The UCCE Rice Team is conducting a field survey to collect watergrass samples over the next few weeks. The samples will be grown out in the greenhouse to help us start figuring out the identification and phenotypic characteristics (how to distinguish one from another) for the watergrass species found in California rice fields. The hope is that this will give us data for developing chemical and non-chemical management plans for watergrass, similar to what we have been working on with weedy rice over the past few years. 

The project was funded by the California Rice Research Board, and is led by Whitney Brim-DeForest (UCCE Sutter-Yuba) and Marie Jasieniuk (UC Davis). 

We are reaching out to ask for locations of rice fields from growers and PCA's, so our team can go out and collect seed. We are looking for all types of watergrass: "mimic", early watergrass, late watergrass, barnyardgrass (Figure 1), and the new species that we started seeing a couple of years ago (Figure 2). We hope to start collecting in the next week or two, through the end of September. 

For more information, and if you are interested in having us come out and sample your field(s), please contact Whitney Brim-DeForest (wbrimdeforest@ucanr.edu), or call 530-822-7515. 

 

The period between panicle initiation (PI) and heading is critical with respect to grain formation. During this time, cold temperatures can result in pollen sterility as the plants go through meiosis. Pollen sterility results in blanking. Nighttime temperatures below 58 ^oF can result in sterility. The Figure shows the relationship between average low temperatures during booting and statewide yields. Data are from 1992 to 2018. The data represent the average low temperature for a 15-day period beginning about one week after panicle initiation to one week before heading.

Varietal selection is important to minimize blanking. Varieties such as M105 and M206 are more cold tolerant than M209, for example. However, all varieties can be negatively affected by cold temperatures during this period. One way to help minimize the damage is to raise the flood water height in the field during this time to 6-8 inches (or more). The water acts as a blanket and protects the emerging panicle from cold temperatures.

This sensitive period during booting usually occurs in July. For rice planted in mid-May, the critical period is the last two weeks of July. I realize as I write this that it may already be a bit late for many growers. However, I am looking at the forecast and seeing nighttime temperatures in the mid-50s over the next few days in areas south of highway 20.

The UCCE Rice Team has developed a series of Factsheets to simplify and convey information about important topics that we find we are frequently discussing with growers and PCA's. Each fact sheet is 2 pages long, back to front.

There are 6 so far:

• Fact Sheet #1: Nutrients in Rice Grain and Straw at Harvest
• Fact Sheet #2: Managing Potassium in Rice Fields
• Fact Sheet #3: Stem Rot and Aggregate Sheath Spot of Rice
• Fact Sheet #4: Kernel Smut of Rice
• Fact Sheet #5: Growing Season Water Use in California Rice Systems
• Fact Sheet #6: Managing Rice with Limited Water

We are continuously in the process of developing more topics, so if you have suggestions, please reach out to Luis Espino (laespino@ucanr.edu) or Whitney Brim-DeForest (wbrimdeforest@ucanr.edu).

Tadpole shrimp (TPS) are starting to pop up in rice fields. A grower asked me when is the period when rice is “safe” from TPS. He is seeing very small shrimp, and seedlings are already past the first leave stage of rice (lsr).

To determine if rice is going to escape TPS injury, two things need to be considered, the rice seedling stage and the size of the TPS. It is difficult to determine the size of TPS, but if you pull one out of the water and its shell is smaller than half the size of a medium grain rice seed, then it won't injure a germinating seed. TPS larger than that will readily feed on germinating seeds and seedlings.

TPS with a shell size about half the size of a rice seed feeding on developing root. 

TPS will feed on seedlings until they reach the first leave (when the spike is well developed). TPS don't seem to like feeding on the green tissue. However, they will feed on roots. If the main root is exposed, seedlings are still at risk of TPS injury.

TPS feeding on exposed roots of 1 lsr.

Use this guideline when you scout:

If TPS shell size is...	And the rice stage is...	Risk of injury is...
Smaller than half the size of a medium grain rice seed	smaller than 1 lsr	LOW at this point, but may increase as TPS grows
Smaller than half the size of a medium grain rice seed	1 lsr or larger	LOW
Larger than half the size of a medium grain rice seed	smaller than 1 lsr	HIGH
Larger than half the size of a medium grain rice seed	1 lsr or larger	LOW, but check the main root. If exposed, it can be consumed by TPS

One more thing to considering when scouting. If rice escapes injury and TPS are not treated, they will lay eggs that will stay in the soil and hatch next season.

When it comes to TPS management, fields that can be flooded quickly have an advantage over fields that take several days to flood. A quick flood followed by timely seeding will result in seedlings that can reach the 1 lsr before the TPS grow too large. In fields where flooding takes several days, TPS will have a head start and may reach the injuring size before the seedlings reach the 1 lsr.