Download Chance Riggins

Chance Riggins
Department of Crop Sciences
University of Illinois
What is Palmer amaranth (A. palmeri)?
• What do we know about its:
– distribution and identification
• historical and contemporary, Palmer or waterhemp?
– biology
• emergence, growth rate, reproduction, etc.
– competitive ability
• possible yield reduction in corn, soybean, etc.
– herbicide resistance
• multiple resistance, hybridization and resistance transfer
– implications for management
• identification & timing of any option are absolutely critical
Historical Distribution of Palmer amaranth
Amaranthus palmeri. Careless Weed
“This erect, leafy annual has a wide distribution through the Southwest…
Cattle are fond of the leaves and seeds. The amount of seed produced is
enormous. Stockmen in New Mexico and Arizona have a high opinion of
the careless weed, and often save the bottom-land meadows, where it
grows, for winter feed.”
Smith, J. G. 1900. Fodder and Forage Plants Exclusive of the Grasses.
USDA Bulletin No. 2.
Photo by Max Licher
Red Rock State Park, near Sedona AZ
Identification of Palmer amaranth
• Absolutely critical to identify Palmer amaranth before
the plant exceeds 2”
– POST herbicide effectiveness rapidly declines
• How to distinguish between Palmer amaranth and
waterhemp?
?
Is it Palmer amaranth or Waterhemp?
Seedling leaves:
notched
broader, ovate
no waxy sheen
Seedling leaves:
notched
narrow, lanceolate
often with waxy sheen
Is it Palmer amaranth or Waterhemp?
Young plants:
no pubescence
may have watermark
Young plants:
no pubescence
no watermark
Is it Palmer amaranth or Waterhemp?
Mature leaf:
Terminal hair usually
present
Mature leaf:
No terminal hair
Other distinguishing characters
inflorescence in feet
“V” variegation
Mature plants
Long leaf petiole
bracts stiff and sharp
also in leaf axils
Female flowers
Is it Palmer amaranth or Waterhemp?
Characteristic
Palmer
Waterhemp
Young leaves:
Notched
Yes
Yes
Shape
Rounded
Lanceolate
Older leaves:
Petiole
Longer than blade Shorter than blade
Markings “V” variegation
None
Pubescence:
No
No
Inflorescence:
Feet
Inches
Palmer amaranth biology
• Dioecious growth habit
– male and female plants similar to waterhemp, introduces a
great deal of genetic diversity
• Emergence characteristics:
– tends to display a prolonged emergence pattern
– higher germination rates at shallow seed depths
• Palmer amaranth has a higher seed germination rate
than other Amaranthus species (Steckel et al. 2004)
– one of the first Amaranthus species to emerge
– also germinates at higher temps than waterhemp
– may provide for competitive advantages over waterhemp
• emerges sooner and later
Palmer amaranth biology
• Stress tolerance:
– Palmer amaranth can tolerate high temperatures better than
other Amaranthus species
– also tolerates dry soil conditions better; originally evolved in
arid climate of southwestern US
Photo courtesy
Dr. Larry Steckel
Photo courtesy
Dr. Eric Prostko
Palmer amaranth biology
• Growth rate:
– has a high photosynthetic rate, 3–4x that of soybean
(Ehleringer 1983)
• Previous research has demonstrated Palmer
amaranth has a higher growth rate than other
Amaranthus species (Horak and Loughin 2000)
– average height increase per GDD50:
• Palmer = 0.195 cm/GDD Waterhemp = 0.135 cm/GDD
• 30-yr average GDD at Urbana for June 10–11 (42.5) and July
10–11 (50.5):
• Palmer = 3.2–3.8”/24 hr Waterhemp = 2.2–2.6”/24 hr
Palmer amaranth seed production
• Comparable with waterhemp
• 460,000 seeds/plant after full-season growth with cotton
• likely > 1,000,000/plant under non-competitive conditions
5.5 plants m-1 row = 1.2 billion seeds acre-1
Burke et al. 2007
Weed Technol. 21:367–371
Mechanisms of seed transport
• Too many to make an exhaustive list, but consider:
– Equipment purchased from areas where Palmer
amaranth is common
– Contamination of CRP seed mix
• possible source for population in Cass county (2012)
– Livestock feed
• ruminant feed containing either cottonseed hulls (“gin
trash”) or cottonseed meal
Why Palmer amaranth Spreads so Rapidly
• Practical exercise with Palmer amaranth seed
production:
– Single female Palmer amaranth plant produces 1,000,000
seeds at the end of the season
• assume only 10% viable portion added to soil seedbank
• assume only 25% germination of viable seed the following
season
• assume 99% control of these plants
– 250 Palmer amaranth plants survive the following season
How competitive is Palmer amaranth?
• The most competitive Amaranthus species
– reported yield losses include:
•
•
•
•
Soybean
Corn
Peanut
Cotton
78% (Weed Sci. 51:37–43)
91% (Weed Sci. 49:202–208)
28% at 1 plant/m row (Wd. Tech. 21:367–371)
up to 92% lint loss (Weed Sci. 47:305–309)
Predicted soybean yield loss
from one Palmer amaranth
per 3 ft of row:
32%
Klingaman and Oliver 1994
Weed Sci. 42:523–527
Glyphosate-resistant Palmer amaranth
• It’s already here in the Midwest, Folks!
– no longer confined to Southern U.S.
– glyphosate resistance trait spreads by seed and pollen
• Lack of fitness cost associated with Gly-R in Palmer
amaranth (Vila-Aiub et al. 2014; Giacomini et al. 2014)
‒ Resistance will persist in absence of glyphosate
• Problem can spread rapidly if left unchecked
– critical to identify resistance early, even individual plants
– seed production is substantial
– new evidence shows that a single Gly-R female is all it
takes (Ribeiro et al. 2014)
Photo courtesy
Robert Bellm
Glyphosate-resistant Palmer amaranth
2012
2011
2013
2010
2012
2011
2012
2007
2011
2008
2006
2012
2012 2010
2010
2006
2011
2005
2006
2008 2008 2004
2010
2010
Multiple resistance
ALS + Gly, PSII, or HPPD
Based on Heap (2013), Ward et al. (2013) and unpublished data.
Management of Palmer amaranth
• An integrated management approach is absolutely
critical
– PRE or POST only herbicide programs are unlikely to
provide season-long control
• Soil-residual herbicides should be applied within two
weeks of planting
– rainfall or mechanical incorporation needed
• POST herbicides must be applied to small Palmer
amaranth plants
– small means 2–3” plants
– grows inches per day
The Difference of 2 Days!
Flexstar on 6” Palmer
Flexstar on 3” Palmer
Photo courtesy
Dr. Larry Steckel
Hybridization and resistance
• How likely is interspecific hybridization among pigweeds?
‒ Frequency is low, but hybridization can occur!
‒ In field studies, Gly-R Palmer amaranth transferred
glyphosate resistance to:
• Spiny amaranth ≤ 0.4%
• Waterhemp ≤ 0.2%
• Smooth pigweed ≤ 0.01%
(Gaines et al. 2012)
‒ Yet, in controlled crosses, viable Palmer X waterhemp
hybrids are difficult to produce (Trucco et al. 2007)
Chance W. Riggins, Aaron G. Hager and
Patrick J. Tranel
Department of Crop Sciences
University of Illinois
Is Palmer amaranth in your field?
• Morphological characters
‒ Variable and few
‒ Need mature plants with flowers
• DNA-based approaches
‒ Virtually unlimited supply of characters
‒ Only need a small amount of tissue
• Testing of suspect Palmer amaranth plants
initiated during 2013 growing season
Palmer amaranth distribution in Illinois (pre-2013)
• Herbarium records suggest PA
has been in Illinois since the
1950s.
• Primarily found in southern part
of IL
• Confirmed Gly-R populations (*)
*
*
*
*
*
2013 Palmer amaranth survey in Illinois
• Palmer amaranth confirmed in
12 new counties (27 counties
total)
2013 Palmer amaranth survey in Illinois
• Palmer amaranth confirmed in
12 new counties (27 counties
total)
• ALS-R populations found in 4
counties
2013 Palmer amaranth survey in Illinois
• Palmer amaranth confirmed in
12 new counties (27 counties
total)
G
G
G
G
G
G
G
G*
*
*
*
*
• ALS-R populations found in 4
counties
• Gly-R found in 8 counties,
3 of which were multiple
resistant (ALS + Gly)
Summary
• Palmer amaranth is expanding its range northward in
Illinois
• Accurate identification of species is crucial for effective
management
• Herbicide-resistance for PA is likely underestimated
• DNA-based approaches offer opportunities for future
research into resistance mechanisms, population studies,
demographics, & hybridization detection
• Integrate PA survey data with our ongoing waterhemp
multiple resistance survey
Questions?