Introduction
It has become a common practice to delay applications of Kerb when using sprinklers to establish lettuce in the low desert where high volumes of water are applied prior to weed germination. Prior to the 2003-04 season, the only option for making applications to wet fields was by air. A third party special local need registration (24C) label was granted to the Western Growers Association in the summer of 2003 which allows for the application of Kerb through sprinklers in Arizona. According to the Association records, approximately 21,000 acres of lettuce were treated with sprinkler applied Kerb during the 2003-04 season. Tests conducted in 2002-03 season indicated that sprinkler applications were effective and sometimes superior to aerial applications. Additional tests were conducted this season.

Procedure
This project was intended to compare application techniques on a commercial scale and could not be conducted with small plots under controlled conditions. Three tests were conducted this season by dividing 20 to 40 acre blocks in half and applying an equal rate of Kerb through sprinklers on one half and by air on the other half. Sprinklers were run from 4 to 6 hours after application on both halves except in Test Number 5 which was included here not as an equal comparison of aerial and sprinkler applied Kerb but to demonstrate the importance of proper water management when using this technique. In test Number 5 the sprinkler applied half of the field received an additional 2 inches of water following the Kerb application and resulted in significantly inferior weed control compared to the other half applied by air. Weed counts were made just prior to thinning on 10 randomly selected beds and are reported as an average of the 10 with a description of each test.

Test 1

Location: Dome Valley (20E and Co 8th Street)
Grower/PCA: Pasquinelli/Jeff Havins
Plot Size: 18 acres
Date applied: 12-11-03
Days after Sprinklers Started: 4
Rate: 1.3 lb/ac
Evaluated: 1-15-04
Weeds: Nettleleaf Goosefoot

In this test: There were few weeds in this 36 acre block and it appeared as if both the aerial and sprinkler applied Kerb was effective. Weed counts indicated that the aerial applied 18 acres had slightly more needleleaf goosefoot that escaped treatment than the sprinkler applied 18 acres. Crop injury in the form of marginal chlorosis and leaf burn was present in both halves of this field and was thought to be the result of cold temperatures rather than the herbicide.

Test 2

Location: Tacna (41E and County 5th Street)
Grower/PCA: Amigo Farms/Jeff Nigh
Plot size: 11 acres
Date applied: 12-31-03
Days after sprinklers started: 5
Rate: 1.3 lb./ac
Evaluated: 1-30-04
Weeds: Shepardspurse and Sudangrass



In this test: Shepardspurse control was significantly better in the sprinkler applied section of this block than it was on the aerial applied section. Sudangrass control, however, was poor in both the sprinkler and aerial applied sections. There was more Sudangrass in the sprinkler applied section than in the aerial applied section. There may have been a greater infestation in this section than in the aerial applied section but control of this weed was poor in both.

Test 3

Location; Yuma Valley (13th St & Avenue B)
Grower/PCA: Curry Farms/Bill Fox
Plot Size: 17 acres
Date Applied: 10-20-02
Days after sprinklers started: 3
Rate: 1.3 lb./ac
Evaluated: 11-19-02
Weeds: Shepardspurse

In this test: There was a high infestation of shepardspurse in this block. Control was significantly better in the sprinkler applied half than in the aerial applied half.
Test 4

Location: Yuma Valley (Ave H and Co 15th St)
Grower/PCA: Amigo Farms/Jeff Nigh
Plot Size: 13 acres
Date applied: 6-5-02
Days after sprinklers started: 1
Rate: 1.5 lb./ac
Evaluated: 6-25-02
Weeds: Common Purslane, Wright Groundcherry

In this test: This test was conducted in mid-summer to compare aerial and sprinkler applied Kerb applications. This test was conducted 3 months before lettuce was planted and was not intended to represent a typical Kerb application. Weed counts indicated that the sprinkler application was significantly more effective in controlling both Groundcherry and Purslane than the aerial application.

Test 5

Location: Yuma Valley (Ave C and Co. 12th Street)
Grower/PCA: E. Harrison/Bill Fox
Plot Size: 17 acres
Date applied: 12-4-03
Days after sprinklers started: 3
Rate: 1.7 lb./ac
Evaluated: 1-6-04
Weeds: Shepardspurse

In this test: This test was not an equal comparison between aerial and sprinkler applications of Kerb but is included here because it demonstrates the importance of proper water management when making delayed applications of Kerb to minimize leaching of the herbicide. Our intention was to treat half of this 34 acre block with 1.7 lb./ac Kerb applied by air and half with 1.7 lb./ac Kerb applied through the sprinklers. The entire 34 acre block was mistakenly treated by air with 1.7 lb./ac. causing in the sprinkler applied half to receive two applications totaling 3.4 lb./ac. To minimize crop injury, the sprinklers were run an additional 24 hours on this half of the block. No crop injury occurred due to the leaching of the herbicide but weed control was also reduced significantly compared to the half of the field that did not receive the additional water.

Discussion
Broadleaf weed control was better in all tests from the sprinkler applied Kerb than from the aerial applications. Test 5 was not an equal comparison of the two application techniques because of the extra water applied to the sprinkler applied section of this field. Sudangrass control was poor in Test 2 and worse in the sprinkler applied section. The reason for this is unclear. Crop injury occurred only in Test 1 and this was thought to be from cold temperatures rather than from the herbicide. It was equally present in both the aerial and sprinkler applied sections of the field. It can be concluded from these tests that applying Kerb through sprinklers to lettuce is effective and often superior to aerial applications. Proper timing and water management are necessary for the success of both aerial and sprinkler applications.

Full Disclaimers

Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director Cooperative Extension, College of Agriculture and Life Sciences, The University of Arizona.

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