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Hort Update for June 21, 2017

Nebraska Extension Hort Update - June 21, 2017,
Tree failure in high winds. Image by Jim Skiera, International Society of Arboriculture,
LawnsMajor Symptom:
1. Summer annual weed control Time for 2nd PRE application
2. Crabgrass Early POST application beneficial for controlling crabgrass seedlings
3. Tall fescue control in Kentucky bluegrass lawns No selective controls for home lawns, parks, athletic fields  
4. Winter annual weed control Best window for winter annual weed control is September
5. Turf diseases Brown patch, dollar spot, summer patch showing up 
6. Yellow nutsedge Identify correctly; time to treat
7. Water wisely Correct irrigation practices promote turfgrass health
Trees & ShrubsMajor Symptom:
8. Storm damage series Nebraska Forest Service resource helpful
9. Tree storm damage Reasons for tree failure vary
10. Spruce spider mite Cool season mite; damaged appearing but control will not work now  
11. Summer pruning Not ideal time, but fine to do if needed
12. Iron chlorosis Pale green to yellow leaves with darker green veins
13. Herbicide drift Risk increases with hotter weather
14. Powdery mildew Showing up heavily on Ninebark shrubs and other plants
Landscape OrnamentalsMajor Symptom:
15. Powdery mildew - peony & other ornamentals Whitish-gray powdery growth on leaf surfaces
16. Sunburn Pale, bleached or faded leaf areas, often develop following storm damage
Fruit & VegetablesMajor Symptom:
17. Cedar-apple rust, apple scab Leaf spots and dropping leaves; too late to treat
18. Plum pockets Unripe plums grow abnormally large; hollow with a spongy texture
19. Codling moth "Apple worm" a serious pest of apple & pear; grayish browh moth, 5/16 inch length
20. Cherry maggots Worms immature stage of cherry fruit fly; use sanitation to reduce next year's population
21. Spotted wing drosophila Monitor for insect presence; male fruit fly with red eyes and one dark spot on wing tip
22. Tomato leaf spots Yellow, brown, tan leaf spots on lower leaf surfaces
MiscellaneousMajor Symptom:
23. Chiggers Immature harvest mites; active now; cause itchy bumps
24. Mosquitoes Eliminate stagnant water in pools, tires; control adult mosquitoes
25. Grasshoppers Control while still small

1. Summer annual weedsTime for 2nd PRE application

If needed, a second application of preemergence herbicide to control summer annuals including crabgrass, foxtail, goosegrass, sandbur, prostrate spurge, and purslane can be applied now to control weed seedlings as germination continues into summer.  

Crabgrass and Other Summer Annuals, Nebraska Extension Turfgrass Science


2. Crabgrass seedling controlearly post application beneficial for controlling crabgrass seedlings

By now, crabgrass plants may be present in lawns where no preemergence (PRE) herbicide was used or where breakthroughs occurred.  If a turf is dense and mowed as high as practical, herbicides may not be necessary. Simply control the few crabgrass plants that emerge in thinner areas by hand weeding or spot treating with a postemergence (POST) herbicide. While a PRE can still be applied to control germinating seeds, spot treating with a POST product will decrease the amount of herbicide used on a turf. Drive and other Quinclorac products will control larger crabgrass as long as the appropriate spray adjuvant is used, usually methylated seed oil. Tenacity (mesotrione) and fenoxaprop (Acclaim Extra) are also effective on crabgrass. Check the label for specific species, rates, and precautions.

Crabgrass Turf Info, Nebraska Extension Turfgrass Science


3. Tall Fescue control in Kentucky bluegrass lawnsNo selective controls for home lawns, parks, athletic fields

Clumps of coarse textured, wide-bladed grass in finer bladed KBG lawns is most likely tall fescue.  Homeowners may refer to this grass as water grass and confuse it with yellow nutsedge, also called water grass as a common name. The two do not resemble one another and are easily distinguishable. Positively identify all weeds and other pests prior to controlling. For tall fescue in KBG lawns, mechanical removal by digging or nonselective control with glyphosate (Roundup) are the only options.

Controlling Tall Fescue, Nebraska Extension Turfgrass Science


4. Winter annual weed controlBest window for winter annual control is september

Mid-summer postemergence control of winter annual weeds is usually not needed or recommended. Winter annuals, like henbit, field speedwell and annual bluegrass, die off on their own as summer temperatures get hotter. The risk to non-target plants increases greatly and lowered effectiveness of herbicide control at this time of year is not worth the risk. Hand dig broadleaf weeds if needed and apply a preemergence herbicide in September to kill the next generation as they begin to germinate.  


5. Turf diseasesbrown patch, dollar spot, summer patch showing up

Turf diseases are showing up in some lawns. Most commonly are brown patch that causes one to two foot tan patches in lawns and dollar spot that causes smaller brown spots in a lawn. On close inspection, grass blades infected by brown patch have irregular shaped dark tan lesions with dark red margins. Dollar spot lesions are light tan, completely encircle the grass blade and also have a red margin but only on the top and bottom of the lesion.  Look for lesions prior to mowing, not right after or they may be removed during mowing. As a general rule, in most home lawn situations fungicide control may not be needed or recommended. Where control is justified, see link below for fungicide treatment options.

Diseases Looming, Nebraska Extension Turfgrass Science


6. Yellow nutsedge Identify correctly; time to treat

Yellow nutsedge is a perennial sedge that typically emerges from underground tubers in late May in Nebraska. From the first week of June up to June 21, before plants develop new tubers, is considered prime time for control. To reduce nutsedge, mow tall and avoid overwatering. Hand-pulling is effective where there are fewer plants.  When herbicides are used, sulfentrazone (Dismiss), imazosulfuron (Celero), halosulfuron (SedgeHammer), and mesotrione (Tenacity) are labeled for postemergence control in cool-season turfgrasses and buffalograss.

When treated in turf, halosulfuron has provided the best yellow nutsedge control in UNL experiments over the last four years, perhaps because it is absorbed foliarly.  Sulfentrazone is root-absorbed, and may provide similar control in thin turf where herbicide more readily reaches soil. Additionally, sulfentrazone and mesotrione provide preemergence control of germinating tubers. Because of tuber persistence in soils, herbicide applications in successive years are often required for control.

Yellow Nutsedge, Nebraska Extension Turfgrass Science


7. Water wiselyCorrect irrigation practices promote turfgrass health

Water wisely 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.  

Waterwise Turf Irrigation Practices, Nebraska Extension Turfgrass Science


Trees & Shrubs

8. Storm Damage SeriesNebraska Forest Service REsource Helpful

With recent storms and tree damage, below is a link to the Nebraska Forest Services storm damage publications series. It includes ten fact sheets with the titles.

  1. Immediate Care of Storm Damaged Trees
  2. How to Select an Arborist or Tree Service
  3. Pruning Storm-Damaged Trees
  4. Large Tree Pruning & Care
  5. Don’t Top Trees
  6. Recognizing & Correcting Tree Hazards
  7. Tree Selection & Placement
  8. Tree Planting
  9. Care of Newly Planted Trees
  10. Storm Damage Resources

Storm Damage Series, Nebraska Forest Service


9. Tree storm damageReason for tree failure vary

Trees failing during a storm leads to question about why a tree fails in a wind storm. There can be a variety of reasons, not to mention wind velocity, for why a tree fails.  These range from tree species with weak or brittle wood to issues like decay, poor structure from lack of or incorrect pruning, stem girdling roots and site problems such as shallow, compacted or saturated soils; or confined root areas. For some prevention tips, see

Storm Damage to Landscape Trees: Prediction, Prevention and Treatment, University of Minnesota 


10. Spruce spider miteCool season mite; damage appearing but conrol will not work now

The most common mite that attacks spruce and juniper is the spruce mite. Spruce mites are cool season mites. Their damage may be showing up now as they were feeding during spring. They have finished feeding and most are now in the dormant egg stage to over-summer. Products applied for control now will not be effective; and the damage is already done. Monitor trees with damage later this summer and fall. As temperatures cool, eggs will hatch and more damage may occur. 

Warm season mites, like two-spotted spider mites, feed during summer. If present on plants, control may be needed now. Always confirm mites are present prior to controlling. Use the white paper test. Tap a few branches over a white paper and watch for mites (specks) crawling on the paper. It is helpful to run your hand over the paper. If the specks are mites, they will smear green, red or yellow.  Control ranges from a water spray to dislodge mites (recent heavy rains may have helped); to using labeled horticultural oils, miticides or insectcides. 

Spider Mites, Colorado State University Extension


11. Summer tree pruningnot ideal time, but fine to do if needed

Summer pruning is not the ideal time to prune many plants, but if needed it is fine to prune. Limit the amount of pruning done and stop pruning by mid-August. As always, make correct pruning cuts and do not apply any type of wound dressing or pruning paint to the wound. 


12. Iron chlorosispale green to yellow leaves with darker green viens

Iron chlorosis is showing up as pale green to yellow leaves with darker green veins. A common cause of iron chlorosis in the Great Plains is our high pH or alkaline soils. Iron is not as readily available to plants in a high pH soil and certain plants, like pin oak, silver and red maple, develop chlorosis. Other factors, like compacted or saturated soils, can compound the issue. Treatment involves providing iron, and/or manganese, through soil application or trunk injections. Depending on what part of Nebraska you live in, see the appropriate pamphlet below for recommendations based on tree size. Avoid planting trees and shrubs known to not be tolerant of alkaline pH.

Chlorosis of Trees in Eastern Nebraska, Nebraska Forest Service

Chlorosis of Trees in Central and Western Nebraska, Nebraska Forest Service


13. Herbicide driftrisk increases with hotter weather

Trees and shrubs with curled or cupped leaves, along with distorted veins, may have been hit by herbicide drift. With windy conditions and hot temperatures, the risk of drift occurring increases. Ideally, avoid the use of herbicides whenever conditions are windy, temperatures are above what the label recommends, usually 85 degrees Fahrenheit; or when conditions are very calm and hot or humid. Such conditions can lead to volatization of an herbicide and a drift situation. As a rule, most healthy trees will survive a drift situation with not long term issues. Chronic exposure over the years, combined with other stresses, can eventually lead to a trees decline. 


14. Powdery mildewshowing up heavily on ninebark shrubs and other plants

Powdery mildew on ninebark is extra heavy in some areas of Nebraska. Powdery mildew is a fungal disease that affects a wide variety of landscape plants. It appears as a white powdery growth on leaf surfaces that can be wiped off. Powdery mildew is rarely fatal to plants. In years when environmental conditions such as heavy shade, poor air circulation and favorable temperatures come together, mildew can be severe enough to kill leaves and cause some defoliation. Management includes not planting mildew susceptible plants in locations with these environmental conditions, selecting resistant cultivars of susceptible plants and reducing shade and poor air circulation with correct pruning. Sanitation may help decrease fungal pressure.

Powdery Mildew on Landscape Plants, Nebraska Extension 


Landscape Ornamentals

15. Powdery mildew - peonies and other ornamentalswhitish-gray powdery growth on leaf surfaces

This disease causes grayish white powder-like patches on upper leaf surfaces. It is promoted by warm temperatures and high humidity. Extended wet conditions this spring and early summer have caused early infections on many garden plants.  Many types of plants are susceptible, such as Phlox, Monarda and Zinnia. If plants are heavily infected consider replacing them with resistant varieties.  Place susceptible plants in areas with good air circulation.  Avoiding overhead irrigation and excess nitrogen fertilizer. Fungicides will provide some protection as new healthy foliage emerges. Refer to the publication below for recommended fungicides. 

Powdery Mildew on Landscape Plants, Nebraska Extension


16. Sunburnpale, bleached or faded leaf areas, often develop following storm damage

Sunburn is often seen in annual or perennial plants when they are suddenly exposed to higher intensity light. Symptoms appear as pale, bleached or faded leaf areas that progress to brown. Patches become brittle as leaf tissue dies. Sunburn is usually due to a sudden increase in sunlight exposure caused by tree removal, heavy pruning or storm damage. Of if plants are transplanted into sunnier locations. Drought can also cause leaf scorching along the margins or leaf tips. 

Avoid transplanting perennials in mid-summer. Keep plants well watered and mulched. If tree pruning or storm damage results in sunburn on nearby perennials, consider moving affected plants to shadier locations in September. Realize that new growth next season, which is exposed to higher light levels right from the beginning in spring, may be better adapted to the sunny location and have fewer problems.   


Fruits & Vegetables

17. Cedar-apple rust, apple scableaf spots and dropping leaves; too late to treat

Leaves infections early this year were favored due to extended cool wet weather. Heavily infected leaves are now starting to fall, causing concerns to homeowners. Unfortunately, it’s too late to treat; fungicide applications are not effective at preventing infections this late in the growing season. Encourage homeowners to rake up and discard fallen leaves to reduce disease pressure on trees next year. Keep trees well watered this summer to prevent additional stress and make sure trees are mulched around the base. Otherwise healthy vigorous trees usually tolerate some leaf loss without serious long-term consequences. Fungicides should be applied next spring on trees with a history of serious defoliation.

Apple Scab, Nebraska Extension
Cedar Apple Rust and Related Rusts of Apples and Ornamentals, Nebraska Extension
Diseases of Broadleaf Trees, Nebraska Forest Service


18. Plum pocketsUnripe plums grow abnormally large; hollow with a spongy texture

Plum pockets is a common disease on wild and American type plums, caused by the fungua Taphrina communis.  It's too late for fungicide control now. Dormant sprays of fungicides are effective controls if applied in late winter before buds begin to swell and when temperatures are above 40° F. These diseases cannot be controlled once leaves have started to expand. Use the fungicides ferbam, chlorothalonil (Daconil), Bordeaux or liquid lime-sulfur. Do not add oil to lime-sulfur or spray oil treatments for three weeks after application of lime-sulfur. Lime-sulfur should not be applied to trees when temperatures are below 45 or above 80 F. Follow recommended label rates for all commercial fungicides.

Plum Pockets, University of Minnesota Extension


19. Codling moth"Apple worm' a serious pest of apples & pears; grayish brown moth, 5/16 inch length

Codling moth is a non-native insect and a serious pest of apple, but also attacks pear, crabapple, quince, and English and black walnuts.  Insects overwinter as fully grown larva inside a silken cocoon under flaps of loose bark, in brush, on posts, or other areas around the home orchard. Adults begin to emerge in spring, as the last petals fall from apple trees. They are a grayish-brown moth with a crisscross pattern of light gray lines on their forewings and a bronze or copper colored patch near the forewing tip. They are 5/16 inch in length with an 11/16 inch wing spread. Females lay eggs on fruits and leaves.

After hatching, larvae seek a rough patch on the apple skin, such as a scab lesion, wound, or calyx end of the fruit, to begin tunneling into the fruit. They spend about 3 weeks tunneling through the fruit and growing. At maturity the larvae are white or a pale pinkish color with a brown head. They leave the apple, fall to the ground to pupate, and reemerge as adults for a second generation or "summer brood" in July. Insect tunneling greatly reduces the appeal and marketability of fruits, as well as creating openings for rot fungi.

Codling moth attack often results in fruit drop. One important method to minimize insects is to pick up and destroy fallen fruits as quickly as possible throughout the summer. Chemical control involves applications every 7-14 days from petal fall to near harvest. For a complete schedule, including recommended pesticides, refer to the spray schedule below.

Codling Moth on Fruit Trees, Ohio State University
Fruit Spray Schedules for Homeowners, University of Missouri


20. Cherry maggotsWorms immature stage of cherry fruit fly; Use sanitation to reduce next year's population

Cherry fruit fly adults active now, laying eggs on developing fruits of tart, sweet, black and pin cherries. Immature stage is the cream-colored maggot found in ripe cherries. Usually there is only one maggot per fruit. Infested fruits often decay or develop brown rot infections.

Too late to control for this year. Remove and dispose of any fallen fruits; cherry fruit fly populations will increase each year of larvae are allowed to pupate and overwinter in the soil beneath trees. If insecticidal control is needed, use sticky traps to monitor for the presense of adult flies next year. Apply first insecticide application as soon as the first adult flies are found.

Fruit Tree Spray Schedules for Homeowners, University of Missouri Extension  


21. Spotted wing dropsophilamonitor for insect presence; male fruit fly with red eyes and one dark spot on wing tip

Spotted wing drosophila is active now attacking the soft fruits of brambles (raspberry, black berry), strawberry, blueberry, grape, cherry, plum, peach and many small wild berries. Adult females make a slit through the fruit skin and insert eggs inside. Larval feeding inside the fruit causes fruits to become wrinkled and dimpled and they are prone to fungal infection causing decay and rot. In its native range in Japan roughly 13 generations occur each year.  Upwards of 10 generations are predicted in the United States depending on climate.

Monitor for SWD through trapping to distinguish it from native fruit flies. Fruit growers especially need to be monitoring frequently, but also to be checking for evidence of ovipositional or early larval damage. Traps do not always keep in real time sync with what is going on in the field.

Treatment is warranted immediately once one or more SWD flies are discovered, or if larvae are found in fruit. Remember to take notice of PHI's for whatever insecticide is used. Sanitation is also important as a means of helping to minimize fly numbers, and consequently, yield losses.

If SWD occurs, manage it through sanitation including prompt remove of infested fruits and insecticide applications.

Spotted Wing Drosophila in Home Gardens, University of Minnesota Extension


22. Tomato leaf spotsyellow, brown, tan leaf spots on lower leaf surfaces

Be on the look out now for early blight and septoria leaf spot, fungal diseases that begin as leaf spots on lower leaves, then work their way up the plant causing leaves to die; often leading to fruit sunscald. Both can be reduced with fungicides labeled for use on tomatoes. For best results, applications need to begin as soon as symptoms first appear on lower leaves and applications made about every 7 to 10 days. Avoid overhead irrigation and increase air circulation around plants with proper spacing and caging. Mulch the soil around tomatoes to reduce soil splash of fungus onto lower leaves. Plant resistant varieties and avoid planting tomatoes in the same area each year. Severely infected plants are best pulled and destroyed. Use fall sanitation to reduce the amount of overwintering fungus.

Common Vegetable Diseases, Backyard Farmer on YouTube
Tomato Leaf and Fruit Diseases & Disorders, Kansas State University



23. Chiggersimmature harvest mites; active now causing itchy bumps

Chiggers are the larval state of harvest mites. In early spring, adults lay eggs in the soil that hatch in June. Adults are harmless, but the tiny, six-legged larval stage is parasitic on animals and humans. On hosts, chiggers move about until reaching a confined place, such as around ankles, under socks, waistbands or arm pits. Chiggers do not burrow into the skin, but pierce the skin and inject a fluid that causes tissues to be inflamed and itchy. Once fully fed, chiggers drop from hosts and enter the ground. In the fall, it becomes the bright red overwintering adult.

To monitor for chiggers, place six-inch squares of black paper vertically in the grass. If chiggers are present, they will climb to the top of the paper. Because several hours elapse before chiggers settle down to bite, bathing soon after exposure to chigger-infested areas may wash chiggers off the body and prevent feeding. Clothing should also be washed. Insect repellents containing "DEET" (diethyl toluamide) are effective in reducing chiggers.

Where chiggers are a problem in landscapes, keep lawns and shrubbery well manicured and mowed, especially in areas adjacent to dwellings.

Chiggers can also be reduced by treating turf with insecticidal sprays. UNL Extension Entomologist Fred Baxendale found a liquid treatment of bifenthrin reduces chiggers 75-95 percent for several weeks. Use 0.2 pounds active ingredient per acre. To escape the highest chigger populations, your first treatment should be early- to mid-June.

Itchy Chiggers, Nebraska Extension


24. Mosquitoeseliminate stagnant water in pools, tires; control adult mosquitoes

Mosquito numbers are on the rise.  Mosquito control involves:

  1. Applying larvicides, such as Bactimos or Vectobac which contain BTI (Bacillus thuringiensis israliensis) to stagnant water pools.
  2. Spraying grassy areas and shrubbery with insecticides such as permethrin or malathion (check label for use on the landscape plants to be sprayed.
  3. Preventing water from standing in containers such as flower pot basins, children's wading pools, bird baths, clogged roof gutters.
  4. And using personal repellents containing DEET (diethyl toluamide).

Residential Mosquito ControlNebraska Extension
Flies, Gnats & MosquitoesNebraska Extension


25. Grasshopperscontrol while still small

Grasshoppers are still small and should be controlled before they reach mature size and become more difficult to control. As adults, they can severely defoliate garden and landscape plants if populations are high. Effective control includes treating egg-hatching areas (roadsides and weedy areas) at egg hatch while grasshoppers are still small, since adult grasshoppers are very difficult to control.

A Guide to Grasshopper Control in Yards and Gardens, Nebraska Extension
Grashoppers in the Field and Garden, Nebraska Extension
Grasshopper Control, Backyard Farmer on YouTube
Grasshoppers of Nebraska, Nebraska Extension