Defoliation Tests with Ginstar at the
Maricopa Agricultural Center in 1997
John M. Nelson, Maricopa Agricultural Center
Defoliation tests were conducted on Upland and Pima cotton at the Maricopa Agricultural
Center to evaluate rates of Ginstar, tank mixes of Ginstar with other defoliants and Ginstar
used as a preconditioner. The cotton used in these tests was generally difficult to defoliate,
probably because of an excessive supply of nitrogen and cool temperatures in October and
November. In early October, only the Ginstar + Def treatment gave good defoliation of upland
while all treatments gave good defoliation of Pima cotton. In late October tests,
temperatures were cool and only Ginstar + Def and Ginstar followed by Ginstar treatments
gave effective defoliation in 14 days. In October and November tests, Ginstar used as a
preconditioner was effective in helping to defoliate cotton under cool weather conditions.
Research conducted the past several seasons has indicated that the defoliant Ginstar is as
effective or more effective than the Dropp + Def treatment for defoliating cotton in a single
application (Nelson and Hart, 1993; Nelson and Hart, 1994; Nelson and Hart, 1995; Nelson and
Hart, 1996; Nelson and Hart, 1997).
However, information is needed on the rates of Ginstar to use under different environmental
conditions. In central Arizona, cotton is defoliated and harvested under a wide range of
weather conditions. For example, when harvest is in September air temperatures can be over
100° F at the time defoliants are applied, while for October harvests, temperatures can be much
cooler during defoliation. In addition, research is needed to determine if other defoliants
and adjuvants will enhance the activity of Ginstar. In tests reported here, we evaluated
different rates of Ginstar used alone and tank mixes of Ginstar with other defoliants.
Preliminary tests have indicated that acceptable defoliation of cotton may be obtained
under adverse conditions using Ginstar as a preconditioning treatment. In this season, we
evaluated the use of Ginstar at several rates as a preconditioning treatment on hard to
defoliate cotton under cool weather conditions.
Materials and Methods
Defoliation tests were conducted on 1 October and 31 October 1997 using DP5415 and Pima S-7
cotton. Separate tests evaluating Ginstar preconditioning treatments on DP5415 cotton were
conducted on 1 October and 4 November 1997. The cotton for all tests was planted in moist
soil on 10 April 1997. Standard practices for irrigation, cultivation and pest control were
followed. The cotton received a total of 140 lbs of N per acre during the growing season and
10 furrow irrigations with the final irrigation on 5 September.
Weather conditions and heat units (HU) for all defoliation tests are shown in
Table 1. Descriptions of the defoliation treatments are
shown in Tables 2, 3,
6 and 7. Preconditioning
treatments of Ginstar were applied 5 to 7 days prior to application of standard defoliation
treatments. In all tests, defoliation treatments were applied with a Hi Boy sprayer with a
7 nozzles per row spray boom at 9:00 - 11:00 a.m. A 25 GPA application rate was achieved
using 40 psi pressure, disc-core type cone spray tips (Disc No. 1.5 and Core No. 13) and
a ground speed of 3 MPH. Plots were 4, 40-inch rows wide by 38 ft. long. Each test
utilized a randomized complete block experimental design with 4 replications. Plots were
rated for leaf drop by 2 to 3 person 7 and 14 days after defoliants were applied.
Petioles collected from cotton used for defoliation tests contained 2,800 ppm NO3-N for
DP5415 and 1,800 ppm for Pima S-7 on 1 October, 1997. At the time of the first test, 1
October, DP5415 cotton had 2-3 NAWB and Pima S-7 had 1-2 NAWB. A September infestation of
whitefly resulted in honeydew deposits on cotton leaves in early October.
The defoliation tests reported here were conducted under a wide range of temperature
conditions. Heat units decreased from 241 for the 14 day period after defoliants were
applied on 1 October to 111 for the 4 November test (Table 1).
It is generally thought that 200 or more HU are needed in the 14 day period after application
of defoliants to achieve acceptable defoliation (70-75% leaf drop).
In the 1 October upland test (Table 2), only one treatment
(Ginstar + Def) gave acceptable defoliation, even though the temperatures were favorable for
defoliation (241 HU). In the Pima test, using Ginstar as a preconditioner gave almost complete
defoliation in 8 days (Table 3). All defoliation treatments
gave excellent defoliation of Pima cotton 14 days after application. In the upland test, the
cotton was still growing and contained a dense, green canopy when defoliants were applied.
Excessive N in cotton at the end of the season can delay senescence and make defoliation
difficult. Our research has shown that the effectiveness of defoliants generally decreases as
the petiole NO3-N content increases (Nelson and Hart, 1992). The 2,800 ppm NO3-N content of
petioles in the upland cotton in early October indicates an excessive supply late in the season
that probably contributed to the vegetative condition of the cotton and the lack of response
In the 31 October upland and Pima tests, temperatures were cool and only the Ginstar + Def
and Ginstar followed by Ginstar treatments were effective in defoliating cotton in 14 days
(Tables 4 and 5). In both
of the 31 October defoliation tests, tankmixing Def with Ginstar improved defoliation compared
to using Ginstar alone. When defoliating cotton under cool conditions late in the season,
considerable patience is required since very little leaf drop occurs in the first week after
defoliants are applied.
Separate tests to evaluate Ginstar as a preconditioning treatment for hard-to-defoliate
upland cotton were conducted on 1 October and 4 November (
Tables 6 and 7). In the October test, Ginstar used as
a preconditioner was equally effective at rates of .047 and .071 lb a.i./A
(Table 6). Both preconditioning treatments resulted in
almost 100% leaf drop 8 days after a regular treatment (.071 lb a.i.) of Ginstar was applied.
In the November test, there were no differences in percent defoliation among rates of Ginstar
used for preconditioning cotton ranging from .047 to .071 lb a.i./A. All preconditioning
treatments gave acceptable defoliation in 14 days whereas a single application of .094 or .117
lb a.i./A of Ginstar did not.
- Nelson, J.M. and G. Hart. 1992. Effect of plant nitrogen status on defoliation of short-season upland cotton. Cotton, A College of Agriculture Report. The University of Arizona, Series P-91: 317-319.
- Nelson, J.M. and G. Hart. 1993. Defoliation research on Pima and upland cotton at the Maricopa Agricultural Center in 1992. Cotton, A College of Agriculture Report. The University of Arizona, Series P-94:56-60.
- Nelson, J.M. and G. Hart. 1994. Defoliation research on Pima and upland cotton at the Maricopa Agricultural Center in 1993. Cotton, A College of Agriculture Report. The University of Arizona, Series P-96:57-63.
- Nelson, J.M. and G.L. Hart. 1995. Defoliation research on upland and pima cotton at the Maricopa Agricultural Center in 1994. Cotton, A College of Agriculture Report. The University of Arizona, Series P-99:40-45.
- Nelson, J.M. and G.L. Hart. 1996. Defoliation tests with Ginstar at the Maricopa Agricultural Center in 1995. Cotton, A College of Agriculture Report. The University of Arizona, Series P-103: 46-52.
- Nelson, J.M. and G. Hart. 1997. Defoliation tests with Ginstar at the Maricopa Agricultural Center in 1996. Cotton, A College of Agriculture Report. The University of Arizona, Series P-108: 67-75.
This is a part of publication AZ1006:
"Cotton: A College of Agriculture Report," 1998, College of Agriculture, The University of
Arizona, Tucson, Arizona, 85721.
Any products, services, or organizations that are mentioned, shown, or indirectly
implied in this publication do not imply endorsement by The University of Arizona.
The University is an Equal Opportunity/Affirmative Action Employer.
This document located at http://ag.arizona.edu/pubs/crops/az1006/az10061g.html
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