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Hort Update for April 16, 2020

Hort Update for April 16, 2020, Nebraska Extension,
Morel mushroom
Serious ConcernsMajor Symptom:
3. Oaks & woodpecker damage Bark shedding
Minor Issues
4. Vegetable garden sites & 2019 flood Safe to plant and harvest this year? 
5. Morel mushrooms & 2019 flood Safe to harvest this spring from 2019 flooded areas?
6. Bagworms Way too early to spray yet; insecticides, including systemics, will NOT go through bag wall to reach overwintering eggs
Timely Topics  
7. Pruning flowering shrubs Base pruning on shrub bloom season and pruning needs
8. Pruning hydrangeas Base pruning on hydrangea type
9. Crabgrass control timing 55 F degree soil temperature for several days needed for germination
11. Reseeding turf areas affected by flooding Remove sand and silt deposits for best turf establishment
12. Identification of weedy grasses in turf Resources for accurate weed identification
13. Digital Diagnostic Network Have questions? Get answers. 
14. Zimmerman pine moth control in spring Ultimately results in branch death or breakage
15. Soon time to control fungal diseases on pine & spruce  Needle browning and early needle drop caused by Diplodia, dothistroma, rhizosphaera and stigmina
16. Backyard Farmer picture submissions Tips for taking better pictures

3. Oaks & woodpecker damageShredding of bark due to gall wasp larvae presence and woodpecker feeding

Exerpt from John Ball, Forest Health Specialist, April 8 Pest Update linked below, which also includes a picture of tree damage and the wasp larvae.

"Woodpeckers and oaks are still a bad combination. I received a picture of a bur oak that was declining and had the bark shredded from the twigs and branches. The problem is woodpeckers drilling into the bark searching for the small larvae of the gall wasp Callirhytis flavipes. During the winter these small, white larvae are found within the inner bark of the branches and twigs of mature oak trees and the trunks of young trees.

The gall wasps emerge in the spring as adults and move to the newly expanded leaves where they insert eggs into the midrib, the central vein of the leaf. Once the eggs hatch, the larvae form a gall on the vein and live out their short lives within this structure. Adults emerge later in the season and lay eggs on the twigs and branches. The galls formed by this gall wasp are not particularly harmful to the tree, no more than the many other galls that form on oaks. What makes this gall wasp a problem is the woodpeckers that feed on the larvae during the winter. The woodpeckers can shred most of the bark from young trees, enough that the trees are be killed by this injury. The trees that are not killed by the woodpecker activity, often have the tops killed back enough that the trees become misshaped and of little value as a windbreak tree.

Management of the problem is difficult. Some people have tried protecting their small oaks with Tanglefoot Bird RepellentR on the trunk. This is a sticky material that comes in a caulking tube and can be smeared on the trunk to discourage woodpeckers. This is a very time-consuming task and must be repeated every year. Insecticides to kill the gall wasps have not be completely evaluated yet. The timing for insecticide sprays is critical and the gall wasps are flying for an extended time period in the spring and late summer. Injecting insecticides to kill the larvae as they feed is still limited though emamectin benzoate, an insecticide used for emerald ash borer, is labelled for this use. We are planning to evaluate the effectiveness of these injections this year.

Not all trees are infested by the gall wasps. It is very common to find several bur oaks growing near one another and only one tree infested by the wasps. The bark on the infested trees appears to be less furrowed than the uninjured tree but this is difficult to evaluate as the woodpeckers have often removed so much bark it is hard to tell the origin texture."

April 8, 2020 Pest Update, South Dakota State Cooperative Extension 


4. Vegetable garden sites & 2019 floodSafe to plant and harvest this year?

Yes, as long as these areas did not flood again in 2020, they should be safe to plant and harvest. 


5. Morel mushrooms & 2019 floodSafe to harvest this spring from 2019 flooded areas?

Yes, as long as these areas did not flood again in 2020, they should be safe to harvest. 


6. BagwormsWay too early to spray yet; insecticides, including systemics, will NOT go through bag wall to reach overwintering eggs

Clients may be calling asking if they should start spraying for bagworm control now. The answer is NO! Eggs do not begin to hatch until approximately mid-May. Spraying too early is a waste of chemical, time and money. Chemicals will NOT go through the bag covering to kill the overwintering eggs, not even systemic products like imidacloprid or orthene. Young larvae must be hatched out and actively feeding before spraying starts, but not all eggs hatch at exactly the same time. Give the insects about two weeks to hatch and plan to spray in early June. Then one thorough spray, soaking the entire plant should be all that is needed.

For now, continue to encourage clients to scout plants affected last year. Remove and destroy bags on high value, smaller evergreen trees will help reduce next year's bagworm population. Destroy bagworm eggs by removing bags from the plant and crushing or immersing them in soapy water. If bags containing eggs are discarded on the ground, eggs may survive winter fine then hatch and larvae return to the surrounding plants next summer. As many as 500 to 1000 eggs can overwinter in one female bagworm's bag.

Bagworms, Nebraska Extension
Bagworms, Backyard Farmer


7. Pruning flowering shrubsBase pruning on shrub bloom season and pruning needs

When to prune depends on season of bloom and if the shrub needs only annual or biennial pruning (thinning and heading back) or complete renovation (cutting to the ground).

Spring blooming shrubs form flower buds the previous season. Pruning these in late winter/early spring removes flower buds and prevents or reduces blooming for that year.

For thinning and heading back, wait until after blooming to prune spring bloomers; or let customers know blooming will be impacted if the shrub must be pruned prior to flowering.

For renovation, this is best done when shrub are dormant, ideally in April.

Summer blooming shrubs are pruned from about April into June. When pruning shrubs, avoid using only heading back cuts that shorten the height. It is important to also use thinning cuts that remove entire stems near the ground or back to another stem to maintain good form and full leaf.

Pruning Flowering Shrubs, South Dakota State University Extension


8. Pruning hydrangeaBase pruning on hydrangea type

When and how to prune Hydrangeas depends on the type of Hydrangea and what age wood it blooms on.

Smooth hydrangea, Hydrangea arborescens, blooms on current season’s wood and last year’s stems usually die back each winter. Smooth hydrangea is pruned by cutting all stems near the ground in fall or spring before new growth begins.

Panicle hydrangea, H. paniculataalso blooms on new wood but stems are hardier. In spring, it can be cut back to about three to four feet tall to control size and shape, or pruned near the ground.

Oakleaf hydrangea, H. quercifolia, also blooms on new wood, but this shrub will not flower if terminal buds are removed or winterkilled. If needed, minimal pruning is done in late spring. Prune out dead twigs, spent flowers, and crisscrossing branches.

Bigleaf hydrangea, H. macrophylla, blooms on old wood. Flower buds develop during fall of the previous year, so late fall through spring pruning will prevent early summer flowering. If needed, prune just after flowering to remove dead wood or for minimal shaping.

Pruning Hydrangeas, Backyard Farmer
Pruning Hydrangea, Nebraska Extension


9. Crabgrass control timing55 F soil temperature for several days required for germination

As a warm season annual, the majority of crabgrass seed germinates at soil temperatures of 60 to 70 degree Fahrenheit hence preemergence (PRE) herbicides need to be applied before soil temperatures reach 60 F. A soil temperature of 55 F (daily average) for several consecutive days is a reasonable estimate for preemergence application timing. Depending on weather conditions each year in Nebraska, this typically occurs sometime from mid-April into May.

Cool Season Lawn Calendar - Eastern Nebraska, Nebraska Extension


11. Reseeding turf areas affected by floodingRemove sand and silt deposits for best turf establishment

Some areas affected by flooding last year will be reseeded this year. If sand and silt deposition has not been dealt with, it is important to do so prior to seeding. Even a thin layer of silt can have negative effects on turfgrass.

Failure to remove silt creates a fine-textured layer on top of existing soil. This slows water infiltration and penetration deeper into the soil. The top layer will remain wet and only drain when it is near saturation. This makes for sloppy conditions which can lead to compaction and shallow rooting.

Heavy deposits of soil and debris may also be contaminated with unknown petroleum products and pesticide.

Remove the layer of silt and sand with excavation equipment – tracked equipment is preferred – such as a skid steer, tractor with a box blade, a sand pro machine, sweeper, blower or by hand. There are also companies and equipment that can mill off the top surface.

If removal is not possible, till the area to thoroughly mix the flood deposits with the previous grass and soil. When tilling, be sure to break up the old sod layer. Once the silt is removed or incorporated, aggressive cultivation such as aeration, slicing, or vertical mowing can create channels to promote drainage.


12. Identification of weedy grasses in turfResources for accurate weed identification

Identification of weeds is key to determining management options and timing control methods. Following are links to two Extension resources for weed identification. The Purdue publication is updated annually and sells for $20.00. The Michigan State website provides on-line assistance with weed identification.

Turfgrass Weed Control for Professionals, Purdue University
Turf Weeds, Michigan State University


13. Digital Diagnostic NetworkHave questions? Get Answers.

Homeowners, farmers, lawn care professionals, pest control operators and others are invited to submit questions and photos through the website. Whether you have a question about bed bugs, a weed in your lawn, or a disease outbreak in your crop, we want to hear from you. An expert panel of Extension professionals will promptly review and respond to your question. To get started you will need to create an account so that our experts can review and respond to your question via your email address.

Digital Diagnostic Network


14. Zimmerman pine moth control in springUltimately results in branch death or breakage

The first signs of infestation is the appearance of soft, pinkish pitch masses on the trunk or branches. These pitch masses, which form where larvae are feeding beneath the bark, may be found anywhere on the tree. After larvae finish feeding, pitch masses dry and become light yellow to cream colored, hard, and brittle. Mostly affects ponderosa and Austrian pines. 

Signs of damage are broken or dead branches or tops of trees may be broken or dead. Larvae hatched last fall and spent the winter under loose bark scales or in old tree wounds and are now susceptible to control. 

To control, spray bark with a drenching spray of permethrin or bifenthrin the second week of April and the second week of August. Remove heavily infested trees.

Insect Pests of Evergreens, Nebraska Forest Service
Early Spring Pest Control for Pines: Zimmerman pine moth, Diplodia tip blight & Dothistroma needle blight, Nebraska Extension


15. Soon time to control fungal diseases on pine & spruceNeedle browning and early needle drop caused by sphaeropsis, dothistroma, rhizosphaera and stigmina

Sphaeropsis (Diplodia) Tip Blight commonly infects established pines causing new growth to be stunted, black pycnidia to develop on bottoms of cones and entire branches to die with needles turning brown and often hanging straight down. To control with fungicides, the first application is made at bud break (around the third week of April), a second just before needles emerge (early May), and a third 7 to 14 days later. The active ingredients of Thiophanate-methyl, Propiconazole, Copper Salts of Fatty & Rosin Acids, or Bordeaux mixture are recommended.

Sphaeropsis Tip Blight of Pine, Nebraska Extension

Dothistroma Needle Blight appears as reddish-purple spots or bands on previous years needles. Infected needles die and turn brown from the tip back to the lesion. Lower branches in trees are most heavily infected. To control, make the first fungicide application in mid-May to protect existing needles and a second application about mid-June to protect this year’s new growth.

Dothistroma Needle Blight, Nebraska Extension

Rhizosphaera needle cast mainly affects spruce in eastern Nebraska. Needles are infected in spring, but symptoms do not become evident until a year later when the needles turn reddish brown.  Older needles on the interior of the branch are affected.  Black fungal fruiting structures can be seen with a hand lens protruding from the stomata of infected needles. 

Fungicides are effective if disease is not well-established in the canopy. Make first application when new growth is half grown, and a second application 3-4 weeks later. For severely infected trees, chemical applications will be needed for 2-3 consecutive years. Chlorothalonil is commonly recommended, but certain formulations have label restrictions that advise “DO NOT use on blue spruce”.  If using a chlorothalonil-based product, make sure the label is registered for the type of spruce affected.  Fungicides containing azoxystrobin, mancozeb, propiconazole, copper salts of fatty acids, and copper hydroxide are also effective at controlling this disease.  However cultural controls that improve airflow through the canopy is most effective and needed in conjunction with fungicides to see the best control.

Rhizosphaera Needle Cast, Iowa State University Outreach and Extension

Stigmina Needle Cast is a fungal disease of spruce often mistaken for Rhizosphaera needle cast. Microscopic observation is required to distinguish both diseases from each other. Norway, black, blue, and white spruce are hosts to this pathogen. Due to the recent emergence of this fungus, fungicides specifically labeled for Stigmina are rare; however fungicides may be used if they are registered for the intended target site in the state where application occurs.  There are conflicting reports about the efficacy of fungicides for this disease, however chlorothalonil has provided protection in Canada and North Dakota.  Current research indicates a spray program similar to Rhizosphaera, although applications may be needed for 4-5 consecutive years for established infections. 

Stigmina Needle Cast, Iowa State University Outreach and Extension


16. Backyard Farmer pictures submissionsTips for taking better pictures

During this time of coronavirus restrictions, Backyard Farmer will not be accepting sample submissions. But your pictures are still very welcome. In the following video, Brad Mills, BYF videographer and producer, outlines tips for taking great pictures. 

Taking Better Pictures


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.