The following is excellent information on common diseases of mums. With the wet weather, growers should be watching for these diseases.
The primary diseases of garden mums are bacterial leaf spot, Fusarium wilt, Pythium root rot, and Rhizoctonia stem rot and foliar blight. Bacterial leaf spot is caused by Pseudomonas cichorii which is often more prevalent following periods of heavy summer rains.
Bacterial leaf spot development is favored by moisture, high humidity, high temperatures, and/or use of susceptible cultivars. Symptoms include dark-brown to black irregularly-shaped spots that can cover half the leaf. Small spots expand to large lesions under wet conditions. The disease typically begins with the lower leaves and will spread upward. For control, avoid growing cultivars that have been destroyed by bacterial leaf spot in the past: cultivars vary immensely in their susceptibility. Copper sprays may reduce disease spread, but use overhead irrigation as little as possible, and irrigate early in the day so that foliage dries off as quickly as possible.
Fusarium wilt is caused by Fusarium oxysporum f. sp. chrysanthemi. It may be received with mum cuttings or picked up by the roots of the growing crop if the area has been contaminated in previous years. Some cultivars may show no symptoms, others may exhibit yellowing or stunting, and some will be severely wilted and die. To minimize Fusarium wilt losses, avoid growing cultivars that have succumbed to the disease in your experience. Drenches with thiophanate-methyl may be helpful. A pH above 6.0 and nitrate rather than ammonium forms of nitrogen will reduce Fusarium wilt losses, but may create other cultural problems.
Pythium aphanidermatum is the species of Pythium most commonly causing root rot losses to mums in recent years. The pathogen thrives in hot, summer weather. Avoid puddling around containers, deep planting or overwatering. Provide even moisture and avoid high EC values: any root stress may open the plant up to Pythium attack. For control (New York recommendations), utilize etridiazole-containing fungicides (Truban, Terrazole, Banrol) at a monthly interval. An occasional treatment with mefenoxam (e.g. SubdueMAXX) is advisable in rotation with the etridiazole, but beware of using mefenoxam exclusively because of widespread fungicide resistance issues with that active ingredient. 5
Rhizoctonia solani is occasionally a problem either as a stem rot or a foliar disease agent. Affected plants will show wilting or tan-to-brown lesions on leaves, depending on the nature of the Rhizoctonia attack. Practice careful sanitation to keep Rhizoctonia under control: do not allow contact between the mum crop and field soil, which is a source of inoculum. A number of fungicides are effective against Rhizoctonia, including thiophanate-methyl (in 3336, 6672, Banrot), strobilurins (e.g. Heritage, Insignia, Compass) and PCNB (Terraclor).
Information from 'Optimizing Garden Mum Production" by Dr. Mark Bridgen, Professor,
Cornell University http://www.canadiangreenhouseconference.com/talks/2008/2008-TK-Bridgen.pdf
Other diseases we see on garden mums in Delaware are Septoria leaf spot which can be controlled with protectant fungicide sprays if started early and foliar nematodes which can be very difficult to control if present and requires the use of systemic insecticides. Gordon Johnson, Extension Horticulture Agent, UD, Kent County
Showing posts with label bacterial leaf spot. Show all posts
Showing posts with label bacterial leaf spot. Show all posts
Monday, August 3, 2009
Sunday, July 5, 2009
Landscape and Greenhouse - Bacterial Leaf Spot on Zinnia
The following is information on bacterial leaf spot of Zinnia, a disease present in landscapes at this time.
Bacterial leafspot on Zinnia has been evident in gardens for several weeks. Look for small angular brown spots with yellow borders on lower leaves. It can spread quickly with wet weather. The disease will move higher on the plants and make them look poorly by fall. There is no effective control at this time. Copper fungicides/bactericides may cause some reduction or halt spread if applied now. Be sure to check the label for safe times to apply. This bacteria can overwinter in old infected leaf tissue and is seed-born, which is the primary source of infections we see. Greenhouse growers should make efforts to eliminate this disease before plants are sold. Suspect plants should be destroyed. Protective sprays of copper may be needed if this is a persistant problem in greenhouse plant production, but be careful with rates to avoid copper injury to plants.
Bacterial leaf spot of Zinnia. Photo by Bob Mulrooney, UD.
Adapted from an article by Bob Mulrooney, Extension Plant Pathologist, UD.
Bacterial leafspot on Zinnia has been evident in gardens for several weeks. Look for small angular brown spots with yellow borders on lower leaves. It can spread quickly with wet weather. The disease will move higher on the plants and make them look poorly by fall. There is no effective control at this time. Copper fungicides/bactericides may cause some reduction or halt spread if applied now. Be sure to check the label for safe times to apply. This bacteria can overwinter in old infected leaf tissue and is seed-born, which is the primary source of infections we see. Greenhouse growers should make efforts to eliminate this disease before plants are sold. Suspect plants should be destroyed. Protective sprays of copper may be needed if this is a persistant problem in greenhouse plant production, but be careful with rates to avoid copper injury to plants.
Bacterial leaf spot of Zinnia. Photo by Bob Mulrooney, UD.Adapted from an article by Bob Mulrooney, Extension Plant Pathologist, UD.
Thursday, June 4, 2009
Landscape - Leaf Spots on Ivy
Wet weather can favor leaf spots in English Ivy. The following is more information.
Frequent rain events can promote leaf spot diseases in many English ivy beds. In the landscape, there are two important English Ivy (Hedera) leaf spot diseases, one caused by a fungus and the other caused by a bacterium. The two diseases are sometimes difficult to tell apart, however, the bacterial leaf spot tends to occur more frequently in summer.
Fungal leaf spot (anthracnose) appears as large, irregularly shaped tan or brown spots. Within the dead spots numerous slightly raised dark blister-like fungal fruiting structures may be observed when examined with a hand lens. The dead areas may be surrounded by a yellow “halo.” The causal fungus is Glomerella cingulata, however, the imperfect fungal state, Colletotrichum trichellum is normally seen now. Close examination with a hand lens may show spine-like formations associated with the fungal fruiting structures though they are not always present. There are other fungal leaf spot diseases of English Ivy which also produce fungal fruiting structures; this distinguishes them from bacterial spot, which produces none.
Growers should avoid planting diseased plant material, and avoid sprinkler irrigation which splashes fungal spores from diseased to healthy plants. To prevent fungal leaf spot disease, treatments with fungicides containing fixed copper, thiophanate-methyl, or mancozeb can be tried. These fungicides will not “cure” already infected leaves.
Bacterial leaf spot is favored by periods of warm, wet weather typical of summer. This disease, caused by the bacterium Xanthomonas hortorum (campestris) pv. hederae, can be especially damaging to Ivy growing in many landscapes. The bacteria invade leaves, shoots, and stems through stomata and wounds causing a greenish-brown angular leaf spot 1/4 to 1/2 inch or larger in size. The spots sometimes appear greasy and may have a yellow margin; as they age, spots turn dark brown and may crack as they dry. Rainstorms and overhead irrigation help spread the disease in the landscape by splashing bacteria from diseased to healthy plants.
Bacterial leaf spot disease is diagnosed in the laboratory by observing bacterial streaming under the microscope, however, the disease is often so active that county agents or landscape industry specialists can also diagnose the disease in the field in the same way. Cut through several leaf spots with a sharp knife and place small infected leaf pieces on a glass slide. Add a drop or two of clean water to the infected tissue and cover with a small glass cover slip. After a few minutes to an hour, bacterial streaming can be seen just by holding the glass slide up to the light and observing the milky color of the water near the dissected leaf spot. Fungal spots do not produce bacterial streaming as described above.
Avoid sprinkler irrigation. Treatment with copper-based fungicides is helpful in slowing the spread of bacterial leaf spot.
Information from "Leaf Spot Can Damage English Ivy" By John Hartman in the current edition of the Kentucky Pest News.
Frequent rain events can promote leaf spot diseases in many English ivy beds. In the landscape, there are two important English Ivy (Hedera) leaf spot diseases, one caused by a fungus and the other caused by a bacterium. The two diseases are sometimes difficult to tell apart, however, the bacterial leaf spot tends to occur more frequently in summer.
Fungal leaf spot (anthracnose) appears as large, irregularly shaped tan or brown spots. Within the dead spots numerous slightly raised dark blister-like fungal fruiting structures may be observed when examined with a hand lens. The dead areas may be surrounded by a yellow “halo.” The causal fungus is Glomerella cingulata, however, the imperfect fungal state, Colletotrichum trichellum is normally seen now. Close examination with a hand lens may show spine-like formations associated with the fungal fruiting structures though they are not always present. There are other fungal leaf spot diseases of English Ivy which also produce fungal fruiting structures; this distinguishes them from bacterial spot, which produces none.
Growers should avoid planting diseased plant material, and avoid sprinkler irrigation which splashes fungal spores from diseased to healthy plants. To prevent fungal leaf spot disease, treatments with fungicides containing fixed copper, thiophanate-methyl, or mancozeb can be tried. These fungicides will not “cure” already infected leaves.
Bacterial leaf spot is favored by periods of warm, wet weather typical of summer. This disease, caused by the bacterium Xanthomonas hortorum (campestris) pv. hederae, can be especially damaging to Ivy growing in many landscapes. The bacteria invade leaves, shoots, and stems through stomata and wounds causing a greenish-brown angular leaf spot 1/4 to 1/2 inch or larger in size. The spots sometimes appear greasy and may have a yellow margin; as they age, spots turn dark brown and may crack as they dry. Rainstorms and overhead irrigation help spread the disease in the landscape by splashing bacteria from diseased to healthy plants.
Bacterial leaf spot disease is diagnosed in the laboratory by observing bacterial streaming under the microscope, however, the disease is often so active that county agents or landscape industry specialists can also diagnose the disease in the field in the same way. Cut through several leaf spots with a sharp knife and place small infected leaf pieces on a glass slide. Add a drop or two of clean water to the infected tissue and cover with a small glass cover slip. After a few minutes to an hour, bacterial streaming can be seen just by holding the glass slide up to the light and observing the milky color of the water near the dissected leaf spot. Fungal spots do not produce bacterial streaming as described above.
Avoid sprinkler irrigation. Treatment with copper-based fungicides is helpful in slowing the spread of bacterial leaf spot.
Information from "Leaf Spot Can Damage English Ivy" By John Hartman in the current edition of the Kentucky Pest News.
Saturday, April 11, 2009
Greenhouse - Geranium Pointers and Troubleshooting
The following are some pointers and troubleshooting hints for geranium production from the University of Maryland.
Sudden pH Drops:
Your geraniums may be humming along but make sure you are maintaining a correct pH level. If you let the pH fall off the plants will go downhill rapidly. Check your pH level at least weekly to detect any downward turns. There is a condition called sudden pH decline (SPD) where geranium crops growing at the optimum pH rapidly (1- 2 weeks) have the substrate pH shift downward 1 to 2 units. Taylor et al., 2008, reports that this occurs when phosphorus is deficient in the substrate and high temperatures cause stress of the geranium crops.
Proper pH:
The optimal pH varies by the type of geranium and root medium used. For zonal geraniums, the range for a soilless root medium is 5.8 to 6.2 and for a soil-based medium is 6.0 to 6.5. The optimal range is up to 0.3 units lower for ivy and regal geraniums (5.5 - 6.2). If modifications are required, the pH can be lowered with an acid-based fertilizer or acid injection. The pH can be increased with dolomitic limestone or hydrated lime.
Electrical Conductivity (EC):
The optimal EC range is 1.5 to 2.5 mS/cm for zonal and regal geraniums. Slightly lower levels are required by ivy geraniums, usually 1.0 – 2.0 mS/cm. Aphids on Geraniums: Monitor ivy geraniums for melon aphids and green peach aphids. We are seeing populations increasing in some greenhouses this week.
Control: Imidacloprid (Marathon), dinotefuran (Safari), Acetamiprid (TriStar), Endeavor, Aria, insecticidal soaps.
Diseases to watch out for on Geraniums:
One disease to watch out for on geraniums is bacterial leaf spot. This disease is caused by the bacterium Xanthomonas pelargonii and is especially prevalent in warm, wet weather where plants are grown in crowded conditions. Disease symptoms include small (pinhead size), circular or irregular, brown, sunken spots on older or lower leaves. Large numbers of spots will occur on a single leaf, these will coalesce and can kill a large portion of the leaf which will then drop off. As the disease moves through the plant, the lower leaves wilt and yellow. In severe cases, the stem will possess black stem cankers killing the upper portion of the stem. Leaves infected with bacterial leaf spot should be removed as soon as it is noticed. Severely infected plants should be removed.
Monitor for Botrytis leaf spot or blossom blight. It is caused by Botrytis cinerea. Botrytis is favored under cool, moist conditions or where plants are watered frequently. Leaves develop zonate, brown leaf lesions which develop a grayish brown mass of fungal spores. The lower leaves will yellow and rot. Flowers may also become infected. They show discolored petals which wilt and fall. Remove affected leaves and flowers. Maintain good air circulation in the greenhouse.
Reprinted from the April 3, 2009 edition of the Greenhouse TPM/IPM Bi-Weekly Report from the University of Maryland Cooperative Extension, Central Maryland Research and Education Center http://www.ipmnet.umd.edu/09Apr03G.pdf
Sudden pH Drops:
Your geraniums may be humming along but make sure you are maintaining a correct pH level. If you let the pH fall off the plants will go downhill rapidly. Check your pH level at least weekly to detect any downward turns. There is a condition called sudden pH decline (SPD) where geranium crops growing at the optimum pH rapidly (1- 2 weeks) have the substrate pH shift downward 1 to 2 units. Taylor et al., 2008, reports that this occurs when phosphorus is deficient in the substrate and high temperatures cause stress of the geranium crops.
Proper pH:
The optimal pH varies by the type of geranium and root medium used. For zonal geraniums, the range for a soilless root medium is 5.8 to 6.2 and for a soil-based medium is 6.0 to 6.5. The optimal range is up to 0.3 units lower for ivy and regal geraniums (5.5 - 6.2). If modifications are required, the pH can be lowered with an acid-based fertilizer or acid injection. The pH can be increased with dolomitic limestone or hydrated lime.
Electrical Conductivity (EC):
The optimal EC range is 1.5 to 2.5 mS/cm for zonal and regal geraniums. Slightly lower levels are required by ivy geraniums, usually 1.0 – 2.0 mS/cm. Aphids on Geraniums: Monitor ivy geraniums for melon aphids and green peach aphids. We are seeing populations increasing in some greenhouses this week.
Control: Imidacloprid (Marathon), dinotefuran (Safari), Acetamiprid (TriStar), Endeavor, Aria, insecticidal soaps.
Diseases to watch out for on Geraniums:
One disease to watch out for on geraniums is bacterial leaf spot. This disease is caused by the bacterium Xanthomonas pelargonii and is especially prevalent in warm, wet weather where plants are grown in crowded conditions. Disease symptoms include small (pinhead size), circular or irregular, brown, sunken spots on older or lower leaves. Large numbers of spots will occur on a single leaf, these will coalesce and can kill a large portion of the leaf which will then drop off. As the disease moves through the plant, the lower leaves wilt and yellow. In severe cases, the stem will possess black stem cankers killing the upper portion of the stem. Leaves infected with bacterial leaf spot should be removed as soon as it is noticed. Severely infected plants should be removed.
Monitor for Botrytis leaf spot or blossom blight. It is caused by Botrytis cinerea. Botrytis is favored under cool, moist conditions or where plants are watered frequently. Leaves develop zonate, brown leaf lesions which develop a grayish brown mass of fungal spores. The lower leaves will yellow and rot. Flowers may also become infected. They show discolored petals which wilt and fall. Remove affected leaves and flowers. Maintain good air circulation in the greenhouse.
Reprinted from the April 3, 2009 edition of the Greenhouse TPM/IPM Bi-Weekly Report from the University of Maryland Cooperative Extension, Central Maryland Research and Education Center http://www.ipmnet.umd.edu/09Apr03G.pdf
Friday, October 10, 2008
Greenhouse - Bacterial Leaf Spot of Poinsettia
Bacterial leaf spot can be a problem on poinsettias. The following is some information.
Watch for bacterial leaf spots on poinsettias. Xanthomonas leaf spot on poinsettias begins with dull gray water-soaked areas. Yellow or tan spots can develop across the leaf. As the disease progresses, spots turn brown and angular so it could be confused with poinsettia scab. It is a good idea to send samples to the diagnostic laboratory if you see leaf spot symptoms.
Like all bacterial diseases, Xanthomonas is spread by water splash from overhead irrigation, high humidity and close plant spacing. If detected early, discarding plants showing symptoms and reducing leaf wetness help reduce disease spread. The use of bactericides such as Bacillus subtilus (Cease) or coppers (Phyton 27) may also help.
Reprinted from "Xanthomonas Leaf Spot on Poinsettias" by Leanne Pundt, University of Connecticut in the New England Greenhouse Update http://www.negreenhouseupdate.info/greenhouse_update/index.php.
Watch for bacterial leaf spots on poinsettias. Xanthomonas leaf spot on poinsettias begins with dull gray water-soaked areas. Yellow or tan spots can develop across the leaf. As the disease progresses, spots turn brown and angular so it could be confused with poinsettia scab. It is a good idea to send samples to the diagnostic laboratory if you see leaf spot symptoms.
Like all bacterial diseases, Xanthomonas is spread by water splash from overhead irrigation, high humidity and close plant spacing. If detected early, discarding plants showing symptoms and reducing leaf wetness help reduce disease spread. The use of bactericides such as Bacillus subtilus (Cease) or coppers (Phyton 27) may also help.
Reprinted from "Xanthomonas Leaf Spot on Poinsettias" by Leanne Pundt, University of Connecticut in the New England Greenhouse Update http://www.negreenhouseupdate.info/greenhouse_update/index.php.
Friday, April 11, 2008
Greenhouse and Landscape - Current Disease and Insect Issues
The following are some current pest issues in greenhouse crops and landscapes in Delaware and the nearby region.
Sclerotinia is being found in bedding plants in greenhouses. It has been seen on on lobelia and petunia. Please be on the look-out for this, as it may be a supplier issue. Plants can die quickly and have sclerotia at the base. A chlorotic ringspot virus is being found on angelonia (a chlorotic ringspot), and bacterial black leaf spot is being found on celosia.
In the landscape, Juniper webworm has been found, Eastern tent caterpillars are actively feeding and White pine sheath mites should be active. Diagnostic lab samples have been mostly overwintering insects (scales).
Sclerotinia is being found in bedding plants in greenhouses. It has been seen on on lobelia and petunia. Please be on the look-out for this, as it may be a supplier issue. Plants can die quickly and have sclerotia at the base. A chlorotic ringspot virus is being found on angelonia (a chlorotic ringspot), and bacterial black leaf spot is being found on celosia.
In the landscape, Juniper webworm has been found, Eastern tent caterpillars are actively feeding and White pine sheath mites should be active. Diagnostic lab samples have been mostly overwintering insects (scales).
Friday, July 13, 2007
Ornamentals Hotline Disease Pictures For Issue 16, July 13, 2007
Bacterial Leaf Spot of Zinnia 
Aster Yellows on Rudbeckia 
Aster Yellows on Coneflower 
Brown Patch on Tall Fescue Leaves All Disease Pictures by Bob Mulrooney, University of Delaware, Extension Plant Pathologist
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