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Hort Update for January 16, 2020

Hort Update for January 16, 2020, Nebraska Extension, http://communityenvironment.unl.edu/update01162020
Serious ConcernsMajor Symptom:
1. Winter desiccation Lack of snow cover increases injury risk
2. Turf desiccation Dry winter conditions may result in damage by spring
Minor Issues
3. Leaf drop on houseplants / holiday plants Often an adjustment to change of growing conditions
4. Houseplant insect pests Common culprits and recommended control strategies
5. Wait to cut back herbaceous plants Wait until late winter or early spring
Timely Topics  
6. Pesticide recertification Check your license expiration date
7. Updated turfgrass nitrogen recommendations Common question & answer review
8. Holiday plant care Each plant type requires specific care
9. Ice melt products Choose with care to avoid plant damage
10. Know invasives when ordering Nebraska Invasive Species Program
11. Ideal time to prune woody plants Ideal time recommendation changed - Late March into June



1. Winter desiccationLack of snow cover increases injury risk

Cold, dry, windy winter conditions with little snow cover and extreme winter temperature fluctuations increase winter desiccation injury on evergreens, especially arborvitae and boxwood, but also pine, spruce, fir, juniper and yew, because evergreens lose more moisture from green foliage during winter than deciduous plants with no foliage.

Damage occurs when the amount of moisture lost is greater than what can be replaced by roots, often due to frozen or dry soil. Plant tissue dries out resulting in browning of foliage and dieback, which is often not seen until spring. Injury is found on the outer portion of the branches and is most severe on the side of the tree facing the wind or a source of radiated heat, such as a south or west-facing brick wall or street.

Actions that can be taken now are placing burlap wind screens between plants and prevailing winds or radiated heat sources; applying antidesiccants according to label directions when temperatures are above 40º F; and watering at mid-day if soils are not frozen and air temperatures are above 45º F. A once a month watering, if needed, is typically sufficient during winter.

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2. Turf desiccationDry winter conditions may result in damage by spring

In the absence of rain or snow cover, turf may experience winter desiccation injury, particularly turf with a high percentage of perennial ryegrass. The risk is greatest for golf and sports turf growing on sand soils. Stands with lots of thatch are more likely to have issues with winter desiccation (i.e. tees and fairways). Lawns of predominately Kentucky bluegrass, fescue, or buffalograss are much more tolerant of winter desiccation stress.

On lawns, the risk of desiccation is usually greatest on exposed or elevated areas where water surface runoff is greatest, and on poorly rooted turf that cannot take up water that is deeper in the soil profile. An example would be turf growing in heavy clay soils that were compacted and not prepared properly before seeding/sodding.

If needed on exposed sites, water only when the soil is not frozen and air temperatures are above 40º F. Apply water at mid-day so it has time to percolate into the soil before potential freezing overnight. Water just enough to moisten the crown of the plants. Apply water slowly enough that it soaks in and does not run off or pool and freeze around plant stems or crowns overnight.

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3. Leaf drop on houseplants / holiday plantsOften an adjustment to change of growing conditions

Customers may complain about leaf drop on houseplants that had been summered outdoors or on recently purchased holiday plants. When a plant's growing environment suddenly changes, some leaf drop is expected. This often happens when plants grown outdoors for summer are brought indoors for winter. Similarly, greenhouse-grown plants may drop leaves if placed in dim indoor light after being grown in high light intensity of a greenhouse.

Most plants are simply adjusting to lower light intensity and shorter days of winter. Leaf drop brought on by a change in environment is usually temporary and not life threatening to plants. New leaves adapted to the new conditions will develop. If an inspection of the plant does not find any insect issues, adjustment to new growing conditions is the likely scenario.

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4. Houseplant insect pestsCommon culprits and recommended control strategies

Warm indoor temperatures allow houseplant insects to multiply rapidly. Early detection is key to management. Common houseplant insects are fungus gnats, white flies, spider mites, and mealybugs. Others are scales, thrips and aphids. Positive identification is important. Signs of insects include honeydew, a shiny, sticky substance on leaves, fine webbing, leaf discoloration, and the insects themselves.

For flying insects, yellow or blue sticky traps can be placed near plants for monitoring purposes. Nonchemical controls include washing or spraying leaves, hand removal of insects and pruning out heavily infested stems and leaves.

There are chemical insecticides labeled for use on houseplants. Make sure the pesticide label says the product can be used indoors and on houseplants. Lower risk pesticides include insecticidal soaps, neem oil, and plant oil extracts.

Managing Insects on Indoor Plants, University of Minnesota Extension 

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5. Wait to cut back herbaceous perennialsWait until late winter or early spring

Warmer than average conditions may entice gardeners out to their gardens to get a jump on spring tasks. Encourage customers not to cut back herbaceous plants too early in winter. The ideal time to do this is late winter into early spring. Cutting plants back too early in winter sets them up for cold temperature injury or winter desiccation. If conditions remain fairly warm, new growth may occur that is then killed by subsequent cold temperatures.

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6. Pesticide recertificationCheck your license expiration date

Check your applicator license for the expiration date. If needed, go to www.pested.unl.edu for training dates at various locations in February, March and April. 

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7. Updated turfgrass nitrogen recommendationsCommon question & answer review

With late fall fertilization no longer recommended, our turfgrass specialist have received a number of related questions. For these questions and answers, see “Timing of Nitrogen Fertilizer Applications” in the December 30, 2019 Turf Info.

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8. Holiday plant careEach plant type requires specific care

Customers often ask what to do with a holiday plant after it finishes blooming or how they can help the plant bloom again next season. Once blooming is finished, remove the spent flowers but leave the foliage. Over the next months, the goal is to keep the foliage healthy so it can replace stored food used during blooming. Place plants in good light conditions, maintain a just moist soil and fertilize about once every two weeks. Each plant needs to be treated slightly different for reblooming. See resource link below.

Popular Holiday Plant Care, University of Arkansas Research & Extension

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9. Ice melt productsChoose with care 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.

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.

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10. Know invasives when orderingNebraska Invasive Species Program

Along with selecting plants adapted to our growing conditions and with curb appeal to customers, another consideration is to be sure a plant is not considered invasive. Invasive species are defined as non-native plants whose introduction causes or is likely to cause harm. But not being native does not make a plant invasive either. Unlike plants designated noxious weeds, like purple loosestrife and musk thistle which are illegal to sell, invasive species are specific to a region. They may be listed as invasive in one state and considered acceptable in another, so they are available for sale. Be aware of what to avoid. To learn more, go to the Nebraska Invasive Species Program.

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11. Ideal time to prune woody plantsIdeal time recommendation changed - Late March into June

Prune woody plants while they are dormant had been the standard recommendation for trees and shrubs. Technically this could mean anytime from November through March.  New research shows the ideal time to prune woody plants is during the early growth period which would be late March into June in Nebraska. At this time, cells are most active so there is quicker callus growth. Also, a trees defense system is fastest on pruning cuts made shortly before or early in the season of most active growth. 

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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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