How to Cure Black Spots on Plants
Black spots are among the most common symptoms of plant disease, whether the problem is a fungus or a bacterial infection. A problem for the casual gardener is that the spots of various diseases may look strikingly similar, and knowing the best way to cure black spots on plants depends on diagnosing the cause. Always begin by researching the common diseases of the plant species. It’s important to reach a define diagnosis before you attempt to treat the plant. Fortunately, a consistent control program is all that’s needed to deal with most plant diseases.
Examine the plant for other disease symptoms known to be associated with black spots on the species. For example, search roses for other black spot disease symptoms caused by the fungal pathogen Diplocarpon rosae, including diminished health, black spots on upper sides of leaves, yellowed foliage, and leaf drop. Look over canes for the presence of purple-hued areas of dying plant tissue. Look closely at spots for the presence of tiny fruiting bodies.
Examine both deciduous and evergreen trees and shrubs displaying black spots for signs of anthracnose. The University of California Integrated Pest Management Program says symptoms to look for include black, “tar-like” spots, necrotic leaf tissue, cankered branches and curled leaves. Examine trees that lose their leaves early for distorted branches.
Regularly monitor vegetable crops such as tomatoes. Look for blight issues, such as early blight, caused by the fungal pathogen Alternaria solani, which causes black spots in the form of a bull’s eye on lower leaves. Examine the ground for yellowed leaves that have dropped early. Search fruit for dark, sunken areas of plant tissue. Touch spots to see if they are wet, a sign of late blight caused by the fungal pathogen Phytophthora infestans, which may cause large, callused spots.
Examine fruit trees for the presence of a bacterial spot infection caused by the bacterial pathogen Xanthomonas pruni. Look for tiny, black, irregular spots, which group near the ends of leaves and along veins. Spots may appear wet. Search for areas on the leaf where spots have died and fallen from the plant, leaving holes.
Examine ornamental plants, as well as fruits and vegetables, for Botrytis blight, also referred to as gray mold. Search for symptoms caused by the fungal pathogen Botrytis cinerea, including raised black spots on plant tissue, wet spots on flowers and other soft plant tissue, and the tell-tale sign of infection, a gray-hued, soft mold growth on areas of dying plant tissue.
Control black-spot diseases with cultural methods first, as employing toxic chemicals when they’re not needed can cause needless harm to desired plants and the environment, and may contribute to chemical resistance.
Use pruning shears to remove affected plant parts, and destroy the removed material, including fallen debris. This helps to reduce the severity of disease and prevent its spread. Sterilize all equipment, such as pruning tools, between each cut and each plant. Wash your hands regularly, or change gloves, to guard against becoming an agent of disease transfer.
Avoid overhead watering. Instead, irrigate soil directly with methods such as drip irrigation. Overhead irrigation causes standing water on leaf surfaces, which can provide the ideal environment for proliferation of both fungal and bacterial pathogens.
Put a 2- to 3-inch layer of organic mulch such as wood chips under surrounding plants without pressing it against stems or trunks. Mulch assists in weed prevention, conserves moisture and protects plants from accidental injuries that may weaken plants and provide an entry point for disease.
Apply low-toxicity fungicides or bactericides when possible, to avoid damaging the balance of beneficial bugs in the garden and to prevent further injury to the desired plant. Saturate roses with neem oil or a sulfur-based pesticide, for example.
Apply higher-toxicity fungicides and bactericides when the problem is severe or when low-toxicity methods fail. Follow the directions on the labels carefully. Though some diseases respond best to fungicide applications as a preventive measure, fungicides also can decrease the intensity of disease or protect new growth.
Apply a fungicide with an active ingredient, such as chlorothalonil or mancozeb, to roses with black spot disease every one to two weeks. Apply fungicides with chlorothalonil to plants affected with anthracnose at bud break, and again in two weeks in the case of wet weather; apply to blighted vegetables as well, before symptoms occur and during active growth. Apply chlorothalonil to plants infected with gray mold as a preventive measure once every five to seven days in wet weather or every week to 10 days during warm, dry weather, applying only one-third the usual rate to plant blossoms, advises the University of Illinois Extension. Apply a copper-based spray and an antibiotic, alternating between the two, to prevent and control bacterial spot.
How to Cure Black Spots on Plants. Black spots are among the most common symptoms of plant disease, whether the problem is a fungus or a bacterial infection. A problem for the casual gardener is that the spots of various diseases may look strikingly similar, and knowing the best way to cure black spots on plants …
Black spot disease is the scourge of rose growers. Not only does it make the plant look unsightly, but it also causes the leaves to drop prematurely, resulting in weakening the plant if it occurs repeatedly.
Black spot is a common fungal problem on roses but can be found on other plants too. The spots can be of various colours – grey, brown or black. The spots are in fact dead leaf tissue caused by the fungus which spreads the disease. Spots can sometimes join together to form larger areas of dead tissue. Roses can also develop smaller black spots on their stems.
There are a few other symptoms than the spots themselves. However, diseased plants frequently have other problems causing weaknesses, which enable the fungal disease to develop. It is worthwhile carefully checking any plant with leaf spot.
Treatment And Control
Immediately remove and destroy all infected leaves and plant parts. Pick up any fallen foliage and destroy it, whenever it happens but especially in autumn. To reduce the chances of re-infection for the following season, prune back plants hard. Where roses were infected with black spot disease in the previous season, then start spraying with a suitable fungicide as new leaves open and repeat at fortnightly intervals.
Spray with a suitable fungicide from April onwards. Continue spraying at recommended intervals throughout the summer.
Black spot disease is the scourge of rose growers. Not only does it make the plant look unsightly, but it also causes the leaves to drop prematurely.