1. What is the reaction of my varieties to the major diseases? Check the Rice Varieties & Management Tips publication. You need to know how susceptible a variety is to sheath blight, blast, bacterial panicle blight or Cercospora.
2. What disease is in my fields? Get out in the field and scout! Every year is different, and you need to check which disease is present and how severe it is.
3. What growth stage is my rice at? Scout for growth stage at the same time you scout for disease. Timing is critical to effective disease control. You do not want to miss an important application growth stage.
4. Are conditions favorable for disease development? Warm and moist conditions favor sheath blight, blast and Cercospora. Hot, above 95, favors bacterial panicle blight and inhibits sheath blight, blast and Cercospora development.
5. What’s happening in my neighbor’s fields? Likely what’s happening in their fields is happening in yours. Or if blast is in the area, it will increase disease in your fields.
6. Is my agronomic management plan helping or hurting disease development? Excessive N, thick stands, rice-rice and rice-soybean rotations, or late planting all favor rice diseases.
7. Is my fungicide timing correct or is it too early or too late? If you apply a fungicide too early, it will not last. If you apply it too late, especially after heading, you lose activity.
8. Which fungicide should I use? Propiconazole containing fungicides (Tilt, Bumper,PropiMax, Quilt, Quilt Xcel, and Stratego) are best for Cercospora, kernel smut and false smut. Xemium (Sercadis), strobilurin (Quadris, Gem, Quilt, Quilt Xcel, and Stratego), and flutolanil (Convoy) containing fungicides are best for sheath blight. The strobilurin fungicides are the only ones with blast activity.
If you have or suspect you have the strobilurin-resistant sheath blight fungus, you need to use a Xemium or flutolanil-containing fungicide. Xemium and flutolanil fungicides should be alternated with the strobilurin fungicides for resistance management in fields where the resistant sheath blight fungus has not yet appeared.
9. What will it cost? Compare fungicide prices, premixes vs. tank mixes, etc., and then add the application cost.
10. Is a fungicide justified? You need enough disease in a field to economically justify using a fungicide. Fields with low yield potential probably do not need fungicides. Resistant or moderately resistant varieties seldomneed fungicides.
The delayed phtyotoxicity syndrome
There is a disorder referred to as the rice delayed phtyotoxicity syndrome (DPS), which is caused by severe herbicide damage from herbicides that normally do not cause damage. It is associated with herbicides that have halogenated aromatic compounds as part of their structure, including thiobencarb, quinclorac, triclopyr, propanil and 2, 4-D. The disorder was first identified in Japan during the mid-1970s and in the United States in the mid-1990s. It is caused by the biologic mediated declorination of the benzene ring on the herbicide, making it toxic (nonselective) to the rice.
Unknown soil inhabiting fungi and bacteria dechlorinate the benzene ring on the herbicides and make them toxic to the rice. These populations appear to increase with continued herbicide use. Symptoms usually appear several weeks after application. Symptoms include stunting, excessive tillers, curvature or “fishhooking” of the tillers, dark green color, stem brittleness and, eventually, plant death.
Damaged plants appear in irregular shaped areas unevenly distributed within the field. Damage does not start developing until several weeks after application of the herbicide and flooding when the soil becomes anaerobic. High soil organic levels and green plant materials incorporated into the soil increase occurrence and severity.
The most effective control measure is to drain the field and permit the soil to dry to cracking as soon as possible. Draining causes nitrogen loss and additional weed problems, but if the field is not drained, the rice will continue to die. Switching to alternative herbicides is the only long-term solution.
Several other herbicides can produce similar fishhook tillers on rice. Although these problems are not caused by declorination, the control measure is based on draining the field in most cases. Contact your local LSU AgCenter extension agent for assistance.