Hort Update for August 18, 2014

Seasonal information for Nebraska's green industry professionals
Lawns Major Symptom:
1. Time to seed/renovate The sooner the better for cool season turfgrass
2. Power raking/aerating Use these practices from late August into September
3. Yellowing Kentucky bluegrass Unsure of cause. Yellowed turf responds to iron.
4. Summer patch Straw colored patches. No control now.
5. Dollar spot in lawns 4 to 6" spots; blades have tan lesion with red margins.
6. White clover Control with nitrogen and/or fall applied herbicides
7. Prepare for broadleaf weed control Late September/early October ideal time to control
8. Yellow nutsedge/crabgrass We are well past ideal time for herbicide control.
9. White grubs As of August 12, there have been no reports of grub
   
Trees & Shrubs  
10. Maple leaf scorch Likely delayed drought or winter injury
11. Spruce twig and branch dieback Likely delayed winter injury
12. Evergreen bagworms Up to two inch long brown bags feeding on twigs
13. Fireblight in ornamental pear Up to one foot of terminal growth dying
14. Blackened maple leaves Check for maple tar spot
15. Emerald ash borer Contradicting messages about when to begin treatment
16. Fall tree planting See recommended tree list to prevent future issues
   
Landscape Ornamentals  
17. Dividing, transplanting perennials Fall is ideal time to divide and transplant
18. Dividing, cutting back peonies September is a good time to divide and/or cut foliage back
19. 'Endless Summer' hydrangeas not blooming Flower buds on old wood killed by cold winter temperatures
20. Japanese beetle management Linden, birch, roses favored hosts; skeletonized leaves and numerous beetles
   
Fruits & Vegetables  
21. Poor fruit set - tomato, pepper, cucurbits Weather conditions effecting pollination
22. Vegetable garden wilts Several causes for wilt problems in tomatoes and cucurbits
23. Downy mildew - cucurbits Irregularly shape yellow leaf lesions, leaf death
24. Onions with soft centers Fungal rots likely
25. When to harvest fruits & vegetables Know and follow maturity indicators for each type
26. Fall vegetable gardening Great way to get more harvest from the garden
   
Miscellaneous  
27. Disposing of old pesticides Call for information on your community's next household hazardous cleanup day
28. Chigger management Immature harvest mites; causing itchy bumps

 

1. Time to seed/renovate cool season turfgrass lawns - Now is the prime time to seed turf-type tall fescue and Kentucky bluegrass. Ideally, seeding is best done by September 15. Any practice that will improve seed to soil contact will greatly increase success. During late August into September, power raking and core aerating are two practices to use to help achieve seed to soil contact.

Time is Now to Start Improving Lawns,  Turf iNfo
Establishing Lawns From Seed, University of Nebraska-Lincoln Turfgrass Science Program
Improving Turf in Fall, University of Nebraska-Lincoln Turfgrass Science Program

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2. Time to core aerate and power rake - Core aeration removes plugs from soil to relieve soil compaction. This is a very good cultural practice for lawns growing on urban soils that tend to be compacted. It could be done annually and should be done at least once every few years.

Power raking removes excess thatch, the reddish-brown layer of dead roots and rhizomes found between the grass crown and soil. Grass blades contribute very little to thatch, hence leaving clippings on the lawn does not increase thatch. It is promoted by compacted soils and high maintenance fertilization and irrigation levels. A one-half inch thatch layer is beneficial providing turfgrass with insulation from traffic and temperature extremes. Only power rake when thatch exceeds one-half inch or prior to overseeding.

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3. Yellowing Kentucky bluegrass in late summer is becoming a common sight in Nebraska. While unsure of the exact cause, it appears connected to high soil temperatures and high soil pH; likely compounded by excess irrigation maintaining a continuously wet soil layer. Work continues on determining the reason for late summer yellowing. In the meantime, yellowing Kentucky bluegrass does respond to applications of iron.

Mysterious Yellowing of Kentucky Bluegrass, University of Nebraska - Lincoln

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4. Summer Patch symptoms develop at this time of year as straw colored patches in full sun areas. No lesions can be found on grass blades. Kentucky bluegrass roots were infected by the fungus in May. By this time of the season, roots are weakened by the disease and symptoms appear. Other than correct cultural care practices, fungicide control is not recommended this late in the season on home lawns. Overseeding with new and resistant bluegrass cultivars or renovating the lawn to tall fescue are the best management methods. 

Necrotic Ring Spot and Summer Patch, University of Nebraska-Lincoln

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5. Dollar Spot is a fungal disease that causes four to six inch tan spots scattered through lawns. On close inspection, prior to mowing, tan lesions with red margins will be found encircling grass blades. Dollar spot is promoted by low nitrogen. Maintaining adequate nitrogen fertility and fall fertilization will aid turfgrass recovery at this time of year.

Dollar Spot Disease in Turfgrass, University of Nebraska-Lincoln

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6. White Clover thrives in cool, moist weather, especially in under-fertilized turf. We have a bumper crop this year. Although tempting to apply herbicides now, wait until the ideal time of year to do so. Combination type herbicides, not straight 2,4-D, will control white clover when applied in October. For long term control, maintain adequate soil fertility to promote turfgrass growth.

White Clover Thriving in Lawns, University of Nebraska-Lincoln

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7. Prepare for perennial broadleaf weed control. The most effective time to control perennial broadleaf weeds is approaching. Use a combination of fall care practices that improve the turfs ability to compete with weeds and fall applied herbicides to effectively control perennial broadleaf weeds. Now is the time to prepare for this fall battle. See link for useful tips.

Lawn Pro Series: Broadleaf Weed Control, University of Nebraska - Lincoln Exension

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8. Nutsedge and crabgrass present, but now is not the ideal time for herbicide control. While hand pulling and herbicide applications are recommended prior to July for yellow nutsedge, hand-pulling can continue and the following  herbicide products could be used now. Postemergence herbicides include Basagran or SedgeHammer or ProSedge (formerly Manage), and FMC's Dismiss (sulfentrazone). Since yellow nutsedge can regrow from rhizomes or tubers that the plant begins to form after the summer solstice, multiple applications are usually needed. Even so, nutsedge will likely persist for multiple years. More information on nutsedge control can be found at these links.

Yellow Nutsedge Thriving, University of Nebraska-Lincoln

Postemergence Crabgrass Control is best achieved when crabgrass is young, prior to mid July: Preemergence control of crabgrass is ideal. While there are post-emergence herbicides available that will control crabgrass, they are best applied when crabgrass is young, typically before mid-July. Once crabgrass matures beyond three to five tillers it becomes difficult to control. After mid-July, it is best to allow crabgrass to die out with frost rather than attempt herbicide control. While elimination of crabgrass is not possible, a healthy dense turf maintained through proper mowing, irrigation, and fertilization can help reduce crabgrass.

Crabgrass Control in Home Lawns, University of Nebraska- Lincoln

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9. White grubs not reported yet. As of August 12th, there have been no reports of white grubs in turfgrass to Extension. If over 8 grubs per square foot are found in the next month, Dylox is the insecticide of choice to use after egg hatch. Adequate irrigation can also help keep turfgrass alive until new roots grow to replace those eaten by white grubs.

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10. Maple leaf scorch appears as browning on leaf edges. Since our cooler temperatures and moist growing conditions have not been conducive to leaf scorch, it is suspected this leaf scorch is a sign of a delayed response to drought from two years ago, likely compounded by cold temperature injury this past winter.

It is not unusual to see a delayed response in trees to environmental stress such as drought or extremes in temperatures, especially when weather extremes follow one another in close proximity, such as in consecutive years. While a tree may have been injured in the last year or two, a tree can survive well on stored food found in roots and branches and symptoms are delayed.

For stressed trees, use adequate irrigation and correct mulching. Avoid nitrogen fertilization.

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11. Spruce twig and branch dieback is being observed, with no signs of fungal disease found. In these cases, it is suspected that this is likely residual effects of drought and winter dessication. It is not unusual to see effects of environmental stress well after the stress occurred, especially in trees. For stressed trees, use adequate irrigation and correct mulching practices. Avoid nitrogen fertilization.

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12. Evergreen bagworm populations have returned to higher levels this year. Bagworms are feeding on Junipers and other evergreen trees and shrubs. Evergreen bagworms are NOT the large, ugly webs that develop on shade trees. To check for bagworms, look closely at evergreens. At this time, bagworms are one to two inch, tan bags hanging from twigs. The insect forms the camouflage bag by webbing needles around its body. Bagworms move around the tree and feed by sticking their head outside their bag. Severe defoliation will kill an evergreen. Bagworms are best controlled in June after egg hatch. Populations might be reduced now by applying an insecticide such as acephate or permethrin. However, once late August arrives, larvae will have pupated, and insecticides will no longer work if larvae are not feeding. Reduce bagworms by removing and destroying bags during winter. Destroy them by crushing or dropping into a soapy solution.

Bagworms, University of Nebraska-Lincoln

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13. Fire blight is a bacterial disease that affects apple, crabapple, pear, and related trees. It is often seen following conditions of cool temperatures, frequent rains with windy conditions, and when plant growth is rapid and succulent. Fire blight is present this year, especially on ornamental pear. At this time of year, leaves on the terminal ends of branches are turning reddish brown to black. The ends of new shoots may also be curved like a shepherds hook. Twigs and branches become infected through wounds, such as those made by pruning or hail. The bacteria also moves from infected blossoms or shoot tips into branches. Cankers then develop and appear as discolored, sunken, or oozing areas. The best way to avoid fire blight is to not plant susceptible varieties and to avoid applying unneeded nitrogen to susceptible trees.

Once a tree is infected, reduce fire blight by pruning and destroying diseased branches. Always prune eight to 12 inches below a canker or the infected area. Avoid spreading bacteria during pruning by dipping or spray the pruning tool cut with a 10 percent solution of bleach, one part bleach to nine parts water, between each cut. Streptomycin is a bactericide applied for fire blight. It is too late to apply this product now. If used, it needs to be applied in spring. A minimum of two applications are needed. Read and follow all label directions for safe and effective control.

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14.  Blacked maple leaves may be tar spot - This is a minor fungal leaf disease of maples promoted by leaf moisture. It causes dark, tar-like spots to form on maple leaves. While it may cause some defoliation, rarely would it cause long term harm to trees and fungicide controls are not recommended for this cosmetic disease.

Tar Spot of Maple, University of Wisconsin Extension

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15. Emerald ash borer (EAB) remains in the news. Some green industry professionals may recommend treatment now; however the Nebraska Forest Service and UNL Extension recommend waiting until EAB has been found within 15 miles of a tree.  To aid professionals and consumers in their decision-making, below are links to educational resources.

Emerald Ash Borer, Nebraska Forest Service
EAB Look-a-likes, University of Nebraska - Lincoln

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16. Tree lists for fall planting. Now through October is a good time to plant shade trees. When planting, avoid planting a future problem. For example, ash trees should not be planted in Nebraska since the Emerald Ash Borer will invade our state. Use recommended tree lists from your local Extension office and from the Nebraska Statewide Arboretum to aid in choosing a quality tree.

Trees Planting to Replace, Nebraska Statewide Arboretum
Trees for Eastern Nebraska, Nebraska Statewide Arboretum
Trees for Western Nebraska, Nebraska Statewide Arboretum

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17. Dividing perennials is an important management practice for many species, helping to encourage vigorous growth and optimum blooming. Many perennials benefit from division once every 3-5 years. Dividing is also a good way to propagate perennials.

Dividing Perennials, Backyard Farmer on YouTube

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18. Peony division/cutting back- September is a good time to divide peonies. The tops can be cut back after September 1 or wait until after the first frost if the foliage is green and healthy. Old peony clumps which are blooming well should not be divided unless there is a good reason to do so. It generally takes three years after dividing and replanting for a peony to return to desirable size and flower display.

When dividing, lift and divide the roots after the plants go dormant (September 1). Before lifting, cut the leaves and stems off to the ground. Carefully dig around and under the plant, taking care not to break off the roots or eyes. Wash off soil. Use a sharp, sterilized knife to cut the roots into divisions containing three to five strong buds and a generous portion of fleshy root. Shorten roots to four to six-inch stubs and remove the smaller, threadlike roots.

Be sure to replant at the correct depth (the buds or eyes should be no deeper than one to two inches) or peonies may fail to bloom in the future.

Dividing Peonies, Iowa State University

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19. ‘Endless Summer' hydrangeas not blooming - Colorful flowering hydrangeas are popular with the gardening public.  The ‘Endless Summer' group of big leaf hydrangeas, H. macrophylla, when released offered greater winter hardiness and a longer bloom period, flowering on both old and new growth.

Last winter's cold temperatures killed most or all of the flower buds on existing plants.  So this year gardeners saw their plants put out new growth, but no flowers.  New flower buds should form on the new growth and may give gardeners flowers in late summer or fall.  To prevent winter flower bud death in the future, plants may need additional winter protection.
  • ‘Endless Summer Bailmer' - large mop-head blooms, either pink or blue
  • ‘Bloomstruck' - purple or rose-pink mop-head flowers
  • ‘Blushing Bride' - white flowered version of Bailmer
  • ‘Twist-n-Shout' - lacecap flowers, either pink or blue flowers

Overwintering Hydrangeas, Endless Summer Collection

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20. Japanese beetles continue feeding on favored trees and ornamentals in extreme eastern Nebraska. Japanese beetles are aggressive feeders on the foliage and fruit of nearly 300 species of landscape plants. Japanese beetles feed on the upper leaf surface, removing the soft green tissue and leaving the veins in a lace-like pattern. Japanese beetles release a strong aggregation pheromone that attracts additional beetles to a food source. The larva (grub) of Japanese beetles feeds on the roots of plants from late summer into early fall. Grub control in lawns is the same as for annual white grubs.

Control of adult beetle feeding is best done in small plantings by handpicking.  In early morning, shake beetles from branches into a collection container. 

Japanese Beetles, Colorado State University

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21. Poor fruit set (Peppers, Zucchini, Tomatoes, etc.) – has been reported on fruit bearing vegetables, especially tomatoes, and is likely weather related. Vegetable garden plants had a slow start this spring, with late freezes and cool temperatures.  This delayed plant growth, development and blooming. 

More recently daytime temperatures above 90 degrees, and/or nighttime temperatures above 70 degrees interfere with pollination.  Ideal conditions for pollination are moderate temperatures, 59-68 degrees.

Plants receiving excessive fertilization and abundant moisture often produce excessive foliage growth that inhibits flower formation.  However, very low fertility levels, substantial damage from insects or diseases, and inadequate moisture can also inhibit flower development.

Provide plants with good basic growing requirements, without over or under fertilizing, so that flower clusters are produced.  In small gardens, hand pollination can be done to encourage fruit formation.  If the lack of fruit set was due to high temperature conditions, plants should begin to set fruits again now that temperatures have cooled.

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22. Vegetable garden wilts, in tomatoes and cucurbits, can be caused by several pests.  In tomatoes, vascular wilt diseases include bacterial, verticillium and fusarium wilts.  In cucurbits, wilt symptoms are caused by insect pests, including squash bugs and squash vine borer, and disease pathogens, such as bacterial and fusarium wilt.  Diagnosis of the exact cause of wilt symptoms can be difficult. 

Carefully inspect wilting plants for the presence of insects or insect tunneling at the base of cucurbit stems.  If no insects or sign of insect activity are found, then a disease pathogen may be the problem.  Submit samples of wilting plants to your local UNL Extension office or the UNL Plant and Pest Diagnostic clinic for diagnosis. 

Squash Bugs, Colorado State University
Squash Vine Borer and Squash Bug, University of Kentucky
Fusarium and Verticillium Wilts of Tomato, Ohio State University
Bacterial Wilts of Cucurbits, Ohio State University
Bacterial Wilt of Tomato, Clemson University

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23. Down mildew in cucurbits, such as cucumber, squash, pumpkins or watermelon, first appears as pale green areas on upper leaf surfaces which change to yellow irregular shaped spots. A fine white-to-grayish downy growth soon appears on lower leaf surfaces. Infected leaves generally die but may remain erect while the edges of the leaf blades curl inward. Usually, the leaves near the center of a hill or row are infected first. The infected area spreads outward, causing defoliation, stunted growth, and poor fruit development. The entire plant may eventually be killed.

Spores are carried by wind so crop rotation in the home garden is not as effective. Plant resistant cultivars. Avoid overhead irrigation. Space correctly. Improve air circulation. Copper based fungicides are recommended for mildew in cucurbits, but can damage plants. Read and follow label directions.

Cucumber, Squash, Melon & Other Cucurbit Diseases, Clemson University

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24. Onions with soft centers – Onions are susceptible to several diseases causing rotting of the bulb.  One such disease is bacterial leaf streak and bulb rot, caused by Pseudomonas viridiflava.  Leaf infections appear as black leaf streaks.  Severe infections cause entire leaves to collapse and die.  Bulb infections appear as dark spots on the outer scales, and reddish-brown discoloration of inner scales. Early season infections occur when temperatures are cool. Frost damage is thought to predispose plants to infection. Reduce post harvest rotting by harvesting at the right stage of maturity, by reducing wounding and bruising during harvest, and by proper onion curing. After harvest, onions should be cured in a warm, well-ventilated place until the necks are papery dry. With warm temperatures, low humidity and good air circulation onions can be cured in approximately 2 weeks.

Growing Onions in the Home Garden, Ohio State University
Onion Pest Diagnostic Profiles, Colorado State University

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25. When to harvest fruits & vegetables - It is important to harvest fruit at the right stage of maturity for flavor and storage. Information on correct harvesting, curing and storage conditions of fruits and vegetables.

When to Harvest Fruits and Vegetables, University of Nebraska- Lincoln
Harvesting Fruits, University of Illinois
Storing Vegetable and Fruits at Home, Purdue University
National Center for Home Food Preservation

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26. Fall vegetable gardening time is here. Cool season vegetables can be planted to mature during the cooler weather of fall. For tips on fall gardening and information on what and when to plant, checkout the publication below.

Fall Gardening, University of Nebraska- Lincoln Extension

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27. Disposing of old pesticides – Take old products to your community's next household hazardous waste cleanup. Household Hazardous Cleanup days are held periodically by many communties in Nebraska.  Call your city offices and find out when the next one is for your community.  Or visit the UNL Pesticide Education web site , http://pested.unl.edu,  for more information on pesticide waste disposal in your area.

Read and follow label directions for correct storage conditions. Pesticides must be stored in their original containers. Store pesticides in locations away from water sources and in places not easily flooded after a heavy rainfall. Make sure the storage building is in good repair, does not leak and has sturdy shelving. Store pesticides out of reach of children and out of potential paths of runoff or floodwater. Buy only the estimated amount needed in a season to avoid storing larger quantities for a longer period of time.

Pesticide Safety in Landscapes, University of Nebraska - Lincoln

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28.  Chigger management - Chiggers are the larval state of harvest mites. In early spring, adults lay eggs in the soil that hatch in June. Adults are harmless, but the tiny, six-legged larval stage is parasitic on animals and humans. On hosts, chiggers move about until reaching a confined place, such as around ankles, under socks, waistbands or arm pits. Chiggers do not burrow into the skin, but pierce the skin and inject a fluid that causes tissues to be inflamed and itchy. Once fully fed, chiggers drop from hosts and enter the ground. In the fall, it becomes the bright red overwintering adult.

To monitor for chiggers, place six-inch squares of black paper vertically in the grass. If chiggers are present, they will climb to the top of the paper. Because several hours elapse before chiggers settle down to bite, bathing soon after exposure to chigger-infested areas may wash chiggers off the body and prevent feeding. Clothing should also be washed. Insect repellents containing "DEET" (diethyl toluamide) are effective in reducing chiggers.

Where chiggers are a problem in landscapes, keep lawns and shrubbery well manicured and mowed, especially in areas adjacent to dwellings.

Chiggers can also be reduced by treating turf with insecticidal sprays. UNL Extension Entomologist Fred Baxendale found a liquid treatment of bifenthrin reduces chiggers 75–95 percent for several weeks. Use 0.2 pounds active ingredient per acre. To escape the highest chigger populations, your first treatment should be early- to mid-June.

Itchy Chiggers, University of Nebraska-Lincoln Extension

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