Herbaceous flowering plants are an asset to almost any landscape. Healthy plants are essential to maintaining a desirable aesthetic appearance. This publication suggests ways to control important infectious diseases of flowers and ground covers commonly grown in Kentucky.
Diseased plants may show one or more of the following symptoms: leaf spot, blight, scorch, yellowing, stem and root decay, wilt, swellings, malformations and galls, and dieback. To control any of these problems, you need to know the cause.
Plants may show poor health due to adverse growing conditions like drought, flooding, winter cold, poor soil, excess fertilizer, mineral element deficiency, toxic chemicals, air pollution, and mechanical injuries. On the other hand, they may have an infectious disease, caused by specific microorganisms or pathogens like bacteria, fungi, viruses, and nematodes.
To treat diseases caused by adverse growing conditions, you try to correct whatever factors caused the problem. You may change how much you water or mulch or what you add to your soil. You may provide better drainage or cold protection or change many other kinds of cultural or environmental factors.
To control infectious diseases, you do the following:
Control: Destroy old plant debris in the fall. Avoid wetting foliage. Prune out nearby shading vegetation. Provide adequate plant spacing. Use fungicides such as chlorothalonil, dicloran, ferbam, iprodione, mancozeb, maneb, thiophanate-methyl, vinclozolin, or mancozeb + thiophanate-methyl. Read the label for lists of specific plants allowed for each fungicide.
Control: Avoid introducing infected plants into the nursery or landscape. Remove and destroy infected plants. In nurseries, oxamyl can be used to treat plants.
Control: Gently remove and destroy infected plants. Use crop rotation if the soil in a bed becomes infested. Soil fumigation may be an option for commercial applications. Fenamifos nematicide may benefit some plants. See label for application instructions and list of plants cleared.
Control: Remove dead plants and 6 inches of surrounding soil and replace with clean soil or use another kind of plant. In nurseries, PCNB fungicide can be used.
Control: Avoid crowding plants. Grow susceptible plants in a sunny location; prune out nearby shading vegetation. Avoid wetting foliage. Sprays of dodemorph, fenarimol, thiophanate-methyl, triadimefon, wettable sulfur, ziram, or mancozeb + thiophanate-methyl are effective for powdery mildew control. Read the label for lists of specific plants allowed for each fungicide.
Control: Begin with sterilized soil, clean equipment, and disease-free plant materials. Soil drenches containing iprodione, PCNB, thiophanate-methyl, or ethazole + thiophanate-methyl will prevent infections. Read the label for lists of specific plants allowed for each fungicide.
Control: Improve planting site drainage. Remove and destroy infected plants. Begin seedlings using sterilized soil and clean equipment. Soil drenches containing ethazole, fosetyl-Al, metalaxyl, propamocarb, or ethazole + thiophanate-methyl will prevent infections. Read the label for lists of specific plants allowed for each fungicide.
Control: Remove and destroy infected plants and sclerotia.
Control: Remove dead plants and 6 inches of surrounding soil and replace with clean soil or use alternate ground cover. In nurseries, PCNB fungicide can be used.
Control: Remove dead plants and surrounding soil and replace with clean soil.
Control: Select rootstocks from healthy plants. Keep young growth dry. Don’t crowd plants in the bed.
Control: Avoid wetting foliage. Spray plants at first indication of disease using captan, chlorothalonil, ferbam, maneb, mancozeb, ziram, or mancozeb + thiophanate-methyl.
Control: Rake up and destroy old leaves at the end of the season.
Control: Remove and destroy infected plants.
Control: Dig up and destroy infected plants. Plant only tubers from healthy plants. Control aphid vectors.
Control: Prune out and destroy diseased vines. Avoid unnecessary watering. The cultivar Gold Dust is considered resistant and the cultivars California, Eva, Gold Heart, Manda Crested, Perfection, Sweet Heart, and Telecurl are considered tolerant to bacterial leaf spot.
Control: Pick off infected leaves. Apply fixed copper fungicides as needed.
Symptoms: Irregular spots develop at first, often in the form of a yellow or tan V-shaped lesion with dark leaf veins at the leaf edge. Then larger areas of the leaf are killed. Stems appear blackened and may decay, causing leaf yellowing and wilt.
Control: Purchase only disease-free seedlings or cuttings. Remove and destroy infected leaves. Avoid replanting in the same bed next year. Avoid wetting foliage.
Control: Avoid wetting foliage. Provide sunny growing location. Use only disease-free cuttings. Prevent infections by spraying with ferbam, mancozeb, oxycarboxin, or triadimefon.
Control: Avoid injury when digging. Store corms at 35°F to 40°F in dry location. Dust corms with captan, dicloran, or PCNB before planting.
Control: Destroy diseased plants. Control aphid vectors.
Control: Remove and destroy leaves in late fall. Fixed copper sprays may be beneficial.
Control: Cut and destroy leaves in the fall. Spray with clorothalonil, ferbam, iprodione, mancozeb, thiophanate-methyl, or triadimefon fungicides.
Control: Control insect borers that create injury for entry of bacteria. Dig up and destroy infected rhizomes. Cut out rotted areas if only partly decayed.
Symptoms: Stem decay. Dark, raisin-shaped fungal sclerotia present in rotted stem.
Control: Remove and destroy infected plants.
Control: If bulbs are dug, avoid injuries. Dry them rapidly. Discard decayed bulbs.
Control: Usually due to poor growing conditions (i.e., potassium deficiency, drought, cold spring weather, excess shade, too deep planting). Supply good growing conditions.
Control: Avoid wetting foliage. Destroy infected foliage at season’s end. Remove nearby shading vegetation. Spray with fixed copper, mancozeb, or maneb.
Control: Space well for good ventilation and low humidity. Keep leaves dry. Ferbam, maneb, mancozeb, propiconazole, and ziram fungicides control rust.
Control: Remove and destroy affected stems. Thin stand to promote better aeration. Treat plants and soil with a spray of iprodione, mancozeb, or mancozeb + thiophanate-methyl.
Control: Hand pick infected leaves. Apply fixed copper fungicide in spring just before new growth appears.
Control: Avoid splashing water. Use commercially grown, disease-free seed.
Control: Space plants well. Avoid wetting foliage. Sprays with ferbam, iprodione, maneb, mancozeb, or mancozeb + thiophanate-methyl prevent infections.
Below is a list of fungicides, each followed by some trade names under which it is marketed. Use this guide to find chemicals required for your particular need.
Benomyl: Benomyl WP.
Bordeaux: A mixture of copper sulfate (bluestone) and spray lime in water. The first figure in the formula is copper sulfate in pounds, the second figure is spray lime (hydrated lime) in pounds, and the third figure is water in gallons. Mixing instructions: Fill tank 1/2 to 3/4 full of cold water. Add desired amount of hydrated lime and mix thoroughly. Add dissolved copper sulfate and mix thoroughly. Fill tank with the rest of the water and use immediately after mixing. If lumping occurs, strain mixture.
Captan: Orthocide, Captan Wettable Fungicide, Captan 50W.
Chlorothalonil: Daconil 2787, Bravo, Multipurpose Fungicide.
Dodemorph acetate: Milban.
Ethazole (etridiazole): Truban.
Fenamifos: Nemacur (nematicide).
Ferbam: Fermate, Ferbam, Carbamate.
Fixed copper: Tri-basic Copper Sulfate; Basic Copper Fungicide, Corona 53, Ortho Copper 53 Fungicide, Basic Copper Sulfate, Copper Hydroxide; Kocide 101, Kocide 202.
Folpet: Phaltan, Chevron Folpet, Fungitrol 11, Ortho Rose and Garden Fungicide, Stauffer Folpet.
Fosetyl-Al: Aliette WDG.
Iprodione: Chipco 26019, Rovral.
Mancozeb: Fore, Dithane M-45, Mancozeb, Penncozeb, Protect T/O.
Maneb: Dithane M-22, Maneb, Maneb Garden Fungicide.
PCNB: Cleary’s PCNB, Terrachlor.
Propiconazole: Banner, Immunex.
Sulfur, wettable: Corosul S, Magnetic “95,” Micro Flotox Wettable Sulfur, Dusting Sulfur.
Thiophanate-methyl: Cleary's 3336WP, Fungo Flo, Domain.
Thiophanate-methyl plus ethazole: Banrot.
Thiophanate-methyl plus mancozeb: Zyban, Duosan.
Triadimefon: Bayleton, Strike.
Vinclozolin: Ornalin, Ronilan, Curalan.
Ziram: Ziram Bacterial Blight—Geranium