Much of a cotton crop's yield potential and profitability are achieved in the first 40 days after planting, evidenced by the impact of crop uniformity, plant health and fast grow off on yield, quality and profitability, says Craig Bednarz, a plant pathologist at the University of Georgia.
Speaking at the recent Beltwide Cotton Conference in San Antonio, Texas, Bednarz, explains the findings of the First 40 Days Workshop, which brought scientists and crop consultants from throughout the Cotton Belt together to develop best management practices for the first 40 days of the life cycle of a cotton crop.
Benarz contends that some farmers now place efficiency and simplicity over agronomic performance and sound management. “We believe some decisions made primarily for the sake of efficiency may result in losses in yield, quality and profitability,” Benarz says.
The five best management practices developed by the First 40 Workshop are (1) good early season insect control, (2) seed and variety selection, (3) seed bed preparation, emergence and plant population, (4) weed control, and (5) nematode and seedling disease control.
Bednarz contends that at-planting management decisions to reduce inputs for early season pest control can result in delayed maturity, higher overall production costs and reduced yield and quality.
Entomologists in the First 40 Days group recommend use of an at-planting systemic insecticide with long residual activity. Insect control systems highlighting automatic over-sprays for thrips should be avoided because these can lead to aphid or mite infestations, he says.
Cultural practices, especially pre-plant weed control in the field and field perimeters, improve insect control by eliminating host plants and breeding sites. For growers in the western end of the Cotton Belt, this is particularly important for lygus control, Bednarz points out.
In the current era in which cotton seed are sold as individual units, it is more critical for growers to select seed that produce a plant that contributes to yield and to avoid seed that scavenge resources without significantly contributing to seed. The second best management practice — seed and variety selection — is where yield and quality potential begins for a cotton crop.
Since approximately one-third of the total cost of producing a cotton crop comes before cotton plants emerge from the soil, getting a uniform and vigorous stand is essential to profitability. Recommendations on plant population varied greatly within the study group. And Bednarz stressed that re-planting should be done only as a last resort.
The fourth best management practice, good early season weed control, varied greatly from one end of the Belt to another, but the general consensus of the group is to rotate weed control systems as often as possible and residual herbicides should be incorporated into weed control systems, the Georgia scientists says.
In the lower South, Bednarz says there is a strong recommendation to stop sole reliance on the use of glyphosate. He confirmed the findings in 2005 of glyphosate resistance in Palmer amaranth (pigweed) in Georgia, noting that this weed is a good example of “why” to avoid dependence on any one weed control system.
“New evidence, Bednarz says, indicates a seedling crop exposed to weed damage may never recover.” Therefore, the group recommends weed competition should be eliminated for at least the first 21-35 days, or to the five-leaf stage, he contends. The Georgia researcher points out that in one recent test, cotton seedlings exposed to weed competition at the five-leaf stage showed a 23 percent yield loss.
The fifth best management practice, nematode and seeding disease control, is a double-edged sword Bednarz contends. “We can all recognize lethal levels of seedling disease or nematode damage, but sub-lethal levels can be difficult to identify and often results in significant yield, quality and overall profitability losses,” Bednarz explains.
The group agreed that soil sampling should be done to monitor both nematode species and populations. Depending on pressure and species of nematodes, crop rotation and/or nematicides should be used.
“From my own experience, I know it is much easier to maintain a nematode population at a manageable level than to reduce a nematode population that has been allowed to build to damaging levels,” Bednarz adds.
How plants look
Oklahoma State University Cotton Specialist J.C. Banks explained what a healthy cotton plant should look like, if growers follow the five best management practices.
At 40 days, Banks says a cotton plant should be 8 inches tall and in the 8 leaf stage and have 2-3 squares. Final stand should have at least one-foot spacing and there should be a minimum number of gaps that are two or more feet.
Healthy cotton plants at 40 days, the Oklahoma scientist says should have a root system that is 24-30 inches deep and have healthy stems to overcome crusty soils that are critical in the early part of the growing season.
The First 40 Days group also developed a list of research and development needs for the future, based on the five best management practices.
More tools for insect management include new chemistry, landscape ecology and transgenic varieties for controlling plant bugs and thrips.
For seed and variety selection the group recommends a better definition of seedling vigor, new varieties for cool conditions, better drought tolerant varieties, screening for molecular trait markers in the lab rather than the field, and resistance in seeds to nematodes and other pests.
Among agronomic research needs defined are vegetative growth versus yield and vigor to yield standards, development of cross discipline crop management systems need to be linked and packaged to growers, and heat shock proteins and plant compensation capabilities need to be explored.
Better diagnostic tools tied to precision agriculture need to be developed, according to the group. More rapid and reliable sampling techniques and early season crop models that incorporate DD-60s and solar radiation are needed.
In conclusion, the group stressed the need for nematicides that provide longer and/or stronger nematode control.
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