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Potassium deficiency symptoms appear on an estimated 250,000 to 350,000 hectares of cotton in the San Joaquin Valley, CA each year. Symptoms are usually associated with the occurrence of Verticillium wilt. Soil fumigation with fertilizer K, solarization with and without added K, foliar and soil K application all either reduce or correct the foliar symptoms and increase lint yields. Soil test K levels are adequate and no K response occurs when mixed soil profile samples are cropped with 6 successive cuttings of Ladino clover. Uptake of (86)Rb is restricted in affected plants which show vascular plugging in electron micrograph sections. A strong sink exists in cotton burs and together with impaired K transport during the reproductive growth stage, contributes to K deficiency in the upper 1/3 of the plant and reduced seed cotton yields. Potassium (K) deficiency, apparently induced by a soil pathogen or pathogenic complex, affects an estimated 250,000 to 350,000 hectares of cotton grown in the San Joaquin Valley, CA. The problem is most acute on soils with high levels of Verticillium wilt and among cotton varieties most susceptible to wilt injury. Symptoms are similar to classical K-deficiency except that they develop late in the season and occur in the top one-third of the plant. Leaves initially turn a yellowish-green with mottled patterns between the veins. Intravernal portions ultimately develop patterns changing from yellow to brownish-red colors while the leaf tips and margins cup and the blade develops an unusual thickening. Affected leaves do not exhibit the typical "rust" symptom and may defoliate prematurely. The photosynthetic processes are arrested and lint yield reductions are typically 15 to 30 percent with moderate symptoms, but with combined K-deficiency and wilt, total crop losses may occur. |
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©National Cotton Council, Memphis TN |
Document last modified Sunday, Dec 6 1998
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