Rice Weed Control 101

Rice Weed Control Is Both Complicated And Simple

Andy Kendig, State Extension Weed Specialist

Printed/Posted with permission of Mid America Farmer Grower

This is the first in a series of eight weed control articles aimed at new rice growers. Rice agronomics and weed control are different from most row crops. It took me about two years to figure out how to make things work. Timing and weed size is always critical, but it's more critical in Rice. To further complicate things- herbicides are often used in different ways depending upon conditions. Finally drill seeded and water seeded rice also follow different sets of rules.

An entire book could be written about rice growing methods; however we'll emphasize drill seeded rice as it is generally the preferred method. But, to avoid confusion, we'll briefly discuss water seeding. While there are at least 6 different named methods of growing rice, for the sake of weed control they boil down to two main systems: 1) drill-seeded-delayed-flood and 2) water -seeded-permanent-flood. You may be familiar with another common Mid-South method called "pinpoint flood." However, for all practical purposes, it is the same as permanent flood. In pinpoint, the "permanent" flood is lowered for a very short time period to help the rice seed root or peg- but this lowering is not necessarily required and the shorter it is, the better. The "flood" is essentially permanent because the soil stays saturated and oxygen free if the pinpoint drain is done properly.

Drill seeding is generally preferred because water seeding locks you into several, expensive airplane applications. However, water seeding is currently the only method to suppress existing red rice problems- something unlikely to affect new rice ground. You should know that some rice growers like water seeding for simplicity. After a big rain their favorite joke is to moan and groan about how they don't get a day off from planting. These growers have big airplane bills, but make up for it by having very little farm equipment. Although the airplane costs a little more don't hesitate to call on an aerial applicators even in drill-seeded situations. Remember pesticide and fertilizer timing are critical and if you can't get to it, the airplane is a bargain and doesn't cost that much more than ground application.

Water seeded rice controls red rice through the following mechanism: Rice can emerge through soil OR water BUT NOT BOTH. Red rice seed in the soil, under the flood cannot germinate. The commercial, desirable rice is pregerminated and sits on top of the soil where there is a thin layer of oxygen. Water seeding does not provide perfect weed control as a few red rice seeds always wind up on top of the ground where they can germinate through water. The herbicides Bolero and Ordram provide additional weed control.

In either drilled or water seeded systems, the flood provides over 50% of the weed control. In fact, one of the biggest problems in drill seeded rice is that it can be hard to build levees on time and it can be hard to establish the flood. One school of thought suggests that levees be pulled immediately after planting. However, in unleveled fields, curved levees usually prevent ground application of herbicide and fertilizer. When growers wait to build levees until the time of preflood herbicide and fertilizer application, untimely rains sometimes result in harmful delays in the establishment of the flood. Levee's are especially hard to build on Gumbo or clay soils. Growers with precision leveled land and a permanent berm have the best of both worlds- They can build levees whenever they want and to drive ground equipment in-between the straight levees.

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