Hort Update for the week of 6/3/2009
1. Ascochyta Leaf Blight: Patches or large areas of lawn suddenly turn straw or tan color. Resembles drought stress. Leaf blades have bleached white tips and blade is constricted where dead tissue merges with green tissue. Considered a minor disease related to weather and management practices. Turfgrass usually recovers in one month or less without treatment. Fungicides are generally not recommended or needed.
Aschocyta Leaf Blight, http://www.ext.colostate.edu/pubs/garden/02901.html
2. White Grubs overwinter as larvae. In spring, they move to the surface, feed for a short period, then pupate to later emerge as masked chafer adults who mate and lay eggs. The new generation is the damaging generation at which insecticide controls are aimed if needed. Control is not needed for overwintering annual white grubs found in landscape beds or lawns.
White Grubs in Turf NebGuide, http://www.ianrpubs.unl.edu/sendIt/g1619.pdf
3. Powdery Mildew appears as a light layer of flour on grass blades. It is found in shaded turf areas with reduced air movement and high moisture or humidity levels. The fungus grows on leaf surfaces, shading the underlying leaf blade and reducing photosynthesis. Some yellowing and thinning of turf may be seen in heavily infected areas. Reduce shade and improve air movement through pruning where possible. Preventative fungicide applications may be needed in areas with a history of mildew.
Powdery Mildew Disease in Turfgrass NebGuide, http://www.ianrpubs.unl.edu/sendIt/g1911.pdf
4. Crabgrass has begun to germinate. The best control of crabgrass is proper cultural practices; in particular a mowing height of 3” and the use of preemergence herbicides applied from late April to mid May. For crabgrass that has germinated, control by hand-pulling or with post emergence herbicides. Post emergence herbicides are most effective when crabgrass plants are small and coverage of plants is uniform. Adjuvants are often needed. Follow label directions carefully as some of these products may injure turfgrass. Postemergence herbicides for crabgrass control include the methanearsonates MSMA and DSMA, Fenoxaprop (Acclaim Extra), Dithiopyr (Dimension), and Quinclorac (Drive). Postemergence herbicides can be combined with preemergence herbicides to insure late germinating summer annual grasses are controlled along with weeds that have already emerged. Be sure to follow label directions when considering combinations of herbicides.
Control of Crabgrass in Home Lawns, http://www.agry.purdue.edu/turf/pubs/AY-10.pdf
5. Yellow Nutsedge is or will soon begin to grow. Yellow nutsedge is a 3-ranked, yellow-green, waxy, grass-like weed. Handpulling and herbicide applications are most effective in controlling yellow nutsedge when done prior to June 21st. Prior to this date, the tubers (nutlets) attached to the visible plant (mother plant) are in the maturation process but will normally not break dormancy and grow if the mother plant is damaged from pulling, spraying or other injury.
After June 21st, any activity which removes the mother plant results in the now mature tubers breaking dormancy and sprouting. If a plant has multiple tubers attached to it, it is not uncommon for 3-5 sprouts to emerge resulting in an increase in nutsedge plants. Ideally, spray before June 21st to control the mother plant before it can make daughter tubers. This is not always possible so go ahead and spray after June 21st realizing it is not the optimal time for maximum efficacy. Use Sedgehammer (replaced Manage) or Certainty (Sulfosulfuron) which can be applied by commercial applicators. Certainty should only be applied to pure stands of Kentucky bluegrass. It will injure ryegrass and fescue.
6. Winter Injury to lawns in western Nebraska is being seen on Kentucky bluegrass & perennial ryegrass where there is a thick thatch layer and where snow drifts lay for a long time. Reseed or resod damaged areas.
7. Cedar dieback has been observed in windbreaks from southeast and south central Nebraska to north of Columbus. Younger cedar trees, ranging in age from about 7 to 10 years, appear to have turned brown suddenly. Winter injury is suspected, which is unusual for cedar trees, specifically a sudden, large temperature drop in early spring. Mark Harrell, Nebraska Forest Service- Forest Health Specialist, says other factors, such as stress from recent drought combined with root damage from disease by soil fungi, have been killing smaller groups of trees at some locations, but a freeze injury is the most likely cause where large numbers of trees are affected at this time of year over a wide area. It is possible there may be a genetic issue with some trees of this age.
Harrell found no evidence of any significant disease or insect problem on the foliage or anything that could be controlled with a pesticide treatment, so there's no reason to spray the trees to try to control anything. Applying fungicides is not recommended.
Wait a few weeks to see if some of the brown trees grow out new foliage, Harrell suggested, because it is possible that the freeze killed only the foliage and the branches may grow new foliage if given enough time.
8. Spruce Rhizophaera Needle Cast- Second year needles turn brownish purple and drop. Disease usually starts at bottom branches and moves up. Treat with chlorothalonil or Bordeaux mixture fungicide in late May or when new shoots are ½ to 2 inches long. Repeat spray in four weeks. Trees that suffered damage in last year’s hail storms especially need to be watched.
Rhizosphaera Needle Cast of Spruce, http://www.unl.edu/nac/diseasetrees/chap56.pdf
9. Scale Insects can be hard to notice but easy to see once observed. They attack a variety of plants but are common on dogwood, lilac and maples. Scales attach to twigs and branches and grow a waxy covering that helps camouflage them as they feed on plant sap. Branch dieback occurs when high populations of scale are present. Prune and destroy heavily infested branches. Apply systemic insecticides such as malathion or Orthene to young crawlers soon after egg hatch, usually in May. Read and follow label directions as Acephate (Orthene) is NOT recommended for some maples.
Oystershell scale, http://extensionhorticulture.unl.edu/Current/OystershellScale.shtml
10. Trees not leafing out were likely damaged by fluctuating winter temperatures during late winter. There is nothing to do except wait a bit longer to see if new growth occurs. Provide adequate water and avoid fertilizing. Fertilizer will not help push a tree or shrub to leaf out. If there is no sign of growth by early June, the tree or affected branches are unlikely to recover. Remove the tree or prune affected branches.
11. Pine Sawflies look like small, black-headed caterpillars. They are found clustered on the branch ends of pines where they chew off needles. The easiest control is the greenest. Take a stick and lightly tap the branch, knocking the insects to the ground. Few if any will crawl back into the tree. For chemical treatment, products containing permethrin (Eight), carbaryl (Sevin), insecticidal soap, or neem oil will work. The smaller the caterpillar, the easier they are to control.
Pine Sawfly, http://extensionhorticulture.unl.edu/Current/Sawfly.shtml
12. Oak Leaf Blister causes yellowish, blister-like, circular, raised areas to form on leaves. It is a fungal disease. It does not cause serious damage to trees as they can still photosynthesize even though infected by the disease. Control is not needed and it is too late to achieve control for this year, anyway. Fungicides need to be applied just before bud break to be effective.
Oak Leaf Blister, http://plantclinic.cornell.edu/FactSheets/oakblister/oakblister.htm
13. Anthracnose is a common fungal disease on ash, maple, sycamore and oak that causes irregular brown areas on leaves. Leaves may become distorted and minor to severe defoliation of a tree can occur. It is too late to treat trees effectively. Anthracnose is rarely a serious problem for otherwise healthy trees. Most trees will produce new leaves to replace lost leaves.
Anthracnose Diseases of Shade Trees, http://www.oznet.ksu.edu/path-ext/factSheets/Trees/Anthracnose%20Diseases%20of%20Shade%20Trees.asp
14. Phlox Plant Bug Feeding occurs on upper leaf surfaces of young phlox leaves and buds. Injury appears as white or pale-green spots that later become yellow-stippled areas. Blossoms may be deformed. In extreme cases, plants become stunted and die. Adult bugs generally have contrasting colors, i.e. orange and black or red and black, sometimes gray and white or yellow; all with black legs. Nymphs are orange or bright red. This insect overwinters in the egg stage with nymphs emerging in early May. Remove infested plant parts. The use of insecticidal soaps, horticultural oils, or systemic insecticides will reduce damage.
15. Winter ingury- chrysanthemum- Mums that are not showing any new growth to date are not likely to do so and are best replaced. If mums are replanted, provide winter protection by placing a thick layer of coarse mulch over the plants in mid November to reduce the risk of winter kill.
16. Redbud Dieback Eastern Redbud is native to Nebraska but it is not unusual for these trees to be killed by cold winter temperatures. If the seed or tree source is a southern source, these will be susceptible to winter kill. When selecting Redbud trees, buy from a reputable nursery and ask if the seed source for their trees is a northern source.
17. Cedar Apple Rust or Apple Scab is causing leaves of apples and crabapples to yellow and drop. Fungal infections occurred early this spring just as leaf buds were beginning to break and show some green color. While severe defoliation can occur, and this is a stress for the tree, few trees will die unless severe defoliation occurs year after year. Fungicide applications need to be applied just as tree leaves are breaking bud in early spring and repeated as recommended.
Cedar Apple Rust NebGuide, http://www.ianrpubs.unl.edu/sendIt/g1907.pdf
18. Poor fruit set- Last year, fruit tree crops were abundant. Heavy fruiting one year can trigger a tree to go into alternate year bearing where they bear a heavy crop one year and a very light crop the next year. To avoid this, fruit needs to be thinned during heavy fruit crop years.
Fruit Tree Thinning, http://hort4.unl.edu/fruit/thin.html
19. Fruit Tree Spray Schedules Timing of pesticide applications is critical to effectively controlling the targeted pests. For recommended fruit tree spray schedules see the publication below.
Fruit Tree Spray Schedules for the Homeowner, http://extension.missouri.edu/publications/DisplayPub.aspx?P=G6010
20. Houseplant Root Rots symptoms include tip dieback, yellowing of leaves and wilted leaves or stems. Root rots are common when plants are overwatered, grown in containers without drainage holes, or if a poorly drained soil, such as outdoor garden soil, is used. To avoid this, use containers with drainage holes and use a well drained soilless potting mix. Water enough for water to drain out of the drainage holes; empty the catch basin after watering (remove with a turkey baster if a large container); then water again when the upper one inch of soil becomes dry.
Houseplants: Proper Care and Problem Solving, http://www.ag.ndsu.edu/pubs/plantsci/landscap/pp744w.htm
21. Preservation and Care of Community Trees Workshop June 18th and 19th
22. New Emerald Ash Borer Web site by Nebraska Forest Service
The Nebraska Forest Service has compiled a web site containing EAB information especially pertaining to Nebraska, which can be accessed online at http://nfs.unl.edu/EAB.asp
23. Nebraska Statewide Arboretum Plant Sale (Lincoln) Including Trees, June 6th
Plant sale location and plant list is available at http://arboretum.unl.edu/plantsales/index.html
| Current Problems: | Major Symptom: |
| Lawns | |
| 1. Aschochyta tip blight | Browning of turf. Similar to drought. Grass blade tips are white. |
| 2. White grubs | Overwintering larvae are present but not causing damage. |
| 3. Powdery mildew | Grass in shady areas appears dusted with flour. Turf may thin. |
| 4. Crabgrass germination | Young plants can be controlled post emergence |
| 5. Yellow nutsedge | From now to June 21st is most effective time to control. |
| 6. Winter injury | Kentucky bluegrass & perennial ryegrass showing injury |
| Trees/Shrubs | |
| 7. Cedar dieback | Sudden dieback of younger cedar trees in windbreaks |
| 8. Spruce Rhizophaera needle cast | Two year old needles turn purplish brown and drop from tree |
| 9. Scale insects | Hard to notice, but easy to see sapsucking insects on branches |
| 10. Trees failing to leaf out | Winter injury. If no sign of life by early June, tree is dead or will die. |
| 11. Pine sawfly | Light colored, spotted caterpillars feeding the new growth of pines |
| 12. Oak leaf blister | Yellow, blister-like, raised spots on leaves caused by a fungus |
| 13. Maple/ash anthracnose | Irregular brown areas on leaves, often along leaf veins. Leaf drop. |
| Gardens/Ornamentals | |
| 14. Phlox plant bug | White or pale green spots on leaves and deformed flower buds |
| 15. Winter injury- chrysanthemum | If no growth by early June, plants have been winter killed |
| 16. Redbud dieback | Winter injury. If no new growth by early June, tree is a goner. |
| Fruits/Vegetables | |
| 17. Cedar apple rust & apple scab | Leaf yellowing/browning and drop in apples and crabapples |
| 18. Poor fruit set in fruit trees | Heavy fruit set last year is resulting in alternate year bearing |
| 19. Fruit tree spray schedules | Follow recommended spray schedule to control pests |
| Houseplants | |
| 20. Dieback from overwatering | Yellow or brown leaves. Wilting. Roots are brownish and soft. |
| From ReTree Nebraska | |
| 21. Preservation and Care of Community Trees Workshop June 18th and 19th | |
| 22. New EAB Web site by NFS and Insecticide Recommendations for EAB bulletin | |
| 23. Nebraska Statewide Arboretum Plant Sale (Lincoln) Including Trees, June 6th | |
1. Ascochyta Leaf Blight: Patches or large areas of lawn suddenly turn straw or tan color. Resembles drought stress. Leaf blades have bleached white tips and blade is constricted where dead tissue merges with green tissue. Considered a minor disease related to weather and management practices. Turfgrass usually recovers in one month or less without treatment. Fungicides are generally not recommended or needed.
Aschocyta Leaf Blight, http://www.ext.colostate.edu/pubs/garden/02901.html
2. White Grubs overwinter as larvae. In spring, they move to the surface, feed for a short period, then pupate to later emerge as masked chafer adults who mate and lay eggs. The new generation is the damaging generation at which insecticide controls are aimed if needed. Control is not needed for overwintering annual white grubs found in landscape beds or lawns.
White Grubs in Turf NebGuide, http://www.ianrpubs.unl.edu/sendIt/g1619.pdf
3. Powdery Mildew appears as a light layer of flour on grass blades. It is found in shaded turf areas with reduced air movement and high moisture or humidity levels. The fungus grows on leaf surfaces, shading the underlying leaf blade and reducing photosynthesis. Some yellowing and thinning of turf may be seen in heavily infected areas. Reduce shade and improve air movement through pruning where possible. Preventative fungicide applications may be needed in areas with a history of mildew.
Powdery Mildew Disease in Turfgrass NebGuide, http://www.ianrpubs.unl.edu/sendIt/g1911.pdf
4. Crabgrass has begun to germinate. The best control of crabgrass is proper cultural practices; in particular a mowing height of 3” and the use of preemergence herbicides applied from late April to mid May. For crabgrass that has germinated, control by hand-pulling or with post emergence herbicides. Post emergence herbicides are most effective when crabgrass plants are small and coverage of plants is uniform. Adjuvants are often needed. Follow label directions carefully as some of these products may injure turfgrass. Postemergence herbicides for crabgrass control include the methanearsonates MSMA and DSMA, Fenoxaprop (Acclaim Extra), Dithiopyr (Dimension), and Quinclorac (Drive). Postemergence herbicides can be combined with preemergence herbicides to insure late germinating summer annual grasses are controlled along with weeds that have already emerged. Be sure to follow label directions when considering combinations of herbicides.
Control of Crabgrass in Home Lawns, http://www.agry.purdue.edu/turf/pubs/AY-10.pdf
5. Yellow Nutsedge is or will soon begin to grow. Yellow nutsedge is a 3-ranked, yellow-green, waxy, grass-like weed. Handpulling and herbicide applications are most effective in controlling yellow nutsedge when done prior to June 21st. Prior to this date, the tubers (nutlets) attached to the visible plant (mother plant) are in the maturation process but will normally not break dormancy and grow if the mother plant is damaged from pulling, spraying or other injury.
After June 21st, any activity which removes the mother plant results in the now mature tubers breaking dormancy and sprouting. If a plant has multiple tubers attached to it, it is not uncommon for 3-5 sprouts to emerge resulting in an increase in nutsedge plants. Ideally, spray before June 21st to control the mother plant before it can make daughter tubers. This is not always possible so go ahead and spray after June 21st realizing it is not the optimal time for maximum efficacy. Use Sedgehammer (replaced Manage) or Certainty (Sulfosulfuron) which can be applied by commercial applicators. Certainty should only be applied to pure stands of Kentucky bluegrass. It will injure ryegrass and fescue.
6. Winter Injury to lawns in western Nebraska is being seen on Kentucky bluegrass & perennial ryegrass where there is a thick thatch layer and where snow drifts lay for a long time. Reseed or resod damaged areas.
7. Cedar dieback has been observed in windbreaks from southeast and south central Nebraska to north of Columbus. Younger cedar trees, ranging in age from about 7 to 10 years, appear to have turned brown suddenly. Winter injury is suspected, which is unusual for cedar trees, specifically a sudden, large temperature drop in early spring. Mark Harrell, Nebraska Forest Service- Forest Health Specialist, says other factors, such as stress from recent drought combined with root damage from disease by soil fungi, have been killing smaller groups of trees at some locations, but a freeze injury is the most likely cause where large numbers of trees are affected at this time of year over a wide area. It is possible there may be a genetic issue with some trees of this age.
Harrell found no evidence of any significant disease or insect problem on the foliage or anything that could be controlled with a pesticide treatment, so there's no reason to spray the trees to try to control anything. Applying fungicides is not recommended.
Wait a few weeks to see if some of the brown trees grow out new foliage, Harrell suggested, because it is possible that the freeze killed only the foliage and the branches may grow new foliage if given enough time.
8. Spruce Rhizophaera Needle Cast- Second year needles turn brownish purple and drop. Disease usually starts at bottom branches and moves up. Treat with chlorothalonil or Bordeaux mixture fungicide in late May or when new shoots are ½ to 2 inches long. Repeat spray in four weeks. Trees that suffered damage in last year’s hail storms especially need to be watched.
Rhizosphaera Needle Cast of Spruce, http://www.unl.edu/nac/diseasetrees/chap56.pdf
9. Scale Insects can be hard to notice but easy to see once observed. They attack a variety of plants but are common on dogwood, lilac and maples. Scales attach to twigs and branches and grow a waxy covering that helps camouflage them as they feed on plant sap. Branch dieback occurs when high populations of scale are present. Prune and destroy heavily infested branches. Apply systemic insecticides such as malathion or Orthene to young crawlers soon after egg hatch, usually in May. Read and follow label directions as Acephate (Orthene) is NOT recommended for some maples.
Oystershell scale, http://extensionhorticulture.unl.edu/Current/OystershellScale.shtml
10. Trees not leafing out were likely damaged by fluctuating winter temperatures during late winter. There is nothing to do except wait a bit longer to see if new growth occurs. Provide adequate water and avoid fertilizing. Fertilizer will not help push a tree or shrub to leaf out. If there is no sign of growth by early June, the tree or affected branches are unlikely to recover. Remove the tree or prune affected branches.
11. Pine Sawflies look like small, black-headed caterpillars. They are found clustered on the branch ends of pines where they chew off needles. The easiest control is the greenest. Take a stick and lightly tap the branch, knocking the insects to the ground. Few if any will crawl back into the tree. For chemical treatment, products containing permethrin (Eight), carbaryl (Sevin), insecticidal soap, or neem oil will work. The smaller the caterpillar, the easier they are to control.
Pine Sawfly, http://extensionhorticulture.unl.edu/Current/Sawfly.shtml
12. Oak Leaf Blister causes yellowish, blister-like, circular, raised areas to form on leaves. It is a fungal disease. It does not cause serious damage to trees as they can still photosynthesize even though infected by the disease. Control is not needed and it is too late to achieve control for this year, anyway. Fungicides need to be applied just before bud break to be effective.
Oak Leaf Blister, http://plantclinic.cornell.edu/FactSheets/oakblister/oakblister.htm
13. Anthracnose is a common fungal disease on ash, maple, sycamore and oak that causes irregular brown areas on leaves. Leaves may become distorted and minor to severe defoliation of a tree can occur. It is too late to treat trees effectively. Anthracnose is rarely a serious problem for otherwise healthy trees. Most trees will produce new leaves to replace lost leaves.
Anthracnose Diseases of Shade Trees, http://www.oznet.ksu.edu/path-ext/factSheets/Trees/Anthracnose%20Diseases%20of%20Shade%20Trees.asp
14. Phlox Plant Bug Feeding occurs on upper leaf surfaces of young phlox leaves and buds. Injury appears as white or pale-green spots that later become yellow-stippled areas. Blossoms may be deformed. In extreme cases, plants become stunted and die. Adult bugs generally have contrasting colors, i.e. orange and black or red and black, sometimes gray and white or yellow; all with black legs. Nymphs are orange or bright red. This insect overwinters in the egg stage with nymphs emerging in early May. Remove infested plant parts. The use of insecticidal soaps, horticultural oils, or systemic insecticides will reduce damage.
15. Winter ingury- chrysanthemum- Mums that are not showing any new growth to date are not likely to do so and are best replaced. If mums are replanted, provide winter protection by placing a thick layer of coarse mulch over the plants in mid November to reduce the risk of winter kill.
16. Redbud Dieback Eastern Redbud is native to Nebraska but it is not unusual for these trees to be killed by cold winter temperatures. If the seed or tree source is a southern source, these will be susceptible to winter kill. When selecting Redbud trees, buy from a reputable nursery and ask if the seed source for their trees is a northern source.
17. Cedar Apple Rust or Apple Scab is causing leaves of apples and crabapples to yellow and drop. Fungal infections occurred early this spring just as leaf buds were beginning to break and show some green color. While severe defoliation can occur, and this is a stress for the tree, few trees will die unless severe defoliation occurs year after year. Fungicide applications need to be applied just as tree leaves are breaking bud in early spring and repeated as recommended.
Cedar Apple Rust NebGuide, http://www.ianrpubs.unl.edu/sendIt/g1907.pdf
18. Poor fruit set- Last year, fruit tree crops were abundant. Heavy fruiting one year can trigger a tree to go into alternate year bearing where they bear a heavy crop one year and a very light crop the next year. To avoid this, fruit needs to be thinned during heavy fruit crop years.
Fruit Tree Thinning, http://hort4.unl.edu/fruit/thin.html
19. Fruit Tree Spray Schedules Timing of pesticide applications is critical to effectively controlling the targeted pests. For recommended fruit tree spray schedules see the publication below.
Fruit Tree Spray Schedules for the Homeowner, http://extension.missouri.edu/publications/DisplayPub.aspx?P=G6010
20. Houseplant Root Rots symptoms include tip dieback, yellowing of leaves and wilted leaves or stems. Root rots are common when plants are overwatered, grown in containers without drainage holes, or if a poorly drained soil, such as outdoor garden soil, is used. To avoid this, use containers with drainage holes and use a well drained soilless potting mix. Water enough for water to drain out of the drainage holes; empty the catch basin after watering (remove with a turkey baster if a large container); then water again when the upper one inch of soil becomes dry.
Houseplants: Proper Care and Problem Solving, http://www.ag.ndsu.edu/pubs/plantsci/landscap/pp744w.htm
21. Preservation and Care of Community Trees Workshop June 18th and 19th
Understanding trees in our communities, how they grow and even how they age is important when considering where to plant and how to maintain trees.
Learn what a tree needs; beginning with your new purchase at the nursery through the young, growing stage, on to middle age and then into the tree's over-mature stage.
Registration form: http://www.nfs.unl.edu/documents/retreenebraska/calendar/MPTS%20brochure.June09.alt2.pdf
22. New Emerald Ash Borer Web site by Nebraska Forest Service
The Nebraska Forest Service has compiled a web site containing EAB information especially pertaining to Nebraska, which can be accessed online at http://nfs.unl.edu/EAB.asp
23. Nebraska Statewide Arboretum Plant Sale (Lincoln) Including Trees, June 6th
Plant sale location and plant list is available at http://arboretum.unl.edu/plantsales/index.html
