The Persistence of Thiram in Soil and Its Relationship to the Microbiological Balance and Damping-Off Control

Abstract

A means of determining the thiram content of treated soil was developed, applying the paper disk bioassay technique with Glomerella cingulata as the test organism. It was found that thiram persisted in sandy soil for over two months but disappeared from compost soil within one week. Thiram treatment changed the microbiological balance in the soil, the number of bacteria being increased and the fungi decreased for some time. Thiram was shown to be selective in its action against fungi; Penicillium and Trichoderma, being resistant, increased in number after soil treatment. Thiram treatment rendered soil more difficult to infest artificially with Pythium ultimum and also prevented a natural increase in the population of damping-off organisms resulting from repeated cropping. This protection for seedlings persisted longer than did the fungicide in the soil.

Biodegradation of fungicide Thiram (TMTD) in soil under laboratory conditions

“…They also concluded that degradation yields of Thiram in soil inversely proportional to concentration. Richardson (1954) reported that more than 95% of the TMTD was completely converted to metabolites by soil microorganisms after 55 days of incubation. Kawasaki (1980) reported 30% Thiram degradation when 100 ppm of Thiram was inoculated with activated sludge (30 ppm) at 25°C and pH 7.0 for two weeks.…”

“…Minor degradative products included nitrite ions (nitrate reduction) and dimethylnitrosamine (Ayanaba et al, 1973). Richardson (1954) reported more than 95% conversion of Thiram to metabolites by soil microorganisms after 55 days of incubation. The harmful effects of pesticides are generally studied for many communities and individuals in the ecosystem, but very few studies were devoted for investigating the effects of soil microorganisms on the degradation of pesticides in soil.…”

Principles and Present Status of Chemical Control of Seedling Diseases

“…In this way the chemical and biological control may work together. There is ample evidence of this kind of indirect control action with thiram fungicides (Richardson, 1954, Vaartaja, 1954b, Jaques and Chase, 1954. Although not as well established, the same appears likely with some others of the new best fungicides, such as captan, nabam, ferbam, maneb, zineb, and pentachlorobenzene (Richardson, 1954, Kendrick and Middleton, 1954, Jaques and Chase, 1954.…”

“…A common soil fungus, Trichoderma sp. that is strongly antagonistic towards various pathogens, tolerates several chemicals much better than do the pathogens (Warcup, 1952, Richardson, 1954, Vaartaja, 1954a. Combining chemical and biological control in this way has already given promising results in English nurseries (Warcup, 1952), and appears worthy of special attention in research.…”

“…We can only guess when the applications should be repeated for any particular weather conditions. In a test by Richardson (1954), the decomposition rate of thiram was 4 days in compost soil but over 60 days in sand. High soil moisture has been found to decrease the control.…”