Hort Update for the week of 5/26/08
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1. General Weed Control- Conditions over the last several years, coupled with relatively slow turfgrass growth initiation this spring, has opened the door for much increased weed pressure in lawns. The winter annual weeds like henbit, downy brome and common chickweed are sustaining their growth longer than normal.
While it is tempting to reach for an herbicide to control winter annuals it is not recommended. Herbicides applied to winter annuals at this time can increase flowering, or if flowering has already occurred, increase seed production. This is a natural response of an annual when under stress, primarily as a survival mechanism. Additionally, herbicide applications to winter annuals at this time rarely results in significant control, resulting in a herbicide injured, but not quite dead, weed in your turf.
Pressure from perennial weeds like dandelion, clover and ground ivy is also very high. Attempts to control these weeds early in the spring have been hindered by temperature fluctuations and minimized herbicide translocation within the weed. While the standard recommendation for optimal control of perennial weeds is herbicide application in the fall, this appears to be a year where spring applications may be warranted.
Be careful to apply broadleaf herbicides when the wind speed is less then 7 MPH (at 5-7 MPH: wind felt on face; leaves rustle; flag movement minimal) to minimize damage to non-target species (trees, tomatoes, grapes etc.). Consider the use of a spray additive, such as a spreader/sticker (available at many garden stores and coops) to help the herbicide stay on the leaf and for better coverage.
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2. Slow turfgrass seed germination- Soil temperatures this year have not increased at a rate comparable to past years. If you planted turfgrass recently, especially Kentucky bluegrass, you may notice an appreciable delay in germination. Do not be overanxious in applying additional seed unless it has been longer than 30 days for Kentucky bluegrass or 2 weeks for turf type tall fescue.
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3. Maple Bladder Galls are bright red, pod or bladder-shaped galls found on upper leaf surfaces of maples. The red galls later turn black and may drop out of leaves resulting in small holes. Heavily infested leaves may drop from trees. Maple bladder galls are caused by the feeding of a tiny mite. They do not affect the overall health of the tree and using a control method is rarely recommended. If control is desired, the time to treat is at spring bud swell with horticultural oil. Treatment is not effective once the galls are visible.
Maple Bladder Galls, http://www.ipm.iastate.edu/ipm/hortnews/1998/6-5-1998/maplegall.html
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4. Aphids and their damage are being observed on Viburnums, serviceberry, ninebark and other ornamentals. Aphids suck plant sap from leaves, twigs or stems causing leaf curling and leaf distortion. Most aphids excrete a sweet, sticky substance called honeydew causing leaves or surfaces below infested plants to become sticky. Sooty mold fungus may grow on the honeydew, producing a grayish-black growth on leaves. Sooty mold is not damaging to plants except when it covers leaves and temporarily reduces photosynthesis. Systemic insecticides are most effective in controlling aphids.
Aphids on Shade Trees and Ornamentals, http://www.ext.colostate.edu/pubs/insect/05511.html
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5. Anthracnose is a fungal disease of ash, maple, sycamore, oak and walnut. It causes irregular brown areas on leaves which often follow leaf veins. Leaves may become distorted and/or drop from the tree. For ash, maple and walnut, control of anthracnose is not needed. These trees typically recover with little overall affect to the tree.
For sycamore and oak, control may be desired if twig death is severe. Fungicides need to be applied at bud break to effectively control the disease. The fungi that infect each type of tree are different. For example, the fungus that causes ash anthracnose cannot infect a maple trees.
Diseases of Broadleaf Trees, http://www.nfs.unl.edu/documents/foresthealth/diseasesbroadleaf.pdf
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6. Cedar Hawthorne rust is a fungal disease that causes orange spots on leaves and string-like structures protruding from the fruit. It is similar to cedar apple rust, but is caused by a different fungus. It rarely kills a tree, but can result in leaf drop. If needed, treat Hawthorne trees with a fungicide in spring just as new growth appears and repeat 3 to 4 times until flower buds open.
Cedar Rust Diseases Backyard Farmer Video Clip, http://www.youtube.com/watch?v=MCMdp2yur_g
Pesticide Selection Guide for Plant Diseases Affecting Woody Ornamentals and Herbaceous Perennials in Nebraska, http://www.ianrpubs.unl.edu/sendIt/ec1895.pdf
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7. Dothistroma Needle Blight- Browning of needles on the lower half of Austrian, ponderosa and Scotch pine trees. On close inspection, needles will have turned brown from the tip down to a reddish-purple lesion or band on the needle. Lesions or bands may be found on other green needles as well.
Dothistroma Needle Blight, http://extensionhorticulture.unl.edu/Current/Dothistroma.shtml
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8. White Grubs found in garden beds at this time of year are overwintering larvae. In spring, they move closer to the soil surface to pupate into adult beetles. White grubs found during spring do not cause plant damage. Applying insecticides to kill this generation of grubs - larvae - of masked chafers, Japanese beetles, or even May/June bugs is not justified.
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9. Penstemons are infected by a fungal leaf spot promoted by cool temperatures and wet weather. Leaf spots can infect a number of perennial and annual flowers and are caused by a variety of fungi. The fungus can attack leaves, petioles and flowers. Symptoms are blue black, brown or reddish leaf spots which often develop a tan center. Use good sanitation, especially during fall. Avoid crowded plants to improve air circulation around plants. Avoid overhead irrigation. Apply fungicides at the first sign of leaf spots developing on the foliage and repeat as directed on the label.
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10. Freeze Damage has resulted in blackening of new shoots and leaf distortion on plants affected by the freeze two weeks ago in western Nebraska. Most healthy plants will generate new growth, then damaged growth can be pruned away.
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11. Slow seed germination- Soil temperatures have increased at a slower rate this spring compared to past years, resulting in delayed seed germination. While this affects many types of plants, it has been noted on peas and cucumbers. The seeds should germinate eventually or they may succumb to damping off disease. Delay planting, or replanting, until soil temperatures are warm enough to promote vigorous plant germination and growth.
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
12. Damping off is a fungal disease that kills young seedlings in vegetable gardens. It is most prevalent when seed is planted into cold, wet soils. Waiting to plant seeds until soil temperatures are conducive to rapid germination and active growth. Planting into raised beds, where soil warms at a faster rate and excess water drains away more quickly than in ground beds, can reduce problems with damping off.
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13. Peach Leaf Curl is a fungal disease (Taphrina deformans) that causes developing leaves of peach and related species to become severely distorted, thickened and puckered, with a reddish or purple cast. Later in the season as spores form on the leaf surface, leaves will become powdery gray in color, may turn yellow or brown, and drop from the tree. This disease is most severe during cool, wet springs. If there is severe defoliation, the tree will be weakened, especially if a heavy fruit crop is allowed to develop. Control is fairly easy if fungicides are applied in very early in spring just prior to leafing, however, that time period has past. No control is recommended once leaves are visibly infected.
Peach Leaf Curl, http://ohioline.osu.edu/hyg-fact/3000/3006.html
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14. Rabbits feed on a wide variety of landscape plants. The best control is exclusion with fencing, such as a chicken wire fence placed securely around a plant or garden. Repellants can provide some short term control. Planting rabbit resistant plants may help if the rabbit has other sources of food.
Prevention and Control of Rabbit Damage Nebguide, http://www.ianrpubs.unl.edu/sendIt/g1526.pdf
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15. Vinegar for weed control- Questions are being asked about using vinegar (acetic acid) as an organic weed control product. When answering this question, keep in mind:
| Current Problems: | Major Symptom: |
| Lawns | |
| 1. General weed control | Increased weed pressure observed in lawns & gardens |
| 2. Slow seed germination | Cool soil temperatures slowing turfgrass seed germination |
| Trees & Shrubs | |
| 3. Maple bladder gall | Bright red or black, puffy raised galls on leaves |
| 4. Aphids | Sticky foliage and leaf curling on new growth |
| 5. Ash anthracnose | Irregular brown areas on leaves and leaf drop |
| 6. Cedar-hawthorne rust | Orange leaf spots; stringy structures on fruit |
| 7. Dothistroma needle blight of pine | Reddish bands and browning on needles on lower half of tree |
| Gardens/Ornamentals | |
| 8. White grubs found in gardens | Overwintering larvae- controls are not needed |
| 9. Penstemon leaf spot | Reddish or bluish-black leaf spots on foliage |
| 10. Freeze damage in W. Nebraska | New shoots turning black and leaves distorted |
| Vegetables/Fruits | |
| 11. Slow seed germination | Cool soil temperatures delaying seed germination |
| 12. Damping off | Seedlings killed by fungal disease often due to cold, wet soils |
| 13. Peach leaf curl | Distinct puckering and reddening of leaves in various fruit trees |
| 14. Rabbit problems | Feeding damage to a variety of plants |
| Miscellaneous | |
| 15. Vinegar for weed control | Use the EPA registered product and read & follow all label directions |
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1. General Weed Control- Conditions over the last several years, coupled with relatively slow turfgrass growth initiation this spring, has opened the door for much increased weed pressure in lawns. The winter annual weeds like henbit, downy brome and common chickweed are sustaining their growth longer than normal.
While it is tempting to reach for an herbicide to control winter annuals it is not recommended. Herbicides applied to winter annuals at this time can increase flowering, or if flowering has already occurred, increase seed production. This is a natural response of an annual when under stress, primarily as a survival mechanism. Additionally, herbicide applications to winter annuals at this time rarely results in significant control, resulting in a herbicide injured, but not quite dead, weed in your turf.
Pressure from perennial weeds like dandelion, clover and ground ivy is also very high. Attempts to control these weeds early in the spring have been hindered by temperature fluctuations and minimized herbicide translocation within the weed. While the standard recommendation for optimal control of perennial weeds is herbicide application in the fall, this appears to be a year where spring applications may be warranted.
Be careful to apply broadleaf herbicides when the wind speed is less then 7 MPH (at 5-7 MPH: wind felt on face; leaves rustle; flag movement minimal) to minimize damage to non-target species (trees, tomatoes, grapes etc.). Consider the use of a spray additive, such as a spreader/sticker (available at many garden stores and coops) to help the herbicide stay on the leaf and for better coverage.
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
2. Slow turfgrass seed germination- Soil temperatures this year have not increased at a rate comparable to past years. If you planted turfgrass recently, especially Kentucky bluegrass, you may notice an appreciable delay in germination. Do not be overanxious in applying additional seed unless it has been longer than 30 days for Kentucky bluegrass or 2 weeks for turf type tall fescue.
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
3. Maple Bladder Galls are bright red, pod or bladder-shaped galls found on upper leaf surfaces of maples. The red galls later turn black and may drop out of leaves resulting in small holes. Heavily infested leaves may drop from trees. Maple bladder galls are caused by the feeding of a tiny mite. They do not affect the overall health of the tree and using a control method is rarely recommended. If control is desired, the time to treat is at spring bud swell with horticultural oil. Treatment is not effective once the galls are visible.
Maple Bladder Galls, http://www.ipm.iastate.edu/ipm/hortnews/1998/6-5-1998/maplegall.html
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4. Aphids and their damage are being observed on Viburnums, serviceberry, ninebark and other ornamentals. Aphids suck plant sap from leaves, twigs or stems causing leaf curling and leaf distortion. Most aphids excrete a sweet, sticky substance called honeydew causing leaves or surfaces below infested plants to become sticky. Sooty mold fungus may grow on the honeydew, producing a grayish-black growth on leaves. Sooty mold is not damaging to plants except when it covers leaves and temporarily reduces photosynthesis. Systemic insecticides are most effective in controlling aphids.
Aphids on Shade Trees and Ornamentals, http://www.ext.colostate.edu/pubs/insect/05511.html
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5. Anthracnose is a fungal disease of ash, maple, sycamore, oak and walnut. It causes irregular brown areas on leaves which often follow leaf veins. Leaves may become distorted and/or drop from the tree. For ash, maple and walnut, control of anthracnose is not needed. These trees typically recover with little overall affect to the tree.
For sycamore and oak, control may be desired if twig death is severe. Fungicides need to be applied at bud break to effectively control the disease. The fungi that infect each type of tree are different. For example, the fungus that causes ash anthracnose cannot infect a maple trees.
Diseases of Broadleaf Trees, http://www.nfs.unl.edu/documents/foresthealth/diseasesbroadleaf.pdf
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6. Cedar Hawthorne rust is a fungal disease that causes orange spots on leaves and string-like structures protruding from the fruit. It is similar to cedar apple rust, but is caused by a different fungus. It rarely kills a tree, but can result in leaf drop. If needed, treat Hawthorne trees with a fungicide in spring just as new growth appears and repeat 3 to 4 times until flower buds open.
Cedar Rust Diseases Backyard Farmer Video Clip, http://www.youtube.com/watch?v=MCMdp2yur_g
Pesticide Selection Guide for Plant Diseases Affecting Woody Ornamentals and Herbaceous Perennials in Nebraska, http://www.ianrpubs.unl.edu/sendIt/ec1895.pdf
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7. Dothistroma Needle Blight- Browning of needles on the lower half of Austrian, ponderosa and Scotch pine trees. On close inspection, needles will have turned brown from the tip down to a reddish-purple lesion or band on the needle. Lesions or bands may be found on other green needles as well.
Dothistroma Needle Blight, http://extensionhorticulture.unl.edu/Current/Dothistroma.shtml
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
8. White Grubs found in garden beds at this time of year are overwintering larvae. In spring, they move closer to the soil surface to pupate into adult beetles. White grubs found during spring do not cause plant damage. Applying insecticides to kill this generation of grubs - larvae - of masked chafers, Japanese beetles, or even May/June bugs is not justified.
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
9. Penstemons are infected by a fungal leaf spot promoted by cool temperatures and wet weather. Leaf spots can infect a number of perennial and annual flowers and are caused by a variety of fungi. The fungus can attack leaves, petioles and flowers. Symptoms are blue black, brown or reddish leaf spots which often develop a tan center. Use good sanitation, especially during fall. Avoid crowded plants to improve air circulation around plants. Avoid overhead irrigation. Apply fungicides at the first sign of leaf spots developing on the foliage and repeat as directed on the label.
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
10. Freeze Damage has resulted in blackening of new shoots and leaf distortion on plants affected by the freeze two weeks ago in western Nebraska. Most healthy plants will generate new growth, then damaged growth can be pruned away.
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
11. Slow seed germination- Soil temperatures have increased at a slower rate this spring compared to past years, resulting in delayed seed germination. While this affects many types of plants, it has been noted on peas and cucumbers. The seeds should germinate eventually or they may succumb to damping off disease. Delay planting, or replanting, until soil temperatures are warm enough to promote vigorous plant germination and growth.
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
12. Damping off is a fungal disease that kills young seedlings in vegetable gardens. It is most prevalent when seed is planted into cold, wet soils. Waiting to plant seeds until soil temperatures are conducive to rapid germination and active growth. Planting into raised beds, where soil warms at a faster rate and excess water drains away more quickly than in ground beds, can reduce problems with damping off.
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
13. Peach Leaf Curl is a fungal disease (Taphrina deformans) that causes developing leaves of peach and related species to become severely distorted, thickened and puckered, with a reddish or purple cast. Later in the season as spores form on the leaf surface, leaves will become powdery gray in color, may turn yellow or brown, and drop from the tree. This disease is most severe during cool, wet springs. If there is severe defoliation, the tree will be weakened, especially if a heavy fruit crop is allowed to develop. Control is fairly easy if fungicides are applied in very early in spring just prior to leafing, however, that time period has past. No control is recommended once leaves are visibly infected.
Peach Leaf Curl, http://ohioline.osu.edu/hyg-fact/3000/3006.html
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14. Rabbits feed on a wide variety of landscape plants. The best control is exclusion with fencing, such as a chicken wire fence placed securely around a plant or garden. Repellants can provide some short term control. Planting rabbit resistant plants may help if the rabbit has other sources of food.
Prevention and Control of Rabbit Damage Nebguide, http://www.ianrpubs.unl.edu/sendIt/g1526.pdf
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15. Vinegar for weed control- Questions are being asked about using vinegar (acetic acid) as an organic weed control product. When answering this question, keep in mind:
- Legally products have to be labeled and registered with EPA to be recommended as an herbicide. An herbicidal vinegar is now labeled and sold as Weed Pharm by Pharm Solutions, Inc. It is available in Nebraska. This product contains 20% acetic acid which studies show is most effective as a weed killer. Most vinegar purchased at super markets are 5% acetic acid. There are commercial food-grade formulations of vinegar that are stronger than 5%; however they are not labeled and registered with EPA as herbicides.
- Acetic acid above 5% concentration can severely burn skin and eyes. The Weed Pharm label signal word is DANGER. It's corrosive and causes irreversible eye damage, so goggles or a face shield is needed when handling this product. If the product is swallowed or splashed on the skin, a poison-control center should be called. Also, the label reads, "Keep unprotected persons out of the treated area until spray residues have dried." Read and follow all label directions carefully.
- Vinegar is nonselective and may damage any plant tissue whether it is a desirable plant or a weed. To be effective as an herbicide, acetic acid needs to contact plant leaves. Thorough spray coverage is critical. The acidity of the spray solution damages and dries out leaves. Desirable plants need to be protected from potential spray drift.
- Vinegar does not move into the roots of treated plants, so only top growth is killed. This means perennial weeds can return. Vinegar is fast acting and most effective on young, actively growing annual weeds.
- If vinegar is the herbicide of choice, look for EPA registered products and read and follow all label directions.
