Hort Update for May 19, 2014

Hort Update for May 19, 2014

Freeze damage on Hostas
Freeze damage on Hostas
In This Issue:
Major Symptom:
1. Crabgrass herbicide application Past the ideal window; use other herbicide choices
2. Knotweed control Too late for control with products like Trimec
3. Turf fertilization Select products with 75% slow release nitrogen sources
4. Spring freeze damage Expect landscape damage from May 12-16 night time freezes on many plant types
5. Hail/wind damage Refer to Nebraska Forest Service storm damage publications
6. Late leaf emergence Wait until June 1st before pruning or removing a tree or shrub
7. Cedar-apple rust Rains provided good conditions for fungal infections
8. Rose pruning Prune to remove winter damage 
9. Spring freeze damage to ornamentals Black/brown shriveled foliage and stems
10. Spring freeze damage to fruits and vegetables Dead flowers, brown leaf lesions on fruits, dead wilting vegetable plants
11. Fruit tree spray applications Now is an important time for pest control applications
12. Fruit tree pollination Cross pollination is imperative in many trees for proper fruit set
13. Protecting pollinators Watch for pollinators when applying chemicals
14. Vegetable garden weed control Mulch and pre-emerge if seedlings have germinated
15. Squash bug management Proper ID, especially of eggs to avoid issues later on
16. Colorado potato beetle management Already active, will feed on multiple plants
17. Apple flea beetle management Will feed on a number of plants other than apples
18. Clover mite management Large numbers can be found invading homes
19. Mole management Raised tunnels caused by moles feeding on earthworms/insects
20. Morel mushrooms At the peak of fruiting body production, make sure found mushrooms are in fact morels




1. Crabgrass herbicide applications -  We are past the recommended window of April 20 to May 5 for making the first application of preemergence herbicides for crabgrass control, but unusually cool soil temperatures have limited crabgrass germination to date depending on location.   Products applied now will control seedlings yet to germinate, but usually have limited effect on seedlings larger than the two-leaf stage. Dithiopyr containing products are the exception to this as it will control crabgrass up to the one-tiller stage. Visible crabgrass plants can be hand pulled or herbicides like Tenacity or those containing quinclorac (i.e. Drive) can be used to provide some post emergence control of young crabgrass plants. 


2. Knotweed control - Prostrate knotweed is a cool-season annual broadleaf weed that germinates very early in spring, typically in March. Knotweed may be confused with crabgrass at this early stage; however crabgrass does not begin germination until May. Knotweed has oblong leaves and wiry stems that produce a mat-like growth.

Knotweed is often found in hot spots next to pavement that are thin and compacted from foot or vehicle traffic. It also prefers thinned areas on athletic fields or golf courses that allow for optimum soil heating in the spring. The best control is to encourage thicker turf with proper cultural methods and limit traffic on the area if possible.

Knotweed is difficult to control. Preemergence herbicide products labeled for knotweed must be applied very early in March and control is minimal. Isoxaben ‐containing products (Isoxaben, Gallery, or Snapshot) provide the best residual control. Young plants can be controlled with postemergence products such as 2,4-D or combination herbicides like Trimec. By this time of the season, knotweed is large enough that these products will no longer be effective. UNL has research studies currently underway looking for herbicides that can provide adequate postemergence control.

Knotweed Control, UNL Turf iNfo
Lawn Care Pro Series: Broadleaf Weed Control, UNL Lawn Care Pro Series


3. Turf fertilization - Select a fertilizer with close to 75% of the nitrogen being a slow release source. Nitrogen comes in two basic forms: quick-release (soluble) nitrogen and slow-release (insoluble) nitrogen. Quick-release nitrogen normally causes a response in one week or less, whereas slow-release nitrogen will cause a response over three to ten weeks or more. Quick-release nitrogen is inexpensive and may burn leaf blades if applied improperly. Slow-release forms tend to be more expensive, but will rarely burn leaf blades even when applied at temperatures above 85F. Both N forms can be used on lawns. Both forms of N are often blended in one fertilizer bag to provide a quick N response shortly after application plus a more gradual and longer response. Fertilizing with phosphorus (P) and potassium (K) is also important in maintaining a healthy lawn. However, many Nebraska soils have adequate P and K levels and these nutrients may not be needed. Fertilizer applications with P and K should always be based on soil tests.

Fertilizing Home Lawns, UNL Turf iNfo


4. Spring freeze damage - Spring 2014 has been a long, cool one for Nebraska and the week of May 12-16 brought several nights of freezing and near freezing temperatures (31-36° F or colder) for many parts of the state. Earlier periods of warmer day and evening temperatures in late April and May encourage plant growth and flower bud development, making plants less tolerant of cold temperatures.  Trees and shrubs that were just beginning to put out spring growth may show damage on leaves and flowers in the next few weeks.  

In deciduous trees and shrubs the stage of bud and leaf development determines the extent of damage from freezing temperatures. Deciduous plants are most susceptible to frost injury during the spring growth flush when young succulent leaves are present, starting from bud break to the development of full sized leaves.  Plants that began growing early and had time for the new growth to harden off, may show little or no damage.

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. 


5. Hail/wind damage occurred on trees during recent storms. Refer to the Nebraska Forest Service Storm Damage publication series when dealing with storm damaged trees. See link below. Always practice safety first. Hire a Certified Arborist when dealing with larger branches and larger trees.

Two points related to hail damaged leaves.

  1. Following a light hail storm, leaves often end up tattered and have small holes in them. Later in the season, do not confuse tattered leaves for insect damage. Tattered leaves are not harmful to the tree as there is enough green leaf tissue for photosynthesis.
  2. Following a heavy hail or wind storm, a shade tree may be stripped of leaves. This early in the season, otherwise healthy trees will develop secondary buds and releaf. Leafing will be later, but will occur in most cases.

Storm Damage Series, Nebraska Forest Service


6. Late leaf emergence of shade trees is common this spring on oak trees. In most cases, it is due to our cooler spring temperatures this season. With some trees, leaf buds that were produced last fall may have sustained winter injury due to the combination of high winds and extreme cold temperatures this past winter. In all cases, do not prune or remove a late leafing tree or shrub until after June 1st to allow time for growth to occur.


7. Cedar-apple rust is a fungal disease that requires moisture on leaf surfaces to infect susceptible apple and crabapple trees. Cedar apple rust will cause orange spots on leaves. If infection is severe, early defoliation can occur in mid to late summer. This disease rarely kills a tree, but heavy leaf drop is stressful, unsightly and apple yields can be reduced. Fungicides were best applied prior to infection. Applications made now may prevent additional leaf infection, however, the majority of infection has already occurred. The best control of cedar apple rust is selecting and planting rust resistant cultivars of apple and crabapple. If you have a susceptible tree you do not wish to replace, and if defoliation due to rust is severe this season; consider a fungicide application next spring. Make the first application just as tree buds are beginning to show some green color. Read and follow label directions.

Cedar-Apple and Related Rusts, UNL Extension


8.  Rose pruning - Pruning roses after winter injury is needed following our cold, dry winter. Remove all winter killed wood back to healthy tissue, making the pruning cut just above on outward facing leaf or leaf bud. If tender roses were killed down to the graft, watch for regrowth occurring from below the graft. If this is the only growth that occurs, it is best to remove the entire rose. The growth is coming from the root stock rather than the desirable grafted portion and this growth is typically not desirable in the rose garden.

Pruning Roses, UNL Extension


9. Spring freeze damage to ornamentals - Spring 2014 has been a long, cool one for Nebraska and the week of May 12-16 brought several nights of freezing and near freezing temperatures (31-36° F or colder) for many parts of the state.  Earlier periods of warmer day time and evening temperatures in late April and May encourage plant growth and flower bud development, making plants less tolerant of cold temperatures. Unprotected landscape ornamentals that had already begun to grow can be expected to show damage on leaves and flowers in the next few weeks.  

Soft succulent plants like bleeding heart may have extensive damage, while others with tougher foliage such as tall sedum are undamaged.  Once it's obvious what parts of the plant have died, prune them away.  But conserve as much of the remaining living tissue as possible. Plants should send up new growth in the next few weeks.  Water and fertilize plants normally.  


10. Spring freeze damage to fruits and vegetables - Unprotected fruits and vegetables that had already begun to grow can be expected to show damage on leaves and flowers in the next few weeks, too.  

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

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. 


11.  Fruit tree spray applications - 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. For recommended fruit spray schedules see the following publication.

Fruits Spray Schedules for Homeowners, University of Missouri Extension


12.  Fruit tree pollination - When planting fruit trees like apples and pears, it is discouraging to see healthy-looking plants that never produce fruit.  Maybe the issue is your pollination, or rather, lack thereof.   Many fruit trees need cross-pollination to produce fruit.  Even some varieties that are able to pollinate themselves, actually produce more fruit if another variety is present for cross-pollination.   For example, 'Honeycrisp' apple needs another variety to pollinate it.  Not every variety is suitable, but 'Golden Delicious' is one good option.  It's important to know if your fruit tree varieties need a cross pollinator, and which ones would be suitable selections.  Keep in mind you'll need varieties that are blooming at the same time! 

For more information on pollinating fruit trees, including charts of appropriate cross-pollinators, check out the publication below.

Pollinating Fruit Crops, University of Missouri


13.  Protecting pollinators - we are all aware that making chemical applications properly saves time and money, but another aspect to consider is the presence of pollinators.  Honeybees, native bees, butterflies, moths, beetles and flies are all important pollinators of fruit and vegetable plants.  Unfortunately, they are also susceptible to direct or indirect chemical applications.  A common suggestion is to spray early in the morning or late in the evening, but that's not always feasible, and many pollinators active during those times can be adversely affected.  Always be aware of the wind speed and direction to avoid drift.  Using pesticides least toxic to pollinators is a good technique as well.  One more point to remember is that in addition to insecticidal sprays, many pollinators are declining because of habitat decline, partly due to the continued use of herbicides on weed plants that are important food sources for various pollinators.  Finding middle ground between customer expectations and what's best for the environment is often difficult.

Protecting Pollinators, U.S. Fish and Wildlife Service
Pollinating Fruit Crops, University of Missouri Extension


14. Vegetable garden weed control includes tillage, hoeing, hand-weeding and the use of mulch. In cases where a gardener has difficulty keeping up with weeding, mulch is especially important. In some cases, the use of Preen labeled for vegetable gardens may be justified. Preen needs to be watered in to be effective for about four weeks in controlling seedlings as weed seeds germinate.  A reminder, though, is that vegetable seedlings need to have germinated before a pre-emergent is applied!


15. Squash bug management - are the most damaging insect pest of pumpkins and winter squash. The adult is a brownish, shield-shaped bug about 5/8 inch long and 1/3 inch wide. Adults are very difficult to control; hence plants must be monitored closely for squash bug eggs and young nymphs to effectively control this insect. Eggs are brick red and found on leaf undersides in the V made by veins. Young nymphs are gray and tear drop shaped. Scout plants often for adults, eggs and young nymphs. Hand-pick adults and squish egg masses. When nymphs are present, carbaryl (Sevin) or permethrin can be applied for control in home gardens.

Squash Bugs, UNL Extension


16. Colorado potato beetle management - While it may seem early for this pest to have emerged, it has and can be seen actively feeding on various crops.  The potato is a favorite crop to feed on, but it will feed on other vegetable crops in the same family such as tomatoes and eggplant.  In Nebraska, the beetle will overwinter as an adult in the soil, emerge in the spring and begin feeding.  Beetles mate, and then the females lays her eggs on the undersides of leaves, and when the larvae hatch and emerge, they begin feeding on the crop foliage.  This stage in the life cycle is the most damaging to the vegetable crop.  Unfortunately, Colorado potato beetle has developed resistance to many insecticides, so it is imperative that chemical rotation, as well as other IPM techniques, are utilized for successful control.

Colorado Potato Beetle Management, University of Kentucky
Colorado Potato Beetles in Home Gardens, University of Minnesota Extension


17. Apple flea beetle management - There are many different species of flea beetles that you may encounter in Nebraska landscapes, but the apple flea beetle might be one that is unfamiliar.  Apple flea beetle is metallic greenish purple in color, and are approximately the size of an eye of a needle.  Apple flea beetles have many of the same traits as other flea beetles; they are small in size, jump when disturbed, and feed on the foliage of various crops.  Apple flea beetles will feed on apples, but also many other plants, especially those in the rose family - roses and plums for example.   Defoliation of plants is worst when populations of the pest are high, so early identification is important.  

Apple Flea Beetle, Colorado State University


18. Clover mite management - Pin-head size, reddish mites massing on window sills or glass windows on sunny sides of homes as mites emerge from overwintering sites, i.e. beneath the siding of homes. Clover mites do not damage buildings and furnishings, or injure humans and pets. They feed on sap of clover, grasses, various trees, ornamental plants and shrubs, but do not cause much damage. Controls rarely suggested. In late summer, prevent entry into homes with physical or chemical barriers.

Managing Clover Mites, University of Nebraska- Lincoln Extension


19. Mole management - Raised tunnels across lawns are the feeding tunnels of moles, which feed on earthworms and insects. Moles are most effectively controlled by trapping. Two bait products, Kaput® and Talpirid®/Tomcat®, show promise. Castor oil and castor oil products, such as Mole-Med® or MoleChase®, have shown minor effectiveness in repelling the eastern mole. 

It does not work to apply insecticides to control moles by controlling their food source. It does not work to use toxic grain or poison peanuts. 

Moles and Their Control, UNL Extension


20. Morel mushrooms - When and where do I pick morel mushrooms? This is a question with a lot of answers grounded in years of folklore and anecdotal evidence. A few things, however, can be discerned for the mushroom hunter.

In Nebraska, morels are usually found starting in mid-April in the southeast part of the state, the beginning of May in central Nebraska, and later as you head north and west. However, due to this spring's cool temperatures, morels were slow to emerge. Morels don't all emerge at once, so the morel season can last several weeks.

Prime morel habitat is more common in the eastern part of the state than the west, but you can find morels throughout Nebraska. They require loose soil, high humidity, and decaying vegetation. With that in mind, it is clear that morels like riparian habitats, but they will grow in ravines or deciduous woodlands that are not close to streams. They love rich soils with a lot of humus and rotting fallen trees and stumps. You won't find morels growing on the crest of a wind-swept prairie hill.

Both the time and habitat for morel hunting coincides with that for ticks. Lyme disease is serious, so remember to take proper precautions.

The Great Morel