The UCCE Rice Team will be starting a survey of weedy rice across the rice-growing counties in the next week. We are surveying fields that are known to have weedy rice infestations (from reports from the past 3 years). We will use this opportunity to update the extent of the infestation, collect samples, and pull out as many weedy rice plants as possible (from fields that have low infestations). 

If you are a grower or PCA with a field that has had an infestation in the past, we will be reaching out to you to let you know when we will be visiting. 

A big thank you to the California Rice Commission for providing the funding for this survey. For more information about weedy rice in California, visit caweedyrice.com. 

For questions regarding the survey, feel free to reach out to Luis Espino (laespino@ucanr.edu), Whitney Brim-DeForest (wbrimdeforest@ucanr.edu), or Michelle Leinfelder-Miles (mmleinfeldermiles@ucanr.edu). 

The 2017 season kicked off with much fanfare regarding weedy rice. Thanks to the vigilance of the entire rice industry, the UCCE Rice Advisors received many calls regarding weedy rice, starting in late June, as growers finished their herbicide applications. Calls continued to come in through July and August. The California Crop Improvement Association (CCIA) began inspecting fields as the rice headed, and suspected plants were pulled and sent to the UCCE Weedy Rice Team for genetic testing.

By the end of the season, we had a total of:

• 53 samples submitted for testing
• Out of the 53, 15 have been confirmed to be weedy rice
• 7 are still pending genetic testing

Eight seed fields were found to be infested with weedy rice and rejected as seed fields:

• 3 were new medium grain seed fields
• 1 was an established medium grain seed field
• 4 were specialty variety seed fields

Commonly Confused with Weedy Rice

There were many calls throughout the season, which indicated that everyone was out inspecting their fields. Thankfully, many of the calls were not weedy rice!

Some commonly things that can be mistaken for weedy rice:

1)     Sprangletop: like rice, it has a ligule, so early in the season, before heading, it may be easy to confuse it with weedy rice. However, sprangletop has a white stripe down the middle of the leaf (mid-vein).

2)     Elongated Upper Internode (EUI): this is a genetic abnormality of common medium grain rice varieties that causes the part of the stem attached to the rice panicle to elongate. The panicles stick up above the canopy, just like weedy rice. However, the rest of the plant will look just like the variety planted in the field.

3)     Bakanae: this disease of rice causes the plants to elongate and appear taller than the surrounding plants, and they also appear lighter in color. However, any panicles produced by the infected plants will be blanks.

4)     Fertility Differences: if the field has more or less nitrogen in certain areas, some of the rice plants may appear lighter in color than others.

 

Elongated upper internode (left) and sprangletop (right) can be confused with weedy rice plants.

 

New Information for Management

We have been working on characterizing some of the biological characteristics of the weedy rice populations. We made considerable progress over the summer, and are happy to report that the dormancy and shattering status of each of the five populations is now known.  

Characteristics	Populations	Duration of time in soil
High dormancy, high shattering	Type 1, Type 3, Type 4	Long-term (may be 10 or more years)
Low dormancy, high shattering	Type 2, Type 5	Shorter (likely to be a few years, but only if more seed is not being put into the soil seedbank)

 

For images of all the weedy rice types found in California, go to www.caweedyrice.com

 

Implications for Management

All weedy rice types found in California so far are high shattering, which means that many of the seeds will fall off the panicle before harvest. Therefore, it is critical to remove plants from the field before they can shatter completely. Any seeds shattering on the soil surface will have the potential to be deposited into the soil seedbank, lengthening the amount of time weedy rice will be infesting the field.

Three of the types found in California have high dormancy: Type 1, Type 3, and Type 4. High dormancy means that once the seeds are in the soil, they will remain there for a long period of time without germinating, even if the grower is doing everything possible to get the plants to germinate so that they can be killed. Two of the types have low dormancy: Type 2 and Type 5. These types will readily germinate the following spring if they are close to the soil surface, so they can be more easily eradicated from a field, if a grower follows all best management practices.

 

Summary: We Are Working Together!

Overall, grower and PCA participation in scouting for weedy rice was really high in 2017. Since we can only get rid of it if we know that it is there, this is very encouraging, and we hope that the participation continues into the future. Likewise, those growers that already know they have weedy rice infestations are working hard to eradicate it, following the Best Management Practices. Again, this is very encouraging, as the only way that we can eradicate this pest is as a group, working together.

Every year we see some off-types in our public varieties that have a genetic mutation we call elongated upper internode. This mutation causes the internode below the panicle to elongate, resulting in panicles that stick above the canopy. Some have confused this abnormality with weedy rice. 

It seems that the occurrence of this abnormality may be related to weather - some years we see it more often than others. In any case, the frequency with which it occurs is so low that it does not affect yield.

Over the past year, weedy rice has become a top issue in California rice, both for individual growers and for the industry as a whole. Working together, the University of California Cooperative Extension and the California Rice Commission have come up with a set of tools to assist in getting control of this pest. Of course, none of it would be possible without the input and cooperation of the Pest Control Advisers (PCAs) and California rice growers, who are the first line of defense in dealing with weedy rice. Additional assistance in material development and funding have come from the California Rice Research Board, the California Crop Improvement Association and the staff at the California Rice Experiment Station. 

California Weedy Rice Website

A new website, www.caweedyrice.com, contains all of the most up-to-date information regarding weedy rice in California. The website covers identification, management, and weedy rice sample submission. 

 

 

 

Pamphlets and Posters

An identification pamphlet was mailed out by the California Rice Commission a couple of weeks ago to most growers and PCAs. If you need additional pamphlets, they are available at your local UCCE office. Identification posters will be distributed to Agriculture Commissioner's offices, PCA offices, and rice mills and distributors in each county in the next few weeks. They are also available at your local UCCE office upon request. 

 

"Weedy Rice Reporter" Application 

To report an infestation of weedy rice, a new app is also available for download from the Google Play and ITunes stores. 

The "Weedy Rice Reporter" app will let you send up to six pictures and aGPS location taken with your phone toUCCE RiceAdvisors so that we can confirm or rule out weedy rice. OnlyUCCE RiceAdvisors will be able to access any app submissions. We hope that the app will help us identify  infestations early so that management actions can be implemented to eliminate weedy rice from the fields.