ISSUE 10 July 7, 2005
TOPDRESSING FOR WHEAT PROTEIN-A FEW LAST DETAILS
Previous pest report articles have outlined the process and timing for protein enhancement through the application of liquid N fertilizer as a foliar spray at the kernel watery ripe stage of wheat development. Most of the calls I have received lately are related to nozzle recommendations and the possibility of leaf burn.
Burn is a result of water evaporation from the spray solution, resulting in urea crystals forming on the leaf surface. The urea disrupts the leaf cuticle and the exposed leaf cells die from an overload of ammonia. Therefore, the goal of any foliar N fertilization is to use low rates and keep the fertilizer as a thin film on the leaf surface for as long as possible to maximize N absorption in a controlled manner through the leaf. This goal is achieved by working with the best climatic conditions available. If the day is cool (50's, 60's) and previous weather has been damp, leaves will remain wet nearly all day and the thin film is maintained. If the day is hot and air is dry, a thin film is maintained for less than an hour and crystals will form and burn will be more severe. In weather that is being forecast for this coming weekend and into next week, we may see 90-100 degrees across the state with the exception of the northeast. Under these conditions, it may be best to wait to apply the fertilizer until evening and spray if possible through the night into the morning hours and finish up about 8AM. That would result in perhaps 3-4 hours for the last sprayed acres before leaves dried. Definitely do not spray during the heat of the day, which for the next 7 days will probably be between 10 AM and 6 PM.
A good choice for nozzles would be flat fans. The forward and back nozzles used for scab fungicide application are meant to cover the head. We donít want to cover the head. This fertilizer application is meant to cover the leaf, so flat fans are better.
Remember that burn is likely whatever precautions are made with 28%. However, burning in trials conducted in the state have shown little if any decrease in yield when precautions are taken.
Dr. Dave Franzen
NDSU Extension Soil Specialist