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Hort Update for Aug 21, 2017

Nebraska Extension Hort Update for August 21, 2017
LawnsMajor Symptom:
1. Turf diseases Showing up with warmer weather and rains
2. Seeding window open Early seeding is better for tall fescue
3. Watering new sod Water a few times a day until rooted, then cut back on water
4. Annual grassy weed control Control to prevent adding to seed bank
5. Fall fertilization window open Older lawns versus younger lawns
6. Yellow lawns Warm soil issue, avoid overwatering and try straight iron application
7. Aeration/power raking Avoid until mid-September
Trees & ShrubsMajor Symptom:
8. Tar spot of maple Black spots on leaves
9. Late summer/early fall pruning Best avoided for tree health
10. Lace bugs on oak Leaves turn speckled, whitish and may yellow or brown
11. Two-lined chestnut borer in oak Found in Douglas County oaks; symptoms include branch dieback, sparse foliage, small leaves
12. Hydrangeas not blooming Macrophylla species not reliable bloomers; paniculata species reliable
13. Watering trees & shrubs Late summer/fall watering important to preventing winter injury and for leaf and fruit bud development
Landscape OrnamentalsMajor Symptom:
14. Cutting back peonies September is a good time to divide and/or cut foliage back
Fruits & VegetablesMajor Symptom:
15. Spider mites on tomatoes Yellow stippling on the leaves of tomato; also attacks watermelon & muskmelon
16. Cutting back asparagus Allowing stems to stand over winter provides some benefits
MiscellaneousMajor Symptom:
17. Yellow jackets  Actively foraging for food; aggressive, avoid

1. Turf diseasesshowing up with warmer weather and rains

Lawn diseases are showing up now, promoted by environmental conditions conducive to infection. They include dollar spot and stem rust in Kentucky bluegrass and brown patch in bluegrass and tall fescue. No grey leaf spot has been seen in Nebraska at this time. Fall fertilization will improve dollar spot as well as stem rust. If we have a warm, extended fall like last year, stem rust can thin turf and lead to some winter kill issues; and a fungicide application may be justified. For these diseases, homeowner available fungicides, such as propaconizole, will reduce further spread of these diseases.

Brown Patch, Nebraska Extension
Dollar Spot, Nebraska Extension Rusty Turf, Nebraska Extension


2. Seeding window openearlier seeding is better for tall fescue

Late summer turfgrass seeding is ideally done from mid-August to mid-September. The earlier tall fescue can be seeded, the better. If seeded too late, seedlings may not survive the winter. Prepare a good seed bed, purchase quality seed and seed as soon as possible.

Establishing Lawns From Seed, Nebraska Extension


3. Watering new sodWater a few times a day until rooted, then cut back on water

Moisten the soil prior to laying sod, then make watering after installation a priority.  During the first two weeks, sod requires daily watering. During warm weather, sod may need to be watered up to three times per day. After 10 days, check for root development by firmly grasping the grass blades with both hands and lifting. When the sod resists being lifted, usually within 10 to 14 days, the frequency of irrigation needs to be reduced but the amount of water applied during each irrigation increased. Daily watering of new sod longer than two to three weeks after installation is not conducive to healthy, well established sod. 

Establishing Lawns From Sod, Nebraska Extension


4. Annual grassy weed controlcontrol to prevent adding to seed bank

Annual grassy weed control, such as foxtail and crabgrass, can be done now with postemergence herbicides; or preemergence herbicides can be applied at the correct time next spring and early summer. If not controlled now, annual grassy weeds will produce seed to increase the soil seed bank. The best cultural control of annual grassy weeds is a dense turf mowed at a tall height of 3 to 3.5 inches for a turf that can complete with annuals.  If postemergence herbicides are used now, Drive or Acclaim are two recommended.

Crabgrass and other Summer Annual Weedy Grasses Control, Nebraska Extension


5. Fall fertilization window openOLDER LAWNS VERSUS YOUNGER LAWNS

On older lawns (10 to 15 or more years) that typically need only two applications, make the fall application in late August/early September using a fertilizer with a slow release nitrogen.  

On younger lawns, two fertilizer applications this fall are recommended; one in late August/early September and one in mid to late October. For the first one, use a slow release nitrogen source, but for the last one, use a fast release nitrogen source.

Improving Turf in Fall, Nebraska Extension
What’s the Ideal Fertilizer Ration for Turf?, Nebraska Extension
Fertilizing Home Lawns, Nebraska Extension


6. Yellow lawnswarm soil issue, avoid overwatering and try straight iron application

Yellowing in Kentucky bluegrass lawns has been prominent in recent weeks. It is most common on Kentucky bluegrass and creeping bentgrass greens. It is most severe on alkaline soils and when soils are warmest in August. It is also more prominent where soils are wettest, such as around irrigation heads or in low areas. It is believed to be a micronutrient deficiency, most likely iron chlorosis, compounded by environmental factor and possibly some root dysfuntion related to turfgrass species. As temperatures cool, turf usually greens up.  Avoid applying nitrogen to solve yellowing. Nitrogen forces growth and increases the plants need for iron, leading to further yellowing. Avoid overwatering and allow soil to dry between irrigation. A foliar application of a chelated iron has been shown to improve color.  

Late Summer Yellowing, Nebraska Extension


7. Aeration/power rakingwait until mid-september to begin; enables best grass recovery from damage

Aeration and power raking are considered fairly aggressive cultivation of lawns. Hold off on these practices until mid-September for optimum turfgrass health and recovery from these cultivation practices. Keep in mind power raking is only recommended when the true thatch layer exceeds three-fourths of an inch. Core aeration can be done annually to relieve soil compaction, increase infiltration of water and improve root growth and root function. It should be done at least once every three years; and more often on lawns growing on clay soils or which experienc a lot of foot traffic. 


8. Tar spot of mapleblack spots on leaves

This fungal disease characterized by raised, tar-like black spots on leaves that are up to one-half inch across. Tar spot occurs primarily on silver maple and is seen on Autumn Blaze or Freeman maple, which is a cross between silver and red maple. Fortunately, tar spot does not cause serious harm to established trees. Some early leaf drop may occur. Raking and removing fallen leaves can help to destroy overwintering fungal inoculum. Although fungicides can be applied in the spring to protect newly emerging leaves, this is seldom warranted.

Maple Tar Spot, Iowa State University Extension


9. Late summer/early fall pruningbest avoid for tree health

Late summer/early fall pruning is not recommended. Wait until late winter to prune. Pruning now can trigger growth that may not harden off before winter. Pruning can also delay development of cold tolerance or winter hardiness in trees and shrubs, increasing the risk of cold temperature injury. 


10. Lace bugs on oakleaves turn speckled, whitish and may yellow or brown

Lace bugs are tiny insects with white lacy wings. They feed on plant sap from leaf undersides, causing leaves to develop a white or yellow stippling and eventually turn brown. The undersides of leaves may also have shiny black specks which are the insect’s feces. Lacebug damage typically shows up in late summer, making the damage less of an issue since shade trees will soon lose their leaves to a fall freeze. Insecticide control is seldom warranted. It may be justified for trees that are, or have recently, experienced another stress, such as drought, construction injury, or recent transplanting. 


11. Two-lined chestnut borer in oakLate summer pruning & fertilization may delay hardening off and development of winter hardiness

Two-lined chestnut borer has been found in oaks in Omaha.  Like most borers, this insect is attracted to stressed and weakened trees.  Environmental extremes (e.g., drought), construction injury to roots, soil compaction, road salt injury, defoliation by leaf-feeding insects, storm damage and weakening from disease are all stresses that predispose trees to attack by borers like two-lined chestnut borer.

Symptoms of borers include dieback at the end of branches, sparse, small or discolored foliage, or leaves that wilt suddenly, turn uniformly brown and typically remain attached to branches. Death of a tree due to borers may take from one to five years.  To confirm borer activity, peel away the bark on dead or dying branches or trunks.  Look for slender, whitish larvae and thin, random, feeding galleries (trails) under the bark.

The best defense against borers like two-lined chestnut borer is prevention.  Healthy, non-stressed trees will not attract two-lined chestnut borer adults, and vigorous trees are able to fight off invading borers.  Water oaks (approximately one inch of water per week) during dry periods to minimize drought stress.  Avoid compacting soil, or changing the soil grade or water drainage pattern during construction.  Also avoid damaging the bark; or allowing significant defoliation by insects.  Systemic insecticides that are applied to trees by drenching or injection (e.g., those containing imidacloprid) can also be used for control.  These products are best applied by a professional arborist.  Trees with significant dieback will be difficult to save.

Source: Two-lined Chestnut Borer, University of Wisconsin Extension  


12. Hydrangeas not bloomingHydrangea macrophylla species not reliable bloomers; H. paniculata species better choice

Garderners continue to have problems with Hydrangea macrophylla cultivars, such as ‘Endless Summer’ not blooming up to expectations. As appealing as these blooming shrubs are in garden centers, they simply are not consistent bloomers in Nebraska landscapes.

H. paniculata types, like ‘Limelight’, and H. arborescens ‘Annabelle’ are the most consistent bloomers. They are larger shrubs and blooms are white. 


13. Watering trees and shrubslate summer/fall watering important to prevent winter injury; for leaf & flower bud development

Some parts of the state still have abnormally dry conditions. Trees and shrubs need late summer and fall watering to prep them for winter survival. This is a critical time for watering trees and shrubs to prevent winter injury, especially evergreens. It is also a critical time for tree buds. A dry fall can reduce the number of leaves, blooms and fruits trees produce the next season. When watering, moisten the soil around trees and shrubs, up to just beyond the dripline, to a depth of 8 to 12”. Avoid overwatering; but continue to water well into fall as long as dry conditions persist. 


14. Cutting back/dividing peoniesSeptember is a good time to divide and/or cut foliage 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



Spider mites on tomatoes can cause problems in the late summer garden, particularly on tomato, watermelon and muskmelon growing in light or sandy soil.  Damage symptoms progress from stippling to yellowing, wilting, browning, and eventually to death of the leaves or whole plant. Mites may move from soybean fields into vegetable gardens, as the soybean plants begin to turn yellow and dry out. To check for spider mites, place a white piece of paper beneath the branch or leaves and tap several times. The mites will appear as very small, bits of dust that are crawling across the page.

Controlling spider mites is difficult because they reproduce so rapidly. One method to try involves spraying the plant with a strong jet of water once or twice a day to dislodge some of the insects and to create an environment that is cooler, more humid and less favorable for spider mite reproduction. Several days or even weeks of this treatment will be required to make a noticeable difference in spider mite populations.

In the late summer garden chemical control may not be needed as plants near the end of their harvest season. Removal of infested plants may be the best option.  Refer to the publications below for additional chemical control options. Be sure any chemical you use is labeled for use in the vegetable garden.


16. Cutting back asparagusAllowing stems to stand over winter provides some benefits

Cutting back asparagus in fall is a common practice for many gardeners. But allowing asparagus stems to stand does provides some benefits to plants.

  • Standing asparagus fronds trap snow during winter, providing moisture for the crown as the snow melts.
  • Nutrients in the stems are transported into the plants' crown if stems are allowed to stand until later winter, February or March. By then the stems will be brown and all nutrients will have moved into the plant crown.
  • Allowing asparagus fronds to stand in late winter delays new stem emergence, which can be a useful technique where late freezes are common.

However, if you have an older female cultivar of asparagus, such as Mary or Martha Washington, asparagus seedlings can become a problem in the garden. In this case, cutting back stems in the fall and removing as much seed as possible from the garden minimizes asparagus weed problems next year.


17. Yellow jacketsActively foraging for food. Aggressive, avoid

Yellow jacket wasps become a nuisance during fall as they scavenge for food. If yellowjackets are disturbed, give them plenty of room as they are capable of inflicting multiple stings. If yellow jackets become excited and appear about to attack, do not panic; retreat slowly and calmly. Yellow jackets construct paper nests, usually in underground cavities. Favorite nesting sites include rodent burrows, compost piles, wood piles and wall voids. Occasionally, yellow jackets build aerial nests in garages, crawl spaces or other enclosed areas.

They feed on insects, spiders and a variety of food items. Most stinging wasps and bees are beneficial and should be preserved unless they pose a direct hazard to humans. Colonies of yellow jackets are annual and nests are not reused. Freezing temperatures in November and December kill all stinging workers and only fertilized queens survive the winter. If yellow jackets pose a hazard, recommendations for treating the nests safely are available in the following publication.

Stinging Wasps and Bees, Nebraska Extension