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Hort Update for April 20, 2016

Major Symptom:
1. Overseeding Do as soon as possible or wait until late summer
2. Crabgrass control Preemergence timing okay in mid-April this year
3. Annual bluegrass control Hot weather will control this weed
4. Dandelion control options Hand dig or spot treat with herbicides; fall ideal time to control
5. Henbit control Manage lawn to compete; pre-emergence herbicides can be applied in September
6. Powdery mildew White, powdery growth on surface of leaf blades
Trees & Shrubs  
7. Lilac/ash borer control Clearwing moths to emerge soon to lay eggs; preventive sprays
8. Zimmerman pine moth control Infestation leads to branch breakage; first spray 2nd week of April
9. Spruce needle-miner Cause inner needles to turn brown in webbed together clusters
10. Bark loss on trees Cold temperature injury on ornamental pears and maples
11. Avoid mulch volcanoes Do not pile any mulch against tree trunks
12. Hold off on pruning Wait until new growth is complete sometime in June
13. Stop pruning oaks and elms Wait until dormant to prune to avoid attracting insects vectoring diseases specific to these two tree genera
Landscape Ornamentals  
14. Nebraska average last spring freeze

Normal spring nighttime freezing temperatures still expected

15. Unusually dry spring conditions Check soil for signs of dryness, water if needed
16. Inspecting and planting container plants Address heavily matted root systems before planting
Fruits & Vegetables  
17. Fruit spray safety for pollinators Know pesticide toxicity before use and avoid spray during bloom
18. Cold protection for the vegetable garden Relative effectiveness of Wall-O-Water, hot caps and milk jug protectors
19. Manure use in the vegetable garden Best management guidelines for manure use
20. Grape pruning Ideally pruned when dormant, begin now if not already done
21. Ticks Numbers are high this spring

1. Overseed sooner rather than later: If a lawn has thinned areas, overseed these as soon as possible before hot weather arrives. Prior to overseeding, core aerate lawns to improve seed to soil contact. Purchase quality certified seed to avoid introducing weed seeds. After overseeding, keep the area moist to promote germination. If the area is bare, consider sodding for increased success if hot weather arrives early.

Lawn Overseeding, Nebraska Extension


2. Crabgrass Control - Crabgrass seed germination begins when average daily soil temperatures reach 57 to 64 °F at a one-inch depth; although large quantities of crabgrass seedlings will not begin germinating until soil temperatures increase to 73 °F or above at a one-inch depth (Fidanza et al., 1996). As of April 14, the 7 day average for soil temperatures at a four inch depth on bare soil ranged from 48 to 58 °F across Nebraska with the majority being in the 52 to 56 °F range. Soil temperatures are variable and cold, wet weather can cause them lower.

In Nebraska, crabgrass seed germination typically begins in May and continues well into June. This is why the recommended window for application of preemergence herbicides (PREs) applied by do-it-yourself (DIY) homeowners is April 20 to May 5 in eastern Nebraska, and about one week later for western Nebraska. This is early enough for PREs to activate, but late enough for the product to remain effective during the active germination period. Most products available to homeowners are active for about 60 days. Many of these are available only as weed-n-feed products; and late April into early May is also a better time for making the first application of nitrogen to cool season turfgrass.

This year, with our unusually warm spring, and average soil temperatures being higher, applications of PREs for crabgrass control can begin in mid-April by DIY’s.

Crabgrass and Other Summer Annual Grassy Weeds, Nebraska Extension


3. Annual Bluegrass - Many samples of annual bluegrass are being brought in, many from the perimeters of lawns. As hot weather arrives, this annual grass will die out. Hold off on control measures and let hot weather manage it.


4. Dandelion control - Spring and early summer is the second most effective time of year to control dandelions and other broadleaf weeds in turf.  In spring, applications made during peak flowering will increase weed control.  Spot-apply herbicides rather than treating the entire lawn. This is more effective and less expensive. Use caution when applying herbicides near ornamentals or trees as these are easily damaged by direct overspray or indirectly by volatilization of herbicide.

Herbicides containing the traditional active ingredients (ai's) 2,4-D, MCPP and dicamba are effective for control of dandelions and other broadleaf weeds. Relatively "newer" ai's like carfentrazone, triclopyr, fluroxpyr, quinclorac, and sulfentrazone combined with the traditional ai's can increase the speed of burn down, expand the spectrum of weeds controlled, and/or improve overall effectiveness depending on the product used.

The most effective time of year to control dandelions and other perennial broadleaf weeds (white clover, ground ivy, violets, and/or plantain) continues to be fall. Herbicides applied at spring flowering do not translocate as effectively and usually do not provide as effective control as when fall applied. Remember, the best way to limit weeds like dandelion is to grow a healthy turf stand.  Proper fertilization, timely irrigation, and consistent mowing are essential to combat the weed invasion.


5. Henbit control is done during fall - This is the purple blooming plant many people have reported in lawns and landscapes this spring. It may be widespread this year due to warm weather in early March jumpstarting plant growth. Henbit is a winter annual. As a member of the mint family, it has square stems. It also has distinctive leaves with crenate leaf margins and purple to pink flowers.

As a winter annual, Henbit seed germinated last fall. Small plants overwintered to grow aggressively in early spring with blooming in April to May. The plants will die with hot, dry weather. Seed production can be high and is one reason infestations may become worse each year.

Control of henbit at this time of year is not recommended since the plants will die shortly.  The best option at this time is to hand pull henbit to allow turfgrass to fill in the area and to minimize seed production for next fall.

If the henbit infestations are becoming unacceptable, then apply a PRE in late summer to early fall. Also, henbit that germinates in fall can be killed with the same POST herbicides used to control weeds like dandelions and creeping Charlie.

Other management options for henbit control include maintaining a healthy and vigorously growing lawn to compete with this annual; or using a two inch layer of mulch in landscape beds to reduce seed germination.

Henbit Control, Nebraska Extension


6. Powdery mildew appears as a grayish-white growth on the surface of grass blades. It is common in shady areas with poor air circulation and is mainly a cosmetic concern. Cloudy, overcast weather and high humidity promote infection and spread of the fungus. Powdery mildew is managed by reducing shade and increasing air circulation to reduce leaf wetness. If this is not feasible, replace Kentucky bluegrass turf with tall fescue which is more shade tolerant. The disease typically disappears during dry summer weather and treatment is generally not required. Under heavy pressure, fungicide treatment is an option. Applications need to be repeated as needed and treatments started prior to significant mildew development.

Powdery Mildew in Turfgrass, Nebraska Exension


7. Lilac/Privet borer adults are day-flying, clear-winged moths that resemble wasps. They emerge from infested stems in May and June. After mating, adult females deposit eggs on lower portions of the main stems of lilac or privet. The caterpillars bore into and feed within stems. Feeding may cause the leaves to yellow and wilt. Frass is produced by borers and pushed out from their burrows. Infested canes are scarred, unsightly, and may eventually die. Severely infested stems should be cut at the soil level and destroyed in early spring. The borer spends winter in the pupa stage and there is only one generation each year.

Lilac Ash Borer, Colorado State University


8. Zimmerman Pine Moth larvae tunnel beneath the bark of pine trees, especially in branch crotches, causing branches to die or break off readily in wind and snow storms. A pinkish mass may be found at the base of infested branches. Insecticides, such as Permethrin or bifenthrin, applied during the second week of April and during the second week of August are required for control. Use the label rate for borers and apply to the trunk and major branches. Also remove heavily infested branches.

Insect Pests of Evergreen Trees, Nebraska Forest Service
Zimmerman Pine Moth Fact Sheet, Ohio State University


9. Spruce Needle-miner causes inner needles to turn brown. Clusters of dead needles are webbed together. Dead needles have a hole at the base of the needles. Since this insect infests the inner needles, rarely will this insect kill a tree. Once the miner is inside the needle, most insecticides are not effective in controlling the insect. If needed, spray foliage with Carbaryl (Sevin) when new damage is first noticed, sometime in June.


10. Bark loss on trees like Bradford Pears and Norway Maples is fairly common.  This is likely due to abrupt temperature changes that we’ve experienced during fall and winter.  There is no treatment.  No need to spray a sealant or a pesticide or to use tree wrap.  Allow the tree to heal itself naturally.  Avoid fertilizing with nitrogen.


11. Avoid mulch volcanoes when planting. Mulch around trees needs to be two to three inches deep, spread out in at least a four foot diameter around the tree, and kept away from the tree trunk. Mulch piled up against a tree trunk holds moisture against the trunk to create conditions for bark to decay leading to trunk issues. Roots also tend to grow in deep layers of mulch instead of outward into surrounding soil. This can lead to circling roots and root dieback during winter or hot summer months, further stressing trees.


12. Hold off on pruning until June. During active spring growth is one time to avoid pruning shade trees. The tender bark is more likely to tear as a branch drops from the tree, creating a larger wound. The tree is expending energy for leaf, twig and flower production and may have less energy to put into chemical defense of pruning wounds. And pruning wounds often ooze sap that may concern homeowners, even though it is harmless to trees. The sap would have flown into the branch that was removed. Since the branch is no longer there, it no longer needs the sap. Using a pruning paint or wound dressing to try and stem the flow of sap will cause more harm than good. Assure homeowners sap loss is not harmful to trees.


13. Avoid pruning oaks until dormant – Now is the time to pause on pruning oak or elm trees.  Both are susceptible to diseases that are vectored by insects and these insects are attracted to fresh cuts.  Pruning should be avoided from April 15th to October 15th.  Learn more about Oak Wilt and Dutch elm disease below.

Oak wilt, United States Department of Agriculture Forest Service
Dutch elm disesase, United States Department of Agriculture Forest Service


14. Nebraska average last spring freeze – Warm spring weather that arrived in February and March have many Nebraskans thinking cold weather should be done for the year. But we are still experiencing normal spring nighttime freezing temperatures. Average spring freeze (32° F) dates are a measure of when the average last spring frost will occur in a region. They 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. In southeastern Nebraska that average autumn 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. Gardeners should be encouraged to hold off planting tender plants, unless they are willing to protect them from nighttime freezes.

Nebraska Average Last Spring Freeze, Nebraska Extension Hort Update for April 20, 2016,


15. Unusually dry spring conditions – Warm temperatures and little rain in the last two weeks have resulted in dry soil conditions for many parts of the state. If soil in a landscape is dry or cracking, then watering would be beneficial for landscape plants and turf. 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.

Drought Monitor


16. Inspecting and planting container plants – Fixing stem girdling roots is an important practice when planting woody plants. Heavily matted root systems of annuals and perennials also need to be addressed at planting for plants to perform their best. Clients won’t be happy with plants that perform poorly or fail to thrive in the landscape due to underlying root issues. Even quick-growing annuals often fail to develop a good root system if circling roots are not fixed. Their roots often stay in a tight mass and fail to spread out through the soil. Plants can be popped out of the ground even several weeks after planting, showing little root development. 

If a plant’s root ball is matted with roots, either pull the root ball apart with your hands or make several cuts down the side of the root ball to loosen it.  Pull the root mass apart and spread the roots out in the planting hole.  Annual plants with a mat of roots at the base of the root ball also need attention. Tear the base mat of roots off or gently pull the root system apart so it can be spread out in the planting hole. Plants will quickly develop new roots and establish a good root system.

Growing Perennials, Nebraska Extension
Growing Annual Flowers, Nebraska Extension


17. Fruit spray safety for pollinators – Protecting pollinators from the adverse effects of pesticides is an important concern for all fruit growers. Know the toxicity of products for fruit pest control and choose one with the lowest possible toxicity. Never use an insecticide product on a blooming crop or on blooming weeds when bees are present. According to Penn State research, most fungicides are considered pretty safe for bees, with the exception of captan, chlorothalonil and mancozeb. Methods to reduce the negative effects of these products include 1) using them at half rate in combination with other fungicides, 2) use of captan and penncozeb, commonly referred to as “Captozeb”, or 3) avoiding their use when pollinators are actively flying. The first publication below discusses tree fruit fungicide toxicity and the second includes a table of commonly used fruit insecticides and their toxicity to bees.

Pollinators and Pesticide Sprays during Bloom in Fruit Plantings, Penn State University
Tree Fruit Production: Protecting Honey Bees, Penn State University


18. Cold protection for the vegetable garden - Wall of waters and waxed paper hot caps are devices commonly available at garden centers. Home gardeners often create their own protection devices using plastic gallon milk jugs. Research shows Wall-O-Water maintained the highest internal air and soil temperatures around the plants, moderating daytime and night-time temperatures better than either of the other protection methods. Highest night air temperatures in the plastic tubes were 3.4 degrees above the outside air. And they sped up ripening of the first fruit by 10 days. 

Waxed paper hotcaps provided the highest average increase in daytime air temperature, over 21 degrees, but they did not retain heat at night. They averaged only one degree warmer than the outdoor night air. They did provide protection from wind damage and plants protected by paper hotcaps produced their first ripe fruit 6 days earlier than unprotected plants. 

Plastic milk jugs could not maintain interior temperatures above the outside night temperature, so did not provide effective temperature protection.  However, they did hasten ripening of the first fruit by 5 days, compared to unprotected plants, and did protect plants from wind damage.

Early Season Extension Using Hotcaps, Nebraska Extension


19. Manure use in the vegetable garden – Manure is a great soil amendment, providing both organic matter and nutrients to the soil. But when used in the vegetable garden, food safety issues must be considered. Composting manure for several months before use is one way to minimize pathogens. Fall manure applications are another good practice; incorporating the manure after garden harvest is completed and allowing the winter dormant period to decrease pathogen load in the soil.

If vegetable growers use fresh manure for soil amendment, the current Food Safety Modernization Act requires them to follow the guidelines below.

  • Apply manure at least 90 days before harvest if the vegetable’s edible portion does not contact the soil.
  • Apply manure at least 120 days before harvest if the vegetable’s edible portion does contact the soil.

Compost created using only plant waste, such as grass clippings, leaves or kitchen waste, does not pose the food safety risks associated with animal manure and can be incorporated in the soil at any time of year.

Safely Using Manure in the Garden, University of Wisconsin


20. Grape pruning – Grapes are vigorous growers needing annual pruning. Ideally plants are pruned while still dormant, in late March. However pruning grapes that have begun to grow is better than not pruning at all.  Most home grape growers don’t prune heavily enough. About 90% of the previous years growth should be removed. For more information, refer to the publications below.

Grape Training Systems, University of Missouri Extension
Growing Table Grapes, Oregon State University


21. Ticks – Larger numbers of ticks are being reported early this year. For information on control and/or bite prevention refer to the Tick Control Resources by Nebraska Extension.


Seasonal information for Nebraska's green industry professionals.

Local Conditions

Image of water

Dry conditions are a frequent condition in Nebraska.  Stay informed on current conditions, and public water utilities restricting water use. Visit UNL Drought Resources.