Symptoms of bakanae first appear about a month after planting. Infected seedlings appear to be taller, more slender, and slightly chlorotic when compared to healthy seedlings. The rapid elongation of infected plants is caused by the pathogen's production of the plant hormone, gibberellin. Plants with bakanae are often visible arching above healthy rice plants; infected plants senesce early and eventually die before reaching maturity. If they do survive to heading, they produce mostly empty panicles.
Comments on the Disease
Bakanae is one of the oldest known diseases of rice in Asia but has only been observed in California rice since 1999 and now occurs in all California rice-growing regions. While very damaging in Asia, the extent to which bakanae may effect California rice production is unknown.
As diseased plants senesce and die, mycelium of the fungus may emerge from the nodes and may be visible above the water level. After the water is drained, the fungus sporulates profusely on the stems of diseased plants. The sporulation appears as a cottony mass and contaminates healthy seed during harvest. The bakanae pathogen overwinters as spores on the coat of infested seeds. It can also overwinter in the soil and plant residue. However, infested seed is the most important source of inoculum.
The most effective means of control for this disease is the use of noninfested seed. Also, when possible, burning plant residues with known infection in fall may help limit the disease. Research is under way to identify effective seed treatments. Field trials indicate that a seed treatment with sodium hypochlorite (Ultra Clorox Germicidal Bleach) is effective at reducing the incidence of this disease. Using a thoroughly premixed solution of 5 gallons of bleach to 100 gallons of water, seed is soaked for 2 hours, then drained and soaked in fresh water.
|Common name||Amount per acre||REI‡||PHI‡|
|(Example trade name)||(hours)||(days)|
|Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide’s properties and application timing, honey bees, and environmental impact. Always read the label of the product being used.|
|(Ultra Clorox)||2.5% solution (2.5 gallons in 97.5 gallons water)||24||NA|
|MODE-OF-ACTION GROUP NAME (NUMBER1): Unknown|
|COMMENTS: Preplant rice seed treatment. Replace water with 2.5% Ultra Clorox solution during the seed soaking period. Drain and seed within 12–24 hours of draining, as fungal inoculum may increase on seed being held in trailers about 24 hours after draining.|
|‡||Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.|
|1||Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions. Fungicides with a different Group number are suitable to alternate in a resistance management program. For fungicides with mode-of-action Group numbers 1, 4, 9, 11, or 17, make no more than one application before rotating to a fungicide with a different mode-of-action Group number; for fungicides with other Group numbers, make no more than two consecutive applications before rotating to fungicide with a different mode-of-action Group number.|