Documentation of Weed Infestations in South Carolina Cotton

E.C. Murdock


 
ABSTRACT

Thirty cotton fields in South Carolinas leading (top six) cotton-producing counties were randomly surveyed in mid-September, 1991, to determine weed infestation levels at harvest. One field was sampled for each 5,000 acres of cotton in these counties; this corresponds to one field per 7,000 acres of cotton produced in South Carolina. Cotton was planted on 210,000 acres in South Carolina in 1991, and 3,200 acres were sampled in this survey. Weed species and population levels presented in Table 1 reflect only mature weeds present at harvest. Mature weeds per 50 ft of row on two adjacent rows were counted and recorded from four randomly-selected sites in each field (100 ft of row/site; total of 400 ft of row/field).

Only eleven species were observed as problem weeds at harvest. Palmer amaranth was the most prevalent species, and was present in 33% of the surveyed fields at an average population of 7.6 plants/100 ft of row. The second and third most common weeds were yellow nutsedge and common cocklebur. These species were present in 10% of the surveyed fields at average population levels of 8 and 2.7 plants/100 ft of row, respectively. Southern crabgrass and sicklepod were present in 7% of the surveyed fields at average population levels of 6 and 3 plants/100 ft of row, respectively. Pitted morningglory, red morningglory, and prickly sida were observed in several fields, but only at trace levels.

In general, South Carolina cotton producers have achieved excellent season-long weed control. This is reflected in the low populations observed averaged across all the surveyed fields. However, Palmer amaranth has become established as our most prevalent weed species in cotton. This likely reflects the appearance of a dinitroaniline-resistant Palmer amaranth biotype which has been confirmed in eight South Carolina cotton fields.



Reprinted from 1992 Proceedings Beltwide Cotton Conferences pp. 1296 - 1297
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998