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Hort Update for April 25, 2019

Nebraska Extension Hort Update for April 25, 2019, http://communityenvironment.unl.edu/update04222019
Harvest morel mushrooms from upland areas that did not flood this year.
Serious ConcernsMajor Symptom:
1. Fruit and vegetable safety from flooded garden sites  Food safety guidelines determined by whether the crop grows in direct contact with the soil and whether it is commonly eaten raw
2. Sedimentation after flooding Even a few inches of sediment can have a long-term negative impact on turf and woody plants
3. Morel mushroom harvesting from flooded areas Harvest from areas not affected by flooding
4. Soil testing for contaminants Should soil from areas impacted by flood waters be tested for contaminants?
5. Assess tree risks after flooding  Inspect trees for physical injury - broken branches, leaning trees, bark damage - and eroded soil around the base
6. Spruce rhizosphaera needle cast Prepare to treat trees with a history of infection soon
Minor IssuesMajor points:
7. Freeze and frost damage Symptoms include black/brown shriveled foliage and stems; dead flowers; brown leaf lesions on fruits; dead wilting vegetable plants
8. Wildlife damage Damage migitation and recovery prognosis 
9. Lawn seeding time is now Seed as soon as possible, or wait until late summer
Timely TopicsMajor points:
10. Bagworms - when to spray? Monitor evergreens; hand pick old bags now; apply controls in June
11. Fruit tree pest application timing Base pesticide applications on plant growth stages, not calendar dates
12. Lawn preemergent application timing Preemergent and early season crabgrass control options
13. Current soil temperatures View current soil temperature averages at CROPWATCH.UNL.EDU



1. Fruit and vegetable safety from flooded garden sitesFood safety guidelines determined by whether the crop grows in direct contact with the soil and whether it is commonly eaten raw

In garden areas impacted by flood waters, questions about the safety of eating asparagus, rhubarb, strawberries and others to be planted this spring may arise. It is difficult to know exactly what is in flood waters.  Aside from the standard level of pathogens or contaminants that may be in the water, there could be additional contamination from sewage systems, manure storage, industrial chemical storage, pesticide or fertilizer storage, and more. Due to unknowns in regards to flood water, gardeners and produce growers should exercise caution in flooded gardens, even when flooding occurs outside of the active growing season.

The recommendation for how long to wait before harvesting and eating produce from flood impacted areas depends on 1) whether or not the crop comes into contact with soil and 2) whether the crop is commonly eaten raw.

For crops that do not have direct contact with the soil, such as tomatoes, peppers, beans, etc. the waiting period between the end of flooding and harvest should be at least 90 days.

For crops that do have direct contact with the soil, such as asparagus, lettuce and leafy greens, pumpkins and root crops that are often eaten raw like carrots the waiting period should be at least 120 days.

Flooded Vegetable Garden Sites and Food Safety Considerations - Nebraska Extension

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2. Sedimentation after floodingEven a few inches of sediment can have a long-term negative impact on turf and woody plants

Large amounts of sediment deposited over tree roots and on turfgrass should be removed as quickly as possible once the soil is dry enough to prevent much traffic/wheel damage and soil compaction. Deposits of sediments bury the original root system deeper in the soil, creating a long-term oxygen deficit. Plant roots require oxygen to grow and function. As little as a few inches of sediment can have a negative and long term impact, particularly on flood intolerant species.

Trees and Sedimentation:  If flood waters have deposited soil beneath trees, remove this material down to the tree’s original soil grade in as large of an area as possible. This must be done carefully and quickly. Once flood tolerant trees begin active growth in spring, they will soon grow roots into these new soil deposits. Damaging those new roots while removing the soil deposits can kill an already stressed tree.

Floods and Trees: Helping Your Tree Recover, Nebraska Extension

Turfgrass and Sedimentation: The sediment layer needs to be removed 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. It is best to remove heavy deposits of soil and debris because they may be contaminated with unknown petroleum products and pesticide. Plywood boards may be needed to resist compaction and rutting on access roads from the excessively saturated soils.

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. Soil deposits of 1-2 inches can be spread and dragged into the grass surface as a beneficial layer of topdressing. Once the silt is removed or incorporated, aggressive cultivation such as aeration, slicing, or vertical mowing can create channels to promote drainage. For areas needing reseeding, this needs to be done as quickly as possible in spring.

Recovery After Historic Flooding, Nebraska Extension

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3. Morel mushroom harvesting from flooded areasHarvest from areas not affected by flooding

During Morel mushroom hunting season, it is advised not to harvest mushrooms from areas affected by flood waters. Flood waters may contain contaminants like E. coli, chemicals and more. While it is recommended that garden produce that comes into contact with soil can be harvested after 120 days, this recommendation is not being used for morel mushrooms.  Morel mushrooms porous and fragile structure would make it difficult, if not impossible, to adequately clean them; or to cook them to high enough temperature to kill bacteria. In the absence of specific research related to this, it is being advised to err on the side of safety and avoid harvesting morel mushrooms from areas impacted by flood waters.

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4. Soil testing for contaminantsShould soil from areas impacted by flood waters be tested for contaminants?

When labs conduct testing, they need to know what specific contaminants to test for. It is difficult to know exactly what is in flood waters.  Aside from the standard level of pathogens or contaminants that may be in the water, there could be additional contamination from sewage systems, manure storage, industrial chemical storage, pesticide or fertilizer storage, and more.

Unless you have a specific contaminant to test for, a soil test will not be of great use. Given the time of year our flooding occurred, pathogens such as E. coli and Salmonella may be the biggest concern since they can reproduce and multiply. Pesticides and other chemicals are possible if a storage area was flooded and stored products moved off-site.

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5. Assess tree risk hazards after floodinginspect trees for physical injury - broken branches, leaning trees, bark damage- and eroded soil around the roots

Strong flood waters, especially when accompanied by large slabs of ice, cause serious physical damage to trees. Branches are broken and bark is gouged from the tree’s trunk. Water erodes soil around the roots, causing the tree’s root plate to become unstable. Trees can easily be pushed over or pulled from the ground by racing flood waters.

Once waters recede, assess trees. Look for broken branches hanging in the tree, leaning trees or significant bark damage. If broken branches can be reached safely from the ground, remove them, making a clean cut. Do not apply pruning paint or wound dressing to the cut.

Leaning trees are an imminent fall hazard and should be removed in most cases, however, working in large or damaged trees can be extremely dangerous. Contact a certified arborist to have damaged trees assessed and removed. More information – Hiring an Arborist, Nebraska Forest Service.

Trees may survive bark damage, depending on the severity. Assess how much of the trunk circumference is affected. If 10% or less of the tree’s circumference is affected, a previously healthy tree with little to no root damage has a good chance of recovery. If 50% or more of the tree’s circumference is affected, removal of the tree is the safest option as disease and decay are likely to create an unstable tree.

Soil erosion or removal by flood waters may leave tree roots exposed. If the tree is still standing and strongly rooted, add soil around the roots to cover them and fill any gaps. It’s important to do this before the roots have been allowed to dry out. When applying soil over the root system do not bury the main roots flaring off the trunk. There should be a visible flare at the base of a well-planted tree trunk.

Inspecting Flood Damaged Trees, Nebraska Forest Service
Floods and Trees: Helping Your Tree Recover, Nebraska Extension

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6. Spruce rhizosphaera needle cast Prepare to treat trees with a history of infection soon 

Symptoms of this common disease are showing up in spruce, in large part due to above average moisture we had last summer. Timing of fungicide applications to infected trees is fast approaching. This fungal disease is usually most prevalent in the lower parts of the tree first, then spreads upward. Infected needles turn a purplish-brown color and are prematurely cast. Infection of the tree's needles takes place in the spring, but the tree does not begin to show symptoms until the following spring - a year later. At that time, very small black specks begin to appear on the upper surface of the needles. These specks, which can be seen with a hand lens, are fungal spores growing out of the natural openings in the needles called stomata. These fungal spores will go on to infect more needles on the tree.

New infections on established trees can be prevented by spraying the tree with chlorothalonil (Fung-onil, Daconil, Bravo) or Bordeaux mixture when new shoots are 1/2 to 2 inches in length (May) and every 3 to 4 weeks if frequent rains occur. 

Diseases of Evergreen Trees, Nebraska Forest Service

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7. Freeze and frost damagesymptoms include black/brown shriveled foliage and stems; dead flowers; brown leaf lesions on fruits; dead wilting vegetable plants

Freezing night temperatures are common in eastern Nebraska until April 24th and May 21st in the west. Freezing or near freezing temperatures (31-36° F or colder) often damage plants encouraged to grow by warm day and evening temperatures in late April and May. Early plant growth and flower bud development is very susceptible. 

Average Last Spring Freezes in Nebraska

On tree and small fruits the stage of bud, flower and fruit development determines how susceptible fruits are to damage.  Flowers and young fruits can be killed.  Refer to Critical Spring Temperatures for Tree Fruit Development Stages for the amount of potential damage at specific temperatures. Tree and small fruits may have a significant reduction in crop production if many flowers and young fruits were killed.  

Assessing Spring Freeze Damage to Apples, Purdue Extension
Assessing Spring Freeze Damage to Peaches, Purdue Extension
Assessing Spring Freeze Damage to Grapes, Purdue Extension
Assessing Spring Freeze Damage to Strawberries, Purdue Extension
Assessing Spring Freeze Damage to Blackberries, Purdue Extension

Damage Symptoms & Prognosis
Damaged leaves develop irregularly shaped black or brown lesions.  Flowers turn brown and die.  On evergreens, spring frost damage appears as dead, light tan, downward curling new shoots. 

What's the prognosis for freeze-damaged plants?  For healthy woody plants, spring freeze damage should have little lasting effect.  Plants will put on additional new growth as spring progresses.  If the plant was not vigorous, or was declining before freeze damage occurred, this will make it worse.  If a low-vigor tree's newly emerging leaves were killed, it may not have enough energy to send out a second flush.  Damaged trees that have not re-leafed by June 1 probably never will.  Until the extent of damage is determined, water trees normally and do not apply fertilizer. 

In the vegetable garden cold temperatures and frost can kill warm-season crops like tomatoes, muskmelon and watermelon.  Affected plants wilt and die. 

Biennial vegetables may prematurely develop seed stalks after prolonged exposure to cold temperatures, including Brussel sprouts, cabbage, carrot, beet, onion, leek, and turnip.

Gardeners often questioned whether rhubarb is safe to eat after a freeze. If the leaves are not damaged too much and the stalks remain firm, it is still safe to eat. If the leaves are severely damaged or the stalks become soft or mushy, do not eat these stalks. Remove and discard them so new stalks will grow. New stalks can be harvested and eaten.  Rhubarb often bolts, or develops seedheads following cold temperatures, but this also does not affect eating quality of the stalks.  Remove rhubarb seedheads and discard. 

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8. Wildlife damageDAMAGE mitigation and plant prognosis

Rabbit, deer and voles commonly damage plants over winter. In most urban home landscapes, the principle culprits are rabbits and voles. On farms and acreages, whitetail deer are also a problem. Economic damage is most common on young trees if they are girdled and killed.

Considerations

  • Other than the current damage, was the plant basically healthy and vigorous? If so, the plant has a better chance of recovery. 
  • On trees, was bark stripped from the main trunk? How much? If 10% or less of the tree’s circumference is affected, a previously healthy tree will usually grow new tissue over the damaged section within a few years. If 50% or more of the tree’s circumference has been stripped, the chance for full recovery is low. Insects, disease and decay are likely to attack the tree.
  • How big are the wounds on branches? The larger the wound in relation to branch size, the less likely the branch is to seal over the damaged area and survive. 

Management of Damaged Plants

  • Do not apply wound dressings to damaged sections of the trunk or branches
  • Prune out stems that have been completely girdled and are not showing any signs of new growth. 
  • Shrubs may die back to the ground but will often regenerate new stems from the base and recover. 

Vole feeding on lawns will repair itself during spring growth. To prevent a repeat next spring, plants must be protected this coming fall with a physical barrier that will prevent damage.

For information on identifying wildlife damage and exclusion/control methods, go to Wildlife.unl.edu.

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9. Lawn seeding time is nowseed as soon as possible, or wait until late summer

Fall remains the best time to seed cool season turfgrass. If spring seeding needs to be done, the sooner seed bed preparation and seeding can be done, the better. There are challenges to spring seeding. This year, we may go from cool conditions to hot weather very quickly which will make seedling survival tough.

One of the largest issues with spring seeding is weed pressure. UNL Turfgrass Specialist, Bill Kreuser, recommends the use of Scott’s Turf Builder Starter Food for New Grass. It contains mesotrione which provides PRE and POST control of weeds. While Siduron has been the recommended in the past as a preemergence to use on new seedings, this product can be difficult to find and has no post emergence control of weeds.

Establishing Lawns from Seed, Nebraska Extension
Spring Seeding Tips for Kentucky bluegrass or Tall fescue in Lawns, Nebraska Extension

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10. Bagworms - when to spray? 

MONITOR EVERGREENS; HAND PICK OLD BAGS NOW; APPLY CONTROLS IN JUNE

It is too early to apply insecticidal products to evergreens for bagworms. Wait until after egg hatch. Products are most effective in reducing damage if applied during the early stages of bagworm development. Insecticides, as well as Bacillus thuringiensis, are best applied from mid-to late- June. They can be applied up until about mid-August, but increased damage will occur the later they are first applied.

For now, check evergreens, especially spruce, Juniper and Arborvitae, for overwintering bagworms. As many as 500 to 1000 eggs can overwinter in one female bagworm. Removing and destroying bagworms from now until May 1st can help reduce the bagworm population. Destroy bagworms by crushing or immersing in soapy water. If bags containing eggs are discarded on the ground, eggs may still hatch and larvae return to the tree.

Bagworm, Nebraska Extension

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11. Fruit tree pest application timingBase Pesticice applications on plant growth stages, not calendar dates

Many fruits are susceptible to a number of disease and insect pests. Often, selection and planting of resistant cultivars will reduce the need for pesticides. When needed, timing of pesticide applications is critical to effectively controlling targeted pests. Applications should be made based on the developmental stage of the plant, rather than calendar dates. For more information on fruit growth stages and the terms associated with them, refer to Growth Stages in Fruit Trees: From Dormant to Fruit Set, Cornell University

For recommended fruit spray schedules see the following publication.
Fruits Spray Schedules for Homeowners, University of Missouri Extension

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12. Lawn preemergent application timingPreemergent and early season crabgrass control Options

The seed of crabgrass, a summer annual, begins germination when soil temperatures reach 55 degrees F at a two to four inch depth for a few consecutive days. In most years, this typically does not occur until May in Nebraska. In years when crabgrass germination occurs early, young seedlings are often killed by spring freezes. The targeted window to apply preemergence herbicides for crabgrass in eastern Nebraska is April 20 to May 5.

If early germination is a concern, use a fertilizer plus preemergent product such as Scott's Turf Builder Starter Food for New Grass Plus Weed Control containing mesotrione. This herbicide provides both preemergent control of germinating seeds and kills young crabgrass seedlings. Or follow up the traditional preemergent products with a post emergent crabgrass control application of the following products. 

  • Carfentrazone - apply anytime on established lawns or 7 days after seedling emergence on new lawns
  • Quinclorac - apply anytime to established lawns or 28 days after seeding a new lawn 
  • Sulfentrazone - apply only to established lawns  

Crabgrass Control in Home Lawns, Nebraska Extension Turf iNfo 
Lawn Care Pro Series: Crabgrass and Other Summer Annual Grassy Weeds, Nebraska Extension Turf iNfo

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13. Current soil temperaturesVIEW CURRENT SOIL TEMPERATURE AVERAGES AT CROPWATCH.UNL.EDU

These reports are provided daily by the Nebraska State Climate Office. Visit the NSCO and Nebraska Mesonet websites for more detailed local and state climate data. Soil temperatures are taken at 4 inches below the soil surface under bare soil.

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