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Efficacy of Bacillus thuringiensis Berliner against the first three larval instars of Heliothis virescens (F.) was studied under greenhouse and field conditions. The primary objective of these studies was to determine the susceptibility of the tobacco budworm to Dipel, a commercial preparation of Bacillus thuringiensis. Both greenhouse and field studies showed that first-instar larvae were more susceptible to all dosage levels of Dipel tested (0.125, 0.25, 0.5, and 1.0 1b/A). The higher rates of 0.5 and 1.0 1b/A gave better control and remained effective for longer periods against the first-, second- and third-larval instars than did the lower rates of 0.125 and 0.25 1b/A. The efficacy of all Dipel rates decreased significantly with each subsequent post-application-date bioassay, and only the higher dosages of 0.5 and 1.0 1b/A remained effective at the three-day residue period in the field studies. The addition of a feeding stimulant, Coax, at 0.25 1b/A, to all Dipel treatments resulted in a significant increase in larval mortality of all instars tested. Dipel plus Coax exhibited longer residual activity than did Dipel alone, indicating that Coax may protect the spores and toxin from degradation by the direct sunlight. When second-instar tobacco budworm larvae were allowed to feed on Dipel-treated terminals for 6, 18 or 30 hours and then transferred to untreated diet, they showed a great capacity to recover from the effect of the toxin. However, as the Dipel rate or exposure time was increased, the ability of larvae to recover was decreased. Dipel did have an effect on the biological activity of treatment-surviving larvae. Larval and pupal development was delayed, pupal weight was decreased, and female fecundity was reduced. In all cases the changes were proportional with the Dipel rate and with the length of exposure. No apparent effect was shown relative to adult longevity or egg viability for those surviving Dipel treatments as larvae. When Dipel was applied directly on tobacco budworm eggs, it had no effect on egg hatch but did significantly affect survival of newly-emerged larvae, indicating the larvae consumed a lethal dose of the toxin during eclosion. The compatibility of Dipel in combination with Geocoris punctipes (Say) against first-instar larvae of Heliothis virescens was also studied under greenhouse and field conditions. Results of these studies indicated the possibility of utilizing the two biological agents to suppress tobacco budworm populations in the field. A minimum density of one Geocoris nymph per 4 row feet is required, plus an effective field rate of Dipel. When adult tobacco budworms were fed on Dipel at 32000 IU/ml, their longevity and fecundity were significantly reduced. An adult feeding stimulant is needed to lure the adults to a Dipel source.

The occurrence of the cotton root rot fungus, Phymatotrichum omnivorum (Shear) Duggar, in sharply defined, localized areas in certain fields led to the suggestion that there may be a specific soil chemical factor which limits the spread of the fungus. The available sodium, potassium, calcium, and magnesium contents of infested and adjacent noninfested soils in 13 fields were determined and compared. At seven sites, there were no significant differences in cation contents of infested and adjacent noninfested areas (p = 0.05). Available sodium levels were higher in infested areas at three sites, and higher in noninfested areas at three sites. Potassium and calcium levels were higher in the infested area at one site, and higher in the noninfested areas at two sites. Magnesium levels were higher in the noninfested areas at three sites. Contrary to previous reports, the fungus was found to cause severe disease in soils with available sodium contents as high as 4.2 milliequivalents per 100 g soil. Applications of sodium chloride at rates ranging from 1800 to 4000 kg/ha did not reduce disease severity or increase yield significantly in ten field trials.

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This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

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