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Hort Update for July 16, 2020

Hort Update for July 16, 2020, Nebraska Extension, http://communityenvironment.unl.edu/update07162020
Serious ConcernsMajor Symptom:
1. Brown patch Irregularly shaped tan leaf lesions with red margins; roughly circular brownish patches in turf
2. Turf dormancy Kentucky bluegrass vs. Tall Fescue
3. Yellow lawns & iron chlorosis Weather conditions favor denitrification and yellowing of turfgrass
4. Japanese beetles  Watch for skeletonized or lacy leaves on favored plants - rose, linden, grape and many more
Minor Issues
5. Eastern red cedar browning May have a variety of causes
6. Cedar-apple rust and apple scab Bright yellow or olive-green leaf spots on apples and crabapple
Timely Topics  
7. Tomato problems Many maladies appearing now; common symptoms of blossom end rot, curly top virus, mosaic virus, spotted wilt virus, early blight, bacterial spot/speck, wilts
8. Turfgrass watering Encourage customers to use correct irrigation practices promote turfgrass health
9. Fall lawn overseeding - site preparation Seedbed preparation key to seeding success
10. Pigeon Tremex Horntail & Ichumonid wasps These unusual insects may cause customer questions
11. Cicada killer wasps Common native insect is active now; they are NOT Asian giant hornets (aka murder hornets)
12. GRO Big Red Virtual Learning Series Help your clients learn more about vegetable gardening and trees through this series of online programs



1. Brown patchIrregularly shaped tan leaf lesions with red margins; roughly circular brownish patches in turf

Brown Patch disease shows up as reddish-brown patches in lawns. Grass blades within or near the affected area will have tan colored, irregular shaped lesions with a reddish margin. Fungicides are usually not recommended on residential lawns as most turfgrass will grow out of this disease. To aid recovery, maintain consistent growth; not too slow and not too fast. Try to keep grass growing about 1 to 1.5” per week. If it is below that, a summer fertilization is recommended; especially if the lawn is less than 10 years old. When turfgrass shows signs of needing irrigation, water in the mornings when the wind is calm, humidity is high, and evaporation rates are lowest. Know that turfgrass does not need, and will not benefit from, “cooling” irrigation (syringing) in the afternoons.

Brown Patch Disease of Turfgrass, Nebraska Extension
The Brown Patch-Growth Rate Connection in Tall Fescue Lawns, Nebraska Extension Turf iNfo

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2. Turf dormancyKentucky bluegrass vs. Tall Fescue

A tall fescue lawn should NOT be allowed to go dormant as it is not likely to recover.

Kentucky bluegrass (KBG) can be allowed to go dormant for a short period to conserve water. Why the difference? KBG physiologically has the ability to go dormant (turn brown but still be alive) to escape drought conditions during hot, dry summers. On the other hand, tall fescue tolerates drought due to a much deeper root system but cannot physiologically go dormant to avoid drought. If tall fescue turns brown, it is likely dead.  Due to a deeper root system that uses soil moisture deeper in the profile, tall fescue does require less frequent irrigation than shallow-rooted Kentucky bluegrass.

If a homeowner chooses to let KBG to go dormant, remind them that during very hot, dry conditions, the lawn may need about ¼” of water a week to moisten crowns; and KBG can remain dormant for about 4 to 5 weeks only. If fall conditions remain hot and dry, irrigation should resume.

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3. Yellow lawns & iron chlorosisWeather conditions favor denitrification and yellowing of turfgrass

While summer yellowing of Kentucky bluegrass lawns is due to iron chlorosis, the chlorosis is believed to be caused not only by high pH soil but also by a root dysfunction from hot and/or wet soils. Iron chlorosis will NOT respond to an application of nitrogen. When yellowing occurs, apply a foliar only application of iron, such as iron sulfate. Do not water it in.  Discuss with client correct irrigation practices to help avoid overly wet soils from excess or too frequent irrigation. 

Iron Chlorosis Intensifying in Lawns, Nebraska Extension Turf iNfo

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4. Japanese beetlesWatch for skeletonized or lacy leaves on favored plants - rose, linden, grape and many more

Adult Japanese beetles are abundant in many locations. As beetles, the stage they are now in, they feed on leaves, flowers and fruits of more than 300 plant species. Linden trees, roses, grapes and soybeans are favorite foods. The beetles feed over a 4 to 6 week period beginning in late June. They eat green tissue between leaf veins leading to lacy leaves. Severe defoliation can stress trees and reduce yields in orchards and crops. 

Reduced risk beetle control consists of collecting beetles (7 PM at night is a good time) and placing them in a bucket of soapy water or using plant covers to exclude them where feasible. Fine mesh nets can be placed over roses. Two organic sprays, Neem and Pyola, will protect plants for 3-7 days.

Chemically, adults can be controlled with pyrethroid products like Tempo and Bayer Advanced Lawn & Garden Multi-Insect Killer (cyfluthrin) or Ortho Bug B Gone (bifenthrin). Sevin (carbaryl) is another option. These all provide about 2 weeks of protection for foliage and flowers after thorough treatment. 

Because insecticides affect pollinators, try to spray in the evening only and after trees have finished blooming. Follow label instructions explicitly to avoid harming pollinators and damaging plants.

Japanese Beetles, GRO Big Red Gardening Podcast
How to ID and Manage Japanese Beetles, Nebraska Extension GRO Big Red Blog

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5. Eastern red cedar browningMay have a variety of causes

Environmental issues (winter injury and/or dessication from high temperatures and high winds in early June) comes on fairly sudden and is often on one side of the tree or from the top, down. Other than irrigation, there is not much to do for this type of injury but wait and see if new growth occurs next year. Do not prune out the brown areas/branches. 

Cercospora blight is a fungal disease that will cause browning from the bottom of the tree up and from the inside of the branches out. If this disease is confirmed, applications of Bordeaux mixture or a liquid copper fungicide such as Tenn-Cop 5E will effectively control this disease. At least two applications are needed for good control. The first application should be made during the first half of June, just prior to initial infection. The second treatment should be made during the last half of July. The second application normally gives good protection against infection for the remainder of the season. However, additional applications may be necessary during periods of frequent rains.

Cercospora blight, Backyard Farmer

Bagworms will attack cedar. Check trees for last year’s bags. If they are abundant, an insecticide application may be warranted. After the month of June, when bagworms are bigger, conventional insecticides need to be used and these may include malathion, acephate, carbaryl, bifenthrin, permethrin etc. Preventive or systemic insecticides containing dinotefuran are applied to the soil but these must be applied weeks before hatching, hence it is too late to use these products now.

Bagworms on the Loose, Nebraska Extension GRO Big Red

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6. Cedar-apple rust and apple scabBright yellow or olive-green leaf spots on apples and crabapple

Symptoms of cedar-apple rust are bright yellowish-orange leaf and fruit spots, which often have a band of red or yellow around the outer edge. Apple scab causes olive to greenish-black leaf spots. Similar cracked, scabby spots appear on the fruits with heavily infected fruits becoming misshapen.

Fungal infections by these two diseases occur mainly during spring as trees are leafing out and spring rains are providing moisture needed for infection. It is during the infection period (April into June) that fungicides need to be applied to reduce summer leaf drop. Fungicides applied after leaf drop have very little affect. Encourage customers to wait until the following spring to apply a fungicide. Cedar-apple rust and apple scab will not kill a crabapple or apple tree; but repeated infections will reduce tree vigor and health. The best control of these two diseases is to plant resistant cultivars of apple and crabapple.

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7. Tomato problemsMany maladies appearing now; symptoms and links to additional information available

Unfortunately tomatoes are affected by many disease problems. Below are symptoms and links to additional information for the most common problems. 

  • Blossom end rotLeathery to soft brown/black rot on the blossom end of tomatoes.
  • Curly top virus - Leaves roll upward, turn yellow with purple veins. Leaves become thickened, stiff and crisp. No spots or flecks on foliage. Plants are stunted; eventually whole plant is yellow and dies. Transmission by beet leafhopper. 
  • Spotted wilt virus - Upper young leaves bronze and develop small dark spots or flecks; fruit lesions develop unique concentric rings. Transmission by thrips.
  • Tomato mosaic virus - Green mottling of leaves; yellowing and stunting of plants; fruit lesions with yellow halos. 
  • Early blight - Starts with small brown spots on lower leaves. Lesions develop a "bulls-eye" pattern of concentric rings. Infected leave yellow and die. Infection progress up the plant. 
  • Bacterial spot/speck - Begins as very small black spots on leaves and fruits. Severe infection causes leaf loss and unmarketable fruits. 
  • Wilts - Several wilt disease affect tomatoes includine Fusarium, Verticillium and walnut wilt. Symptoms of each can be very similar, starting with leaves turn yellow, often on one side of stem or branch. Symptoms get progressively worse and whole plant wilts. Eventually plant dies. 

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8. Turfgrass wateringEncourage customers to use correct irrigation practices promote turfgrass health

Watering turf wisely during mid-summer is especially important to promote a healthy turf, reduce insect and disease pressure, and conserve a natural resource. It is much better to stay on the dry side than to over-water. Excess moisture in the root zone reduces soil oxygenation, increases soil heat retention, and increases disease risk. The following TurfiNfo link provides recommendations for home owners and professional managers to maximize plant health and reduce over-irrigation this summer. 

Key Points

  • Make sure customer irrigation systems are working correctly
  • Adjust irrigation schedule according to weather conditions
  • Know how much water each irrigation system puts out
  • Don't overwater
  • Resist the temptation to syringe turf

Waterwise Turf Irrigation Practices, Nebraska Extension Turfgrass Science

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9. Fall lawn overseeding - site preparationSeedbed preparation key to seeding success

Late August into early September is the ideal time to seed the cool season turfgrasses tall fescue and Kentucky bluegrass. For success, make plans to finish seedbed preparation before August 15th. Early seeding allows more growing time for new seedlings.

New construction: 1). Remove all construction debris, branches, etc. 2). Control perennials weeds with glyphosate (Roundup). Two to three applications at the recommended timing may be needed. 3). Establish grade for proper surface drainage. 4). Use a rotary tiller or other cultivation equipment to work the soil to a depth of six inches, incorporate compost while tilling. Avoid tillage of wet soil as this creates compaction. Do not try to improve clay soil by tilling in sand as this can increase compaction. For clay soils, spread a one inch layer of compost over the site and till it in. Then spread another one inch layer and till perpendicular to the first tillage. 5). Allow soil to settle after tilling and prior to seeding. 6). Keep the soil moist after seeding.

Overseeding/Renovating an Established Lawn: 1). Mow the area 1 to 1.5 inches tall. 2). If there is excess thatch, one-half inch thick or more, power rake aggressively and removed debris. 3). Aerify the area, punching 20 to 40 holes per sq. ft. with the largest tines available. Make at least two to three passes over the area to be seeded. 4). Apply a starter fertilizer. 5). Seed using a drop spreader or power overseeder (slit or slicer seeder).  6). Keep the soil moist.

Establishing Lawns from Seed, Nebraska Extension Turf iNfo
Improving Lawns in Fall, Nebraska Extension Turf iNfo

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10. Pigeon Tremex Horntails & Ichneumon waspsThese unusual insects may cause customer questions

Pigeon Tremex horntail adults are non-stinging wasps; they are large insects with a tubulal body, brown in color with yellow wasp-like markings. Females, which are larger than males, have a stout ovipositor spine projecting from the hind end of their body. The ovipositor is used to place eggs under the bark of trees. Immature insects are wood borers of hardwood trees species such as silver maple, ash, cottonwood and elm. These insects are not considered a serious tree pest since they primarily choose trees or branches that are in serious decline or have recently died. However, adult insects are emerging now and may cause questions from your clientele. 

An associated insect, the Giant Ichneumon Wasp, is a natural predatory of horntail larva. Adults are large and wasp-like in appearance, and have a very long ovipositor. Altogether the insect's body and ovipositor can be more than 5 inches in length.  Adult females insert their eggs into horntail larva. 

Both insects may be found in declining or dead trees, trees that are being taken down or fallen branches. Neither of them are Asian giant hornets. 

Pigeon Tremex Horntail and the Giant Ichneumon Wasp, Colorado State University 

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11. Cicada killer waspsCommon native insect is active now; they are NOT Asian Giant Hornets (aka Murder hornets)

Midsummer is the season of our native solitary wasps. These wasps are called solitary because they do not build large colonies like paper wasps or yellow jackets. They are predators and prey on spiders, crickets, cicadas and other insects. Solitary wasps paralyze their prey and drag it to a burrow. They lay an egg on the paralyzed prey, which hatches into a larva that feeds on the paralyzed insect. Solitary warps are not aggressive and would only sting someone who is foolish enough to handle the live wasp.

One of the most common is the cicada killer wasp, the largest wasp species in Nebraska. They are up to two inches long and boldly marked with yellow stripes on a black body. Females are larger than males. Cicada killer wasps create underground burrows. These burrows can be found near walks, driveways, and retaining walls and can usually be identified by the presence of fresh soil around the 1/2-inch entrance hole. These wasps can create clusters of nests within a preferred area.

It makes sense that cicada killers are most abundant during midsummer when their prey - cicada, grasshoppers and crickets - are active. Each individual nest is provisioned with 2-3 cicadas for the developing wasp larva to feed on, then sealed. Larvae will develop in the soil until they emerge as adults next summer.

Control Is Usually Not Needed
Due to their docile nature and the fact they are beneficial predatory insects, solitary wasps should be tolerated as much as possible. They are active for only a short time in mid to late summer, then will be gone again for another year.

Ground nesting wasps prefer to dig in areas of dry soil. If their nest building is a problem in some areas of your landscape, one way to discourage them is to run a sprinkler where they are trying to nest. You may have to do this a couple times a day to keep the soil moist until they find another location.

If control is desired an application of carbaryl dust (Sevin) or cyflutrhin (Tempo) made directly into the burrow entrances is effective. If you're nervous about approaching the nests, put the carbaryl dust on a shovel and sprinkle it over the holes.  Applications should be made at dusk, when the wasps are the least active.

Don't broadcast applications of liquid insecticide over the area where solitary wasps are nesting. This method of application is unlikely to reduce their populations.

Cicada killer wasps should not be confused with Asian giant hornets, which have not been found in Nebraska. Asian giant hornets have only been found within the United States in Washington state and the find did not locate an active nest. 

Remain Calm, It's Just a Cicada Killer Wasp!, Nebraska Extension GRO Big Red Blog

Murder and Mayhem: Are "Murder Hornets" Really on the Loose? (Answer: Nope), Nebraska Extension GRO Big Red Blog

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12. GRO Big Red Virtual Learning SeriesHelp your clients learn more about vegetable gardening and trees through this series of online programs

GroBigRed flyerNebraska gardeners can join the experts from Nebraska Extension to learn about vegetable gardening and tree issues. Each session will include a short presentation on the topic and time for discussion and question/answer. Programs are free. Program flyer Registration 

7/21 Fall Gardening
7/28 Tomato Troubles
8/4 Preserving the Harvest
8/11 Tree Problems
8/18 Growing, Harvesting, Drying, and Cooking with Herbs
8/25 Tree Selection
9/1 Tree Planting
9/8 Tree Care
9/15 Incorporating Cover Crops
9/22 Composting
9/29 Putting the Garden to Bed

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