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[R] Helianthus annuus L. (Asteraceae).
Fr: Tournesol; Ge: Sonnenblume; Pt: Girassol; Sp: Girasol; It: Girasole.
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- Annual plant, about 2m in the natural state, with large capitula that support yellow flowers and produce large, black achenes (*) . These capitula tend to orient themselves towards the rising sun. Introduced to Europe from South America at the end of the 17th century, its general characteristics have been modified by geneticists, particularly in the following areas:.
* height reduction (<2m);.
* the number of capitula, most cultivars have a single head;.
* reproduction is by seeds and not by rhizomes.
- Sunflowers are chiefly used to produce edible vegetable oil which is extracted from its seeds. The residues, rich in nitrogen compounds, are used for animal feed in the form of oilseed cakes. They can be cultivated as green forage, and have market potential as a biological fuel.
- The principal European sunflower producers are Germany, France and the Netherlands.
- The capitulum consists of a fleshy receptacle containing in the centre the ovaries of many fertile flowers, and tubules or florets (disk florets). After fertilization, the ovaries transform into achenes. Around the periphery of the inflorescence is a single row of sterile, yellow, strap-shaped flowers (ray florets) (often incorrectly described as "petals"). Surrounding these ray florets is an involucre of bracted capitula, more or less large and leaf-like, imbricate in 2 or more layers (*) .
After the beginning of the flowering season, the inflorescences remains facing towards the south-east. The capitulum begins to tilt towards the soil, the extent of the inclination depending on the cultivar. Harvesting is in autumn,when the seeds are as dry as possible, in order to reduce the drying cost.
-The phenological stages, distinguished on this basis, are: germination, seedling, flower bud, flowering season, yellow stage and maturity (*) .
- In the case of green forage, harvesting occurs earlier, 3 to 6 weeks after capitulum formation.
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- Herbicide treatments are essential and supplementary cultivating is recommended.
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- Diseases: the most frequently contracted diseases at this time (1992), in order of declining importance are: white rot, (Sclerotinia sclerotiorum), Phomopsis helianthi (Diaprothe helianthi), downy mildew (Plasmopara helianthi), grey mould (Botrytis cinerea), (Alternaria helianthi), (Macrophomina phaseoli) and verticillum wilt (Verticillium alboatrum,V. dahliae).
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- Principal European pests: less important than diseases, various pests attack sunflowers: the field slug (Deroceras reticulatum), the (Arion hortensis) and the marsh crane fly (Tipula paludosa) attack mainly young plants as does the onion thrips (Thrips tabaci). The leaf-curling plum aphid (Brachycaudus helichrysi) attacks the leaves. The house sparrow (Passer domesticus), green finch (Carduelis chloris) and linnet (Carduelis cannabina) devour the seeds in the capitulum, especially in small isolated plots (seed production).

[R] Images

* Sunflower (Minost C.)
1: sunflower plant.
a: root; b: cotyledons; c: first opposite leaves; d: superior alternate leaves; e: inflorescence in large capitulum;.
2: section of capitulum.
a: yellow ligulated flower; b: fruit (black akene); c: tubulated flower with female organs at maturity; d: tubulated flower with male organs at maturity.

* Phenological stages of the sunflower (Minost C.)
a: plantlet; b: floral bud; c: flowering, yellow stage; d: maturity.

To read this page in French

HYPPZ on line: Species (scientific names), Pests (common names), Glossary, Crops.

HYP3 : HYPP Phytopathology.

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