1712 Claflin, 2021 Throckmorton Plant Science Center
Manhattan, KS 66506 (785) 532-6173
Horticulture Resource Center

Access PDF Online: Hort Newsletter #13

ANNOUNCEMENTS
K-State Garden Hour – Innovations in Horticulture Research at Kansas State University
Wednesday, August 6, 2025 Noon to 1:00 PM CST
Register here.

Join Dr. Cheryl Boyer, professor and Extension specialist, in this free webinar as she highlights recent emerging horticultural research projects addressing specialty crops such as ornamentals, fruits, vegetables and turfgrass.

Register for this free Zoom webinar at: ksre-learn.com/KStateGardenHour

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Welcome! You are invited to join a webinar: K-State Garden Hour Webinar Series. After registering, you will receive a confirmation email about joining the webinar.
ksu.zoom.us
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Kansas Turf & Ornamentals Field Day
Thursday, August 7, 2025
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

GARDEN TO-DO
Deadhead annual flowers as needed.
Spray sweet corn for corn earworm if silks haven’t turned brown yet.
Take soil test if establishing or overseeding a lawn this fall.
Remove sucker growth and watersprouts from fruit trees
Prepare to plant the fall garden – avoid deep tilling
Mid-August direct seed: leafy lettuce varieties, beets, mustard, arugula, Swiss chard, kale, turnips, radishes, green onions, Bok choy

FRUIT
When to Harvest Grapes
Waiting for grapes to ripen takes extra patience as the color matures before the rest of the fruit. Harvesting based on color alone will likely leave a bitter taste in your mouth as it takes several more weeks for the sugars to reach their peak and the tartness to subside. Waiting for the fruit to fully develop is important since grapes do not continue to ripen after harvest.
Prior to harvest look for a whitish coating on the grapes which indicates ripeness. Fully ripe grapes are usually slightly less firm than unripe fruit. Open one of the grapes and observe the seed color. Seeds of ripe grapes often change from green to brown. Finally, if all other measures indicate the grapes are ripe, do a taste test.

Grapes can be stored for up to eight weeks at 32 degrees F with 85 percent relative humidity. They can also be processed into jams and jellies.

Watering Fruit Plants During Summer
Ensure fruit trees are receiving adequate water to get the best harvest. Heat and drought stress restrict cell division which affects the size of the mature fruit even if water is added later. It can also lead to leaf wilt and discoloration as well as leaf and fruit drop. Bud development for next year’s crop could also be hindered.

Monitor the soil at the rootzone to prevent problems. A wooden dowel or metal rod can be used to probe the soil. If it is difficult to insert the probe 8-12 inches the soil is likely too dry. Add water to the rootzone slowly. Test with a probe again and once it can reach 12 inches easily, the moisture level should be adequate.

When the weather is hot and dry, monitor the fruit plants. Moisture level of newly planted and shallow-rooted crops should be checked at least twice a week.

VEGETABLES
Anthracnose on Cucumbers
Description: Anthracnose is a disease caused by a fungus which is most severe in cucumbers, muskmelons and watermelons. Anthracnose survives in plant debris and seeds. Infected leaves and fruit develop spores that spread easily by splashing water or contact with hands/tools. Anthracnose favors warm, moist conditions.

Damage: Infected leaves exhibit irregularly shaped brown spots that may have a hole in the center. Stems may become elongated and sunken when infected.

Control: Begin with resistant varieties and clean seed from a reputable distributor. Do not collect seed from infected plants. Practice crop rotation allowing three years between crops from the squash family. Use mulch and drip irrigation to prevent soil and water from splashing on the plants. Infected plants should be destroyed, not composted. Sanitize tools between use if they contact diseased plants.

Contact your local Extension office for other control recommendations.

Green Beans Producing Flowers but not Beans
Temperature is a key factor affecting bean production. High (above 85 degrees F) and low (below 70 degrees F) can cause plants to create flowers but not beans. Inconsistent soil moisture can also inhibit bean development and is exacerbated by hot, dry winds.

Proper crop management is the best way to mitigate these problems. Mulch surrounding plants regulates soil temperature and moisture. Using a windbreak crop, such as corn, can protect the bean plants from drying winds. Harvest regularly to encourage plants to continue producing. If beans are left on the plant past their peak harvest time the plant will use energy to produce seed rather than create new beans.

FLOWERS
Dividing Irises
Irises have a rhizome root system. Every year, each rhizome yields additional rhizomes creating a larger network of roots. After several years of this development, bloom production may slow down or halt altogether if the rhizomes become too crowded. This indicates it’s time to divide the rhizomes.
When the bloom season has ended dig the entire plant including all the rhizomes. Break the rhizomes apart by hand at the joints where they are connected. Healthy rhizomes should have roots extending below and a fan of leaf blades above. The rhizome should be firm and at least the width of your thumb. Discard any rhizomes that are soft, have an odor or do not have leaves protruding.

Trim the fan blades to about eight inches, cutting each blade at an angle to keep water from collecting in the thick, open leaves. Trimming the leaves prevents the plant from falling over while the roots become established. Dig a hole just deep enough that the top of the rhizome is slightly exposed when placed inside. Irises will tolerate poor soil conditions, but well-drained soil is best. Space plants 12 to 18-inches apart and do not mulch. Irises do not respond well to over-watering; however newly planted rhizomes need to be watered in thoroughly.

Fertilize according to soil test recommendations or by applying a complete fertilizer, such as a 10-10-10, at the rate of 1 pound per 100 square feet. Mix the fertilizer into the soil to a depth of 6 inches. If your soil test shows high phosphorus levels, use a fertilizer that has a much higher first number (nitrogen) than second (phosphorus). It is important to get irises planted early enough in the season to allow roots to establish before the first hard frost.
Peonies

It’s the time of year when two fungal diseases may appear on peony plants. Preventative care each year is the best control against them.

Peony measles, also referenced as red spot and leaf blotch, appears initially as purplish-brown circular spots on the top of the leaves. The spots on the undersides of the leaves are brown. Over time, more spots develop and eventually merge creating large, irregularly shaped blotches. Spots can appear on the stems, flower buds, petals and seed pods as the disease progresses.
Powdery mildew can infect a variety of plants. It presents as a white-grey powder on plant material. Powdery mildew is quite common in Kansas due to the warm, humid conditions.

Fortunately, both diseases are primarily aesthetic problems unless they become severe. Promote good air flow by spacing peonies several feet apart when planting. Individual plants can be pruned selectively during the growing season to improve circulation. Powdery mildew and measles overwinter in the soil on diseased plant material. At the end of the growing season cut peonies to the ground and throw out the plant material. Do not compost, especially if the plants are diseased. Use drip irrigation, if possible, to keep water from splashing on the leaves. When leaves are wet, avoid handling them.

PESTS
Fall Armyworm
Large numbers of Fall Armyworms have been spotted in West Wichita recently. While it is normal this time of year to start seeing Fall Armyworm caterpillars, the populations in Kansas appear to be more prevalent this year than last year.

Fall Armyworm caterpillars are usually found in large numbers when they are present, and the caterpillars can be identified by:
Young caterpillars are 1/16 inch long and light green in color.
Older caterpillars are 1.5 inches long, tan to olive-green in color, and have stripes extending the length of both sides of the body.
A light-colored, inverted Y-shaped marking on the front of the head
Four black tubercles on the back of each abdominal segment

Fall armyworm moths started arriving in southern Kansas a few weeks ago, and since then numbers in K-State monitoring traps placed in agricultural fields around the state have been increasing weekly. This time of year, Fall Armyworms are usually found in corn, sorghum and other summer agricultural crops but Tall Fescue lawns are another common food source for the caterpillars.

If Fall Armyworms are found in a lawn, it’s best to control the caterpillar populations when the caterpillars are young and small in length. When mature sized caterpillars are found, the amount of feeding they can do is potentially greater, however, once caterpillars reach a size of approximately 1.5 inches long, they begin to pupate into a cocoon and transform into the adult moth to begin the next generation.

In Kansas, there are generally 2 generations of Fall Armyworm each year with a partial third generation, but this is impacted by weather. Each new generation occurs approximately every 23-25 days, and often generations can overlap. It is important to scout for Fall Armyworm in your lawn regularly through September.

TURF
Crabgrass Control
Crabgrass is a common weed in lawns this time of year particularly in sparse lawns. The blades of this warm-season, annual are flat, wide and lighter green than the desired turfgrass.

Crabgrass dies back after setting seed or the first frost leaving bare spots in the lawn. At that time cool-season grasses should begin to flourish and fill in the spaces. If you have crabgrass in your lawn now you can expect it again next year since it is so efficient at re-seeding.

Preventing crabgrass from establishing in the lawn is the best method of control. Maintain a thick, healthy lawn to stop crabgrass seeds from germinating. Mow your lawn no shorter than three inches to help prevent sunlight from reaching the seeds on the soil surface. Pre-emergence can be used in spring.

At this point in the season, it is too late for a crabgrass preventer. Manually removing crabgrass plants is recommended for small areas and light infestations. There are some herbicides that will kill crabgrass including: Ortho Weed-B-Gon Max + Crabgrass Control, Fertilome Weed-Out with Crabgrass Control, Monterey Crab-ERad and BioAdvanced Lawn Weed & Crabgrass Killer. Each of these contains quinclorac, which is a crabgrass herbicide, as well as other active ingredients that control broadleaf weeds. Quinclorac can also provide control for foxtail and certain other broadleaf weeds such as field bindweed, black medic and clover. Be sure to bag your clippings if you use a crabgrass killer and don’t use them as mulch or compost.

Summer Watering for the Lawn
Buffalograss is a drought-tolerant grass and often survives summers without regular watering. Bermudagrass and zoysiagrass require less water during stressful summers than cool-season species. The recommended approach for watering established lawns is to wait for signs of general drought stress and then apply sufficient water to moisten the soil to the depth of the root system. Established turfgrass indicates drought stress by turning a dull, blue-green color. When you walk on drought stressed grass it tends to stay flattened rather than popping back upright.

Use a screwdriver or metal rod to determine how deeply water has penetrated the soil. Push the tool into the ground until you reach dry soil. The tool will pass easily through moist soil but will stop when it comes in contact with dry ground. Remove the tool from the soil and measure to determine depth of watering.

An established tall fescue or Kentucky bluegrass lawn has the capacity to enter a dormant condition when under drought stress and may survive several weeks or more without water. After that, it’s important to provide ¼ inch of water, if rainfall is insufficient, every couple of weeks to keep the crowns alive. With this approach, properly maintained, established bluegrass and fescue lawns, growing on good soil, can survive up to eight weeks without substantial irrigation.

Note: Because early fall is the time to perform important cultural practices on cool-season lawns such as fertilization, core aeration, and overseeding, it is wise to water dormant lawns deeply in mid to late August to establish the soil’s moisture reserve and revive dormant lawns so they can respond to these practices.

MISCELLANEOUS
Prioritizing Water in the Landscape
During periods of drought, it may be necessary to prioritize which plants will be first to receive supplemental water due to city-imposed water restrictions, cost and time.

Start with the large, established trees. These are the most difficult and expensive to replace if they don’t survive. They also take the longest to become established. While they may not require supplemental water during a short drought period, if prolonged established trees can suffer. Next, care for the young trees which are still developing their root systems.

Shrubs come next, followed by perennials, lawn and finally, annuals. This order will direct your attention to the plants that have had the most invested in them saving you time and money if you must replace plants that don’t survive. See below for tips to increase watering efficiency.
Watering Young Trees and Shrubs

Young trees and shrubs have not established the root system necessary to survive extreme heat and dry spells without supplemental water. After planting, it is essential to keep the root ball area moist for several weeks, but even a couple years later it may be necessary to periodically apply water to the area. Newly planted trees should receive 10 gallons of water weekly. Here are some tips for watering to eliminate waste and meet plant needs.

Direct water where it is needed (avoid watering hardscapes!)
Do not water on windy days
Water between 6 PM and 10 AM to reduce evaporation
Assess soil moisture before adding water to the landscape
Apply the water slowly so it can sink deep into the root zone
Build a reservoir (three to four-inches tall) around trees to keep the water in the desired area.
Use a water bag, or five-gallon bucket with a 1/8-inch hole drilled in the base, to direct water to the base of trees.
Mulch around plants to retain moisture and moderate soil temperature
Understand water requirements of your plants. Provide water to plants only if needed, not based on a schedule.
QUESTION of the WEEK
Raccoons and Sweet Corn
Can electrified fencing be used to prevent raccoons from getting to my sweet corn plants?

Electrified poly-net fencing is a great solution for keeping raccoons out (see example: https://www.premier1supplies.com/p/raccoonnet-4-18-12-kit-electric-netting?cat_id=160).
If you already have fencing panels or welded garden fencing, adding 1 electrified strand above can also exclude raccoons when they climb. Another option is the fencing seen in the photo. Though less expensive, this fence is also less durable and takes more time to set up.
Contributors:
Cynthia Domenghini, Horticulture Instructor
KSRE Sedgwick County
K-State Plant Pathology
K-State Entomology
K-State Turf and Landscape Blog
K-State Wildlife, Plant Pathology and Turfgrass Extension Specialists

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

For questions or further information, contact: [email protected] OR [email protected]
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There is a lot of confusion concerning pollination in many vegetable crops. It is important to know how different crops are pollinated. Sweet corn is wind pollinated — by pollen falling from the tassel (male) to the silk (female) part of the plant. Tomatoes, peppers, eggplant, beans, and peas are nearly completely self-pollinated. The flowers of these plants are arranged so that the flowers are pollinated by the natural growth process of the flower shedding pollen from the male to female parts. It is the vine crops — including squash, pumpkins, cucumbers, muskmelons, watermelons and gourds — that are bee pollinated. These plants all produce separate male and female flowers and bees are necessary to transfer pollen from one to the other. Bees only work on bright sunny days and are easily injured by insecticide sprays applied during the time the bees work (from sun-up to mid-afternoon). If bees fail to pollenize these flowers, the fruit will start to develop but shrivel and fall off. If bees pollenize the flowers only sparingly, the fruit may develop but be misshapen or poorly filled.

Many questions also arise regarding cross-pollination of plants in the garden. This usually comes in the form of “I planted my X next to my Y and now all of my X’s taste just like Y’s !” Horticulturist get more questions regarding crossing in the vine crop (cucumber, muskmelon, watermelon, pumpkin, and squash) family than any others. For all practical purposes, this does NOT happen. Each of these crops has different chromosome numbers which means they will not cross with one another even if you tried. Cucumbers cross only with other cucumbers, etc. In addition, you would not see the result of any cross until you planted the seed from a fruit produced this year and grew out the resultant fruit in the next generation next year. Remember self-pollenize crops do not cross with anything else. The vine crops are insect pollenized so that crossing might happen ONLY for crosses within the crop and ONLY if you save your seed for next year’s crop.

Another common question is “why do flowers drop off after blooming?” In plants that are self pollenized, this is not a problem with bees. Many plants set more flowers than the plant can develop fruit. Tomatoes, for example, may produce 15 to 20 flowers in a cluster of blooms but only 5 to 6 of those can develop into a fruit. The rest abort or fall off and it’s a good thing they do; otherwise, the tomatoes would be small and there would be breakage of the plant as a result. Extensive vine growth is usually associated with poor blossom set.

Anything that creates lush vine conditions usually discourages bloom set. The most common ‘culprit’ is excessive fertilization — especially with nitrogen (N) fertilization. In areas that have had generous manure applications or areas where extensive N fertilizers have been applied, there is usually a corresponding decline in the failure of plants to bloom properly and some flower abortion. This is often corrected as the season progresses and some of that excessive fertilization is used up or leached from the plant root zone.

Of course, many crops develop their edible portions without any relation to flowering. These include potatoes, sweet potatoes, leafy green crops, cabbage and rhubarb. A few crops are grown for their large, edible flowers including broccoli and cauliflower but pollination is not involved. So, there is your lesson about the ‘birds and the bees’ in horticulture — without much about birds!

Recommendations: Sweet corn: Ears may have missing kernels if the plants go through a hot, dry period. Keeping the corn well watered will help maximize pollination but heat alone can interfere with pollination. Tomatoes: Tomatoes won’t set fruit unless night temperatures stay at 55 degrees or above at least part of the night. They also won’t set if temperatures stay above 75° at night. The heat causes the blossoms to drop. There is little that can be done other than waiting for temperatures to moderate. Vine crops: Check to make sure that you have bees working the flowers. Insecticides should only be used late in the day to avoid injuring the bees.