Management Areas. Field Selection

Meeting Quality Specifications for Confectionary Sunflowers Arvel Lawson, Business Development Specialist – Oilseeds, Manitoba Agriculture, Food and R...
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Meeting Quality Specifications for Confectionary Sunflowers Arvel Lawson, Business Development Specialist – Oilseeds, Manitoba Agriculture, Food and Rural Initiatives, Carman, MB R0G 0J0 Email: [email protected]

Approximately 80% of all Manitoba sunflowers are confection-type, which are primarily marketed as a roasted snack food in the shell or as dehulled seeds for the baking industry. Although a significant percentage of this market is domestic (North America), Canadian processors are accessing an increasing foreign market in Europe, the Middle East, and Asia. Yields of confectionary sunflowers are closely tied to the quality of the seeds; large seeds with minimal bird, insect, and environmental damage are most desirable when targeting a human consumption market. Since seed quality is critical to the marketing of confection-type sunflowers, it is essential that producers and agronomists target key management areas, which will aid in meeting the stringent quality specifications of processors. General specifications require samples to be at 10% moisture and contain less than 1% sclerotia, less than 1% dark roast, and less than 0.5% brown spot. In terms of seed sizing jumbo seeds are generally considered those larger that a 22/64-inch round hole sieve, large seeds between a 20 to 22/64-inch round hole sieve, and medium seeds between a 16 to 20/64-inch round hole sieve. The Canadian Grain Commission specifies the standard bushel weight for confection-type sunflowers as 25 lbs/bushel. Management Areas Field Selection Sunflowers grow best on loam, silty loam, and silty clay loam soils with good drainage. It is important to choose a good, clean field with a weed spectrum that can be managed with the tools available in sunflowers. Sunflowers are sensitive to herbicide residues, such as Lontrel and Pursuit. Consult the product label or the current Guide to Crop Protection for specific details. Sunflowers have medium tolerance to saline soils and are extremely susceptible to sclerotinia. It is important to consider rotation of sunflowers with other sclerotinia susceptible crops such as canola and edible beans. Seeding Select a variety appropriate for the production area; consideration of both days to maturity and the disease package is critical. Sunflower seeding should usually begin anytime after May 1 and ideally be finished by June 1. Seedlings are relatively frost-tolerant up to the four-leaf stage. Confection-type varieties are longer maturing than oilseed types. Thus if seeding is delayed into the first week of June, consider oilseed-type varieties as well as earlier maturing varieties. The seeding rate for sunflowers depends on the sunflower type and the rate selected will influence head size, seed size, bushel weight, and maturity. Sunflowers compensate for differences in plant population through changes in head and seed size and managing such compensation is particularly important with confection-type sunflowers. The goal with confection-type sunflowers is to achieve an equidistant plant space that will allow for uniform head size and large seed size. Equidistant plant space decreases intraplant competition for space, sunlight, and soil moisture. As such confection-type sunflowers should not exceed 18,000 plants/acre (0.4 plants/ft2). This is in contrast to oil-type sunflower populations, which typically range from 20,000 to 22,000 plants/acre (0.6 plants/ft2). Seeding rates for both confection- and oil-type sunflowers should be adjusted when germination is low and for the number of weed control harrowing operations expected.

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Many studies have been conducted on the effects of plant population density on sunflower growth and yield. However, considerable differences exist among the results of these studies due to the sunflower plant’s ‘tremendous ability to modify yield components and physical characteristics in response to a wide range of environmental conditions. Also, the optimum plant population density varies with environment, with higher levels recommended for more favourable environments’ (Schneiter, 1997). Sunflowers need to be placed in moisture but not deeper than 3 inches. The ideal seedling depth is 1.5 to 2 inches. Planting equipment should firm the soil over the seed row to maintain a moist seedbed. Weed Management In sunflowers, weeds can be controlled by using pre-emergent herbicides, harrowing before or after crop emergence, inter-row cultivation when the crop is in the five to six leaf stage, and post-emergent herbicides. Weeds should be removed within the first four weeks of crop growth to minimize yield losses. For information on identification, economic thresholds, and weed control options, consult the Guide to Crop Protection. One weed that requires particular mention in sunflowers is cocklebur, an annual weed that is spread by seed. There are currently no in-crop herbicide options for cocklebur in sunflowers. Producers should avoid seeding sunflowers in fields with high populations of cocklebur since this weed is a serious downgrading factor for processors. The cocklebur seed pod or bur is difficult to clean out of sunflower seeds because it is approximately the same size and weight as an individual sunflower seed. As such, processors must use a Velcro roller and trip line to clean out cocklebur seed pods, which slows a processing line and adds an incremental cost to the processing of sunflower seeds containing this contaminant. Insect Management When field scouting for insects, it is important to not only look for pests, but also beneficial organisms such as pollinators, and predators and parasites of potential pests. Pollinators such as honeybees can increase sunflower yield by enhancing pollination and natural controls can keep some potential pests below damaging levels. If a pest level is above economic threshold and a pesticide application is economical, consider applying the pesticide at a time and in a method that minimizes harm to the beneficial insects in a field. For example, if applying an insecticide to a sunflower field that is flowering, apply the insecticide in the evening or early morning when the honeybees are not foraging. Additionally, if aware of any beehives nearby, contact the beekeeper 48 hours in advance of insecticide application, which will allow the beekeeper to move or protect the colonies from insecticide damage. In sunflowers, it is extremely important to scout for insects from the seedling stage, right through the flowering stage. Cutworms, sunflower beetle, and thistle caterpillars are all defoliators of sunflowers. Sunflower bud moth, sunflower stem weevil, and sunflower maggots can be found in sunflower stems. The insects that tend to be of greatest concern for processors of confection-type sunflowers are the seed head insects: sunflower seed weevil, banded sunflower moth, and lygus bug. Sunflower seed weevils have not been a major concern in Manitoba for over a decade. However, the ability to identify this pest is important since high levels of larval feeding can reduce seed weight and oil content of sunflowers. Since most seeds are only partially fed upon, it is difficult to separate healthy from weevil-damaged seed and this results in downgrading of confection-type sunflower seed. Insecticides are available to control sunflower seed weevils; consult the Guide to Crop Protection for product information. In confection-type sunflowers, the economic threshold is one to two weevils per plant.

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Banded sunflower moth larvae feed on sunflower florets and seeds; the larvae do the most damage at early flowering when the seed hulls are still soft. In confection-type sunflowers, the economic threshold is one banded sunflower moth per two plants. It is important to note that holes in sunflower seed hulls are most often attributed to sunflower seed weevil feeding. However, banded sunflower moth feeding can also leave holes in the hulls of sunflower seeds. Lygus bug damage is different as lygus bug feeding on developing sunflower seeds can cause small brown to black spots on the kernel inside the hull (known as kernel brown spot); there is no visible damage on the hull. Lygus bugs are capable of damaging 30 to 35 seeds per head per adult. With the industry standard allowing for a maximum of 0.5% kernel brown spot, the economic threshold for lygus bug on sunflowers is proposed to be approximately one lygus bug per nine heads. In research trials damage to sunflower heads was approximately twice as severe when infestations occurred at late bud and early bloom compared to stages when heads had completed flowering. Thus, lygus bug management should be initiated prior to or at the beginning of the bloom stage if adult densities approach the economic threshold. Disease Management There are several diseases that can infect sunflowers, including downey mildew, phoma, rusts, verticillium wilt, and sclerotinia. Sclerotinia is generally considered the most economically important disease affecting sunflowers. In sunflowers, sclerotinia has three manifestations (wilt, mid-stalk rot, and head rot) and two routes of infection. Sclerotinia survives in the soil for up to four years as irregularlyshaped fungal bodies called sclerotia. A study conducted in Manitoba (Duncan et al., 2006) found a significant negative relationship between sclerotial viability and elapsed time factors and depth of burial. After twelve months, sclerotia on the soil surface had the highest viability (57.5%), followed by those at two inches (12.5%), followed by those at the four inch depth (2.5%) (Duncan et al., 2006). Sclerotia can germinate in two different ways in the summer. With myceliogenic germination, sclerotia germinate and produce mycelia that infect sunflower roots causing wilt. With carpogenic germination, sclerotia germinate and produce mushroom-like structures called apothecia that release wind-borne spores called ascospores, which can cause mid-stalk or head rot. Myceliogenic germination occurs independent of weather conditions (only normal soil moisture conditions are required) and once mycelia infect the roots of a plant, adjacent plants can be infected through root to root contact with the infected plant. The symptoms of sclerotinia wilt usually appear at flowering. Carpogenic germination requires soil saturation or ‘wet’ soil conditions. With the provision of free water and sugars for approximately 24 hours, the wind-borne ascospores can cause either mid-stalk or head rot infection. Head rot usually occurs late in the season, after initial flowering and extended period of wet weather. See disease cycle below.

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Figure 1. Disease cycle of sclerotinia wilt, mid-stalk rot, and head rot of sunflower (from North Dakota State University: http://www.ag.ndsu.edu/pubs/plantsci/rowcrops/pp840w.htm#Disease). Fungicides are not effective in controlling sclerotinia in sunflowers. The key to managing this disease, particularly the wilt manifestation is to plant sunflowers in non-infested soil and to prevent the buildup of sclerotia in the soil. A crop rotation of four years between susceptible crops should be followed. For the mid-stalk and head rot manifestations, these steps may not be enough to limit infection because the windborne ascospores may blow in from neighboring fields. Although no resistant hybrids are currently available, progress is being made in reducing the susceptibility of sunflower to sclerotinia.

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Harvest Sunflowers are usually the last crop to be harvested in the fall, since fall frosts help in drying down the crop. The period between maturity and harvest should be kept as short as possible to minimize losses from bird damage and head-rot diseases. Chemical desiccation can be used to hasten dry-down of the sunflower heads. Desiccation is effective before a killing frost in enhancing head dry-down but should not be applied before physiological maturity. The two main visual indicators of physiological maturity in sunflowers are when the backs of the heads turn a deep, dark yellow and the bracts are brown and dry (crispy to the touch). Seed moisture will be 20 to 50% at physiological maturity. Refer to the current Guide to Crop Protection for details on desiccation products. Sunflowers can be safely combined when seed moisture reaches approximately 20%. However, sunflowers at this moisture content will require drying before storage. Storage Sunflower seed is safe to store at a moisture content of 9.5% or less. At 10 to 12% moisture content, seed can be stored in bins with aeration. Any moisture content over 12% will require drying. It is important to watch drying temperatures, particularly with confection-type sunflowers as seeds may scorch or wrinkle at high temperatures. After drying, sunflower seed should be cooled before storage, since even sunflowers at 8.5% moisture can spoil if stored when warm.

Resources Duncan, R. W., W. G. D. Fernando, and K. Y. Rashid. 2006. Time and burial depth influencing the viability and bacterial colonization of sclerotia of Sclerotinia sclerotiorum. Soil Biology & Biochemistry. 38:275-284. Schneiter, A. A. 1997. Sunflower Technology and Production. Madison, WI: American Society of Agronomy. Pp. 649-651. The Sunflower Production Guide. 2006. Manitoba Agriculture, Food, and Rural Initiatives.

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