Whether spilling out of baskets and boxes or filling the fronts of beds with their bright flowers, petunias make every space a little more merry. These tough flowers tolerate a lot of abuse and neglect, though pests and diseases can create problems with growing petunias. Read carefully through the list of common petunia flower issues to learn how to treat petunias ailing from a variety of causes.
There are a number of pests of petunias that can affect these plants. Here are the most common:
Mites – Mites are nearly microscopic pests that suck the juices directly out of petunia cells. These cousins to the spider may cause leaves to curl or cup or flowers to discolor and stiffen. Spider mites also leave thin webs behind where they feed. Spray your petunias with neem oil once a week until all signs of mites are gone.
Caterpillars – Caterpillars chew through foliage and buds, sometimes causing extensive damage in no time. They’re easy to see if you pick through thick foliage. The best solution is to remove them by hand and drown them in a bucket of water daily, but if you can’t bring yourself to do it, sprays of Bacillus thuringiensis applied weekly should knock them out quickly.
Thrips – Thrips can carry viruses to petunias, and may cause leaves to turn papery or flowers to develop white spots, known as “color break.” They can be difficult to see, but look like very tiny, fat ants when running around on your plants. Neem oil or insecticidal soap will knock them out in a few thorough weekly sprays.
Below are common diseases affecting petunia plants:
Root, Stem and Crown Rots – Root, stem, and crown rots commonly affect petunias planted in areas of poor drainage or that are chronically over watered. Leaves wilt despite regular watering and stems may begin to soften. Correcting the drainage and watering less frequently is the only solution if an affected petunia can be saved at all. Often, it’s easier to pull plants and start over early in the season.
Botrytis Blight – Botrytis blight may cause spots or other discoloration on flowers and leaves that eventually sprout brown-grey spores. Again, this disease is favored by wet bedding conditions, so let up on the watering when it appears. Prune out any diseased sections of your plants and pick up fallen debris; drying out the bed should prevent reinfestation.
Powdery Mildew – Powdery mildew doesn’t need soaking wet conditions to thrive, but often appears where plants are spaced too tightly, obstructing airflow. Look for white, powdery spots of spores that spread or cover leaves and flowers completely. Powdery mildew can be treated with neem oil, but you should also correct the conditions allowing this disease to get a foothold.
Verticillium Wilt – Verticillium wilt causes an overall decline in plant vigor, often causing older leaves to wilt before younger ones, or only part of a plant to die at first. There is no cure for verticillium wilt, so pull your plants and try again in pots. In some areas, the soil can be heated enough through soil solarization to kill the fungal pathogen.
Viruses – Several viruses affect petunias, causing leaves to develop yellow spots, mosaics, halos or bullseyes. Unfortunately, petunia viruses cannot be cured. If you suspect virus in your plants, use extra caution when pruning or working with the plants to slow the spread of disease. Many plant viruses are vectored by small insects, check your plants carefully and treat any you find if you hope to save the non-symptomatic plants in your beds.
Valued for their brightly colored, ruffled flowers, petunias (Petunia spp.) are treated as annuals in cool-climate regions, but gardeners in U.S. Department of Agriculture plant hardiness zones 10 and 11 can enjoy planting these long-blooming perennials outdoors. Colorful petunias work well in flower beds and borders or can be used as a flowering ground cover. Petunias enjoy overall good health, but you must keep an eye out for a few minor pests.
|Blooming Stops Blooms Are Soaked Disintegrate||Cultural Problems|
|Leaves Chewed On Edge, Not In Middle of Leaf||Caterpillars|
|Foliage Curls Puckers Turns Yellow Often the leaves and blooms become stunted. Sometimes ants are visible, crawling along plant stems and foliage, attracted by the presence of the sticky honeydew secreted by aphids.||Aphids|
|Plants Wilt Turn Yellow||Various Viruses|
|Plant Blooms and Stem Tips Eaten, Whole Plant Can Disappear||Deer|
|Plants Nibbled To Ground||Rabbits|
|Over night holes appear in the leaves and sometimes you can see a trail of silvery mucous on the plant and down on the ground||Controlling Slugs|
If petunias stop producing blooms in the middle of the season and show no signs of pest or disease problems, chances are they just need to be pinched back. Clip or pinch leggy stems back by 1/3 to 1/2 and feed the plants. After a week or two they will begin to form new buds.
The extremely large blooms of large blossomed petunias such as grandiflora types become so heavy when they are wet that they fall on the soil and are ruined. These are best grown indoors in greenhouses and sunspaces or under lights. Choose from among the multiflora or floribunda varieties for sturdier blooms.
Petunias are susceptible to several viruses that also plague their relatives in the tomato and tobacco family. Curly top, mosaic, ringspot, and spotted wilt are spread by various sucking insects and are not curable. Affected plants become sickly and wilted. Foliage may show spots and then it yellows and dies. Controlling pest insects such as aphids that may transmit disease in and around the yard is the best defense. Dig up affected petunia plants and discard them in the trash so that they so not become a source of infection for other plants. Do not use tobacco products around petunias. Disinfect any tools that come in contact with infected plants by dipping them in a solution of hot water and household bleach.
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Phytophthora (phytophthora parasitica) root and crown rot are soil-borne organisms and are common problems affecting bedding plants such as the petunia. The fungus attacks the base of the petunia and is evidenced by dry rot near the soil line. Rot can also appear on one side of the petunia or on lateral branches. The roots of the petunia may not show excessive rotting, but the roots will not grow as large as they should. The fungus generally occurs in beds where the same plant species is planted year after year. It can survive in the soil indefinitely, according to the Utah State University Cooperative Extension website.
Phytophthora root and crown rot of petunias is caused by the fungus Phytophthora parasitica. This soil-borne pathogen continues to live within soil without a definite life expectancy. The use of resistant plants like snapdragons and marigolds is ideal because they are much less likely to become infected. If you are removing a petunia plant that has died from root rot, replace it with a resistant option instead of with another petunia. Symptoms include decay near the soil line including the crown, or base, of the petunia plant as well as the roots. Visible symptoms are hard to come by but discoloration and dying plant tissue may occur. Additionally, your petunias may stop growing and producing flowers or the entire plant will die. For control, contact a licensed professional to set up a preventive fungicidal soil drench program. Maintain extremely well-drained soil and apply a fungicide with the active ingredient metalaxyl. Only apply a fungicide if you are providing the optimal maintenance to your petunia plants, according to the Utah State University Cooperative Extension.
Petunias are low-growing perennial plants generally treated as annuals. Leaves are thick and somewhat sticky. Flowers may be ruffled or funnel-shaped and are of various colors including white, yellow, red, blue, and purple. They bloom from spring into winter. Petunias are often grown in beds, containers, window boxes, or as ground covers.
Petunias require regular water and fertilizer, and they must be planted in soil that drains well. Plants do well in areas with full sun. After the bloom period, remove old flowers to promote new plant growth.
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Aster Yellows: Plants are stunted, develop witch's brooms (excessive growth), petals turn green and become deformed. This virus-like condition is spread by leafhoppers. Burpee Recommends: Remove infected plants and control leafhoppers. Remove weeds in the area which serve as alternate hosts to the disease.
Botrytis: This fungus causes a grey mold on flowers, leaves, stems and buds. It thrives in cool wet weather conditions. Burpee Recommends: Remove affected plant parts, avoid watering at night and getting water on the plant when watering. Make sure plants have good air circulation. Contact your Cooperative Extension Service for fungicide recommendations.
Damping Off: This is one of the most common problems when starting plants from seed. The seedling emerges and appears healthy then it suddenly wilts and dies for no obvious reason. Damping off is caused by a fungus that is active when there is abundant moisture and soils and air temperatures are above 68 degrees F. Typically, this indicates that the soil is too wet or contains high amounts of nitrogen fertilizer. Burpee Recommends: Keep seedlings moist but do not overwater avoid over-fertilizing your seedlings thin out seedlings to avoid overcrowding make sure the plants are getting good air circulation if you plant in containers, thoroughly wash them in soapy water and rinse in a ten per cent bleach solution after use.
Fasciation: Fasciation is an abnormal flatting of stems,which may cause them to have a fused appearance. Distortion often develops at the base of the plant. It is usually caused by a bacteria or virus and enters through a wound in the plant. Burpee Recommends: Be very careful when handling plants. Remove and destroy any plants that show signs of the disease.
Powdery Mildew: This fungus disease occurs on the top of the leaves in humid weather conditions. The leaves appear to have a whitish or greyish surface and may curl. Burpee Recommends: Avoid powdery mildew by providing good air circulation for the plants by good spacing and pruning. Contact your Cooperative Extension Service for fungicide recommendations.
Aphids: Greenish, red, black or peach colored sucking insects that can spread disease as they feed on the undersides of leaves. They leave a sticky residue on foliage that attracts ants. Burpee Recommends: Introduce or attract natural predators into your garden such as lady beetles and wasps who feed on aphids. You can also wash them off with a strong spray, or use an insecticidal soap.
Cyclamen Mite: These mites damage plants by sucking juice from stems and leaves. They multiply rapidity in hot, dry weather. They can only be seen using a magnifying glass. Plants will look distorted and stunted, and may not bloom. Flowers will be distorted, streaked and blotched. Leaves can become cupped, curled, dwarfed and thickened. Burpee Recommends: Discard plants that are severely infested. Avoid working with infested plants. Keep plants watered in dry weather. For heavy infestations consult your Cooperative Extension Service for insecticide recommendations.
Leafhoppers: Leafhoppers cause injury to leaves and stunt growth. They also spread disease. Burpee Recommends: Remove plant debris. Use insecticidal soaps. Consult your Cooperative Extension Service for other insecticide recommendations.
Spider Mites: These tiny spider-like pests are about the size of a grain of pepper. They may be red, black, brown or yellow. They suck on the plant juices removing chlorophyll and injecting toxins which cause white dots on the foliage. There is often webbing visible on the plant. They cause the foliage to turn yellow and become dry and stippled. They multiply quickly and thrive in dry conditions. Burpee Recommends: Spider mites may be controlled with a forceful spray every other day. Try hot pepper wax or insecticidal soap. Check with your Cooperative Extension Service for miticide recommendations.
Thrips: Thrips are tiny needle-thin insects that are black or straw colored. They suck the juices of plants and attack flower petals, leaves and stems. The plant will have a stippling, discolored flecking or silvering of the leaf surface. Thrips can spread many diseases from plant to plant. Burpee Recommends: Many thrips may be repelled by sheets of aluminum foil spread between rows of plants. Remove weeds from the bed and remove debris from the bed after frost. Check with your Cooperative Extension Service for pest controls.
Why did my petunias change color or produce a stripe in summer? Petunias are sensitive to high temperatures and may change color or produce a stripe when they too warm. Once temperatures cool, new flowers will resume their original color.
Which petunia is self-cleaning? All Wave-variety petunias, as well as ‘Baby Duck’, are self-cleaning and do not require deadheading.
Why don’t ‘Shock Wave’ petunia seeds look like regular petunia seeds? ‘Shock Wave’ petunia seeds are pelleted for ease of handling. Once seeds are pressed into the soil, the coating will break down and can be misted off.
What do petunias attract to the garden? Petunias attract hummingbirds, butterflies and bees, as well as other beneficial insects.
How many Wave petunias do I need for a 12-inch hanging basket? Three plants of Wave-varieties, four for other mounding-habit types are just right for a 12-inch hanging basket.
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