Content uploaded by Derrick Oosterhuis
Author content
All content in this area was uploaded by Derrick Oosterhuis on Jun 02, 2015
Content may be subject to copyright.
22
THE USE OF PLANT GROWTH REGULATORS
AND OTHER ADDITIVES IN COTTON PRODUCTION
Derrick Oosterhuis and William C. Robertson
1
INTRODUCTION
The cotton plant is a perennial with an indeterminate growth habit, and reputed
to have the most complex growth habit of all major row crops. Furthermore, it is very
responsive to management and changes in the environments and responds to any per-
turbations in its environment with a dynamic growth response that is often unpredict-
able. Cotton producers and researchers have, therefore, used plant growth regulators
(PGRs) and other cultural practices as a means to manage the balance between vegeta-
tive and reproductive growth for efficient cotton production. The following provides
some information on why we use PGRs, the problem with many of the existing PGRs,
and a summary of field and growthroom research on the evaluation PGRs at the Uni-
versity of Arkansas. Starter and foliar fertilizers will not be dealt with here.
WHY USE PGRS?
Chemical PGRs have been widely used in cotton production in an attempt to
adjust plant growth and to improve lint yield and fiber quality. Obviously, the best
means to achieve these aims is through the use of desirable genetics in the form of
well-adapted high-yielding varieties. However, due to the very varied environment
(e.g., soil, temperature, insects, and rainfall) in which cotton is grown, it is almost
impossible to have a perfectly adapted variety capable of providing high yields in all
circumstances. Therefore, PGRs and other stress management practices have been used
in an attempt to consistently achieve high yields.
WHAT IS A PGR?
PGRs encompass a broad category of compounds that promote, inhibit, or other-
wise modify plant physiological or morphological processes. Some PGRs are plant
hormones or their analogues; others are simply metabolic regulators. PGRs are classi-
fied as organic compounds that alter the growth and development of plants. Unlike
plant hormones that are endogenously produced by the plant, PGRs may be considered
chemical compounds either produced naturally by the plant or synthetically by a chem-
ist. PGRs are biologically active at very low concentrations and elicit responses similar
to those observed from plant hormones. Since most plant growth and development
1
Distinguished Professor, Department Crop, Soil and Environmental Sciences, University of Arkansas,
Fayetteville; Cotton Extension Specialist, Cooperative Extension Service, University of Arkansas, Little Rock.
23
Proceedings of the 2000 Cotton Research Meeting
processes are regulated by natural plant hormones, these processes may be manipu-
lated by either (1) altering the plant hormone level, or (2) changing the capacity of the
plant to respond to its natural hormones. In recent years, synthetic PGRs have been
investigated for their ability to alter cotton growth and development in an attempt to
control growth and improve productivity. PGRs should be considered as management
tools in the producer’s arsenal that can be used to ensure efficient production. These
compounds are diverse in both their chemistry and use. A comprehensive review of the
use of PGRs in cotton production has been presented by Cothren and Oosterhuis (2000).
THE PROBLEM!
In the past two decades, many new PGR compounds have been developed or
“accidentally” discovered and subsequently tested on cotton with variable and some-
times disappointing results due to a variety of reasons, including poor chemical com-
pounds, changing environments, and varied production practices. Producers are bom-
barded with a barrage of PGRs and incredible claims about their benefits. Usually there
are no creditable data to support these claims on which producers can base their deci-
sions about using these PGRs.
Producers would be wise to keep an eye open for unsubstantiated claims about
PGRs and, at the same time, develop a thick skin against all the wonderful claims made
for these products. When a question arises about whether to use a new or existing PGR,
research results from an accredited institution should be requested and evaluated. The
main points to look for are: Does the PGR do what it is supposed to? Does it perform
consistently from one year to another? Is it economical? The basic problem is that plant
responses to PGRs are complicated by the interaction of environment and cultural prac-
tices. Therefore, for a PGR to be widely accepted, it must perform consistently in a
given production scheme.
EVALUATION OF PGRs
PGRs have been evaluated at the University of Arkansas for the past two decades
(e.g., Urwiler et al., 1987; Oosterhuis and Janes, 1994). The overall aim of the PGR
program at the University of Arkansas is to improve our understanding in order to
control plant growth and enhance yield. This necessitates field studies with normal
cotton production practices, as well as growthroom evaluation for mechanistic studies.
Recent research has focused on the physiological effects and underlying mechanisms
of PGRs (e.g., Guo et al., 1994; Oosterhuis, 1996; Zhao and Oosterhuis, 1997a, 1997b)
in an effort to adapt their use to the growth requirement of specific crops and environ-
ments. Specific objectives of the research program, depending on the compound con-
cerned, are:
• Compare commercially available PGRs in field tests for effect on growth
and yield.
• Determine the optimum application rate and timing for the more promising PGRs.
• Investigate the effect of PGRs on emergence, root growth, and seedling
development.
AAES Special Report 198
24
• Determine the mode of action of the more promising PGRs.
The information from these studies is used to adapt the technology to best fit into
current cotton production systems, and to provide information for farmers to select and
use PGRs.
PGRs STUDIED
PGRs encompass a broad category of compounds that promote, inhibit, or other-
wise modify plant physiological or morphological processes. In the past two decades,
many PGR compounds have been developed and tested on cotton. However, the major-
ity of them have not proven satisfactory for one reason or another and have either been
discarded or are not used very much. The PGRs that have been used and tested in
cotton production in the mid-South in recent years (Table 1) include Atonik, cycocel,
Crop+2, Cytokin, Early Harvest, Maxon, PGR-IV, mepiquat chloride, Pix Plus, and
PHCA. There are also numerous other so-called PGR compounds that have not been
listed because they did not prove to be effective in preliminary testing, they were with-
drawn by their manufacturers, or we were unable to get test samples from the compa-
nies concerned.
It is important to know and understand for what purpose a particular PGR was
designed. For example, a distinction is usually made between growth retardants (e.g.,
mepiquat chloride, Pix Plus, and cycocel) and growth or yield enhancers (e.g., PGR-IV
and Cytokin). However, a growth retardant such as mepiquat chloride, by the nature of
its effect on plant growth, may often also elicit other positive growth features such as
earlier maturity and a yield enhancement. Zhao and Oosterhuis (2000a) have demon-
strated that the main advantage of Pix Plus over mepiquat chloride may lie in the im-
proved partitioning of dry matter by Pix Plus into fruiting structures.
PGRs AND YIELD
A routine field test comparing commercially available PGRs has been conducted
for over 20 years at University of Arkansas experiment stations in the Mississippi Delta.
The rates and timings of the PGRs tested were according to best-scenario recommen-
dations from either the chemical companies concerned or University research findings.
The PGRs tested in the 1990s include Atonik, Cycocel (CCC), Maxon, Early Harvest,
PGR-IV, PHCA, Cytokin, Crop+2, Mepiquat Chloride (Pix™), and Pix Plus (formerly
MepPlus). Foliar spray treatment applications were made with a CO
2
backpack sprayer
calibrated to supply 10 gal/acre of solution. Fertilizer, weed control, and insect mea-
sures were added according to Cooperative Extension Service recommendations. The
experiments were furrow-irrigated as needed throughout the growing season. Routine
records were made of plant height and main-stem node number, petiole nutrient con-
centration, maturity, boll weight, boll number, lint percentage, fiber quality, and yield.
The yield response with added PGRs has been variable and inconsistent (Table 2).
There were no significant treatment effects on yield during the past 3 years, possibly
due to the unusually stressful seasons masking any possible PGR effects. Part of the
reason for variable yield responses from PGRs is the extremely varied environments
25
Proceedings of the 2000 Cotton Research Meeting
and crop conditions under which the PGRs are used, and also the lack of understanding
of the nature and performance of the specific chemical compounds. Another obvious
reason is that some of these chemicals do not really do the job they are supposed to!
The most consistent response has been shown with PGR-IV (a significant yield
increase 43% of the time), compared to PHCA (40%), Cytokin (33%), Pix (29%), and
Crop+2 (20%). Early Harvest has not shown any significant effect on yield in the 3
years it has been tested. The average yield increase over the past 7 years from PGR-IV
was 46 lb lint/acre, and from Pix was 20 lb lint/acre. However, Pix is a growth retardant
and as such was not conceived as a yield enhancer. Pix studies in Arkansas have shown
significant yield increases from Pix about 25% of the time associated with the con-
trolled plant growth (Oosterhuis et al., 1991). The effect of PGRs on boll weight and
boll numbers has shown no clear trend.
Another way to use these data is to consider the percentage increase for each
PGR compared to the untreated control. For example, the average response to mepiquat
chloride was 2.7% (or 13 lb lint per bale of yield), for PGR-IV it was 4.0%, and for
Early Harvest it was 2.0% (or 13 lb lint per bale of yield).
OTHER GROWTH EFFECTS OF PGRs
Plant height was significantly and consistently decreased by mepiquat chloride
and Pix Plus by 15-20%, sometimes with a slight accompanying decrease in main-stem
node number. Cycocel decreased height significantly but not as much as Pix; however,
cycocel (which is still used on cotton in many developing countries) significantly de-
creased yield in other related studies. Most other PGRs had either no effect on plant
height and node number or a small increase in height due to the growth-promoting
properties of the compound. In general, PGRs increased the concentration of certain
nutrients in the petiole, but as with yield, the results have been inconsistent. There have
been no significant effects of the PGRs tested on fiber quality.
SEED TREATMENT AND IN-FURROW
APPLICATIONS OF CHEMICAL ADDITIVES
Cotton is often planted in the mid-South under unfavorable planting conditions
(e.g., cool, wet soils). Therefore, producers have been interested in PGRs or fertilizer
additives for enhancement of seedling growth as well as increased yield. Earlier
growthroom studies showed enhanced root growth and seedling vigor from using in-
furrow seed treatment with PGR-IV (Oosterhuis and Zhao, 1995) and with ASSET
(Steger et al., 1998). However, field studies have been less than conclusive, often with
variable results (Robertson, 1998). Ongoing field studies continue to evaluate chemi-
cals added at planting to enhance seedling growth and increase yield (e.g., Oosterhuis
and Coker, 2000).
EFFECT OF PGRs ON ROOT GROWTH
Poor root growth early in the season in Arkansas, as a result of cool, wet soils has
been a serious limitation to optimum yields. PGRs, in addition to fungicides and insec-
AAES Special Report 198
26
ticides, may offer an opportunity for enhancing early-season plant development. Our
research has shown that in-furrow or seed treatment with certain PGRs is beneficial to
early root growth and seedling development in cotton. For example, growthroom stud-
ies revealed that the in-furrow applications of PGR-IV resulted in dramatic increases in
root length, root dry weight, number of lateral roots per plant, and nutrient uptake
1 week after planting (Oosterhuis and Zhao, 1995). These differences were still appar-
ent 5 weeks later at pinhead square but to a lesser degree. A range of PGR substances
have been evaluated in growth chamber studies for their effect on root growth and
seedling development. A number of compounds such as PGR-IV and ASSET applied
in-furrow or as a seed treatment have shown promise for enhancement of root growth
and early shoot development, although field results have not always been consistent.
We have also shown that indole butyric acid (IBA) and Pix plus IBA stimulated root
growth, but Pix alone did not stimulate root (Urwiler and Oosterhuis, 1986).
RATE AND TIMING
The complex growth pattern of cotton and its dynamic response to management
and environment necessitates precise application timing and rate of foliar-applied PGRs
for maximum control of plant growth for optimum yield response. Generally, the com-
pany that manufacturers the PGR provides the recommended rates and timing for its
compounds, but in many cases University of Arkansas scientists use field and
growthroom tests to determine or confirm these rates for the more promising com-
pounds. We have evaluated only PGR-IV, Early Harvest, Atonik, and mepiquat chlo-
ride for rate and timing, while the rates and timing of the other PGRs have been recom-
mended by the respective manufacturers. Information concerning rate and timing needs
to be continually updated as we learn more about each specific PGR (benefits and
mode of action) so as to best adapt the technology to our existing cropping systems.
PHYSIOLOGICAL EFFECTS OF PGRs AND MODE OF ACTION
A second level of research involves studying the more promising PGRs for their
effect on the physiology of the cotton plant and their mode of action. Detailed studies
have been conducted in Arkansas on mepiquat chloride (Oosterhuis et al., 1991), PGR-
IV (Oosterhuis, 1995), and recently on Pix Plus (Zhao and Oosterhuis, 2000a). The
effects of selected PGRs on photosynthesis, carbohydrate status, membrane integrity,
and nutrient uptake have been documented and the results used to explain the mode of
action (Guo et al., 1994). The use of PGRs to enhance nutrient uptake has also been
shown (Guo et al., 1994).
Our research has implemented sugar alcohols (polyols) in the action of PGRs
(Guo and Oosterhuis, 1995). Pix Plus has been shown to increase the levels of the
polyol myo-inisotol, which is believed to be related to the improved partitioning of dry
matter into cotton bolls (Zhao and Oosterhuis, 2000b). Phenolic acids play a possible
role as modulators of hormonal activity. We recorded the temporal patterns of phenolic
acids in cotton fruit in relation to abscission, sensitivity to environmental stress (shade
and water stress), ethylene evolution, and abscisic acid concentration of fruits. This
27
Proceedings of the 2000 Cotton Research Meeting
research suggested that phenolic acids modify growth and development of cotton fruit
during stress, and indicated the potential for use of phenolic acids as growth regulators
in cotton (Hampton and Oosterhuis, 1990).
Since leaf carbohydrates represent the primary metabolic carbohydrate pools for
cotton plants, an understanding of their dynamics during cotton growth and boll devel-
opment is essential. Our interest has focused on understanding the dynamics of carbo-
hydrate changes during leaf, canopy, and fruit development (Zhao and Oosterhuis,
2000b), and the possibility of influencing carbohydrate translocation out of the leaf
using PGRs. We have used
14
carbon-labeling techniques to show the influence of PGRs
on translocation. Certain PGRs, e.g., PGR-IV and possibly mepiquat chloride, can en-
hance translocation of carbohydrates out of the leaf, which was associated with an
increase in leaf photosynthesis and a yield advantage. Photosynthesis is often improved
when PGRs are used, but this is thought to be an artifact of the improved movement of
carbohydrates out of the leaf, allowing photosynthesis to occur at a maximum rate.
Bacillus cereus (IN PIX PLUS)
Field and growthroom studies are being conducted to understand the role of Ba-
cillus cereus, the new bacterial component of Pix Plus. Information to date implicates
B. cereus in increased dry matter partitioning to the fruit (Zhao and Oosterhuis, 2000a)
through improved efficiency of biochemical pathways in the leaf, possibly from bacte-
rial metabolites on the leaf surface.
EFFECTS OF PGRs ON STRESSED COTTON
Research at the University of Arkansas has shown that PGR-IV can have a reme-
dial effect on stressed cotton. For example, under conditions of mild water deficit,
PGR-IV can partially alleviate the detrimental effect of water stress, i.e., on photosyn-
thesis (Zhao and Oosterhuis, 1997b). We have also shown similar advantageous alle-
viation of stress effects under conditions of mild flooding and canopy shading (Zhao
and Oosterhuis, 1997a). PGR-IV has also been reported to help under conditions of
low temperature (Tom Cothren, Texas A&M University, personal communication). This
remedial action of PGRs may ultimately turn out to be one of their more important
roles in cotton production in the future.
PGRs AND EARLY MATURITY
The nature of the action of PGRs, e.g., decreasing vegetative growth, increasing
fruit set, and improving partitioning to fruit, often causes earlier maturity of the devel-
oping boll load. In our studies, only Pix has shown a consistent trend toward hastening
maturity, as indicated by reaching physiological cutout of NAWF=5 about 7 days ear-
lier, with a slightly larger percentage harvest at first pick. There was not a clear trend
for any other PGR compared to the control toward early cutout. In general, mepiquat
chloride causes a significantly earlier maturity about 50% of the time (Oosterhuis et
al., 1991).
AAES Special Report 198
28
COMPATIBILITY OF PGRs
Producers are often tempted to combine agricultural chemicals in the same tank
to save on application costs. Questions have arisen about the compatibility of mepiquat
chloride and PGR-IV because one is an anti-GA and the other contains GA as a central
component. Research has shown that these two PGRs can be safely applied together
without any harmful effect on yield, although the reduction in plant height from mepiquat
chloride may be slightly decreased (Guo and Oosterhuis, 1994). Although PGR-IV and
mepiquat chloride were shown to be compatible, it is recommended to apply them
1 wk apart.
NEW DEVELOPMENTS
The discovery of most commercial PGRs appears to have resulted from seren-
dipitous events, and therefore, the nature and action of the chemicals has been quite
varied. It is difficult to predict what new variations of PGR will arise. Current trends in
the selection and design of specific PGRs has involved multi-entity PGRs, polyhy-
droxy carboxylic acids, and the addition of micronutrients. It is obvious that the dis-
covery and acceptance of three new classes of PGRs—namely jasmonates, salicyclic
acid, and brassinosteriods—will lead to the development of new commercial PGRs.
The use of future PGRs will probably focus more on the fruit development period and
on remedial applications, as well as a more coordinated systems approach to manage-
ment coupled with more precise crop monitoring techniques.
CONCLUSIONS
PGRs allow for manipulation of physiological processes in plant growth and
development for more efficient crop management and increased yields. Research at the
University of Arkansas has shown that the use of PGRs in cotton is a useful production
practice for controlling plant growth and enhancing yield. However, the effect of avail-
able PGRs on growth and yield has generally been inconsistent and disappointing. This
is partially attributed to seasonal variations in weather and crop conditions, but also to
poor PGR materials and a lack of previous testing of the chemicals concerned. In some
cases, the chemicals are not suited for use in cotton. Good management decisions are
therefore necessary in deciding whether to use a PGR and also in selecting the most
appropriate compound. Continued research at both applied and basic levels will eluci-
date the specific effects and mode of action of PGRs and thereby aid in adapting their
use to current cotton production systems while also improving their performance and
consistency.
REFERENCES
Cothren, J.S. and D.M. Oosterhuis. 2000. The use of plant growth regulators in
cotton production. In: J.M. Stewart, D.M. Oosterhuis, and J. Heitholt (eds.).
Handbook of Cotton Physiology, Kluwer Publisher, New York. (in press)
29
Proceedings of the 2000 Cotton Research Meeting
Guo, C. and D.M. Oosterhuis. 1995. Pinnitol occurrence in soybean plants as
affected by temperature and plant growth regulators. J. Exp. Bot. 46:249-253.
Guo, C. and D.M. Oosterhuis. 1994. Compatibility of PGR-IV and PIX. Proc.
Beltwide Cotton Production Research Conferences. San Diego, 5-8 January,
1994. p. 1325.
Guo, C., D.M. Oosterhuis, and D. Zhao. 1994. Enhancing mineral nutrient uptake
with plant growth regulators. Proc. 21st Annual Meeting Plant Growth Regulator
Society of America. pp. 244-251.
Hampton, R.E. and D.M. Oosterhuis. 1990. Application of phenolic acids to manipu-
late boll distribution in cotton. Arkansas Farm Res. 39(2):11.
Oosterhuis, D.M. 1995. Physiological effects of PGR-IV on the growth and yield of
cotton. In: C.A. Constable and N.W. Forrester (eds.). Challenging the Future.
Proc. World Cotton Research Conference 1. CSIRO, Brisbane, Australia. pp.
133-146.
Oosterhuis, D.M. and D.L. Coker. 2000. Evaluation of ASSET
TM
and ASSET RTU
TM
as in-furrow applications to enhance cotton growth and yield. In: D.M.
Oosterhuis (ed.). Proc. 2000 Cotton Research Meeting and Summaries of Re-
search in Progress. University of Arkansas Agricultural Experiment Station Special
Report 198:98-101.
Oosterhuis, D.M. and C. Guo. 1995. Research on plant growth regulators. In: D.M.
Oosterhuis (ed.) Proc. 1994 Arkansas Cotton Research Meeting and Summaries
of Research. University of Arkansas Agricultural Experiment Station, Special
Report 166:169-174.
Oosterhuis, D.M., S.D. Wullschleger, and S. Rutherford. 1991. Plant physiological
responses to PIX. In: D.M. Oosterhuis (ed). Proc. 1991 Cotton Res. Meeting.
University of Arkansas Agricultural Experiment Station, Special Report 149:47-55.
Oosterhuis, D.M. and L.D. Janes. 1994. Research on plant growth regulators in
cotton. In: D.M. Oosterhuis (ed). Proc. 1993 Cotton Research Meeting and
Summaries of Research in Progress. University of Arkansas Agricultural
Experiment Station, Special Report 162:196-199.
Oosterhuis, D.M. and D. Zhao. 1995. Increased root length and branching by soil
application of the plant growth regulator PGR-IV. Plant and Soil 167:51-56.
Oosterhuis, D.M. and D. Zhao. 2000. Field evaluation of plant growth regulators. In:
D.M. Oosterhuis (ed.). Proc. 2000 Cotton Research Meeting and Summaries of
Research in Progress. University of Arkansas Agricultural Experiment Station
Special Report 198:89-93.
Robertson, W.C. 1998. Yield response of cotton to starter fertilizer containing
Amisorb, Asset, or PGR-IV. In: D.M. Oosterhuis and J.M. Stewart (eds.). Proc.
1998 Cotton Research Meeting and Summaries of Research in Progress. University
of Arkansas Agricultural Experiment Station Special Report 188:157-158.
Steger, A., D.M. Oosterhuis, W.C. Robertson, C. Guo, D. Coker, and A. Daniel.
1998. Asset as an in-furrow application for enhanced early season growth and
increased yield. Abstracts, Second World Cotton Research Conference, Athens,
Greece. 6-12 September 1998.
AAES Special Report 198
30
Urwiler, M.J. and D.M. Oosterhuis. 1986. The effect of growth regulators Pix and
IBA on cotton root growth. Arkansas Farm Research 36(6):5.
Urwiler, M.J., C.A. Stutte, S. Jourdan, and T.H. Clark. 1987. Bioregulant field
evaluations on agronomic crops. University of Arkansas Agricultural Experi-
ment Station, Research Series 358.
Zhao, D. and D.M. Oosterhuis. 1997a. Physiological and yield responses of shaded
cotton plants to application of the plant growth regulator PGR-IV. J. Plant
Growth Regulation 17:47-52.
Zhao, D. and D.M. Oosterhuis. 1997b. Physiological response of growth chamber-
grown plants to the plant growth regulator PGR-IV under water deficit stress. J.
Environ. Exp. Bot. 38:7-14.
Zhao, D. and D.M. Oosterhuis. 2000a. Pix Plus and mepiquat chloride effects on the
physiology, growth and yield of field-grown cotton. J. Plant Growth Regulation
20 (in press).
Zhao, D. and D.M. Oosterhuis. 2000b. Dynamics of nonstructural carbohydrates in
developing cotton leaves, bracts and floral buds. Environmental and Experimen-
tal Botany (in press).
31
Proceedings of the 2000 Cotton Research Meeting
Table 1. Plant growth regulator common names, chemical makeup, timing, and rates of chemicals field tested.
Treatment Chemical makeup Company Timing Rate
z
Atonik Na salts of ortho-nitrophenol, Asahi Chem. Mfg. Co. PHS
y
, FF
x
, FF+3 wks 500 ml/A, 600 ml/A,
para-nitrophenol, and 5-nitro-guaiacol 600ml/A
Crop+2 protein digest extract Cytozyme Labs Inc. 3-4 leaf, PHS, FF 16 oz/A, 16oz/A,16 oz/A
Cytokin natural cytokinins PBT Inc. PHS, FF, FF+3 wks 4oz/A, 8oz/A, 8oz/A
Early Harvest IBA, GA, cytokinin Griffin Corporation IF
w
, PHS, FF 2oz/A,4oz/A,4oz/A
Maxon IBA, GA Terra International IF, PHS, FF 2 oz/A, 2 oz/ A, 4 oz/A
Pix Plus
v
Mepiquat Chloride and Bacillus cereus BASF (Microflo Company) PHS, FF 6 oz/A, 8 oz/A
PGR-IV IBA, GA plus fermentation broth Microflo Company IF, PHS, FF 2 oz/A, 4 oz/A, 4 oz/A
PHCA polyhydroxycarboxycylic acid Microflo Company PHS, FF, FF+3 wks 8 oz/A, 16 oz/A, 16 oz/A
Pix mepiquat chloride BASF PHS, FF 6 oz/A, 8 oz/A
z
According to manufacturer recommendations or previous research.
y
PHS = pinhead square.
x
FF = first flower.
w
IF = in-furrow at planting.
v
MepPlus was renamed Pix Plus in 1999.
AAES Special Report 198
32
Table 2. Effect of plant growth regulators on lint yield in Arkansas 1993-1999.
PGR 1993 1994 1995 1996 1997 1998 1999 % of control
z
------------------------------------------------------------- lb/acre ----------------------------------------------------------- %
Control 790 1094 1100 1297 1108 896 1080 ---
Atonik 850 1153 1070 1245 ----
y
---- ---- +5.5
Cycocel ---- ---- ---- ---- 1047 ---- ---- –5.5
Crop+ 941 1124 1064
x
1339
y
---- ---- ---- –0.3
Cytokin 879 1161 1028 1266 1122 ---- ---- +1.9
Early Harvest ---- ---- ---- 1308 1148 901 1114 +2.0
Maxon ---- ---- ---- 1328 ---- ---- ---- +2.4
PHCA 975 1159 1151 1308 --- --- --- +8.6
Pix Plus
w
---- ---- ---- ---- 1130 922 1087 +1.0
PGR-IV 906 1169 1121 1374 1158 860 1063 +4.0
Mepiquat chloride 960 1129 1027 1389 1076 907 1034 +2.7
Bacillus cereus ---- ---- ---- ---- ---- ---- 1074 –0.6
LSD 73 54 142 69 NS NS NS ---
z
Calculated for individual years and meaned overall.
y
Not evaluated in that year.
x
Crop+2 used in 1995 and 1996.
w
MepPlus was renamed Pix Plus in 1999.
