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Hort Update for December 15, 2020

Spotted Lanternfly, image from Pennsylvania Department of Agriculture
Spotted Lanternfly, image from Pennsylvania Department of Agriculture
Serious ConcernsMajor Symptom:
1. Drought conditions continue Current state conditions range from abnormally dry to extreme drought
Timely Topics
2. Whiteflies Tiny pure-white gnat-like insects; fly up from undersides of plant leaves when disturbed
3. Fungus gnats Tiny dark-colored gnats commonly infest overly wet soil
4. Broadleaf evergreens susceptible to dry conditions  Monitor plants; water when soils are not frozen if dry conditions persist
Minor Issues
5. Too late to fertilize lawns December fertilizer applications are not recommended; low plant uptake and contributes to surface water pollution
6. Too late to overseed lawns Good seed-soil contact important for dormant seeding success
7. Assessing landscape trees Spotting tree hazards easiest during dormancy; Tree Hazard Awareness publication aids identify potential problems
8. Spotted lanternfly Has not been found in Nebraska yet
Continuing Issues
9. Use deicing salts correctly Choose products carefully to avoid plant damage

1. Drought conditions continueCurrent state conditions range from abnormally dry to extreme drought

Nebraska's drought conditions continue. For more detail, refer to the Nebraska Drought Monitor map. This makes winter watering extremely important. Along with an increased risk of winter dessication and cold temperature injury, drought stressed trees and shrubs become more susceptible to attack by harmful pests like borers, canker disease and Verticillium wilt. Plant owners often believe their landscape plants survived a drought year, but then dieback shows up three to five years after a drought.

While most plants benefit from fall watering, the priority should be evergreens (conifers and broadleaves), newly planted trees and shrubs and younger woody plants. Try to keep soils moist to about an 8” to 12” depth from the trunk/stems out to at least the dripline of trees and preferably well beyond. If plants are not mulched, a 3” to 4” deep layer of organic mulch, like wood chips, can be applied in at least a 4’ diameter ring around plants to conserve soil moisture. Be sure mulch is not piled against tree trunks and avoid continuously saturated soils. For winter watering, apply water early in the day when soils are not frozen and air temperatures are above 40 to 45 degrees Fahrenheit.

U.S. Drought Monitor Map


2. WhitefliesTiny pure-white gnat-like insects; fly up from undersides of plant leaves when disturbed

Whiteflies are a fairly common pest of poinsettia. If brought into a home on infested plants, whitefly populations multiply rapidly. Inspect plants closely for signs of white flies, such as sticky leaves; or for the insect itself. Whiteflies are not flies. They are related to aphids, mealybugs and scale insects and feed on plant sap. Adult whiteflies are very tiny and have wings covered with a white powdery wax. Adult females can lay between 200 and 400 eggs. Upon hatching, flattened nymphs or crawlers attach themselves to leaf undersides and feed for about four weeks before pupating.  Whitefly feeding leads to weakened plants and leaf yellowing and dropping.

Consider recommending to clientele that heavily infested plants be discarded as white flies are challenging to control. For smaller populations, recommend yellow sticky traps to reduce their numbers and see the information at the link below for recommendations on how to safely apply insecticides.

Poinsettia Gift May Include Whiteflies, Nebraska Extension GRO Big Red Blog


3. Fungus gnatsTiny dark-colored gnats commonly infest overly wet soil

Fungus gnat adults are one-eighth inch long flies seen flying around houseplants and near sunny windows. Adults do not feed on plants or bite people and pets. The larvae are tiny, worm-like and translucent with dark heads. They mostly feed on fungus and organic matter in soil and might feed on plant roots. Fungus gnats thrive in poorly drained soils that remain too wet and allow fungus to grow. Often, letting the soil mix to dry out between watering along with using a well-drained potting mix in a container with drainage holes (with excess water poured out of the catch basin after each watering) is all that is needed to reduce fungus gnats. Use of yellow sticky traps will help reduce numbers quickly. Houseplant labeled insecticides containing active ingredients such as bifenthrin or permethrin and microbial insecticides containing Bacillus thuringiensissubsp. israelensis are effective.

Managing Houseplant Pests, Colorado State University Extension


4. Broadleaf evergreens susceptible to dry conditionsMonitor plants; water when soils are not frozen if dry conditions persist

Broadleaf evergreens such as boxwood and Rhododendrons are best monitored closely for winter watering needs, especially those planted in 2020. With conditions remaining dry, winter desiccation will be a greater issue. With their larger leaf surfaces, these plants lose even more moisture on warm or windy winter days than needled conifers. While both benefit from winter watering, broadleaf evergreens are generally at a higher risk. Recommend winter watering when soil if somewhat dry and temperatures are above 45 degrees F.


5. Too late to fertilize lawnsDecember fertilizer applications are not recommended; low plant uptake and contributes to surface water pollution

Research has shown nitrogen uptake efficiency declines in November. Nitrogen not taken up by plants can leach during winter and early spring.  In the future, for the final fertilization, make the application at a rate of three-fourths to one pound of nitrogen per 1000 square feet and select a fertilizer with fast release nitrogen sources. These are typically listed on the label as urea or ammonium sulfate. The reason for fast release or water soluble sources is so nitrogen is quickly taken up by the plant.  Avoid products that contain water insoluble, slow release nitrogen, for the late October/early November application.  Avoid fertilizers containing phosphorous unless a soil test indicates this nutrient is needed.  Phosphorous is an expensive nutrient and excess phosphorous leads to surface water pollution.

Fertilizing Home Lawns, Nebraska Extension Turf iNfo


6. Too late to overseed lawnsGood seed-soil contact important for dormant seeding success

It is too late to seed or overseed turfgrass, however dormant seeding can be done now through late March. Dormant seeding is defined as such because seed lies dormant until soil temperatures warm in April or May. It can be done as early as Thanksgiving or as late as March in most Nebraska locations. The key is to seed after the soil is cold enough that germination will not occur until after soils warm in spring. The benefit of dormant seeding is as soil heaves and cracks during winter, crevices are created for seed to fall into, providing ideal germination conditions in spring. Dormant-seeding may be easier to schedule than spring seeding, because spring rains can make it difficult to seed after March.

There are risks with dormant seeding. It is most effective if weather remains cold enough to delay germination until spring. Occasionally, extended warm periods in winter could allow seed to germinate, and seedlings may then be killed by ensuing cold weather.

As with any seeding, soil preparation needs to be done prior to seeding. For dormant seeding, this would be in fall before the soil freezes or during dry winter periods when the soil is not frozen. If using dormant seeding, monitor the area in mid spring for the need to do additional over-seeding.

Establishing Lawns from Seed, Nebraska Extension Turf Fact Sheet


7. Assessing landscape treesSpotting tree hazards easiest during dormancy; Tree Hazard Awareness publication aids identify potential problems

Winter is a great time to assess trees for potential hazards; branch structure and areas of damage are easy to see when trees are not in leaf. Look for co-dominant leaders, cracks, decay, fungal conks, girdling roots, trunk lean, and root plate defects. Refer to the publication below for images of all these defects. If client trees have any of these defects, recommend they contact an arborist certified with either the International Society of Arboriculture (ISA) or Nebraska Arborist Association (NAA) to protect themselves and their property. Certified arborists have specialized training and experience evaluation tree defects and hazards.  

Tree Hazard Awareness, Nebraska Extension 


8. Spotted lanternflyHas not been found in Nebraska yet

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 including apple, plum, cherry, peach, apricot, grape and pine. 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.

Spotted Lanternfly, Nebraska Invasive Species Program
Invasion of the Lanternflies: Response, Impact and Management of this New Invasive Insect Pest, Heather Leach, Penn State Entomology


9. Use deicing salts correctlyChoose products carefully to avoid plant damage

De-icing agents are sometimes needed for safety but can be harmful to plants. Common deicing compounds are listed below in order of potential plant damage, with the most damaging first. These may be used alone or blended together to improve performance or reduce damage to concrete or landscapes.

  • Sodium chloride is the least expensive product and commonly used on roadways. It has a high burn potential for landscape plants.
  • Urea can harm landscape plants and cause runoff pollution in ponds and waterways.
  • Potassium chloride, also known as muriate of potash, is less damaging than sodium chloride.
  • Calcium chloride is the most effective deicing product at low temperatures, working down to ­‐25°F. It will not damage vegetation if used as directed.
  • Magnesium chloride is sprayed on roadways before a snowstorm to prevent ice bonds from forming, making ice and snow removal easier. It causes very little damage to concrete or metal. It's also gentle on landscape plants and pet safe if used as directed.
  • Acetates can be found in three forms - ­calcium magnesium acetate (CMA), sodium acetate and potassium acetate. CMA is a salt-­‐free product and is the safest product for use around pets and landscape plants. CMA is made from dolomitic limestone and acetic acid (the principal component of vinegar). Studies have shown the material has little impact on plants. It also has a very low level of damage to concrete or metal.
  • Beet juice deicers - A newer organic option are products derived from beet juice. They contain only 12% sodium chloride (salt), much less than traditional sodium chloride. Beet juice products are fully biodegradable, however some research has shown potential problems with aquatic insects. So ideally it should not be applied where melt runoff will move to aquatic areas. Available to homeowners as Green Gobbler Pet Safe Ice Melt, Snow Joe Beet It Snow & Ice Melter, Organic Melt Premium Granular Ice Melter and others.  

Also keep on hand products that improve your footing on slick surfaces, like sand, sawdust, or cat litter. They can be used instead of traditional deicing products, or blended with them to improve traction and limit deicer use.

Winter De-icing Agents for Homeowners, Nebraska Extension
Salt Damage in Landscape Plants, Purdue Extension


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.