scholarly journals Simulated insect defoliation and duration of weed interference affected soybean growth

Weed Science ◽  
2006 ◽  
Vol 54 (4) ◽  
pp. 735-742 ◽  
Author(s):  
Travis C. Gustafson ◽  
Stevan Z. Knezevic ◽  
Thomas E. Hunt ◽  
John L. Lindquist
Keyword(s):  
Leaf Area ◽  
Defense Mechanism ◽  
Field Studies ◽  
Area Index ◽  
Early Season ◽  
Weed Interference ◽  
Insect Defoliation ◽  
Weed Growth ◽  
Simultaneous Control ◽  
Vegetative And Reproductive Growth

An improved understanding of crop stress from multiple pests is needed for better implementation of integrated pest management (IPM) strategies. Field studies were conducted in 2003 and 2004 at two locations in eastern Nebraska to describe the effects of simulated early-season insect defoliation of soybean and duration of weed interference on soybean growth. Three levels of simulated defoliation (undefoliated, 30, and 60%) and seven durations of weed interference (weedy and weed free; weed removal at V2, V4, V6, R3, and R5) were evaluated in a split-plot design. Defoliation significantly reduced soybean leaf-area index (LAI), total dry matter (TDM), and crop height in season-long weedy treatments only. Biomass partitioning during vegetative and reproductive growth was affected by both defoliation and weed interference. Increase in soybean relative growth rate (RGR) and biomass production soon after defoliation occurred (e.g., V5 stage) indicated potential defense mechanism by which soybean is able to adjust its physiology in response to the loss of leaf area. Weed interference combined with defoliation caused the greatest yield losses up to 97%. Results from this study indicate the need for monitoring early-season insect density and weed growth to determine if simultaneous control of both pests may be needed.

scholarly journals Effect of nitrogen addition on the comparative productivity of corn and velvetleaf (Abutilon theophrasti)

Weed Science ◽  
2006 ◽  
Vol 54 (02) ◽  
pp. 354-363 ◽  
Author(s):  
Darren C. Barker ◽  
Stevan Z. Knezevic ◽  
Alex R. Martin ◽  
Daniel T. Walters ◽  
John L. Lindquist
Keyword(s):  
Leaf Area ◽  
Field Experiments ◽  
Yield Loss ◽  
Biomass Accumulation ◽  
Nitrogen Addition ◽  
Corn Yield ◽  
N Addition ◽  
Area Index ◽  
Nitrogen Levels ◽  
Weed Growth

Weeds that respond more to nitrogen fertilizer than crops may be more competitive under high nitrogen (N) conditions. Therefore, understanding the effects of nitrogen on crop and weed growth and competition is critical. Field experiments were conducted at two locations in 1999 and 2000 to determine the influence of varying levels of N addition on corn and velvetleaf height, leaf area, biomass accumulation, and yield. Nitrogen addition increased corn and velvetleaf height by a maximum of 15 and 68%, respectively. N addition increased corn and velvetleaf maximum leaf area index (LAI) by up to 51 and 90%. Corn and velvetleaf maximum biomass increased by up to 68 and 89% with N addition. Competition from corn had the greatest effect on velvetleaf growth, reducing its biomass by up to 90% compared with monoculture velvetleaf. Corn response to N addition was less than that of velvetleaf, indicating that velvetleaf may be most competitive at high levels of nitrogen and least competitive when nitrogen levels are low. Corn yield declined with increasing velvetleaf interference at all levels of N addition. However, corn yield loss due to velvetleaf interference was similar across N treatments except in one site–year, where yield loss increased with increasing N addition. Corn yield loss due to velvetleaf interference may increase with increasing N supply when velvetleaf emergence and early season growth are similar to that of corn.

The Critical Period of Weed Control in Grain Corn (Zea mays)

Weed Science ◽  
1992 ◽  
Vol 40 (3) ◽  
pp. 441-447 ◽  
Author(s):  
Michael R. Hall ◽  
Clarence J. Swanton ◽  
Glenn W. Anderson
Keyword(s):  
Zea Mays ◽  
Leaf Area ◽  
Weed Control ◽  
Critical Period ◽  
Field Studies ◽  
Southern Ontario ◽  
Leaf Stage ◽  
Individual Leaf ◽  
Logistic Equations ◽  
Weed Interference

Field studies were conducted in southern Ontario to determine the critical period of weed control in grain corn and the influence of weed interference on corn leaf area. The Gompertz and logistic equations were fitted to data representing increasing durations of weed control and weed interference, respectively. The beginning of the critical period varied from the 3- to 14-leaf stages of corn development However, the end of the critical period was less variable and ended on average at the 14-leaf stage. Weed interference reduced corn leaf area by reducing the expanded leaf area of each individual leaf and accelerating senescence of lower leaves. In addition, weed interference up to the 14-leaf stage of corn development impeded leaf expansion and emergence in 1989.

Influence of Herbaceous Interference on Growth and Biomass Partitioning in Planted Loblolly Pine (Pinus taeda)

Weed Science ◽  
1990 ◽  
Vol 38 (6) ◽  
pp. 497-503 ◽  
Author(s):  
John R. Britt ◽  
Bruce R. Zutter ◽  
Robert J. Mitchell ◽  
Dean H. Gjerstad ◽  
John F. Dickson
Keyword(s):  
Leaf Area ◽  
Pinus Taeda ◽  
Loblolly Pine ◽  
Growth Efficiency ◽  
Biomass Partitioning ◽  
Lower Percentage ◽  
Total Biomass ◽  
Growth Responses ◽  
Area Index ◽  
Weed Interference

Three herbaceous regimes were established, using herbicides, to examine the effects of interference on growth and biomass partitioning in loblolly pine (Pinus taedaL.). Trees were sampled near Auburn and Tallassee, AL. Trees at the Auburn site grown with low weed interference (LWI) had 4, 10, 10, 8, and 4 times greater total aboveground biomass than did trees with high weed interference (HWI) for ages one through five, respectively. Medium weed interference (MWI, Auburn site only) resulted in three times greater biomass the first 4 yr and two times greater total biomass by the fifth year compared to trees grown with HWI. Trees growing with LWI were 5, 8, 10, and 6 times larger than those with HWI for ages one through four, respectively, at the Tallassee site. At all levels of interference, the percentage of total biomass in foliage decreased, and stem and branch components increased, with increasing tree size at both sites. Trees growing with HWI had a lower percentage of total biomass in foliage and a greater percentage of total biomass in stem than those growing with LWI when compared over a common size. Growth efficiency per tree, expressed as annual increase in stem biomass per unit leaf area (g m−2), was slightly greater for trees growing with LWI compared to HWI when leaf area index (LAI3, total surface) was less than 0.2. For LAI values greater than 0.2 the relationship was reversed. The latter contradicts the idea that growth efficiency can be used as a measure of vigor for young loblolly pine. Changes in carbon partitioning to the development of leaf area are suggested to be driving the accelerated growth responses associated with a reduction of weed interference.

Leaf Area and Competition for Light between Plant Species using Direct Sunlight Transmission

1988 ◽  
Vol 2 (2) ◽  
pp. 159-165 ◽  
Author(s):  
Graham K. Walker ◽  
Robert E. Blackshaw ◽  
Jack Dekker
Keyword(s):  
Leaf Area ◽  
Plant Species ◽  
Chenopodium Album ◽  
Field Studies ◽  
Individual Species ◽  
Light Competition ◽  
Direct Sunlight ◽  
Area Index ◽  
Wild Mustard ◽  
Competition For Light

A technique based on the relationship between leaf area index (LAI) and the transmittance of direct sunlight was developed for thein situstudy of competition for light between plant species. Field studies were conducted in 1984 and 1985 using monocultures and mixtures of rapeseed (Brassica napusL.), wild mustard (Sinapis arvensisL. # SINAR), and common lambsquarters (Chenopodium albumL. # CHEAL). LAI estimated nondestructively by this method agreed closely with LAI determined by conventional destructive techniques. Light measurements at several heights in the canopy were used to determine the vertical distribution of canopy leaf area. Combining this information with species heights allowed the separation of the canopy LAI into individual species LAI, from which light competition could be estimated by calculating the sunlit LAI of each species. The technique permits many detailed measurements in the same canopy throughout the growing season. The light sensor required is not costly and is simple to operate and to maintain.

Laser point-quadrat sampling for estimating foliage-height profiles in broad-leaved forests

2001 ◽  
Vol 31 (3) ◽  
pp. 410-418 ◽  
Author(s):  
Philip J Radtke ◽  
Paul V Bolstad
Keyword(s):  
North Carolina ◽  
Leaf Area ◽  
Field Studies ◽  
Area Index ◽  
Quadrat Sampling ◽  
Range Finding ◽  
The North ◽  
Broad Leaved Forest ◽  
Western North Carolina ◽  
Point Quadrat

A technique for estimating the vertical distribution of foliage area in broad-leaved forests was developed. The technique is similar to optical point-quadrat sampling, where estimates are based on heights to the lowest leaves above numerous sample locations beneath a canopy. In optical point-quadrat sampling, heights to lowest leaves are measured with a telephoto lens. Here, heights were measured using a commercially available laser range-finding instrument. The laser point-quadrat technique was tested in field studies conducted under broad-leaved forest canopies in western North Carolina and east-central Minnesota, U.S.A. Foliage-height profiles obtained by laser point-quadrat sampling were consistent with two of four published foliage-height profiles observed in 1995 at the North Carolina field locations. Total leaf area estimates obtained by laser point quadrats were not significantly correlated with values of leaf area index estimated by recent litter fall analyses at the North Carolina and Minnesota field locations. Although further evaluation and refinement of the technique is needed, laser point-quadrat sampling shows promise as a means of obtaining foliage-height profiles at a significantly reduced effort and with greater accuracy than methods commonly in use today.

Carbon Production of Sunflower Cultivars in Field and Controlled Environment. II. Leaf Growth

1980 ◽  
Vol 7 (5) ◽  
pp. 575 ◽  
Author(s):  
HM Rawson ◽  
GA Constable ◽  
GN Howe
Keyword(s):  
Water Stress ◽  
Leaf Area ◽  
Leaf Growth ◽  
Field Studies ◽  
Leaf Number ◽  
Area Index ◽  
Average Growth ◽  
Unit Leaf Area ◽  
Unit Leaf ◽  
Stomatal Apparatus

In field studies of several cultivars of sunflower grown on stored soil moisture or with irrigation, yield was positively related to leaf area at anthesis. The regression which described this relationship stated that 1370 kg seed ha-1 were associated with a unit increment in leaf area index. Cultivars differed in final leaf number, rate of leaf appearance, and in the vertical distribution of leaf area in the profiles. Final leaf number of plants grown on stored moisture remained the same as in irrigated plants, but the period for which each leaf grew was reduced from 19 to 16 days while the average growth rate was reduced from 13 to 6 cm2 day-1. These changes reduced the final leaf area from 5700 to 1900 cm2 per plant. As water stress increased, the period when leaves grew fastest became progressively earlier, from approximately 35% Amax to when leaves were less than 5 cm2. Water stress increased stomatal frequencies but reduced the area of individual stomata so that the area of the stomatal apparatus per unit leaf area was unchanged. This may partially explain the constancy of peak gas exchange per unit leaf area of sunflower grown under different water regimes. There was evidence that leaves could recommence growth when the stress was alleviated.

Wild mustard (Sinapis arvensis) response to field pea (Pisum sativum) cultivar and seeding rate

1996 ◽  
Vol 76 (4) ◽  
pp. 907-914 ◽  
Author(s):  
D. A. Wall ◽  
L. Townley-Smith
Keyword(s):  
Leaf Area Index ◽  
Leaf Area ◽  
Field Studies ◽  
Field Pea ◽  
Yield Losses ◽  
Seeding Rate ◽  
Area Index ◽  
Canopy Development ◽  
Wild Mustard ◽  
Cultivar Selection

Field studies were conducted at Morden, Manitoba from 1992 to 1995 and Wadena, Saskatchewan in 1995 to investigate the effect of cultivar selection and seeding rate on field pea competitiveness with wild mustard. Cultivars that had both long vines and rapid canopy development (leaf area index) were more competitive with wild mustard than those with short vines and slow canopy development. Cultivars differed markedly in their ability to suppress weed growth. Wild mustard density was affected in 2 of 4 yr by cultivar selection, while weed biomass was affected in 3 of 4 yr. Field pea yield losses under weedy conditions differed among cultivars and those cultivars that more effectively reduced wild mustard density or biomass had the lowest yield losses. Yield losses from wild mustard competition did not differ among cultivars when weed pressure was high and weeds emerged 1 wk before the crop. Seeding rate of Titan, a cultivar with long vine length, affected wild mustard biomass more than Trump, a cultivar with a short vine length. Key words: Competitiveness, leaf area index, yield

scholarly journals Canopy Variation Among Three Sweet Corn Hybrids and Implications for Light Competition

HortScience ◽  
2006 ◽  
Vol 41 (6) ◽  
pp. 1449-1454 ◽  
Author(s):  
Martin M. Williams ◽  
Rick A. Boydston ◽  
Adam S. Davis
Keyword(s):  
Leaf Area ◽  
Weed Management ◽  
Sweet Corn ◽  
Correlation Coefficients ◽  
Field Studies ◽  
Light Competition ◽  
Corn Hybrids ◽  
Area Index ◽  
Canopy Development ◽  
Weed Suppressive Ability

Research in dent corn has found significant variation in crop/weed competition for light among hybrids. However, little has been published on the extent of variation in sweet corn competitive ability. Field studies were conducted under weed-free conditions to quantify canopy development and light environment among three sweet corn hybrids and to determine associations among canopy characteristics to crop yield. An early-season hybrid (Spirit) and two midseason hybrids (WHT2801 and GH2547) were grown at experimental sites located near Urbana, Ill., and Prosser, Wash., in 2004 and 2005. Maximum leaf area index (LAI) and intercepted photosynthetically active radiation (PAR) was typically highest for GH2547 and lowest for Spirit. Most differences in vertical LAI among hybrids was observed above 60 and 150 cm in Illinois and Washington, respectively, with WHT2801 and GH2547 having leaf area distributed higher in the canopy than Spirit. Both number and mass of marketable ears were positively correlated with maximum relative growth rate (correlation coefficients 0.60–0.81), leaf area duration (0.68–0.79), total LAI (0.56–0.74) at R1, and intercepted PAR (0.74–0.83) at R1. Differences in canopy properties and interception of solar radiation among Spirit, WHT2801, and GH2547 lead us to hypothesize that variation in weed-suppressive ability exists among hybrids. Future testing of this hypothesis will provide knowledge of interactions specific to sweet corn useful for developing improved weed management systems.

Insect Herbivory in a Eucalyptus maculata Forest on the South Coast of New South Wales

1998 ◽  
Vol 46 (6) ◽  
pp. 735 ◽  
Author(s):  
E. W. Pook ◽  
A. M. Gill ◽  
P. H. R. Moore
Keyword(s):  
Leaf Area ◽  
New South ◽  
New South Wales ◽  
Insect Herbivory ◽  
South Coast ◽  
The South ◽  
Leaf Production ◽  
Area Index ◽  
Insect Defoliation ◽  
South Wales

In most years between 1977 and 1992, insect defoliation was negligible in a regrowth stand of E. maculata Hook. on the south coast of New South Wales. However, leaf consumption by winter–spring infestations of cup moth larvae accounted for c. 6%, 19% and 4% of the total leaf loss from the canopy in 1989–90, 1990–91 and 1991–92, respectively. During the most serious infestation of 1990, cup moth larvae produced 0.56 t ha–1 of frass, equivalent to the consumption of c. 0.8 t ha–1, or c. 0.5 m2 m–2 of eucalypt leaf (c. 12% of winter leaf area index). In early November 1990, shortly after the infestation, an assessment of insect defoliation in the crown of a dominant tree revealed that (i) 47% of the leaf population was damaged, (ii) a larger proportion of older than younger leaves was damaged, (iii) the proportion of damaged leaves increased down the tree-crown profile, and (iv) 13% of the potential leaf area was missing. In the absence of further insect attack, the process of canopy renewal (leaf production and leaf fall) reduced the proportion of damaged leaves to 23% by June 1991.

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