Hort Update for the week of 5/21/07
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1. Yellow nutsedge - is a 3-ranked, yellow-green, waxy grass-like weed. At this time of year it can be controlled by pulling. Nutlets will not start to form until after the longest day of the year, June 21 st. Pulling before this stage is worthwhile. Chemical treatment is most effective when applied before June 21- Sedgehammer (replaces Manage). Certainty (Sulfosulfuron) is a new product that can only be applied by commercial applicators.
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2. Mushrooms & slime molds -With the warm moist weather this week, we may see development of fungal slime molds & mushrooms in home lawns. There is no treatment for them. Clients should pick and throw away the mushrooms before mowing to reduce the number of spores. But the mushrooms will continue to pop up until the decaying material they feed on is gone, such as buried wood, decaying tree roots, or thatch.
Slime molds sometimes look like dog vomit (hence the name dog vomit fungi) and can come in many bright colors, while others appear as grayish mass on turf leaf blades. Symptoms of leaf blade smile molds may be seen as irregular patches of discolored turf ranging in size from several inches to several feet in diameter. Some slime molds feed on decaying material and are often found in mulched ornamental beds, while others use turf leaf blades strictly as a structure to grow on.
Slime Molds on Turfgrass, http://ohioline.osu.edu/hyg-fact/3000/3074.html
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3. Zoysiagrass in bluegrass – As a weed in bluegrass lawns, zoysiagrass appears as thick, dense patches of grass that is slow to greenup in spring. There is no selective chemical control for zoysiagrass in turf. Spray patches with a non-selective herbicide, such as glyphosate, going at least 12 inches beyond the visible borders of the weedy patch. Two or more applications of glyphosate may be needed to completely kill the existing zoysia. When the patch is dead, scrape of the dead vegetation then re-seed or re-sod the area.
To discourage zoysia from moving into a lawn from neighboring areas create a mulched area between the client’s yard and the existing zoysia. As zoysiagrass pops up in the mulch between the yards, it can be sprayed with a non-selective herbicide.
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4. Sod webworm - reported in western Nebraska. The larval stage of this tan moth, feeds on turf leaf blades resulting in small, dead, bare patches or generalized thinning within a home lawn. They prefer sunny areas, with hot, dry conditions and are often found on south facing slopes. The larvae are seldom found in shaded locations.
Sod webworm Management in Lawns, http://ohioline.osu.edu/hyg-fact/2000/2011.html
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5. Drought stress - Cool season turfgrasses are showing symptoms of spring drought stress in western Nebraska. Kentucky bluegrass and tall fescue lawns require one inch of water per week for optimum growth. Two applications of ½ inch water are recommended each week, if a similar amount of rain has not been received.
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6. Powdery mildew- often found in shaded turf areas, with reduced air movement and high moisture or humidity levels. This fungus grows on turf leaf surfaces, shading the underlying leaf blade and reducing photosynthesis. Thinning of the turf may be seen in heavily affected areas. Reduce shade and improve air movement through pruning if possible. Preventative fungicide applications may be necessary in areas with a history of infection. Recommended fungicides include Bayleton (triadimefon) or Banner (propiconozole).
Powdery Mildew in Turfgrass, http://ohioline.osu.edu/hyg-fact/3000/3081.html
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7. Moss- flat patches of bright green plants with fine, thread-like stems. Moss is an opportunistic plant that will grow where turfgrass stands are thin and weak. Most commonly associated with shallow soils; poor soil fertility; low soil pH (acid soils); heavy shade; and excessive moisture. If any of these factors are limiting turf growth, moss can invade the lawn and establish itself. For effective moss control start by modifying the site conditions to favor lawn grasses.
Moss Control in Lawns, http://lancaster.unl.edu/hort/articles/2006/Moss.shtml
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8. Dead patches in lawn - reported in western Nebraska. Brown, dead patches or thinning of cool season lawns may have resulted from perennial ryegrass winterkill, at reported levels of up to 50% this winter.
Another potential cause is late fall 2006 Denver billbug activity, which thinned and weakened some turfgrass stands, resulting in winter stress that killed plants. Overseed affected lawns. Apply the insecticide Imidacloprid when adult billbugs are present.
Billbugs and White Grubs, http://www.ext.colostate.edu/PUBS/insect/05516.html
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9. Leaves falling off of trees – is mostly likely the result of wind damage The combination of stressful weather conditions (rapid fluctuations in temperature, etc) followed by wind, are knocking off the leaves. This does NOT appear to be insects or squirrel damage. Deciduous tree will not be seriously effected and will recover.
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10. Freeze damage – Freezing night temperatures in early April killed flowers, leaves, new growth and some twigs on many woody ornamentals. Many leaves still in the bud stage during the freezes were also partially damaged, resulting in scorched, tattered or misshapen leaves that are now becoming evident. Tattering may look similar to insect damage, but insecticide applications are not necessary or recommended. As new growth resumes, dead twigs and branches should be removed making cuts back to the point of living tissue.
Do not fertilize freeze damaged woody plants. Continue to provide normal watering and mulch throughout the growing season. Prevent secondary damage from opportunistic insects and diseases. Replace severely damaged plants, matching the new plant to the available site.
Oak leaf tatter, http://www.ipm.iastate.edu/ipm/hortnews/1998/5-15-1998/tatters.html
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11. Maple bladder galls - bright red galls that later turn black, usually on the upper leaf surface of maple leaves. When the galls turn black, they may fall off the leaves, resulting in small holes. A few leaves may be so infested that they fall off, but this is not common. These galls are caused by the feeding of a tiny mite and do not affect the health of the tree. If 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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12. Hackberry nipple gall- round green galls are found on most hackberry leaves, and are the result of feeding by the hackberry gall psyllid, which under a microscope look like tiny cicadas. Leaf feeding by psyllids in spring causes the leaf for form a small, hollow pocket of tissue where the psyllid passed the summer, sucking sap from the leaf tissues. No serious damage is done to the tree as a result of psyllid feeding or the presence of the galls, however, aesthetically the galls are very unattractive. Application of Imidacloprid, a liquid, systemic insecticide with up to a year residual effect, can provide some control. Apply the insecticide in fall so it can reach full strength within the tree before the following year’s leaves begin to emerge.
Hackberry Gall Psyllids, http://lancaster.unl.edu/pest/resources/hackberrypsyllids.shtml
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13. Chlorosis- yellowing of leaves, frequently found on pin oaks, silver maple and river birch. Leaves are yellowed, but the veins remain green. In pin oak and birch this condition is due to iron deficiency, however, in maples it is usually due to manganese deficiency. In both cases, there is plenty of iron and manganese in the soil, but high soil pH levels bind up the existing nutrients. Trees with severe, untreated chlorosis develop branch dieback, poor canopy development and eventually death.
In severe cases the best option for pin oak and birch is an iron injection. But this should be done no more than every 3 years to prevent girdling of tree’s vascular system.
Soil treatments that involve acidifying the soil with sulfur are sometimes effective. However, a new method called the Whitcomb treatment has been found to have long-term benefits to chlorotic trees. It involves putting tubes of MicroMax (a micronutrient fertilizer), sulfur, and a general purpose, NPK fertilizer in the soil around the tree.
Whitcomb Chlorosis Treatment, http://extensionhorticulture.unl.edu/Weekly/WhitcombMethod.pdf
Iron Chlorosis in Trees, http://www.oznet.k-state.edu/dp_hfrr/extensn/problems/irnchlor.htm
Iron Chlorosis in Trees, http://www.oznet.ksu.edu/library/forst2/mf718.pdf
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14. Spruce and Fir needle drop- browning of last year’s growth and shedding of needles has been seen in spruce and fir trees this spring. In some cases, symptoms are scattered randomly throughout the tree, in other cases damage is concentrated on one or two sides of the tree. New growth is not affected and in most cases is developing normally. No symptoms of fungal diseases, cankers or insect activity are present, and it is suspected that this damage is environmental in nature. Possibly last year’s needles started to lose their winter hardiness following the two weeks of 60-80 degree temperatures in March and were subsequently damaged by the week of below freezing night temperatures experienced in early April. Normal best maintenance practices are recommended to maintain tree vigor.
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15. Pine sawflies - clusters of caterpillar-like critters feeding one year old or older needles. They leave new growth alone. These are the larvae of a predatory wasp. They can be knocked off the branch with a stick or water and are unlikely to return. The end of the branch can be cut off. If chemical control is needed, clients can use a permethrin, carbaryl, or an Acephate.
European Pine Sawfly, http://ohioline.osu.edu/hyg-fact/2000/2555.html
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16. Pine tip moth- the larva of several moths tunnel into needles, buds and new shoots, killing the shoots and stunting tree growth. Old infested tips crumble when squeezed. Shoots infested with southwestern pine tip moths commonly turn brown and bend over in a shepherd’s crook. Spray acephate or dimethoate on foliage in spring when new shoots are elongating but before needles are more than ½ inch long. Repeat application in late June or early July.
Pine Tip Moths, http://www.ext.colostate.edu/pubs/insect/05529.html
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17. Spruce spidermites - the mite is a commonly called a 'cool season' mite because it is active during the cooler periods of spring and fall. It is found on all types of conifers including spruce, pine, juniper and arborvitae. Spruce spidermite overwinters as an egg, hatching from March to April. They feed by piercing leaf tissues with a needle-like mouth, and sucking sap from the plant tissues. Conifers often react slowly to the feeding of this mite. Yellowing and bronzing of the needles may not become apparent until the heat of the summer, even though the damage may have occurred the previous fall and spring, and active mites are no longer present.
The mites complete their development in 3 to 4 weeks, going into a dormant egg stage when summer temperatures rise. They may resume activity in the fall when cooler temperatures return.
Spidermites and Their Control, http://ohioline.osu.edu/hyg-fact/2000/2012.html
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18. Balsam twig aphid - twisted or curled needles at the tips of the new growth on spruce or fir trees can be caused by the balsam twig aphid. In most cases the damage is cosmetic and not harmful to the plant. Aphids will be present on the plants until about mid-June, then will be dormant for the rest of the year. Insecticide control for heavily infested trees should be done in April or early May, before new shoot growth begins using Permethrin.
Balsam Twig Aphid, http://www.ext.vt.edu/departments/entomology/factsheets/baltwaph.html
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19. Pine wilt- is now considered to be present throughout the state. Affected trees go off color, sometimes a few branches at a time but more often the entire tree is affected at the same time, and die within a few weeks. Greyhound by Arbor Systems is available for injection to prevent Pine wilt but the approximate cost is $300.00 per tree with a 10” diameter trunk. Scotch pine trees that die need to be removed and chipped or destroyed ASAP.
Pine Wilt: A Fatal Disease of Exotic Pines in the Midwest, http://www.extension.iastate.edu/Publications/SUL9.pdf
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20. Mushroom identification – UNL Extension staff will not identify mushrooms as edible or inedible for mushroom hunters, due to potential liability. In an emergency, clients should call the Poison Control Center at (800) 955-9191.
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21. Winter kill of ornamentals - several perennial ornamental plants have been severely affected by adverse spring weather conditions. Dieback of chrysanthemum, caryopteris (Bluemist spirea), buddleia (Butterfly bush), ‘May Night’ salvia, red hot poker ( Kniphofia uvari) and other ornamentals have been reported.
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22. Rhubarb freeze injury - plants damaged by freezing temperatures had leaves dieback. Vigorous plants have developed new top growth that is firm and healthy, and it is safe to eat. As always, eat only the stems and not the leaves.
| Current Problems: | Major Symptom: |
Lawns |
|
| 1. Yellow nutsedge | Yellowish-green, grass-like weed in landscapes |
| 2. Mushrooms & slime molds | Sporadic appearance of mushrooms in turf, or small gray masses on turf leaf blades |
| 3. Zoysiagrass in bluegrass | Dense patches of grass that is slow to green up |
| 4. Sod webworm | Browning & thinning of turf areas |
| 5. Drought stress | Water needs for Kentucky bluegrass |
| 6. Powdery mildew | Scattered white patches, resembling powder on leaf blades |
| 7. Moss | Flat patches of bright green plants with fine, thread-like stems |
| 8. Dead patches | Brown, dead patches or thinning of cool season lawns |
| Trees & Shrubs | |
| 9. Leaves falling off trees | Individual, green leaves falling from trees |
| 10. Freeze damage | Dead, “scorched”, or misshapen leaves, twig dieback of woody plants |
| 11. Maple bladder gall | Bright red or black, bladder-shaped galls on leaves |
| 12. Hackberry nipple gall | Round, green galls on hackberry leaves |
| 13. Chlorosis | Leaf yellowing, commonly found on oak, birch and maple |
| 14. Spruce and fir needle drop | Browning of older growth, and shedding of needles |
| 15. Pine sawfly | Olive-green “caterpillars” feeding in clusters on older needles |
| 16. Pine tip moth | New shoots turn brown and die, sometimes develop “shephard’s crook” |
| 17. Spruce spidermites | Yellowing or discoloration of interior needles |
| 18. Balsam fir aphid | Curled, twisted needles on tips of new growth on spruce and fir |
| 19. Pine wilt | Browning of entire pine trees in spring |
| Vegetables & Ornamentals | |
| 20. Mushroom identification | Will UNL Extension identify edible mushrooms? |
| 21. Winter kill of ornamentals | Failure of plants to send out new growth |
| 22. Rhubarb freeze injury | Are plants safe to eat? |
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1. Yellow nutsedge - is a 3-ranked, yellow-green, waxy grass-like weed. At this time of year it can be controlled by pulling. Nutlets will not start to form until after the longest day of the year, June 21 st. Pulling before this stage is worthwhile. Chemical treatment is most effective when applied before June 21- Sedgehammer (replaces Manage). Certainty (Sulfosulfuron) is a new product that can only be applied by commercial applicators.
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
2. Mushrooms & slime molds -With the warm moist weather this week, we may see development of fungal slime molds & mushrooms in home lawns. There is no treatment for them. Clients should pick and throw away the mushrooms before mowing to reduce the number of spores. But the mushrooms will continue to pop up until the decaying material they feed on is gone, such as buried wood, decaying tree roots, or thatch.
Slime molds sometimes look like dog vomit (hence the name dog vomit fungi) and can come in many bright colors, while others appear as grayish mass on turf leaf blades. Symptoms of leaf blade smile molds may be seen as irregular patches of discolored turf ranging in size from several inches to several feet in diameter. Some slime molds feed on decaying material and are often found in mulched ornamental beds, while others use turf leaf blades strictly as a structure to grow on.
Slime Molds on Turfgrass, http://ohioline.osu.edu/hyg-fact/3000/3074.html
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3. Zoysiagrass in bluegrass – As a weed in bluegrass lawns, zoysiagrass appears as thick, dense patches of grass that is slow to greenup in spring. There is no selective chemical control for zoysiagrass in turf. Spray patches with a non-selective herbicide, such as glyphosate, going at least 12 inches beyond the visible borders of the weedy patch. Two or more applications of glyphosate may be needed to completely kill the existing zoysia. When the patch is dead, scrape of the dead vegetation then re-seed or re-sod the area.
To discourage zoysia from moving into a lawn from neighboring areas create a mulched area between the client’s yard and the existing zoysia. As zoysiagrass pops up in the mulch between the yards, it can be sprayed with a non-selective herbicide.
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4. Sod webworm - reported in western Nebraska. The larval stage of this tan moth, feeds on turf leaf blades resulting in small, dead, bare patches or generalized thinning within a home lawn. They prefer sunny areas, with hot, dry conditions and are often found on south facing slopes. The larvae are seldom found in shaded locations.
Sod webworm Management in Lawns, http://ohioline.osu.edu/hyg-fact/2000/2011.html
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5. Drought stress - Cool season turfgrasses are showing symptoms of spring drought stress in western Nebraska. Kentucky bluegrass and tall fescue lawns require one inch of water per week for optimum growth. Two applications of ½ inch water are recommended each week, if a similar amount of rain has not been received.
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6. Powdery mildew- often found in shaded turf areas, with reduced air movement and high moisture or humidity levels. This fungus grows on turf leaf surfaces, shading the underlying leaf blade and reducing photosynthesis. Thinning of the turf may be seen in heavily affected areas. Reduce shade and improve air movement through pruning if possible. Preventative fungicide applications may be necessary in areas with a history of infection. Recommended fungicides include Bayleton (triadimefon) or Banner (propiconozole).
Powdery Mildew in Turfgrass, http://ohioline.osu.edu/hyg-fact/3000/3081.html
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7. Moss- flat patches of bright green plants with fine, thread-like stems. Moss is an opportunistic plant that will grow where turfgrass stands are thin and weak. Most commonly associated with shallow soils; poor soil fertility; low soil pH (acid soils); heavy shade; and excessive moisture. If any of these factors are limiting turf growth, moss can invade the lawn and establish itself. For effective moss control start by modifying the site conditions to favor lawn grasses.
Moss Control in Lawns, http://lancaster.unl.edu/hort/articles/2006/Moss.shtml
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8. Dead patches in lawn - reported in western Nebraska. Brown, dead patches or thinning of cool season lawns may have resulted from perennial ryegrass winterkill, at reported levels of up to 50% this winter.
Another potential cause is late fall 2006 Denver billbug activity, which thinned and weakened some turfgrass stands, resulting in winter stress that killed plants. Overseed affected lawns. Apply the insecticide Imidacloprid when adult billbugs are present.
Billbugs and White Grubs, http://www.ext.colostate.edu/PUBS/insect/05516.html
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9. Leaves falling off of trees – is mostly likely the result of wind damage The combination of stressful weather conditions (rapid fluctuations in temperature, etc) followed by wind, are knocking off the leaves. This does NOT appear to be insects or squirrel damage. Deciduous tree will not be seriously effected and will recover.
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10. Freeze damage – Freezing night temperatures in early April killed flowers, leaves, new growth and some twigs on many woody ornamentals. Many leaves still in the bud stage during the freezes were also partially damaged, resulting in scorched, tattered or misshapen leaves that are now becoming evident. Tattering may look similar to insect damage, but insecticide applications are not necessary or recommended. As new growth resumes, dead twigs and branches should be removed making cuts back to the point of living tissue.
Do not fertilize freeze damaged woody plants. Continue to provide normal watering and mulch throughout the growing season. Prevent secondary damage from opportunistic insects and diseases. Replace severely damaged plants, matching the new plant to the available site.
Oak leaf tatter, http://www.ipm.iastate.edu/ipm/hortnews/1998/5-15-1998/tatters.html
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11. Maple bladder galls - bright red galls that later turn black, usually on the upper leaf surface of maple leaves. When the galls turn black, they may fall off the leaves, resulting in small holes. A few leaves may be so infested that they fall off, but this is not common. These galls are caused by the feeding of a tiny mite and do not affect the health of the tree. If 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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12. Hackberry nipple gall- round green galls are found on most hackberry leaves, and are the result of feeding by the hackberry gall psyllid, which under a microscope look like tiny cicadas. Leaf feeding by psyllids in spring causes the leaf for form a small, hollow pocket of tissue where the psyllid passed the summer, sucking sap from the leaf tissues. No serious damage is done to the tree as a result of psyllid feeding or the presence of the galls, however, aesthetically the galls are very unattractive. Application of Imidacloprid, a liquid, systemic insecticide with up to a year residual effect, can provide some control. Apply the insecticide in fall so it can reach full strength within the tree before the following year’s leaves begin to emerge.
Hackberry Gall Psyllids, http://lancaster.unl.edu/pest/resources/hackberrypsyllids.shtml
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13. Chlorosis- yellowing of leaves, frequently found on pin oaks, silver maple and river birch. Leaves are yellowed, but the veins remain green. In pin oak and birch this condition is due to iron deficiency, however, in maples it is usually due to manganese deficiency. In both cases, there is plenty of iron and manganese in the soil, but high soil pH levels bind up the existing nutrients. Trees with severe, untreated chlorosis develop branch dieback, poor canopy development and eventually death.
In severe cases the best option for pin oak and birch is an iron injection. But this should be done no more than every 3 years to prevent girdling of tree’s vascular system.
Soil treatments that involve acidifying the soil with sulfur are sometimes effective. However, a new method called the Whitcomb treatment has been found to have long-term benefits to chlorotic trees. It involves putting tubes of MicroMax (a micronutrient fertilizer), sulfur, and a general purpose, NPK fertilizer in the soil around the tree.
Whitcomb Chlorosis Treatment, http://extensionhorticulture.unl.edu/Weekly/WhitcombMethod.pdf
Iron Chlorosis in Trees, http://www.oznet.k-state.edu/dp_hfrr/extensn/problems/irnchlor.htm
Iron Chlorosis in Trees, http://www.oznet.ksu.edu/library/forst2/mf718.pdf
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14. Spruce and Fir needle drop- browning of last year’s growth and shedding of needles has been seen in spruce and fir trees this spring. In some cases, symptoms are scattered randomly throughout the tree, in other cases damage is concentrated on one or two sides of the tree. New growth is not affected and in most cases is developing normally. No symptoms of fungal diseases, cankers or insect activity are present, and it is suspected that this damage is environmental in nature. Possibly last year’s needles started to lose their winter hardiness following the two weeks of 60-80 degree temperatures in March and were subsequently damaged by the week of below freezing night temperatures experienced in early April. Normal best maintenance practices are recommended to maintain tree vigor.
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
15. Pine sawflies - clusters of caterpillar-like critters feeding one year old or older needles. They leave new growth alone. These are the larvae of a predatory wasp. They can be knocked off the branch with a stick or water and are unlikely to return. The end of the branch can be cut off. If chemical control is needed, clients can use a permethrin, carbaryl, or an Acephate.
European Pine Sawfly, http://ohioline.osu.edu/hyg-fact/2000/2555.html
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16. Pine tip moth- the larva of several moths tunnel into needles, buds and new shoots, killing the shoots and stunting tree growth. Old infested tips crumble when squeezed. Shoots infested with southwestern pine tip moths commonly turn brown and bend over in a shepherd’s crook. Spray acephate or dimethoate on foliage in spring when new shoots are elongating but before needles are more than ½ inch long. Repeat application in late June or early July.
Pine Tip Moths, http://www.ext.colostate.edu/pubs/insect/05529.html
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17. Spruce spidermites - the mite is a commonly called a 'cool season' mite because it is active during the cooler periods of spring and fall. It is found on all types of conifers including spruce, pine, juniper and arborvitae. Spruce spidermite overwinters as an egg, hatching from March to April. They feed by piercing leaf tissues with a needle-like mouth, and sucking sap from the plant tissues. Conifers often react slowly to the feeding of this mite. Yellowing and bronzing of the needles may not become apparent until the heat of the summer, even though the damage may have occurred the previous fall and spring, and active mites are no longer present.
The mites complete their development in 3 to 4 weeks, going into a dormant egg stage when summer temperatures rise. They may resume activity in the fall when cooler temperatures return.
Spidermites and Their Control, http://ohioline.osu.edu/hyg-fact/2000/2012.html
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18. Balsam twig aphid - twisted or curled needles at the tips of the new growth on spruce or fir trees can be caused by the balsam twig aphid. In most cases the damage is cosmetic and not harmful to the plant. Aphids will be present on the plants until about mid-June, then will be dormant for the rest of the year. Insecticide control for heavily infested trees should be done in April or early May, before new shoot growth begins using Permethrin.
Balsam Twig Aphid, http://www.ext.vt.edu/departments/entomology/factsheets/baltwaph.html
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19. Pine wilt- is now considered to be present throughout the state. Affected trees go off color, sometimes a few branches at a time but more often the entire tree is affected at the same time, and die within a few weeks. Greyhound by Arbor Systems is available for injection to prevent Pine wilt but the approximate cost is $300.00 per tree with a 10” diameter trunk. Scotch pine trees that die need to be removed and chipped or destroyed ASAP.
Pine Wilt: A Fatal Disease of Exotic Pines in the Midwest, http://www.extension.iastate.edu/Publications/SUL9.pdf
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20. Mushroom identification – UNL Extension staff will not identify mushrooms as edible or inedible for mushroom hunters, due to potential liability. In an emergency, clients should call the Poison Control Center at (800) 955-9191.
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21. Winter kill of ornamentals - several perennial ornamental plants have been severely affected by adverse spring weather conditions. Dieback of chrysanthemum, caryopteris (Bluemist spirea), buddleia (Butterfly bush), ‘May Night’ salvia, red hot poker ( Kniphofia uvari) and other ornamentals have been reported.
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22. Rhubarb freeze injury - plants damaged by freezing temperatures had leaves dieback. Vigorous plants have developed new top growth that is firm and healthy, and it is safe to eat. As always, eat only the stems and not the leaves.
