THE VALUE OFFUNGICIDE SEED TREATMENTS AND SEED TREATMENT CHEMISTRIES FOR COTTON STAND ESTABLISHMENT: TWELVE YEARS OF RESULTS FROM THE COTTON DISEASE COUNCIL'S NATIONAL COTTONSEED TREATMENT TRIALS

摘要

Historically, seed treatments for cotton have meant the use of fungicides. Fungicides are now universally sold on cottonseed to control a number of seed-borne and soilborne fungi that affect the germination of seed and the emergence, survival and vigor of seedlings. By using a series of experiments in the National Cottonseed Treatment Program organized by the Cotton Disease Council, the value of fungicide seed treatments, improvements in seed treatments, and the value of hopper-box (custom seed) andin-furrow applications versus seed treatments were examined. Fungicides are only a part of a seedling disease management program that should include planting high quality seed, planting on raised seedbeds, and planting when conditions are favorable for germination and emergence of cotton. The National Cottonseed Treatment Program has 15 to 20 trials annually in which industry nominates a number of seed treatment combinations for evaluation. A standard fungicide treatment, Vitavax-PCNB + Allegiance, anda nontreated control are included to assess efficacy of the nominations and seedling disease pressure. In addition, the fungicide treatments Allegiance or PCNB are included to aid in determining the importance of Pythium spp. or Rhizoctonia solani, respectively. Disease ratings and pathogen isolations for seedlings and soil populations of selected soilborne fungi are conducted by collecting seedlings and soil from the nontreated control plots at each location. Soil temperature and water data also are collected for the sites. From 19932004, a total of 214 trials were conducted by cooperators, with fungicides improving stand over the nontreated control in 120 trials or 56% of the time. This indicates the value of fungicide seed treatments across the Cottonbelt. For states with a response, fungicides improved stand in 17% to 80% of the trials in those states. Seedling disease pressure was determined by comparing the stand for the nontreated control and the standard fungicide treatment. Stands were generally improved by 10% to 25% with the use of fungicides. The fungicides and fungicide combinations used for treating cottonseed are constantly changing as new chemistries become available and with a greater understanding of disease causing agents. Some ofthe more recent changes have included the shift in control of Rhizoctonia solani from PCNB to Triazoles (Baytan, Nu-Flow M, and Systhane) and Azoxystrobin (Dynasty and Protege). Treatments including these new chemistries have improved stands over PCNB when examining treatments over all sites and years, confirming that advances are being made in controlling this pathogen. These tests have also given us information on seedling diseases of cotton. Isolation of Thielaviopsis basicola, Rhizoctonia solani andPythium species was correlated with their soil populations. Hypocotyl disease severity was correlated with isolation of Rhizoctonia solani and Thielaviopsis basicola and root disease severity with isolation of Thielaviopsis basicola. In-furrow or hopper-box fungicides do not improve stand over the base fungicide seed treatment as consistently as the seed treatment and stand response is environmentally dependent indicating the use of these products should be targeted for when seedling disease pressure is greatest. Seed treatment fungicides will continue to be the foundation for the control of seedling diseases, with the level of disease control and safety increasing with improvements in seed treatment technology.