UC Cooperative Extension is conducting a survey of rice diseases this fall. The objective of the survey is to document the incidence of rice diseases in Sacramento Valley rice fields so that the Air Resources Board agrees to continue to allow the rice industry to burn up to 25% of the acreage. Every five years, the Board has to re-approve the straw burning program. One of the reasons for letting growers still burn is disease control. Therefore, it is important to show that diseases are still present in rice fields.

A crew of four to five will be stopping in random fields in the major rice producing counties and inspecting for the presence of diseases in 30 sites in each field. We will look for stem rot, aggregate sheath spot, kernel smut, and blast. The precise location of each field won't be disclosed, only the general location and County. So far, we have inspected 10 fields in Butte County, and have found very low levels of blast and kernel smut. Stem rot and aggregate sheath spot are more variable; we have found fields with very little of these diseases and fields with a lot. 

The last time we saw a severe blast epidemic was 2011. Since then, we haven't had much blast; in fact, I had not see any blast at all during several years. I don't think 2019 qualifies as a severe blast year, but there is more blast than in the previous few years. 

Blast is caused by a fungal pathogen, Pyricularia oryzae. This fungus can affect any plant part, and usually we refer to blast according to the tissue affected. Leaf blast, node blast, collar blast, and neck blast (when it affects the node right below the panicle) are all caused by the same pathogen. 

Typical and larger leaf blast lessions, collar and node lessions.

Neck blast

Blast can surive in crop residue, move with seed, and move between fields by producing airborne spores called conidia. In California, we typically see leaf blast starting at mid tillering. Blast infection at this time causes leaf lesions that in severe cases can burn plants to the water level. However, most of the time these severe symptoms are limited to small areas of the field. During heading, neck blast can cause empty heads when infections occur soon after the panicle emerges from the boot.

Left, leaf blast that has burned plants to water level in circular pattern. Right, larger area of field affected with leaf blast.

Several factors favor blast development. Moderate warm daytime temperatures, cooler nights, and long periods of leaf moisture are good for blast development. High nitrogen rates tend to aggravate blast, and typically one can see blasted circles where plants have been killed to the water level in areas of aqua overlap. Draining fields during the season increases the risk of blast infection. 

Of the rice varieties grown in California, M-205 and M-104 were considered more susceptible than M-206. Variety M-205 has been replaced by M-209, which was released in 2015. Since there hasn't been much blast pressure in the past few years, it was not known how M-209 was going to react to blast. This year seems to indicate that M-209 might be more susceptible to blast than M-206. I still have not heard much about M-105, the M-104 replacement released in 2011. Variety M-210, released in 2018, is resistant to the blast races present in California.

If leaf blast is very severe, a fungicide application may be appropriate. However, this level of disease is uncommon under our conditions. Leaf blast does indicate the need to protect the panicles during heading with a fungicide application at about 50% heading.

The 2019 Rice Weed Course will take place: 

Friday, September 6, 2019

from 8:00AM to 4:10PM (Registration begins at 7:30AM)

at the 

Hamilton Road Field (on West Hamilton Rd. between Hwy. 99 & Riceton Hwy.)

and Rice Experiment Station, Biggs, CA

Participants head to the field (2016). Photo by Dana Dickey

This year will mark the third rice-specific weed course at the Hamilton Road Field and the Rice Experiment Station in Biggs, CA on Friday, Sept. 6, 2019. The day will begin with an interactive field tour of the research plots (Hamilton Road Field) where attendees can get up close to the weeds and rice (bring your boots!) The course will include a hands-on weed identification session on emerging and mature weeds. In the afternoon, speakers will address several pertinent topics in CA rice, including algae, weedy rice, regulatory update, best management for grasses, and how to construct a weed management program. This course is a great opportunity to interact directly with the UCCE and UC Davis Rice Weed Research Team! 

For a full agenda and registration go to: 

https://wric.ucdavis.edu/events/rice_weed_course_2019.html

For questions, please contact Whitney Brim-DeForest at 530-822-7515, or by email at wbrimdeforest@ucanr.edu 

Credits for PCA, QAC, QAL, Private Applicator:  6.0 other, 0.5 laws

CA Certified Crop Adviser: 6.0 IPM

If you grow rice in California, you already know that effective weed management is not only essential for economical rice production, but also very challenging, complex, and regulated. The good news is that there is a new resource to help growers and pest control advisors with the prevention, monitoring, and control of the most common rice weeds in California. The University of California Integrated Pest Management (UC IPM) Pest Management Guidelines: Rice now includes a brand new weed management section!

Infographic showing what is in the revised Pest Management Guidelines for Rice.

Infographic showing what is in the revised Pest Management Guidelines for Rice.

The guidelines are authored and reviewed by University of California's advisors, specialists, and faculty to bring the latest university research on rice pest management into one easy-to-find place. The new Integrated Weed 

Infestation of barnyardgrass, Echinochloa crus-galli, in a rice paddy. Photo credit: Jack Kelly Clark (http://ipm.ucanr.edu/PMG/E/W-GM-ECRU-IF.002.html)

Management section shows how to effectively use early-season cultural controls like water management, land leveling, tillage, and crop rotation to reduce weed pressure on the young rice stand. This webpage also includes useful information on detecting and preventing herbicide resistance. Furthermore, the entire Pest Management Guidelines: Rice is now presented in a new mobile-friendly format, allowing easy access on the go. Use this information along with the table on Susceptibility of Weeds to Herbicide Control to help tailor the herbicide mixes and timing of applications to best match the problems in each individual field.

For more pest management information for other California crops, visit the UC IPM homepage.