Defoliation of Pima and Upland Cotton at the Safford Agricultural Center, 1997

L.J. Clark, Safford Agricultural Center
E.W. Carpenter, Safford Agricultural Center

Abstract

Nine defoliation treatments were applied to Pima and upland cotton to compare the treatment effects on percent leaf drop and percent green leaves left and any effects they might have on yield or fiber qualities. All of the treatments were beneficial compared to the untreated check, the treatments including Ginstar performed better than those without.

Introduction

Defoliation of cotton plants prior to harvest is a practice introduced many years ago to reduce leaf trash in the harvested cotton. At higher elevations defoliation is practiced by a smaller percentage of the growers than other parts of the state because cool temperatures at harvest time reduces the effectiveness of many of the chemicals used as defoliants and frost can effectively defoliate the plants with no cost. This study was initiated in 1991 on Pima cotton, and was expanded to include upland cotton as well. The objective of the study was to see how effective each of the defoliation treatments was under the prevailing weather conditions present this year.

Materials and Methods

The study was implemented using Pima S-6 and DP 90. Treatments were applied to plots 4 rows wide and approximately 50 feet long, in a replicated randomized complete block design. The following crop history indicates the cultural practices employed in the experiment:

Crop history

Soil type: Pima clay loam variant
Previous crop: Cotton
Planting date: 8 April,1997         Rate: 25 lbs/ac
Herbicide: 1.5 pts/ac Triflurilin applied pre-plant, Cotton Pro applied at lay-by
Fertilizer: 100 lbs/ac urea under a green manure crop 2/10, 100 lbs/ac side dressed 6/2 and 7/14
Irrigation: Planted into moist soil plus 7 irrigations (28 ac in + 6 in rain)
Last date: 9 Sept
Defoliation date: Applied 26 September (14 gal/ac, 40 psi)        Observations: 3 October
Cumulative heat units: At defoliation 3439, at obs. 3606 ( =167)
Harvest: 1st pick: 16 October         2nd pick: Not taken

The treatments listed below were applied at a rate of 14 gallons of water per acre through Teejet flat fan nozzles on 20 inch spacings over 4 rows. One week after defoliation treatments were applied each plot was evaluated to determine the amount of leaf drop and the green leaves remaining on the plants. At harvest grab samples were taken from two of the replicates to determine if the defoliants had any effect on the lint qualities.

Number Treatment Treatment
1 GS Ginstar 180 EC 9 oz/ac
2 GS + NIS Ginstar 180 EC 9 oz/ac + Bond 2 pt/100 gal
3 GS + D-RET Ginstar 180 EC 9 oz/ac + Chemtrol 3 qt/100 gal
4 GS + PRP/2 Ginstar 180 EC 9 oz/ac + Prep pt/ac
5 GS + PRP Ginstar 180 EC 9 oz/ac + Prep 1 pt/ac
6 CHL2 + SF Sodium Chlorate (2 gal/ac) + Starfire (11 oz)
7 CHL2.5 + SF Sodium Chlorate (2.5 gal/ac) + Starfire (7 oz)
8 CHL Sodium Chlorate (3 gal/ac)
9 CK Untreated Check

Results and Discussion

As is shown in the crop history and Table 1 below, climatic conditions were ideal for defoliants to work. High temperatures were in the 90's, low temperatures near 60, lots of sunshine (solar radiation near 500 langleys) and light to moderate winds (maximum wind >20 mph helped to remove leaves). This gave excellent results from all the defoliation treatments.

Table 2 shows defoliation observations made one week after treatments on the long staple cotton plots. Ginstar at 9 oz per acre with Prep added gave complete defoliation and the treatments with Ginstar alone and with Ginstar plus the drift retardant were not far behind. The addition of a non-ionic surfactant seemed to slow the activity slightly. Chlorate and Chlorate plus Starfire were slightly less effective and it was noted that the addition of Starfire enhanced the defoliation activity. The untreated check was a stark contrast, with all its leaves intact.

Table 3 shows the observations made on the short staple cotton. All of the treatments containing Ginstar were statistically the same. In this case the non-ionic surfactant and drift retardant seemed to decrease the activity. The Chlorate treatments had statistically less leaf drop and more green leaf retention at the one week observation period. It may be noted that the % drop and % green values do not add up to 100%. That was because the ratings were made separately.

Table 4 has the lint yields and lint turnout by treatment for both the long and short staple studies. On lint yield, there was no treatment that produced a yield different from the untreated checks in either the long staple or short staple studies. It was not expected that the defoliation treatments would alter the yield. In the lint turnout, treatments could alter this value if sufficient trash were in the sample. The untreated check plots should have had the lowest lint turnout since they had more potential leaf trash than the other plots. This was not the case, so explanation is not given for the statistical differences shown.

In Table 5 the HVI data from the long staple plots are shown. Values that lie away from the norm are bolded to make observation easier. Similar effects were not observed in the previous study so no speculation nor explanation are given for these differences. If they were to appear in more studies, then additional studies would be justified to find their cause.

HVI data for the short staple study were not available for this report.

The message that can be taken from this study is that almost any defoliant is effective under the conditions of this trial even though some are more effective than other. One must evaluate the costs of the various defoliants against their effectiveness to determine if their use is justifiable.

References

  1. Brown, P.B. The University of Arizona AZMET system. http://ag.arizona.edu/azmet
  2. Clark, L.J. and E.W. Carpenter. 1997. Defoliation of Pima and Upland cotton at the Safford Agricultural Center, 1996. Cotton, A College of Agriculture Report, The University of Arizona, Tucson, AZ. Series P-108, pp. 82-87.

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/az10061h.html
Return to Cotton 98 index