Information from 1998 Missouri Rice Research Update, February 1999.

Effects of Pre-Emergence Herbicides On Water Seeded Rice

Gene Stevens, Andy Kendig, Eric Tanner, and Robert Barham1


A greenhouse experiment was conducted at the University of Missouri-Delta Center to evaluate water-seeded rice injury from pre-emergence herbicides. Dry and presoaked rice seeds were broadcast planted in containers with flooded soil treated with different herbicides. Averaged across all herbicide treatments, rice plants grown from presoaked seed were 59% taller and had 52% more plants per container than plants grown from dry seed. When Ordram herbicide was incorporated in the soil before flooding, rice plants from presoaked seeds were healthier than plants from dry seeds. Prowl and Bolero caused complete stand loss in presoaked and dry seeded treatments. No significant difference in plant height and stand was observed between untreated containers and containers with Command and Facet herbicides.


In 1994, only three thousand acres of water-seeded rice were grown in Missouri. In the last five years, water-seeded acreage has increased to thirteen thousand acres, and expected to continue increasing. Most of the water-seeded rice acreage in Missouri is planted by aerial seeding pre-soaked rice seeds into flooded fields. However, an increasing portion of the water-seeding is being done with dry seed. The main advantage of dry seeding is that it gives airplane pilots more flexibility in their schedule. When seeds are presoaked, airplane pilots have to fly the seed on a field when the roots begin to protrude from the seed regardless of the weather.

Herbicide injury to seedlings in dry seeding fields is a potentially greater problem than fields with presoaked seed. Presoaked rice seed imbibe most of the water needed for germination before planting as compared to dry seed that imbibe all their water from the flood water which may contain herbicides. Currently, Bolero and Ordram herbicides are labeled for water-seeded rice but only under specific conditions. Prowl, Facet, and Command are not currently labeled for water-seeded rice application. This experiment was design to determine which herbicides are safe to use in dry and pre-soaked planting methods.

Materials and Methods

Five herbicide treatments were applied with a CO2 sprayer to Sharkey clay soil in 121/2 inch x 7 inch x 6 inch plastic containers. Each container was filled with four inches of soil. Herbicides used were Prowl at 1lb.a.i./A, Facet 0.375 lb../A, Bolero 4 lb./A, Ordram 4 lb./A, and Command at 0.50 lb./A. Ordram was incorporated into the top two inches of soil. Before seeding the rice, containers were filled with water to a level of 2 inches above the soil. Containers were arranged in a randomized complete block with four replications.

The containers were flooded six hours before seeding. Presoaked and dry rice seed (Cypress variety) were broadcast at a rate of 3 bu./A ( 35 seeds per container). The presoaked seeds were soaked for 24 hours and allowed to drain for 24 hours before being sown. The root radicle had begun to bulge from the seeded. The dry seeds were sown at the same day as the presoaked seeds.


One week after seeding, root pegging was graded by a visual rating. In presoaked applications Facet, Ordram, and Command treatments all pegged very well. Many of the rice plants in containers treated with Command had white areas on their leaves one week after seeding. The Prowl and Bolero treatments only had a 7% and 17% lower rating than the untreated check. Roots in the dry-seeded treatments were less established. Prowl had the same rating as the untreated check. Seedlings from container treated with Facet, Command, and Bolero had 4 to 12% less root pegging than the untreated check. Seedlings from Ordram treated containers had 40% less root pegging than the untreated check. These results suggest an overall advantage to presoaking seeds.

Two week after seeding, Ordram and Facet had 22% and 35% shorter roots than the untreated check. When presoaked seeds were used, Command treatments, on average, were the same as the untreated check. Prowl and Bolero treatments killed the rice by the second week. After completing the test we realized that we had not followed the label instructions for Bolero. We should have waited at least 24 hours after applying the Bolero before flooding and seeding. There were only minor differences in results where non-soaked seed were used. Facet treatments had 11%, Command 23%, and Ordram 61% shorter roots than the untreated check. Facet and Ordram treatments both caused a significant amount of height reduction (29% and 50% shorter than the untreated check). We observed some "corkscrewing" of plants in containers treated with Facet. The Command treatment was 10% shorter, but was not significantly different from the check. The white areas on the rice plants from Command treated containers appeared to be smaller at the second week evaluation.

Table 1. Average height and plant populations two weeks after planting from presoaked seeds.

Herbicides        Plant height (inches)              Plants per square foot
Prowl                     0                                    0
Facet                     9                                   34
Bolero                    0                                    0
Ordram                    6                                   23
Command                  11                                   36
Untreated                13                                   48
LSD.05                    2                                    3
CV %                     27                                   39

Table 2. Average height and plant populations two weeks after planting from dry seeds.

Herbicides        Plant height (inches)              Plants per square foot
Prowl                     0                                    0
Facet                     7                                   25
Bolero                    0                                    0
Ordram                    2                                   15
Command                   7                                   27
Untreated                 7                                   28
LSD.05                    2                                    3
CV %                     27                                   39


Rice plants from pre-soaked seeds were taller and had more plants per square foot than plants from dry seeds. We found that Command and Facet pre-emergence herbicides caused minimal injury to water seeded rice plants. Ordram caused less damage when rice seeds were presoaked. Prowl and Bolero completely killed the rice. Command and Facet worked equally well with soaked or dry seeds. There was some bleaching of leaves with Command but plants most recovered. Field tests are needed to verify these results.

1Crop Production Specialist, State Extension Weed Specialist, Rice Farm Manager, Research Specialist, University of Missouri-Delta Center.