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University of Nebraska–Lincoln

UNL Extension Horticulture

Healing Landscapes, Healthy Crops, and a Safe Environment

Hort Update for the week of 7/16/07

Current Problems: Major Symptom:
Lawns
  
1. White clover Weeds with white flowers and clover-shaped leaves in lawns
2. Lawn yellowing Light green or yellow coloration in turf
3. Bluegrass billbug

Browning of leaf blades and thinning of turf

   
Trees & Shrubs  
4. Magnolia scale Shiny, sticky honeydew on leaves often with black sooty mold
5. Spidermites Leaves turning off-color with stippling; some webbing
6. Arborvitae leaf scorch Browning of leaf tips or margins
7. Black willow aphids Curling or distortion of leaves, accompanied by a shiny, sticky substance on the leaf surface
 
Ornamentals  
8. Botrytis blight Tan to grayish fuzzy mold on flowers, buds, leaves or stems.
9. Aster yellows Poorly developed flowers that remain green when open
10. Rose black spot Round to irregularly-shaped black spots on upper leaf surfaces
 
Vegetables/Fruits  
11. Onion thrips Silver streaking of onion leaves
12. Blister beetles Long, slender beetles with a round head
13. Blossom end rot Sunken brown or black lesions on the underside of tomatoes
14. Poor fruit set Failure of flowers to set fruit, or fruit abortion
15. Dividing asparagus Renovate crowded plants or those with only thin stems
   
Miscellaneous  
16. Cicada killer wasps Large black & yellow wasps nesting in ground
17. Ground beetles Black elongated beetles in home

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1. White clover- can be a sign of low nitrogen. If homeowners choose to control white clover, they should check their lawn management practices. If needed, make changes in management practices that will help promote a dense turf better able to compete with weeds. The preferred time to control broadleaf weeds, like white clover, with herbicides is late summer through early fall, before a hard freeze.

White Clover Control in Lawns, http://www.ext.colostate.edu/ptlk/1542.html

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2. Lawn yellowing of large sections of lawns or a splotchy appearance to lawns at this time of year is usually due to root issues brought on by lawn watering practices; in many case overwatering. If soils remain consistently wet, roots do not function as well and absorption of nutrients, like iron, is affected. Denitrification, resulting in a loss of nitrogen, can also occur on too wet of soils. When watering lawns, moisten the soil four to six inches deep; then wait until the lawns shows signs of needing water, i.e. darker, blue-green color; footprints remaining after walking across the lawn, before watering again.

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3. Bluegrass billbug damage is being reported in Lancaster County. In May and June, newly-hatched billbug larvae tunnel in grass stems which discolor and when pulled, readily break away at or near the crown. Subsurface feeding by older larvae through July can damage roots, causing turf to appear drought stressed. Under heavy billbug pressure, areas of lawn turn brown and die. The greatest billbug injury usually occurs from mid-June through late July. Billbug injury is easily mistaken for white grub or sod webworm damage, disease, or plant stress. Damaged turf should be carefully examined to confirm the presence of billbugs before making a management decision. Insecticide controls are best applied in May and targeted at the adult weevil.

Billbug Grubs, http://entomology.unl.edu/turfent/documnts/billbugs.htm
Bluegrass Billbugs Guide, http://lancaster.unl.edu/hort/factsheets/085.shtml

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4. Magnolia Scale –one of the largest, soft-shelled scales found in home landscapes, attacking all species of magnolia. Adult females have a shiny, smooth light tan shell that is often covered with white mealy wax. This wax is lost at the time that the next generation of crawlers emerge. Feeding reduces tree vigor, resulting in weak branch growth and poor canopy fill. Excreted honeydew is often colonized by sooty mold fungi, turning the upper leaf and twig surfaces black. Control in late July or August when crawlers are present.

Magnolia Scale And Its Control, http://ohioline.osu.edu/hyg-fact/2000/2003.html

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5. Spider Mites – Spider mites have been reported on burning bush, but these mites can affect a wide variety of plants from evergreens to shrubs and ornamentals. Mites, which can barely be seen with the naked eye, feed by sucking plant sap with piercing-sucking mouth parts, causing white or yellowish specks on the leaves. Leaves eventually turn yellow to bronze colored. Dust may build up in the very tiny webs, making them noticeable. Controls range from hosing down the plants with a strong spray of water (syringing) to using insecticidal oils or soaps, or insecticides such as Kelthane, malathion, Cygon or Orthene when the mites are active.

Spidermites and Their Control, http://ohioline.osu.edu/hyg-fact/2000/2012.html

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6. Arborvitae leaf scorch- results in leaf tips and/or margins turning brown to tan. May look like a fungal leaf disease. Leaf scorch is due to leaves losing water faster than roots can replace it, especially on hot, windy days. Check for unhealthy growing conditions, such as poorly drained soils or overwatering that leads to unhealthy roots unable to efficiently supply water. Recently transplanted trees or those with trunk or root damage may show leaf scorch.

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7. Black willow aphids- Curling or distortion of leaves, accompanied by a shiny, sticky substance on the leaf surface is usually caused by aphids. Aphids range in color from green to black, with the black willow aphid being a common species found on willows. Aphids are soft-bodied insects that feed on plants by sucking sap out of the plant tissues. They excrete excess plant sap, called 'honeydew', that results in a shiny, sticky covering on the leaves below where the aphids are located. Aphids are particularly common on peppers and cause reduced vigor or stunting of heavily affected plants. Control with applications of insecticidal soap, carbaryl or permethrin.

Aphids on Landscape Plants, http://edis.ifas.ufl.edu/MG002

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8. Botrytis blight is a wide-spread fungal disease affecting many ornamental plants. Occurring in wet or humid weather, a tan to gray fuzzy mold develops on affected plant parts. Blight of coneflowers is being seen now, as the individual flowers in a flower's central cone are killed. Sections of affected coneflowers become brown or black and fail to develop properly. Avoid overhead irrigation and provide maximum air cirulation around plants.

Botrytis Blight or Gray Mold of Ornamental Plants, http://web.aces.uiuc.edu/vista/pdf_pubs/623.pdf

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9. Aster yellows- is a common disease that affects many ornamental flowers. Susceptible plants include asters, chrysanthemum, coreopsis, cosmos, echinacea (coneflowers), dianthus, gladiola, marigold and petunias. Vein clearing, or loss of green pigment within the veins, is often the first symptom. Stunting, stiff extra bushy yellow growth, deformed or poorly developed flowers which remain green are all common symptoms. There is no cure for infected plants. Remove and discard them to reduce further spread.

Aster Yellows, http://www.oznet.ksu.edu/library/hort2/MF1086.pdf

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10. Rose black spot- is a wide-spread, fungal disease of roses that causes round to irregularly-shaped black spots on upper leaf surfaces of susceptible cultivars. Infected leaves often fall from the plant. Repeated defoliation weakens plants, resulting in poor blooming and greater susceptibilty to stress. Many hybrid tea roses are susceptible, while many newer shrubs roses have increased resistance. Keep plant foliage dry and avoid overhead irrigation. Remove infected leaves. Apply preventative fungicides.

Black Spot of Roses, http://ohioline.osu.edu/hyg-fact/3000/3072.html

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11. Onion thrips- tiny, slender winged insects with rasping mouthparts. Very common on onions, but they also feed on many other vegetable and ornamental plants. Feeding causes silver streaking or blotches on leaves or flower petals. Severely injured leaves turn brown and die. Thrips feed in the growing points of developing plants, making them difficult to reach with insecticide applications. Injury is most severe under dry growing conditions, and often mild damage can be mitigated with additional irrigation.

Onion Thrips- http://insects.tamu.edu/fieldguide/bimg120.html

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12. Blister Beetles have been found in vegetable gardens. Blister beetles have long, slender bodies with a relatively large head. They vary in color but we usually see gray beetles. These insects release a caustic substance when crushed that can raise blisters on the skin. The adult stage causes the damage, not the larvae. The beetles tend to move in swarms and can cause a great deal of defoliation, but may not stay in one area for long. Often beetles move on in a day or two. If beetles are handpicked, be sure to wear gloves. The beetles will feed on beans, peas, potatoes and other vegetables. The immature beetles feed on grasshopper eggs. Sevin is registered, but generally not great at killing the insects.

Blister Beetles, http://www.ext.nodak.edu/extpubs/plantsci/pests/e1002w.htm

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13. Blossom End Rot: Sunken brown or black lesions on the underside or blossom end of developing tomatoes, eggplant or peppers are caused by a calcium deficiency resulting from a water deficit in the plant during early tomato development. Keep tomato plants evenly moist, avoid root injury when weeding and apply organic mulch. Do not allow plants to wilt between waterings. Remove affected fruits.

Blossom-End Rot of Tomato, Pepper and Eggplant, http://ohioline.osu.edu/hyg-fact/3000/3117.html

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14. Poor fruit set- vegetable plants require successful flower pollination for good fruit set. However, many environmental conditions do not favor good pollination. For example, temperatures above 90°F or below 50°F are not favorable for pollination to occur, so very few fruits will set during extended periods of 90°F temperatures or when nighttime temperatures fall below 50°F. Extended periods of cloudy or wet weather inhibit bee activity and subsequent fruit set. Extremely hot, dry weather can cause poor pollen adhesion to flower structures or fruit abortion due to a lack of water within the plant. Excess nitrogen applications can promote foliage development at the expense of fruit set. Providing good management of vegetable crops, including adequate water, mulch and proper fertilization, can help mitigate pollination problems.

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15. Dividing asparagus- Usually asparagus is planted from dormant crowns in early spring. However, existing plants can also be divided in fall, approximately early to mid September, particularly if plants are crowded or stems are thin. This allows plants time to develop roots before winter.

Dig up the existing plants and divide them into sections, with a minimum of one "eye" or growing point per plant. Ideally divide plant into large clumps with several "eyes" per section. Follow the replanting instructions in the publication below, as far as bed preparation. However, it would not be necessary to dig trenches for these plants, they could simply be replanted at the same depth in the soil. Provide winter protection to prevent frost heaving. That would include a 2-3" layer of loose mulch applied after the ground freezes.

Do not harvest the plants in 2008. A few spears could be harvested in 2009, then the plants should be back into full production in 2010.

Growing Asparagus in the Home Garden, http://ohioline.osu.edu/hyg-fact/1000/1603.html

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16. Cicada Killer Wasps are up to two inches long and boldly marked with yellow stripes on a black body. Cicada killer wasps are most active during midsummer when their prey, the cicada, is active. Cicada killers attack, sting, and carry paralyzed cicadas to underground burrows. These burrows are found near walks, driveways and retaining walls and can be identified by the presence of fresh soil around one-half inch holes. Once the paralyzed cicada has been dragged underground, the cicada killer wasp deposits an egg on it and upon hatching, the larval wasp uses the cicada for food. While this all sounds ominous, cicada killer wasps are solitary wasps, meaning they do not live in hives they protect. They are very docile and unlikely to sting humans unless provoked.

Cicada Killer Wasps, http://ohioline.osu.edu/hyg-fact/2000/2078A.html

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17. Ground Beetles are usually black and elongate; often found under mulch, rocks or firewood. They may find their way indoors and create concerns. As predators, ground beetles are beneficial insects and are best protected. They are not harmful to plants, people, pets or buildings. To reduce their numbers indoors, remove objects where beetles can hide such as leaf piles, old boards, rotting logs, stone piles, firewood piles, etc. near home entrances. Caulk and screen potential entry ways into homes.

Ground Beetles, http://ohioline.osu.edu/hyg-fact/2000/2102.html
Beneficial Beetles, http://entomology.unl.edu/images/beneficials/beetles/bene_beetles.htm