Late Planted Rice
Seedbed PreparationFertilizer ManagementVariety Selection and Planting DatesWater Management
Rice Blast ControlCrop ResistanceCultural PracticesChemical Control
Nitrogen Management of Akitakomachi and Koshihikari
Office Telephone NumbersLate Planted Rice
This year's high rainfall and flooding have seriously delayed seedbed preparation and planting of area rice fields. Many fields have been too wet for spring straw burning and/or initial tillage operations until recently. Much work still needs to be done on the four to five hundred thousand acres to be planted. Typically, fields are planted from April 20 to May 25. This situation could cause problems with crop establishment, weed and pest management and yield loss. Some of these problems and suggestions for dealing with them follow:Seedbed PreparationIt is important to dry the soil down to 4-6 inches during seedbed preparation to avoid or minimize several rice stand establishment and pest management problems. Wet soils may contain chemically reduced compounds toxic to rice, but these compounds can be oxidized to nontoxic products with sufficient aeration. Oxygen in the soil is also important for vigorous rice seedling growth. Wet or moist soils may also favor early development of tadpole shrimp, algae and weeds. Watergrass especially may emerge from wet soils even before flooding. Carefully monitor for these pests and take appropriate control measures to minimize these problems.
A reasonable delay in planting in order to prepare a dry seedbed is a better course than to slam the crop into a wet and sour soil. Both of these situations increase the crop loss risk, but in my opinion a reasonable delay to plant a field properly is much less risky than planting under poor conditions. Obviously, these are the extremes and sometimes circumstances require that compromises be made.To save time some growers have elected to skip the planing operation and/or apply fertilizers by air. These short cuts may save a significant amount of time without compromising on the need for a dry seedbed.If a significant amount of straw must be incorporated in the spring try to get good straw/soil contact and consider planting affected fields last to encourage decomposition of the residue.Fertilizer ManagementApplying urea or ammonium sulfate by air rather than aqua ammonia by ground can save a lot of time. These dry fertilizers should be incorporated into the soil soon after application to avoid high nitrogen losses.
Regardless of the nitrogen source, rates should be gradually reduced with delays in planting. Nitrogen rates should be reduced by about 10% for May15th plantings and 25% for June 1st plantings. If a starter fertilizer is used the reduction should be taken from the main N source and not the starter. Use of high nitrogen rates, especially with late plantings, could delay maturity, increase blanking and lodging, and increase blast and stem rot severity.Some soil nutrients such as zinc may not be as available if seedbeds remain wet or if temperatures are cool.Variety Selection and Planting DatesIn the warmer rice areas, the recommended planting dates range from April 20 to May 25 with late maturing varieties being planted first and early maturing varieties planted next. At normal planting dates, the late maturing M-401 usually takes 165 days to mature, while the early varieties S-201, M-202, M-204 and L-204 take about 140 days and the very early varieties S-102 and M-103 take 130-135 days. These times will usually shorten with later planting dates.
In the warm areas, the latest recommended planting date for M-401 is May 5, May 15 for for S-201 and M-201, May 20 for M-202 and M-204 and May 25 for S-102 and M-103. These varieties have been planted after these dates, but the probability of reductions in yield increase the later you go. Some local growers have successfully planted M-202 into June, even as late as June 15. While this is possible under favorable conditions it is not something I would encourage. If planting extends into June, M-103 may be a good choice, but seed supplies are very limited.In the cooler areas, such as the Yolo By-pass and Natomas, the recommended planting date window is smaller ranging from April 25 to May 20. The varieties M-401, S-201, M-201 and L-204 are not recommended for these areas.Water ManagementAvoid overly shallow water (1-2 inches) and extended drain periods since they will delay maturity. At panicle initiation, raise water to 8 inches to minimize blanking problems.
Rice Blast Control
Most rice scientists would agree that the rice blast disease has become established in California and is here to stay. In 1997, county agricultural commissioners estimated that the disease was present in fields totaling about 58,000 acres in Colusa, Glenn, and Sutter counties. The disease was found on about 25,000 acres throughout Glenn County, 31,000 acres in northern Colusa County, and 1,400 acres near the town of Sutter in Sutter County. The disease appears to be spreading through the rice areas of the Sacramento Valley.Controlling blast will likely be a challenge, especially when conditions favor disease development. The best way to control the disease is to develop an integrated control program utilizing all available strategies. Such a program should include crop resistance, cultural practices and chemical control when available. Utilizing only parts of an overall integrated program are less likely to be successful.Crop Resistance: The development and use of resistant varieties is an important control strategy in many parts of the rice growing world. This approach is probably the most effective, economical and environmentally friendly method of control. However, breeding for resistance is not easy and may take many years.All of our California varieties appear to be susceptible to the disease. Our industry breeders tell us that unless some of our developing rice lines have resistance it may take 8-10 years to develop a resistant variety from scratch. The breeders are currently testing their rice lines for any resistance. Race screening indicates that we may only have one race of the blast fungus in California at the present time. It will be easier to develop a resistant variety with only one race. However, if we have or get more than one race, then the development of resistant varieties will be more difficult and take longer.Since we do not currently have any resistant varieties, the best we can do for now is avoid growing the most susceptible varieties. Field observations and disease ratings from our statewide variety testing program indicate that M-201 may be the most susceptible public variety. Further testing is needed to confirm this, but in the meantime, growers may want to avoid this variety.Cultural Practices: Various cultural practices can be used to minimize the incidence and/or severity of the disease. They include destroying crop residues, fertilizer management, using clean seed, and water management.
Destroying crop residues:
Rice straw and stubble from blast infected fields should be burned, if possible, to reduce the blast fungal population (primary inoculum) that might otherwise be available to cause disease the next season. While burning reduces the primary inoculum for the disease, it will not eradicate the disease, nor will it protect fields from airborne or seed sources of the fungus. Fertilizer management:
Avoid excessive nitrogen rates since they encourage the disease. Apply the optimum amount of nitrogen for maximum yield, but no more. Also, avoid fertilizer spills and overlaps since these enhance disease development and severity. Because nitrate nitrogen favors the disease more than ammonium nitrogen avoid or minimize complete drainage of fields since it allows nitrates to form. Clean seed: Use rice seed that is not infected or infested with blast whenever possible. This is particularly important in areas that do not have the disease currently. Proper seed sampling and testing should be used to detect and avoid blast affected seed. The California Crop Improvement Association submitted all 1998 certified rice seed lots to the California Department of Food and Agriculture for blast testing. Of 194 samples submitted, 99.5% (193 of 194) tested negative for blast. The one positive sample has been pulled from the certification process and the seed trade, so all certified rice seed in California has tested negative for the disease. Water management: Water seeding and continuous flooding are recommended since complete drainage of fields, especially for extended periods, allows nitrate to form and may cause drought stress, two factors which favor blast. Drainage shortly after seeding may also allow seed transmission of the disease.Chemical control: A new fungicide, developed by Zeneca Ag. Products and known as Quadris®, received an emergency registration for blast control in California and several southern states for 1997 and 1998.Quadris® is a protectant type fungicide that must be applied prior to infection to be effective. The manufacturer recommends that it be applied at the boot split to mid boot split and/or 60-90% panicle emergence stages to protect against panicle blast. Applications should be 7-14 days apart at the recommended timings and at the recommended rates (0.2 - 0.3 lbs ai/acre). Studies have shown that single and/or double applications at the lowest recommended rate have helped control panicle blast, increased rice yield and improved milling quality. What is not clear is whether one or two applications is best. Further studies are needed.
Nitrogen Management of Akitakomachi and KoshihikariThe following is a brief summary on nitrogen and Japanese variety studies prepared by Cass Mutters, Farm Advisor in Butte County. It is based on nitrogen field trials he conducted in 1996 and 1997. For further information on these trials contact Cass at (530)538-7201.
Below are some of the results from nitrogen studies on Akitakomachi and Koshihikari averaged over 2 years. These data should be considered preliminary pending the results from the 1998 experiments and further analysis. The results must be considered in relation to your cultural practices and field history. Koshihikari appears to be particularly sensitive to residual nitrogen present following a medium grain fertility program. The three numbers in the treatments represent the pounds of nitrogen applied as ammonium sulfate at preplant, panicle initiation, and/or heading. For example, 20-20-0 represents 20 lb/a preplant N and another 20 lb/a N applied at PI; none was applied at heading.
Comments to jayoung@ucdavis.edu