By: Teo Spengler
Begoniasare among America’s favorite shade plants, with lush leaves and splashyblossoms in a multitude of colors. Generally, they are healthy, low-careplants, but they are susceptible to a few fungal diseases like botrytis ofbegonia. Begonias with botrytis is a serious disease that can endanger the lifeof the plant. Keep reading for information about treating begonia botrytis, aswell as tips about how to avoid it.
Botrytis of begonia is also known as botrytisblight. It is caused by the fungus Botrytiscinerea and is most likely to appear when temperatures dip and moisturelevels rise.
Begonias with botrytis blight decline rapidly. Tan spots andsometimes water-soaked lesions appear on the foliage and stems of the plant.Cuttings rot at the stem. Established begonia plants rot as well, starting inthe crown. Look for dusty gray fungal growth on infected tissue.
The Botrytis cinereafungus lives in plant debris and multiples quickly, especially in cool, highmoisture conditions. It feeds on wilting flowers and senescent leaves, and fromthere, attacks healthy leaves.
But begonias with botrytis blight are not the only victimsof the fungus. It can also infect other ornamental plants including:
Treating begonia botrytis begins with taking steps toprevent it from attacking your plants. While it won’t help your begonias withbotrytis, it will prevent the disease from passing to other begonia plants.
Cultural control starts with removing and destroying alldead, dying or wilting plant parts, including dying flowers and foliage. Thesedying plant parts attract the fungus, and removing them from the begonia andpotting soil surface is a very important step.
In addition, it helps keep the fungus away if you increaseair flow around the begonias. Don’t get water on the leaves as you are wateringand make an attempt to keep the leaves dry.
Fortunately for begonias with botrytis, there are chemicalcontrols that can be used to help infected plants. Use a fungicide that isappropriate for begonias every week or so. Alternate fungicides to preventfungi from building up resistance.
You can also use biological control as begonia botrytistreatment. Botrytis of begonia was reduced when Trichoderma harzianum 382 wasadded into a sphagnum peat potting media.
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Clean the pot with bleach, then add sterile potting mix. Replant the begonia and water it, making sure the water drains well, as root rot is more common in waterlogged soil. If the plant is outdoors, move the plant to new location to help prevent reinfection by the root rot fungus.
Likewise, why do my begonias rot? The most common reason begonia leaves rot is too frequent watering. Begonias are succulent plants with stems that are mostly water, which makes them very sensitive to moisture and fungus. Overwatering begonias causes their leaves to turn yellow, a process called chlorosis.
Beside this, why are the leaves on my begonia turning brown?
Too much sunlight can lead to fading and wilting of the leaves, and continued excessive sunlight can cause the edges of the begonias' foliage to turn brown. Begonia plants do not like very wet soil, and too much soil moisture can cause the plants' roots to rot.
How do I know if my begonia has root rot?
When begonia stem and root rot infects your plants, they are likely to show a variety of symptoms. These include darkened foliage, blackened and rotting roots, rotting stems just above ground level, and collapsing crown. Stem and root rot of begonia usually kills seedlings by damping off.
Stem and Root Rot (fungi – Pythium spp., Rhizoctonia spp. and others): Affected plants wilt and break over at the soil line due to decayed spots being formed on stems. This problem is often severe when cuttings are placed in beds for rooting. Fungi responsible for this condition may be introduced on cuttings or be present in soil. Use sterilized soil. Fungicides may be used as a drench. Use cuttings from healthy plants only.
Botrytis Blight and Stem Rot (fungus – Botrytis cinerea): This fungus is most severe when temperatures are cool and moisture levels are high. Affected plants decline rapidly with stems and leaves developing brown, water-soaked lesions. In advanced stages all tissues may be penetrated by the fungus. This disease is especially severe under greenhouse conditions where begonias are propagated. Growers should be sure to start with disease-free cuttings, use a sterilized medium and keep the growing area free of any type of weak or decaying plant material that might serve as a food source for the fungus.
Leaf Spots (fungi – several): Brown spots appear on foliage and reduce plant vigor. Most leaf spotting fungi thrive under high moisture conditions. Change the location of potted plants if conditions are overly wet and use appropriate protectant fungicides.
Powdery Mildew (fungus – Erysiphe cichoracearum): Affected leaves have a white powdery substance on the upper surfaces. This problem is occasional in nature but may occur when environmental conditions are ideal for disease development.
Bacterial Spot (bacterium – Xanthomonas campestris, pv. begoniae): Small blister-like spots appear on leaves. These become clear with age and may run together to form larger spots. Affected leaves may shed prematurely. Chemical control may be only partially effective.
Root Knot (nematode – Meloidogyne spp.): This nematode causes knots to form on roots. This problem can be prevented by using nematode-free planting stock and a sterilized potting medium.
Rust (fungus – Coleosporium solidaginis): Orange-red pustules form on the underside of leaves. In severe cases, foliage turns yellow and dies. Alternate host is pine where it produces a blister rust on the needles. Use rust resistant varieties when available. Fungicides should be used at the first sign of disease and continued on a 7-14 day schedule.
Aster Yellows (mycoplasma): First symptoms are observed as a yellowing or chlorotic appearance along the veins of young leaves. As the chlorosis becomes severe, defoliation occurs. Affected plants do not wilt or die, but have a spindly type growth which detracts from the plants overall appearance. Yellows may attack only a portion of the plant. Secondary shoots are formed profusely on infected plants. The disease is spread by leafhoppers. Control is obtained by insect control and removal of diseased plants.
Plant Health Problems
Diseases caused by Fungi:
Powdery mildew, Erysiphe, Oidium.
White powdery spots or patches develop on leaves and occasionally on stems. Symptoms often first appear on the upper surfaces of the leaves and are usually most pronounced during hot, humid weather. Heavily infected leaves turn brown and shrivel.
Disease can be minimized by avoiding overcrowded spacing of plants and by carefully picking off affected leaves as soon as symptoms are evident. Symptomatic leaves can be placed into a plastic bag in order to avoid spreading the spores of the fungus to other plants. Use of fungicides is usually not necessary. However, applications can be made as soon as symptoms are visible. Among the compounds registered for use in Connecticut are horticultural oil, potassium bicarbonate, copper sulphate pentahydrate, and thiophanate-methyl. Consult the label for dosage rates and safety precautions.
Leaf spots, Phyllosticta, Gloeosporium, Cladosporium.
Circular to irregular tan to brown spots develop on leaves. These can vary in size, color, and number.
Efforts to maximize plant vigor by fertilizing and watering are helpful. However, watering should be done early in the day to give the foliage a chance to dry before nighttime. It is also helpful to pick and remove symptomatic leaves as soon as they develop. Although not usually necessary, applications of fungicides can be made when new growth emerges in the spring. Among the compounds registered for use in Connecticut are chlorothalonil, mancozeb, and thiophanate-methyl. Consult the label for dosage rates and safety precautions.
Botrytis blight or blotch, Botrytis cinerea.
Flowers turn a papery brown and become covered with gray, fuzzy masses. Senescing flowers are particularly susceptible. Tan to brown spots with a target-like appearance can also develop on the leaves. These patches are often associated with flowers which have dropped onto the leaf surface. This disease is particularly troublesome during periods of extended cloudy, humid, wet weather.
Good sanitation practices including grooming the plants and removing spent or senescing flowers can minimize the potential for infection. These affected tissues should be carefully removed and discarded when they are dry. It is also important to avoid wetting the flowers when watering and crowding plants. Adequate spacing between the plants can promote good air circulation. Use of fungicides is usually not necessary. However, control can be enhanced with the use of fungicide sprays applied as soon as symptoms are visible. Among the compounds registered for use in Connecticut are chlorothalonil, mancozeb, and thiophanate-methyl. Consult the label for dosage rates and safety precautions.
Root rots, Thielaviopsis basicola, Pythium sp., Rhizoctonia solani.
The above-ground symptoms of root rots are non-specific and include a general wilting, decline, and collapse of the foliage and the entire plant. This general droopiness or flaccid appearance is often accompanied by browning and rotting of the roots and the crown. Yellowing and death of the outer leaves follows, until finally the entire plant is dead.
Control can be difficult once plants are infected so prevention is important. It is helpful to avoid overwatering, especially in heavy soils, and to avoid watering directly into the crown area of the plant. Highly symptomatic plants can be rogued and removed since recovery is unlikely.
Diseases caused by Bacteria:
Bacterial leaf spot, Xanthomonas begoniae.
Symptoms include small blister-like spots that appear on both tuberous and fibrous begonias. The spots are translucent at first and as they age, the centers dry to a tan color. The margins of the spots usually remain translucent or water-soaked. The bacteria may become systemic and cause collapse and death of the plants.
This disease can be minimized by improving air circulation by thinning the plants and by avoiding overhead irrigation. Picking and destroying infected leaves is also helpful. Chemical control is not usually necessary but can supplement other methods for disease management. Among the compounds registered for use in Connecticut are elemental copper, copper hydroxide, and copper sulphate pentahydrate. Consult the label for dosage rates and safety precautions.
Diseases caused by Nematodes:
Foliar nematodes, Aphelenchoides spp.
These plant-parasitic worms attack virtually all plant parts and may cause leaf lesions, yellowing, necrosis and leaf drop, and bud malformation. Water-soaked blotches appear on the underside of the leaf but soon involve the entire leaf. The whole plant may become stunted. The nematodes live and move in water films.
Reducing leaf moisture and removal of infected tissues, debris, or plants is important.
Diseases caused by Physiological/Environmental Factors:
Corky scab or oedema, physiological.
Raised, scab-like swellings appear on the underside of leaves. These first appear as water-soaked blisters and may turn rusty-brown with age. This condition is often associated with inadequate light levels as well as overwatering, especially during periods of cloudy, cool weather.
This problem can be minimized by careful attention to soil moisture levels, especially during periods of cloudy, humid weather.
Aphids, Aphis gossypii.
The melon aphid and probably other species occasionally infest begonia. They may be controlled by spraying with insecticidal soap, ultra-fine horticultural oil or malathion, which are among the compounds registered for use against this pest in Connecticut, when needed. Imidacloprid applied as a systemic to be taken up by the roots will also provide season-long control. Consult the label for dosage rates and safety precautions.
Black vine weevil, Otiorhynchus sulcatus.
Another common pest is black vine weevil. The larvae of this weevil often injure tuberous begonias in nurseries and ornamental plantings. The grubs devour the small roots and feed inside the tubers, weakening them. Severely injured plants die. The 1/2" long adult weevil is black, with a beaded appearance to the thorax and scattered spots of yellow hairs on the wing covers. Only females are known, and the adults are flightless. They feed nocturnally, notching the margins of the foliage. The legless grub is white with a brown head and is curved like grubs of other weevils. Adults and large larvae overwinter, emerging from May - July. The adults have to feed for 3-4 weeks before being able to lay eggs. Treating the soil with insect pathogenic nematodes may control the larvae, and should be the first line of defense. Acephate and fluvalinate are among the compounds registered for control of this pest in Connecticut, and should be applied when adults are feeding and before they start laying eggs. The usual timing for these foliar sprays is during May, June and July at three week intervals. Insecticide resistance is very common be aware that adults may appear to be dead following contact with fluvalinate, but may recover from poisoning within a few days. Consult the label for dosage rates and safety precautions.
See African violet for indoor plants. On begonias used as annuals outdoors, insecticidal soap, ultra-fine horticultural oil as well as malathion, which are among the compounds registered for use against this pest in Connecticut, can be used to control this insect if needed. Imidacloprid applied as a systemic, to be taken up by the roots, will also provide season-long control. Consult the label for dosage rates and safety precautions.