In this country three dates of planting tomatoes in greenhouses have been established: early in October (early production), in mid December (midseason production) and at the end of January (late production). Diseases develop to the greatest degree on tomatoes for early production and least on tomatoes for late production.
Early greenhouse tomato production in this country expanded substantially in the last few years.
In this connection certain alterations occurred in the epidemiology of the individual diseases.
Tomatoes for early greenhouse production are usually grown in outdoor beds in the latter part of August.
At that time the maximal day temperatures are often very high, the fluctuations of moisture in the surface soil layer are very great, which results in false damping off.
Under the effect of the high temperatures damages occur in the skin near the surface of the hot dry soil.
Many plants with hardly detectable damages by false damping off are introduced in the greenhouses at the time of transplanting.
Some of them perish some time after planting, others (the larger portion) become rooted, begin to increase and in the anthesis phase disorders become manifested at first-second inflorescence.
Only a very small portion of plants damaged by false damping off show no visible disorders after planting and rooting and continue to develop almost normally.
The timely dressing with earth and digging in of the affected plants makes it possible for them to grow new adventitious roots.
False damping off is not observed in midseason and late greenhouse production.
In addition to false damping off in early greenhouse production, other nonparasitic diseases are also observed.
Hollow stem occurs most frequently as a result of the poorly developed root system and the strongly developed overground mass owing to abnormal conditions and incorrect regime of raising.
Tomato field production is widespread in this country.
The pathogen of verticillium wilt (Verticillium dahliae Kleb) causes damages only on tomatoes for early field production, usually to a very limited extent.
Under greenhouse conditions, however, this disease acquires great economic importance.
It is especially injurious to tomatoes for early field production.
In many places in South Bulgaria greenhouses were recently built on areas infected to a various extent by this fungus.
The disease is observed already in the first year.
It affects nearly all plants in some greenhouses.
A case in point is the greenhouse of the Purvenets Cooperative Farm, Plovdiv district, where already in the first year after the greenhouse was built, during the growing season 1965–1966, about three months after transplanting i.e. about New Year, nearly all plants showed symptoms of verticillium wilt.
The yields may be cut by as much as 30–40 per cent if respective agrotechnical measures are not undertaken to