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Hort Update for March 14, 2016

Major Symptom:

1. Winter annuals blooming

Ideal control window is past

2. Repairing thinned turf areas

Solve cultural problems before seeding/sodding
3. Spring seeding Soil preparation first, seed as early as possible
4. Spring care practices Wait on most practices, some okay to do early
5. Earthworm castings No labeled products, ‘Early Bird’ fertilizer may help
Trees & Shrubs  
6. Ash tree borer holes Native borers often responsible - identify which borer by hole
7. Male ash flower gall Hard, small black clumps in tree are ugly but not harmful
8. Fire blight Complete pruning before growth begins
9. Black knot disease, ornamental cherry & plum Irregular hard black galls on branches and trunk
Landscape Ornamentals  
10. Cutting back herbaceous perennials & ornamental grasses Remove last years’ top growth before new growth starts
11. Pruning roses Wait until mid to late April to prune roses
Fruits & Vegetables  
12. Horticultural oil applications Understanding confusing terminology
13. Nebraska spring frost dates More variable this year due to warmth
14. Early season vegetable gardening Cold tolerant vegetable planting can begin soon
15. Fruit cultivars for home plantings Disease resistant cultivar recommendations
16. Pyemotes itch mite May be encountered when pruning or working around oak trees
17. Asian lady beetles Insects are becoming active, use exclusion methods
18. Time to water? Monitor lawn and landscape soil for moisture needs.

1. Winter annuals like henbit and speedwell have been blooming with purple and blue flowers. The seed of most winter annuals germinated last September/October. The plants overwinter to bloom in spring, produce seed, and then die. Henbit is a good, early season nectar plant for pollinators. If control is not essential, leave these weeds for pollinators. Where control is desired, preemergence herbicide applications are not recommended in spring as seed germination has already occurred. Advise homeowners to hand-pull weeds where feasible. Applications of postemergence herbicides for broadleaf winter annuals can be used in areas where turfgrass will then grow to fill in the area and compete with these weeds.

For long term control, determine why turfgrass is not competing with winter annuals and change cultural practices to promote grass density in the area. In the future, if herbicide control is needed, applying a preemergence herbicide in early September is most effective.


2. Repairing thinned turf areas - If turfgrass has thinned in an area, determine causal factors and correct these before seeding/sodding. If not corrected, thinning is likely to reoccur. Assess the site for compacted soil, heavy shade or foot traffic, overwatering, inefficient irrigation, lack of fertilization, poor timing of fertilization, disease or insect issues. Correct issues where possible and/or instruct homeowners on correct cultural practices to reduce future thinning. See instructions for “Improving lawns with significant thin or damaged areas” or “Improving the lawn through complete renovation” at the link below. Practices recommended for fall apply to spring.

Improving Turf in Fall, Nebraska Extension


3. Spring seeding cool season turgrasses - While late summer is the ideal time to seed/overseed cool season turfgrass, seeding often needs to be done in spring. Spring seeding should take place as early as possible to take advantage of spring rains and cool temperatures, typically in April. Along with timing and use of quality seed, seedbed preparation to obtain seed to soil contact and promote rooting is key to success. Detailed information is available in the following publication on establishing lawns from seed:

Establishing Lawns from Seed, Nebraska Extension


4. Lawn care practices – how soon to begin? When record high temperatures occur in early March, it is difficult to assess when to begin lawn care practices. As a rule, cleaning debris from lawns, raking leaves, and watering to maintain moist crowns if soils become very dry can be done. Bill Kreuser, UNL Turfgrass Specialist, recommends avoiding foot traffic on wet lawns to avoid soil compaction. Avoid mowing too early as this may further stimulate growth. Service mowers so they are ready for the spring growth surge. Seeding should take place as early as possible in April. Core aeration and power raking are good practices for April. It is too early to apply preemergence herbicides and mid-April into early May remains the recommended target date to begin fertilization.

Early Spring Turf Care - March 2016, Nebraska Extension


5. Earthworms leave castings (small, hard mounds) leading to rough surfaces. While the mounds are a nuisance and create some walking/mowing difficulty, earthworms are beneficial by increasing air and water movement in soil and helping with thatch decomposition. Core aerification, power raking and verticutting will break down some of the castings and reduce bumpiness. Use of a heavy roller is not recommended due to creation of soil compaction.

While no product has earthworms listed as a pest controlled on the label, several have negative effects on them.  Carbaryl (Sevin) has been demonstrated to last 1-3 weeks against them and the same is true for combination insecticides (pyrethroid + neonicotinoid). Early Bird fertilizer is also known to have an impact on earthworm populations.

Earthworm Damage in the Home Lawn, Nebraska Extension Hort Update for March 14, 2016 -

Controlling Earthworm Casts on Golf Courses, USGA Green Section Record
Earthworm and Night Crawlers in the Lawn, Colorado State University Extension


6. Ash tree borer holes – which borer is it?  With growing concern about when Emerald Ash Borer will be found in Nebraska, ash trees are being closely monitored as they should be. When borer holes are found, the assumption may be that EAB is the culprit. However, our native ash borers (lilac-ash borer, banded and red-headed ash borers) are more likely the culprit. It is helpful to be familiar with the appearance of the different emergence holes to reduce misidentification.  EAB adults create a D-shaped hole when they emerge from trees; while the other three adults create more of a round hole. See the graphic for identification. When monitoring trees, try to look at a majority of the emergence holes. It is possible for a tree to be infested with more than one type of borer.  

Comparison of Ash Borer Insects, Nebraska Extension Hort Update for March 14, 2016 -


7. Male ash flower galls begin as clusters of light green (broccoli-like) galls on seedless (male) ash trees. The galls eventually turn hard and black and remain on trees over winter. They are unsightly but harmless to tree health. The galls are caused by the ash flower gall mite feeding on male flowers in early spring.  Control is not needed.


8. Avoid pruning fire blight infected ornamental trees too close to growth beginning, which has already started due to above normal temperatures. Fire blight is a bacterial disease affecting apple, crabapple, pear, hawthorn, and related species. The bacteria commonly overwinter in cankers (sunken diseased areas) on the tree, which produce a sticky exudate in spring. The bac­teria are spread from cankers by insects, wind-blown rain, careless pruning or pruning at the wrong time.

While pruning to remove infected branches is an important control method, it needs to be done while trees are dormant and before cankers begin to exude. If pruning is done too late, late winter or during spring growth, this increases the spread of bacteria. Along with pruning at the correct time, cut infected branch at least 8 to 12 inches below the canker. Ideally, infected branches should be removed at the point of attachment with another branch or the trunk, without damaging the branch collar. Remove pruned material from the area. To help avoid spreading bacteria during pruning, dip or spray the pruning tool before each cut with a 10 percent solution of bleach (one part bleach to nine parts water). Dry and oil tools after use to prevent rust.

Prune out Fire Blight in Winter, Michigan State University


9. Black Knot Disease, Ornamental Cherry & Plum - Black knot is a fungal disease that causes hard, black woody growths to encircle the stems of infected plants. Established orchards or backyard trees should be scouted or examined each year for the presence of black knot, and infected twigs should be pruned out and destroyed or removed before bud break. It is important to prune at least 2-4 inches below each knot because the fungus grows beyond the edge of the knot itself. If pruning is not possible because knots are present on major scaffold limbs or the trunk, they can be removed by cutting away the diseased tissue down to healthy wood and out at least 1/2 inch beyond the edge of the knot. Burn or bury the prunings before April 1st. Fungicides can offer significant protection against black knot, but are unlikely to be effective if pruning and sanitation are ignored.

Black Knot, University of Minnesota Extension


10. Cutting back herbaceous perennials and ornamental grasses in spring, before new growth begins, is an important management practice for pest control, creating an optimal environment for new growth and aesthetics. Last year's growth is dead and needs to be removed. It is fine to delay this practice until just before new growth begins as old growth does provide some protection from spring freezes. However, this practice needs to be done before much new growth occurs. Delay pruning on suffrutescent plants until new growth can be seen, including Caryopteris (blue mist spirea), Buddleia (butterfly bush), Lavandula (lavender), to better assess the amount of winter injury and to protect the crowns of plants from cold temperatures.


11. Pruning roses - While some of the hardier roses can be pruned in March, most hybrid tea rose growers should wait until just before new growth begins to prune roses. This can help reduce the risk of additional cold temperature injury that may occur as a result of early pruning. On all roses, first prune out any winter killed canes by making an angled cut just above the nearest outward facing healthy bud. Shrub roses require very little pruning; thinning of canes smaller than pencil diameter, crossing canes, and canes too densely arranged in the crown should be done.

Shrub Rose Pruning, Nebraska Extension
Roses: Care After Planting, University of Missouri Extension


12. Dormant oil vs. Horticultural oil – Confusing terminology exists regarding horticultural oils.

  • Horticultural oils are products used to control pests on plants.
  • Dormant oil is a term that was originally used to refer to heavy grade oil products used on woody plants during the dormant season. These older products caused phytotoxic effects if used during the growing season, so were limited to dormant season applications. These products have now been replaced in the horticultural market with lighter grade, more highly refined products that can be used both in winter and summer. The term dormant oil now refers to the time of application rather than the product. Dormant oil applications target overwintering insects and can kill adults, nymphs and eggs of insects like mites.
  • Summer oil is a term that refers to lighter grade oil products that can be used when plants are actively growing and in full leaf. The leaf damaging components like sulfur have been largely removed, therefore summer oils can be used in both winter and summer. The term is now more commonly used to refer to the time of application rather than the product used.
  • Superior oil refers to oil products that have reached a level of purification that allows year-round use without phytotoxicity if used according to label directions. These products distill over a narrow range of temperatures.
  • Supreme oil is a term used to categorize highly refined oils that distill at slightly higher temperatures. Most supreme oils meet the characteristics of a superior oil.
  • Some common brand names of commercially available oil products include Sunspray ®, Ultra-Fine and Volck ®. These products are superior oils and can be used both in summer and during the dormant season.

There is still time for dormant or delayed dormant applications with horticultural oil to trees that have not yet reached the half-inch green stage of development, to control overwintering scale or mites.

Using Dormant and Horticultural Oil Applications for Insect Control, Nebraska Extension
Fruit Tree Spray Schedules for Homeowners, University of Missouri Extension


13. Nebraska average last spring freeze (32° F) dates indicate that half of all final spring freezes will occur before the dates shown and half will occur after, based on 47 years of data from 1949-1995. This year warmer than normal early spring temperatures is causing early growth in many plants and making frost predictions difficult.

In southeastern Nebraska that average last spring freeze date is approximately April 30 and May 21 in the northwest corner of Nebraska's panhandle. These dates are guidelines only. Freezing temperatures may occur after the dates listed below. Also remember that local microclimate conditions can significantly affect the occurrence of frost in your landscape.  These dates can be used as guidelines for gardeners planting early spring crops. Frost sensitive plants will not tolerate freezing temperatures and must be protected if freezing temperatures occurs after planting.

Nebraska Average Last Spring Frost Dates, Nebraska Extension's Hort Update for March 14, 2016 -


14. Early season vegetable gardening – Early warmer temperatures this spring mean many gardeners are anxious to start planting their vegetable garden. Gardeners need to be aware of the last average spring frost date for their area and either wait until after that date to plant cold sensitive crops or have a plan to provide cold temperature protection if it is needed.  However, many vegetables are very cold tolerant and can be planted long before the spring frost date. The following is a partial listing of cold tolerant vegetables, with the potential spring planting dates for eastern Nebraska.

  • March 15th - Asparagus crowns, collards, onion sets, garden peas, radishes, spinach and turnips
  • March 30th - Leeks, mustard, potatoes and swiss chard
  • April 5th - Beets, cabbage, carrots, bibb lettuce and leaf lettuce

Making use of these cool season vegetables can provide an early vegetable harvest with extra sweet flavor. Some vegetables, like carrots and radishes, taste better when grown in cool weather and tend to get bitter or hot if growing temperatures are too warm. Most other vegetables including beans, cucumbers, eggplant, muskmelons, okra, peppers, pumpkins, squash, sweet corn, sweet potatoes, tomatoes and watermelon should not be planted until after the spring frost date, unless extra cold protection is provided.


15. Fruit cultivars for home plantings- Many customers ask for tree or small fruit cultivar recommendations. Selecting the right cultivars in the beginning can save them a lot of headaches, money, and maintenance in the long run. Disease resistance, harvest dates, winter hardiness and plant size are important considerations.

Fruit Cultivars for Home Plantings, University of Missouri Extension


16. Pyemotes (oak) Itch Mites – Reports of itch mite bites are being received from early season workers, performing landscape clean up tasks beneath oak trees. Female itch mites may overwinter in oak leaf margin galls and could fall on people working beneath trees in spring. Signs of itch mite attack on humans are red welts on the neck, face, arms and upper torso. Normally bites are not found on the legs, which distinguishes these bites from those of chiggers.

Oak trees with margined leaf fold galls indicate the likelihood of itch mite activity. When working under trees, especially if raking leaves, wear long sleeves, long pants and a hat. Use an insect repellent containing DEET or picaridin. Avoid direct handling of leaves and lawn clippings. Remove clothing each day and launder them, since mites can remain in the fabric for several days. Take a warm shower soon after coming indoors, since the mites need about four hours on your body to produce a bite. Let homeowners know about this problem and advise that they should not sit under these trees.

Pymotes Itch Mites, Nebraska Extension


17. Multicolored Asian lady beetles are becoming active during warm days. They are harmless but a nuisance. Exclusion is the best means of reducing nuisance pests and mice indoors. Caulk cracks, crevices and conduits of the home. Repair window screens and check that doors are tight fitting.

Multicolored Asian Ladybird Beetles, Nebraska Extension


18. Time to water? – Warm temperatures and dry conditions have allowed soil in many parts of the state to dry out, following the melt of our last snow. Is it time to start watering? Maybe. But before starting up the irrigation systems, do some digging to determine soil moisture levels. If the soil is moist at a depth of 4-6 inches, wait another week and check again. Another method for checking soil moisture is to use a 6” screwdriver as a soil probe. If the probe inserts easily in the soil, watering is probably not needed.

For the week of 3/3/2016-3/9/2016 soil temperatures reported by the High Plains Regional Climate Center range from 42-48 degrees in eastern Nebraska and 42-43 degrees in the panhandle.  That’s anywhere from 8 to 13 degrees above normal for this time of year. To follow current HPRCC soil temperatures, visit – Soil Temperature Update.