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Hort Update for March 15, 2021

Hort Update for March 15, 2021, Nebraska Extension,
Close up of a gray snow mold patch in a lawn. Image by Jody Green, Nebraska Extension.
Serious ConcernsMajor Symptom
1. Temperature-related plant damage Early and late frosts and freezes create potential for serious injury
2. March growing degree days (GGD) Lincoln Airport 3/12/21 GGD -  33,  Understanding Growing Degree Days
3. Gray snow mold Active now in turf, mainly lawns; matted grass areas with a white or gray coloration
4. Spruce tree browning Several possible causes, including drought stress, winter dessication and temperature swings
Minor Issues
5. Rabbit damage to trees Percent of bark damaged determines long term impact on tree
6. Squirrel damage in trees Many small twigs clipped and laying beneath trees; long-term damage to large trees minor
7. Vole damage in lawns Surface feeding tunnels created in turf beneath snow cover; become apparent after snow melt
8. Raccoon/skunk damage in lawns Rolled or shredded turf vs. cone-shaped holes
Timely Topics
9. Bagworms and cold temperatures Lower populations possible this year
10. Spring clean-up Cold temperature injury still possible with early clean-up

11. Grape bud survival

Cautious optimism for this year's grape crop

1. Temperature-related plant damageEarly and late frosts and freezes create potential for serious injury

In an ideal climate, fall temperatures would gradually get colder, allowing plants to harden off and be fully dormant before they are exposed to very cold temperatures. In spring, temperatures would gradually warm, encouraging plants to come out of dormancy after there any chance of returning cold temperatures. But that's not the way it happened in Nebraska. 

Justin Evertson, Nebraska Forest Service (NFS) Green Infrastructure Coordinator, said it well in a recent email to the Shady Lane listserv - "Spring has almost sprung here in Nebraska. After record lows in mid-February, we’ve had much milder weather in recent days. In fact, Lincoln’s temperature has swung nearly 110 degrees in the last 3 weeks from a near all-time record low of -31 on Feb 16, to 79 degrees earlier this week. Now a winter storm is baring down on much of the state. Sounds like March." 

He goes on to say "Although the record low weather in mid-February may have damaged some marginally-hardy trees, it’s the sudden cold snaps in the spring and fall that do the most damage. Sap is now running in many deciduous trees and several species are now starting to flower. In the coming weeks, trees will be their most vulnerable to sudden hard freezes." 

Many areas in Nebraska also experienced a sharp temperature drop last fall, from November 10 to 13. Night temperatures had been in the 20s and 30s, then suddenly dropped into single digits for four nights. It's likely we will see plant damage this spring from injury incurred either last fall or early this spring, including frost cracks, sunscald, desiccation (especially on evergreens), twig or branch death, or bud death (both leaves and/or flower buds), especially on marginally hardy trees.  

What should landscape managers do? In the first publication below, David Olson, NFS Forest Health Specialist, writes "In many cases, freeze damage can take some time to show up, and there is relatively little that can be done to “treat” it. Dead branches can be pruned out, but unfortunately, we can’t control the weather. It is important to make sure that trees are planted at a proper depth, receive adequate amounts of water, and are otherwise healthy. Any additional stressors that are acting on a tree will make it more susceptible to damage during severe weather events, and less likely to recover if it does get damaged. Care should also be taken when planting trees to select species and cultivars that are proven to do well in Nebraska." For recommendation on trees well-adapted to Nebraska's extreme climate, visit the Nebraska Statewide Arboretum's Native Plants website. There you'll find multiple lists of trees and shrubs, along with planting and care information. 

Early and Late Frosts and Freezes, Nebraska Forest Service
Winter Injury to Trees and Shrubs, The Morton Arboretum


3. Gray snow moldActive now in turfgrass, mainly lawns

Gray Snow MoldThis disease is caused by two species of Typhula fungus: T. incarnata and T. ishikariensis. This is a true snow mold in that it requires extended periods of snow cover, at least 60 days. Symptoms develop beneath snow cover and become evident as snow melts. The disease appears in perfect circles or irregular patches up to 3 feet or more in diameter. The turf within these patches is white or gray and matted together. Examination of diseased plants reveals tiny tan or brown pea-like structures (sclerotia) on infected leaves or imbedded within them. Gray snow mold is most severe when heavy snow falls on unfrozen ground. In severe cases, gray snow mold can kill large areas of turf and recovery can be quite slow. Fungicide applications will not work at this time of year.

This years weather was atypical, resulting in extensive snowmold. If a client requests it preventative fungicide applications could be applied next fall.  Most turf recovers with spring growth and fungicides are not recommended for home lawns. Affected areas should be hand raked to encourage recovery. Overseeding may be needed, especially with fescue cultivars that have no rhizome growth.

Gray Snow Mold in Turf, NC State Extension


4. Spruce tree browningSeveral possible causes, including drought stress, winter dessication and temperature swings

Spruce trees have been turning reddish-brown in some areas of the state, i.e. Platte County. While spruce are affected by a number of disease and insect issues, given the time of the year the browning is occurring, the main factors are likely a combination of drought stress from last summer/fall, winter desiccation and possibly cold temperature injury from a period of sudden temperature drops last November. Spring irrigation in the absence of rainfall, mulching trees, and avoiding nitrogen fertilization is recommended. If 50 % or more of an evergreen has turned brown, it is unlikely to recover.


5. Rabbit damage to treesPercent of bark damaged determines long term impact on tree

Becoming noticeable now. Damage shows up in mid to late winter when other food sources are not available or covered by snow. Once rabbit damage occurs, a question asked is "Will the tree survive"? According to Dr. John Ball with SDSU, the general rule-of-thumb is if more than 2/3s of the bark has been removed from around the lower stem or trunk, the tree is likely to die since food produced by leaves during summer will not be able to reach the roots and water taken up by roots will not reach the leaves due to girdling damage. If damage is less than 1/3 the way around the trunk, a healthy tree can survive. The tree should seal the wound with wound wood eventually closing the wound.


6. Squirrel damage to pine treesMany small twigs clipped and laying beneath trees; long-term damage to large trees minor

If pine twigs are littering the ground at this time of year, squirrels are likely nipping off the twigs. They do this to feed on the buds, gain access to tender inner bark tissues, access sap as a moisture source, and sometimes to mark their territory. This damage will usually not kill a healthy pine but may result in distorted growth. Exclusion of squirrels is difficult but the best solution where feasible. Prevent squirrels from climbing isolated trees by encircling them with a 2-foot-wide collar of metal 6 feet off the ground. Attach metal using encircling wires held together with springs or adjustable clamps to allow for tree growth. Spraying the trees during winter with a labeled taste repellant may reduce feeding. These products need to be reapplied as recommended.

Pine Tips Dropping, Ask Extension 


7. Vole damage in lawnsSurface feeding tunnels created in turf beneath snow cover; become apparent after snow melt

Vole damage appeared as “runs” in turfgrass as our snow melted. Vole damage to lawns is superficial and lawns eventually repair themselves during spring growth. Voles create “runs” in turf by clipping grass close to the ground. Overseeding may be needed to speed recovery. Controlling voles to prevent turfgrass damage is not neccessary. However, valuable landscape trees should be protected in the fall with a ring of hardware cloth to exclude voles from gnawing and girdling tree trunks. Trapping can be done to reduce vole populations.

Controlling Vole Damage, Nebraska Extension


8. Raccoon/skunk damage in lawnsRolled or shredded turf vs. cone-shaped holes

While vole damage beneath snow has been our most common wildlife damage question, there have been reports of what appears to be raccoon or skunk damage to some turf.  Damage to turf by these animals typically occurs in fall , but here is how to distinguish this type of damage.

  • Raccoon damage indicators include rolled up or shredded sod in the yard. 
  • Skunk damage appears as cone-shaped holes dug at surface of lawn as skunks dig for insect larvae.

Controlling Raccoon Damage,  Nebraska Extension
Dealing With Skunks, Nebraska Extension


9. Bagworms and cold temperaturesLower populations possible this year

After a period of extreme cold, a question asked is if insect populations will be affected. The answer is usually no. During fall, most insects produce glycerol and other compounds to lower the lethal freezing point of their bodies. This, and other factors, determines the supercooling temperature for each insect and they’re unlikely to be killed at temperatures above their supercooling threshold, which is often quite low. For example, the threshold for emerald ash borer could be as low as minus 30 degrees F, according to John Ball with South Dakota State University.

One insect that may have been impacted by the extreme cold, however, is the bagworm, which overwinters as eggs. Most bagworm eggs which rely on the silk bag to survive the winter, die at temperatures below 1 degree F. If the temperature falls to one degree and remains there for at least 24 hours, more than 75% of bagworm eggs can be killed. Check to see if temperatures in your area were warmer than 1 degree and plan to manage bagworms accordingly.

Find weather temperature data for your area at the High Plains Regional Climate Center (HPRCC).

  • Under Product Selection, click on Daily Data Listing.
  • Under Options Selection, choose the weather variables to be included in your report; for temperature data, click on Max temp and Min temp. Select a date range for the report. To get temperature data for the entire winter, select 11/1/2020 through today. 
  • Under Station/Area Selection - enter your zip code. From the Station drop down box, choose a nearby weather station. 
  • Finally, hit Go to generate your data report. 

Does Extreme Cold Weather Kill the Emerald Ash Borer?, Iowa State University Research & Extension 
John Ball's Pest Update for 2/17/2021, South Dakota State University 


10. Spring landscape bed clean-upCold temperature injury still possible with early clean-up

Remind clientele about the benefits of keeping winter mulch in place as long as possible. Removed too early, plants can break dormancy during warm days in late winter and early spring and be damaged by subsequent cold temperatures. Leaving mulch and plant tops in place as long as possible also protects overwintering pollinators. Delay cutting back suffrutescent shrubs, i.e. Caryopteris, Buddleia and less hardy shrubs like roses until mid to late April to also avoid cold temperature injury.


11. Grape bud survivalCautious optimism for this year's grape crop

Based upon the extreme temperatures experienced in Nebraska vineyards in mid-February, many growers have expressed concern about bud survival. This led your University of Nebraska Viticulture Program to survey some pertinent cultivars by examining a minimum of 40 buds per cultivar to determine the extent of primary bud damage. Sampling took place on February 21 and 22, with the following results (see table below).  Sampling was done starting 5 to 6  buds from the cordon for field sampling; for the High Tunnel table grape cultivars, sampling began at 6 to 8 buds from the cordon (80 buds per cultivar were checked).  The numbers reported in the following table make us cautiously optimistic for the 2021 vintage, but we recognize that some parts of the state will have more damage, especially central and western Nebraska.

Per Cent Primary Bud Survival
Cultivar East Campus Vineyard Rural Lincoln
Brianna 100% NA - not assessed
Delaware NA 90%
Edelweiss 98% (Some canes were buried in the snow, a great insulator.) 80%
Frontenac NA 100%
Frontenanc Gris 100% NA
Itasca 100% NA
LaCrescent 97% 88%
Leon Millot NA 85%
Marquette 96% 93%
Norton 94% NA
Vignoles 92% NA

High Tunnel Cultivars

  • Canadice 95%
  • Everest 92%
  • Marquis 98%
  • Mars 98%
  • Somerset Seedless 98%
  • Thomcord 97% 

Remember to prune as late as feasible and to prune the most cold-hardy cultivars first (e.g. Frontenac cultivars) and the least cold-hardy ones later (Edelweiss, Vignoles).

University of Nebraska Viticulture Program


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