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Hort Update for October 16, 2020

Hort Update for October 16, 2020, Nebraska Extension, http://communityenvironment.unl.edu/update10162020
Serious ConcernsMajor Symptom:
1. Drought concerns going into winter Current conditions range from abnormally dry to extreme drought
2. Irrigation systems and cold weather Protect client systems and components from freezing temperatures
Minor Issues
3. Cottonwood/poplar rust Minor problem; rake up and dispose of infected leaves
4. Stem rust in turfgrass Usually found in older turf cultivars; seldom seen in newer cultivars
5. Fall pre-energence herbicide applications for prostrate knotweed and crabgrass Fall annual weed control justified for serious infestations
Timely Topics
6. Mowing trees leaves into lawns Up to three inches of leaves can be mowed into turf at a time
7. Fall vole activity Prevent winter feeding that can girdle and kill trees & shrubs
8. Wildlife & turf damage Identifying damage; control measures
9. Evergreen natural needle drop Yellowing & browning in fall of interior needles
10. Protecting young trees from winter sunscald damage Prevent this common type of damage to young, tender-barked trees
11. Too late to seed; still okay to lay sod Dormant seeding can begin in late November
12. Fall lawn fertilization best completed before October 30th Later applications not well utilized by turf
13. Late fall perennial weed control Guidelines for late fall applications
14. Fall insect invaders Boxelder bugs, Asian lady beetles, millipedes, mice...


1. Drought concerns going into winterCurrent conditions range from abnormally dry to extreme drought

Nebraska's current drought conditions range from abnormally dry to extreme drought. For more detail, refer to the Nebraska Drought Monitor map. This makes fall/winter watering extremely important. Along with an increased risk of winter dessication and cold temperature injury, drought stressed trees and shrubs are 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, newly planted trees and shrubs and younger woody plants. Soil needs to be kept moist to 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, should 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. Winter watering may be needed in the absence of rain/snowfall. Water can be applied early in the day when soils are not frozen and air temperatures are above 40 to 45 degrees Fahrenheit.

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2. Irrigation systems and cold weatherProtect client systems and components from freezing temperatures

When clients are watering during fall, instruct them to disconnect hoses at night to prevent freezing of water trapped in the lines and damage to irrigation components. Irrigation lines should be drained and prepped for winter. 

Home Sprinkler Systems: Preparing Your Sprinkler Systems for Winter , Colorado State University

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3. Cottonwood/poplar rustMinor problem; rake up and dispose of infected leaves

If the leaves of cottonwood, aspen or other poplars have rusty orange spots, this is a minor fungal disease. Although common, this rust disease is essentially harmless to trees because it develops in late summer and rarely causes early leaf drop. This means the disease infects leaves after most photosynthetic needs of the tree are met for the year. Like most rust diseases, the life cycle of this fungus requires two different tree hosts. During wet spring weather, spores are released from the fungus which overwinter on fallen cottonwood or aspen leaves. The spores infect evergreen needles, such as pine, fir or spruce, where they cause little to no damage and go unnoticed. After two to three weeks, spores are produced on evergreen hosts and blow to cottonwood or aspen leaves. By late summer, raised orange spots become noticeable. As the fungus overwinters on infected leaves, raking and removing leaves will help reduce infections.

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4. Stem rust in turfgrassUsually found in old turf cultivars; seldom seen in current cultivars

Stem rust is a fungal disease that develops late in the season on lawns with older bluegrass varieties and slow growth due to low nitrogen. The obvious symptom is rust colored "powder" (fungal spores) on grass blades, shoes and lawn mower. Heavily infected turf may show some yellowing of grass blades. Fungicide controls are rarely recommended or needed for home lawns. Fall lawn care, especially correct nitrogen fertilization, along with cooler fall weather promotes turfgrass growth and rust disappears.

Note for Sports Turf- If stem rust occurs on low maintenance athletic fields, the fungal spores can cause problems for allergy/asthma sufferers. Control of stem rust is recommended on sports turfs using a combination of wise turf management and timely fungicide applications. It is too late this season for fungicide controls.

Rusty Turf, Nebraska Extension Turf iNfo

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5. Fall pre-emergence herbicide applications for prostrate knotweed and crabgrass controlFall annual weed control justified for serious infestations

When chemical control is justified, an application with the correct herbicide, isoxaben, in the fall can be effective for knotweed. If both crabgrass and knotweed were serious problems this year, prodiamine can be used. It is not as effective as isoxaben at knotweed control, but will provide control of both crabgrass and knotweed.  

Control of Prostrate Knotweed (and Crabgrass?) with Preemergence Herbicides This Fall, Nebraska Extension Turf iNfo

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6. Mowing tree leaves into lawnsUp to three inches of leaves can be mowed into turf at a time

While many homeowners bag tree leaves each fall, most professional turf managers mulch mow leaves. Mulch mowing can be easier and returns complex organic matter and nutrients to the soil. Some research suggests mulch mowing can even help control weeds. While this weed control benefit can be sporadic, it can help improve the health of your lawn and soil. Mulching leaves is also easier and less time consuming than bagging. Sometimes a double mowing at a slightly higher cutting height will help shred those leaves and bury them in the lawn. The ground tree leaves won’t add to thatch.  Sometimes tree leaves come fast and quickly pile over the lawn. If you need to rake and bag, compost those leaves and don’t put them on the street or other concrete surfaces. Leaves can leach nutrients that pollute waterways; or be carried to surface water through storm drains where they release nutrients leading to algal problems.

Mow Tree Leaves and Other Fall Lawn Care Tips, Nebraska Extension Turf iNfo

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7. Fall vole activityPrevent winter feeding that can girdle and kill trees & shrubs

Vole feeding can girdle and kill trees and shrubs, usually in late fall and winter. Gnaw marks of voles are irregular in appearance and at different angles. Depending on the type of vole, voles create surface runway systems or burrows.

Trapping is an effective method for vole control if damage is over a limited area (less than an acre) and a sufficient number of traps are used (two to three per runway and/or hole). Set single mouse snap traps perpendicular to vole runways with the triggers in the runways, or set two traps together within the runways with triggers facing away from each other. Bait is not required. If you use bait, smear peanut butter mixed with oatmeal on trap triggers. Cover baited traps with a box with a 1-inch hole cut in it, to reduce access to birds and squirrels. Make sure boxes are secured. Trap enclosures can also be made of PVC pipe. Multiple-catch mouse traps are useful since several voles can be captured at one time. Locate traps near visible burrows and adjacent to vole trails. Place a small amount of seed material, either bird or grass seed, at both entrance points. If the location is correct, traps should contain a few voles in 24 hours. If you catch nothing after two nights of fair weather, move the traps to a new location.

Exclusion can be used to protect highly valued trees. Use ¼-inch hardware cloth or plastic cylinders to protect individual trees and shrubs. The cylinder should be tight to the ground or buried about two to six inches and extend to a height above expected snow depth. When making the cylinder, overlap the edges at least 1 inch and fasten securely so gaps do not form.

Habitats can be modified to reduce suitability for voles. High vole populations cannot become established without food and protection from predators. Control grass and weeds around young trees and shrubs through cultivation, herbicides, and mowing. Since voles often thrive under plastic weed barriers, remove these or use other control methods listed below. Remove bird feeders or substantially reduce spillage from feeders to avoid attracting voles.

Repellents provide short term protection unless reapplied. Those made with thiram and capsaicin are registered for controlling vole damage on ornamental plants only. Coyote and fox urine may help to disperse voles and have been proven to increase stress and, therefore, reduce reproduction in voles. Wear waterproof gloves and avoid contact with urines as they may not be sterile.

Controlling Vole Damage, Nebraska Extension
Vole Control, Backyard Farmer

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8. Wildlife turf damageIdentifying damage; control measures

Raccoon - Damage indicators include rolled up or shredded sod in the yard. Controlling Raccoon Damage, Nebraska Extension

Skunks - Cone-shaped holes dug at surface of lawn indicate skunks have been digging for grubs and other insect larvae. Dealing With Skunks, Nebraska Extension

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9. Evergreen natural needle dropYellowing and browning in fall of interior needles

Older needles on the inside of evergreen trees are shed each fall after they turn yellow, brown or reddish tan in color. Sometimes this natural process is very subtle and goes unnoticed, but this year is quite evident in many trees, particulary spruces. However, the bottomline is natural needle drop is a normal process, not a disease or insect problem. 

Pine trees can hold their needles for 2-5 or more years, depending on the species. Spruce trees generally hold onto their needles longer than pine trees do, approximately 5-7 years, which serves to hide the browning needles.

However, if there is question about a potential pathogen causing browning needles and needle drop, contact your local Extension office or submit pictures through UNL's Digital Diagnostic Network

Natural Needle Drop, Nebraska Extension
Evergreen Needles Are Falling, Iowa State Research and Extension

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10. Protecting young trees from winter sunscald damagePrevent this common type of damage to young tender-barked trees

The trunks of young, tender barked trees are prone to winter sunscald until the tree is mature enough for the trunk's bark to become thick and woody. Damage occurs to the south or southwest side of trees during warm winter days. Sun shining on the bark heats it up; research has found bark on the south side of a tree can be 77° F warmer than bark on the north side on a sunny winter day. Damage occurs when bark cells lose some of their cold-hardiness during the day, then are damaged as temperatures fall below freezing at night. Damage can be seen as discolored and/or sunken bark, peeling bark or bark cracks in the years following the incident. 

A partial list of trees susceptible to sunscald include apple, ash, aspen, birch, crabapple, cherry, cottonwood, honeylocust, linden, maple, mountain ash, oak, peach, tuliptree and willows. Drought stressed young trees are also more susceptible to damage than well-hydrated trees. 

Protection methods all work to shade or insulate the bark against temperature rises during winter. Wait until after leaves have dropped to put protection in place. If trunk wraps are used, remove them in spring after freeze damage is past. If left on too long, wraps can girdle young trees; and moisture may build up beneath tree wrap to promote decay organisms.

  • Wrap trunk with tree wrap after tree leaves have fallen. Common products to use include white paper wrap, white plastic tree spirals or white corrugated plastic tree guards. Light brown tree wrap can be used but does not reflect winter light and keep the underlying bark as cool as white products do. 
  • Insert a lightcolored or white-painted board in the soil on the south and west side of trees. 
  • Fruit orchard trees - paint the entire trunk or south side only with white exterior latex paint diluted 1:1 with water.

Sunscald Injury or Southwest Winter Injury on Deciduous Trees, Utah State University - Forestry Extension

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11. Too late to seed; okay to lay sodDormant seeding can begin in late November

It is too late to seed or overseed turfgrass, but sod can still be laid; or soil preparation can be completed now for dormant seeding from late November through early March.  See links below.

Establishing Lawns from Sod, Nebraska Extension Turf Fact Sheet
Establishing Lawns from Seed, Nebraska Extension Turf Fact Sheet

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12. Fall lawn fertilization best completed before October 30thLater applications not well utilized by turf

Mid-September is the best time to apply fertilizer to cool season lawns. If fall fertilizer has not yet been applied, or a second application is to be made, only use fertilizers with fast release nitrogen sources and make the application no later than mid-late October.

Rethinking Fall Fertilization, Nebraska Extension Turf iNfo

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13. Late fall perennial weed controlGuidelines for late fall applications

Herbicide applications for perennial weed control can still be made effectively while the following conditions apply. 

  • Daytime temperatures are above 50°F.
  • Weeds have green leaves and can uptake herbicides.
  • Soils are not frozen. 

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14. Fall insect invadersBoxelder bugs, Asian lady beetles, millipedes, mice...

Nuisance insects and mice 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 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.

Fall Invaders: What You Can Do, Nebraska Extension
Boxelder Bugs, Nebraska Extension
Centipedes and Millipedes, Nebraska Extension
Controlling House Mice, Nebraska Extension
Identification Guide to Common Spiders in Nebraska, Nebraska Extension
Multi-colored Asian Ladybird Beetles, Nebraska Extension

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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.