Hort Update for the week of 5/22/06
1. Ash rust is not a serious disease and control is not needed on established trees. Leaves and petioles of ash may become twisted and distorted and bright, orange to yellowish powdery cups form on the leaves. Some leaf drop may occur.
2. Rose rust first appears on the undersides of leaves and other plant parts as orange powdery "pustules". Plant resistant varieties. Follow good sanitation by removing infected stems and leaves at first appearance of the disease. Careful pruning of old canes helps reduce rust carry-over on the canes and promotes air movement and drying of leaves. Use preventive fungicides [chlorothalonil (Daconil 2787)] or systemic fungicides [triadimefon or triforine (Funginex)].
3. Sycamore anthracnose is fungal disease that infects leaves and twigs. It can cause severe defoliation but this is not a problem on mature trees. They will releaf. There is no treatment once the disease appears. Trees must be treated with a fungicide just as the leaves unfurl in spring to provide control. Unless it is a highly valuable tree, there is no need to treat.
More online info: Sycamore anthracnose
4. Ash anthracnose is similar to sycamore anthracnose. The leaves will look deformed and fall off. The tree will re-leaf. If it is a valuable tree, the client can treat in the spring just as the leaves are unfurling with a fungicide. Otherwise, anthracnose usually does not seriously harm mature trees.
5. Maple Bladder galls - tiny mites are the cause of these bright red galls that turn black and cause some leaf drop. Galls do not affect the health of the tree. If desired, the time to treat is with a dormant oil just as the buds swell in spring. No treatments work once the galls are visible.
6. Herbicide drift - leaves usually cupped, veins distorted and stems curled or twisted. If the client has not sprayed for weeds, then the usual culprit is from weed killer being sprayed in the neighborhood. Mature trees and shrubs usually recover.
7. Peony thrips - buds not opening, or open partially, but flower is partially bad. Most likely cause is thrips. These are tiny insects that can get into the bud and suck out the nutrients and can cause serious damage. Thrips are difficult to control because they can get into an unopened bud where insecticides can’t reach. Insecticidal sprays can control thrips on the leaves and opened flowers. A systemic insecticide may help. Next year, use an insecticide before the buds form.
8. European currant caterpillar - on currants and other species in the Ribes family. One generation per year. Must use insecticides labeled for food crops.
9. 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.
10. Yellow nutsedge – Hand-pull until about mid June to avoid tuber (often called nutlets) production. Improve soil drainage with core aeration and avoid over-watering. The herbicide Manage (Halosulfuron) is no longer being produced to control it, but is still be available at retail outlets for homeowners to purchase and apply. Certainty (Sulfosulfuron) is a new product that can only be applied by commercial applicators.
11. Ash trees dying from top down - Dr. Mark Harrell with the UNL Forest Service has had calls about this. He is not sure of the cause. It is unlikely to be emerald ash borer. If you get calls, ask if we can pass the client’s information on to Mark or e-mail him at mharrell2@unl.edu. He will be inspecting some trees.
| Current Problems: | Major Symptom: |
| 1. Ash rust | Small, bright orange or yellowish pustules on leaves |
| 2. Rose rust | Small, bright orange or yellowish pustules on leaves |
| 3. Sycamore anthracnose | Leaves with brown blighted dropping off trees |
| 4. Ash anthracnose | Leaves with brown blighted dropping off trees |
| 5. Maple bladder gall | Bright red bladder shaped galls on leaves that turn black |
| 6. Herbicide drift | Cupping of leaves. Vein distortion. Curling of stems. |
| 7. Peony thrips | Buds not opening or opening partially. Petals brown. |
| 8.European Currant Caterpillar | |
| 9. Pine sawflies | Numerous “worms” feeding in clusters on older needles |
| 10. Yellow nutsedge | 3-ranked, yellow-green, waxy grass-like leaved weed |
| 11. Ash Trees dying from top down |
1. Ash rust is not a serious disease and control is not needed on established trees. Leaves and petioles of ash may become twisted and distorted and bright, orange to yellowish powdery cups form on the leaves. Some leaf drop may occur.
2. Rose rust first appears on the undersides of leaves and other plant parts as orange powdery "pustules". Plant resistant varieties. Follow good sanitation by removing infected stems and leaves at first appearance of the disease. Careful pruning of old canes helps reduce rust carry-over on the canes and promotes air movement and drying of leaves. Use preventive fungicides [chlorothalonil (Daconil 2787)] or systemic fungicides [triadimefon or triforine (Funginex)].
3. Sycamore anthracnose is fungal disease that infects leaves and twigs. It can cause severe defoliation but this is not a problem on mature trees. They will releaf. There is no treatment once the disease appears. Trees must be treated with a fungicide just as the leaves unfurl in spring to provide control. Unless it is a highly valuable tree, there is no need to treat.
More online info: Sycamore anthracnose
4. Ash anthracnose is similar to sycamore anthracnose. The leaves will look deformed and fall off. The tree will re-leaf. If it is a valuable tree, the client can treat in the spring just as the leaves are unfurling with a fungicide. Otherwise, anthracnose usually does not seriously harm mature trees.
5. Maple Bladder galls - tiny mites are the cause of these bright red galls that turn black and cause some leaf drop. Galls do not affect the health of the tree. If desired, the time to treat is with a dormant oil just as the buds swell in spring. No treatments work once the galls are visible.
6. Herbicide drift - leaves usually cupped, veins distorted and stems curled or twisted. If the client has not sprayed for weeds, then the usual culprit is from weed killer being sprayed in the neighborhood. Mature trees and shrubs usually recover.
7. Peony thrips - buds not opening, or open partially, but flower is partially bad. Most likely cause is thrips. These are tiny insects that can get into the bud and suck out the nutrients and can cause serious damage. Thrips are difficult to control because they can get into an unopened bud where insecticides can’t reach. Insecticidal sprays can control thrips on the leaves and opened flowers. A systemic insecticide may help. Next year, use an insecticide before the buds form.
8. European currant caterpillar - on currants and other species in the Ribes family. One generation per year. Must use insecticides labeled for food crops.
9. 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.
10. Yellow nutsedge – Hand-pull until about mid June to avoid tuber (often called nutlets) production. Improve soil drainage with core aeration and avoid over-watering. The herbicide Manage (Halosulfuron) is no longer being produced to control it, but is still be available at retail outlets for homeowners to purchase and apply. Certainty (Sulfosulfuron) is a new product that can only be applied by commercial applicators.
11. Ash trees dying from top down - Dr. Mark Harrell with the UNL Forest Service has had calls about this. He is not sure of the cause. It is unlikely to be emerald ash borer. If you get calls, ask if we can pass the client’s information on to Mark or e-mail him at mharrell2@unl.edu. He will be inspecting some trees.
