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Hort Update for September 11, 2020

Hort Update for September 11, 2020, Nebraska Extension,
Several pests or pathogens can cause problems in evergreen trees. Diagnosis is key to management.
Serious ConcernsMajor Symptom:
1. Fall watering of trees Despite recent rain, significant drought conditions still exist
2. Snow/cold temperature damage on non-dormant landscape plants Care for storm damaged trees, landscapes and gardens
3. Lawn reseeding/overseeding Time for lawn seeding is getting short; complete seeding/overseeding ASAP
Minor Issues
4. Lilac leaf browning Severe leaf browning caused by fungal leaf spot disease
5. Pin oak maladies Many trees looking very rough this fall; several potential pest problems
6. Bat bugs Home invader carried by bats; very similar in appearance to bed bugs
Timely Topics
7. Fall lawn fertilization recommendations September best time to fertilize cool season lawns
8. Fall weed control in new seedlings Mesotrione provides systemic pre/post emergence control of broadleaf and grassy weeds
9. Perennial weed control Avoid use of weed and feed products; apply by mid-October
10. Fall garden/landscape sanitation Reduce iris borer and other insect pests in flower and vegetable gardens
11. Evergreen tree issues Several pest problems possible; accurate diagnosis key
12. Time to stop pruning wood plants Ideal time for pruning late February into spring
13. Pear rust Severe infection rates this year; reddish-orange leaf spots turn entire leaves orange-brown

1. Fall watering of treesDespite recent rains, significant drought conditions still exist

Many parts of Nebraska have received precipitation in the last week, but according to the U.S. Drought Monitor's National Drought Summary report for September 8th significant drought conditions still exist. Their report included the following information.

"The dramatic change to cold and wet (often snowy) conditions... only brought notable improvement to southwestern North Dakota and part of interior southeast Colorado. Elsewhere, a few tenths of an inch of precipitation fell on the central Dakotas, scattered parts of Nebraska, and much of Wyoming, but given the hot and dry weather that prevailed until the end of the period, no areas experienced notable improvement. In fact, sizeable parts of northern North Dakota, the southern half of Wyoming, central and western Colorado, and Nebraska deteriorated."

U.S. Drought Monitor - High Plains

While your location is still under drought conditions, trees and shrubs need watering to rehydrate and replace water lost this summer. This is a critical time to prepare woody plants for winter and prevent winter injury, especially evergreens. It is also a critical time to provide moisture for developing tree buds, to ensure good leaf production next year.

Damage from drought stress is often slower to appear in woody plants, not becoming evident until months or years after the drought event, but can have long-term consequences. Even after the drought has ended, trees that experience drought stress are more susceptible to secondary attack by insect pests and disease problems, such as borers and canker diseases, which can cause tree death. Dry fall conditions can reduce the number of leaves, blooms and fruits trees produce the next season. When watering, moisten the soil around trees and shrubs, up to just beyond the dripline, to a depth of 8 to 12”. Avoid overwatering; but continue to water until the ground freezes as long as dry conditions persist. 

Keeping Your Landscape Healthy During Drought, Nebraska Extension 


2. Snow/cold temperature damage on non-dormant landscape plantsCare for storm damaged trees, landscapes and gardens

Parts of western Nebraska and the panhandle recieved their first snow earlier this week. Damage to woody plants, which had not yet shed their summer foliage, is almost a certainty anytime ice or snow comes early. The weight of accumulated ice and snow, coupled with the wind which usually accompanies weather fronts, creates the perfect storm for tree damage. The only question is how much damage and how to best repair it.

Refer to the Nebraska Forest Service series for help in dealing with storm damaged trees. This series contains 10 short publications with the following titles:

  • Immediate Care for Storm-Damaged Trees
  • How to Select an Arborist or Tree Service
  • Pruning Storm Damaged Trees
  • Large Tree Pruning & Care
  • Don’t Top Trees
  • Recognizing & Correcting Tree Hazards
  • Tree Selection & Placement
  • Tree Planting
  • Care of Newly Planted Trees
  • Storm Damage Resources

 Nebraska Forest Service Storm Damage Series  

Damage to perennials and vegetable gardens is unfortunate, but not serious problem. It just brings the gardening season to an end a little sooner than expected. Cut back dead perennial foliage and remove vegetable garden plants killed by the low temperatures. Don't can tomatoes harvested from frost-killed plants. 

Canning Tomatoes: Do's and Don'ts, Nebraska Extension 
Canning, Freezing and Drying, Nebraska Extension 


3. Lawn reseeding/overseedingTime for lawn seeding is getting short; complete seeding/overseeding ASAP

For cool season grasses, Kentucky bluegrass and tall fescue, late August into mid-September is the best time for seeding. The time frame for Kentucky bluegrass seeding can be stretched a little later into September if absolutely necessary, but not tall fescue. Perennial ryegrass is not recommended for use in Nebraska lawns. 

The seeding window is getting smaller, but there is still to seed. Preparing the seed bed is always a very important first step, whether doing a complete renovation or overseeding. The key to success is seed to soil contact. See information links below for step by step seed bed preparation information. When purchasing seed, buy from a reputable retailer and look for blue tag certified seed to avoid planting a problem.

Western parts of the state and the northern panhandle saw their first snow earlier this week. If client lawns had recently been seeded or overseeded some damage may be expected on newly germinated lawns if temperatures dipped below 28° F. As cool season grasses, newly germinated Kentucky bluegrass and tall fescue seedlings can tolerate light frost, down to approximately 30-32° F, but hard freeze temperatures below 28° F will likely cause some seedling death if plants are less than 7 days old. 

Improving Turf in Fall, Nebraska Extension
Establishing Lawns from Seed, Nebraska Extension


4. Lilac leaf browningSevere leaf browning caused by fungal leaf spot disease

In the last few weeks, many lilacs have suffered severe leaf browning. This is caused by the fungal disease Pseudocercospora. It shows up as brown spots on the leaves, moving from the edge of the leaves inward, sometimes splotchy in appearance. The fungus is favored by moderate summer temperatures and high humidity. It is common when temperatures are around 76 degrees but the infection occurs at least 7 days before any symptoms are seen on the plant.  

Because high humidity favors disease development, increasing airflow around and through lilac stems will help reduce disease severity by decreasing leaf wetness time following rain or a heavy dew. Prune affected plants by cutting out 1/3 of stems, removing the largest canes and those canes that are cankered, girdled or completely dead. 

The fungus can survive for at least 2 years on plant debris, so fall cleanup of the infected leaves will also help reduce disease pressure next year.

Fungicides are not effective at this time on plants already infected. Next year, fungicide should be applied in the spring when the leaves first emerge. 

Lilac Pseudocercospora Leaf Spot, Iowa State University Extension


5. Pin oak maladiesMany trees looking very rough this fall; several potential pest problems

This has been another difficult summer, particularly for pin oaks and other oak species. Many trees are looking very rough this fall. Some of the common issues found this summer include the following. Identification of each tree's problem or pest is essential to good management. 

  • Freeze death of oak flowers resulted in a smaller than normal amount of acorns. Many squirrels that rely on acorns for food resorted to stripping bark from young thin-barked trees.
  • Oak twig girdler damage has been severe on many trees. Twig Girdler, Kansas State University
  • Kermes oak scale has also caused twig death in some oaks. Kermes Oak Scale, Kansas State Research and Extension
  • Aphid infestations have resulted in black sooty mold on leaves and a rain of sticky sap to cars or anything else beneath affected trees. Aphids on Shade Trees and Ornamentals, Colorado State University
  • Lacebug infestations have caused many leaves to turn yellow or brown. Lace Bugs, University of Minnesota Extension


6. Bat bugsHome invader carried by bats; very similar in appearance to bed bugs

Bats are a common uninvited guest in may Nebraska homes, often bring bat bugs with them. At first glance, bed bugs and bat bugs are almost identical but using a magnifying glass shows differences to use for proper identification. Learn the differences and control measures. 

Going Batty: Bugs on Bats, Nebraska Extension


7. Fall lawn fertilization recommendationsSeptember best time to fertilize cool season lawns

Early September is a one of the best times to fertilize cool season turfgrass like Kentucky bluegrass and tall fescue. If it has not yet been done, there is still time to apply. On older lawns (10 to 15 or more years), one fall application may be all that is needed as older lawns typically only require two fertilizations per season. Recommend a fertilizer with at least a 50% slow release nitrogen source.

On younger lawns, two fertilizer applications during fall are recommended; one in late August/ early September and one about mid-October. For the first application, use a slow release nitrogen source. For the last one, use a fast release nitrogen source. Avoid fertilization after late October. Applications much past this time are less efficient because plant uptake is low. This causes nutrients to leach away during winter or linger in soil until spring; resulting in too early succulent growth.  A specific winterizer-type fertilizer is not needed, but have homeowners buy a fertilizer with their particular fertilizer spreader settings listed on the label.


8. Fall weed control new seedingsMesotrione provides systemic pre/post emergence control of broadleaf and grassy weeds

With late August into September being a key time to seed cool season turf, homeowners may become concerned with competing weeds. There are two options here. The homeowner can choose to ignore the weeds and focus on turfgrass establishment to obtain a dense turf that will compete with weeds next season. A wider range of weed control methods can then be used next season on the established turf if needed. If weeds are seriously competing with new seedlings to prevent establishment, the product Tenacity (mesotrione) can be used for postemergence weed control in new Kentucky bluegrass or tall fescue seedings 28 days after emergence. Label directions need to be read and followed closely.     


9. Perennial weed controlAvoid use of weed and feed products; apply by mid-October

Fall is the best time to control perennials broadleaf weeds in turf. Fall applications are more effective because weeds are translocating stored energy (and properly applied herbicide) into roots and other underground structures. For the best control, 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 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 spot applied to actively growing weeds that are not stressed by extreme temperatures, drought, etc. 


10. Fall garden/landscape clean upReduce iris borer and other insect pests in flower and vegetable gardens

Some insect pests overwinter in or on overwintering garden debris. For example, Iris borers spend the winter as eggs on old iris leaves and plant debris at the base of iris stalks. Squash vine borers overwinter as cocoon in the ground or on leaf litter, and squash bugs find shelter in the fall under dead leaves, rocks, wood, and other garden debris. As the garden season winds down, practicing fall sanitation and removing plant debris is an important piece of the management puzzle for reducing serious pest population levels. 

How Do Insects Overwinter?, Nebraska Extension


11. Evergreen tree issuesSeveral pest problems possible; accurate diagnosis key

From heat and wind injury on new growth in early June to bagworm infestations, needle blights and the appearance of injury from canker diseases that likely infected trees some years ago, evergreen issues have been common and are on the rise. When homeowners asks questions at this time of year, it is important to diagnose the actual cause of signs/symptoms to know what management practices may be needed next season. It is too late for bagworm control other than hand-pulling bags off of the tree and destroying them; and fungicides applied to control needle diseases will not be not effective until spring. There is no control for canker diseases. Encourage homeowners to deeply water evergreens to keep the soil moist, but not saturated well into fall.


12. Time to stop pruning woody plantsIdeal time for pruning late February into spring

Other than dealing with broken branches from wind, ice or snow, pruning of trees and shrubs is best avoided from about mid-August through January. Pruning in fall might delay dormancy or trigger some new growth that would not harden off before winter. And research shows that trees will seal wounds best, which helps reduce decay, if pruning is done just before new growth begins in spring.


13. Pear rustSevere infection rates this year; reddish-orange leaf spots turn entire leaves orange-brown

Bright reddish-orange spots on ornamental pear have been very common this year. This is cedar-hawthorne rust, similar to cedar-apple rust. It is a minor disease for which control is not necessary. If homeowners do not like the reddish-orange spots, they can apply the fungicide myclobutanil to ornamental pear trees next spring during rainy periods.

Pear Rust, Backyard Farmer
Pear Rust, Kansas State University


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