Chrysanthemum Fusarium Control – Treating Mums With Fusarium Wilt
By: Mary Ellen Ellis
Chrysanthemums, or mums, are hardy favoritesfor cooler weather. Their pretty, cheerful flowers brighten up spaces whenothers won’t grow. One disease to watch out for with your mums is fusarium wilt. This fungal disease, caused by Fusariumoxysporum, is transmitted through roots to vascular tissue and can be verydestructive to plants.
Identifying Mums with Fusarium Wilt
It is easy to misidentify fusarium on mum plants as rootrot, but there are some key differences. One sign of either problem iswilting of leaves, but with fusarium it may occur only on one side or part ofthe plant. Also, roots look healthy when fusarium is the issue.
Yellowing or browning of leaves follows wilting. The plant’sgrowth will be stunted and it may not produce any flowers. If you cut a stem ona mum with fusarium wilt, you can see browning in the vascular tissue.
Does Fusarium Kill Mums?
Unfortunately, yes, this fungal infection will killchrysanthemum plants if not managed properly. It is important to know andrecognize the signs of the disease. If you catch it early, you should be ableto destroy the diseased plant material and prevent it from spreading to otherplants.
Chrysanthemum Fusarium Control
The most important thing you can do control chrysanthemumfusarium wilt is to buy plants that are certified disease free. The fusariumfungus can survive for years in soil, so it can be difficult to eliminate ifyou get it in your garden.
If you do see signs of wilt in your mums, destroy theaffected plant material immediately. Clean any tools or pots thoroughly to prevent the spread of thefungus. Always clean up plant waste from the area where you grow chrysanthemumsto keep fungus from building up in the soil.
Another step you can take if fusariumhas gotten a foothold in your garden is to amend the pH of the soil. A pH between 6.5 and 7.0 willbe unfavorable to the fungus.
Adding fungicide to the soil will also help control it.Check with your local garden center or extensionoffice to find out what type of fungicide is best.
This article was last updated on
Read more about Chrysanthemums
Leaf spots: Chrysanthemums are subject to several leaf spot fungi including Septoria chrysanthemi, S. chrysanthemella, Alternaria species, and Cercospora chrysanthemi. Symptoms first appear as yellow spots which turn brown to black. Spots often occur on lower leaves first and can coalesce into large necrotic areas and finally death of the entire leaf. Small black fruiting bodies may be seen in the lesions of some leaf spot fungi. Leaf spot diseases are encouraged by prolonged periods of leaf wetness and high relative humidity.
Practice good greenhouse sanitation. Regularly clean up and destroy infected plant debris and hand pick symptomatic leaves from lightly infested plants. Workers should be wash their hands frequently. Avoid splashing water onto plant foliage if possible. If overhead irrigation must be used, water early in the day to allow foliage to dry quickly. In severe cases, applications of fungicides containing azoxystrobin, chlorothalonil, fludioxonil, mancozeb, myclobutanil, propiconazole, or thiophanate methyl may be applied according to label instructions. Septoria leaf spot was once a more common problem in chrysanthemum production than it is now, largely due to the use of fungicides and plant sanitation programs that ensure clean stock.
Powdery mildew (Golovinomyces cichoracearum) is characterized by a white to ash-gray powdery growth on leaves and occasionally stems. Leaves may become distorted severely infected leaves will shrivel and die. The disease is most serious during hot, humid weather. Unlike most fungal diseases, free water is not required for powdery mildew infection, but high humidity encourages disease development. Management is similar to that of leaf spots. Powdery mildew can be minimized by proper plant spacing, good air circulation, low relative humidity, and adequate light levels. Apply preventive fungicides at the first sign of disease with the active ingredients copper, azoxystrobin, pyraclostrobin, triflumizole, myclobutanil, triadimefon, propiconazole, sulfur, potassium bicarbonate, horticultural oil, or thiophanate methyl according to label instructions.
Gray mold (Botrytis cinerea ) may occur on petals, leaves, or stem cankers as brown, water-soaked spots. Infected plant parts may be covered with gray to brown, powdery masses of spores. Infected buds fail to open. Tender new growth and senescing tissues are most susceptible. Gray mold is favored by extended periods of cloudy, humid, wet weather. The pathogen gains a foothold in small wounds, then progresses to cause disease in healthy tissues.
Practice good sanitation including removing senescing flowers and leaves. Avoid wetting flowers when watering and don't overcrowd the plants. Provide good air circulation and keep humidity down to 80°F, and high humidity. It is easily spread on infested tools, hands, or plants. Start with pasteurized growing media, use pathogen-free stock plants, reduce humidity and increase air circulation, avoid wetting foliage, and practice good sanitation. Regularly inspect crops and dispose of infected plants.
Foliar nematodes (Aphelenchoides ritzemabosi and A. fragariae): Nematodes are microscopic roundworms that live in the soil or in infested plant material. They swim in a film of water on wet plant surfaces and enter leaves through stomata. The development of yellow to brown, V-shaped lesions on lower leaves which advance up the plant is a good indication of nematode infection. Lesions are delimited by leaf veins. Lesions on the leaves eventually coalesce to cover the entire leaf which dies, withers, and falls. Carefully inspect cuttings and plants received from propagators. Remove infested plants and crop debris. Avoid wetting the foliage and overhead irrigation. Both A. ritzemabosi and A. fragariae have wide host ranges and can infect many common ornamentals.
Viruses and other infectious agents: Chrysanthemums are susceptible to a large number of virus diseases including Chrysanthemum Mosaic Virus, Cucumber Mosaic Virus, Impatiens Necrotic Spot Virus, and Tomato Spotted Wilt Virus. Viroid diseases include Chrysanthemum chlorotic mottle viroid and Chrysanthemum stunt viroid. Symptoms of virus and viroid infected plants can be similar and include stunting, spindly growth, and formation of dense rosettes. Flowers may be small, distorted or exhibit streaking and color break. Leaf symptoms are diverse and may appear as leaf yellowing, ring spots, lines, mottling, mosaics, vein clearing, distortion, crinkling, wilt and leaf drop.
Aster Yellows is a serious disease caused by organisms called phytoplasmas. It results in chlorotic foliage, plant stunting, profusion of spindly upright yellow shoots (witches' brooms), few or no flowers, flower distortion, transformation of flowers into leaves and shoots (phyllody), and yellow-green discoloration of flowers (virescence). Aster yellows is transmitted by the feeding activity of the Aster leafhopper (Macrosteles quadrilineatus, AKA M. fascifrons).
There is no cure for virus, viroid, or phytoplasma infected plants. Start with pathogen-free plants from a culture indexing program. Remove and destroy infected plants. Remove weeds that may also be hosts for pathogens and/or their vectors. Control the insects that transmit these diseases. Disinfect tools and equipment frequently.
Pythium Root Rot
Pythium spp. are water mold pathogens that favor cool and wet conditions. Water molds produce swimming spores that move in freestanding water that may puddle underneath pots. Pythium infects at the tip of the roots and then colonize the root system, causing root damage and loss.
Signs of poor root health are blackened or rotted roots. Thus, plants will wilt from lack of water uptake. Diseased roots will not take up fertilizer, compounding the problem with high soluble salts in the growing medium.
Research shows fungicides effective in fighting Fusarium wilt of watermelon
by American Phytopathological Society
Patchy distribution of diseased and healthy watermelon plants. Credit: Jeff Standish
Fusarium wilt is one of the most economically important diseases of watermelon and a major problem to growers worldwide. In the past, watermelon growers based in the Southeastern United States were able to use methyl bromide to manage this disease, but this is no longer an option due to environmental concerns.
There are two fungicides available, but, until recently, little information was available on the efficacy of these two chemicals, Prothioconazole and pydiflumetofen, against Fusarium wilt in North Carolina. As a result, North Carolina State University plant pathologists sought to characterize Fusarium wilt under seven fungicide programs and determine the efficacy.
Their results show that both fungicides provide effective control of Fusarium wilt, regardless of application rate or method. According to Jeff Standish, one of the scientists behind this research, "Based on our results, pydiflumetofen and prothioconazole were equally as effective at reducing Fusarium wilt, and pydiflumetofen seemed to be more effective at preserving yield when disease was severe. This provides evidence that pydiflumetofen could be used as an additional mode of action for watermelon growers, which will likely reduce selection for fungicide resistance."
"Documenting that efficacy of pydiflumetofen was similar to that of prothiconazole regardless of rate was a nice and surprising finding," Standish explains, adding that "Despite there only being one year of yield data, the plants grown in nontreated control plots produced no marketable fruit, which really highlights the importance of managing this disease."
Before the publication of this work, the sensitivity of Fusarium oxysporum f. sp. Niveum (the fungus that causes Fusarium wilt) isolates to pydiflumetofen had never been described. This knowledge will be useful for determining when and if fungicide resistance management strategies are needed in the future.
More details about this development can be found in "Sensitivity of Fusarium oxysporum f. sp. niveum to Prothioconazole and Pydiflumetofen In Vitro and Efficacy for Fusarium Wilt Management in Watermelon" published in Plant Health Progress Volume 20, Issue 1.
Common diseases diagnosed in recent years have been root rots caused by Pythium and Rhizoctonia and bacterial leaf spot (Pseudomonas cichorii). Fusarium wilt occurs when cuttings are infected or soil is contaminated with the pathogen. Leaf spots caused by Alternaria, Botrytis and Septoria are not common on mums but occur ocassionally. White rust (Puccinia horiana), also not common, has shown up in the Northeast in recent years.
Mums suffering from root diseases will often look nutrient deficient and they are, considering the roots are not functioning correctly. Plants with root rot often look stunted, wilted and have veinal reddening even when adequate nutrition is being applied. Fungicide drenches for root rots include, thiophanate methyl & etridiazole (Banrot) for Pythium and Rhizoctonia mefenoxam (Subdue MAXX), etridiazole (Truban) propamocarb (Banol) for Pythium and fludioxonil (Medallion), thiophanate methyl (Cleary's 3336, Fungo Flo) or iprodione (Sextant) for Rhizoctonia.
Fusarium is a vascular disease that develops within stems. Fusarium wilt results in symptoms similar to root rot but plants infected with Fusarium generally wilt in sectors, or one branch at a time and roots often appear healthy. Root rot usually results in the entire plant wilting. In later stages of Fusarium wilt, a white or pinkish fluffy mold may develop on the affected stems. Managing Fusarium centers on disease-free cuttings and pathogen-free root media. Thiophanate methyl (Cleary's 3336) and fludioxonil (Medallion) have been reported to suppress Fusarium.
Bacterial leaf spot, caused by Pseudomonas cichorii often occurs during hot humid weather in August. This disease tends to be problematic during years of heavy rains or where overhead watering is practiced. Plants with this disease have large black spots concentrated at the base of the plant. The spots often begin at the leaf margin but may also occur randomly. From the leaf, the bacterium can move through the petiole and into the stem resulting in a canker. The sepals of infected flower buds will become brown to black and up to several inches of pedicel may be killed. Copper hydroxide sprays such as Kocide 101 77 WP or Phyton 27 will help protect against this disease. These materials do not cure the disease, they limit spreading to uninfected plants. Also there are differences in cultivar susceptibility. Make notes when you see susceptible varieties and avoid growing them in the future.
Alternaria, Botrytis and Septoria can be managed using thiophanate methyl (Cleary's 3336), iprodione (Sextant), chlorothalonil (Daconil Ultrex, Pathguard 6F), chlorothalonil & thiophanate methyl (Spectro 90 WDG) or fludioxonil (Medallion). As the plants grow rapidly in August and develop a dense canopy of leaves, treatments may be necessary. White rust (Puccinia horiana) is a federally quarantined pathogen. Look for white to yellow spotting on the upper sides of the foliage with corresponding pustules of white spores which look bumpy on the undersides of leaves. Cooler weather conditions in fall tend to favor this disease. Although not a common disease, be aware of it. Materials used to protect against rust contain chlorothalonil (Daconil Ultrex, Pathguard 6F), mancozeb (Dithane T/O), azoxystrobin (Heritage), trifloystrobin (Compass), propiconazole (Banner Maxx) and triadimefon (Bayleton). Bacterial leaf spot and foliar diseases are spread by splashing water, which is why we see more of these diseases during rainy years. Drip irrigation helps to prevent foliar diseases. If overhead watering, foliage should always be dry before evening hours.