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 82^o 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

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.

Rice Straw - A New Method to Get Through a Drought

Veterans Memorial Hall

525 West Sycamore Street

Willows, CA

Tuesday, July 29, 2014

9am - noon

UC Cooperative Extension research has found that baling rice straw right behind the harvester greatly increases cattle's ability to utilize it. Making rice strawlage involves baling the straw the same day as the rice is harvested at 50 to 60% moisture and then placing it under a tarp cover.

With the present drought conditions, a meeting will be held to discuss how to make rice strawlage. It will cover the nutritional advantages of strawlage over straw, the challenges of baling at 50 to 60 percent moisture, additives that can be provided, how to stack and tarp it, nutrients removed from field with the process, and the cost associated with the process. Most important will be the discussion with two ranchers that fed rice strawlage last year.

Because of the high moisture associated with this product and transportation costs, it is assumed that the most prudent use will be by ranches adjacent to rice production areas. With limited water for rice straw decomposition this fall, this could also provide rice operations an alternative method of the straw management. The goal of the meeting is to give producers information that will allow them to implement rice strawlage during this fall's harvest. Both cattle and rice producers are encouraged to attend the meeting.

For more information contact Glenn Nader at 822-7515 or ganader@ucanr.edu

With the approach of late summer and the possibility for lower nighttime temperatures, this is the time when blanking can occur. Keep in mind how water management helps to mitigate this problem.

Spikelet sterility, sometimes referred to as "blanking", occurs when the developing pollen grains are exposed to nighttime temperatures at or below 55 degrees F for several hours. Pollen is sensitive to low temperatures about 7 to 10 days after panicle initiation. The pollen is at the temperature sensitive stage when the collar of the flag leaf and collar of the previous leaf are aligned (Figure 1). While there are varietal differences in blanking susceptibility, in normal years, blanking is around 12 percent. Blanking can be detected in the field about 10 days after flowering. The occurrence of translucent hulls when the panicle is held up to the sun identifies unfilled grain. 

Figure 1. The low temperature sensitive stage of pollen development occurs when the collar of the flag leaf and the collar of the previous leaf align (center plant in photo).

Proper water management helps to mitigate the occurrence of blanking. About three weeks before heading, the base of the panicle is about 4.5 inches above the ground, and the tip of the panicle is about 10 inches above the ground. Raising the water level above the base of the developing panicle can help to reduce the incidence of blanking because the water acts as a heat sink. The minimum nighttime water temperature will be about 3-5 degrees F warmer than the minimum nighttime air temperature, depending on water depth. The warmer water temperature will also warm the air temperature immediately above the water level.  In a 1980 paper, UC Davis researchers found that shallow water (3-4 inches) resulted in 22.2 percent blanking among eight varieties, whereas deeper water (6-8 inches) resulted in 17.8 percent blanking among the same eight varieties. Currently, we are recommending a water depth of 6 inches at 7-21 days before heading to help reduce blanking. Given drought concerns this year, we suggest that growers allow the flood water to subside naturally rather than drain the fields. In practice, this means that water flow into the field can be stopped well in advance of the drain date. How far in advance will depend on the amount of water already in the field, as well as soil and field properties such as percolation. Therefore, raising the water before heading does not necessarily use more water provided the water is turned off earlier at the end of the season.

Variety and fertility management can also result in varying amounts of blanking. Varieties that tend to have lower levels of blanking have true genetic tolerance to cooler temperatures, and they generally are shorter in stature and mature early. High nitrogen rates may increase blanking by increasing vegetative growth and delaying heading. The increased vegetative growth draws away sugars that the plant would otherwise use to fill the grain. Keep in mind that different varieties and fertility practices could result in neighboring fields reaching the susceptible development stage for blanking at different times. Different varieties and fertility practices could result in neighboring fields that were planted at about the same time being more or less susceptible to low temperature events, therefore, resulting in different levels of blanking.

Unfortunately, blanking is not like thinning fruit trees – it does not result in larger grains where grain forms. A 1972 UC Davis study showed that panicles do not compensate for high blanking by producing larger grains. In fact, the study showed that grains from high-blanking panicles had weights that were 3 percent lower than grain from panicles where blanking was low.