Several Factors Affect Weed Control Program


Looking back at the 2018 season, cooler temperatures resulted in some of the best yields we have seen in a long time. This was pretty much the case for all rice growing regions in California.

We also learned we have at least two new species of watergrass that are resistant to almost all the current chemistries. This makes good weed control more difficult to achieve, especially in a monoculture rice system. We used to get by with one application of a foundation herbicide followed by a propanil spray. Now, a three-mode-of-action-type program is needed to get acceptable weed control. We also must continue to rotate different chemistries to keep the seed bank from increasing and becoming more herbicide resistant.

Application Restrictions, Plant Growth Stages
Today, people are planting walnuts and almonds on ground that has been in rice for a long time, creating orchard encroachment in some areas. The counties and the state have changed the regulations to include larger buffer zones and not allow aerial application of some herbicides. The application buffer restriction in some places where I work may be as much as 1 mile from an adjacent orchard crop. As a result, about 80 percent of our herbicide applications are made with ground rigs. Ground rigs also are popular because many of the herbicides require a large volume of water to work properly.

Before applying an herbicide, we have to note the rice and weed growth stages. Sometimes the weeds are at the right stage, but the rice isn’t big enough. Certain herbicide chemistries dictate when you can make an herbicide application to avoid root pruning and a dramatic stand reduction. For example, before applying Granite GR herbicide to control grass and certain broadleaf weeds, rice should be at least at the 3 1/2-leaf stage. I like the flexibility of Granite GR, which will take out some pretty good-sized watergrass where I had to wait until the rice was ready for an application. Because of the granular formulation, this herbicide can attach to the soil surface and provide some residual activity.

Water Management Is Critical
Level fields and proper water management are also important factors in a weed control program. For example, it’s critical to maintain 4 to 5 inches of water when applying Granite GR because lowering the water can increase the concentration and cause injury to the rice. I typically attribute weed escapes or crop injury to a mistake in water management. It’s a delicate balancing act to make sure there is enough water for the herbicide to work and still keep at least one rice leaf above the water to allow the plant to breathe and not drown.

Granite SC herbicide, which controls essentially the same weed spectrum as Granite GR, is a liquid formulation typically applied by ground. It works well when we remove water from the field to help with stand establishment if we have problems with algae and scum or unlevel fields where water depth may be an issue. If conditions are windy right after we seed a field, we may need to take the water off to avoid seed float and allow the rice to peg.

After removing the water, we apply Granite SC and then bring water back onto the field as quickly as possible. If the ground dries, the herbicide won’t work, and the rice can’t metabolize the chemical to get rid of it. I’ve also had good luck combining Clincher CA herbicide with Granite SC to help with sprangletop and watergrass control.

Bright Outlook For 2019
The good news is we are close to record rainfall and will get 100 percent of our water allotment this year. Medium-grain rice prices are up, so the economics are good, too. Another positive is the excellent job the California Rice Commission has done in educating the public about programs rice growers support to enhance the habitat and survival of salmon and water birds. I believe rice is now perceived as being one of the most environmentally friendly crops grown in California.

Jake Onstott
PCA, Grow West
Yuba City, California

About the Author

  • B.S., agribusiness — Cal Poly, San Luis Obispo

  • Member of California Association of Pest Control Advisers (CAPCA)

  • Has consulted for 23 years

  • Consults on rice, walnuts, almonds and prunes

  • Two children: Levi, 16, and Elizabeth, 13

  • Enjoys duck hunting, fly fishing and traveling

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