- Author: Bruce Linquist
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.
- Author: Whitney Brim-DeForest
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
- Author: Luis Espino
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.
- Author: Luis Espino
This year, with the help of Dow AgroSciences, I will increase the number of armyworm traps that I have been monitoring. The idea is to give growers and PCAs more localized information so that they can have a better idea of what's going on near them, and when to increase their monitoring efforts. Weekly trapping numbers will be posted on our website, UC Rice Online, http://rice.ucanr.edu/armyworm_traps/
I will be sending a weekly “armyworm alert” email once the trap numbers are updated on the website. The email will go out to those who are subscribed to one of our electronic newsletters (Rice Briefs, Rice Leaf, or Field Notes). If you receive the armyworm email but are not interested, just click on the unsubscribe link at the bottom of the email. For those who do not receive our newsletters electronically, you can subscribe to the alert email in the armyworm website: http://rice.ucanr.edu/armyworm_traps/
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.
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./table>