|Seed Treatment Advantages-72
Project Leader and Principal UC Investigators
R.K. Webster,Cause and Control of Rice Diseases
Greenhouse and field studies determined the most effective fungicides
against seed rot and seedling disease of water-sown rice, and the best rates
and methods of application. The tests included more than 30 chemicals that
had shown biological activity against Achlya klebsiana and Pythium.
Consistently most effective in improving total stand establishment were
Difolatan® and captan. Treating and drying seed before soaking reduced seed
rot and seedling disease better than treating after soaking or adding the
chemical to the soak water, even though substantial portions of the
fungicide were lost to the soak water. Application before soaking was either
by slurry or spray mist with flowable formulations; the chemicals did not
damage treated seed during storage up to 4 months.
Seed treatment gives the biggest advantage during the early planting season, when the environment is often unfavorable for rapid germination and seedling growth. Seed treatment can therefore be considered insurance for more uniform and better stands and reduced need for reseeding.
To determine whether seeding rates (commonly 150-200 lb/A) can be reduced by fungicide treatment, yields of treated and untreated seed sown at different rates were compared over a 3-year period. Also compared was the seed delivered per square foot with the seeding rate intended (aircraft setting) and the actual numbers of plants established per square foot.
At all seeding rates compared, plants established per square foot (stand density) were 12-36% greater for treated seed than for untreated seed. Fungicide seed treatment (as already indicated in small trials) is clearly effective under commercial conditions in minimizing seed rot and seedling disease in water sown rice. The various seeding rates in different trials gave quite varied ranges of stands (in plants per square foot): 11.3 to 25.2, 9.0 to 22.3, 17.2 to 21.2, 25.1 to 35.4, and 10.1 to 16.6. Even with these wide divergencies, yields did not differ significantly, although stands denser than 25 per square foot tend to have thin stems and greater lodging problems.
These results support the following conclusions: 1) the increase in percent stand resulting from seed treatment justifies considerably lower seeding rates; 2) the saving in seed may more than offset treatment costs; and 3) where seedling disease is a problem, seed treatment provides more uniform stands, reducing replant needs. (RP2)