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Hort Update for May 17, 2017

Hort Update May 17, 2017,
African Sunset Petunia, Genetically Engineered Petunia Pulled from the U. S. Market
LawnsMajor Symptom:
1. Turfgrass for shade Tall fescue best choice to try; use good cultural practices
2. Fertilizing/combo products May is still a good time to apply
3. Seedling crabgrass Dimension a better PRE to use once some germination has begun   
4. Blooming dandelions 2nd best time to control with digging or post emergence products
5. Fairy ring Darker green ring in the turf
6. Fungal leaf spot diseases Control typically not needed in home lawns
7. White grubs Wait to make application
8. Power raking Still okay in May as long as weather remains cool
Trees & ShrubsMajor Symptom:
9. Emerald Ash Borer (EAB) treatments May is the best timing for injecting insecticides for EAB
10. EAB insecticide restrictions Note labels, some products have limits on quantities per acre
11. Tordon not for landscapes Due to translocation issues and killing of non-target plants
12. Hackberry twig drop About 6” of tips (tender growth) dropping off
13. Ninebark dieback Most likely environmental issue; cold temperature injury
14. Spruce browning Variety of factors can be the cause
15. Leaf curl aphids Leaves twisted and curled; may be sticky
16. Bark sloughing Ornamental pears, maple, linden crabapples
17. Sucker control Cut them off with pruners. Products may slow but not stop. 
18. Shrub pruning Prune spring blooming shrubs after flowering
Landscape OrnamentalsMajor Symptom:
19. Pollinators and insecticide toxicity Educating gardeners on insecticide toxicity and protecting pollinators
20. Genetically engineered petunias pulled from market Plants pose no risk to the environment or human health
Fruit & VegetablesMajor Symptom:
21. Peach leaf curl Red or pink puckered sections on deformed leaves
MiscellaneousMajor Symptom:
22. Ticks Seed ticks are not a unique species; they are baby ticks

1. Turfgrass for shadeTall fescue best choice to try; use good cultural practices

Tall fescue is the best turfgrass to try and grow in shade in eastern NE. “Shade mixtures” typically contain fine-leaved fescues (chewings, sheep or red fescues), but these do not handle heat or traffic well and are easily overwatered. When using tall fescue, it is best to start with sod, rather than direct seeding. Use lower rates of fertilizer and avoid overwatering in shady areas. If tall fescue will not grow in an area, stop trying to grow turfgrass in the area and use shade loving perennials or mulch in place of turfgrass. 


2. Fertilizing/combo productsMay is still a good time to apply

As soils warm and microbes become more active in May, turfgrass color may become off, making this a good time to fertilize. Select a fertilizer that contains 50 to 70 percent controlled release nitrogen, i.e. polymer coated products. If premergence products for crabgrass have not yet been applied to a lawn, these combo products can still be applied in May.


3. Seedling crabgrassDimension a better PRE to use once some germination has begun

By May, some crabgrass seedlings are likely present in lawns. While there is still time to apply preemergence herbicide for effective crabgrass control, products containing the herbicide dithiopyr (Dimension) will control crabgrass both pre- and postemergence (up to one tiller).


4. Blooming dandelions2nd best time to control with digging or post emergence products

Fall remains the ideal time to control dandelions with herbicides. During spring, just before or just after peak blooming is the key time for herbicide control of dandelions. Avoid applying herbicides during peak blooming. Research shows this to be a less effective time. 


5. Fairy ringDarker green ring in the turf

Fairy Ring may appear as a dark green ring in turf. Mushrooms may be present within the dark green ring. Fairy ring fungi may go unnoticed in a lawn; or, other than the dark green ring, cause no damage. In some cases, it can indirectly affect plants due to the hydrophobic (water repelling) fungal mat that may develop. In such a case, turfgrass within the darker green ring may dieback. Fairy ring can be caused by up to 50 different species of soil-borne fungi. The dark green ring is due to fungus activity releasing nutrients in the soil. Fungicide efficacy is sporadic for fairy rings, and applications are typically not recommended in homes lawns.  Fertilize to mask symptoms, and improve water infiltration with aeration or power raking if needed.

Mushrooms, Fairy Rings, and Other Nuisance Fungi in the Landscape, Nebraska Extension


6. Fungal leaf spot diseasesControl typically not needed in home lawns

Fungal leaf spots, such as dollar spot or those cause by Drechslera pathogens, may develop in some lawns after recent rainfall and due to warming air and soil temperatures. Kentucky bluegrass is typically more susceptible than tall fescue. These are minor diseases that mainly cause aesthetic injury. Control is not needed for home lawn situations.

Leaf Spot on Turf, Nebraska Extension


7. White grubsWait to make application

White grubs adult beetle (masked chafers and May/June beetles) are just beginning to emerge. If a lawn had white grub damage last season and an insecticide application is planned for this season, it is still too early to apply products for the most effective white grub control. Wait until June or early July to apply preventive insecticides. Wait until August to apply curative products.

White Grub Management, Nebraska Extension Turf iNfo


8. Power rakingStill okay in May as long as weather remains cool 

Power raking is a cultivation practice that is stressful for turfgrass. It is recommended only if the true thatch layer (made up of living and dead roots, rhizomes, stolons, etc.) exceeds ¾ of an inch. If needed, power rake Kentucky bluegrass or tall fescue lawns when temperatures are cool. Avoid power raking during stress periods. It is best if turfgrass has about 30 days to recover from power raking before stressful growing conditions, like summer heat, arrive. The exception is buffalograss, which should be cultivated when most actively growing in midsummer.


Trees & Shrubs

9. EAB treatmentsMay is the best timing for injecting insecticides for EAB

Injection treatment window for EAB is during May to greatly increase effectiveness. For Ash trees that are good candidates for treatment, and those growing 15 miles from the Omaha or Greenwood areas where EAB was found last summer, injection treatments used in May to apply insecticides will be about 70 percent more effective in controlling EAB than injection treatments used later in the growing season.

EAB Trunk Injection Options for Professionals, Nebraska Forest Service


10. EAB insecticide restrictionsNote labels, Some products have limits on quantities per acre

Read the label and follow directions for mixing, applying and label rates. It is the law. For example, there are label restrictions for the insecticide imidacloprid. Only 0.4 pounds of active ingredient can be applied per acre per year. And this includes imidacloprid products applied for white grub control. For tree treatment, this rate would be hit if one 64” diameter tree or two 20” diameter trees and one 24” diameter tree were treated in a one acre area.


11. Tordon not for landscapesDue to translocation issues and killing of non-target plants

Tordon best not used in landscape settings due to translocation issues. Tordon is readily translocated to other plants and often results in killing nontarget plants. Avoid the use of Tordon in landscape settings. 



Across eastern Nebraska, dropping of young hackberry leaves or twigs (about 4 to 6” of tender new tips) is being observed. This is most likely due to cold temperatures occurring at a critical point in the development of new hackberry growth. It will not harm trees. 


13. Ninebark diebackMost likely environmental issue; cold temperature injury

Ninebark dieback is being reported in Nebraska. There is no disease or insect known to be causing this at this time. It is suspected that ninebarks bred for different colors may have reduced the hardiness in some of these otherwise very tough shrubs. 


14. Spruce browningVariety of factors can be the cause

Spruce browning at this time of year may be due to a number of different causes. Winter dessication or winter burn. In this case, the browning is usually fairly uniform and often on the north or west side of the tree. Wait until June 1 before pruning out any brown needles/twigs. New growth may occur and to eventually hid the brown needles. Browning may be due to sirroccocus shoot blight. If so, only the tips of twigs may be affected randomly throughout the tree, usually near the lower half of the tree. If shoot blight is confirmed, fungicide treatment during May can be effective.

Diseases of Evergreen Trees, Nebraska Forest Service


15. Leaf curl aphidsLeaves twisted and curled; may be sticky

Leaf curl aphids are causing leafs to be curled, twisted or deformed on a number of plants, especially those in the rose family such as Viburnums and Prunus. While leaves become deformed and may be sticky, the damage is more aesthetic than harmful to established plants. Aphids are small, about 1/8 inch long, soft-bodied, pear-shaped insects that feed on plant sap. Aphids are usually controlled effectively by nature – beneficial insects and/or weather conditions. Since insecticides also kill beneficial insects, control is not recommended for leaf curl aphids. 


16. Bark sloughingOrnamental pears, maple, linden crabapples

Bark sloughing continues on ornamental pears, maples, lindens and crabapples. It is due to sudden cold temperature injury to the trunk cambium, most likely during November 2014. If trees are killed by a disease, such as fire blight; this too may lead to bark sloughing off. There is nothing to do for these trees but provide ideal growing conditions and enjoy them as long as they survive. 


17. Sucker controlCut them off with pruners; Products may slow but not stop

Tree and shrub sucker control is best done by pruning off the suckers on a regular basis. While some products, such as Sucker Stop are available, these will only slow sucker growth; not stop it. Some trees and shrubs are more prone to suckering. For example, crabapples, purple leafed plums and lilac.  If suckering is undesired, avoid planting these trees/shrubs. 


18. Shrub pruningPrune spring blooming shrubs after flowering

Shrub pruning of spring blooming shrubs is best done shortly after flowering has ended. Correct pruning leads to a more aesthetic shape and desirable growth. For example, avoid only shearing shrubs (cutting back the height), and use thinning type pruning cuts as well.  Tips on Pruning Ornamental Shrubs, University of Missouri Extension.


Landscape Ornamentals

19. Pollinators and insecticide toxicityEducating Gardeners on insecticide toxicity

Nationwide, in recent years, gardeners have turned away from nurseries & garden centers selling ornamental bedding plants grown using neonicotinoids for insect pest control. Gardeners ask if there is an easy way to know whether plants they wish to purchase have been treated with neonicotinoids. The best way is still to ask nursery professionals or look for special labels in plants that have been treated with neonicotinoids. Gardeners should also understand the toxicity level of insecticides they use in their landscapes and minimize pesticide use as much as possible through adoption of integrated pest management strategies to protect pollinators in their landscapes.

Insecticides Used in Greenhouse and Landscape, and Toxicity to Pollinators, University of Minnesota Extension
Integrated Pest Management Strategies for Home Gardens and Landscapes, Iowa State University


20. Genetically engineered petunias pulled from marketplants pose no risk to environment or human health

Several petunia cultivars have been pulled from the U.S. market, including two past All-America Selection winners, after the discovery they were bred from genetically engineered (GE) plants. The U.S. Department of Agriculture states consumers who may have purchased these petunias don't need to take any special action. Plant breeders may have used the original GE plants without realizing they had been genetically modified. Affected petunia cultivars include:

  • African Sunset (AAS 2014)
  • Trilogy Mango
  • Trilogy Deep Purple
  • Trilogy Red (AAS)
  • Trilogy '76 Mix-Liberty Mix
  • Fortunia Early Orange
  • Hells Bells Improved
  • Petunia Salmon Ray
  • Sweetunia Orange Flash

U.S. Flower Sellers Rush to Destroy Illegal G.E. Petunias,


Fruits & Vegetables

21. Peach Leaf Curlred or pink puckered leaf sections on deformed leaves

Peach leaf curl, caused by Taphrina deformans, is easy to recognize. The most characteristic symptoms are curling and crinkling of the leaves as they unfurl in spring. Usually, the entire leaf is affected, but sometimes only small areas are involved. In addition to curling, diseased leaves are thickened and often turn red or pink. As the season progresses, diseased leaves turn gray and appear powdery. This is the result of the fungal pathogen producing spores on the leaf surface. Eventually, the leaves turn yellow or brown and are prematurely cast.

Too late for control now. Plan to apply a dormant fungicide application next winter on trees with a history of infection. Peach leaf curl is one of the easiest fruit diseases to control. In most years, leaf curl can be effectively prevented with a single application of an appropriate fungicide, including lime sulfur, chlorothalonil, Bordeaux mixture, or a copper fungicide. Because infection occurs when the buds begin to swell, the fungicide must be applied during the dormant season. In Nebraska this can be done in the fall, after the leaves have dropped, through late winter. Remember, for effective disease control the fungicide must be applied at the proper time, and the tree must be thoroughly covered with the fungicide spray. When applying any fungicide, be sure to read and follow the label directions.



22. TicksSeed ticks are not a unique species; they are baby ticks

Ticks, Hort Update May 17, 2017, http://hortupdate.unl.eduTick season begins in the spring, usually during May and June. Get to know these diminutive Draculas and learn how to prevent exposure.