Characterisation of a Malawian isolate of Beauveria bassiana, a potential control agent of coffee stem borer, Monochamus leuconotus.

The radial growth, sporulation and viability of a Beauveria bassiana isolate were assessed at three temperatures (23, 28, 33 degrees C) under light and dark conditions. Optimum radial growth and sporulation occurred at 23 degrees C regardless of photoperiod with the highest spore concentration being attained after incubating for 28 days. Loss of viability was highest at 33 degrees C and there was no significant loss in viability at 23 degrees C for up to five weeks. It would appear that 33 degrees C is too hot for the sporulation, growth and viability of this insect fungus. Photoperiod effects were insignificant for all the parameters evaluated. The infectivity on white coffee stem borers at 2.5 x 10(8) spores ml(-1) was high with 100% of the test larvae immobilised and not feeding within 24 h and dying within two to twelve days.

Chemical alternatives for soil fumigation with methyl bromide on tobacco seedbeds in nematode and weed control.

The proposed phase out of methyl bromide necessitated the evaluation of a number of chemical alternatives to replace it. The recommended rate of application for methyl bromide, 50 g/m2 was evaluated over three years against various rates of 65% 1,3-Dichloropropene mixed with 35% chloropicrin (1,3-D/C-35); a combination of metham sodium and ethylene dibromide (EDB) and 65% 1,3-Dichloropropene (1,3-D) alone. Chloropicrin and 1,3-D have long been registered and used in Zimbabwe as individual chemicals and their combination as a single product had never been tested. 1,3-D/C-35 at 36.9 ml/m2 was as effective as methyl bromide in nematode and weed control and led to similar seed germination and seedling growth rate. A combination of EDB at 21 ml/m2 and metham sodium at 35 ml/m2 was also equally effective. The use of 1,3-D alone at 35 ml/m2 gave unsatisfactory weed control and led to a reduced seedling growth rate. Metham sodium alone at 35 ml/m2 gave comparable weed control, seed germination and seedling growth comparable with methyl bromide. However nematode control evaluated using a gall rating scale was reduced. 1,3-D/C-35 at 36.9 ml/m2 and metham sodium at 35 ml/m2 used in combination with EDB at 21 ml/m2 are therefore, possible replacements for methyl bromide soil fumigation in tobacco seedbeds.