Attracted by high market prices, there are likely a number of growers this year who haven’t harvested sunflower in awhile, or maybe never before. Whether you’re new to the crop or an old hat, it’s always good to brush up on the harvest fundamentals to help maximize crop yield and quality.
Maturity: The sunflower plant is physiologically mature when the back of the head has turned from green to yellow (although stay-green hybrids may stay green longer) and the bracts are turning brown (Stage R-9) about 30 to 45 days after bloom, and seed moisture is about 35%. Generally, when the head turns brown on the back, seeds are usually ready for harvest.
Combine headers: Platform (wheat), row-crop, and corn headers have all been used successfully with sunflower. Row-crop heads are perhaps the best choice because they can be used without modification. Corn heads need to be modified with a stationary cutting knife before use with sunflower. Combines used for threshing small grains can be adapted to harvest sunflower with a variety of header attachments available with many operating on a head stripper principle. Platform heads can be used without modification, but often have a higher amount of seed and head loss than a row head. Adding pans to the front of the platform, and/or modifying the reel can improve efficiency. Twelve-inch pans are best for 30-inch row spacings; 9-inch better for other row sizes and solid seeding.
Common threshing mistake: waiting to harvest and seeds become too dry and shell out. Better: combine at 14-15% moisture and use air/dry down to under 10% moisture. Waiting too long to harvest can result in excessive field losses.
Threshing goal: Have the header platform raised high enough to take in the heads, minimizing stalks as much as possible. The overall goal of the threshing process should be passing the head nearly intact through the combine, or in a few large pieces, with all developed seed removed from the head. If the head is being ground up into small pieces, there will be excessive trash in the grain.
Air speed: Air speed should be lower, due to the lighter weight of sunflowers (oils weigh about 28 to 32 lbs/bu, confection 22 to 26 lbs/bu). Excessive wind may blow seed over the chaffer and sieve, and seed forced over the sieve and into the tailings auger will be returned to the cylinder and may be dehulled. Set the fan so only enough air flow is created to keep trash floating across the screen/sieve. The concave should generally be run wide open (on a rotary combine, a rotor-to-concave setting of 3/4 to 1 inch is appropriate). A bottom screen or lower sieve of 3/8 inch, and a top screen/upper sieve of 1/2 to 5/8 inch is typical.
Forward speed: Combine forward speed should usually average between 3 and 5 miles per hour. Forward speed should be decreased as moisture content of the seed decreases to reduce shatter loss as heads feed into the combine. Faster forward speeds are possible with seed moisture between 12 and 15%.
Cylinder/rotor speed: Slow cylinder/rotor speed to 250 to 400 rpm. Combines with smaller cylinders will require a faster speed and combines with a larger cylinder diameter will require a slower speed.
Concave clearance: When crop moisture is at 10% or less, conventional machines should be set open to give a cylinder to concave spacing of about 1” at the front of the cylinder and about 0.75” at the rear. A smaller concave clearance should be used only if some seed is left in the heads after passing through the cylinder. If seed moisture exceeds 15 to 20%, a higher cylinder speed and a closer concave setting may be necessary, even though foreign material in the seed may increase. Seed breakage and dehulling may be a problem with close concave settings. Make initial adjustments as recommended in the operator's manual. Final adjustments should be made based on crop conditions.
Rule of thumb for acceptable harvest loss: 10 seeds per square foot (don’t forget heads that have seed left in them) represents a loss of 100 pounds per acre.. Adjust seed counts taken directly behind the combine discharge for the concentrating effect from the width of cut down to the separator width. Do this by dividing the number of seeds found by 4. In other words, in the discharge area, 40 seeds per square foot represent a loss of 100 pounds per acre.
Watch for moisture rebound: When taking a moisture reading on sunflower seeds that are being dried in a bin, keep in mind that the hull dries faster than the kernel. Thus, a moisture reading taken on sunflower being dried may be artificially low; for example, a moisture meter may give a reading of 10%, then climb back up to 12% the next day. To get a more accurate reading, place some seed in a covered jar overnight and take a moisture reading the next day, after the hull and kernel moisture have equalized.
Are your bins ready? Bins with perforated floors work better for drying sunflower than those with ducts. Aeration is essential, especially in larger bins. Aeration may be accomplished with floor-mounted ducts or portable aerators. Aeration fans should deliver 1/10 to 1 cfm per cwt of sunflower. If aeration is not available, sunflower should be rotated between bins to avoid hot spots developing in the stored grain.
Cleaning before storage: When excessive trash is present in the harvested grain, cleaning before storage can greatly reduce incidence of storage problems. Ambient air can be used to cool and dry sunflower. If heated air is used, generally a 10 degree F. increase in temperature over ambient is sufficient to increase rate of drying. Be aware that sunflower dries more rapidly than corn or soybeans, and should be monitored to avoid overdrying.
Prepare for fire hazards: Always keep in mind that sunflower is an oil-based crop, and fine fibers from sunflower seeds pose a constant fire hazard, especially when conditions are dry. Keep combine and grain dryer free of chaff and dust (consider having a portable leaf blower on hand for this). Keep a small pressure sprayer or container filled with water on hand in the combine in case of fire. If the threat of extreme dry conditions and combine fires persists, try nighttime harvesting, when humidity levels are higher.
Sources: North Dakota State University Extension Service, Kansas State University Extension Service, University of Missouri Extension Service
When to consider a sunflower desiccant
If bird pressure is expected, disease levels are high, or lodging problems are occurring, the use of a harvest-aid desiccant for sunflower may be considered when the crop is mature and an early harvest would be an advantage.
Early drydown of sunflower plants may slow or stop development of head rot and reduce sclerotia and destruction of seeds. Desiccation can also reduce head seed shattering, control weeds (especially large weeds like kochia and marshelder) and ease concern of late-harvest drying.
Desiccant and application costs must be weighed with prospective advantages. Warm sunny days following a desiccant application are needed to give the best results. Two types of desiccants can be used. These include paraquat (Gramoxone Max) and sodium chlorate (Drexel Defol) for use on oilseed and confection sunflower. Allow a minimum of 7 to 10 days prior to harvest to get maximum killing and drydown of the sunflower. Apply desiccant by air after the back of sunflower heads are yellow, bracts are turning brown, and after seed moisture content falls below 35%. See product label for rates, adjuvants, and application directions.
Online resources for more harvest and storage information
(NDSU EB-25, considered the ‘bible’ on sunflower production)
http://www.oznet.ksu.edu/library/ (search publications for “grain storage”)
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