¹Departments of Agronomy and Plant Genetics, Entomology and Plant Pathology. University of Minnesota, St. Paul, MN 55108.
²Departments of Agronomy and Soil Science, College of Agricultural and Life Sciences and Cooperative Extension Service, University of Wisconsin-Madison, WI 53706.
November, l990.

I. History:

Sunflower (Helianthus annuus L.) is one of the few crop species that originated in North America (most originated in the fertile crescent, Asia or South or Central America). It was probably a "camp follower" of several of the western native American tribes who domesticated the crop (possibly 1000 B.C.) and then carried it eastward and southward of North America. The first Europeans observed sunflower cultivated in many places from southern Canada to Mexico.

Sunflower was probably first introduced to Europe through Spain, and spread through Europe as a curiosity until it reached Russia where it was readily adapted. Selection for high oil in Russia began in 1860 and was largely responsible for increasing oil content from 28% to almost 50%. The high-oil lines from Russia were reintroduced into the U.S. after World War II, which rekindled interest in the crop. However, it was the discovery of the male-sterile and restorer gene system that made hybrids feasible and increased commercial interest in the crop. Production of sunflowers subsequently rose dramatically in the Great Plains states as marketers found new niches for the seeds as an oil crop, a birdseed crop, and as a human snack food. Production in these regions in the 1980s has declined mostly because of low prices, but also due to disease, insect and bird problems. Sunflower acreage is now moving westward into dryer regions; however, 85% of the North American sunflower seed is still produced in North and South Dakota and Minnesota.

II. Uses:

A. Edible oil:

Commercially available sunflower varieties contain from 39 to 49% oil in the seed. In 1985-86, sunflower seed was the third largest source of vegetable oil worldwide, following soybean and palm. The growth of sunflower as an oilseed crop has rivaled that of soybean, with both increasing production over 6-fold since the 1930s. Sunflower accounts for about 14% of the world production of seed oils (6.9 million metric tons in 1985-86) and about 7% of the oilcake and meal produced from oilseeds. Europe and the USSR produce over 60% of the world's sunflowers.

The oil accounts for 80% of the value of the sunflower crop, as contrasted with soybean which derives most of its value from the meal. Sunflower oil is generally considered a premium oil because of its light color, high level of unsaturated fatty acids and lack of linolenic acid, bland flavor and high smoke points. The primary fatty acids in the oil are oleic and linoleic (typically 90% unsaturated fatty acids), with the remainder consisting of palmitic and stearic saturated fatty acids. The primary use is as a salad and cooking oil or in margarine. In the USA, sunflower oils account for 8% or less of these markets, but in many sunflower-producing countries, sunflower is the preferred and the most commonly used oil.

High oleic sunflower oil (over 80% oleic acid) was developed commercially in 1985 and has higher oxidated stability than conventional oil. It has expanded the application of sunflower oils for frying purposes, tends to enhance shelf life of snacks, and could be used as an ingredient of infant formulas requiring stability.

B. Meal:

Non-dehulled or partly dehulled sunflower meal has been substituted successfully for soybean meal in iso-nitrogenous (equal protein) diets for ruminant animals, as well as for swine and poultry feeding. Sunflower meal is higher in fiber, has a lower energy value and is lower in lysine but higher in methionine than soybean meal. Protein percentage of sunflower meal ranges from 28% for non-dehulled seeds to 42% for completely dehulled seeds. The color of the meal ranges from grey to black, depending upon extraction processes and degree of dehulling.

C. Industrial Applications:

The price of sunflower oil usually prohibits its widespread use in industry, but there are several applications that have been explored. It has been used in certain paints, varnishes and plastics because of good semi-drying properties without color modification associated with oils high in linolenic acid. In Eastern Europe and the USSR where sunflower oil is plentiful, sunflower oil is used commonly in the manufacture of soaps and detergents. The use of sunflower oil (and other vegetable oils) as a pesticide carrier, and in the production of agrichemicals, surfactants, adhesives, plastics, fabric softeners, lubricants and coatings has been explored. The utility of these applications is usually contingent upon petrochemical feedstock prices.

Sunflower oil contains 93% of the energy of US Number 2 diesel fuel (octane rating of 37), and considerable work has been done to explore the potential of sunflower as an alternate fuel source in diesel engines. Blends of sunflower oil and diesel fuel are expected to have greater potential than the burning of pure vegetable oil.

D. Non-Oilseed:

The use of sunflower seed for birdfeed or in human diets as a snack, has grown consistently over the past 15 years. Varieties used for non-oilseed purposes are characterized by a larger seed size and require slightly different management practices. During processing, seed is divided into 1) larger seed for in-shell roasting, 2) medium for dehulling, and 3) small for birdseed. Standards for different uses vary.

E. Forage:

Sunflower can also be used as a silage crop. It can be used as a double crop after early harvested small grains or vegetables, an emergency crop, or in areas with a season too short to produce mature corn for silage.

Forage yields of sunflower are generally less than corn when a full growing season is available. In one study, sunflower dry matter yields ranged from 2.0 to 3.0 ton/acre compared with 3.1 to 3.8 ton/acre for corn. Moisture content of sunflower at maturity is usually high (80 to 90%) and would require wilting before ensiling.

Nutritional quality of sunflower silage is often higher than corn but lower than alfalfa hay (Table 1). Crude protein level of sunflower silage is similar to grass hay and higher than corn silage. Generally, crude protein of sunflower decreases and lignin percentage increases after the flowering stage. High plant populations increases fiber and lignin percentage. Seed size does not seem to affect yield or quality.

Sunflower silage contains considerably more fat than many other forages, (Table 1). Some producers and researchers in Oregon have experimented with sunflower/corn intercrops to increase energy content of a silage, but results of this work are not yet complete. In South Dakota trials, milk yields were reduced by 9% when straight sunflower silage was compared with corn. The nutritional quality of sunflower silage is generally recognized as adequate for dry cows, steers, and low milk producers.

Table 1: Nutritional quality of sunflower, immature corn, and mature corn silage, alfalfa hay (harvested in early bloom) and timothy hay (harvested in late Vegetative stage).¹
	Silage			Hay
	Sunflower	Immature Corn	Mature Corn	Alfalfa	Timothy
	--------------- % of Dry Matter ---------------
Total Digestible Nutrients	67.0	60.0	69.0	58.0	68.0
Crude Protein	11-12	8.2	7.8	18.0	11.4
Ether Extract	10-12	2.6	2.9	2.2	2.4
Crude Fiber	31.0	31.0	23.0	31.0	31.0
Acid Detergent Fiber	32.0	--	31.0	38.0	33.0
Lignin	10-16	--	--	9.0	3.1
IVDDM²	63-70	--	--	66.0	63.0
¹Data from Miller, Oplinger and Collins, 1986. ²In vitro dry matter disappearance.

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 12^o 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. Environmental requirements:

A. Climate:

Sunflower is grown in many semi-arid regions of the world from Argentina to Canada and from central Africa into the Soviet Union. It is tolerant of both low and high temperatures but more tolerant to low temperatures. Sunflower seeds will germinate at 39^o F, but temperatures of at least 46 to 50^o 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^o F. At later stages freezing temperatures may injure the crop. Temperatures less than 28^o F are required to kill maturing sunflower plants.

Optimum temperatures for growth are 70 to 78^o F, but a wider range of temperatures (64 to 91^oF) 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 of North America. 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. Levels were 577 (g H₂O/g DM) for sunflower, 349 for corn, 304 for sorghum in an Akron, Colorado study. It is similar to wheat, soybean, fieldbean, oat, and rape in that respect. Efficiency is measured at an optimum moisture level and is not a measure of drought resistance.

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.

Both germination percentage and lodging have been shown to increase in ridge-till systems vs. level plantings. Several tillage systems have been used with some success in specific environments. Major considerations are: 1) firm placement of seed near moist soil, 2) absence of green vegetation during emergence, 3) maintaining an option to cultivate and 4) reduce the risk of soil erosion.

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. In the northern midwest and Canada this is often May 1 through 20 and mid-March through early April in the southern USA. Resistance to frost damage decreases as the seedlings develop into the 6-leaf stage, so too-early sowings in the northern USA or Canada can be risky.

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. A planting date of early to mid May is recommended in Minnesota and Wisconsin.

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. In Minnesota trials, sunflower yield, oil percentage, seed weight, test weight, height, and flowering date did not differ at narrow vs. wide rows over five plant populations. 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.

Sunflower stands have the capacity to produce the same yield over a wide range of plant densities (Table 2). The plants adjust head diameter, seed number per plant, seed size, to lower or higher populations, so that yield is relatively constant over a wide range of plant populations. Trials in eastern North Dakota show increases in yields with densities up to 29,000 plants/acre, but most studies have shown less effect of seeding rate. Higher densities are often recommended for irrigated or high rainfall areas.

Table 2: Effect of plant population on yield and yield components-average of 12 trials in Minnesota.
Plant Density	Seed Yield	Seed Number	Seed Weight	Large Seed¹	Oil Content	Lodging
Heads/acre	lbs/acre	Seeds/head	mg/seed	--------- % ---------		Score²
14,970	2,004	831	73	52	42.1	1.5
19,830	2,131	727	67	44	43.2	1.8
25,090	2,169	632	62	33	43.2	2.1
29,940	2,173	548	60	31	43.4	2.4
34,800	2,231	501	58	26	43.8	2.5
¹Non-oilseed cultivars held on an 0.8 cm round-hole screen ²1=erect, 9=prostrate.

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. Current recommendations in Minnesota and Wisconsin are 17,000 plants/acre (4 lb seed/acre) for non-oilseed and 23,000 plants/acre (3 lb seed/acre) for oilseed.

Some have suggested that north-south orientation of rows produce higher yields than east-west rows, but studies to examine this effect have found no differences in yield.

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. In the wetter regions of eastern and southern Minnesota and Wisconsin, recommendations are based upon soil organic matter and previous crop history. Recommendations of approximately 18 lb N/acre after fallow or legume sod, 60 lb N/acre after small grain or soybean and 80 to 100 lb N/acre after corn or sugarbeet are common. On higher organic matter soils, amounts should be lowered. 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. Recommendations for applications of P and K should be made from soil tests and the yield goal for each field. Recommendations range from 40 to 70 lbs P₂O₅ and 60 to 140 lbs K₂O/acre for soils testing very low in P or K, depending on soil yield potential. These recommendations decrease as soil test P and/or K increase. Response to P is not expected if soil P exceeds 30 lb/acre nor to K if the K test is greater than 300 lb/acre.

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. Performance results from the Upper Midwest are usually available annually from North Dakota State University, University of Minnesota, and South Dakota State University.

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. Almost all North American sunflower plantings are cultivated and/or harrowed for weed control, and over 2/3 are treated with herbicides. 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.

Several herbicides are currently approved for weed control in sunflowers. Information on chemical weed control in sunflowers is available at most county extension offices.

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 3: 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 (hull) development is normal but no ovules or meat develop. Wind is relatively unimportant in cross-pollination of sunflower. Some of the older open-pollinated varieties such as Peredovick set only 15 to 20% of seed without pollinators, whereas many hybrids set 85 to 100% seeds without pollinators.

Insect pests have become major potential yield-reducing factors in sunflower production in the northern Midwest (Table 4). Insects specific to sunflower that feed on the heads include the larvae of three moths; sunflower moth, banded sunflower moth and sunflower bud moth. Sunflower midge has caused widespread damage in some years. Sunflower headclipping weevil, sunflower beetle, sunflower maggot, wireworm, grasshopper, cutworm, sugarbeet webworm, ragweed plant bug, woolybear and painted lady caterpillar have caused occasional damage to sunflower. Adults of insect pests of other crops (such as corn rootworm beetle and blister beetle) can be found as pollen feeders on sunflower heads, but usually cause little injury.

Resistance to seed insects can be improved by the presence of a dark colored "armor" layer in the seed coat. Resistance to midge has been suggested but is not currently effective. Only currently approved insecticides should be used for control of insects.

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 warranted. Currently, no chemicals are approved for bird control in sunflower.

Table 4: 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 (.5 in.). Larvae are not dark striped, smaller than head moth. Makes a smaller hole in top of seed, feeds on meat.
Sunflower bud moth Suleima helianthana	Dark gray moth. Larvae .5 to 1 in. in length. 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 (.1 in.) gnat with tiny (.1 in.) 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, about .25 in. long, causes head drop.
Sunflower beetle Zygogramma exclamationis	Adult is .25 in. long 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 about 1/8 in. long, 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 about 1/8 in. long, 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. It is about ¼ in. long. 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 drouthy sites and years.

I. 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.

Commercially available sunflower headers are useful in decreasing loss of seed as the crop is direct combined. This equipment usually includes 9 to 36 in. width metal pans for catching matured seed and a three-armed or similar reel. A narrower (9 in.) pan width enables harvesting diagonal to the row, which produces fewer harvest losses in some situations.

Windrowing has been demonstrated to be effective, but probably would not be economical, given the added cost of windrower and pickup-modifications.

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.

VIII. Information Sources:

The sunflower crop in Minnesota. 1973. R.G. Robinson. Extension Bulletin 299. Agricultural Extension Service, University of Minnesota, St. Paul, MN.

Sunflower science and technology. 1978. Jack F. Carter (ed.). Agronomy Monograph 19. American Society of Agronomy, 677 South Segoe Rd, Madison, WI 53711.

Sunflower production in Wisconsin. 1979. E.S. Oplinger. Publication A3005, University of Wisconsin-Extension. Agric. Bulletin, Rm. 245, 30 N. Murray St., Madison, WI 53715.

Pest control in sunflowers. 1980. J.D. Doll and J.L. Wedberg. Publication A3075. Univ. of Wisconsin-Extension. Agric. Bulletin, Rm. 245, 30 N. Murray St., Madison, WI 53715.

Irrigation and nitrogen for sunflower and fieldbean on sandy soil. 1985. R.G. Robinson. Minnesota Report AD-MR-2862. Agric. Expt. Stn. University of Minnesota, St. Paul, MN.

Sunflower monoculture and crop rotation. 1979. R.G. Robinson, L.J. Smith, J.V. Wiersma. Misc. Report 166 - Agricultural Expt. Stn. Univ. of Minnesota, St. Paul, MN.

Sunflower planting date: An important decision. 1985. R.G. Robinson, D.L. Rabas, J.V. Wiersma, D.D. Warnes. Minnesota Report AD-MR-2737. Agric. Expt. Stn. University of Minnesota, St. Paul, MN.

Sunflowers for silage in Idaho. 1986. G.A. Murray, D.L. Auld, V.M. Thomas, B.D. Brown. Bulletin No. 652. Agric. Expt. Stn. University of Idaho.

Oil crops of the world, their breeding and utilization. 1989. G. Robbelen, P.K. Downey, A. Ashri, eds. McGraw Hill, NY. 553 pages.