Mexican sprangletop that has already set seed (about 20 days after rice seeding)

I went out on a few farm calls in the past week, and have noticed a trend. Due to the unusually wet weather this spring, some of the weeds are already producing seed out in the field! This occurs when the field was moist or wet in the spring, and was not tilled or sprayed prior to planting.

If you have weeds that are already setting seed, follow the steps below:

1)      First, make sure to get proper identification of the weed species. Some weed species will produce seed and that seed can germinate and send up a second flush of weeds, in the same season! They are:

1. Smallflower umbrella sedge
2. Mexican sprangletop

NOTE: There are two types of sprangletop: Mexican and Bearded. Only the Mexican sprangletop will set seed that will germinate this season. Bearded sprangletop seed is dormant and won't germinate until the 2018 season.

Bearded sprangletop (left) and Mexican sprangletop (right). Photo: Matthew Quinton

2)      If you have one of the above-listed species that is already setting seed, it is important to make sure that your follow-up herbicide application will control this second flush of germinating seeds. Otherwise, the amount of seed produced and deposited into the seedbank will be exponentially higher than in a normal year, because there will be two generations of plants that set seed in the same season!

3)      If you have a weed species setting seed that is NOT listed above, you will likely not be able to do much this year, as the weeds are likely too large to control with herbicide and any impacts on yield have already occurred. Plan to have an aggressive program for next year (2018)!

BUTTE®, a rice herbicide, has received federal registration in the USA as well as state registration in California. It will be available to California rice growers for the upcoming 2017 season. Gowan Company, along with SDS Biotech and Nissan have collaborated to bring this product to California rice growers. 

Early BUTTE® trials at the Rice Experiment Station, 2012

BUTTE® is a granular into-the-water herbicide that combines two modes of action: an HPPD-inhibitor (benzobicyclon), and an ALS-inhibitor (halosulfuron). It is the first HPPD-inhibitor available to California rice growers. Since weeds in CA rice have widespread herbicide resistance, BUTTE® offers a new option for resistance management for affected growers, particularly those with herbicide resistant sedges. 

BUTTE® offers excellent control of many sedges, broadleaves and grasses. For a complete list of weeds controlled and suppressed, please refer to the herbicide label. BUTTE® is applied early in the season, and requires a 20-day water hold period. As always, growers and applicators should follow all label requirements, to ensure the best weed control, and to prevent the development of resistance. 

There will only be enough product available for 2017 to treat approximately 50,000 acres, so growers interested in purchasing BUTTE® this season should talk to their Pest Control Adviser and the retail location where they normally purchase rice pesticides. 

The University of California Davis Weed Science Program has been working with Gowan to research BUTTE® over the last several years. Studies on the weed control spectrum and timing began with Dr. Albert Fischer's program, and research on rates and formulations have continued under Dr. Kassim Al-Khatib. The UC Weed Program will continue to look at herbicide combinations that best compliment BUTTE® this year. The trials will be available for viewing at the 2017 Rice Field Day. 

Whitney Brim-DeForest, UCCE Rice Advisor

We talk about herbicide resistance all of the time in California rice. But how does it evolve in a field? Understanding how herbicide management selects for resistant populations is an important part of preventing the problem from occuring in your fields.

We have many weed species in CA rice that are confirmed to be herbicide resistant. The major herbicide-resistant species are: late watergrass, early watergrass, barnyardgrass, smallflower umbrella sedge, ricefield bulrush (roughseed), sprangletop, and redstem. For this illustration of how herbicide resistance evolves in a field, we use redstem as our example. 

Year 1, Beginning of season: A population of redstem is found in a field and are emerging at the beginning of the season. In this illustration, the plants with the blue background are naturally susceptible to an herbicide (Granite SC). The plants with the yellow background are naturally herbicide resistant to Granite SC. There is nothing that the grower has done at thispoint to select for  resistance. The genes that make the plant resistant are naturally found in the redstem population in the field.

Year 1, Mid-season: The grower applies Granite SC.

Year 1, End of season: One herbicide resistant plant survives. This plant goes on to produce seed, and the seeds are deposited onto the soil surface, where they are tilled into the soil seedbank at the end of the season.

Year 2, Beginning of season: The redstem population emerges from the soil at the beginning of the season. Because there are more seeds in the soil seedbank from the resistant plants, more of the emerged plants are resistant to Granite SC this year (yellow background = herbicide resistant).

Year 2, Mid-season: The grower again applies Granite SC or another herbicide with the same mode of action (Regiment, Halomax/Sandea or Londax).

Year 2, End of season: All of the herbicide resistant plants again survive the herbicide application. Again, they go on to produce seed, and the seeds are deposited onto the soil surface, where they are tilled into the soil seedbank.

Year 3, Beginning of season: The redstem population emerges from the soil at the beginning of the season. There are even more herbicide resistant plants than the previous 2 years, as the proportion of herbicide resistant seed in the soil has increased.

Year 3, Mid-season: For the third year,the grower applies Granite SC or another herbicide with the same mode of action (Regiment, Halomax/Sandea or Londax).

Year 3, End of season: All of the herbicide resistant plants again survive the herbicide application. Again, they go on to produce seed, and the seeds are deposited onto the soil surface, where they are tilled into the soil seedbank.

Year 4, Beginning of season: The redstem population emerges from the soil at the beginning of the season. This year, all of the plants are herbicide resistant, as the soil seedbank contains mostly herbicide resistant redstem seed.

The illustrations above are an example of how herbicide resistance evolves and is selected for in a field. A grower may not notice during the first year or two, as there are just a few plants that survive the herbicide applications. However, if the grower continues to use the same herbicide year after year, or the same herbicide mode of action, eventually, the population of redstem (or another weed species) will shift to become composed of only plants that are herbicide resistant.

The best way to prevent the development of herbicide resistance is to rotate herbicide modes of action, both between seasons and within seasons. Refer to the UC Herbicide Susceptibility Chart for CA rice when planning an herbicide program.

The 1st Annual Rice Weed Course will take place: 

Friday, September 16, 2016

from 8:30AM to 4:15PM (Registration begins at 8:00AM)

at the 

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

and Rice Experiment Station, Biggs, CA

The day will begin with an interactive tour of the Weed Science research plots at Hamilton Road. Participants will also spend time learning about weed identification for important rice weeds both at emergence and at heading. Presentations will cover emerging pests of rice, such as weedy red rice and winged-leaf primrose willow. Attendees will hear about new pesticide registrations and updates to current pesticides, as well as information regarding the new Butte herbicide. This course is also a great opportunity to interact directly with the UCCE and UC Davis Rice Weed Research Team! 

For a full agenda and registration go to: 

http://wric.ucdavis.edu/events/rice_weed_course_2016.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, and CA Certified Crop Adviser are pending.