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Sunflowers - a growers guide

Dr Sarah Cook, ADAS UK Ltd, ADAS Boxworth, Boxworth, Cambs CB23 4NN. Sarah.Cook@adas.co.uk

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NETWORK

January 2008

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50.0

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150.0

200.0

250.0

300.0

350.0

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2004/05 2005/06 2006/07 2007/08

mill

ion tonnes

Soya Rapeseed Cotton Peanut Sunflower Palm Copra

World sunflower production

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Total e

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Sud

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India

China

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thousand tonnes

INTRODUCTION

This guide to growing sunflowers is based upon one written by the United Kingdom Sunflower Association (UKSA). The UKSA was formed in 1994 and closed in 2007. The current guide was funded through the Defra Innovation Network, led by the University of Warwick (www.warwick.ac.uk/go/climatechange/innovation-network), G B seeds Ltd and HGCA.

THE MARKETS

Seed oil and meal from oilseed crops are major world commodities, the major crops being soya, rapeseed, palm and sunflower. Globally soya is the largest oilseed crop area, dominating both the oil and meal markets. Soya meal is valuable as a protein source for animal feeds and this means soya meal and oil supply affects the price of all oilseeds.

The major producers of sunflower are the EU, Argentina, Russia and Ukraine. The soft black-seeded sunflowers are the ones favoured by the UK pet-food market. The UK produces up to 3,000 tonnes of sunflower seed each year and is a net importer of seed, oil and meal.

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CROP PLANNING

Varieties

A range of sunflower varieties have been trialed in the UK by the UK Sunflower Association, trials ceased in 2006. Sanluca (Syngenta seeds) and Antonil (Pioneer Hi-bred) are the most commonly grown varieties suited to the UK climate.

Crop rotation

Growing sunflowers in the rotation offers:

• An overwinter fallow period which allows control of grass and broad-leaved weeds through the use of non-selective herbicides.

• An effective take-all break providing grass weed control is good.

However rotation planning should take account of:

• Susceptibility to Sclerotinia which may pose threats to high value crops in the rotation such as potatoes and others.

• Avoid sowing sunflowers after crops that leave a large nitrogen residue e.g. Kale, sugar beet or grassland.

• Short rotations of four years or less which increase the risk of Sclerotinia to any oilseed crops

Economics

Sunflowers yield between 1.5-2.5 t/ha in the UK. Seed is the most expensive input and there is no scope for home-saved seed as the crop is a hybrid. Fertiliser costs are low.

Soils and cultivation

Sunflower can be grown on a wide range of soil types. However, a well-drained soil that will warm up rapidly in spring is preferred. The drought-tolerance of sunflowers also makes it suitable for use on more drought-prone soil types.

The optimal pH range is from 6.0 to 7.5.

Seedbed preparation is crucial for sunflowers and a fine firm seedbed, similar to that for sugar beet and peas should be prepared.

SOWING

Seed treatment

Seed is imported and is pre-dressed. Consult your supplier for further information.

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Drilling date

The soil temperature in the top 10 cm of soil at drilling should be at least 6-8°C. If the soil is too cold then germination will be patchy and delayed making the crop vulnerable to a greater degree of pest damage. Drilling usually occurs from mid-April onwards in southern and eastern England.

Seed rate

Plant population is an important factor in the production of a sunflower crop since it can affect a variety of yield components.

Low populations result in plants with large heads, these tend to ripen slowly.

An established plant population of between 80,000 and 110,000 plants/ha with a row width of 34 cm is optimal. Actual sowing rates should be between 10% and 20% higher than the target plant population to allow for losses during establishment. The lower figure applies to later sowings, light soils, warm seedbeds and conditions generally favourable to germination; the higher to heavy clay soils under less favourable conditions.

Due to the nature of the sunflower crop there are no opportunities for reductions in seed rate.

Drilling

Seed should be sown to a depth of from 2.5 to 5.0 cm (1 to 2 inches), according to seed size and soil type and condition. In dry conditions, seed should be sown more deeply into moisture.

Most seed-drills can be adapted for use with sunflower but seed rate, seed spacing and row width are critical. Sunflower is a non-branching crop and cannot compensate for uneven plant-spacing and low plant populations. Accuracy of drilling has an important bearing on yield and quality.

Pneumatic disk drills, belt drills and pneumatic cereal drills have all been used to establish successful sunflower crops.

Near optimal seed spacing can be achieved with the precision drills. With a pneumatic cereal drill optimal row spacing can be achieved blocking-off alternate coulters, but these drills are not well adapted to the low populations required by the crop. Plant spacing within the rows can be very uneven,

Drill calibration.

For drills of all types, accurate calibration is essential, both to achieve the optimal plant population and to conserve expensive seed. Grower experience has shown that best results are achieved by calibrating the drill over a full hectare. Unless the drill has a press-wheel behind the seeder unit, the seedbed

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should be consolidated immediately after drilling, using a Cambridge roller. This not only conserves moisture and improves seed-soil contact but also increases the effectiveness of subsequent herbicide applications.

CLIMATE CONSTRAINTS

There are two major constraints on sunflower production, both heat-related, firstly soil temperature at sowing, which determines the earliest practicable sowing date and secondly the amount of heat available for use by the crop during the available growing season.

Soil temperature

The soil temperature at drilling should be 6-8°C in the top 10 cm of soil. A map of soil temperatures at 30cm depth in May (Fig 1) shows where temperatures are >10°C, these areas are suitable for sunflower establishment.

Heat accumulation

The principal factor determining the rate of crop development is the accumulation of heat, as influenced by mean daily air temperature above a base level of 6 °C, as for maize. Areas that achieve 1400 day degrees are best suited to production (Fig 2.)

Fig 1. Mean Soil temperatures on 1 May at 30cm

Fig 2. Average accumulated temperature (May-September >6°C)

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CROP NUTRITION

Nitrogen

The deep-rooting nature of sunflower can remove nutrients from depth in the soil profile. As a result the crop will yield satisfactorily at quite low levels of soil nitrogen and nitrogen fertilizer applications may be unnecessary.

High levels of nitrogen can lead to excessive vegetative development, encouraging disease, delaying maturity and reducing seed oil content.

UK experience indicates that applications of more than 25-50 kg/ha are rarely required.

Phosphate and potash

Phosphate is required at relatively low levels by the crop. A maintenance application of from 40 kg to 60 kg/ha is usual.

Sunflowers require a relatively high level of potassium but most of this is returned to the soil after harvest. A maintenance application of from 40 kg to 60 kg/ha is usual, often as part of a compound fertilizer with phosphate.

Micronutrients

Sunflowers are sensitive to boron deficiency, and can be a particular problem on calcareous or sandy soils where boron levels are often naturally low.

Boron is taken up chiefly during the vegetative period prior to heading and signs of deficiency usually become apparent during flowering and seed maturation. A characteristic feature is poor seed-set, with many heads having large areas of hollow seeds. Other symptoms are red-brown necrotic patches and abnormal head and neck development. The timing and rates of boron application are shown below.

Soil and climate factors Soil Boron level (ppm) Treatment

Non-calcareous pH<7.5 0.5 1.2kg/ha incorporated at drilling

Calcareous pH>7.5 0.5

Sandy 0.5 300-500 g/ha as a foliar spray at GS 2.5-3.2

Molybdenum, copper and manganese deficiencies can be problems in very acid soils (<pH 5.0).

EMERGENCE

Weeds

The height and broadly spreading leaf-canopy of sunflower enables it to compete very effectively with weed growth from as early as the fourth week from emergence. Despite this the crop is highly sensitive to competition during establishment. The

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effects of early competition are particularly marked where low soil temperatures and/or poorly aerated soil slow the growth of the crop relative to that of the weeds and where low plant populations or uneven drilling delay canopy closure. Maturity can be delayed and this can cause harvesting problems.

Control

The late drilling date of sunflowers allows ample opportunity to control weeds by cultivation and/or non-selective herbicide prior to drilling.

Pendimethalin is approved for pre-emergence use in sunflowers. It is most effective where the soil surface is firm with few clods.

Mechanical weed control

Sunflower crops grown in wide rows allow an ideal opportunity for weed control through cultivation. A tractor mounted steerage hoe been used successfully in the UK. Mechanical weed control is most successful when soil conditions are dry and the weather is set fair.

PEST AND DISEASE

Pests

In the UK the crop is most vulnerable to slugs from drilling until one pair of true leaves is visible. All soils are at risk but particularly cloddy or stony soils with high levels of organic debris. Slug pellets should be applied to all crops at risk.

Pigeons are a major pest of UK sunflowers; they graze the crop as it emerges, snipping off the growing point. Similar damage has been attributed to pheasants. Rabbits can also cause damage by grazing emerging crops.

Finches can damage ripening crops, but they tend to venture only up to 24 m into the crop, because of predators. In a small field (less than 4 ha), bird damage can be considerable and the whole crop can be lost. To decrease damage to seed-heads, plant spacing should be controlled to reduce head size and increase head angle to discourage perching.

Other mammals, such as mice and badgers, can also damage crops during ripening, but this is generally a localized problem.

Insects - There have been reports of minor damage caused by Tortrix larvae, leaf minors and looper caterpillars, thrips and silver Y moths (Autographa gamma L.). Various aphids, including Brachycaudus helichrysi, Aphis fabae and Myzus persicae have been recorded but caused little damage; colonies of up to 1000 individuals have been noted.

Currently no insecticides are approved for use in sunflowers.

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Disease

Sunflower is host to a number of fungal, bacterial and viral pathogens that can cause varying amounts of crop damage, the two most common being Botrytis cinerea and Sclerotinia sclerotiorum

Botrytis head rot

Botrytis head rot or grey mould is caused by Botrytis cinerea, a fungus widely spread throughout a range of crops. It occurs frequently in sunflower growing under relatively cool (15-25ºC) and wet conditions and may cause extensive damage.

Botrytis can develop on seedlings, stems and leaves, but only if the fungus gains entry through wounds. However, it is most damaging when it infects heads.

Botrytis makes its first appearance on the back of the head as sunken brown spots. As the infection develops, the lesions spread and eventually the back of the head becomes soft and grey.

A late season infection on the head can result in increased seed losses during harvest; earlier infections may reduce both yield and quality.

There are no chemical options for controlling Botrytis in the sunflower crop. Applying a desiccant when seed moisture is about 30 per cent can aid ripening or advancing the harvest date by up to seven days.

Mycotoxins are not an issue for sunflowers as the husks are removed before consumption

Sclerotinia wilt and rot

Sclerotinia causes stem and head rot in sunflower

Stem rot is caused by fungal threads (mycelium) already in the soil at the beginning of the season and leads to wilting and finally the total collapse of the plant. Head rot is due to air-borne spores infecting the plant during the growing season and may result in the total destruction of the head and plant.

Sclerotinia is not restricted to sunflower but has a wide range of hosts, of varying susceptibility (Table 1). The severity of attacks on susceptible

crops is related to the number of such crops grown in the rotation. Increasing the interval between susceptible crops reduces the risk of infection. There is no chemical control available in sunflowers.

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Table 1. Relative susceptibility of different crops to infection by S. sclerotiorum Crop Degree of Crop Damage Production of sclerotia

Sunflowers **** *****

Phaseolus beans **** ****

Winter oilseed rape *** ***

Potatoes ** **

Spring field beans ** *

Spring oilseed rape ** *

Linseed ** *

Carrots ** ***

Peas * ****

GROWTH

Sunflowers are planted at the end of April and grow rapidly given warm conditions. Buds begin to form in mid June and begin to show colour during the second week of July. Flowering lasts for approximately 2 weeks and then the crop begins to senesce ready for harvest in early October. In the UK water availability is not limiting, but excess rainfall will tend to result in taller crops. Predictions of global warming would bring drilling and harvesting dates earlier. Currently weather conditions in the UK mean successful crops 9 years out of 10 in southern England. April May June July August September October

1.0 1.1 2.1 - 2.n 3.1 3.5 4.1 4.3 5.0 5.1 5.2 5.3

Emergence Vegetative

growth

Bud

formation

Flowering Maturity

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HARVESTING AND POST HARVEST

Moisture content at harvest

Harvest should take place when seed moisture content reaches 30% or less. Oil quality does not suffer between 15-30% moisture content.

Appearance Moisture

content

(%)

Back of the head is lemon yellow, bud scales surrounding the disk are brown mottled. Too early

40-30

The back of the head becomes deep yellow and the bud scales brown. Approximately two thirds of the leaves from the base have senesced. Early

>20

Bud scales are totally brown and the back of the head is marbled brown. All leaves have senesced and stems are drying out. Ideal

15-20

Harvesting

A conventional cereal combine can be used with little modification, but if sunflowers are grown regularly then harvesting trays can be fitted to the cutter bar. The reel tines should also be covered to avoid impaling the flower heads. Combine settings should be similar to those used for harvesting beans and the crop should be harvested during

the day and when dry. Care should be taken to avoid overloading the returns auger.

Preferred combine settings are as follows:

Drum speed 400-600 rpm

Concave setting Wide open

Sieve size 10-12mm

Fan speed Adjusted to avoid losses over the back

Forward speed 5 to 6 mph (running speed)

Check manuals for specific details.

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To minimize the amount of admixture with the grain, only a small amount of the stem should be cut. Some heads may fall forward, away from the combine table, when harvesting. This can be reduced by a relatively fast forward speed.

The stubble can be chopped by the combine or by using a forager or heavy discs. The field can then be ploughed and drilled if the following crop is a cereal. Volunteers can be dealt with using a

broad-leaved herbicide, but they may continue to appear throughout the spring.

Grain quality

Seed destined for the birdseed market is usually sold at 9% moisture with a maximum admixture content of 2%. UK companies do not commonly specify oil content.

DRYING AND STORAGE

Sunflower seed dries quickly but the seed should never be stored wet. Sunflower seed will heat up if allowed to stand while wet. Use of a drying floor is the safest method and the seed should be at a maximum depth of 1 metre. The best method of drying is to use cold air until the moisture content falls to 15 per cent. The seed can then be cleaned and sufficient heat applied (using the same temperature as for oilseed rape) to reduce the moisture to 9 per cent for long term storage.

The seed should be left for seven days to allow the seed moisture to equalize before drying again if necessary.

BEWARE Sunflower seed has a lint-like coating that can easily be rubbed off to form a light oil bearing dust. If this is taken into the unprotected intake of a continuous drier there is a high risk of fire. Drying methods that include any form of agitation or movement of the seed should, therefore, be used carefully. One technique that has proved successful is to reduce the bulk of the moisture using a floor drier and then complete the operation in a continuous drier.

FOLLOWING CROPS

Sunflowers were grown at ADAS Boxworth, Cambridgeshirefor ten years, beginning in 1990. Over a five year period sunflowers were harvested on average 74 days after oilseed rape and the following wheat crop was drilled within 25 days of harvest (see Table 2).

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Table 2. Average dates of drilling and of harvest and yields of wheat following crops of sunflower, winter beans and oilseed rape during the period 1992-1997.

Break-crop Average date of harvesting

break-crop

Average date of drilling wheat

crop

Days between harvest and drilling

the following crop

Yield after break-crop as a % of

mean yield

Sunflower 7 October 27 October 20 102.0

Winter beans

18 August 8 October 51 103.3

Winter oilseed rape

25 July 28 September 68 103.6

Cultivations following sunflowers were usually non-inversion, such as discing. The stems break up easily and cause no problems with seedbed preparation.

Sunflower as a weed

The seeds of sunflower can persist in the soil for up to five years and have the ability to germinate at a considerable depth and over a long period. At ADAS Boxworth, on a clay soil susceptible to cracking, sunflowers were found to germinate in the cracks and appear in following crops. The growth of these volunteers was more vigorous where the crop was less competitive, especially on headlands and in gateways. In cereals metsulfuron-methyl, tribenuron-methyl and thifensulfuron –methyl all provide control of volunteer sunflower.

Volunteer control in sugar beet with clopyralid provides some control at the 2 leaf stage (G.S. 2.2). In peas, bentazone provides an effective means of control.

FURTHER INFORMATION.

UK sunflowers http://www.hgca.com/content.output/3308/3308/Crop%20Research/Crop%20Research/Sunflowers.mspx National Sunflower Association (USA) http://www.sunflowernsa.com/ CETIOM (France) http://www.cetiom.fr/#

WWW.ADAS.CO.UK WWW.GBSEEDS.CO.UK WWW.HGCA.COM

Written by Sarah Cook, ADAS UK Ltd (sarah.cook@adas.co.uk ). This document was funded through the Defra Innovation Network, led by the University of Warwick, G B Seeds Ltd and HGCA. January 2009

WWW.WARWICK.AC.UK/GO/CLIMATECHANGE/INNOVATION-

NETWORK

For more information visit: http://www.hgca.com/content.output/3308/3308/Crop%20Research/Crop%20Research/Sunflowers.mspx