In vitro dry matter disapperance

III. Growth Habit:

Sunflower is an annual, erect, broadleaf plant with a strong taproot and prolific lateral spread of surface roots. Stems are usually round early in the season, angular and woody later in the season, and normally unbranched.

Sunflower leaves are phototropic and will follow the sun's rays with a lag of 120 behind the sun's azimuth. This property has been shown to increase light interception and possibly photosynthesis.

The sunflower head is not a single flower (as the name implies) but is made up of 1,000 to 2,000 individual flowers joined at a common receptacle. The flowers around the circumference are ligulate ray flowers without stamens or pistils; the remaining flowers are perfect flowers (with stamens and pistils). Anthesis (pollen shedding) begins at the periphery and proceeds to the center of the head. Since many sunflower varieties have a degree of self-incompatibility, pollen movement between plants by insects is important, and bee colonies have generally increased yields.

In temperate regions, sunflower requires approximately 11 days from planting to emergence, 33 days from emergence to head visible, 27 days from head visible to first anther, 8 days from first to last anther, and 30 days from last anther to maturity. Cultivar differences in maturity are usually associated with changes in vegetative period before the head is visible.

IV. Environment requirements:

A. Climate:

Sunflower is grown in many semi-arid regions of the world from Argentina to Canada and from central Africa into the former Soviet Union. It is tolerant of both low and high temperatures but more tolerant to low temperatures. Sunflower seeds will germinate at 39°F, but temperatures of at least 46 to 50°F are required for satisfactory germination. Seeds are not affected by vernalization (cold) in the early germination stages. Seedlings in the cotyledon stage have survived temperatures down to 23°F. At later stages freezing temperatures may injure the crop. Temperatures less than 28°F are required to kill maturing sunflower plants.

Optimum temperatures for growth are from 70 to 78°F, but a wider range of temperatures (64 to 91°F) show little effect on productivity. Extremely high temperatures have been shown to lower oil percentage, seed fill and germination.

Sunflower is often classified as insensitive to daylength, and photoperiod seems to be unimportant in choosing a planting date or production area in the temperate regions. Oil from northern regions tends to be higher in linoleic acid and has a higher ratio of polyunsaturated to saturated fatty acids than oil produced in southern latitudes.

Sunflower is an inefficient user of water, as measured by the amount of water transpired per gram of plant above-ground dry matter.

Sunflower is not considered highly drought tolerant, but often produces satisfactory results when other crops are damaged during drought. Its extensively branched taproot, penetrating to 6.5 ft, aids the plant during water stress. A critical time for water stress is the period 20 days before and 20 days after flowering. If stress is likely during this period, irrigation will increase yield, oil percentage and test weight, but decrease protein percentage.

B. Soil:

Sunflower will grow in a wide range of soil types from sands to clays. The demands of a sunflower crop on soil macronutrients are not as great as corn, wheat or potato. As with other non-leguminous grain crops, nitrogen is usually the first limiting factor for yield. Medium to high levels of macronutrients are usually required for good plant growth. Sunflower stover contains a large proportion of these elements, which means sunflower is relatively inefficient in the use of these elements. However, most of these nutrients are returned to the soil with the stover.

Sunflower is low in salt tolerance but is somewhat better than fieldbean or soybean in this respect. Corn, wheat, rye and sorghum are rated medium, and sugarbeet and barley are high in salt tolerance.

Good soil drainage is required for sunflower production, but this crop does not differ substantially from other field crops in flooding tolerance.

V. Cultural Practices:

A. Seedbed Preparation:

Many different tillage systems can be used effectively for sunflower production. Conventional systems of seedbed preparation consist of moldboard plowing or chisel plowing to invert residue and several secondary field operations. Conventional systems have been shown to increase the availability and improve the distribution of potassium and nitrogen and to increase the seed zone temperatures. However, the risk of erosion and expense of the several tillage operations has led to greater interest in minimum or ridge tillage systems.

B. Seeding Date:

Sunflower can be planted at a wide range of dates, as most cultivars are earlier in maturity than the length of growing season in most areas. In areas of the world with no winters, sunflower has been planted at any month of the year to obtain satisfactory yields. In northern regions, highest yields and oil percentages are obtained by planting early - as soon after the spring-sown small grain crops as possible.

A later planting date tends to increase the proportion of linoleic acid in sunflower, especially at southern locations. Damage of sunflower heads by insect larvae may be increased by early planting. Test weight tends to decrease with late plantings.

C. Method and Rate of Seeding:

A planting depth of 1 to 3.5 in. allows sunflower seeds to reach available moisture and gives satisfactory stands. Deeper plantings have resulted in reduced stands and yields. If crusting or packing of the soil is expected, with silt loam or clay soils, a shallower planting depth is recommended.

Sunflower row spacing is most often determined by machinery available, which might be 30 or 36 in. for corn, soybean or sorghum growers, or narrower rows for sugarbeet growers. Hence, row spacings can be chosen to fit available equipment. Row spacings of 30 in. are most common. There is evidence that earlier, semidwarf varieties may perform better in narrower rows at high populations.

Plant population has a strong effect on seed size, head size, and percent oil. A medium to high population produces higher oil percentage than does low populations, and the smaller heads dry down faster at higher plant populations.

A lower plant population is critical for maximizing seed size for non-oilseed use.

D. Fertility and Lime Requirements:

Research has shown that sunflower responds to N, P and K. Nitrogen is usually the most common limiting factor for yield. Nitrogen fertilizer tends to reduce oil percentage of the seed, change the amino acid balance, and increase leaf area of the plant. Yield increases from N fertilizer rates up to 175 lb/acre have been observed, but rates considerably lower than this are usually recommended. Nitrogen recommendations in dryer regions can be made from estimates of nitrate nitrogen in the soil, but in wetter regions, this is not feasible. Nitrogen can be supplied from mineral or non-mineral sources (manures, legumes, compost). Row placement of P and K may be important in sunflower for maximizing efficiency of fertilizer use, as it is with many species.

More yield increases are reported as a result of applications of P than from K in Europe and North America.

Sunflower is not highly sensitive to soil pH. The crop is grown commercially on soils ranging in pH from 5.7 to over 8. The optimum depends upon other properties of the soil; no pH is considered optimum for all soil conditions. The 6.0 to 7.2 range may be optimal for many soils.

E. Variety Selection:

The development of a cytoplasmic male-sterile and restorer system for sunflower has enabled seed companies to produce high-quality hybrid seed. Most of these outyield open-pollinated varieties and are higher in percent oil. Performance of varieties tested over several environments is the best basis for selecting sunflower hybrids. The choice should consider yield, oil percentage, maturity, seed size (for non-oilseed markets), and lodging and disease resistance.

F. Weed Control:

As a crop, sunflower yields are reduced, but rarely eliminated by weeds which compete with sunflower for moisture and nutrients and occasionally for light. Sunflower is a strong competitor with weeds, especially for light, but does not cover the ground early enough to prevent weed establishment. Therefore, early season weed control is essential for good yields. Annual weeds have been the primary focus of weed control research. Perennial weeds can also present problems but are usually not specific to sunflower.

Successful weed control should include a combination of cultural and chemical methods. Postemergence cultivation with a coilspring harrow, spike tooth harrow or rotary hoe is possible with as little as 5 to 7% stand loss when sunflowers are at the four to six leaf stage (beyond cotyledon), preferably in dry afternoons when the plants are less turgid. One or two between row cultivations are common after the plants are at least 6 in. tall.

G. Diseases:

The most serious diseases of sunflower are caused by fungi. The major diseases include rust, downy mildew, verticillium wilt, sclerotinia stalk and head rot, phoma black stem and leaf spot. The symptoms of these diseases are given in Table 3. The severity of these disease effects on total crop yield might be ranked: 1) sclerotinia, 2) verticillium, 3) rust (recently more severe), 4) phoma, and 5) downy mildew. Resistance to rust, downy mildew, and verticillium wilt has been incorporated into improved sunflower germplasm.

Table 9: Major sunflower diseases and symptoms.

Downy mildew Plasmopara halstedi	Cottony fungus on underside of leaves. Dwarfing, contrasting discoloration of yellow-green and green. Blackening and sometimes swelling at base of stem. Disease most severe when rain occurs before and after emergence.
Powdery mildew Erysiphe cichoracearum	Cottony fungus on green leaves late in summer - not largely damaging.
Leaf spot Septoria helianthi	Dead blotches on flower leaves before heading. Has not caused appreciable loss.
Verticillium wilt Sclerotinia sclerotiorum	Before heading, dead areas along leaf veins, bordered by light yellow-green margins. Decayed vascular tissue in cross-section of stem.
Rust Puccini helianthi	Rust colored pustules on leaves, latter black specks on stems.
Sclerotinia head and stem rot Verticillium dahliae	Wilt soon after flowering. Light tan band around the stem at soil level. Grey-black sclerotia (size of seed) in rotted heads and stems. Seed and meats discolored.
Phoma black stem Phoma macdonaldii	Large chocolate colored blotches on stems at maturity.

H. Insects, Pollinators, and Birds:

Bees are beneficial to sunflower yield because they carry pollen from plant to plant which results in cross pollination. Some sunflower varieties will not produce highest yields unless pollinators are present. All varieties will produce some sterile seed (without meats), but varieties differ in their degree of dependence on insect pollinators. Autogamous sunflower hybrids do not require bees for maximum yield and will yield the same when covered by bags as uncovered. In non-autogamous sunflower varieties, pericarp (bull) development is normal but no ovules or meat develop. Wind is relatively unimportant in cross-pollination of sunflower.

Table 9: Common Insects in Sunflower

Sunflower moth Homoeosoma electellum	Eggs are laid at flowering and hatch in 1 week. Larva have dark bands running length of body. Feeds on floral parts, tunnels in Seed.
Banded sunflower moth Cochylis hospes	Moth has brown area mid-wing Larvae are not dark striped, smaller than head moth. Makes a small hole in top of seed, feeds on meat.
Sunflower bud moth Suleima helianthana	Dark grey moth. Feeds on young stem and head. Headless or damaged heads or large hole on stem near a leaf petiole is symptom.
Sunflower midge Contarinia schulzi	Small gnat with tiny cream-colored larvae laid when head is 1" in diameter. Brown spots at base of individual florets or absence of ray flowers, cupping of heads is symptom.
Sunflower headclipping weevil Haplorynchites aeneus	Black weevil causes head drop.
Sunflower beetle Zygogramma exclamationis	Adult with yellow strips length of wing covers. Humpback yellow larvae causes large areas of defoliation.
Sunflower maggot Strauzia longipennis	Adult a yellow fly with dark wing markings, smaller than housefly. Maggots burrow in stem.
Red sunflower seed weevil Smicronyx fulvus	Adult is rusty colored, and found in head. Adult female drills egg hole in developing seed and lays egg in hole. Larvae internal to seed; white legless with dark head capsule.
Gray sunflower seed weevil Smicronyx sordidus	Adult is gray colored; has behavior similar to red sunflower seed weevil.
Sunflower stem weevil Cylindrocopturus adspersus	A robust brown and white spotted snout beetle found on the stem and in leaf axils. Drills egg hole in stem in which it lays its egg. The larva, a white legless larva, burrows in the stem pith. Much more abundant in droughty sites and years.

Birds can be major pests in sunflowers. Especially important are blackbird, goldfinch, dove, grosbeak and sparrow. Many approaches to disruption of feeding have been tried, including scarecrows, fright owls, aluminum strips that flutter in the wind, and carbide exploders. No techniques are 100% effective, as birds will adapt to many of these techniques. However, in many environments, some attempt is wanted. Currently, no chemicals are approved for bird control in sunflower.

VI. Harvesting:

Sunflowers are generally mature long before they are dry enough for combining. Seed maturity occurs when the backs of the heads are yellow, but the fleshy sunflower head takes a long time to dry. Often, there are only a few good combining days in October when the seed is dry enough for storage. Seeds should be below 12% moisture for temporary storage and below 10% for long term storage. Seed up to 15% moisture is satisfactory for temporary storage in freezing weather, but spoilage is likely after a few days of warm weather.

VII. Economics of Production and Markets:

The cost of production and return over variable costs for sunflower is similar to that for small grains. The culture of sunflower and growing season requirements makes them a good niche in cropping systems where small grains are the predominant crops. Markets are generally available in most areas where sunflower has been traditionally grown. However, if a grower considers sunflower as an alternative crop, marketing opportunities should be pursued prior to making the decision to grow sunflower, particularly for non-oilseed varieties.

Questions and tasks for comprehension.

1. What kinds of oilseeds do you know?

2. When and where was sunflower originated?

3. How can we use sunflower?

4. What do you know about sunflower oil?

5. In what way can environment requirements influence the sunflower oil quality?

6. What must any agronomist know while planting sunflower seeds?

7. What is the best way of weed control?

8. What diseases and insects can be dreadful for sunflower-yield?

9. What is the best sunflower maturity time for harvesting?

Task 1. Give general morphological characteristics of sunflower. Use the following words and expressions: annual, insensitive to daylength, low in salt tolerance, broadleaf plant, not sensitive to soil pH, erect, an alternative crop, a strong taproot.

Task 2. Record information from the Nutrition Facts of the vital oils in the spaces provided. Then answer the questions following the table.

A) Sunflower oil – contains about 40% oil, a good source of calcium, protein, vitamins B₁ and B₆, and potassium. Sunflower oil is very high in polyunsaturates. The natural oil also contains relatively high levels of vitamin E (27 mg per 100 ml).

B) Soybean oil – an excellent source of vitamin E (87 mg per 100 ml) and contains more lecithin than any other vegetable oil, one of the very best sources of vegetable protein.

C) Groundnut oil – is highly nutritions and valuable quantities of iron and vitamin B (niacin). Peanuts are a source of vitamin E (21 mg per 100 ml).

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