Experiments on the use of some chloronitrobenzene and organic mercury compounds for the control of low-temperature parasitic fungi on winter cereals

The cause of damage from low-temperature parasitic fungi during overwintering was in the experiments with winter rye mainly Fusarium nivale (Fr.) Ces., in the experiments with winter wheat both F. nivale and the Typhula spp. fungi, T. itoana Imai and T. idahoensis Remsb. The pentachloronitrobenzene compounds PCNB and the organic mercury compounds phenylmercuryacetate (PMA) and phenylmercurysalicylate (PMS) were effective against both the Fusarium and the Typhula fungi in the experiments in which the treatments of the seedlings had been performed in November under weather conditions normal for South Finland. The effect of treatments performed correspondingly earlier in October was slighter. In experiments made in South Finland in the winter 1955—56 and in the winter 1957—58, when low-temperature parasitic fungi appeared in abundance, the increases in yield due to treatment of the seedlings with PCNB and with the mercury compounds PMA and PMS performed in November were very considerable; winter rye (7 tests) 12—122 per cent, winter wheat (4 tests) 31—735 per cent, and winter barley (one test) 124 per cent. – In the experiments made in 1956—57 in South Finland no increase in yield was obtained through treatment of the seedlings because low-temperature fungi did not appear. The mercury compounds PMA and PMS when applied on the stands in autumn were more effective against low-temperature parasitic fungi on winter cereals than the PCNB preparations. The effect of zineb and hexachloronitrobenzene (HCNB) preparations in controlling low-temperature parasitic fungi on winter cereals by treating the stands in autumn was found to be much slighter than the effect of PCNB and of the organic mercury fungicides. The amount of active ingredient in the PCNB preparations was in most experiments 5 kg per hectare. In the two PMA preparations used in the experiments the amount of active ingredient was 125 and 425 kg per hectare, the corresponding amounts of Hg were 75 and 212.5 g per hectare. The amount of active ingredient in the two PMS preparations was 235 and 470 g per hectare, the corresponding amounts of Hg were 110.5 and 221 g per hectare. In the experiment on seed dressing with winter rye in 1955—56 it was ascertained that in addition to the organic mercury preparations also the thiram preparation was effective against Fusarium mould. In seed dressing experiments in Finland considerable increases in yield especially of winter rye have been obtained by using organic mercury compounds when the seed has been normally germinating and not infested by mould. This shows that the small amount of mercury that accompanies the seed into the soil is effective in controlling the low-temperature fungi during the winter.