Critical minimum temperatures for fruit crops in the first half of April

At the beginning of the month an increased likelihood is forecast for negative minimum temperatures and critical values (below minus 2°C) for the blossoms and fruit set of fruit trees. During this period the winter cereal crops will enter the beginning of the stem elongation stage. In successfully overwintered winter rapeseed stands the budding stage will take place.

At the beginning of April the agrometeorological conditions will be determined by relatively dry weather. The conditions will be suitable for carrying out seasonal agrotechnical activities, the most important of which is the sowing of sunflower. In many places in Southern Bulgaria the optimal periods for sunflower sowing, in the second half of March, have been missed. For Northern Bulgaria these periods fall within the first ten days of April.

During the first ten-day period the vegetation of agricultural crops will proceed at a moderate rate, with average daily temperatures close to the climatic norms. At the beginning of the month an increased likelihood is forecast for negative minimum temperatures and critical values (below minus 2°C) for the blossoms and fruit set of fruit trees. During this period the winter cereal crops will enter the beginning of the stem elongation stage. In successfully overwintered winter rapeseed stands the budding stage will take place.

During the first half of the second ten-day period a substantial increase in temperatures and accelerated development of autumn-sown crops and perennial plantations is expected. By mid-April, wheat and barley will be predominantly in the stem elongation stage. At the end of the period, in part of the rapeseed stands, the beginning of the flowering stage will be observed. In sunflower sown at the end of March, the emergence stage will predominate.

During the subsequent period the expected precipitation will provide moisture for the normal course of vegetation in autumn-sown crops and in the early and medium-early spring crops. At the beginning of spring, soil moisture reserves in the 50 cm and 100 cm layers in most of the country are very good, above 90% of field capacity (FC). Exceptions occur in places in the Danube Plain (agrometeorological stations Kneja, Novachene) and in the Sub-Balkan valleys (Kazanlak), where the level of moisture reserves is lower (below 80% of FC).

During the period, more suitable conditions for conducting plant protection spraying against certain economically important diseases (blossom blight, peach leaf curl, shot-hole disease, scab, fruitlet drop in quince, etc.) and pests (leaf miners, aphids, moths, weevils, etc.) will occur at the beginning and end of the first and in the middle of the second ten-day period of April.

Source: NIMH-BAS