Helianthus or sunflowers is a genus of plants comprising about 70 species in the family Asteraceae. Except for three species in South America, all Helianthus species are native to North America (Mexico and Western United States). The common name, "sunflower", typically refers to the popular annual species Helianthus annuus, or the common sunflower, whose round flower heads in combination with the ligules look like the sun. It is an annual plant, with a vigorous development in all its organs and a pivotal root system which allows it to reach down to a depth of 2 m. Sunflower is a typically oleaginous plant having a fundamental role in human food and also as a fodder plant. It is one of the most cultivated herbaceous oil extraction plants in the world.
Climate: It is a very important factor in the development of sunflower, adapting very well to a wide range of temperatures ranging from 25-30 to 13-17ºC. If the temperature is very high during flowering and grain filling stages, it causes a significant loss in final production, both in weight and in fat content.
Soil: It is a non-demanding crop in relation to soil type, although it prefers clay-sandy and rich in organic matter soils. It is essential that the soil has a good drainage and the water table is shallow. The sunflower is very little tolerant to salinity, and the oil content decreases when salinity increases in the soil.
Light: The appearance of leaves, date of flowering and the duration of the growth and development stages are attributed to photoperiod.
Sunflower is very sensitive to B deficiency on calcareous or sandy soils and under moisture stress. Therefore, special attention should be paid to B nutrition. B may be applied to the soil either at sowing time (1–2 kg B/ha) or at the ten-leaf stage as a foliar application of 500 g B/ha (0.1-percent B solution).
Foliar fertilization is the fastest and most effective method to supplement and enrich plant nutrition and to correct nutritional deficiencies when needed. This contributes significantly to higher and better quality productions.
To verify the safe rate under local conditions, it is advisable to spray recommended rate on a few plants. After 3-4 days check the tested plants for scorching symptoms.