Rust, phoma and downy mildew also can appear. Sclerotinia is hard to avoid, since varietal resistance is minimal and sclerotinia organisms can be built up in a field by soybean, alfalfa, canola, and weeds such as lambsquarter and wild mustard. Harvesting and storage Sunflower is ready to harvest when the back portion of the head turns brown. The seeds actually mature somewhat earlier, but the head will be too wet for efficient harvest until the brown color appears. Timely harvest is important to minimize losses due to birds and late season diseases.
Efficient harvest requires a modified grain head on the combine.
A standard combine header will cause excessive seed loss to the ground from shattering, so a special sunflower header should be obtained, or a conventional header can be modified by adding catch pans, deflectors and possibly a smaller reel. The modifications are intended to collect the sunflower head while minimizing stem material collection. Cylinder speeds should be relatively slow, from 300 to 450 rpm. A proper concave adjustment is necessary to prevent dehulling the seeds. Seeds can be stored at up to 12 percent moisture for short periods, but should be dried to 9 percent moisture for long-term storage.