Feeding the Enemy: How Nitrogen Management Can Feed or Starve Pest Attacks

Bob Gunzenhauser, Director of Agronomy

Introduction

In general, proper nitrogen management for crops like corn, cotton, and wheat, among others, is focused primarily on the yield of the crop or partial net profit vs the amount of nitrogen required.  We want to apply the proper amount of nitrogen that is not limiting yield but is also not costing more than it should.

While this should be the primary focus on nitrogen management, there are other reasons to monitor excessive nitrogen application beyond downstream environmental effects. 

As plants grow and develop, they can take advantage of extra free nitrogen and take part in “luxury consumption”.  If a large amount of inorganic nitrogen is available during rapid vegetative growth, the plant will consume it and promote lush vegetative growth.  This excessive nitrogen increases free amino acids and soluble proteins.

Supporting Research

Over the years, research has found that excessive nitrogen uptake by plants can lead to increased levels of disease and insects.

A study by Veromann, et al (2013) of oil rapeseed found that treatments of higher nitrogen fertilizer applications, both acetic acid and several lipoxygenase pathway products increased, attracting both insects and disease fungi as chemical signals.

A meta-analysis of 135 studies over 50 years from SARE found that nitrogen-fertilized crops had more damage and/or greater number of leaf-chewing insects or mites.  It was also found that higher nitrogen levels in the plant tissues can decrease resistance and increase susceptibility to pest attacks.  Included in the meta-analysis was this example:

Rose-Grain Aphid on a Corn Leaf

Conventional winter wheat fields in England had greater levels of rose-grain aphids than their organic counterparts.  Synthetic nitrogen fertilizer was top-dressed on the conventional fields in April; the plants had higher levels of free protein amino acids when tested in June and attracted greater numbers of aphids by that time.

Another study conducted in Australia on wheat found that increased nitrogen fertilizer application significantly increased the cherry-oat aphid’s ability to reproduce along with plant nitrogen content. (Navarro, et al, 2020).

A study (Scarpino, 2022) from north-west Italy included corn planted with 5 nitrogen rates of 0 to 400 kg/ha N (0 to 356 lbs N/ac).  In this study it was found that corn with the 400 kg/ha N rate had the highest levels of deoxynivalenol (DON), also known as vomitoxin that can cause health issues for both animals and humans.  In addition, the 400 kg/ha treatment also had excessive levels of zearalenone, an estrogenic mycotoxin produced by Fusarium molds that has been linked to reproductive health issues, also in animals and humans.

How Can Proper Nitrogen Management Help?

Addressing the issue of excessive free proteins and amino acids appears to be the proper path forward to reducing incidence of disease and insects.  Management for this can include:

• Proper Nitrogen Rates:

• More doesn’t always mean better.  Knowing that excessive nitrogen can bring disease and insects, as well as hurt the checkbook, backing off total nitrogen rates will assist.

• Split and Timed Applications of Nitrogen:

• Instead of applying all nitrogen at one time, consider splitting the application into two or more, and timing the applications to coincide with rapid plant uptake to reduce luxury consumption.

• Slow Release and Stabilized Nitrogen:

  
  

  • Consider using slow-release, polymer coated urea or nitrogen sources with stabilizers (urease or nitrification) to slow down the conversion of ammonium to nitrate, thereby metering the amount of free inorganic nitrogen in the soil:water solution.

• Reduce Free Inorganic Nitrogen in the Soil:

  
  

  • This may include using cover crops to scavenge free nitrate.  Proper termination to release the nitrogen back to the growing primary crop is necessary.

• Allow Mineralization to Assist:

  
  

  • Maintaining healthy soils with good levels of organic matter and biological activity can contribute organic-derived N to the crop during the growing season at metered levels.

These are all tools to utilize towards reducing over-consumption of nitrogen and creating attacks by insects and disease.  Using these can also reduce the need for extra insecticides, fungicide, and traited biotech seed, thereby reducing costs of production.  Consider how these could fit into your operation in the future...