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Hort Update for November 1, 2021

Hort Update for November 1, 2021, Nebraska Extension,
Spotted Lanternfly adult. Image from Pennsylvania Department of Agriculture.

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Serious ConcernsMajor Symptom
1. Perennial garden cleanup Optimize plant health; protect pollinators and other beneficial insects
2. November growing degree days (GGD) Lincoln Airport 11/1/21 - 4000 GGD,  Understanding Growing Degree Days
3. Spotted lanternfly update  Be on the look out for this new invasive insect; has not been found in Nebraska yet
4. Thousand cankers disease Confirmed in Cheyenne, WY in August 2021; walnut twig beetles found in Gering, NE April 2020
5. Emerald ash borer  New confirmation in Platte County; spring best time for treatment
6. Evergreen winter watering & anti-transpirants  Continuing dry conditions increase potential for winter desiccation; watering and anti-transpirant applications can help
7. Fruit tree fall fallow watering Best practice for home and commercial fruit production
8. Fall garden cleanup Fruits, vegetables and landscape plants; fall garden sanitation helps control pests and diseases
Timely Topics
9. Winter weather forecast Forecast for near normal temperature & precipitation; or slightly colder
10. Nuisance home invading insects, spiders and mice Exclusion is the best control
11. Cluster flies in the home Nuisance fall invader; winter control
12. Brown marmorated stink bug Newest nuisance fall invading pest
13. Wildlife damage Damage prevention is best; visit for additional information
14. Black knot disease of plums Prune and destroy branches with galls before April 1st
15. Cankers Inspect trees in winter for signs of disease

1. Perennial garden cleanupTo cut back or not to cut back the tops of herbaceous perennial in fall – how does one decide?

Fall sanitation or clean-up is beginning to be frowned upon due to pollinator conservation, winter interest and even drought concerns. Alternatively, it is promoted as a management practice in the landscape to help reduce overwintering pathogens and some insects. And some gardeners prefer a tidy winter landscape, thoroughly removing all dead plant material in the fall.

What is the best recommendation for clients? There are good reasons for removing the tops of some plants after they are killed by a fall freeze; but equally good reasons for leaving the tops of some plants until spring. The trend is to leave the tops whenever possible. The ideal situation may be to do a little of both depending on the type of plant and other factors.

Reasons for leaving plant tops until spring:

  • Catch snow to increase soil moisture as snow melts. After a dry year or drought, this would be especially important.
  • Catch and trap plant debris, like leaves, which act as a mulch to protect plant crowns and roots from winter extremes.
  • Provide nesting sites for pollinators. About 30% of native bees nest inside hollow plant stems over winter and emerge the next growing season.
  • Provide seeds and protection for some overwintering birds.
  • Avoids moisture reaching plant crowns through hollow cut stems which can lead to crown rots or freeze/thaw damage. This is a known problem for Chrysanthemum, Buddleia (butterflybush) and Caryopteris (blue mist spirea).
  • Provide winter interest in the landscape such as the tops of ornamental grasses.

Reasons for removing plant tops in fall:

  • Reduce overwintering sites for disease pathogens and some insects. Plants that have common disease issues, like peonies, are best cut back each fall. Other plants can be left most years and only cut back if they had a pest issue that season.
  • Tidy up the appearance of the garden. For clients preferring a clean garden, opt to cut plants back by leaving at least 8-24 inches of stem to trap snow and leaf debris, and to minimize removal of pollinator nesting sites.
  • Lower the fire risk during an open, dry winter if ornamental grasses are planted right next to a building.

Because native bee emergence from hollow stems occurs throughout the growing season, the stems of perennials should not be cut back to the crown in spring. This ensures pollinator nesting sites are not destroyed. Pruning to vary the length of remaining stalks from 8-24 inches will give emerging pollinators a fighting chance to survive. By early summer, emerging new growth will hide the dead stalks.

If plant tops are to be cut back in fall, encourage clients to wait until after a hard freeze. If foliage is green, photosynthesis is taking place and the plant is storing carbohydrates in roots and the crown for next season’s growth. In some instances, there is no ideal situation but to do some pruning in the fall and some in the spring. While there may be mitigating factors, where feasible, the recommendation is to leave the tops in place for winter


3. Spotted lanternfly updateBe on the look out for this new invasive insect; has not been found in Nebraska yet

Back in September, a Kansas student's state fair entomology 4-H insect collection made the news because it included a dead spotted lanterfly. Up to that point, this insect was not thought to be in Kansas. The Kansas Department of Agriculture is still investigating to determine if the insects have become established in the state. As of 11/01/2021, it has been found in 11 states including Connecticut, Delaware, Indiana, Maryland, Massachusetts, New Jersey, New York, Ohio, Pennsylvania, Virginia and West Virginia. 

The spotted lanternfly is neither a moth or a fly, it is more closely related to leafhoppers, aphids or planthoppers. Adults are 1 inch long and ½ inch wide at rest. The forewing is gray with black spots of varying sizes and the wing tips have black spots outlined in gray. Hind wings have contrasting patches of red and black with a white band. The legs and head are black, and the abdomen is yellow with black bands.

It's preferred host is Tree of heaven, Ailanthus altissima, but is also found feeding on over 70 other plant species. It is an introduced pest, native to China, India and Vietnam. As of December 2020 this insect has not been found in Nebraska, but it is important for horticulture professionals to be alert and watchful for this pest which could pose a serious problem for vineyards and orchards. Plants attacked by spotted lanternfly ooze or weep sap with a fermented odor. There is a build-up of sticky honeydew on and beneath plants, which is colonized by sooty mold fungi. To report a sighting, contact Nebraska Department of Agriculture State Entomologist, (402) 471-2351. 

Threatened crops include the following.

  • Almonds
  • Apples
  • Apricots
  • Cherries
  • Grapes
  • Hops
  • Maple trees
  • Nectarines
  • Oak trees
  • Peaches
  • Pine trees
  • Plums
  • Poplar trees
  • Sycamore trees
  • Walnut trees
  • Willow trees

Spotted Lanternfly, Nebraska Invasive Species Program


4. Thousand cankers diseaseConfirmed in Cheyenne, WY in August 2021; walnut twig beetles found in Gering, NE April 2020

Thousand cankers disease has killed walnut trees throughout the western United States over the past two decades. It was particularly devastating in the communities along the Front Range of Colorado, where the majority of black walnut are now gone. The only walnut species native to Nebraska, the eastern black walnut, is highly susceptible to the disease. In addition to its use for timber, nuts and wildlife habitat, black walnut is commonly planted in community and rural landscapes. 

Walnut twig beetles are tiny brown insects that feed under walnut tree bark, introducing fungal pathogens during their feeding. Many small cankers develop in infected areas, which causes twigs to die. Diseased trees initially exhibit yellowing foliage, followed by brown wilted foliage, branch dieback and tree death. Tree death occurs two to three years after initial symptoms appear.

No diseased trees were found in Gering, when twig beetles captured in detection traps were found at Monument Shadows Golf Course in Gering in 2020, but trees may be infected for many years without visible symptoms. At this time there are no treatments available to control diseased walnut trees.

The NDA implemented a quarantine prohibiting the movement of walnut wood into Nebraska in 2010. The walnut twig beetle and canker fungus are easily moved long distances in diseased wood. Regulated material includes walnut branches, logs, roots, firewood, green lumber, bark, wood chips and nursery stock.

Horticulture professionals should be aware of this disease and on the look out. More information can be found at Walnut Twig Beetle & Thousand Cankers Disease, Nebraska Forest Service.


5. Emerald ash borer (EAB)New confirmation in Platte County; spring best time for treatment

In August 2021, EAB was confirmed in Columbus, NE by the Nebraska Department of Agriculture in partnership with the U.S. Department of Agriculture and the Nebraska Forest Service. This is the first confirmation in Platte county. Current EAB confirmation map.  

NFS recommends the following practices to prevent human-assisted spread of the insect. 

  • Since EAB can easily be moved in firewood, always use locally-sourced firewood and burn it in the same county where you purchased it. 
  • Consider treating healthy, high-value ash tress located within a 15-mile radius of a known infestation. Treatment will need to be continually reapplied and will only prolong the tree’s life, not save it. Trees that are experiencing declining health should be considered for removal. 

If you are in a non-infested county and think you have found an EAB infestation, please report it to the Nebraska Department of Agriculture at 402-471-2351, the Nebraska Forest Service at 402-472-2944 or your local Extension office.

The federal quarantine officially ended on January 14, 2021, but continue to encourage people not to move firewood. APHIS Changes Approach to Fight Emerald Ash Borer, 12/14/2020 


6. Evergreen winter watering & anti-transpirantsContinuing dry conditions increase potential for winter desiccation; watering and anti-transpirant applications can help

Nebraska's dry fall conditions continue, with more areas of the state are advancing to moderate or severe drought. Continue to monitor moisture in turf and landscape plantings. Plants going into winter in drought stressed conditions have increased risk of winter desiccation. 

Use of an anti-transpirant product can also help protect plants, especially broadleaf or conifer evergreens planted in fall under dry conditions. The most commonly available product for home gardeners is Wilt-Pruf®, a natural pine oil polymer that forms a clear, flexible coating on plant leaves and stems. It slows the rate of water loss, but does not interfere with normal plant respiration or photosynthesis. The coating gradually weathers and degrades after application. Use the winter application rate and wait to make the first fall application AFTER plants have hardened off and become dormant, usually late November or early December. Allow at least 3 to 4 hours of drying time, with air temperatures above freezing to make an application. Spray plants thoroughly, covering both upper and lower leaf surfaces to the point of runoff. When the application is complete, clean the sprayer thoroughly according to label directions to prevent product residues from gumming up nozzle tips and other sprayer components.  

Additional anti-transpirant products include Transfilm®and Vapor Gard® (do not use on arborvitae, juniper, cedar). Refer to the label for a full set of restrictions. 

Note: The oil base of anti-transpirant products removes the waxy coating in Colorado Blue Spruce and other blue evergreens, which gives their needles the characteristic blue color, changing plants to green. New growth will emerge with the blue coloration.  

Read and follow all label directions carefully, particularly the re-application recommendations, to avoid plant damage and maintain the product's effectiveness throughout the winter. 

Terminology - The terms anti-desiccant or anti-transpirant are often used interchangeably in relation to these products, which can be confusing. Technically, an anti-desiccant prevents desiccation or drying of plant tissues. An anti-transpirant limits transpiration, a natural plant process in which water is released from natural openings in the leaf surfaces. Just remember, that if transpiration is reduced through the application of an anti-transpirant, winter drying or desiccation is reduced. 

Improve Tree, Shrub Health through Fall Watering, Nebraska Extension


7. Fruit tree fall fallow wateringBest practice for home and commercial fruit production

Checking the soil moisture for fruit tree plantings is very important in the fall, going into the winter and the next growing season.  The first 100 days of the spring growing season is critical for branch and bud development for new and established trees; if trees do not have good stores of moisture during this time, overall growth is affected.

In fall, to check for adequate soil moisture levels, shove a long Phillips head screwdriver or a rod with a sharpened point into the ground at least 12 places under the tree canopy and beyond the drip line. Measure how deep each test location can go down into moist soil. If there is little or no moist soil, then slow dripping irrigation can be used on warm days in late fall to help alleviate the lack of moisture in the first 12 inches of soil where water conducting roots will pull and store moisture. Use caution to not over irrigate, which can lead to promotion of weak and tender branch growth.

Next fall, consider planting short term cover crop for the purpose of water fallowing around fruit tree plantings. Water fallowing through growing annual cover crops around fruit tree planting is another option to help moderate soil moisture levels in the fall, winter and early spring. Some cover crop examples that are treated as short term annuals include annual rye, chickpeas, field peas, barely, alfalfa, and wheat. The cover crop reduces weed competition with the fruit trees for nutrients. Organic matter from the cover crop can be incorporated into in the soil the next spring to help improve soil microbial health, soil water drainage, and nutrient holding capacity when the function of the cover crop is finished for the year.

For more information on watering fruit tree, please refer to the  Water Wise Vegetable and Fruit Production NebGuide.


8. Fall garden cleanupFruits, vegetables and landscape plants; fall garden sanitation helps control pests and diseases

Many disease organisms carry over from one season to the next on infected branches, leaves or fruits. Diseased leaves fall to the ground beneath the infected plant and, if they are not removed and discarded, will produce new fungal spores or bacteria to reinfect the plant the following growing season. Removing infected plant debris reduces the disease pressure the following season. Keep this control method in mind for common shade tree foliage infections, including Anthracnose, powdery mildew, apple scab, Septoria and many other leaf spot pathogens. Black spot of rose is another very common fungal pathogen.  

In a similar manner, fruit tree disease problems often overwinter on fruit "mummies"; dried infected fruits that may remain in the tree or fall to the ground beneath the tree. If mummies are still in the tree or beneath it, they serve as an infection source the following year. 

Diseases also remain active from year to year through infected twigs, branches or cankers. Fireblight is one of the most serious fruit and ornamental diseases which overwinters on infected woody tissue. Fireblight is a bacterial disease which infects and kills twigs and branches, most commonly during spring and early summer. However, it can also infect the mature bark of older branches or tree trunks; this infected bark is called a canker and often serves as a source of additional spores or bacteria, allowing the disease to progress throughout the plant during a growing season or reinfect it’s foliage or new branches in future years. Unfortunately there are many other disease pathogens that can infect woody branches or bark and cause cankers, such as brown rot of peach, apricot, plum and cherry. 

Many insects overwinter on plants they attacked the previous summer or nearby plant debris, such as iris borer (overwinter as eggs on iris leaves or nearby plants) or common stalk borers (overwinter as eggs on nearby grass stems or weeds).  Cucumber beetles overwinter as adults in plant debris and other protected areas. Common fruit insects – plum curculio overwinters as adults in plant debris, cherry fruit fly inside fallen fruits. 

Sanitation Steps 

As you can see, sanitation is very important for reducing disease and insect pressure in your garden or landscape each year. Important steps include the following. 

  1. Rake up and discard or burn all debris beneath infected plants each fall, including leaves and fruit.  This includes infected trees, shrubs and ornamentals such as peonies. In the vegetable garden, remove disease infected plants like tomatoes or peppers and rake up as much old foliage as possible along with all discarded fruits. 
  2. Inspect woody plants for cankers and dead stems. Prune out and destroy all dead or diseased branches and twigs each spring. If you suspect the branches were killed by a disease, cuts should be made at least 4-6 inches below the margin of visible infection. Ideally, fruit tree pruning should be done in spring just before new growth starts. 
  3. If your tree is susceptible to fireblight or has a history of infections, be sure to clean the pruners between each cut. Clean pruners by dipping them in a 10% bleach solution (9 parts water to 1 part bleach) between cuts. With a known fireblight infection, make cuts 8-12 inches below the margin of visible infection. Dry and oil tools after use to prevent rust. 
  4. In Iris plantings, remove old dead foliage before April 1.  
  5. Black spot of rose can be reduced by removing all infected leaves and mulch beneath plants in fall. Prune out canes with dark colored lesions, then reapply a fresh layer of new mulch. 
  6.  Do not compost this material. Most home compost piles do not get hot enough to kill all pathogens
Herbaceous perennials - If and when to cut plants back in fall is a commonly asked question. Perennials eventually need to be cut back as their stems and leaves do not live from year to year and the dead tops needs to be removed. Wait until the foliage is killed by frost to cut back perennials. After that, whether to cut plants back in late fall or spring is up the homeowner and may depend on the ecosystem value and/or winter interest of the plant. Plants with hollow stems provide nesting sites for solitary bees which are important pollinators. Seeds of some dried flowers, like Rudbeckia, are a food source for birds. The plumes of ornamental grasses provide winter interest as do the spent flower cones of plants like Rudbeckia and coneflowers. Note that tall ornamental grasses can be a fire hazard, especially if grown next to a house and left over winter. 


9. Winter weather forecastForecasts for near normal temperature & precipitation; or slightly colder

The official National Oceanic and Atmospheric Administration (NOAA) forecast for Nebraska is calling for equal chances for above and below normal temperature and precipitation.  What that basically means is that overall, our temperatures and precipitation this winter will be near normal.  That doesn’t mean we can’t have cold periods or wet periods.  It’s an overall prediction of an average winter for us.  Note: This is a preliminary forecast as NOAA’s official winter forecast will be issued in the middle of November.  So, it could change.

This is NOAA’s climatological temperature and precipitation winter forecast (Dec, Jan, Feb). 

This is NOAA’s climatological temperature and precipitation winter forecast (Dec, Jan, Feb).  This is NOAA’s climatological temperature and precipitation winter forecast (Dec, Jan, Feb).

Scott's forecast - With that said, I do not agree with NOAA’s winter forecast for us.  NOAA has a bias to over-forecast warm temperatures in recent years for their monthly and seasonal forecasts.  But more importantly, I see several indicators that contradict their forecast.  My reasons are below.

  1. La Nina - The La Nina from last winter is continuing into this winter.  La Nina winters typically see colder temperatures across the northern Rockies and Great Plains extending down into the Midwest and eastward across the Great Lakes.  The current official forecast hints at this but it’s not large enough and doesn’t extend eastward towards the Great Lakes or southward into the central Plains.  Omaha should be in the colder area, in my opinion.  La Nina winters are generally dry for us.  Doesn’t mean we can’t have a blizzard or a big snow.  But overall, snow from Dec – Feb will be less than the normal 32” we receive.
  2. Analog years - There’s a branch of meteorology that looks back through decades of weather data to see how spring and summer weather patterns correspond with winter weather.  These analog forecasts also consider the number of tropical storms and hurricanes in the Atlantic, Caribbean and Gulf. 

So how do past analog years look for this winter?  Cold springs (April and May) followed by an active tropical storm season in the Atlantic during upcoming forecast La Nina winters historically mean colder than normal winters for the Midwest.  In general, these conditions which we had in Omaha this year (cold April/May and high numbers of tropical storms this year) signal a cold start to winter for us followed by milder temperatures in February.  So, that would indicate for Omaha, a colder than normal December and January followed by a warm February.  I expect winter will get off to a cold start.  Precipitation correlates less reliably.  But typically, with La Nina winters, below normal snow amounts occur.

Here’s a private forecast company I follow closely who leans heavily on analog forecasting.  This is their winter temperature forecast.  As you can see, it’s significantly different than NOAAs. (Note: blue area is -3 to -1 colder than normal).

Scot Risch is a retired Air Force meteorologist, with a BS in Synoptic Meteorology and an MS in Synoptic Meteorology and Climatology. He is also a Master Gardener with Nebraska Extension in Douglas-Sarpy Counties.


10. Nuisance home invading insects, spiders and miceExclusion is the best control

These pests may enter homes in fall as temperatures cool and they begin to look for overwintering sites. Pests like boxelder bugs, millipedes and Asian lady beetles are common. Most are harmless but still a nuisance.

Exclusion is the best means of reducing nuisance pests and mice indoors. Caulk cracks, crevices and conduits of the home. Repair window screens and check that doors are tight fitting. If needed, insecticides can be applied to building foundations according to label direction. Ideally, apply the insecticide from the foundation out to five to 10 feet.

Accidental and Occassional Invaders, Nebraska Extension 
Insects That Overwinter in Your Home, Nebraska Extension
Keeping Occasional Invaders Out, Nebraska Extension
Boxelder Bugs, Nebraska Extension  
Controlling House Mice, Nebraska Extension 
Identification Guide to Common Spiders in Nebraska, Nebraska Extension 
Millipedes, Nebraska Extension
Multi-colored Asian Ladybird Beetles, Nebraska Extension 


11. Cluster flies in the homeNuisance fall invader; winter control

Cluster flies, also called attic flies, are a nuisance fall invader. These flies are slightly larger than house flies and fly sluggishly, making them easier to swat. Unlike many flies whose larvae feed on dead things, cluster fly larvae feed within earthworms after adults lay eggs in soil cracks. Until fall arrives and adults begin looking for overwintering sites, these flies largely go unnoticed. As with most nuisance invaders, the best management tactic is to caulk or fill cracks and crevices around homes. Before cluster flies move indoors for overwintering, treatments can be applied to upper stories of building exteriors for fly control. When flies become active during sunny days in winter, insecticide bombs containing permethrin may be useful in attics and other rooms that can be isolated from the rest of the house, and if the attic is NOT over a room where food is prepared. Consult the label for safe application information and reentry times.

Cluster Flies - Nebraska Extension


12. Brown marmorated stink bug (BMSB)Newest nuisance fall invading pest

BMSB is a little over one-half inch in length and brown in color. Marmorated means they have a marbled or spotted appearance. Nebraska has native brown stink bugs, but their underside is lime green which helps distinguish between the two. The chief issue most Nebraskans will deal with is fall invasion of their home by BMSB. Stink bugs are looking for overwintering sites and our homes offer a multitude of crevices to hide in. While they won’t breed in the home or damage the structure they are annoying and smelly. To reduce entry, seal entry points into your home. If there are no easy routes inside, the insects can’t become a nuisance. Check for cracks around windows, doors, pipes, and chimneys and seal openings with silicone or silicone-latex caulk. It is also advisable to check screens on doors and windows for holes and to repair trouble spots or replace the entire screen. If stink bugs are found inside, vacuum and dispose of them outside. Do not use insecticide foggers as they provide little control over this pest.

Brown Marmorated Stink Bug, Nebraska Extension


13. Wildlife damage preventionDamage prevention is best; visit for additional information

It’s the time of year to prepare for protecting landscape plants from wildlife damage during winter. When green foliage is no longer present, wildlife often turn to other plant parts, such as tree bark and inner wood of young trees. This type of feeding causes damage that is more harmful to plants in the long run.

Managing Deer Damage in Nebraska, Nebraska Extension
Managing Rabbit Damage, Nebraska Extension
Excluding Rabbits, Backyard Farmer
Controlling Vole Damage, Nebraska Extension
Vole Control, Backyard Farmer


14. Black knot disease of plumsPrune and destroy branches with galls before April 1st

As trees drop leaves, black knot galls become easier to see; however, removal of infected branches is best done in late winter or early spring. Black knot is a fungal disease that causes hard, black, elongated galls on branches and twigs. It affects plum, cherry and occasionally other plants in the Prunus genus. Pruning is the most important control measure and can reduce infection by 80%. Knots should be removed in late winter or early spring before growth starts with branches pruned at least 2 to 4 inches below each knot. Sterilize pruning tools between cuts. Fungicides offer protection against black knot, but will not be effective if pruning and sanitation are ignored. Fungicides provide the greatest benefit if applied before rainy periods in spring when temperatures are greater than 55 degrees F.


15. CankersInspect trees in winter for signs of disease

Inspect susceptible trees for signs of canker. These are typically sunken or discolored areas on the main trunk or branches. Some may have a distinct border. Common canker diseases are fireblight on apple and crabapple, nectria canker on honeylocust and cytospora canker on willows and poplars. Once infected, pruning to remove cankered branches is the only management option. Preventing wounds and tree stress are the best prevention tools. Branches infected with cankers need to be removed completely or at least 8 inches below the canker. Removal should take place while plants are dormant and before new growth begins next spring. If cankers are found, mark the branch with paint or flagging tape. 


Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by Nebraska Extension is implied. Use of commercial and trade names does not imply approval or constitute endorsement by Nebraska Extension. Nor does it imply discrimination against other similar products.

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