Project Summaries

01-143FL  Project Manager: R. L. Nichols


David L. Wright and James J. Marois, University of Florida

Hardlock is a frequent problem in the Southeast, which can result in large yield losses. Previous studies have shown that hardlock can be induced by inoculation with Fusarium verticillioides. Fungicide applications during bloom mayreduce the problem. This study investigated the role of fungicide and insecticide applications in reducing hardlock and increasing yield. Flower thrips, Franklinella spp. may contribute to hardlock, and significant control was obtained with insecticide applications. Insecticide applications significantly reduced hardlock in all instances. Fungicides were effective in most cases. When significant yield improvements were attained, it was usually due to insecticide applications alone or in conjunction with fungicides. Studies were conducted at Quincy and Marianna, Florida. The cultivar ‘DPL 555 BR’ was used. The insecticides, Orthene® or Karate® were used when needed to control the southern green stinkbug and the brown stinkbug. In Quincy, the studies were conducted on a Dothan sandy loam. The study in Marianna was conducted on a Chipola loamy sand. Cotton was harvested with a spindle plot picker. 

A randomized complete block design was used in Marianna, Florida, with 4 blocks and 4 treatments. The experiment included unsprayed control plots and three other treatments. An insecticide treatment was Tracer® at 2 oz./acre alternated weekly with Orthene® at 1.0 lb./acre. The fungicide treatment consisted of Topsin M at 1.25 lb./acre applied weekly. A fourth treatment included both the weekly insecticide and fungicide sprays listed above. Flowers were sampled weekly, 8 from each plot, and stored in isopropyl alcohol until thrips could be counted. Hardlock and yield were determined as described for Quincy.

Leaf area index was significantly increased in treatments that included the fungicide. More applications, particularly those occurring at the end of the season provided the most benefit. Hardlock was significantly reduced by fungicides, particularly in conjunction with insecticides. Differences in number of bolls per plant were significant, but not consistent among treatments. Yield was not significantly affected. Yields were excellent, with the control plots making over 1,500 lbs./acre. There may not have been an opportunity to increase yields with these treatments.

Fungicides and insecticides both appear to be useful in management of hardlock. Despite this, they do not eliminate the problem entirely. In the studies presented here, and in others, hardlock severity tends not to drop below 15-20%. Hardlock was less severe in 2005, probably due to climate conditions. There was a large reduction in the number of locules displaying pink coloration due to F. verticillioides in 2005 compared with previous years.


Project Year: 2005

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