Crop Phenology for Irrigated Chiles (Capsicum annuum L.) in
Arizona and New Mexico.
Roberto Soto-Ortiz, Jeffrey C. Silvertooth, and Abraham Galadima,
Department of Soil, Water and Environmental Science
University of Arizona
Abstract
To determine growth and development patterns of irrigated green chile plants as a function
of heat units accumulated after planting (HUAP), as well as to develop a general irrigated
chile plant development model as a function of HUAP. Field experiments were conducted in
2004 and 20055 at Sunsites in Cochise County, AZ (about 4,000 ft. elevation) and at the
Massey Farm in the Animas Valley, NM (about 4,392 ft. elevation). Basic plant growth and
development measurements were collected routinely and important phenological stages
that corresponded to first bloom, early bloom, peak bloom, physiological maturity, and red
harvest were identified and recorded. Results indicate that among all sites, all varieties
have performed similarly in relation to HU accumulation patterns and preliminary plant
phenology models are under development in this program. The primary difference between
sites was that at Sunsites varieties tend to reach a 50/50 (green: red chile) ratio at 2900
HUAP and for Animas valley; this same ratio was reached at 3200 HUAP. Also, a general
irrigated green chile plant development model as a function of HUAP for all sites and
varieties was obtained. The purpose of this phenological baseline or model is to assist
growers in predicting and identifying critical stages of growth for crop management
purposes. First bloom occurred at 1369 ± 72 HUAP, early bloom at 1667 ± 79 HUAP, peak
bloom at 1998 ± 84 HUAP; physiological maturity at 2285 ± 159 HUAP, and red chile
harvest was identified to occur at 3295 ± 216 HUAP.
Key Words: Chile, Capsicum annuum L., crop phenology, growth and development, heat units.
Introduction
Chiles (Capsicum annuum L.) remain a stable and important crop for several crop production areas in
the desert Southwest chile belt (New Mexico, Arizona, Texas, and northern Chihuahua, Mexico).
Chiles (green and red) in the Sulfur Springs Valley of Cochise County are primarily produced under
center pivot irrigation. Chile jalapeños are produced in Pinal County in central Arizona.
______________________________________________________________________________
This is part of the University of Arizona College of Agriculture 2006 Vegetable Report, index at:
http://cals.arizona.edu/pubs/crops/az1419/
Recent trends indicate that demands for crops such as chile peppers in the U.S.A. are increasing. As a
result, an increase in cultivated chile acreage is needed to meet the market demands for this crop
(Johnson and Decoteau, 1996; Johnson and Johnson, 1992).
The latest data from the USDA
Agricultural Statistics Service showed New Mexico (NM) to be the leading State in chile production in
the U.S.A. where about 18,000 acres were committed to production in 2002. Planted acreage in
Arizona (AZ) is estimated at 6,000 – 10,000 acres in the recent years. The acreage level has increased
in AZ from about 4,000 acres that were reported for 1998. The increase in demand, coupled with more
land being committed to chile production has created the need to enhance the basic understanding of
chile crop agronomy and general production practices to improve efficiencies.
Accurate prediction of harvest date and developmental stages of a crop has widespread application for
improving management of that crop (e.g. fertilization, irrigation, scheduling multiple harvests, pest
management activities, labor and machinery, etc.). We often can monitor and predict development based
on measuring the thermal conditions in the plant’s environment. Various forms of temperature
measurements and units commonly referred to as heat units (HU) or growing degree units, have been
utilized in numerous studies to predict phenological events for both agronomic and horticultural crops
(Baker and Reddy, 2001).
Wurr et al. (2002) stated that to describe crop growth and development there is first the need to
determine rate functions for various processes; these include the identification of distinct stages and
phases of growth and development, as well as the prediction of duration of developmental phases for
given temperature regimes.
At present, there is very limited information available concerning basic crop growth and development
for irrigated chiles in the desert southwest. Some relevant information does exist in the literature for
chiles but it is very limited in scope and the work has dealt primarily with varieties and cultural
practices that have changed considerably in recent years (Beese et al. 1982; and Horton et al. 1982).
The literature regarding the basic agronomic aspects of chile production in Arizona is virtually nonexistent. Therefore, there is a distinct need to develop an understanding of basic crop phenology in the
desert Southwest. Hence, the objectives of this study were: 1) to determine growth and development
patterns of irrigated chile plants as a function of heat units accumulated after planting (HUAP), and 2)
to develop a general irrigated green and red chile plant development model as a function of HUAP
that could be extended as a crop management tool.
Materials and Methods
Field experiments were conducted in 2004 and 2005 at Curry Farms (Mr. Ed Curry, grower-cooperator)
on a Borderline fine sandy loam (coarse-loamy, mixed, superactive thermic Typic Calcigypsids) near
Sunsites in Cochise County, AZ (about 4,000 ft. elevation) and at the Massey Farm in the Animas
Valley, NM (about 4,392 ft. elevation), to conduct phenological monitoring studies of chiles. The project
involved the evaluation of a total of 10 Chile varieties being evaluated in the Sulfur Springs Valley of
Arizona (near Sunsites, AZ) and the Animas Valley of New Mexico (near Animas, NM). The study
areas were planted on 40 in. wide beds at Curry Farms in AZ and 30 in. beds at Massey Farms in NM.
All inputs such as fertilizer, water, and pest control were managed on an as-needed basis by the growercooperators. Basic agronomic information for all sites is presented in Table 1.
Climatic conditions were monitored and recorded on a daily basis throughout the growing season using
an Arizona Meteorological Network (AZMET) station sited near Sunsites, and a New Mexico Climate
Station Data (NMCC) for the Animas Valley location. The weather stations near the experimental sites
are automated and are used to determine the hourly (AZMET) and daily (NMCC) maximum and
minimum temperature values. Consequently, the HU accumulations (86/55 oF thresholds) are calculated
by a method presented in Baskerville and Emin (1969) and modified by Brown (1989). The daily HU
accumulations are summed up from the time of planting and reported as HUAP.
In-season data collection for each field was taken from 2m row segments at five randomly selected
locations in each field for the entire season and they included the following basic Plant growth and
development measurements: number of mainstem nodes from cotyledons to crown formation, height of
mainstem from cotyledons to the crown (cm), number of branches and height of each branch formed at
the crown, total number of forks and pods formed on each branch, number of white flowers per branch,
the number of nodes above the top white flower (NAWF), and above the newest pod position (NAPOD)
for each branch. Also, on the red-type chile fields; percent green to red ratios were counted on 14 day
intervals. This information provides crop maturity status and a means of comparing earliness or delayed
maturities among varieties or cases under study. Plant measurements were made in regular 14-day
intervals and the following growth stages were identified in each case: pre-bloom, early bloom, peak
bloom (also corresponded to early pod development), and physiological maturity. Statistical analyses
were performed on all in-season data collected with statistical procedures consistent with those outlined
by Steele and Torrie (1980) and SAS (SAS Institute, 199a and 1999b).
Results and Discussion
Plant growth and development measurements. The 2005 in-season data for all varieties and all sites was
collected and tabulated (Figures 1 - 5). In general, the in-season plant measurements provide an
indication of the progression of vegetative/reproductive development of the plant along the fruiting cycle.
Results indicate that for all site-years all varieties performed similarly in relation to HU accumulation
patterns. As a result, preliminary plant phenology models under development in this program can be
presented to the program community and given further testing and evaluation in commercial production
setting. Further testing of this preliminary model is also continued objective of this research program.
Percent green to red ratio. As presented in Figures 6 and 7, all varieties demonstrated similar rates of
transition from green to red chiles. The primary difference between sites was that at Sunsites varieties
tend to reach a 50/50 ratio (red:green pods) at 2900 HUAP and for Animas valley; this same ratio was
reached at 3200 HUAP.
A general irrigated green chile plant development model as a function of HUAP for all sites and varieties
is shown in Table 3. First bloom occurred at 1369 ± 72 HUAP, early bloom at 1667 ± 79 HUAP, peak
bloom at 1998 ± 84 HUAP; physiological maturity at 2285 ± 159 HUAP, and red chile harvest was
identified to occur at 3295 ± 216 HUAP.
Acknowledgements
The authors appreciate the valuable support provided by the Fluid Fertilizer Foundation and the New
Mexico Chile Task Force. Also, we are also very appreciative of the generous cooperation and support
provided by the grower-cooperators at Curry Farms in Arizona and the Massey Farms in New Mexico.
Also the hard work and technical assistance provided by the research assistants from the UA
Agronomy program are greatly appreciated.
References
Arizona Agricultural Statistics Service. 2002. United States Department of Agriculture. National
Agricultural Statistics Service. Annual Statistics Bulletin.
Baker, J.T., and V.R. Reddy. 2001. Temperature effects on phenological development and yield of
muskmelon. Annals of Botany. 87:605-613.
Baskerville, G.L. and P. Emin. 1969. Rapid estimation of heat accumulation from maximum and
minimum temperatures. Ecology 50:514-517.
Beese, F., R. Horton, and P.J. Wierenga. 1982. Growth and yield response of chile peppers to trickle
irrigation. Agron. J. 74:556-561.
Brown, P. W. 1989. Heat units. Ariz. Coop. Ext. Bull. 8915. Univ. of Arizona, Tucson, AZ.
Johnson, C.D. and D.R. Decoteau. 1996. Nitrogen and Potassium Fertility Affects Jalapeño Pepper
Plant Growth, Pod Yield, and Pungency. HortScience 31(7): 1119-1123.
Johnson, J. and C. Johnson. 1992. Two zesty alternatives to bell peppers. Amer. Veg. Grow. May:2427.
Horton, R., F. Beese, and P.J. Wierenga. 1982. Physiological response of chile peppers to trickle
irrigation. Agron. J. 74:551-555.
SAS Institute. 1999a. The SAS system for Windows. Version 8.0. SAS Inst., Cary, NC.
SAS Institute. 1999b. SAS/STAT user’s guide. Version 8.0. SAS Inst., Cary, NC.
Steel, R.G.D. and J.H. Torrie. 1980. Principles and procedures of statistics. McGraw-Hill, New York.
USDA. 2003. Soil Survey of Cochise County, Arizona. United States Department of Agriculture.
Natural Resources Conservation Service-The Hereford, San Pedro, Willcox-San Simon, and
Whitewater Draw Natural Resource Conservation Districts and the Arizona Agricultural
Experiment Station.
Wurr, D.C.E., J.R. Fellows., and K. Phelps. 2002. Crop Scheduling and prediction – Principles and
opportunities with field vegetables. In: Advances in Agronomy. D.L. Sparks (Editor). Volume
76. Academic Press. p.p. 201-234.
Table 1. Basic agronomic information for chile experiments; Sunsites, AZ and Animas Valley,
NM, 2004-2005.
Site
Sunsites
Animas
Valley
Variety
Wet Date
AZ 20
AZ 8
AZ 8
AZ 21
AZ 335-270
Esquina
Ancho X Chile
AZ 20
3/23/04
3/23/04
4/12/05
4/25/05
4/25/05
4/01/05
3/14/05
3/25/05
Grande
B58
300
LB 25
4/04/05
4/07/05
4/07/05
4/07/05
Irrigation
Type
Soil Type
Sprinkler
Drip
Fine sandy loam1
[coarse-loamy, mixed, superactive thermic
Typic Calcigypsids]
Sprinkler
1] USDA. (2003).
Table 2. Sampling dates for chile experiments; Sunsites, AZ and Animas Valley, NM,
2004-2005.
Site
Variety
AZ 8
AZ 20
Sunsites AZ 8
AZ 21
AZ 335-270
Esquina
Ancho X Chile
AZ 20
Animas
Valley
Grande
B58
300
LB 25
First
Bloom
Early
Bloom
Peak Bloom
Physiological
maturity
6/23/04
6/23/04
6/08/05
6/23/05
6/23/05
6/08/05
6/08/05
6/08/05
7/13/04
7/13/04
6/23/05
7/06/05
7/06/05
6/23/05
6/23/05
6/23/05
7/29/04
7/29/04
7/20/05
7/20/05
7/20/05
7/20/05
7/20/05
7/20/05
8/31/04
8/31/04
8/17/05
8/17/05
8/17/05
8/17/05
8/17/05
8/25/05
6/30/05
6/30/05
6/30/05
6/30/05
7/15/05
7/15/05
7/15/05
7/15/05
7/29/05
7/29/05
7/29/05
7/29/05
8/27/05
8/27/05
8/27/05
8/27/05
S u n s ite s 2 0 0 4
20
15
10
AZ 20
AZ8
5
0
AZ 20
A Z8
3
2
1
80
N um ber of pods
H e ig h t to c ro w n
20
AZ 20
A Z8
10
0
3 .2
AZ 20
AZ8
60
Number of pods
30
centimeters
N u m b e r o f f lo w e rs
4
Number of flowers
Number of nodes
N o d e s to c ro w n
40
20
0
B ra n c h e s a t c ro w n
B ra n c h h e ig h t
Number of branches
3 .0
60
centimeters
2 .8
2 .6
AZ 20
AZ8
2 .4
2 .2
2 .0
AZ 20
A Z8
40
20
1 .8
0
6
N u m b e r o f f o rk s
300
X D a ta
Number of nodes
Number of forks
1 .6
AZ 20
AZ8
200
100
0
N o d e s A b o v e w h ite f lo w e r
5
AZ 20
AZ8
4
3
2
1
0
500
1000
1500
2000
2500
o
H e a t U n its A c c u m u la te d A fte r P la n tin g (H U A P 8 6 /5 5 F )
500
1000
1500
2000
2500
o
H e a t U n its A c c u m u la te d A fte r P la n tin g (H U A P 8 6 /5 5 F )
F ig u re 1 . G ro w th a n d D e v e lo p m e n t v a ria b le s a s a f u n c tio n o f H U A P f o r a ll c h ile v a rie tie s .
C u rry 's F a rm . S u n s ite s , A z . 2 0 0 4 .
S u n s ite s 2 0 0 5
20
15
10
AZ 20
AZ 21
A Z 3 3 5 -2 7 0
A Z8
ANCHO
E S Q U IN A
5
0
centimeters
2
1
0
N um ber of pods
20
AZ 20
AZ 21
A Z 3 3 5 -2 7 0
AZ 8
ANCHO
E S Q U IN A
10
0
AZ 20
AZ 21
A Z 3 3 5 -2 7 0
AZ 8
ANCHO
E S Q U IN A
30
20
10
0
B ra n c h e s a t c ro w n
3 .0
Number of branches
AZ 20
AZ 21
A Z 3 3 5 -2 7 0
AZ 8
ANCHO
E S Q U IN A
3
H e ig h t to c ro w n
Number of pods
30
N u m b e r o f flo w e rs
4
Number of flowers
Number of nodes
N o d e s to c ro w n
B ra n c h h e ig h t
centimeters
60
2 .5
2 .0
AZ 20
AZ 21
A Z 3 3 5 -2 7 0
AZ 8
ANCHO
E S Q U IN A
1 .5
40
1 .0
0
N u m b e r o f fo rk s
150
100
AZ 20
AZ 21
A Z 3 3 5 -2 7 0
AZ 8
ANCHO
E S Q U IN A
50
0
600
800
1000
1200
1400
N o d e s A b o v e w h ite flo w e r
6
X D a ta
1600
1800
2000
2200
o
H e a t U n its A c c u m u la te d A fte r P la n tin g ( H U A P 8 6 /5 5 F )
Number of nodes
Number of forks
AZ 20
AZ 21
A Z 3 3 5 -2 7 0
AZ 8
ANCHO
E S Q U IN A
20
AZ 20
AZ 21
A Z 3 3 5 -2 7 0
AZ 8
ANCHO
E S Q U IN A
4
2
0
600
800
1000
1200
1400
1600
1800
2000
2200
o
H e a t U n its A c c u m u la te d A fte r P la n tin g ( H U A P 8 6 /5 5 F )
F ig u re 2 . G ro w th a n d D e v e lo p m e n t v a ria b le s a s a fu n c tio n o f H U A P fo r a ll c h ile v a rie tie s .
C u rry 's F a rm . S u n s ite s , A z . 2 0 0 5 .
Sunsites 2005
6
5
Nodes above newest pod
Vegetative branches
Number of vegetative branches
Number of nodes
5
AZ 20
AZ 21
AZ 335-270
AZ 8
ANCHO
ESQUINA
4
3
2
1
0
4
AZ 20
AZ 21
AZ 335-270
AZ 8
ANCHO
ESQUINA
3
2
1
0
600
800
1000
1200
1400
1600
1800
2000
Heat Units Accumulated After Planting (HUAP 86/55oF)
2200
600
800
1000
1200
1400
1600
1800
2000
o
Heat Units After Planting (HUAP 86/55 F)
Figure 3. Growth and Development variables as a function of HUAP for all chile varieties.
Curry's Farm. Sunsites, Az. 2005.
2200
A n im a s 2 0 0 5
20
10
N u m b e r o f f lo w e r s
Number of flowers
Number of nodes
N o d e s to c r o w n
15
10
GRANDE
B58
300
LB25
6
4
2
60
5
N um ber of pods
H e ig h t t o c r o w n
50
Number of pods
30
centimeters
GRANDE
B -5 8
300
L B -2 5
8
20
GRANDE
B -5 8
300
L B -2 5
10
0
3 .2
GRANDE
B -5 8
300
L B -2 5
40
30
20
10
0
B ra n c h e s a t c ro w n
B r a n c h h e ig h t
Number of branches
60
centimeters
3 .0
2 .8
2 .6
GRANDE
B -5 8
300
L B -2 5
2 .4
2 .2
40
GRANDE
B -5 8
300
L B -2 5
20
2 .0
0
8
N o d e s A b o v e w h ite f lo w e r
GRANDE
B -5 8
300
L B -2 5
X D a ta
GRANDE
B -5 8
300
L B -2 5
150
Number of nodes
Number of forks
N u m b e r o f fo rk s
100
50
0
6
4
2
0
1400
1600
1800
2000
2200
2400
2600
2800
o
H e a t U n its A c c u m u la te d A fte r P la n tin g ( H U A P 8 6 / 5 5 F )
1400
1600
1800
2000
2200
2400
2600
2800
o
H e a t U n its A c c u m u la te d A fte r P la n tin g ( H U A P 8 6 /5 5 F )
F ig u r e 4 . G r o w t h a n d D e v e lo p m e n t v a r ia b le s a s a f u n c t io n o f H U A P f o r a ll c h ile v a r ie t ie s .
M a s s e y 's F a r m . A n im a s , N m . 2 0 0 5 .
Animas 2005
6
Number of nodes
5
Nodes above newest pod
Vegetative branches
Number of vegetative branches
8
GRANDE
B-58
300
LB-25
4
2
0
4
GRANDE
B-58
300
LB-25
3
2
1
0
1400
1600
1800
2000
2200
2400
2600
Heat Units Accumulated After Planting (HUAP 86/55oF)
2800
1400
1600
1800
2000
2200
2400
o
Heat Units After Planting (HUAP 86/55 F)
Figure 4. Growth and Development variables as a function of HUAP for all chile varieties.
Massey's Farm. Animas, Nm. 2005.
2600
2800
Sunsites 2005
100
AZ 335-270
% Green/Red
80
60
40
20
% Green
% Red
0
Esquina
% Green/Red
80
60
40
20
% Green
% Red
0
2200
2400
2600
2800
3000
Heat Units Accumulated After Planting (HUAP 86/55oF)
Figure 5. Percent green to red ratio of AZ 335-270 and Esquina as a function of HUAP.
Curry's Farm. Sunsites, Az. 2005.
Animas 2005
100
B-58
% Green/Red
80
60
40
20
% Green
% Red
0
LB-25
% Green/Red
80
60
40
20
% Green
% Red
0
100
300
% Green/Red
80
60
40
20
% Green
% Red
0
2700
2800
2900
3000
3100
3200
3300
3400
Heat Units Accum ulated After Planting (HUAP 86/55 o F)
Figure 7. Percent green to red ratio of B-58, LB-25 and 300 as a function of HUAP.
Massey's Farm. Anim as, NM. 2005.
Table 3. Chiles phenological stages as a function of Heat units
accumulated after planting (HUAP), Arizona. 2004-2005.
HUAP (86/55 °F threshold).
Site
Phenological
Stage
Mean
Standard
Deviation
Sunsites,
First Bloom
Early Bloom
Peak Bloom
Physiological Maturity
Red Harvest
1359
1616
1945
2213
3112
89
32
37
148
124
New Mexico.
First Bloom
Early Bloom
Peak Bloom
Physiological Maturity
Red Harvest
1388
1769
2104
2430
3416
10
9
9
9
172
Combined
First Bloom
Early Bloom
Peak Bloom
Physiological Maturity
Red Harvest
1369
1667
1998
2285
3295
72
79
84
159
216
Arizona.
Animas,Valley,