ABSTRACT

Acala cotton fields in several production regions of California in 2002 experienced a range of symptoms, including early cessation of main stem and sympodial branch growth, foliar red or bronze coloration followed often by leaf necrosis, and in some limited cases, observable leaf wilting. Most University of CA Advisors and private consultants we met with felt the range and severity of these occurrences were considerably worse than experienced in the same areas in any recent years in Upland / Acala cotton. Variations on these symptoms were observed in widespread locations in several San Joaquin Valley counties in 2002, and field symptoms that were similar in some respects and different in other respects were also observed in the Imperial Valley region in southern California. In most fields, the first observations of problems began about mid-bloom, with the first observable symptoms differing somewhat across locations. In many cases, more severe than normal red and purple coloration in upper canopy stem and petiole tissue, or dark red or bronze coloration in upper canopy leaf blades were among the first plant symptoms observed. In most cases analyzed, plants developed moderate to severe nutrient deficiencies after mid- to late-fruiting. Soil and plant tissue tests available from many, but not all affected fields indicate that although plant tissue levels were low in several nutrients, including nitrogen and potassium, corresponding soil nutrient levels were generally within University of CA recommended levels. The worst-affected fields in the San Joaquin Valley generally had low to moderate yields, but the fruit loads were quite high given the smaller size and reduced vigor of the plants. Observations and soil and plant tissue tests available indicate that this problem was noted in numerous varieties, but foliar symptoms developed earlier and were worse in some varieties than in others. Yield data in these fields is inadequate to determine clearly if varietal differences in timing of symptoms resulted in yield differences. Although definitive causes of observed problems have not been identified based on these field observations, some generalizations are described that may prove useful if problems recur in other years,