Abstract
Waterhemp has emerged as one of the most problematic weeds in agronomic crops in the Midwest because of an extended germination period and widespread occurrence of biotypes resistant to atrazine and sulfonylurea herbicides. However, the competitive effects of late-emerging cohorts on corn yield are not known. Field studies were conducted in 2001 and 2002 at Columbia, Novelty, and Albany, MO, to determine the effects of late-emerging waterhemp interference on corn growth, nitrogen (N) accumulation, and yield. Waterhemp emerged approximately 20 d after planting (DAP) and was treated at heights of 8, 15, 23, 31, 38, or 46 cm with directed applications of dicamba + diflufenzopyr followed by hand hoeing. Soil water status, corn leaf chlorophyll content, and corn and common waterhemp height were recorded at the time of waterhemp removal. N stress was detected with a chlorophyll meter at four of six removal timings at high waterhemp densities (362 or more plants/m 2 ) but only at one of six removal timings at lower densities (82 or less plants/m 2 ). Water stress was observed at five of the six removal timings at high densities but at none of the removal timings at low densities. High waterhemp densities reduced corn yield when allowed to reach 15 cm before removal, and yields were reduced 36% when not controlled. At low densities, yield losses did not occur unless waterhemp was allowed to remain with corn season long. Our research suggests that waterhemp is less competitive with corn than redroot pigweed, smooth pigweed, and Palmer amaranth. In addition, low densities of late-emerging waterhemp would not warrant removal to protect corn yield.
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Claims 9
Claim · model-written summary
High waterhemp densities caused detected nitrogen stress at four of six timings.
- Taxon
- Corn
Zea mays subsp. mayst0 - Interactor
- waterhempe0weed
- Outcome
- N stresse0
- Value
- four of six removal timingse0
- Qualifier
- 362 or more plants/m 2e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“N stress was detected with a chlorophyll meter at four of six removal timings at high waterhemp densities (362 or more plants/m 2 )”
t0“Corn”
Claim · model-written summary
Lower waterhemp densities had detected nitrogen stress at one of six timings.
- Taxon
- CornZea mays subsp. mayst0
- Interactor
- waterhempe0weed
- Outcome
- N stresse0
- Value
- one of six removal timingse0
- Qualifier
- 82 or less plants/m 2e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“N stress was detected with a chlorophyll meter at four of six removal timings at high waterhemp densities (362 or more plants/m 2 ) but only at one of six removal timings at lower densities (82 or less plants/m 2 ).”
t0“Corn”
Claim · model-written summary
High densities had water stress at five of six timings.
- Taxon
- CornZea mays subsp. mayst0
- Interactor
- Common Waterhempt1weed
- Outcome
- Water stresse0
- Value
- five of the six removal timingse0
- Qualifier
- high densitiese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Water stress was observed at five of the six removal timings at high densities but at none of the removal timings at low densities.”
t0“Corn”
t1“Common Waterhemp”
Claim · model-written summary
Low densities had no observed water stress at removal timings.
- Taxon
- CornZea mays subsp. mayst0
- Interactor
- Common Waterhempt1weed
- Outcome
- Water stresse0
- Value
- none of the removal timingse0
- Qualifier
- low densitiese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Water stress was observed at five of the six removal timings at high densities but at none of the removal timings at low densities.”
t0“Corn”
t1“Common Waterhemp”
Claim · model-written summary
High waterhemp densities reduced corn yield when weeds reached 15 cm.
- Taxon
- cornZea mays subsp. mayse0
- Treatment
- High waterhemp densitiese0
- Interactor
- waterhempe0weed
- Outcome
- corn yielde0
- Direction
- reducede0
- Qualifier
- 15 cm before removale0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“High waterhemp densities reduced corn yield when allowed to reach 15 cm before removal”
Claim · model-written summary
Uncontrolled high waterhemp densities reduced yield 36%.
- Taxon
- cornZea mays subsp. mayse0
- Treatment
- High waterhemp densitiese0
- Interactor
- waterhempe0weed
- Outcome
- yieldse0
- Direction
- reducede0
- Value
- 36%e0
- Qualifier
- when not controllede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“High waterhemp densities reduced corn yield when allowed to reach 15 cm before removal, and yields were reduced 36% when not controlled.”
Claim · model-written summary
Low-density yield loss occurred only with season-long interference.
- Taxon
- cornZea mays subsp. mayse0
- Treatment
- waterhemp was allowed to remain with corn season longe0
- Interactor
- waterhempe0weed
- Outcome
- yield lossese0
- Direction
- lossese0
- Qualifier
- low densitiese0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At low densities, yield losses did not occur unless waterhemp was allowed to remain with corn season long.”
Claim · model-written summary
Waterhemp was interpreted as less competitive than three other pigweeds.
- Taxon
- waterhempe0
- Interactor
- cornZea mays subsp. mayse0other
- Outcome
- competitive with corne0
- Direction
- less competitivee0
- Comparator
- redroot pigweed, smooth pigweed, and Palmer amaranthe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Our research suggests that waterhemp is less competitive with corn than redroot pigweed, smooth pigweed, and Palmer amaranth.”
Claim · model-written summary
Low densities of late waterhemp do not warrant removal to protect yield.
- Taxon
- cornZea mays subsp. mayse0
- Interactor
- waterhempe0weed
- Outcome
- would not warrant removale0
- Qualifier
- low densities of late-emerging waterhempe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“low densities of late-emerging waterhemp would not warrant removal to protect corn yield”
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