Weeds are important pests of California rice systems, and weed management can account for roughly 17 percent of total operating costs (Espino et al., 2016). Integrated weed management uses cultural and chemical practices where herbicide are important tools. Certain conditions in California rice production systems, however, increase the likelihood of developing herbicide resistance. Herbicide resistance is the ability of certain weed biotypes to survive certain herbicide treatments when the weed species is usually killed by that herbicide (Al-Khatib et al., 2019). Such conditions include, but are not limited to, lack of crop rotation, the efficacy of certain herbicides on certain weeds causing them to get frequently used, and not having diverse chemistries available.
In 2019 and 2020, trials were conducted to evaluate the efficacy of a new herbicide product called Loyant (florpyrauxifen-benzyl; group 4 herbicide; Corteva Agriscience) in drill-seeded rice in the Delta region. Loyant is registered in rice growing states in the southern US but would be a new chemistry in California. Corteva Agriscience expects to have CA registration in time for the 2021 use season. The objective of the trials, by assessing different rates and treatment combinations, was to understand the efficacy and crop tolerance of Loyant for weed control in drill-seeded rice in California. This article will describe select results of the 2020 trial. Treatments are listed in Table 1 below. Complete information from both years is available from my website.
Crop injury. We made crop injury observations and weed counts on 7-day intervals for about two months following treatment. We observed tip burning in several of the treatments, but the symptoms were no longer apparent by 21 days after treatment (DAT). We observed leaf curling in the Loyant treatments until about 56 DAT. Corteva Agriscience has observed this symptom with Loyant in other trials where environmental stressors impact crop health, such as extreme cold or heat, drought, or poor fertility. We observed this symptom on the side of the plots closest to the field edge. We observed no stunting, stand reduction, or differences in heading with any treatments.
Weed control. Overall weed pressure was relatively low, observing about 1 weed per square foot in an untreated strip next to the trial. The prominent weeds in the field were Echinochloa species (i.e. watergrass, barnyardgrass; Figure 1, below). We did not have a completely untreated control but instead considered the pre-emergent only treatment (i.e. Prowl) the control. There was a trend for the Prowl treatment to have the highest weed counts. The treatments that had the best weed control were the grower standard and Loyant/SuperWham herbicide programs (Table 2, below).
Yield. We found no differences in yield, but there was a trend for the grower standard and the Loyant/SuperWham herbicide programs to have slightly higher yields (Table 3, below). Measured yields were uncharacteristically high for the region. Our explanation of the data is that we did our hand harvest in the early morning hours when there was a heavy dew. Because variability across the replicates was low, as indicated by the coefficient of variation, we believe the data demonstrate relative comparability of herbicide programs, even though the absolute values are high.
Conclusions. The purpose of the trial was to learn the efficacy and crop tolerance of Loyant (florpyrauxifen-benzyl) for weed control in California drill-seeded rice. We observed Loyant to have good activity on watergrass and barnyardgrass, which were the predominant weeds in the trial. We observed Loyant treatments to have similarly low weed counts compared to the grower standard, and a Loyant/SuperWham herbicide program appears to provide comparable weed control to the grower standard. The results demonstrate that Loyant could be used in drill-seeded rice herbicide programs, providing a different chemistry for herbicide resistance management.
The aforementioned information on products and practices is for educational purposes only and does not constitute an endorsement or recommendation by the University of California.
Table 1. Herbicide treatments in the 2020 trial. Treatments were applied on May 8th, when the rice was approximately at the 3rd leaf stage.
Figure 1. Predominant weeds in the trial were watergrass and barnyardgrass.
Table 2. Weed counts on 7-day intervals from 14 DAT to 42 DAT. Data represent total number of weeds in the 400-ft2 plot and are the means across four replicates.
Table 3. Yield adjusted to 14 percent moisture. The trial was hand-harvested on Sept. 29, measuring one 10.8-ft2 (1-m2) quadrat per plot. The grower reported that harvest moisture was around 18.5 percent.
UC Cooperative Extension will offer a virtual Alfalfa IPM Workshop on December 3rd and 4th. The workshop will run from 9am to 12pm on each day. Registration is required, and there is a $25 fee to help cover our costs of delivering a workshop virtually. Continuing education credits will be offered. (5 "Other" credits from DPR and 4 "IPM" credits for CCAs.)
Day 1. December 3 (9 am - Noon PST) Weed and Pest Management Strategies
- Price & Acreage Trends -- Josh Callan, The Hoyt Report, Twin Falls, ID
- California Regulatory Update--Dennis Albiani, Ag. Management, Sacramento, CA
- Key Agronomic Strategies for Pest Management--Dan Putnam, UC Davis
- Poisonous Weeds of Concern in Alfalfa--Larry Forero, UCCE, Redding, CA
- Weed Control Strategies for Establishment and Production -- Earl Creech, Utah State University, Logan, UT
- Recent Weed Control Trials in Alfalfa--Tom Getts & Giuliano Galdi, UCCE, Susanville and Yreka, CA
- Weed Mangement Strategies for Pastures--Josh Davy, UCCE, Redding, CA
Day 2. December 4 (9 am-Noon PST) Insect, Disease Management Strategies
- Process of Pesticide Regulation in California--Aron Lindgren, DPR, Sacramento, CA
- On-Line Tools for Pest Management Information--Jose Luiz Carvalho de Souza Dias, UCCE, Merced, CA
- Management of Insecticide Resistance in Alfalfa--KEvin Wanner, Montana State Univ.
- Biological Insect Control in Alfalfa: A Case Study--Ian Grettenberger, UC Davis
- Update on Low Desert Forage Insects--Michael Rethwisch, UCCE, Blythe, CA
- Summer Worm Management--Rachael Long, UCCE, Woodland, CA
- Potential Use of Drones for Insect Management--Ken Giles, UC Davis
- Key Diseases and Management in Alfalfa--Deborah Samac, USDA-ARS, St. Paul, MN
UC Cooperative Extension in San Joaquin County will host the SJC and Delta Field Crops Meeting on Friday, January 8, 2016 from 8:00am to 12:00pm. The meeting location is the Cabral Agricultural Center in Stockton (2101 E.Earhart Ave., Stockton, CA 95206).
The first half of the meeting will focus on pest management and the new regulations and permit conditions for chlorpyrifos, including results from an industry project to evaluate its critical uses and IPM decision-support tools for insecticide recommendations and stewardship. The second half of the meeting will focus on crop fertility and soil resource management.
The agenda is as follows:
8:00am Doors Open, Welcome and Introductions
8:10am Seed Treatments for Wireworm Control in Field Corn: Michelle Leinfelder-Miles, UCCE, San Joaquin/Delta Counties
8:30am Alfalfa Project Overview Addressing Critical Chlorpyrifos Use: Pete Goodell and Lori Berger, UC IPM, UC Kearney Research and Education Center, Parlier
9:10am Science Behind New Chlorpyrifos Regulations: Randy Segawa, California Department of Pesticide Regulation, Sacramento
9:25am Local Permit Conditions and Restrictions on Chlorpyrifos Use: Barbara Huecksteadt, Agricultural Commissioner's Office, San Joaquin County
9:40am NRCS Conservation Planning and Pesticide Hazard Mitigation: Ora Van Steyn, USDA-NRCS, San Joaquin County
9:55am Local Impacts and On-Farm Management – Panel Discussion: Mick Canevari, UCCE Emeritus, San Joaquin County; Bob Ferguson, Grower, San Joaquin County; Larry Godfrey, UC Davis; Dan Putnam, UC Davis; Mike Wackman, San Joaquin County and Delta Water Quality Coalition
10:40am Using Dairy Manures as Fertility Sources of Silage Corn: Martin Burger, UC Davis
11:00am Use of Online Resources for Nutrient Management Decisions and Nitrogen Budgeting: Daniel Geisseler, UC Davis
11:20am Salinity Management in Alfalfa Fields: Michelle Leinfelder-Miles, UCCE, San Joaquin/Delta Counties
11:40am Wrap-up and evaluations
Continuing education (DPR and CCA) will be available. Our programs are open to all potential participants. If you require special accommodations, please contact UCCE San Joaquin County at 209-953-6100. Thank you, and hope to see you at the meeting.