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Hort Update for October 15, 2019

Hort Update for October 15, 2019, Nebraska Extension, http://communityenvironment.unl.edu/update10152019
Serious ConcernsMajor Symptom:
1. Asian jumping worms New invasive species; found in Douglas, Sarpy, Lancaster and Platte Counties
2. Cytospora canker of spruce Disease incidence on the rise
3. Spring best time to treat for Emerald Ash Borer Do not begin treatment until EAB is confirmed within 15 miles of your location
Minor Issues
4. Lilac bacterial scorch/blight Fall sanitation important
5. Powdery mildew - lilacs/peonies Fall sanitation important
Timely Topics Major Points:
6. Perennial weeds in turf Fall best time for control
7. Mulch mowing leaves Saves time and expense; adds organic matter to soil
8. How late to mow? Continue until grass stops growing
9. Okay to lay sod; too late to seed Dormant seeding can begin in late November
10. Fall lawn fertilization best completed before late October Later season applications not well utilized by turf
11. Avoid pruning spring blooming shrubs now Next year's flower buds are present and will be removed
12. Herbaceous perennial fall clean-up Wait until foliage/stems are killed by frost
13. Home invading nuisance insects Exclusion best method of control



1. Asian jumping wormsNew invasive species; found in Douglas, Sarpy, Lancaster and Platte Counties

This new invasive species has been found in Douglas, Sarpy, Lancaster and Platte Counties in Nebraska. Activity of this work can deplete soil of nutrients and alter the soil's capacity to hold water. While Asian jumping worms look similar to European earthworms, there are distinct differences to aid identification. See links below.

Unlike European earthworms, Asian jumping worms do not create channels in soil nor do they recycle nutrients into soil. Instead, they feed near the surface on leaf litter and mulch leaving behind a dry, grainy soil that deprives trees and other plants of essential nutrients. As a new pest, research is being done on the best way to manage them. One way to slow their spread is to discourage clients from sharing plant materials from yard to yard. If you suspect jumping worms, take a video and/or photo of them to submit to your local Extension office and/or the Nebraska Invasive Species program at this link: https://neinvasives.com/report-a-sighting

Asian Jumping Worm, Nebraska Invasive Species Program
A New Can of Worms, GroBigRed

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2. Cytospora canker of spruceDisease incidence on the rise

This fungal canker-causing disease, a common pathogen of spruce, is on the rise, most likely due to hail storms creating wounds for fungi to infect trees. Once infected, the fungus grows inside the cambium layer and restricts movement of water and nutrients. This disease occurs most commonly on older trees stressed by drought or poor site conditions.  Colorado blue spruce, white spruce (including Black Hills) and Norway spruce can all be affected. As blue spruce is heavily over planted, we tend to see canker in this species most often. Symptoms include branches and tops of trees dying and a grayish-white resin oozing from the trunk or branches. Needle color may gradually change to reddish-brown. 

There are no chemical controls for Cytospora canker. Management includes improving tree health by correctly mulching with organic mulch and providing one inch of water per week, without overwatering. Cankered branches can be removed during dry weather and destroyed. If a tree dies from the top down and 40 percent or more is affected, it would be best to replace these trees with a different type of evergreen.

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3. Spring is the best time to treat for Emerald Ash Borer (EAB)Do not begin treatment until EAB is confirmed within 15 miles of your location

With EAB now confirmed in Greenwood, Omaha, Lincoln, Fremont, and near Ashland, wait until spring to treat healthy trees that are up to 15 miles from these locations. For trunk injections, Mid-May through June is the ideal application timing for good control. For soil treatment, products containing imidacloprid are best applied in April just before trees leaf. Products containing dinotefuran are best applied mid-May to early June. Now is the time to assess ash trees to determine if they are candidates for treatment. For ash trees that homeowners do not plan to treat, removal of the tree should be considered once EAB has been found within 15 miles of that tree, rather than waiting for the tree to become infested and die. At that time, ash trees can become brittle (more so than other species of trees that die from other causes) and they become a risk as well as more challenging to remove.

Selecting Trees for EAB Treatment, Nebraska Forest Service
Nebraska Forest Service - EAB Resource Center

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4. Lilac bacterial scorch/blightFall sanitation important

Cool, wet weather this year promoted a higher incidence of lilac batercial scorch.  Initial symptoms were brown, water-soaked spots on leaves. These spots can coalesce and leaves may become misshapen. Severely infected leaves may die and drop off. If the bacteria infects twigs, young shoots may turn black and droop. Begin disease management this fall by raking and removing fallen leaves. Next spring, remove and destroy diseased plant parts during dry weather. Disinfect pruners between cuts by dipping in a 10 percent bleach solution. 

Bacterial Blight of Lilac, Iowa State University Extension

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5. Powdery mildew - lilacs/peoniesFall sanitation important

Powdery mildew on lilacs and peonies causes  the tops of leaves to appear dusted with a grayish-white powder that cannot be washed off. Since this fungal disease rarely causes long term harm to plants, it can be managed with fall sanitation (rake and remove leaves this fall), by selecting resistant varieties to plant, and by planting in areas with good air circulation and sunlight.

Powdery Mildew, Iowa State University Extension

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6. Perennial weeds in turfFall best time for control

Fall is the best time to control perennials broadleaf weeds in turf. Fall-applied herbicides are preferred for broadleaf weed control because weeds are translocating stored energy (and properly applied herbicide) below ground, and cooler temperatures reduce the likelihood of injuring turf or ornamental plants. For the best control that will be noticeable this fall, an herbicide should be applied by mid-October. A second application can be made 3 to 4 four weeks after the first if targeted weeds have not been effectively controlled by the initial application. Single applications applied later in fall can still be effective if soil moisture isn’t limited at the time of application, but control may not be evident until spring. Herbicides are most effective when applied to actively growing weeds that are not stressed by extreme temperatures, drought, etc.

Fall Weed Control, Nebraska Extension Turf iNfo
Broadleaf Weed Control in Lawns, Nebraska Exension Turf Fact Sheet

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7. Mulch mowing leavesSaves time and expense; adds organic matter to soil

Mulch mowing leaves is good for the lawn, but should not be relied upon for weed control. There was some research that showed mowing leaves into lawns suppressed weeds like crabgrass. While one year of a research study showed this might be the case, the results could not be replicated. A healthy, dense turf will compete better with weeds and mulch mowing returns organic matter and nutrients to the soil to benefit turfgrass growth. Save time and expense; instead of raking and hauling away leaves, mulch mow them into the turf.

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

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8. How late to mow?Continue until grass stops growing

Continue mowing until the grass stops growing. Turfgrass should not go into winter too tall. Taller grass does not protect the turf from cold temperatures. However, too tall of grass can promote diseases like snow mold as well as vole activity. Maintain the same height from the first mowing of the season to the last. For Kentucky bluegrass, that is 2 to 3 inches tall and for tall fescue, 2.5 to 3.5 inches tall.

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9. Okay to lay sod; too late to seedDormant 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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10. Fall lawn fertilization best completed before late OctoberLater season applications are 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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11. Avoid pruning spring blooming shrubs nowNext year's flower buds are present and will be removed

Shrubs like lilac, forsythia, mockorange and some Spireas develop flower buds the previous growing season. If they are pruned from late fall through winter, flower buds will be removed and there will be little to no blooming next spring, which customers may not appreciate. Other than rejuvenation pruning (cutting a shrub back to 4 to 6” tall), wait until after early spring blooming shrubs have finished blooming in spring to prune.

Rejuvenation pruning is best done while the shrub is dormant, ideally just before new spring growth in March or early April. 

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12. Herbaceous perennial fall clean-upWait until foliage/stems are killed by frost

If and when to cut plants back in fall is a commonly asked question. Herbaceous 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. 

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13. Home invading nuisance insectsExclusion best method of control

Home invaders increase during fall as they seek overwintering sites during cooler fall weather. Common invaders include crickets, spiders, and Asian lady beetles. These pose little threat to us or the structure of our homes. Exclusion is the best means of keeping fall invaders outside. Seal cracks and around conduits with caulk and make sure screens are in good repair and screens and doors are tight fitting. If needed, perimeter sprays, like bifenthrin, can be applied around the exterior of the home.

Fall Invaders: https://communityenvironment.unl.edu/pest-month-fall-invaders

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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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  • Emerald Ash Borer Resources - EAB has been found in the following Nebraska locations. 2016 - Omaha and Greenwood, NE; 2018 - Mahoney State Park and Lincoln, NE. 2019 - Ashland. Homeowners are encouraged to wait to begin treating their ash trees until the insect is confirmed within 15 miles of their location. 

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