Field Crops Soybeans. Disease. Seedling Disease (Rhizoctonia solani, Phytophthora, Pythium, etc.)

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1 Seedling (Rhizoctonia solani, Phytophthora, Pythium, etc.) Charcoal Rot (Macrophomina sp.) Phytophthora Root Rot (Phytophthora sp.) Red Crown Rot (Black Root Rot) (Calonectria sp.) Southern Blight (Sclerotium sp.) Aerial Blight (Rhizoctonia sp.) Symptoms: Seed decay and post emergence damping off. Roots and basal portion of stem may deteriorate or be killed. Source of Inoculum: Most of these organisms are soil borne and persist in crop residue. Control: Seed treatment. Symptoms: Seedling infections result in a discoloration at the soil line. Seedlings may die if hot, dry conditions exist, or they may survive in wet weather with disease symptoms reappearing during hot, dry spells. In older plants, a light brown discoloration of internal tissue occurs. Plants turn yellow and mature very early. Below the epidermis, at the soil line, small black bodies appear, giving the tissue a grayish black charcoal appearance. Control: Avoid excessive seeding rates. Rotate with nonhost crops. Maintaining good fertility will reduce the incidence of this disease. Avoid plant stress as much as possible by using good management practices. Symptoms: Destroys roots and tender stems of infected seedlings, resulting in rapid death. Older plants turn yellow and leaves wilt. A brown discoloration develops in the stem. Source of Inoculum: Soil borne. Damage is most severe on heavy clay soils or on poorly drained soils. Control: Avoid planting susceptible varieties on poorly drained soils. Rotate. Symptoms: First symptoms appear as an interveinal yellowing of the tops of individual plants, generally when plants are in the early pod stage. Later, interveinal tissue of leaves turns brown. That is followed by defoliation. On the stems, reddish orange fruiting structures appear at the soil surface and up to 3 inches above. Stem tissue appears reddish. Control: Research and field observations indicate there are differences in varieties, but exact ratings are difficult to achieve. Delay planting until later part of recommended planting time. Symptoms: Scattered plants wilt suddenly and die. White mold appears at the base of the plant and girdles the stem. Tan to brown sclerotia (resting bodies) about the size of mustard seeds appear in the mold. Source of Inoculum: The fungus is soil borne and occurs widely in many soils. It is capable of persisting on almost any type of organic matter. Control: Losses to this disease usually are minimal and do not warrant control measures. Symptoms: The infected area typically involves the lower third of one or more of the three leaflets. The necrotic areas may vary in shape from circular to irregular with reddish brown margins. Leaf blight, leaf spots and defoliation are symptoms of the disease. Lesions may vary from reddish brown to brown or tan. Several leaflets may appear to be glued together with a cottony growth (fungus). Petioles, stems and young pods also are attacked. Source of Inoculum: Weed hosts, field trash and soil.

2 Control: Fall cultivation of stubble. Use good seedbed preparation and weed control. Research and field observations indicate there are differences in varieties. Use Quadris fungicide at first appearance of disease and conditions that favor disease development. See manfacturer s label for suggested rates. Brown Leaf Spot (Septoria sp.) Downy Mildew (Peronospora sp.) Frogeye Spot (Cercospora sp.) Purple Seed Stain (Cercospora sp.) Anthracnose (Colletotrichum sp.) Soybean Rust (Phykopsora pachyrhizi) Pod and stem blight (Diaporthe phaseolorum var. sojae = Phomopsis sojae) Symptoms: Angular brown to reddish brown spots appear first on lower leaves, causing yellowing and later defoliation. Symptoms usually are seen first on young plants during cool weather. Sizes of spots vary from a pinpoint to ¼ inch diameter. Source of Inoculum: The fungus overwinters in crop residue and on infected seed. Control: Plant disease free seed. Rotate. Bury crop residue deeply as soon as possible. Development of the disease is limited by warm weather. Symptoms: Indefinite yellowish green areas on upper leaf surface. Grayish tufts of mold growth on lower leaf surface beneath chlorotic spots. Source of Inoculum: Overwinters in soil, on seed and in soybean residue. Control: Crop rotation. Use of disease free seed. Seed treatment reduces seedling infection. Symptoms: An eyespot type of lesion with a gray or light tan center and a narrow reddish brown border forms on the leaves. May cause premature defoliation. Source of Inoculum: Seed and airborne. Control: Use resistant varieties. Apply foliar fungicides. 1 Symptoms: Pink or light purple to dark purple discoloration of seed. Cracks may occur in discolored areas. Reddish brown angular lesions, approximately 1/16 inch diameter, may occur on leaves, stems or pods late in the growing season. Source of Inoculum: Overwinters in crop residue and on infected seed. Control: Plant disease free seed. Treat seed with fungicides. Apply foliar fungicides. Symptoms: Symptoms appear as irregular brown areas most frequently on stems and pods. In advanced stages, affected tissues are covered with black fruiting bodies. The disease may cause serious losses, especially during rainy periods. Seed may fail to form or be wrinkled and moldy. Control: Plant disease free seed. Some benefit may be derived from seed treatment. Plow under crop residue. Apply foliar fungicides. 1 Symptoms: Rust pustules can be found on the underside of lower leaves when conditions are right for disease development. Pustules are tiny and raised and require at least a 15X hand lens to see the pustules. Control: Fungicides will control Asian soybean rust, but timing is critical. Symptoms: Numerous small black fruiting bodies appear on the pods and stems of mature plants. Blight usually occurs in linear rows on the stem. Under favorable environmental conditions for the disease, it can be observed as a white mycelial growth on seed. Source of Inoculum: Fungus is seed borne and overwinters on diseased plant

3 tissue in the field. Control: Plant disease free seed. Some benefit may be derived from the seed treatment. Apply foliar fungicides. Stem Canker (Diaporthe phaseolorum var. caulivora) Virus or Virus like Complex Reniform Nematodes (Rotylenchulus reniformis) Root Knot Nematodes (Meloidogyne incognita group) Symptoms: First symptom is the appearance of small reddish brown lesions on one or both cotyledons. Late in the season, dead plants are seen with dried attached leaves. Interveinal yellowing is evident on leaflets (similar to foliar symptoms of red crown rot). Infection usually starts as a small lesion at the base of a main stem node. Lesions enlarge rapidly to form a slightly sunken, reddishbrown canker. Plants are brittle and break at the canker. Control: Use resistant varieties. Delay planting until later part of recommended planting time. Avoid stress. Maintain good fertility. Symptoms: Infected plants remain green, especially stems, beyond expected harvest date, with welling appearing at the nodes. Few pods are formed, and those that do form contain only one or two beans. A proliferation of buds may appear. Control: Some of the causal agents are carried over in infected seed. Do not save seed from infected fields. Symptoms: Severely infected plants are stunted and may show chlorosis. Severe yield reduction may occur when nematode populations are relatively high. Control: Plant resistant varieties. Rotate with nonhost crops. Under extreme conditions, use nematicides. Symptoms: Above ground symptoms are poor pod set with wilting and stunting in more or less circular patches on lighter soil types. Below ground symptoms are knots or galls on the roots. These swellings are a part of the root and do not flick off easily, as bacterial nodules do. Source of Inoculum: The nematode overwinters in the soil as eggs or larvae. Control: See varietal resistance table. Rotate with less susceptible crops. Under extreme conditions, use nematicide. Soybean Cyst Nematodes (Heterodera glycines) Other Nematodes Spiral Lance Ring Lesion Stubby root Symptoms: Stunting and various stages of yellowing occur in roughly circular spots. Symptoms vary, depending on nematode population, soil type and fertility and environmental conditions. Symptoms are most pronounced on sandy soil. Source of Inoculum: Nematodes overwinter in soil, primarily inside resistant cysts. They may be spread to new locations by any means that spread soil. Control: Practice two to four year rotation with cotton, corn or sorghum. Symptoms: Stunting, stand loss and reduced yields are associated with high populations of single or mixed populations of these nematodes. Symptoms will vary depending on nematode type and population levels. Control: Rotate with other crops. If populations are high at planting, a nematicide may be used.

4 2012 SOYBEAN FUNGICIDE SUMMARY This is a guide and NOT A LABEL. Always refer to the product label for complete information. The diseases listed in this table are listed on the product label. Before choosing a product, read the qualifying statements cited in this table. These statements are based on the data of LSU AgCenter soybean plant pathologists who evaluate these products annually. FUNGICIDE COMMON NAME CLASS RATE (per acre) DISEASES 1 Alto 100 SL cyproconazole triazole 2 (rust) ounces ounces (others) SBR, AB, AN, CB, FE, PS Domark tetraconazole triazole ounces CB, FE, AN Gem RC trifloxystrobin ounces AB, AN, SBR, CB, FE, PS Headline 2.08EC pyraclostrobin 6 12 ounces SBR, CB, FE, AN, PS, AB Headline SC pyraclostrobin 6 12 ounces SBR, CB, FE, AN, PS, AB Proline 480 SC prothioconazole triazole fluid ounces SBR, FE Quadris 2.08SC ounces SBR, CB, FE, AN, PS, AB Quadris Xtra Quilt Quilt Xcel Stratego Stratego YLD cyproconazole trifloxystrobin trifloxystrobin prothioconazole triazole ounces AB, AN, CB, FE, PS, SBR triazole ounces AB, AN, CB, FE, PS, SBR triazole ounces AB, AN, CB, FE, PS, SBR triazole 2 10 ounces AB, AN, CB, FE, PS, SBR triazole ounces AB, AN, CB, FE, PS, SBR Topguard flutriafol triazole ounces CB, FE, SBR Topsin 4.5FL thiophanatemethyl benzimidazole fluid ounces CB, FE, AN, PS Tilt Bumper triazole fluid ounces AB, AN, FE, SBR

5 1 CB=Cercospora blight / purple seed stain, FE=Frogeye, AN=Anthracnose, PS=Pod and stem blight, AB=Aerial blight and SBR=Soybean rust. 2 Triazoles have been effective against soybean rust but may not be as effective against other diseases, especially Cercospora blight. 3 Strobilurins are effective against aerial blight, anthracnose and pod and stem blight but are less effective against soybean rust and Cercospora blight. There is evidence in other states that resistence exists in the Cercospora diseases (frogeye and Cercospora blight) to the strobilurin products. 4 Benzimidazole fungicides have been inconsistent in their effectiveness against Cercospora blight.