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Hort Update for Nov. 24, 2015

Lawns Major Symptom:

1. Too late to fertilize

Fertilization after first week of November not recommended

2. Winter watering

Beneficial if needed and done correctly

3. Dormant seeding

Alternative option to spring seeding; fall seeding ideal

4. Leaf removal or mulch mowing

Thick layers can suffocate and kill turfgrass over winter
   
Trees & Shrubs  
5. Loss of bark on pears Due to cold fall temperatures when trees not hardened off
6. Protection from wildlife Exclusion with hardware cloth best protection 
7. Remove bagworms Pull off and discard overwintering bags on evergreens
8. Ice and snow loads Tie up evergreen shrubs; brush snow carefully; let ice melt
9. Check for scale insects These are easy to see and identify now, but wait to control
10. Pruning hydrangeas When/what to prune determined by age of blooming wood 
   
Landscape Ornamentals  
11. Cutting back perennials Providing habitat for beneficial insects
12. Mulch fall planted perennials Winter mulch improves survival for some perennials
   
Fruits & Vegetables  
13. Strawberry winter protection Imperative for best overwintering success
14. Tree & small fruit bud damage Extreme winter temperatures may cause bud damage

1. Fertilization after first week of November is best avoided - Research has shown nitrogen uptake efficiency declines later into fall.  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.

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2. Winter watering, if needed, can be used to minimize the effects of dry, winter conditions. Only when needed, water when soil is not frozen and air temperatures are above 40 degrees F.  Apply water at midday so it has time to infiltrate soil before cold overnight temperatures increase the potential for freezing.  Apply water slowly enough for it to soak in and not run off or freeze around plant crowns. 

Standing water can cause crown hydration injury to a lawn if watering is done just before a sudden temperature drop is forecast or when the soil is frozen. Crown hydration occurs naturally in late winter when a day or two of warm daytime temperatures causes snowmelt, which enables plants to start absorbing water.  Problems mainly occur in low areas where water collects and stands due to frozen soil or poor soil drainage.  If warm weather is followed by a rapid drop to freezing temperatures, water taken up by the crown freezes causing ice crystals to form which damage or rupture plant cells.

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3. Dormant seeding involves seeding when it is cold enough that seed germination will not occur until after soils begin to warm in spring. Other than the time of year of dormant seeding, typically mid-December through Valentine’s Day or Spring Break, the actual process of preparing the area to be seeded is the same as for seeding at other times of the year. If seedbed preparation has been done, and soils are not frozen, dormant seeding can be done. The risk of dormant seeding is that warm winter and early spring temperatures may cause seed to germinate; and then a subsequent cold period kills the seedlings. When using dormant seeding, monitor seeded areas in mid spring for the need to do over-seeding.

Establishing Lawns From Seed, Nebraska Extension

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4. Leaf removal or mulching mowing into the lawn is important to prevent leaves matting and suffocating turfgrass during winter. It also keeps leaves from clogging storm drains to cause localized flooding; and from being transported to surface water where they cause pollution. Mowing leaves works as long as the leaf layer is not too thick. Tree leaves should be pulverized enough that they filter down into the turfgrass. After mowing, green grass blades should still be visible. A mulching mower works best. A regular mower can be used as long as the leaf layer is not too thick. Clients are sometimes concerned about thatch build-up. Tree leaves will not contribute to thatch; which is mainly a layer of dead grass roots and rhizomes. These are high in lignin and do not decompose as readily as grass clippings and tree leaves.

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5. Loss of bark on ornamental pears is most likely due to last Novembers sudden cold spell when trees had not completely hardened off for winter. Cold temperature injury occurred causing bark to slough or peel off during the summer. This is not a good sign and most trees eventually decline or die. The area should not be treated with any kind of commercial wound dressing, painted, or covered with tree wrap. One reason ornamental pears are often affected is because they tend to go dormant later in the fall than some other types of trees.

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6. Wildlife protection for young and valuable tree - Barriers of hardware cloth placed around young trees and shrubs is the best means of protection from rabbit and vole damage. Make sure barriers extend well above the usual snow line. Various taste repellants, such as Thiram or Millers Hot Sauce, can be effective in reducing deer and rabbit damage as long as animals have other food sources to turn to. Scent repellants, such as bags of human hair or bar soaps on a rope, have been shown to be effective in some situations.

Managing Rabbit Damage, Nebraska Extension
Managing Deer Damage, Nebraska Extension
Managing Vole Damage, Nebraska Extension

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7. Remove and destroy bagworms - As many as 500 to 1000 eggs can overwinter in one female bagworm. Removing and destroying bagworms overwintering on evergreen trees during winter or spring (by May 1st) can help reduce the bagworm population. Destroy bagworms by crushing or immersing them in soapy water. If bags containing eggs are discarded on the ground, eggs may still hatch and larvae return to the evergreen.

Bagworms, Nebraska Extension

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8. Ice and snow loads often occur during Nebraska winters. For evergreens, this can translate into branch breakage. A method used to protect evergreen shrubs from ice or snow loads is loosely tying stems together. If an ice or snow storm is predicted, twine can be used to loosely tie branches of valuable evergreen shrubs together for support. Start by tying the end of the twine around a sturdy stem near the base of the plant. Then loosely wrap the twine around and up the shrub to encircle about three-fourths of the plant and tie the twine to a sturdy stem. The goal is to prevent a snow or ice load from spreading or bending branches far enough to break. It is not to immobilize branches. Most spread or bent branches return to normal position as long as they do not break. Leave the twine in place until all ice has melted naturally. Never attempt to break ice off of a plant. This is dangerous and can cause branches to break. Snow can be carefully brushed off. Twine can be left in place for future storms, as long as it is removed in spring.

For fruit and small ornamental trees, two by fours can be used to prop up branches when an ice or snow storm is predicted. It is helpful to cut a v-shaped wedge in one end of the two by four to provide more stability when supporting branches.

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9. Monitor for scale insects - Scale insects can be “easy to see” but one may need to look closely at stems and branches, and sometimes leaves, to notice them. Scale insects develop a protective covering that camouflages them and is difficult to penetrate with insecticides. Most overwinter as eggs beneath the shell (scale). Upon hatching, young crawlers move to new locations on the plant. Crawlers are the only mobile stage in the life cycle. They are pale in color and smaller than a pinhead in size. After a few hours, they insert their mouthparts into the plant, begin to suck sap and soon molt. From this point on, they remain in the same spot for the rest of their lives. Within a week they are covered with a waxy scale covering. Old scale shells stay attached to the plant for years before falling off.

Common scale insects in Nebraska include oystershell scale, Kermes scale, Euonymous scale, and pine needle scale. Plants commonly infested and damaged by scales are lilac, dogwood, some shade trees, Euonymous and pines.

During winter is a good time to monitor for scale insects. If found, the population can be reduced by pruning heavily infested branches. When insecticides are used, they need to be applied during the crawler stage. This can vary with different scales, but many hatch in May. Some have two generations with a hatch in May and another in late July or early August.

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10. Pruning hydrangea - When, what and how much to prune is determined by the type of hydrangea being pruned and what age of wood that type produces flowers on. Some can be pruned while dormant; others should be pruned after blooming; and still some can be pruned a little while dormant and again after blooming. See the video link below for pruning information for Hydrangeas.

Pruning Hydrangeas with Kim Todd, Nebraska Extension Backyard Farmer

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11. Cutting back perennials – Insects, depending on their species, overwinter is a specific life stage – adult, egg, larva, nymph, pupa, etc. Many insects enter diapause, a stage of extended dormancy, to enable them to survive winter conditions. They seek out sheltered locations that provide some winter protection, such as hollow plant stems, leaf litter around the base of shrubs, tree bark flaps, or grass and perennial plant crowns. Or they may nest in the ground, in tree or shrub cavities or in wood. Plants with pithy or hollow stems like ornamental grasses, elderberry, raspberry, blackberry and sumac serve as good overwintering sites for solitary bees.

When working with clients on cutting back ornamental grasses and perennials in fall, landscape managers should recommend leaving 12-18” of stems in the garden to allow for increased beneficial insect overwintering habitat. Pollinators and butterflies will benefit from these additional amounts of winter cover.

Where Do They Go For Winter?, Colorado State University Extension

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12. Mulching fall planted perennials – Winter mulching is recommended for strawberries, Chrysanthemums and other perennials on the borderline of hardiness for a given area; and for fall planted perennials to help prevent frost heave uprooting plants. Winter mulch should be put into place after plants are fully dormant and soils begin to freeze or night temperatures are consistently dropping into the 20s, usually around mid November. Use a 12 inch layer of coarse mulch over the tops of plants. Encircling plants or beds with chicken wire and filling the chicken wire with coarse mulch, such as wood chips or leaves, works well.

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13. Strawberry winter protection – Strawberry plantings must be mulched for winter to prevent or reduce winter damage to the strawberry crown and flower buds. Most unprotected strawberry cultivars are injured at 15°F. Do not mulch too early. Wait until late November or early December; then apply loose mulch to a depth of four inches in late November/early December after the soil has frozen to a depth of 1/2 inch, or the temperature has dropped to the 20s.

If mulch is applied too early it can delay hardening off, making plants more susceptible to winter injury, and increasing crown rot. Suitable mulches include wood chips, pine straw, newspapers, coarse sawdust, straw, clean hay or any loose mulch that will not compact heavily. The mulch should remain on the strawberry plants until new growth begins, about mid-April.

Fall and Winter Care of Strawberries, Nebraska Extension

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14. Tree & small fruit bud damage – Extremely cold winter temperatures can cause damage to flower buds.  Bud development stage determines how susceptible it is to damage.  Refer to Critical Spring Temperatures for Tree Fruit Development Stages for the amount of potential damage at specific temperatures. Tree and small fruits may have a significant reduction in crop production if many buds are killed.  The most critical time fruit buds is spring when they begin to lose winter dormancy.

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