- Author: Bruce Linquist
We all know it has been a warm year. In fact, in 2014 the average daily temperature for May and June was 72.2 degrees (CIMIS-Colusa). This is 2.4 degrees warmer than the average of the last 20 years and 3.3 degrees warmer than the average of the last 5 years. What does this mean for crop development? In general, rice develops at a faster rate with increasing temperatures. In the statewide variety trials (funded by the Rice Research Board) we have seen that the crop is progressing at a faster rate than previous years. This year the crop reached PI about 3 to 7 days earlier than in previous years. The difference between this years and others is especially evident in the early plantings (early May). Based on past experience, we expect the crop to reach heading and harvest earlier as well - assuming on big weather changes. Based on this, growers should plan practices accordingly. Also, be sure to monitor the crop rather than just relying on days after sowing.
- Author: Christopher A Greer
It is still too early to know if this is going to be a year with high incidence and severity of rice blast. The most favorable conditions for sporulation, spore germination and infection ofplant tissue by the blast fungusinclude high relative humidity, free moisture on the plant tissue surface and temperatures around 82o F. Temperatures cooler or warmer than this slow down disease development but do not prohibitit. As the season progresses, watch out for mild temperatures, calm mornings and foggy orovercast skies that favor extended free moisture periods, all conditions that promote blast development.
As I have mentioned in the past, there are several factors that may predispose rice plants to infection by the rice blast fungus. First and foremost is the inherent resistance of aspecific rice variety. Our California rice varieties do differ in their tolerance to infection bythe pathogen. M-104 and M-205 appear to be the least tolerant of the most widely grown commercialvarieties while M-202 and M-206 are somewhat more tolerant. M-208 is the only commerciallyavailable rice variety in California with a specific resistance gene to race IG-1 of the blastpathogen. IG-1 was the only race of this pathogen known to exist in California until recently.Unfortunately, confirmed cases of limited leaf and neck blast inM-208 fields in recent years indicate that a new race of the pathogenhas evolved through mutation or has been introduced into California. M-208 is still resistant torace IG-1 but is not resistant to this new race.
I am more convinced than ever that water management plays a critical role in rice blast diseasemanagement. Not only does field drainage increase the risk of disease transmission fromseed to seedling but any practice which leads to aerobic conditions within the soil predisposesrice plants to rice blast disease. Drill seeding and draining for stand establishment or herbicideapplications that require a drain in water seeded systems increase the risk of infection and plant susceptibility torice blast. Additionally, rice plants grown in deeper water exhibit increased tolerance to thedisease over those grown in shallower water depths. This is apparent where we often see localizedincreased disease severities associated withhigh spots within a field or prolonged periods of field drainage. From an irrigation standpoint, maintaining a deep continuous flood isthe bestoption for minimizing the risk associated with rice blast disease.
Rice blast is a very complex disease that has the ability to increase in incidence and severityvery rapidly under favorable conditions. Growers should consult with their pest control adviser todetermine if a fungicide application(s) should be made to protect developing panicles as theyemerge from the boot.
Rice field showing severe blast
Author: Paul Spraycar, The Nature Conservancy
- BirdReturns is a new program from the Nature Conservancy (TNC), organized in cooperation with the California Rice Commission
- BirdReturns compensates growers to provide shorebird habitat – manage your straw and maintain at least 2” of water for 2-8 weeks in fall 2014 or spring 2015
- To apply, farmers submit a competitive bid – name your price
- Deadline to apply: August 1st
The hot, long days of summer have arrived, and that means rice growers are tending their crop, preparing for harvest, and praying for a decent winter. Harvest will be here in no time, but before then growers should consider a shorebird habitat incentive available for fall 2014 and spring 2015.
The program – known as BirdReturns – is being offered by TNC in cooperation with the California Rice Commission. BirdReturns compensates growers to perform straw management and water management of their rice fields. These field conditions, provided at the right times of year, provide critical benefits to shorebirds traveling the Pacific Flyway. The implementation of the program will be as follows:
The pilot BirdReturns program, which took place in February-March 2014, included 10,000 acres of rice fields and several dozen growers. The strong interest and participation demonstrated the significant value of bird-friendly management practices on rice fields. By comparing the participating fields with a collection of other ‘control' fields throughout the valley, TNC scientists were able to determine the value of the participating growers' efforts. Here are the results:
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- Author: Randall Mutters
The milestone signaling the beginning of the reproductive stage is panicle initiation (PI). At this moment, the cells at the shoot apex, which is just above soil, start transforming into the panicle; however, this “primordial” panicle is not visible yet. All that can be noticed is a light green band at the upper-most internode referred to as “green ring” or PI. About a week later, when the panicle grows to 1/16th of an inch long and is visible with the naked eye, rice is at the panicle differentiation (PD) stage. It is very important to correctly identify when plants reach PI and PD since midseason N should be made at or just prior to this growth interval. The internode elongation that is often used as an indicator actually occurs after PI. Calrose varieties do not respond in terms of yield gain to N topdressing beyond PI based on UC research. In fact applying additional N later in the season may increase disease severity and ‘blanking', as well as delay maturity.
Midseason N application may not always be necessary. If the soil has a good supply of N throughout the season, maximum yields can be obtained using pre-plant N fertilizers only. However, there are several factors that prevent this from happening, such as extended drain periods, high soil permeability, or a planned management strategy.
Several methods can be used to estimate the N nutritional status of rice plants at midseason: leaf chemical analysis, chlorophyll meter and the leaf color chart. In all cases, leaf samples should be taken at or slightly before PI. The Y-leaf should be used to determine plant N content. The Y-leaf is the most recently fully expanded leaf. It is important to know the stage of growth when sampling for leaf-N because the N content can vary drastically over time. The adequate N range for tissue N at PI is 3.2 – 3.6% (Table 1); concentrations below this range indicate an N deficiency and warrant topdressing.
Table 1. Guide for leaf nitrogen percentages at different stages of growth.
Source: Rice Nutrient Management in California. UC ANR No. 3516.
The chlorophyll meter can be used to estimate N content by measuring the amount of light absorbed by chlorophyll in leaves. The meter must be calibrated against leaf samples analyzed in the laboratory. For cultivar M-205, a meter reading of 32 corresponds to the critical value of 3.3% N. The UC leaf color chart is a very practical, accurate and reliable method to estimate plant N content. It consists on a series of panels with colors that match the color of plants with different N contents (Fig. 1). By comparing the chart with color of the Y-leaves, an estimation of the N status of the rice plant is possible. The chlorophyll meter and the color chart have the advantage of allowing “real time' determination of plant N concentration, whereas the leaf chemical requires a few days for processing. The chlorophyll meter ‘samples' a very small area of the leaf (2 x 3 mm). Therefore a large number of readings are necessary to get a reasonable estimation of leaf N levels.
Figure 1. Leaf Color Chart for evaluating nitrogen status in rice.
Keep in mind that greener is not necessarily better. Studies conducted on M205 and M206 at multiple locations demonstrated that tissue N levels at PI above the critical level do not translate into higher yields (Fig. 2).
Figure 2. Yield as a function of leaf N at panicle initiation. Pooled across varieties (M-206, M-205) and location.
- Author: Luis Espino
Last year, resistance to the herbicide propanil was confirmed in populations of smallflower umbrella sedge and ricefield bulrush. Considering that propanil is a common “clean up” herbicide, used in almost 400,000 rice acres every year, propanil resistant sedges are a significant threat to the rice industry. To make matters worse, populations of these propanil resistant sedges were also found to be resistant or partially resistant to several ALS-inhibiting herbicides (Londax, Sandea and Granite).
Herbicide trials conducted last year showed sedge populations resistant to propanil and ALS-inhibiting herbicides were susceptible to the herbicide Shark H2O. For control of propanil resistant sedge, Shark H2O herbicide can be applied at one of two timings:
- Early, at the 2 to 4 leaf stage of rice, for control of submerged weeds, at a rate of 7.5 oz/a, or
- Twenty to 45 days after seeding, to the foliage of exposed weeds at a rate of 4 oz/a.
Additionally, the herbicides Bolero and Abolish used at standard rates and timings also control propanil and ALS-resistant smallflower umbrella sedge.
Other herbicides will need to be used to control the whole spectrum of weeds present. For example, programs could include an early application of Shark H2O followed by Regiment or propanil; Cerano or Bolero can be followed by a later application of Shark H2O to control escapes. Remember to read and follow the label.
When dealing with herbicide resistant weed populations, do your best to control all weed escapes and late season flushes. Harvest infested checks last, so your equipment does not spread seeds of resistant weeds to uninfested checks.
Growers who are not experiencing reduced efficacy of propanil should implement these well known strategies to delay the development of propanil resistance:
- Avoid repeated use of herbicides with the same mode of action.
- Use different modes of action in mixtures and sequences.
- Use label rates and avoid low rates.
If you suspect propanil resistance, collect mature sedge seeds in problem fields and bring them to the Rice Experiment Station, where they will be tested during the winter. Control failures are not necessarily due to resistance, but can be caused by application problems such as incorrect timing, dosification errors, mixture incompatibilities, etc.
Smallflower umbrella sedge in rice field