In 2018, we did not see a large increase in the number of weedy rice samples and sites over the 2017 season. Acreage remains around 10,000 acres. We are encouraged by the number of submissions we continue to receive, which is a great indicator of the fact that lots of people are continuing to be on the lookout for weedy rice in their fields. The only way we can get rid of it is if we know that it is in a field.
We did find one new type in 2018, which we are calling “Type 6” (pictured above), but so far it has only been found in one field.
We also conducted a competition study this past year, which gave us preliminary data on yield loss. Some of the key findings so far are:
- Impacts on yield are the same between Types 1-5 (we did not yet have Type 6 to test)
- Significant yield reductions start with as few as 1 plant per square foot
- At 1 plant per square foot, reductions in grain weight per M-206 plant were more than 40%
- At 4 plants per square foot, reductions in grain weight per M-206 plant were more than 70%
For the majority of fields infested with weedy rice, weedy rice densities are around 1 or fewer plants per square foot, but we do have at least two infested fields that are at or above 4 plants per square foot.
Looking forward: 2019 and beyond
We have a large field research project starting this year at the UC Davis campus. The field was seeded in 2018 with weedy rice, to establish a population in the field. From the field experiment, we hope to be able to get yield loss data, timing on flowering, and emergence timing, to better plan our herbicide applications, if using a stale seedbed.
We urge growers and PCA’s to continue to submit suspected samples for testing. The UCCE Farm Advisors will continue to collect samples, so please give us a call if you suspect you might have weedy rice. Again, we encourage folks to not remove suspected plants from the field, to limit the spread of the seeds.