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Hort Update for May 18, 2015

Lawns Major Symptom:
1. Powdery mildew Grayish white growth on leaf surface in shade
2. Leaf spot Diffuse yellow or browning in lawn; leaf spots on blades
3. Weed pressure Know weed name and type prior to herbicide use
4. Wet soils and compaction Avoid foot and vehicle traffic on wet soils
5. Automatic irrigation systems Turn systems off. Only turn systems on when soil dry.
6. June fertilization If needed, apply around mid-June. Use slow release N.
7. White grub control  Only needed on lawns with a history of damage
Trees & Shrubs  
8. Weather extremes Likely explanation for variety of tree/shrub issues
9. Tree fertilization NOT needed in most landscaped areas
10. Check downspouts Monitor plants near downspouts for excess moisture
11. Periodical cicadas about to emerge Protect very young trees from egg laying
12. Pine bark adelgid White woolly material on white pine bark
Landscape Ornamentals  
13. Rose slugs Leaf holes or skeletonized leaves
14. Columbine leaf miners White meandering trails appearing in leaves
15. Spring bulb care after blooming Don't cut down foliage after flowers have faded
Fruits & Vegetables  
16. Rhubarb flowering Flower stalk formation often caused by cold spring temperatures
17. Cold temperature effects on warm season vegetables Yellow or black leaves, plant stunting and wilting, death of flower buds
18. Disease suppression in the vegetable garden  Recommended cultural practices for disease suppression
19. Identification of frogs, snakes, lizards and turtles Amphibians, Turtles and Reptiles of Nebraska website/app helps with wildlife identification


1. Powdery mildew appears as a grayish-white growth on the surface of grass blades. It is common in shady areas with poor air circulation that is rarely more than an aesthetic concern. Cloudy, overcast weather and high humidity promote infection and spread of the fungus.. Powdery mildew is managed by reducing shade and increasing air circulation to reduce leaf wetness. If this is not feasible, replace Kentucky bluegrass turf with tall fescue which is more shade tolerant.. The disease typically dissipates with dry summer weather and treatment is generally not required. Under heavy pressure, fungicide treatment is an option. Applications need to be repeated as needed and treatments started prior to significant mildew development. Routine fungicide applications are not a long term solution. For a listing of fungicides, see NebGuide link below.

Powdery Mildew in Turfgrass, Nebraska Extension
Powdery Mildew in Landscape Plants, Nebraska Extension


2. Leaf spot turf and are a problem on new spring seedlings. Infections are promoted by wet weather. Symptoms begin as round to oval leaf spots with buff-colored centers surrounded by a dark margin. The turf may show diffuse yellowing and browning. There are limited fungicide options to leaf spot, especially for homeowners. It is better managed with resistant cultivars and good turf management practices of correct watering, fertilization and mowing; along with core aeration in spring or fall. Collect clippings when the disease is active.


3. Weed suppression - Henbit, clover and more; wet weather promotes a variety of weeds. Control involves good turf management to promote a dense, vigorous turf that competes with weeds. Use a tall mowing height of three inches to reduce seed germination and to shade out young weed seedlings. If herbicides are used, know the weed type and when to treat to have success. For example, henbit is a winter annual. Henbit plants growing now have or will soon produce seed and the plants will die. If used, the most effective herbicide control is a preemergence product applied in September since fall is when the majority of winter annuals germinate. White clover is a cool season perennial and so applying a postemergence herbicide in fall is most effective.  The best way to control both species is to promote a healthy lawn with adequate nitrogen fertilizer to sustain a dense turf stand.


4. Wet soils and compaction - Frequent rainfall this spring has increased the risk of soil compaction on fine textured soils. . Remind clientele to avoid foot and vehicle traffic on wet loam and clay soils. Compaction leads to a number of turf issues ranging from thinning, to weed invasion, reduced water infiltration, and reduced soil aeration. Core aeration can help reduce compaction. Winter freeze-thaw cycles are the best medicine for relieve of compaction.


5. Automatic irrigation systems - Irrigate only if soils are dry. Irrigations systems should be turned off. Allowing the turf to dry down in spring helps improve summer stress tolerance. . Remind clientele not to set it and forget it when using their irrigation system. The best way to use an automatic irrigation system is to water when the turf looks dry and then turn it off. Water will be conserved, money will be saved and the turfgrass will have fewer issues such as compaction and thatch.


6. June fertilization - Early June is the second most important time to fertilizer turf. Turfgrass naturally grows vigorously during the spring. That growth rate will begin to slow during late spring. The turf can also have a light green color in late May to early June. Consider an application of during this time to promote healthy growth into the summer. Use a fertilizer that's 50% slow-release nitrogen for maximum fertilizer duration. Established lawns typically don't need fertilizer in July because microbes in the soil release nitrogen during summer.


7. White Grub Control - Insecticide applications are recommended only on lawns with a recent history of grub damage. Overwintering annual white grubs are pupating and will begin to merge as adult masked chafers in late May and June to mate and lay eggs. If preventive type insecticides are used, these products need to be applied between late May and mid-July. If a rescue application, such as with dylox insecticide is used, this product is only effective if applied after egg hatch. Rescue applications are justified when eight white grubs can be found per square foot, typically in August.

Grub Control Products for Nebraska Lawns:
Preventative Control  (Early Jun to mid-July application)

Professional use products
Neonicotinoid class - Merit (imidacloprid), Arena (clothiandin), Meridian (thiamethoxam)
Anthranilic diamide class - Acelepryn (chlorantraniliprole), Ference (cyantraniliprole)
Insect Growth Regulators - Mach2 (halofenozide)
Combination Products - Allectus (imidacloprid + bifenthrin), Arena (clothianidin + bifenthrin), DuoCide (carbaryl + bifentrhin)

Homeowner products
Bayer Advanced Season Long Grub Control (imidacloprid)
Scott's GrubEx (chlorantraniliprole)

Curative Control

Professional use products
Dylox (trichlorfon)
Sevin (carbaryl)

Homeowner products
Bayer Advanced 24 Hr Grub Control (trichlorfon)
Sevin (carbaryl)


8. Weather extremes may explain a variety of tree/shrub issues. The drought of 2012, extreme cold winter temperatures in recent years, and sudden changes in temperature may be responsible for a variety of tree and shrub issues we are now seeing. For example, reports of willows dying back, ornamental or Callery pear having sparse leafing, maple branches dying, and severe dieback in roses and other shrubs could be traced to weather extremes.

Trees and shrubs were stressed by the 2012 drought and extreme heat (three weeks of above 100 degrees Fahrenheit). While stressed, plants are more likely to be infected by diseases such as Verticillium wilt and canker causing diseases, and to be infested by insects such as borers. It may then take three to five years for these pests to cause enough damage to kill a tree or shrub or to cause branch dieback.

During the winter of 2013/14, we had extremely cold temperatures and dry conditions leading to outright winter kill of some plants. This past winter we had extremes, such as 5 degree nights in November and 70 degree days in February. Plants are more likely to be affected by extremes or sudden changes in temperature, than by gradual changes.

As a rule, we recommend waiting until about June 1 before removing a plant or bare branch in case secondary buds still develop. Correct watering and mulching can help living, but stressed plants recover. In general, do not fertilize stressed plants.


9. Tree fertilization is NOT needed in most cases: Most Nebraska soils are fertile enough to support tree and shrub growth without applying fertilizer.  Most trees and shrubs, especially those growing in a fertilized lawn, do not require additional fertilization. Vigorous growth and good leaf color is an indication a tree or shrub is receiving sufficient nutrients. Less vigorous plant growth and poor color usually indicates an insect or disease problem, environmental stress, poor root development or damage, moisture deficiency, or other factors not related to fertility. Do not fertilize trees without taking a soil test to determine the need to fertilize.

Determining the Need to Fertilize Landscape Trees and Shrubs, Nebraska Extension


10. Check downspouts and nearby plants - When rainfall is abundant, woody plants and herbaceous perennials growing near downspouts may become too wet, leading to leaf yellowing and root rots that may kill the plant. If needed, redirect the downspout away from the plant. Be sure the downspout is still directed onto a planted or porous surface to reduce runoff and water from lawns and landscapes. Runoff during rainstorms carry sediment and nutrients to surface water which can impair a water ecosystem.


11. Periodical cicadas about to emerge - In Nebraska, periodical cicadas (17 year cicadas) could emerge in counties along the Missouri river in far eastern Nebraska. They may possibly be found in Lancaster County. These cicadas emerge from late May into June, and can damage young trees whose main stems and branches are between 3/16" and 7/16" diameter. Female cicadas cause damage when they puncture or slit the twigs of trees and shrubs to lay eggs. Infested branches appear as if the eggs have been stitched in by a sewing machine. These branches can turn brown, die, and sometimes break off. Female cicadas lay eggs on a variety of woody plants and are common on maple, oak, linden, crabapple and fruit trees. Small ornamental trees and shrubs are best protected by covering them with no larger than 3/8" mesh screening while cicadas are present and laying eggs.


12. Pine bark adelgid was introduced from Europe, but is not found throughout the United States. White pine is the preferred host. The insects are very small and dark, but are covered with cottony white  material.  Infested trees have woolly white material covering the bark of the trunk or branches, where the insects are feeding and reproducing. Adelgids insect their needle-like mouthparts into the tree bark to feed on sap. Healthy, vigorous mature trees suffer little damage from the insect feeding, but young trees can become stunted and weakened. Stressed trees may suffer heavy infestations. 

Monitor trees for infestations from April through early autumn. Use a dormant oil spray in early spring to smother overwintering aphids hiding in bark crevices. Spray active infestations during the growing season with an insecticide, using enough water pressure to penetrate their woolly covering. 

Pine Bark Adelgid Becoming Active in White Pine, Michigan State University Extension
Pine Bark Adelgid, Iowa State University Extension 


13.  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


14. Columbine leafminers are the immature stage of a small, gray fly.  Egg laying begins about the time plants start to flower.  Leafminer larvae are small enough to tunnel between the upper and lower layers of leaf cells, leaving behind meander trails.  Damage progresses through the season, from two or more generations of this fly pest.  Leafminer activity has little, if any, effect on plant health. Clip and destroy mined leaves.

Columbine Leafminers Leave Quite a Mess, Iowa State University Extension


15. Spring bulb care after flowering -  Remove faded flowers to prevent seed formation. Seed production takes energy away from the bulb and may reduce flowering the next year. Deadheading some types of tulips and daffodils can lengthen flowering time for up to two months. Apply a balanced fertilizer, such as a 10-10-10, after the flowers have faded. This will help create a larger bulb to enhance next year's bloom.

After bloom, the dying foliage can be hidden by the developing growth of other flowers and shrubs in the bed, although the leaves should receive some sunlight until they begin to yellow. Future flower production may be reduced by removing, braiding or tying the foliage.  After the leaves have turned yellow, cut and remove the foliage. Removal of dead foliage from the garden will help prevent diseases from affecting next year's bloom. To hide unattractive, yellowing foliage, plant annual flowers in front of spring flowering bulbs.

Mulch should be added each spring to maintain the desired depth of 2 to 3 inches. Mulch also will conserve soil moisture, reduce weed populations and protect the bulbs from temperature fluctuations in the soil. 

Spring Flowering Bulbs, Nebraska Extension 


16. Rhubarb flowering - Bolting, or seed stalk formation, happens to rhubarb plants for a variety of reason including physiological stress, age of planting and varietal differences.  Several environmental stresses can cause flower initiation, such as low fertility, excess heat, periods of hot or cold temperatures, shorter day length and drought. In spring, flower formation is often initiated by cold night temperatures.  Greater amounts of flower stalk development frequently appear on older plants, indicating overcrowded crowns and the need for renovation or division of plants. Variety differences also occur with green stalked varieties being more prone to bolting than red stalked varieties. Old fashioned varieties Victoria and MacDonald are heavy seed producers. Canada and Valentine are less likely to bolt.

Remove flower stalks as soon as possible to prevent plants from using energy on seed development. Removing seed stalks results in a larger amount of crown bud development and will increase harvest the following year. Bolting does not effect the edibility of rhubarb stems; they do not become poisonous and can still be harvested and eaten.

Growing Rhubarb in the Home Garden, Ohio State University


17. Cold temperature effects on warm season vegetables - Gardeners are often tempted to plant vegetable garden plants before the damage of frost and cold night temperatures have past.  Warm season vegetables - tomato, pepper, eggplant, watermelon and muskmelon - can suffer damage if exposed to cold air or soil temperatures. Sypmtoms of cold injury include olive green or yellow leaves, or leaves with a purple underside.  Severely affected leaves may turn black.  Plants may also wilt as cold temperatures impact root function and water uptake.  Severe or prolong cold temperatures may cause plants to be stunted, with flowers on the first fruiting cluster killed or fruits deformed due to poor pollination. Delays in fruit maturity and overall yield can be expected for affected plants.


18. Disease suppression in the vegetable garden - Good cultural practices in the vegetable garden are important to reduce disease probelms, starting with s anitation. Garden sanitation helps reduce disease pressure by eliminating infected plant material and disease spres.  Remove all plant debris that is left in the garden from last season before planting.  Establish a 3-4 year rotation schedule in your garden, by moving those plants most affected by disease to containers or new plots of ground.  Or choose not to grow heavily affected plants for a few years to reduce populations of disease organisms in the soil.

One of the most common methods of tomato leaf infection is through rain splashing on bare soil. All of the diseases mentioned above overwinter on infected plant debris in the soil. During a rainstorm, water droplets hit the soil surface, splashing water and soil up onto the lowest tomato leaves. Prevent rain splash in your garden by covering the soil with mulch. Apply a 2-3 inch layer of mulch, using clean straw, black plastic, newspapers topped with wood chips, or any other coarse organic material. Mulch also helps suppresses weed growth, moderates soil temperature extremes and helps retain soil moisture.

Keep tomato leaves as dry as possible by applying water to the base of plants through soaker hoses, instead of using an overhead sprinkler, since water on the leaf surface promotes germination of fungal spores and leaf infection.

Suppression of leaf spot diseases, once plants have been infected, can be accomplished through sanitation and the application of fungicides. Remove and discard heavily infected leaves and plants. Infections may be slowed by removing diseased leaves as they appear.

Fungicides are protective; they keep healthy leaves from becoming infected.  Fungicides are not curative. This means that infected foliage will remain diseased and may die. Fungicides must be applied on a regular basis to provide continued protection for the healthy leaves. A good fungicides for use in the vegetable garden is liquid copper and is readily available at most garden centers. Read the fungicide label carefully to determine the number of days you must wait after the final fungicide application before fruits can be harvested.

Disease Prevention in Home Vegetable Gardens, University of Missouri Extension


19. Identification of frogs, snakes, lizards and turtles -  You don't have to like snakes to appreciate them – at least that's what Dennis Ferraro says. "My main function is to instill appreciation and awareness," said Ferraro, herpetologist and professor of practice. A part of that effort includes the new and improved "Amphibians, Turtles & Reptiles of Nebraska" website (, managed by Ferraro and his team at UNL's School of Natural Resources.

When the website launched in 2001, it was "a real beta version," Ferraro said. It was updated in 2003 with additional photos and text, but at the time it was limited to covering snakes and turtles. In 2005, the website expanded to include information on frogs, lizards and salamanders.  A decade later, the website underwent its most extensive renovation yet. "We completely redid it," Ferraro said. "We had new photos taken. It's a completely different look." And, most notably, this version is mobile-friendly – meaning the website is much more than, well, a website.

Amphibians, Turtles and Reptiles of Nebraska