequency this needs to be done depends on the plant variety and the environmental conditions. Some plants do not require deadheading at all. Lobelia, Impatiens, Hibiscus and Oxalis are examples of plants that are “self-cleaning” (do not require deadheading).

For plants that benefit from deadheading, use sharp, sterile pruners and cut the stem below the spent bloom just above the next node. The node is the area of the stem where the leaves extend. For plants such as Gerbera daisies that have a bloom atop a long stem, cut the stem down to the base of the plant. Some plants can be deadheaded using just your forefinger and thumb to remove the old flowers. Petunias are one example of this.

In the fall you may consider leaving blooms intact to allow plants to set seed and feed the birds.

TURF
Thatch Control in Warm-Season Lawns
Ornamental plants need to be cleaned up periodically as leaves and blooms die back. The same is true for grass. As grass plants grow, older plant material falls away to the soil level and can build up. This is called thatch and it can become problematic if it is thicker than ½ inch.

A thick layer of thatch can restrict water infiltration and reduce the efficacy of pesticide/herbicide treatments. When thatch accumulates, grass plants tend to root into this layer instead of deeper into the soil. Since thatch dries quickly, the lawn will suffer from drought stress. Kentucky bluegrass, zoysiagrass, bermudagrass and creeping bentgrass are the varieties of turf most likely to be affected by thatch buildup.

Power-raking and core-aerating are the best strategies for preventing thatch buildup. For warm-season grasses, it is best to do this in June or July when the lawn is actively growing and can recover from thinning more efficiently. If the thatch is ½ to ¾-inches thick, core aerating can be done. Repeat passes with the aerator until the holes are about 2-inches apart.

If thatch is thicker than ¾-inches, it will need to be power-raked. Set the blades of the rake only deep enough to remove the thatch so the lawn is not severely damaged.

Thatch can be prevented by fertilizing properly and avoiding excessive nitrogen applications. Water to the root zone and only as needed. Mow at the recommended height.

Brown Patch on Tall Fescue
As summer weather sets, we are experiencing warmer nights and more humidity. These conditions extend the amount of time grass blades stay wet making the lawn more susceptible to the disease, brown patch.

Brown patch is primarily a leaf pathogen, but with a severe outbreak, the fungus can spread down into the crown and cause plant death. However, depending on the weather, typically the turfgrass recovers within two to three weeks.

Symptoms can be similar to those of drought, but look closer at the grass plants around the edge of the symptomatic area. If you notice tan spots with a dark halo similar to the photo here you likely have brown patch.

Brown patch persists in the soil. It cannot be eliminated from a lawn, but is also not carried from one lawn to another. You can, however, provide proper care to reduce your lawn’s susceptibility to brown patch.

Water in the early morning rather than the evening and only as needed. This decreases the number of hours the grass blades stay wet.
Fertilize according to recommendations for your lawn. Don’t fertilize when brown patch is active.

When seeding, follow recommended rates.
Grass growing beneath trees does not dry as quickly. Use a mulch ring around trees so grass isn’t growing beneath the canopy.

Fungicides can be effective to prevent brown patch though the most commonly used products are expensive and typically only available in large quantities. Preventative fungicides are recommended if you want a blemish-free lawn, beginning in mid-June through August, but this does get expensive.

MISCELLANEOUS
Mushrooms after Rain
Mushrooms are the fruiting structures produced by various fungi. The appearance of the mushrooms varies depending on the fungi species. The fungi are present beneath the soil surface all along, but when conditions are right, they are able to set fruit. The result is mushrooms popping up in the landscape.

Warm, moist conditions tend to favor mushroom development. Beneath the soil the fungus feeds on decaying organic matter. Rainy weather speeds up the decay which gives a boost of nutrients to the fungus allowing it to have proper nutrition for fruiting. Therefore, the appearance of mushrooms is often an indicator that the soil is healthy and has a good level of organic matter.

Though many of the mushrooms are harmless to our plants, some can cause or indicate problems. Fungi mycelium grow underground from a center point outward in a circular pattern. When the conditions are favorable, mushrooms appear on the outer edge of the ring above the soil surface in an arc or circular shape. In lawns this is called a fairy ring. This can cause problems in the lawn as the mycelium can form a dense mat that decomposes organic matter and releases nitrates into the soil. The lawn in the outer area of the circle grows more rapidly and turns a darker green color than other areas of the lawn. The mycelium mat can also reduce water infiltration and there may be some turf dieback in this area.

Fairy rings are difficult to control. You can sometimes eliminate the ring by digging to a depth of 6 to 12 inches by 12 inches wide inside and outside of the ring, refilling the hole with non-infested soil. Those in commercial businesses will sometimes use a fungicide to control fairy rings but these products are not available to homeowners. See
http://www.ksre.ksu.edu/bookstore/pubs/EP155.pdf for more information on these fungicides.

Mushrooms will disappear as the weather dries out again or when it gets colder. The fungi remain beneath the surface ready to send up fruit once conditions are favorable again. Because most mushrooms are harmless to the landscape there is little need to try to control or prevent them.

Effects of too much Rain
After multiple heavy rains across many parts of Kansas, gardeners are likely to assume watering won’t be needed for quite some time. However, watering may be needed much sooner than you expect.
Excessive rain can drive oxygen out of the soil and drown the roots. As the weather gets hotter and drier the plants with damaged root systems may be poorly suited to take in water and shows symptoms of drought. Monitor your plants for signs of wilting and leaf scorching and water as needed.

Usually, supplemental water is needed once per week depending on the weather. Plants should be watered deeply and soil should be moist but not waterlogged.

QUESTION of the WEEK
Bagworm Help
Is it time to treat for bagworms now?

Bagworms are showing up. Though right now they are small and hard to see they are also much easier to control. Bagworms overwinter as eggs inside the dead female’s bag. Larvae hatch and emerge from the bags mid to late-May in Kansas. The young larvae begin feeding on their host plants right away. It’s recommended to wait to spray for bagworms until mid-June to ensure most of the eggs have hatched.

Young bagworms look just like the adult version only much smaller. If you see empty bags on your trees/shrubs, that is evidence of bagworms from the previous year and there are likely young bagworms on the plant this year as well.

Insecticides commonly used for controlling bagworms include:

• Acephate (Orthene) Permethrin (38 Plus Turf, Termite & Ornamental Insect Spray; Eight Vegetable, Fruit & Flower Concentrate; Garden and Farm Insect Control)
• Bifenthrin (Bug Blaster II, Bug-B-Gon Max Lawn and Garden Insect Killer)
• Lambda-cyhalothrin (Spectracide Triazicide, Bonide Caterpillar Killer)
• Spinosad (Conserve; Natural Guard Spinosad; and Captain Jack’s Dead Bug Brew). Spinosad is a very effective organic control for bagworms.

  Thorough coverage of the plant material is essential for good control of bagworms regardless of which product you choose.

  Contributors:
  Cynthia Domenghini, Instructor and Horticulture Extension Specialist
  KState Plant Pathology
  K-State Turf and Landscape Blog
  Kansas Garden Guide

  Division of Horticulture
  1712 Claflin, 2021 Throckmorton
  Manhattan, KS 66506
  (785) 532-6173

  For questions or further information, contact: [email protected].
  This newsletter is also available online at:
  http://hnr.k-state.edu/extension/info-center/newsletters/index.html

  The web version includes color images that illustrate subjects discussed. To subscribe to this newsletter electronically, send an e-mail message to [email protected].
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  K-State Research and Extension is committed to making its services, activities and programs accessible to all participants. If you have special requirements due to a physical, vision or hearing disability, or a dietary restriction please contact Extension Horticulture at (785) 532-6173.

Cynthia Domenghini, Ph.D.
Instructor; Horticulture Extension Specialist
Department of Horticulture and Natural Resources
Kansas State University
1712 Claflin Rd.
Manhattan, KS 66503
785-340-3013
[email protected]