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When does it pay to spray at last minute?

Is there still time to dribble some extra N on corn or apply fungicides or insecticides on soybeans? Indiana certified crop advisers tackle the topic.

One neighbor has a high-clearance sprayer. Another bought a rig with optical sensors. Would it do any good to apply more N now? I’m at 33,000, and it looks good. It’s had 185 actual pounds per acre already applied.

Steve Dlugosz, Harvest Land Co-op, east-central Indiana: Many parts of Indiana have lost substantial amounts of N. It’s challenging to estimate loss and even more difficult to apply extra N in a timely way. If you have the technology and equipment available, I would certainly encourage you to proceed.

Gene Flaningam, Flaningam Ag Consulting LLC, Vincennes: Corn finishes with rapid N uptake shortly after pollination is complete. Optimal timings for late N applications should be prior to the 10-leaf stage. Corn deficient on N would show a response from pollination to early grain-fill stages. Equipment available today should allow for optional N placement if sensors are calibrated for the hybrid.

Willis Smith, Senesac Inc., Fowler: What was the previous crop? What growth stage? Has rain caused N loss? If corn is after corn, you need at least 40 more pounds of N. If it’s following soybeans, your N level is on the low side for a crop that “looks” good. You need a high-clearance sprayer if your corn has pollinated or is about to do so. Number of kernels was determined at V6. All you might do is influence test weight and help fight off disease. If you’re going to apply a fungicide, consider foliar N. You’ve already paid for the fungicide application. The only extra cost is foliar N, and it should give you a good return on investment.

Fungicide on soybeans

Is there still time to spray a fungicide on soybeans and expect a response? If so, would it pay to add an insecticide? Can they be sprayed together?

Dlugosz: Many factors affect it, including disease pressure and weather. Most responses are in the 2- to 5-bushel-per-acre range. Many insecticides mix well with the fungicides and may be a good addition for controlling late-season, pod-feeding insects like stinkbug and bean leaf beetle.

Flangingam: Optimal timing for fungicides is R3, R4 growth stages. You should have pods set and starting to develop in one of four uppermost nodes. Fungicide response depends upon environmental conditions and variety tolerance. Adding an insecticide would be good if the insect pest(s) present threaten yield. Scout fields first. Spider mites require a different type of chemistry. Fungicides and insecticides can be tank mixed. Always read pesticide labels.

Smith: If soybeans are at R3 to R4, a fungicide will likely make you money. If it’s later, there may not be an economic return — maybe even a net loss. If insects are a threat and have reached threshold levels, add an insecticide recommended for those pests. If there is no threat, it will be money wasted, and you could wipe out beneficial insets that hold the pest in check. If conditions warrant and you’re applying both fungicide and insecticide, check labels for compatibility before spraying.


Jury still out: Purdue University Extension agronomists Bob Nielsen and Jim Camberato test N sensor equipment. They haven’t issued recommendations yet.

This article published in the August, 2011 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.