In a survey conducted during October 1995, single-lesion isolates of the sugar beet leaf-spot fungus, Cercospora beticola, were tested for sensitivity to the sterol demethylation inhibiting fungicides (DMIs) flutriafol and bitertanol. The isolates were collected from fields in three different areas of northern Greece. Fields at Serres and Imathia had been sprayed with DMIs for about 15 years to control sugar beet leaf-spot. At the third site, Amyndeon, DMI fungicides had not been used. From each area 150 isolates were tested. ED 50 values were calculated for individual isolates by regressing the relative inhibition of colony growth against the natural logarithm of the fungicide concentration. The mean ED 50 values for flutriafol for the Serres, Imathia and Amyndeon populations were 1´07, 0´73 and 0´5 mg mL 21 , respectively (significantly different at P 0´05). For bitertanol the mean ED 50 values for the Serres and Imathia populations were 0´72 and 0´81 mg mL 21 , respectively, which were not significantly different at P 0´05. The mean ED 50 value of the Amyndeon population was 0´48 mg mL 21 , which was significantly lower than those of the other two populations (P , 0´05). A cross-resistance relationship was found to exist between the two triazole fungicides tested when log transformed ED 50 values of 60 isolates were subjected to a linear regression analysis (r 0´81).

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The objectives were to select for resistance to carbofuran in a susceptible field population of Colorado potato beetles, Leptinotarsa decemlineata (Say), assess the progression of resistance, and characterize the inheritance and possible mechanism of resistance. Initial selection in the field resulted in over 99.9% mortality of treated larvae but high resistance in the survivors. Subsequent laboratory selection at c.80°h mortality increased resistance to > 100-fold by the fourth generation. Low level cross-resistance to azinphos-methyl was also present. Resistance appeared to be inherited via a single, autosomal, incompletely dominant gene, resulting in decreased acetylcholinesterase sensitivity. A second Michigan population also appeared to exhibit reduced cholinesterase sensitivity. Resistance to carbofuran in a Colorado potato beetle population from Long Island, NY appears to involve primarily mixed-function oxidase enzymes. The history of insecticide use probably affects which primary resistance mechanism appears in response to carbofuran treatment.

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The reduction of tetraconazole residue levels in field sugar beets (roots and foliage) was investigated, and the effectiveness of this new fungicide against the leaf spot disease of sugar beet was evaluated. The fungicide was used according to the recommended application procedures. Sugar beets received five applications of tetraconazole at rates of 0.05 and 0.10 kg of active ingredient/ha. A multiresidue method was adapted, and tetraconazole residues were determined with gas chromatography using a wide-bore column and an electron capture detector. Recovery of tetraconazole from sugar beet roots and leaves was found in the range of 86-111 and 78-103%, and the detection limits were estimated as 0.001 and 0.002 mg/kg, respectively. A relatively rapid dissipation rate of tetraconazole residues was found with a half-life of 5 days for either sugar beet roots or foliage.