Balsam plants are susceptible to various fungal diseases that can disfigure leaves and stems. Fungal infections thrive in warm, humid conditions and can spread quickly. Left unchecked, fungus can severely weaken or even kill balsam plants. The key is catching issues early and using integrated pest management techniques to control fungus on balsam plants.
Identifying Fungal Diseases
The first step is recognizing the most common fungal diseases of balsam plants so you know what you’re dealing with. Powdery mildew is one of the most prevalent It appears as white or gray powdery spots on leaves, stems, and flowers Downy mildew causes yellow splotches on upper leaf surfaces and grayish fungal growth on lower surfaces. Leaf spots start as small brown spots that enlarge in concentric rings. Botrytis blight leads to rapidly spreading brown lesions. Root and stem rots cause stunting, wilting, and plant death.
Remove Infected Plant Parts
Pruning is an important part of managing fungal diseases on balsam plants. It prevents spread by eliminating infected plant tissue. Inspect balsam plants frequently and cut off any leaves or stems at the first sign of fungus. Make cuts at least 2 inches below infected areas. Disinfect pruners between each cut with rubbing alcohol to avoid transmission. Destroy all diseased plant debris – don’t compost it. For plants with isolated leaf spotting, remove only the affected leaves.
Improve Air Circulation
Fungal spores thrive in stagnant, humid conditions. Improve air movement around balsam plants to make the environment less favorable for fungal growth. Space plants appropriately, prune selectively to open up dense growth, and thin inner branches. Raise plants up on stakes or trellises to promote air flow at soil level. Remove weeds and mulch appropriately, as thick layers can trap moisture. Ample airflow allows leaves to dry out more quickly after watering or rain.
Water at Ground Level
Overhead watering sprinkles spores up onto foliage, encouraging fungal spread. Always water balsam plants at the soil line instead of from above. Drip irrigation, soaker hoses, or water wands are ideal methods. Water early in the day so leaves have time to dry out before night. Avoid frequent light waterings that keep leaves perpetually damp. Monitor soil moisture and let the top few inches dry between thorough waterings.
Use Fungicidal Sprays
For severe fungal outbreaks, chemical fungicides may be needed along with cultural controls. Look for targeted products labeled for control of specific diseases like powdery mildew or botrytis. Options include chlorothalonil, myclobutanil, copper fungicides, and bacterial isolates. Coat leaf surfaces thoroughly and repeat applications per label instructions. Combine with pruning and sanitation practices for most effective disease management.
Apply Baking Soda Spray
Baking soda spray is an easy DIY fungicide for balsam plants. Simply mix 1 tablespoon baking soda with 1 quart water. Add 1/2 teaspoon of insecticidal soap or horticultural oil so the solution sticks to plant surfaces. Shake well and spray leaves stems and flowers, especially new growth. The alkaline solution disrupts fungal growth and spore germination. Reapply every 7-14 days as needed.
Use Milk Spray
Believe it or not, plain milk makes an effective anti-fungal spray. The proteins in milk inhibit the growth and spread of powdery mildew, downy mildew, and other fungal diseases. Mix 1 part milk with 9 parts water and pour into a spray bottle. Spray balsam plant leaves thoroughly, especially the undersides, every 7-10 days when disease is present. The milk coating helps control spore production and fungal growth.
Apply Neem Oil
Extracted from the neem tree, neem oil is both a fungicide and insecticide. It contains azadirachtin and other compounds that disrupt fungal activity. Follow label rates and mix neem oil with water and a small amount of insecticidal soap. Thoroughly coat balsam plant leaves, stems, and flowers, especially new growth. Reapply every 7-14 days to deter fungal diseases. Neem oil also controls many common plant pests as an added benefit.
Use Compost Tea
Compost tea provides natural disease suppression thanks to beneficial microbes that out-compete pathogens. Brew a batch by steeping high-quality compost in water for 3-7 days. Strain, then spray the compost tea onto balsam foliage. The diverse microbial community coats leaf surfaces and prevents establishment of fungal spores and growth. Apply compost tea every 2-3 weeks as a foliar spray to protect balsam plants.
Boost Air Circulation
One of the most vital natural treatments for fungal diseases is improved airflow around plants. Container-grown balsam plants are very susceptible to fungus, so take steps to increase air movement. Space pots appropriately, prune selectively to open up growth, and raise containers up on blocks or racks. Use fans to gently blow air across plants, taking care not to damage tender tissues. Proper spacing and air flow keeps balsam foliage dry.
Control Weeds
Weeds near balsam plants can harbor fungal diseases. Stay on top of weeding to eliminate alternate hosts and sources of spores. Hand pull weeds or spot treat with natural herbicides like vinegar. Remove all weed debris after cultivation. Keep all garden areas clean and free of rotting leaves, fruits, and other organic matter that could breed fungal pathogens. Sanitation limits spread of fungus to balsam plants.
Avoid Wetting Foliage
Fungal spores need a film of moisture to germinate and infect plants. Avoid overhead watering and irrigate balsam plants right at soil level. Water first thing in the morning so leaves have time to dry out over the course of the day. Space plants appropriately and prune to encourage good airflow so foliage dries quicker after rains. Consider installing a rain shield over containerized plants to protect from foliar wetting.
Use Fungus-Resistant Varieties
When choosing balsam plants, look for cultivars bred to resist fungal diseases. Many flower and vegetable varieties have been selected for enhanced disease resistance. Ask local nurseries for fungus-resistant recommendations for your area. The National Garden Bureau is another helpful resource. Resistant varieties are able to better withstand and outgrow certain fungal infections compared to traditional types.
Provide Proper Culture
Healthy, vigorous balsam plants are less susceptible to fungal problems. Meet their preferences for sunlight, soil, moisture, and nutrients to avoid plant stress. Scout regularly for early signs of disease and promptly remove any infected plant parts. Disinfect tools between plants to avoid spreading spores. Keep foliage dry with proper irrigation, spacing, and pruning. With a little diligence, you can maintain healthy balsam plants that are more fungus-resistant.
Through careful inspection, prompt removal of disease issues, and good growing conditions, you can effectively manage fungal diseases on balsam plants. Use organic sprays and compost tea to deter fungal growth and infection. Improving airflow and avoiding wet foliage are also key. Follow integrated pest management guidelines for disease identification, sanitation, cultural practices, and targeted sprays.
Don’t let downy mildew on impatiens surprise you
Use downy mildew fungicides preventively.
Figure 1. A, A yellow leaf, which can indicate downy mildew infection, compared to a healthy green leaf. B, Downy mildew fuzz on the underside of a leaf. C, Impatiens stunted by downy mildew infection.
Impatiens are one of the most popular bedding plants for shade gardens worldwide. In 2011, impatiens downy mildew was an unpleasant surprise for greenhouse growers and gardeners. Sometimes pathogens can seem cyclic and reoccur following several years of being absent.
Seed and vegetatively propagated Impatiens spp. including common seed impatiens (Impatiens walleriana), double impatiens and garden balsam (Impatiens balsamina) are susceptible. Fortunately, New Guinea impatiens (Impatiens hawkeri) appear to be tolerant or resistant to downy mildew. The downy mildew disease that affects Impatiens spp. is caused by a fungal-like microscopic organism called Plasmopara obducens. This downy mildew is unique to impatiens. Snapdragons, roses, impatiens, coleus, basil and other crops are susceptible to downy mildew, but each have a unique downy mildew pathogen. While the disease may look similar on the different crops, they are quite different. The downy mildew on snapdragons cannot blight roses nor can the downy mildew on impatiens spread to any plant outside of Impatiens.
In some cases before the pathogen is halted, the loss of plant material can be severe. Given these recent problems, growers should review the downy mildew basics because this can be an explosive, destructive and costly pest if it is not managed.
Downy mildew is not the same as powdery mildew. Powdery mildew commonly occurs on such plants as roses, gerbera, poinsettias, lilac and begonia.
Don’t forget to look under the leaves. An obvious sign of downy mildew is a white fuzz on the underside of the leaves, but this can go unnoticed (Fig 1B). Perhaps other than an especially severe case of Botrytis, no other disease causes such obvious fuzz, especially on the underside of the leaf. This disease should not be confused with spray residue, which can occasionally result in a whitish film on the leaves. Infected plants become stunted and lose their leaves, flower buds and flowers.
Look for the disease. Downy mildew is often explosive and early detection is critical. The downy mildew pathogen produces plenty of spores called sporangia that are spread via air currents to nearby healthy plants. When scouting, turn the leaves over to look for white fuzz (Fig. 1B). When receiving plug and liners of susceptible Impatiens spp., scout them immediately by examining fully-expanded leaves, paying special attention to the undersides of leaves. Scout a minimum of one out of every 30 plants. If there are symptoms of downy mildew infection such as distorted leaves or yellow foliage, but no white fuzz, they still may be infected with the downy mildew pathogen, but the conditions are not suitable for the pathogen to sporulate. Place the suspect plant in a plastic bag with a wet paper towel and leave it overnight. If the plant is infected, you should see white fuzz on the underside of the leaves the next morning.
Established impatiens crops should be scouted weekly. Be sure to check the impatiens that are in baskets and mixed containers as they can be hard to monitor. If diseased plants are discovered, they should be placed in bags and discarded immediately. Diseased plants should not be placed in a cull or compost pile. Healthy-appearing plants that are right next to the diseased plants should also be discarded as they are likely to be infected but are not yet showing symptoms. All remaining impatiens anywhere on the premises should be immediately treated with fungicides.
Downy mildew likes water and cool temperatures. Limit this disease by venting, reducing the time that leaves are wet, and keeping relative humidity to a minimum. Water plants at a time of day that allows the foliage to dry quickly. Downy mildew is a water mold because it needs water to grow and develop. Any strategy that reduces water, leaf wetness and relative humidity in a greenhouse will help limit downy mildew.
Apply effective fungicides preventively. Systemic fungicides can be especially helpful in managing downy mildew because these products are absorbed by the plant in a limited way and can fight the downy mildew pathogen effectively. Subdue MAXX and Segovis are both systemic fungicides and are especially effective when applied as a drench.
Two fungicide programs are outlined below. One is for the bedding impatiens and double impatiens that have not been bred to be resistant to downy mildew. The second is for those impatiens cultivars (e.g., Imara XDR impatiens and Beacon impatiens) that have been developed to resist infection by the downy mildew pathogen.
Spray program for resistant impatiens cultivars:
- Single application, shortly before shipmentSubdue MAXX (1 fl oz/100 gal) + Segovis (3.2 fl oz/100 gal) drench. (Do not apply more than 9.6 fl oz of Segovis to a single crop annually.)
Follow all label instructions and note warnings; local restrictions may apply. Product names are given for information purposes only and are not an endorsement, nor is any criticism implied of products not mentioned.