How to treat powdery mildew on dogwood trees
Dogwoods Might Need Help Overcoming Powdery Mildew
— Written By Jessica Strickland and last updated by Diane Lynchen Español
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Q: What is this white powdery stuff I’m finding on the leaves of my dogwood?
A: We have had several samples and questions come into the office over the past couple of weeks dealing with white powdery growth on dogwood leaves.
Powdery mildew is a disease which is common on many ornamental trees and shrubs, including dogwoods. Powdery mildew is a powdery white to light gray-colored fungus that will grow on succulent stems, leaves, buds, and flowers. Young plants and new growth are usually more severely damaged than older plants, leaves, or branches. Parts of the plant that are severely infected will usually look distorted and stunted.
Powdery mildew usually occurs in the spring and autumn months during cool weather. Powdery mildew will also show up in shady, damp locations especially where plants are crowded and air circulation is poor. High humidity and rainy conditions (like we had in early May) are good environmental conditions for powdery mildew to occur.
The good news is there are several control measures that can be followed in order to prevent and treat powdery mildew. If you are getting ready to purchase a dogwood, you can immediately manage powdery mildew by purchasing a resistant variety and avoiding susceptible varieties. The level of resistance to powdery mildew varies for particular dogwoods. Location and environmental conditions can also affect the level of resistance in some dogwood varieties. Some dogwood varieties will have good to excellent resistance to powdery mildew, while others will be very susceptible. When shopping for dogwoods note the variety and check for the extent of resistance.
When pruning a dogwood, thin the canopy so that you allow good air circulation throughout the tree. Good air circulation will allow the leaf surface to dry out more quickly after a rain and will reduce wet surfaces for powdery mildew to show up on. Pruning out severely diseased portions of the plant will also help reduce the disease if only a few parts are infected.
If the disease is severe enough, there are some chemical control options available. For a fungicide spray to be effective it should start before the disease appears usually when the flower buds begin to open. A second spray should be made when the leaves are unfolding, a third spray about the last week in July and a fourth before leaf drop in the fall. Full coverage of the plant is necessary. Available fungicides to control powdery mildew on dogwoods and many other trees and shrubs include: myclobutanil (Eagle, Immunox), propiconazole (Banner), horticultural oil (do not apply when temperature is greater than 90°F) and copper-based fungicidies. When using any type of pesticide remember to read the label and follow directions.
For additional lawn and garden information contact the Wayne County Extension Master Gardener Volunteer Plant Clinic on Mondays and Wednesdays from 10 a.m. to 1 p.m. One can reach the Wayne County Extension Master Gardener Volunteer Plant Clinic by phone at 919-731-1433, e-mail at [email protected], or stopping by Room 100 of the Wayne County Extension Office (208 West Chestnut Street, Goldsboro).
Recommendations for the use of agricultural chemicals are included in this article as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this article does not imply endorsement by North Carolina Cooperative Extension nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical.
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How to Get Rid of Powdery Mildew on Dogwood | Home Guides
By Nathalie Alonso Updated August 12, 2021
Dogwoods (Cornus spp.) are spring-blooming ornamental deciduous trees. Hardy in U.S. Department of Agriculture zones 4 through 9, most varieties are extremely vulnerable to powdery mildew, a dogwood tree mold that affects the appearance of the leaves. Preventing this disease is easier than controlling it once it develops. You can avoid this problem by choosing species and cultivars that are resistant to powdery mildew.
Powdery Mildew on Dogwoods
If your dogwood tree is infected with powdery mildew, you will observe a powdery coating on the leaves and buds that may be white or light gray. Warm, dry days and cool, humid nights are most conducive to powdery mildew growth on dogwood trees, which is why this condition often develops in the spring and autumn months, explains the NC Cooperative Extension Wayne County Center. The fungus grows best in shady, humid parts of trees.
Wind helps to spread the fungal spores that cause powdery mildew from one dogwood tree to another. While powdery mildew will rarely kill a dogwood tree, it can weaken the leaves and make the plant more susceptible to other pests and diseases. Severely infected trees can become stunted and less tolerant of winter temperatures. New growth tends to be more susceptible to powdery mildew damage than established branches and leaves. Affected leaves may be distorted.
Best Fungicide for Powdery Mildew
While fungicides will not save a dogwood tree leaf that has been damaged by powdery mildew, these chemicals can help stop the disease from spreading. According to the Clemson Cooperative Extension, myclobutanil and propiconazole are the best fungicides for powdery mildew. Fungicides work best before signs of the diseases are evident. The NC Cooperative Extension Wayne County Center recommends spraying affected dogwood trees four times: before buds open, when the leaves begin to unfold, during the last week of July and prior to leaf drop in the fall.
Horticultural oils as well as sulfur and copper-based fungicides can also be effective. As a general rule, horticultural oil should never be used when temperatures are above 90 degrees Fahrenheit, as doing so can “burn” the plant. The Clemson Cooperative Extension recommends alternating between fungicides in order to prevent the powdery mildew from becoming resistant to any one active ingredient. Regardless of which fungicide you use, be sure to coat plants completely.
Other Control Methods
Pruning the canopy of your dogwood tree to let in sunlight and allow air to circulate can go a long way toward preventing powdery mildew. According to the University of Kentucky Cooperative Extension Service, you should also avoid fertilizing dogwoods with formulas with a high nitrogen content, as nitrogen can stimulate new growth that is more vulnerable to powdery mildew. Prune infected branches and destroy fallen leaves to help limit the spread of the fungus.
Choosing disease-resistant dogwood cultivars can help you avoid powdery mildew altogether. According to the University of Tennessee Agricultural Extension Service, the Tennessee Agricultural Experiment Station has developed three cultivars of the flowering dogwood (Cornus florida, zones 5-9) that are resistant to powdery mildew: Cornus florida 'Jean's Appalachian Snow,' Cornus florida ‘Karen’s Appalachian Blush' and Cornus florida ‘Kay’s Appalachian Mist.' The Clemson Cooperative Extension notes that many cultivars of the kousa dogwood (Cornus kousa, zones 4-8) are also resistant to this disease.
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- NC Cooperative Extension Wayne County Center: 4-H Youth Development Agriculture & Food Animal Agriculture Commercial Horticulture, Nursery & Turf Farm Health & Safety Field Crops Food Safety & Processing Local Foods Pest Management Specialty Crops Community Forest Resources Health & Nutrition Home & Family Lawn & Garden Extension Master Gardener℠ Volunteers Soil, Water & Air Publications & Factsheets Logo for Wayne County Have a Question Now on Twitter Search this website Search Dogwoods Might Need Help Overcoming Powdery Mildew
- University of Kentucky Cooperative Extension Service: Dogwood Powdery Mildew
- The University of Tennessee Agricultural Extension Service: Dogwood for American Gardens
- Clemson Cooperative Extension: Dogwood Diseases & Insect Pests
- When planting new dogwoods, select powdery mildew resistant dogwoods such as Cornelian cherry dogwood (C. mas), Oriental dogwood (C. kousa) or flowering dogwoods (C. florida) "Jean's Appalachian Snow," "Karen's Appalachian Blush" or "Kay's Appalachian Mist."
- Never spray fungicides of any kind on water-stressed plants. Water an infected plant well and wait for signs of wilt to disappear before turning your attention to fungus eradication.
Since beginning her career as a professional journalist in 2007, Nathalie Alonso has covered a myriad of topics, including arts, culture and travel, for newspapers and magazines in New York City. She holds a B.A. in American Studies from Columbia University and lives in Queens with her two cats.
Effective measures to control powdery mildew on fruit crops. Descriptions, symptoms, prevention. Photo - Botanichka
Fruit crops, in addition to pests, are often affected by various diseases. One such disease is powdery mildew. Outwardly, it seems to be harmless, however, in fact, a rather dangerous fungal infection. Powdery mildew is perhaps the most common fungal disease that occurs literally on all crops: flower, vegetable, berry and even fruit. The disease is caused by powdery mildew fungi (Erysiphales). Usually, this fungal infection in fruit crops mostly affects leaf blades, but it also occurs on shoots, flowers, and even fruits. About it in this article and will be discussed.Powdery mildew on gooseberries. © Which?
- Powdery mildew on fruit trees - what is it?
- Powdery mildew causes
- Powdery mildew symptoms
- Powdery mildew spread
- Harmfulness of powdery mildew
- Preventive measures against powdery mildew
- Effective measures to control powdery mildew
Powdery mildew on fruit trees - what is it?
At the very beginning of development, the marsupial fungus begins to form a mycelium, it is attached by appressors to a leaf (shoot, fruit, etc.) and launches haustoria in its tissue. Later, as it develops, powdery mildew mycelium on the affected leaf blades (shoots, etc.) of fruit crops begins to develop quite abundant conidial sporulation and eventually forms cleistothecia with bags and bag spores.
The most interesting thing is that even after the natural death of the leaf blade (fruit), the powdery mildew mycelium often does not die, it is well preserved in the soil, in plant debris or under the old bark. With the advent of heat, the fungus comes to life and, with the help of conidia, spreads quite actively through plants, infecting them. Usually, from the moment of powdery mildew infection to the appearance of a whitish coating containing conidia on the surface of the leaf blades, it takes from four to ten days.
The rate of development of the infection depends on the weather, soil and air humidity, the age of the plant and its general condition. Spores usually develop to full maturity within one and a half or two to three months, extremely rarely - longer. It has been noticed that in warm weather with plenty of moisture in the soil and air, powdery mildew develops much more actively and fruit crops in such seasons are less resistant to it.
Causes of powdery mildew
Powdery mildew is an infection that is easily transmitted through the air. In fact, it is present in the air to one degree or another almost constantly, however, in order for the infection, having got on the leaf blade (fruit, shoot, etc.), to begin to develop on it, it is necessary that several factors come together.
For example, powdery growth develops most actively in the temperature range from +16 to +27 degrees, if the humidity is in the range of 65–85%.
Massive powdery mildew appears on fruit crops at:
- frequent and sharp temperature fluctuations;
- strong anti-aging fruit pruning, which weakens their immunity;
- excessive doses of nitrogen fertilizers, which sharply increase the concentration of nitrogen in the soil;
- dense plantings of fruit crops that do not allow free circulation of air masses and prevent the natural evaporation of moisture from the leaves and soil surface;
- violations of the irrigation regime, when the soil is moistened too much or, on the contrary, is watered extremely rarely.
Symptoms of Powdery Mildew
Powdery mildew usually appears on fruit crops in the spring and at the very beginning of the summer period, that is, in the first half of the warm season. The first affected leaf blades (shoots) on fruit crops can be found already in the phase of bud isolation. Powdery mildew appears, as we have already mentioned, most often in fruit crops on leaf blades, but often it can also be found on shoots.
In some years, when outbreaks of fungal infection are especially strong, powdery mildew can also be found on inflorescences; upon closer examination, one can see a very dense, whitish-gray coating, which leads to significant deformation of inflorescences, their wilting and partial or complete abscission.
At first, a whitish coating also forms on the shoots, and over time, when flying powdery mildew spores ripen, it turns brown-gray, darkening when cleistothecia fungi form on it, externally looking like black dots.
A white-gray coating also appears on leaf blades and petioles, but over time it does not turn black, but more often turns red. The development of powdery mildew fungus on leaf blades leads to inhibition of their growth, twisting, usually along the central vein, drying and falling off much earlier than the due date.
At the beginning of the formation of fruits, powdery mildew may also appear on them, you can also see a whitish coating there, which, however, disappears rather quickly, leaving behind a rusty mesh, which very much resembles tissue, as from hail or other mechanical effects on the fruit.
Interestingly, at the beginning of its development, powdery mildew from any plant organs can be removed without a trace with a simple cloth or other means, but after just a few days, the spots reappear in the same place and already have more serious dimensions. If no measures are taken, then the mycelium becomes denser over time and acquires a brown tint. Fruit crops affected by powdery mildew stop growth and development to a large extent, or these processes slow down greatly, leaf blades wither and fall off ahead of schedule, echoing flowers and buds.
Distribution of powdery mildew
Powdery mildew is widespread in Russia, in the nearest neighboring countries, as well as in the Baltic countries. Powdery growth is most active in Alma-Ata, Central Asia, Kazakhstan, Transcaucasia, as well as Armenia and Moldova. There, the degree of damage to fruit crops by this scourge reaches 90%. In the Krasnodar Territory, Georgia, Kyrgyzstan and Transcarpathia, the degree of damage to fruit crops by powdery mildew usually does not exceed 60%, in the Baltic countries, the Volga region and the Chernozem zone, the degree of damage by powdery mildew reaches 40%.Powdery mildew on grapes. © The Ohio State University
Powdery Mildew Harmfulness
When powdery mildew develops poorly, the damage from it can hardly be noticed, while when it develops strongly, the damage can be very significant and tangible. As we have already indicated, powdery mildew has a negative effect on the entire plant as a whole. A tree affected by powdery mildew is weakened, its immunity is depleted, weakened growth and development is observed, or growth stops altogether. Affected leaf blades fall off significantly ahead of time, and affected flowers and ovaries also fall off.
If shoots are affected by powdery mildew at the initial stages of their development, then their tops begin to dry out or deform. Depending on the degree of development, the yield may decrease from 10-15% to 60%.
In addition to the visible negative signs, powdery mildew also has an invisible effect on plants. So, in plants affected by powdery mildew, winter hardiness is significantly reduced, and usually the tips of young shoots and flower buds freeze out.
Powdery mildew is especially dangerous in nurseries, where seedlings grow very close to each other and the disease actively spreads to neighboring plants.
Preventive measures against powdery mildew
As you know, any disease is much easier to prevent than to cure, powdery mildew is no exception. To minimize the risk of powdery mildew on fruit crops, it is necessary to follow the planting pattern, do not thicken the plantings, carry out moderate watering - only as needed, without over-wetting the soil.
Sanitary pruning, associated with thinning the crown and aimed at preventing its thickening, can also help prevent the appearance of powdery mildew. In addition, it is necessary to maintain order in the near-stem zone: remove debris and plant debris, loosen the soil, and remove weeds. You should not allow weeds to develop near fruit crops, in this case, you need to mow them or treat weeds with herbicides.
To prevent the appearance of powdery mildew, it is also necessary to treat fruit crops with chemicals, these can be fungicides, that is, drugs for the prevention and control of fungal infection, as well as more environmentally friendly drugs containing copper - copper sulfate, Bordeaux mixture, copper oxychloride and the like.
Preventive treatments against powdery mildew should be carried out at least three times per season, starting in early spring and finishing in late autumn.
Helps to increase the immunity of fruit crops and strengthen the body's resistance to powdery mildew and fertilizers. So, it is desirable to add potassium salt and superphosphate to the soil (usually 15-20 g per tree).Powdery mildew on dogwood leaves. © Ric Bessin
Effective measures to combat powdery mildew
If powdery mildew has attacked fruit crops, then you should not delay the fight against it, it should be started as soon as the appearance of a characteristic powdery coating is noticed. It is important here to focus on the period of fruit ripening, if it is less than three weeks before it, then chemicals cannot be used, harmful substances contained in fungicides can also accumulate in fruits.
Usually, diseased fruit crops are treated against powdery mildew when it appears three or four times per season. As we have already mentioned, for these purposes, you can use copper-containing preparations or more effective fungicides - for example, Topaz. Treatment with this drug or another approved fungicide must be started as soon as the first organs of the fruit plant affected by powdery mildew appear, alternating once every 7-11 days, until the signs of fungal infection completely disappear.
In addition to chemicals that are harmful to the environment, there are many completely safe, but no less effective folk remedies for the fight against powdery mildew. These products are especially effective if the plants are still small, which allows the entire vegetative mass to be processed as carefully as possible. In addition, folk remedies for controlling powdery mildew can be used even at a time when the use of fungicides is prohibited for safety reasons.
Perhaps the most common means of combating powdery mildew is a solution of soda and soap. To obtain it, you need to dissolve 60 g of ordinary table soda and 30 g of antibacterial soap in a bucket of water at room temperature. After that, the resulting solution should be treated three times with powdery mildew-affected fruit crops with an interval of 7-8 days.
Whey solution has proven itself well in the fight against powdery mildew. To obtain it, you should dissolve a liter of whey in a bucket of water at room temperature, then mix the resulting solution well and treat the affected plants only in dry weather four times with an interval of three days.Powdery mildew on blackcurrant leaves. © Mariluna
A kefir solution also helps with powdery mildew. To get this solution, you need to take a liter of yogurt or well-fermented kefir and dissolve it in a bucket of water, after which it is necessary to treat the plants with the resulting solution three times with an interval of four days.
Helps control powdery mildew, especially on young trees, and horsetail decoction. You need to take 150 g of horsetail and pour 1.5 liters of water, let it brew for 30 hours, then boil over low heat for 15 minutes. It remains to let the broth cool, strain it, dilute it five times with water and you can carry out up to five treatments with an interval of 3-4 days. It is worth remembering that this decoction can be stored in a cool place without access to light for no more than ten days.
With a slight damage to fruit crops by powdery mildew, a solution of mustard helps to cope with it. To prepare it, you need to take two tablespoons of mustard powder and dissolve in a bucket of water at room temperature. Then you can treat the plants with this solution until the powdery mildew disappears.
Potassium permanganate solution will also help to eradicate powdery mildew if there is not much of it on the plants. It is necessary to take 6-7 g of ordinary pharmacy potassium permanganate and dilute in a bucket of water. With this solution, in addition to shoots and leaf blades, ripening fruits affected by powdery mildew can also be processed.
Ash solution is most effective on young plants with mild powdery mildew. It is also a good foliar top dressing with potash fertilizers and microelements. To prepare the solution, you need to dissolve about 800 g of wood ash in a bucket of water at room temperature, and then let it brew for five days. After this time, 30 g of liquid antibacterial soap should be added to the solution, strain the solution and proceed with the treatment of the affected plants.
Another infusion that serves both as foliar nutrition and powdery mildew control is mullein infusion. To obtain it, you need to pour 1 kg of mullein with 10 liters of water and let it brew for three days. Next, the infusion should be filtered, diluted by half and the affected plants can be treated with it. This infusion is most effective against powdery mildew before flowering.Powdery mildew on honeysuckle leaves. © Steve Willson
Onion peel, infusion, is also a top dressing and powdery mildew control. To get it, you need to take 300 g of onion peel and pour it with 10 liters of boiling water. After that, the container must be tightly closed with a lid and let it brew for 48 hours. After this time, the solution must be filtered and used to combat powdery mildew. Such treatments are especially effective before and after flowering and in autumn, before leaf fall.
In general, powdery mildew is not such a dangerous disease, if the garden is maintained by a person with a certain level of knowledge about this disease. The material provided in this article is quite enough to detect the disease and exterminate it, or, using preventive measures, prevent the appearance of powdery mildew on your fruit crops.
Powdery mildew on roses - control and prevention measures
Powdery mildew attacks most flowers. Roses are especially affected by it. The disease is dangerous, but if measures are taken in time, the plants can be saved.
Powdery mildew is a very common disease of garden, greenhouse and indoor roses. Fortunately, it has vivid symptoms, so the disease can be easily detected and quickly eradicated.
Signs of powdery mildew, why it appears
The most characteristic symptom of powdery mildew is so noticeable that it catches the eye even with a cursory examination. This is a white coating on stems, leaves, buds, flowers and even thorns. At first, the plaque is loose, sparse, similar to a cobweb. Gradually thickens, becomes gray or brownish.
Varieties with dense leathery leaves may not be covered with a bloom, but with reddish spots or rings, similar to a mosaic. Varieties with more tender shoots and foliage are quickly wrapped in a thick bluish felt blanket, the leaves dry up and fall off.
The first symptoms may appear as early as May. In August, the disease reaches its peak.
Downy mildew or downy mildew is similar. False dew differs from real dew in the color of the plaque - it is gray, sometimes even purple. Fluff with peronosporosis is located only on the lower part of the leaves. With true powdery mildew, plaque develops on the front surface, capturing stems and buds.
Spores of the disease persist in winter in cracks in the bark, under scales of dormant buds, in fallen leaves and topsoil. As soon as the temperature and humidity of the air become suitable, the spores wake up. Of these, thin formations - hyphae - appear and begin to grow rapidly. To the human eye, they look like a white coating.
Important. The optimal conditions for the germination of powdery mildew spores are warm weather during the day and cool weather at night, combined with high humidity.
Why powdery mildew is dangerous on roses
Diseased plants quickly lose their beauty. Their leaves fall, the stems are covered with white "felt" and bent. There is not even a question of flowering - a sick rose completely stops laying buds.
By autumn, the plant will exhaust its strength, and in winter it will freeze. Tea and hybrid tea species are especially affected - their delicate leaves are not well adapted to resisting infections.
Powdery mildew on roses - control measures
The disease is more severe if the flowers are planted in soil rich in nitrogen and poor in calcium. In a greenhouse, a lack of light, poor ventilation, and sudden temperature fluctuations can provoke an outbreak - all this weakens the immunity of plants. To increase disease resistance, tender varieties can be sprayed with immunomodulators: Epin, Zircon or Amulet.
How to treat powdery mildew on roses? Noticing a white fluff, you need to use the contact fungicide Thiovit Jet. It not only protects against powdery mildew, but also kills mites. The preparation contains colloidal sulfur. It is detrimental to microscopic fungi at all stages of their development.
To kill the pathogen, the drug must be applied directly to the plaque. Thiovit Jet is especially effective at temperatures of +25 °C and above. It can be used 4 times per season. This is enough for the roses to be completely protected.
Topaz is a latest generation fungicide. It penetrates the tissues of the plant and is not washed out by rain, retaining the ability to kill spores and hyphae for 10-14 days. If weather forecasters promise long rains, then Topaz can be used for prevention.
Powdery mildew on roses - treatment with folk remedies (ash):
- Pour 1 kg of wood ash into 10 liters of hot water;
- insist 7 days;
- stir, strain;
- add some liquid soap for sticking;
- spray the leaves every other day for prevention and when the first signs of the disease appear.