Hort Update for June 20, 2016

Lawns
Major Symptom:
1. Lawn watering tips Irrigate for efficiency and to reduce heat/drought stress
2. Grub control Time to apply preventive grub control products only

3. Bee-friendly turf pesticide applications

Tips to reduce negative effects on pollinators
4. Brown patch/dollar spot Watch for symptoms; control often not needed
   
Trees & Shrubs  
5. Emerald ash borer (EAB)

Key points and wait to treat until found within 15 miles

6. Hackberry decline Yellowing of leaves and dieback of branches
7. Dutch elm disease (DED) Dieback in American Elms
8. Anthracnose Minor disease causing brown blotches in ash, maple, sycamore
9. Sudden limb drop (SLD) Large branches snap off with no signs of decay
10. Bagworms Monitor evergreens for signs of bagworm, treat as needed
   
Landscape Ornamentals  
11. Rose slug Leaf holes or skeletonized leaves
12. Japanese beetle Watch for copper brown and metallic green beetles on rose, apple, maple
13. Weedy tree seedling control Careful weed control needed to eliminate weeds and protect ornamentals
   
Fruits & Vegetables  
14. Herbicide injury Both fruit and vegetable plants susceptible; curled/cupped leaves, distorted veins, thickened leaf tissue
15. Tomato leaf roll Upward rolling of older leaves on heat/drought stressed plants
16. Tomato leaf spots Yellow, brown, tan leaf spots on lower leaf surfaces
17. Bean leaf scorch Brown scorch of tissue on leaf margins
18. Brown rot Infected fruits quickly rot, dry out; covered with masses of brownish-gray spores
19. Cedar-apple rust, apple scab Leaf spots and dropping leaves; too late to treat
20. Bark blasting Dead, sloughing bark on tree branches and/or trunk

1. Lawn watering tip - Hot temperatures stress turfgrass and other plants. A consistently moist soil aids plants in cooling themselves through transpiration; hence reducing heat stress. Maintain a consistently moist, but not saturated soil. When watering, water long enough to moisten soil 4 to 6 inches deep (watering two days in a row may be needed to achieve this depending on soil type and level of soil compaction). Once soil is moistened to this depth, wait to water again until turfgrass shows signs of drought stress (off color, foot prints remain after walking on the turf). Water early in the morning between 4 and 8 AM for irrigation efficiency, but to also aid the plant in dealing with heat stress throughout the day.

Heat is ON!, Turf iNfo from Nebraska Extension
Manual/Automated Sprinkler, Backyard Farmer YouTube

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2. Time for preventively-applied grub control products - Effective white grub control depends on proper timing of the application and moving the insecticide down to the root zone where grubs are feeding. Most of the preventively-applied insecticides including chlorantraniliprole (Acelepryn), clothianidin (Arena), imidacloprid (Merit), and thiamethoxam (Meridian) are systemic in nature and will be taken up by the plant and translocated to the root zone where the grubs are active. These products are typically applied from late May up until July 1, before egg hatch. Curative insecticides such as carbaryl (Sevin) or trichlorfon (Dylox) are applied after egg hatch, typically sometime from mid-August to mid-September. These products must be watered in for acceptable control. Moving the insecticide into the root zone involves applying ½ inch of water immediately after application.

White Grub Management, Turf iNfo from Nebraska Extension

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3. Bee-friendly turfgrass pesticide applications - The best way to have a “bee friendly” lawn is to maintain healthy turf that competes well with weeds and is tolerant of disease/insect invasion so fewer pesticide applications are needed. Mow high and frequent. Water deep and infrequent. Apply fertilizers at the correct rate and the correct time of the season. Core aerate turf on a regular basis to relieve soil compaction. Use pesticides as a last resort. Apply pesticides only on an “as needed” basis rather than part of a regular, ongoing maintenance program. When applied, all label directions need to be followed closely. Since pollinators are visiting blooms, mow prior to pesticide application to remove blooms from weeds like dandelions.

Smart Lawns for Pollinators, Michigan State University Extension

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4. Fungal leaf spots mostly minor diseases - Brown patch disease is mainly an issue on susceptible tall fescue lawns; although it does infect Kentucky bluegrass. It is problematic during periods with extended high humidity and night temperatures greater than 75F. It causes roughly circular patches of blighted grass with a reddish-tan color. On close inspection, long, irregularly shaped tan leaf lesions bordered by a reddish margin will be found.

Recommended cultural maintenance includes avoiding high nitrogen fertilizer applications during summer; using low rates of nitrogen to maintain moderate growth and good recovery from disease; improving air circulation across the turf; avoiding evening and night irrigation; and reseeding or overseeding the turf with resistant species or cultivars.

Although fungicide use on home lawns is rarely recommended for this disease, high label rates of propiconazole or thiophanate methyl could provide three to four weeks of protection when applied prior to onset of symptoms.

Brown Patch Disease, Nebraska Extension

Dollar spot causes small (three to six inch diameter), roughly circular patches in lawns. Spots may coalesce into a large patch. Individual grass blades have tan, band-like lesions with red margins on each end. Damage is usually most severe where there is a nitrogen deficiency. With June, most lawns recover well. Fungicide treatments are available, but not needed on home lawns.

Dollar Spot Disease of Turfgrass, Nebraska Extension

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5. Emerald ash borer (EAB) key points and resources - Now that EAB has been found in Omaha, here are some key points to follow and share with clientele:

  • Identify ash trees (all types of ash are susceptible; Mountain-ash is not a true ash and will not be attacked by the borer).
  • Decide if a tree is a candidate for treatment. Evaluate tree age, health, condition, location (benefits of tree). If it is between 5 and 50 years of age, free of defects and located in a place that casts shade on a home or other important building, it’s a candidate to keep in the landscape.  If it’s very young or very old, has flaws such as co-dominant leaders, decay or stem girdling roots, it may not be worth saving. Use this resource to evaluate ash trees - How to Select Trees for Treatment
  • Understand there are different treatment options, pros and cons to each option, best times of year for application, and treatment needs to be repeated annually or every two years. Trees determined to be good candidates for treatment, and which are under 15 to 20 inches in diameter, can be treated by individual property owners with products available at independent garden centers.  Most trees, and especially larger trees, should be treated by an ISA or NAA certified arborist. Treatment is not recommended until EAB is known to be within 15 miles of a trees location. Use this resource to understand treatments: Misconceptions Regarding EAB Treatments.
  • Trees that are candidates for removal should be replaced with diverse, well-adapted tree species. These Nebraska Statewide Arboretum publications provide good recommendations for trees well-adapted throughout Nebraska - Trees for Eastern Nebraska, Trees for Western Nebraska.

Further information on identification, evaluation and suitable tree species.

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6. Hackberry decline - We are seeing signs of hackberry decline. Yellowing leaves, leaf drop, and branch dieback. Decline is suspected to be the result of a combination of stresses such as weather extremes, repeated herbicide injury, drought, poorly drained soils and more.

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7. Dutch elm disease in American Elm trees causes wilting of leaves and dieback of branches. While fungicide injections can be helpful, they work best when used as a preventive treatment. If symptoms are showing in over 10% of a trees crown, fungicides are much less likely to work. Promptly remove and destroy the wood of dead American elms. Infected branches should be pruned and the wood destroyed by burying, burning or chipping.

Dutch Elm Disease, University of Minnesota Extension

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8. Anthracnose - While anthracnose infects a number of trees like ash, maple and walnut, it causes the most defoliation in Sycamore. Infection is favored by relatively cool temperatures and prolonged periods of leaf wetness; conditions we experienced in May. In exceptionally wet springs, sycamore trees leaf out and then defoliate heavily; as they are doing this year.

In Sycamores, anthracnose results in early spring death of twigs and new shoots. Repeated killing of young twigs results in abnormal branching and gives the tree a ragged appearance. After bud break, sycamores show a scorching and wilting of new shoots and leaves. Later, fully expanded leaves develop elongated tan to brown lesions parallel with the midrib and veins. Infected leaves scorch and shed.

If favorable weather persists, disease development may continue throughout spring into early summer. As temperatures increase, anthracnose becomes less active and trees re-leaf. Preventive fungicide controls are available, but not necessary. And it is too late this year for applications.

Anthracnose, Nebraska Extension

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9. Sudden limb drop - At least 8 reports of ash tree limbs that appear to be strongly attached and have no obvious issues suddenly dropping have been made. Sudden limb drop is basically a tree’s response to very hot, dry conditions. Within arborists circles, there is a lot of discussion on how and why this actually occurs. One thought is that “the wood becomes dry, dry wood is weaker, the limb fails”.  Another explanation is it is the tree’s response to a hot, dry environment where transpiration needs exceed vascular capabilities. When it gets too hot to keep all tissue properly circulated, the tree responds with auto-amputation, letting go of a limb. Eric Berg, with the Nebraska Forest Service, recommends:

  • Be cognizant of the property and potential targets under ash trees that are on your property. For example, if you typically park under a large green ash tree you might consider other location options until at least the weather cools and/or we get some more moisture.
  • Move potential targets such a picnic tables etc. and or limit access to areas directly under the canopy
  • If you are a commercial arborist, take extra precautions of what you are tied into and what you are lowering from. Be extra careful, please….assume the large healthy lateral could snap with no warning.
  • And keep in mind this has nothing to do with EAB.

Sudden Branch Drop, Urban Forest Pro

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10. Bagworms on evergreens - Bagworms have been hatching on evergreens trees. Monitor evergreens for young bagworms. At this time of year, they can be as small as one-fourth inch long. Bagworms are small, brown, triangular shaped and covered with needles for camouflage.  At this size is the time when products like Bacillus thuringiensis will be most effective in controlling bagworms. Other insecticides currently labeled for bagworm control include acephate, carbaryl, cyfluthrin, malathion and permethrin. Affected plants must be thoroughly covered with the insecticide so that it is ingested by the insects as they feed.

Bagworms, Nebraska Extension

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11. Rose slugs & rose chafer - Brown, skeletonized leaves on roses are often caused by either rose slugs or rose chafer. Rose slugs damage leaves by feeding on the green tissue and leaving behind the veins. Rose slug adults are sawflies- small; non-stinging wasps. The larvae are greenish, with a tan head and look much like butterfly or moth caterpillars. If they are not present there is no reason to treat. Most garden dusts or sprays will work. Insecticidal soaps must contact slugs to have an effect.

Rose Chafers are scarab beetles approximately 3/8 inch long, slender, and light tan. Adults feed on rose flowers and foliage. Inspect roses for skeletonized leaves and adult beetles. Rose chafers can be hand picked if the population is small. The insecticides carbaryl (Sevin) and acephate (Orthene) will control these beetles. However, the beetles are quite mobile and new beetles may replace those killed by insecticides.

What's Wrong With My Plant- Roses, University of Minnesota

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12. Japanese beetles - Watch for copper brown and metallic green beetles on ornamentals in extreme eastern Nebraska. Japanese beetles are prodigious feeders on the foliage and fruit of nearly 300 species of landscape plants. Japanese beetles feed on the upper leaf surface, removing the soft green tissue and leaving the veins in a lace-like pattern. Japanese beetles release a strong aggregation pheromone that attracts additional beetles to a food source. The larva (white grubs) of Japanese beetles feeds on the roots of plants from late summer into early fall. Grub control in lawns is the same as for other annual white grubs.

Japanese Beetles in the Urban Landscape, Purdue Extension

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13. Weedy tree seedling control is an ongoing task in many landscapes. Seeds disperse from local trees, birds deposit seeds and seed are often brought in with wood chip mulch. But eliminating weedy tree seedlings in ornamental beds requires care not to damage the ornamentals. Learn to identify common tree seedlings and hand pull or hoe them out when they are young. Careful herbicide spot sprays can also be used. Herbicide can be applied to larger tree seedlings using the glove method.

Glove Herbicide Application Method – Put on a chemical resistant glove, then put over it an absorbent cotton glove. Dip the cotton glove in a herbicide mixture diluted according to label directions. Wipe the chemical on the weeds to be controlled. Be careful not to drip or apply herbicide to desirable ornamentals.

Larger weedy trees can be controlled using a stump treatment method. Cut the plants down close to the ground and paint the freshly cut stumps with concentrated, undiluted glyphosate (RoundUp). Refer to the RoundUp label for more stump treatment information.  If the stumps are not treated, they will resprout and grow back.

Always use proper personal protective equipment when applying herbicides.

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14. Herbicide injury appears as curling, cupping or twisting in leaves as well as distorted veins and leaf yellowing. Leaves often develop an uncharacteristic fan shape. Tomatoes and grapes are highly susceptible, but damage can occur on many fruits and vegetables. If herbicide is suspected, inspect other plants in the area as herbicide injury will typically be found on more than one type of plant. Whether long-term injury will occur is difficult to assess as there is usually no way to know how much herbicide the plant received. Typically plants are stunted for 2-3 weeks following exposure and may abort immature flowers present at the time of exposure. Eventually plants begin developing new growth.

Broadleaf herbicides, such as 2,4-D and dicamba, are volatile, especially during hot weather, and may drift across the yard or even from adjacent yards in concentrations sufficient to cause injury. Avoid applying herbicides for weed control during hot weather to volatilization.

Diagnosing Herbicide Injury on Garden and Landscape Plants, Purdue Extension
Why in the Heck are my Tomato Leaves Curling, University of Illinois Extension

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15. Tomato leaf roll, also called physiological leaf roll, is an environmental response to changing weather conditions. It often appears as spring weather gives way to hot, dry summer conditions. Plants often put on large amounts of foliage growth in spring and may not have enough roots to provide sufficient water uptake to support the plant as weather gets hotter and drier. One method of minimizing plant water loss is rolling of the leaves. Older leaves are usually affected first. Leaves roll upward toward the center mid-vein, without any deformation or twisting. Plant leaves may recover and unroll if the stress is alleviated. Harvest yield is not affected.

Physiological Leaf Curl on Tomato, Penn State Extension

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16. Tomato leaf spots - 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

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17. Bean leaf scorch – The sudden change from cool wet conditions, to hot and dry is causing some problems in the vegetable garden. Leaf scorch is a water-related stress symptom seen as browning of leaves around the edge or margins. Wilting and leaf scorch can be reduced by regular watering during prolonged dry periods. Mulch around the base of plants holds moisture in the soil.

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18. Brown rot is a very common fungal disease of peaches and other stone fruits, including plum, nectarine, apricot and cherry.  The fungus begins infecting blossoms, small fruit spurs and twigs in spring.  Trees wounds, such as hail damage, create many openings for brown rot fungus.  Consequently home orchards that received hail this spring, may see large amounts of brown rot fungus in their trees this year.  Infected twigs and branches develop cankers, resulting in branch dieback.  

In summer, disease spores are mainly wind-blown, but can also be carried in rain splash or by insects.  Healthy young fruits are fairly resistant to infection, but as fruits mature they become more susceptible even in the absence of wounds. Infected fruits rot very quickly and are covered in masses of browish-gray spores.  Fruits quickly dry into mummies and continue to hang onto the tree or fall to the ground.  Harvested fruits quickly rot if not cooled and stored properly. 

Sanitation is very important.  Remove all dropped and infected fruits as quickly as possible and destroy them.  Prune out infected branch cankers. Control insects to minimize disease spread and prevent insects from wounding fruits. Fruits should be cooled and refrigerated (as close to 32 degrees F as possible) after harvest.  Improperly stored fruits can rot within a few days. Use a fungicide spray program to minimize infection.  

Brown Rot of Stone Fruits, Ohio State University
Fruit Spray Schedules for Homeowners, University of Missouri

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19. Cedar-apple rust & apple scab leaf infections early this year were high due to extended cool wet weather that favored infections. 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

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20. Bark blasting - Bark loss on ornamental trees, like Bradford Pears and Norway Maples, and fruit trees, like apple, cherry and peach, has been fairly common in the last two years.  This is likely due to abrupt temperature changes Nebraska has experienced during fall and winter. In November 2014, Nebraska had fairly warm nighttime temperatures through the second week. Then abruptly we had several very cold nights, with temperatures in the single digits. Plants didn't have the gradual exposure to colder nights that induces them to develop increasing levels of cold hardiness. Trees experienced varying amounts of bark death, resulting in twig and branch dieback, and in some cases tree death. Even now, two years later bark death is still showing itself as the old bark sloughs away.

There is no treatment.  No need to spray a sealant where bark has died or use tree wrap.  Allow the tree to heal itself naturally.  Pesticides are only considered if secondary pests like borers attack the exposed inner wood. Avoid fertilizing with nitrogen, since extra nitrogen does not help trees heal damaged bark sections. Provide good tree care through mulch and watering in dry periods to avoid additional tree stress.

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