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Early-season diseases occur in all soil types, but occur more often in wet and poorly-drained soil conditions. Conservation tillage, compacted soil, flat planting, and planting too deep can contribute to a higher incidence of disease. Nematode and thrips damage can delay seedling development and intensify damping-off. Symptoms include decayed seeds or seedlings, delayed emergence, partial or complete girdling of seedling stems, and root rot. Damaged seedlings are pale, stunted, slower growing, and can die within a few days after emergence. The taproot is often destroyed, leaving only shallow-growing lateral roots to support the plant. Stands may be slow-growing with skips in the rows.1
Soil Prep. Prior to planting, be sure the soil pH is within the 6.0 to 6.5 range. Apply fertilizer according to soil test results to help speed germination. For more information refer to the Agronomic Spotlight - Cotton Fertility.
Plant when soil temperature is above 65 °F at a 4-inch depth, with a favorable 5-day weather forecast. Germinating cotton seeds can be injured when soil temperatures fall below 50 °F. Planting into raised beds may improve soil temperature and drainage. It is important to mitigate potential disease risk on soils that cannot be bedded, such as those in a conservation tillage program.
Seed Quality. Plant high-quality seed with standard germination test results of at least 80%, or cool germination test results of above 70%.2
Planting. Planting seed too deep can extend the time required for emergence, increasing disease opportunities.2 For more information refer to the Agronomic Spotlight - Cotton Planting and Stand Establishment.
Scout. Scout for symptoms of early-season diseases while scouting for early-season insect damage.3
Seed Treatments. Fungicide seed treatments can provide cotton seedlings with adequate broad-spectrum protection from early-season diseases. Seed treatment fungicides may be either protectants or systemics. Protectant fungicides protect the seed from possible disease carried on the seed or soil diseases that may be in direct contact with the seed. Systemic fungicides are taken up by the seedling to provide protection from certain types of pre- and post-emergence damping off. Most commercial cotton seed sold is pre-treated with both protectant and systemic fungicides.
Premium seed treatment packages with higher use rates are available to help provide more complete and consistent protection in high disease pressure situations.
Figure 1. Rhizoctonia damage. Source: Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org.
Figure 2. Pythium root damage. Source: Howard F. Schwartz, Colorado State University, Bugwood.org.
Figure 3. Damaged vascular tissue from Fusarium infection. Source: Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org.
Figure 4. Symptoms of Thielaviopsis basicola. Source: Texas A&M University.
Figure 5. Cotton seedlings infected by Ascochyta gossypii. Source: Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org.
Ascochyta gossypii (Phoma exigua)