Masters Thesis

Some effects of Lygus bugs on cotton in Fresno County, California

In a three-month study of the relationship and effects Lygus spp., especially Lygus hesperus Knight, on Upland Cotton, (Gossyplum hlrsutum L. variety, Acala, strain SJ-l), it was shown that Lygus bugs cause the major portion of their damage to the earliest blossoms of the season. This study also showed that Lygus seemed to suppress the initial rate of floral initiation for a period of one to two weeks when present in substantial numbers. This study showed a positive relationship between the Lygus population and the occurrence of bolls with black spots on the carpels. Also associated with Lygus populations were bolls possessing growth abnormalities such as lumps and knots on the carpels. In the study of Lygus activity as affected by air temperature there was a high positive relationship between the ability to catch Lygus bugs in a standard sweep net and an increase in the air temperatures. Lygus bugs appeared to reduce the yield of cotton by causing reductions in the total number of bolls which reached maturity; in the number of seeds per boll; in the weight of lint per boll; and in the weight per 100 seeds. Lygus reduced the early season yield by as much as 15 per cent compared to the late season reductions of less than five per cent. Yield reductions averaged II per cent for the season.

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