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Hort Update for May 16, 2016

Major Symptom:
1. First preemergent application Still time to apply if done soon
2. Crabgrass emerged plant control Herbicide used depends on size of seedling
3. Turfgrass scalping detrimental Mowing off more than one-third of grass blade is scalping
4. Sharpen mower blades/ rebalance Good mowing practices to use throughout summer
5. Pesticide certification requirements Must be certified to apply pesticides to home lawns/landscapes
Trees & Shrubs  
6. Hail/wind damage to trees & shrubs Best management practices for landscape plants
7. Sirrococcus shot blight Branch tips of spruce browning and dropping needles
8. Rhizosphaera needle blight Inner needles of spruce turn brown and fall early
9. Sudden leaf drop on ash trees Sudden shedding of young leaves
10. Consequences of early EAB treatments Trunk injection damage limits number of years trees can be treated
11. Spring leaf diseases common Spring rains increase fungal leaf spot diseases – most minor
12. Proper tree planting techniques Avoid common mistakes for a long lived healthy tree
Landscape Ornamentals  
13. Hail damage on ornamentals

Don’t be too aggressive when cleaning up hail damaged plants

14. To late to divide perennials? Still time to divide fall blooming perennials
15. Grass control in landscape beds Selective grass control products – Fusilade and Ornamec
16. Rust diseases of ornamentals Can affect a wide range of plants, but plants are rarely killed
17. Powdery mildew Grayish white powder on leaf surfaces
18. Working with root bound ornamentals Crowded root mass hinders establishment of annuals, perennials and ornamental grasses if not corrected at planting
Fruits & Vegetables  
19. Hail damage on fruits & vegetables Assessing damage in fruits and vegetables
20. Plum curculio Monitor plants for presence of adults
21. Codling moth Control of this common apple maggot
22. Cedar-apple rust Yellow leaf spots on upper surface; raised orange pustules on leaf undersides
23. Apple scab Olive colored leaf spots and leaf yellowing
24. Fruit spray schedules Spray guides for homeowners & commercial applicators
25. Pollinator habitat certification program Encourage homeowners to develop pollinator habitat in their landscapes

1. First premergence (PRE) herbicide applications can still be made to lawns. The sooner, the better. While some weed seed will have already germinated, a good majority of seed of annual warm season weeds, like crabgrass, will continue to germinate into and through June. PREs applied now will provide control of weed seedlings as seed continues to germinate.

2. Emerged crabgrass control - With our warm spring, some crabgrass seed may have germinated earlier than usual. Seedling plants can be controlled. Where feasible, such as along a driveway, hand-pull small crabgrass plants. If needed, small plants in the 1 leaf stage can be controlled with the herbicide Dimension, which provides both post and pre emergence control. Larger crabgrass plants can be knocked down with quinclorac; and then a preemergence product applied to provide continued control.

3. Avoid turfgrass scalping - Scalping occurs when more than one-third of the turf's foliage is removed at one time, often exposing the stems of the grass plants, resulting in stress and even plant death. Removal of 50% or more of the turf canopy at one mowing results in severe defoliation. At this point, existing root and rhizome growth stops, and the initiation of new tillers, roots and rhizomes stops. The plant's energy reserves are redirected to development of new leaf or shoot growth, at the expense of the root development. Development of a deep, healthy root system, which endows the grass with better disease and drought resistance in the hot, dry months of July and August, is the goal of all turf managers, and anything that slows root development should be avoided.

Mowing or Scalping the Turf, Nebraska Extension

4. Sharpen mower blades/rebalance - Sharply cut leaf blades increase turf health by improving recovery, decreasing water loss, and increasing photosynthesis. Lawns mown with a dull mower blade have poor aesthetics, heal more slowly and have greater water loss. Seed heads are present in many lawns now and they are typically tougher to cut than the grass blades themselves. As such, it might help to switch to a sharp set of mower blades to help slice through these seed heads. Homeowners should sharpen mower blades at least twice a year. To make this easy, buy two sets of mower blades and sharpen both sets each winter. Put a sharpened blade on before the first mowing and then switch when you notice that the leaf blades are becoming ragged in appearance as this is an indicator of a dull mower blade.

For professionals, consider sharpening mower blades weekly, bimonthly, or monthly depending on the amount of turf you are cutting. Again, inspecting the turf leaf blade is the best way to determine when your mower becomes dull.

Source: Aaron Patton, Turfgrass Extension Specialist. Don’t Forget to Sharpen Mower Blades, Purdue University

5. Pesticide certification required - Any person who applies pesticides (general use or restricted use) for hire to lawns and landscapes must be certified by the Nebraska Department of Agriculture (NDA); and they must recertify every 3 years. If misapplications of pesticides are suspected, report misapplications to NDA.

Nebraska Department of Agriculture Pesticide Program

6. Hail damage to trees and shrubs can lead to increased disease potential and other issues. Minor hail damage, such as holes in the leaves or slight defoliation of trees and shrubs, is not of great concern.  Major damage includes the stripping of 50% or more of plant foliage, pocks or tears in tree bark with damage to the underlying xylem and phloem tissues, shearing of evergreen buds from branch terminals, death of evergreen buds due to impact damage, and broken tree or shrub branches.

Other than correct pruning of broken branches, in most cases, homeowners and tree/landscape services should take a "wait and see" attitude. Do not fertilize trees and shrubs to "help them recover." Fertilizer is detrimental at this point. Do not apply a wound dressing, pruning paint or "wrap" to any wounds, including hail wounds, as this can interfere with the trees own response to closing off the wound. Avoid general pruning plants of stressed plants.

Keep trees and shrubs well-watered throughout summer and fall to avoid drought stress. Avoid overwatering.  Correctly mulch plants to prevent secondary injury from mowers and string trimmers.
Secondary pests, such as borers and aphids, should be controlled to avoid additional plant stress. Sphaeropsis tip blight can be a serious problem in Austrian and Pondersosa pine trees the year following serious hail injury. Fungicide applications could be planned for next spring reduce infection from this disease.

Sphaeropsis Tip Blight of Pine, Nebraska Extension
Managing Wind and Hail Damage to Plant, Nebraska Extension

7. Sirrococcus Shoot Blight appears on branch tips as reddish brown needles or bare tips that have lost needles. These symptoms appear similar to injury from winter drying or frost damage; however, shoots killed by Sirococcus are scattered throughout the tree rather than uniformly, such as being only on one side of the tree. Also, small black fruiting bodies called pycnidia, in which spores for the fungus Sirococcus strobilinus are produced, can be found on bud scales and dead shoots. These fruiting bodies can be seen with the naked eye or a 10X hand lens.

Infection of current year shoots occurs during spring once new buds begin to open. To control Sirococcus shoot blight, apply a fungicide such as chlorothalonil (Daconil, Bravo) when new shoots are ½ to two inches long, typically in May; and repeat every 3 to 4 weeks if frequent rains occur.

Diseases of Evergreen Trees, Nebraska Forest Service

8. Rhizosphaera Needlecast is a common fungal disease affecting Colorado blue spruce and other spruces.  Trees in eastern Nebraska are more commonly affected than those in the west. Needles are infected in spring, but symptoms do not become evident until a year later when the needles turn yellow, then a reddish brown.  Older needles on the interior of the branch are affected.  Black fungal fruiting structures can be seen with a hand lens protruding from the stomata of infected needles. 

Infections can be high due to extended wet weather last season and now this spring. Saturated soils increase air humidity around the tree's lower canopy and also contribute to good conditions for disease development.   The disease can be controlled with an application of chlorothalonil in spring when new growth is one-half to two inches long.  Follow-up applications should be made every 3-4 weeks if frequent rains occur during spring and early summer.

Diseases of Evergreen Trees, Nebraska Forest Service

9. Sudden leaf drop on ash trees may be due to Anthracnose disease promoted by wet spring weather. With anthracnose, leaves will show brown, blighted areas. On otherwise healthy trees, anthracnose is not considered a serious issue and control is not recommended. This year, some ash trees failed to leaf out after winter. This most likely was the result of environmental or weather extremes. While tree owners may be concerned the cause of leaf drop or sudden tree death might be related to Emerald Ash Borer (EAB), this would not be the case. EAB has not yet been found in Nebraska and trees would die more slowly from an EAB infestation.

10. Consequences of early EAB treatments - Beginning treatment of ash trees earlier than needed for emerald ash borer can have negative consequences for trees including trunk damage from injection methods. Science has shown that healthy trees can be injected about 7 to 10 times before the injection method causes enough damage to trunks to lead to tree decline. The drilled hole opens the trunk to insect pests and decay fungi. Drilling may break through internal barriers within the trunk the tree uses to wall off internal decay; and cause the spread of decay. The pesticide itself can cause internal damage. This, and other reasons, are why treatment for EAB will not be recommended for trees until the borer has been found within 15 miles of a trees location.

Misconceptions Regarding EAB Treatments, Nebraska Forest Service

11. Spring leaf diseases are common this year due to increased rainfall. We will continue to see an increase in ash rust, anthracnose, cedar/apple rust, apple scab and other minor fungal diseases. Heavily infected leaves are likely to yellow and drop early. While these diseases and leaf drop create concern for homeowners, these are minor diseases that do not cause major stress for trees or shrubs. While fungicide sprays can prevent new infections, they will not cure infections, and are often not recommended. Dryer weather goes a long way in reducing new infections.

Diseases of Broadleaf Trees, Nebraska Forest Service

12. Proper Tree Planting consists of a lot of “do nots”.

  • Do not plant too deep, which usually means not planting a tree the same depth it was in the container. Locate the trunk taper or first lateral root and then dig the planting hole ONLY deep enough to set the root ball on undisturbed soil so the trunk taper is still visible above ground.
  • Do not plant a tree without first cutting encircling roots to avoid girdling roots later.
  • Do not backfill the planting hole with amended soil; use the same soil that was removed from the hole.
  • Do not fertilize newly planted trees with nitrogen or leafy growth will be stimulated at the expense of roots.
  • Do not prune trees at planting or stored food and photosynthetic tissue will be removed at a time it is most needed.
  • Do not overwater young trees but do keep the soil around the roots and outside of the planting hole good and moist to a depth of 12 inches.
  • Do not place deep mulch volcanoes around tree trunks, but do use a two to three inch deep layer of mulch in a four foot or larger diameter ring around the tree.

Avoiding the Top 10 Tree Planting Mistakes, Nebraska Forest Service

13. Hail damage on ornamentals - Don’t be too aggressive when trying to repair hail damage; do not shear plants of their foliage. Plants need to retain as much foliage as possible, even if it is tattered, to photosynthesize and recover.  Selectively prune back broken stems to a secondary shoot or node. Give annuals 10-14 days to begin generating new growth before removing any with severe damage.

Saving Hail Damaged Plants, Backyard Farmer YouTube
Hail Damaged Perennials, Backyard Farmer YouTube

14. Too late to divide perennials? No, there’s still time. Wet weather has delayed work in many landscape beds this spring, but even though perennials are getting bigger there’s still time to divide those that need it. 

Dividing Perennials, Backyard Farmer YouTube
Dividing Perennials, Iowa State University
Dividing Perennials, Clemson University

15. Grass control in landscape beds – Turfgrass becomes a weed when it creeps into landscape beds. Fortunately the herbicide Fluazifop provides selective grass control, but doesn’t damage most ornamental broadleaf plants. Fluazifop is sold to homeowners as Grass-B-Gon and is available to commercial applicators in the following formulations. Read and follow label directions.

  • Fusilade II Turf and Ornamental, Syngenta
  • Ornamec 170 Grass Herbicide, PBI/Gordon
  • Ornamec Over-The-Top Grass Herbicide, PBI/Gordon

16. Rust diseases in ornamentals are easily recognized by the reddish-orange blister-like swellings, called pustules, found on infected leaves. These diseases require a living host plant so they rarely cause plant death, but plant vigor and appearance can decline with severe infections.  Rust spores are spread by wind and infection is favored by mild, moist weather. Leaf wetness is necessary for fungal spores to germinate and infect leaves. Hollyhock rust is very common; right now rust is being found on Penstemon.

Keep plant leaves dry when irrigating to reduce infection. Choose cultivars with good resistance. On plants with a history of infection, preventive fungicide applications may be warranted.

Rust Diseases of Ornamental Crops, UMass Amherst

17. Powdery mildew causes grayish white powder-like patches on leaves. It is most common during periods of cool weather with high humidity, but can be seen during warm dry periods, too. Extended wet conditions this spring have caused early infections on turf and many garden plants.  Many types of plants are susceptible, but the fungi are generally host specific only infecting plants from the same family or genus.  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

18. Working with root bound ornamental plants – Horticulturists often talk about the detrimental effects of root bound plants when talking about trees & shrubs. But a crowded root mass also affects the establishment and health of annuals, perennials and ornamental grasses. If roots are pot-bound, cut or tear the root ball as needed to encourage spreading.

19. Hail damage on fruits & vegetables– it’s no surprise the severity of damage from hail varies based on hail stone size, duration of the storm and how early in the growing season the storm occurs.  Here are some tips on plant damage and recover potential with a storm occurring early in the growing season.

  • Fruit trees – Hail can cause damage to foliage, flowers, branches and the trunk. Small fruits may be knocked out of trees, thinning fruits. This isn’t altogether a bad thing, since fruits usually need thinning anyway. Impact on fruits may cause bruising or skin splitting, making fruit susceptible to disease infection. Bark damage to young, thin-barked trees may be extensive enough to cause tree death. Watch out for fireblight infections following hail injury.   
  • Strawberries – Hail readily defoliates plants and damages or destroys flower buds.
  • Grapes – Leaf and vine damage is expected, however, grapes are vigorous growers and usually recover quickly.
  • Tomatoes – Shredded foliage will regrow. Broken stems should be pruned back to a side shoot.
  • Cucurbits – Their large leaves will look very bad following a hailstorm. But if plants were well established the leaves will partially protect the growing point and plants are likely to recover well.
  • Fungicide application – extensive wounding makes plants very susceptible to disease infection. Fungicides will help minimize disease after injury occurs.

Hail Injury on Apples and Fruit, eXtension
Hail Damage on Grapes, eXtension
Responding to Hail Storms (vegetables), Cornell University

20. Plum curculio is a common pest of apple, plum, cherry, apricot and other fruits. Adults are a mottled brown weevil, which overwinter in soil and leaf litter under affected plants. Females begin egg laying around bloom in young fruitlets. Scars from slits cut by females in the apple skin during egg-laying is the most common damage. Larva are grayish-white legless grubs with curved bodies and brown heads. They develop to maturity only in soft fruits, such as plum and cherry; hard fleshed fruits like apple crush the larva as they develop. However, larval activity does cause early season fruit drop. Developing larva can be found in dropped apples, but not in apples that remain on the tree.

Effective non-chemical controls are not available, but monitor trees for the presence of insects before spraying. In the morning when insects are cold, shade a branch over a white plate. Insects will fall onto the plate rather than flying away.

Plum Curculio, University of Minnesota
Fruit Spray Schedules for Homeowners, University of Missouri

21. Codling moth is 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, University of Minnesota
Fruit Spray Schedules for Homeowners, University of Missouri

22. Cedar-apple and cedar-hawthorne rust are similar but different diseases. Cool, moist conditions this spring increase the potential for infections on susceptible apple, crabapple and Hawthorne trees. Both diseases cause yellow spots on upper leaf surfaces and raised orangish-pustules on leaf undersides. Infected leaves drop resulting in unsightly trees and poor fruit production in apples. Repeated yearly infections can weaken trees and lead to other issues.

The best control of rust is selecting resistant trees. On susceptible trees with a history of infection, fungicides need to be applied starting at bud break, petal fall and 3-4 additional applications at 7-14 day intervals.

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

23. Apple & pear scab - These fungal diseases are favored by wet, humid weather in spring and early summer. Infection causes defoliation and reducing fruit quality and tree vigor. The fungus overwinters on or near trees so we often see this disease before cedar apple rust. Leaf lesions of apple scab are usually olive colored and turn brown.

Pear scab is very similar to apple scab, including leaf and fruit lesions, and is caused by a closely related fungus. 

As with rust, planting resistant cultivars is the best means of control. On susceptible trees with a history of infection, fungicides need to be applied every 7-14 days from pre-bloom through the spring rainy period.

Apple Scab, Nebraska Extension
Diseases of Broadleaf Trees, Nebraska Forest Service

24. Tree & small fruit pest control - For best control of insect and disease problems in tree & small fruits, control measures must be used. Often, selection and planting of resistant cultivars will reduce the need for pesticides. When needed, timing of pesticide applications is critical to effectively controlling targeted pests. For recommended fruit spray schedules see the following publication.

Complete Spray Schedule for Homeowners:
Fruits Spray Schedules for Homeowners, University of Missouri Extension,

Commercial Growers:
2016 Midwest Fruit Spray Guide, Purdue University

25. Pollinator habitat certification program - By creating habitat for pollinators, homeowners are supplying them with their necessary food resources, nesting habitats, water, and pesticide-free environment they need. University of Nebraska – Lincoln Department of Entomology and Nebraska Extension encourage gardeners to certifying their gardens.

The Importance of Developing Pollinator Habitat, Backyard Farmer YouTube
Habitat Certification Application, UNL Department of Entomology and Nebraska Extension