Disease Control

NOTE: For the disease control products listed below, one product trade name and formulation is provided for each active ingredient (common name) as an example of rates, preharvest interval (PHI), restricted entry interval (REI), and special instructions. In many cases, there are other products available with the same active ingredient. Please see Table 26 and Fungicides and Bactericides Alphabetical Listing by Trade Name for more information on products with the same active ingredients.

The symbol ^OG   indicates a product is listed by the Organic Materials Review Institute (OMRI) as approved for use in organic production. See Organic Certification section for more details.

Leaf Spots (Helminthosporium, Cochiliobolus, Cercospora)

Symptoms and the appearance of lesions can differ by pathogen, lesions will appear on leaves, leaf sheaths, and husks. Plant resistant varieties. Improve air circulation by plant spacing and site selection. Plow under crop debris promptly after harvest to speed decomposition. Fungicide rotation is critical for prevention of resistance development- do not make back-to-back applications of products with active ingredients from the same group.

• azoxystrobin (Quadris F AKA Abound F): 6.0 to 15.5 fl oz/A; PHI 7d, REI 4h, Group 11. May be extremely phytotoxic to certain apple varieties. See label for restrictions. 
• azoxystrobin & propiconazole (Quilt): 7.0 to 14.0 fl oz/A; PHI 14d (sweet), PHI 30d (popcorn), REI 12h, Groups 11 & 3. 
• chlorothalonil (Bravo Weather Stik AKA Bravo 720): 0.75 to 2.0 pt/A; PHI 14d, REI 12h, Group M05. Do not apply to sweet corn to be processed. Not labeled for popcorn.
• fluxapyroxad plus pyraclostrobin (Priaxor Xemium): 4.0 to 8.0 fl oz/A; PHI 7d (sweet), PHI 21d (popcorn), REI 12h, Groups 7 & 11.
• mancozeb (Dithane F45): 1.5 qt/A; PHI 7d, REI 24h, Group M03. 
• propiconazole (Tilt): 2.0 to 4.0 fl oz/A; PHI 14d (sweet), PHI 30d (popcorn), REI 24h, Group 3.
• pyraclostrobin (Headline): 6.0 to 12.0 fl oz/A; PHI 7d, REI 12h, Group 11.
• pyraclostrobin plus metconazole (Headline AMP AKA BAS 556 SC): 8.0 to 10 fl oz/A; PHI 7-20d (see label), REI 12h, Groups 11 & 3.
• trifloxystrobin plus propiconazole (Stratego): 10.0 fl oz/A; PHI 14d, REI 12h, Groups 11 & 3.

Northern Corn Leaf Blight (Exserohilum (Helminthosporium) turcicum)

Northern corn leaf blight is an emerging problem on farms up and down the Connecticut River Valley. Northern corn leaf blight can develop very rapidly resulting in a complete blighting of leaves. E. turcicum overwinters in and on leaf debris and conidia can be spread long distances by wind. Under the right conditions (prolonged leaf wetness, extended rainy and humid weather, moderate temperatures), conidia are produced abundantly and disease spread is rapid. Reduce primary inoculum by crop rotation and tilling under of crop residue. Evidence suggests more severe disease in reduced-till systems; 1-year rotations are suggested for conventional practices and 2-year rotations for reduced-till. Resistant hybrids of all maturity groups are available. Lesions may vary in morphology when certain genes for resistance to this disease are present. The presence of these genes results in long, yellow, linear streaks that resemble the symptoms of Stewart's Wilt. Growing susceptible varieties will cause the resistance of nearby resistant varieties to break down. Fungicide rotation is critical for prevention of resistance development- do not make back-to-back applications of products with active ingredients from the same group.

• azoxystrobin (Quadris F AKA Abound F): 6.0 to 15.5 fl oz/A; PHI 7d, REI 4h, Group 11. May be extremely phytotoxic to certain apple varieties. See label for restrictions.
• azoxystrobin plus propiconazole (Quilt):  7.0 to 14 .0fl oz/A; PHI 14d (sweet), PHI 30d popcorn), REI 12h, Groups 11 & 3.
• chlorothalonil (Bravo Weather Stik AKA Bravo 720): 0.75 to 2 pt/A; PHI 14d, REI 12h, Group M05. Do not apply to sweet corn to be processed. Not labeled for popcorn.
• fluxapyroxad plus pyraclostrobin (Priaxor Xemium): 4.0 to 8.0 fl oz/A; PHI 7d (sweet), 21d (popcorn), REI 12h, Groups 7 & 11.
• mancozeb (Dithane F45): 1.5 qt/A; PHI 7d, REI 24h, Group M03. 
• propiconazole (Tilt): 2.0 to 4.0 fl oz/A; PHI 14d (sweet) PHI 30d (popcorn), REI 24h, Group 3.
• pyraclostrobin (Headline): 6.0 to 12.0 fl oz/A; PHI 7d, REI 12h, Group 11.
• pyraclostrobin plus metconazole (Headline AMP AKA BAS 556 SC): 8.0 to 10 fl oz/A; PHI 7-20d (see label), REI 12h, Groups 11 & 3.
• trifloxystrobin plus propiconazole (Stratego): 10.0 fl oz/A; PHI 14d (sweet), 30d (popcorn), REI 12h, Groups 11 &3.

Rust (Puccinia species)

The common rust fungus that occurs on sweet corn does not overwinter in the Northeastern United States; each year it is blown up from the south. Rust can appear as blister-like pustules called uredinia on the leaf epidermis. Rust can cause significant reduction in ear weight and yield on susceptible varieties. Corn is more susceptible to infection prior to tasseling so later maturing plantings may have higher losses. Fungicides will control this disease but should be applied before tasseling. Apply fungicides when 80% of the plants show 1 or more pustules per leaf. Resistant varieties are available. Fungicide rotation is critical for prevention of resistance development- do not make back-to-back applications of products with active ingredients from the same group.

• azoxystrobin plus propiconazole (Quilt): 10.5 to 14 fl oz/A; PHI 14d (sweet), PHI 30d (popcorn), REI 12h, Groups 11 & 3.
• benzovindiflupyr (Trivapro A): 13.7 fl oz/A (see label); PHI 14d, REI 12h, Group 3, 7 & 11.
• chlorothalonil (Bravo Weather Stik AKA Bravo 720): 0.75 to 2 pt/A; PHI 14d, REI 12h, Group M5. Do not apply to sweet corn to be processed. Not labeled for popcorn.
• fluxapyroxad plus pyraclostrobin (Priaxor Xemium): 4.0 to 8.0 fl oz/A; PHI 7d (sweet), 21d (popcorn), REI 12h, Groups 7 & 11.
• mancozeb (Dithane F45 ): 1.5 qt/A; PHI 7d, REI 24h, Group M03.
• propiconazole (Tilt): 4.0 fl oz/A; PHI 14d (sweet), PHI 30d (popcorn), REI 24h, Group 3. 
• pyraclostrobin (Headline): 6.0 to 12.0 fl oz/A; PHI 7d, REI 12h, Group 11.
• pyraclostrobin plus metconazole (Headline AMP): 8.0 to 10 fl oz/A; PHI 7-20d (see label), REI 12h, Groups 11 & 3.
• trifloxystrobin plus propiconazole (Stratego): 10.0 fl oz/A; PHI 14d, REI 12h, Groups 11 &3.

Seed Decay

Buy treated seed. Do not use treated seed for food, feed or oil purposes.

Common Smut (Ustilago maydis)

Smut occurs sporadically from one season to another but usually less than 2% of the plants are affected. The disease is favored by dry conditions when temperatures are between 80° F and 90° F and nitrogen fertility is high. Injury due to cultivation, hail, or wind-blown sand can increase the incidence of disease when environmental conditions are favorable. Symptoms will appear as galls on the ears or stalks and contain black teliospores. Fungicides will not provide effective control of common smut.

Stalk Rots (Gibberella, Stenocarpella, Macrophomina, Colletotrichum, Fusarium)

Fungal stalk rots continue to be serious diseases of corn. Their occurrence and severity vary from year to year. Early symptoms may be plant wilting and later symptoms may be leaf discoloration, browning of lower stalk, and the pith becoming hallow. Stalk rots cause losses by causing premature plant death, difficulties with mechanical harvesting, and ear rot due to contact of ears with the soil. Factors that influence stalk rot include the susceptibility of the hybrids, weather conditions, the presence of foliar diseases, plant densities, insect damage, moisture availability, soil fertility, and tillage practices. Soil fertility, tillage, and plant density can be adjusted to provide control. Stalk rot is more severe and more common where soil fertility is high. Nitrogen (N) levels can both increase and decease stalk rot; an excess of N in relation to potassium (K) increases stalk rot. A balanced and continuous supply of N reduces the occurrence of stalk rot. Adequate K reduces stalk rot severity by strengthening cell walls. In general, corn debris left on the surface of the soil harbors many foliar diseases that increase stalk rot by reducing photosynthesis. As the population of plants increases, the incidence and severity of stalk rot also increase, especially in susceptible hybrids. Control is most successfully achieved through the use of resistant hybrids. Cultural practices such as balanced fertility, proper plant spacing, and reduction of other plant stresses, such as insect damage, can also reduce stalk rot.

Stewart's Wilt (Pantoae (Erwinia) stewartii )

This bacterial disease is spread by the corn flea beetle and is particularly damaging when susceptible varieties are planted following mild winters. P. stewartii overwinters in the alimentary tract of adult corn flea beetles, not in the soil or in plant debris. Severity of Stewart's Wilt depends on three factors: the winter temperatures prior to planting, the amount of disease the previous season, and cultivar susceptibility. If cold winter temperatures occur, fewer flea beetles survive to transmit the disease. The amount of disease in the previous season determines the percentage of emerging beetles carrying the bacterium. Symptoms will include narrow lesions, 5 cm or greater, that will have wavy margins. Hybrids with greater levels of resistance can tolerate more infection with less yield loss. Resistance restricts the movement of the bacteria in the plant. Grow varieties that are resistant to the disease.  Use insecticides to control flea beetles, particularly on susceptible varieties in the seedling stage. This is not as effective as resistant varieties, but reduces losses where susceptible hybrids must be planted. Scout frequently for flea beetles as rapid growth of leaf tissue makes untreated surfaces available.

Maize Dwarf Mosaic Virus (MDMV)

There are several strains of MDMV which are spread by more than 20 species of aphids. The virus can be seedborne in maize and probably in some annual grasses. The virus is nonpersistent but is retained by the aphid for up to 18 hours. This allows time for the vector to be transported from southern states where MDMV is more prevalent and many weed hosts occur. Johnson grass is an important perennial weed host for MDMV occurring in southern New England and it should be eradicated. Early symptoms will be present as chlorotic spots and streaks, leaves will later become mosaic. Plant resistant or tolerant corn varieties. Golden Gleam, Sundance, Spring Gold, Seneca Star, Early Fortune, Sugar Loaf, Dandy and Capitan have some tolerance. Enforcer, Biguard, Silver Red and Seneca 258 are resistant. MDMV is more likely to be a problem for later plantings. Plant late plantings away from peach trees, overwintering host of the green peach aphid.