There has been some reports from various sources suggesting that insecticide seed treatments (IST) have limited value and don’t affect yield. Some of this is related to the anti-neonicotinoid craze that has become a very political issue. It is dangerous and naive to make generalized comments about the value of IST across a wide geography for something as highly variable as crop production and insect pests. There is a need to set the record straight and make sure comments made in other geographies are not generalized to other areas. There has been years of testing and multiple locations in the Mid South that quantify the value of insecticide seed treatments for multiple crops. My counterparts and I routinely conduct standardized IST trials in cotton, soybean and corn. Many of these data are presented at various meetings but seldom make it into the referred literature. Mainstream entomology journals typically discourage publishing “treat and count” kind of trials, but that doesn’t mean these data don’t exist.
I’ve been showing summary data of cotton yield response to neonicotinoid insecticides at various meetings this year. These are data compiled across 22 trials over about 10 years from Tennessee and Arkansas. In a nutshell, neonicotinoid seed treatments increased yield by about 188 pounds of lint/acre compared to untreated plots (linked below). Thrips control matters in cotton!
CottonThrips: summary of cotton 22 trials with insecticide seed treatments
Several years ago, I did a similar exercise for corn for all the data I could get my hands on from Tennessee. These data also showed that a Poncho seed treatment increased average yields by about 4 bushels/acre (LINK HERE). This number will be higher as you go further south. Seed treatments have essentially made non-pests out of some insects that have historically caused severe yield losses in the Mid South. These include critters like southern corn rootworm, chinch bugs, and seedcorn maggot. They have also suppressed other important pests like wireworms and white grubs. I once visited a 600 acre corn field in Mississippi that had to be replanted because of southern corn rootworm where no insecticide was used. Now, with seed treatments, the last time I’ve seen this critter was two years ago in sweet corn that also had no insecticide. When is the last time you saw a significant problem with seedcorn maggot? These are the obvious examples, but the consistency of IST in increasing corn yields also stems from reducing injury from an entire complex of pests that kill or stunt scattered plants in the field. Treatment effects may not be visually obvious, but they are often reflected in yield increases because corn is often quite sensitive to stand loss.
My counterpart, Dr. Gus Lorenz at the University of Arkansas, was recently commenting just how consistently insecticide seed treatments in rice increase yield. He routinely observes yield increases of 8-10 bushels per acre. Tennessee data over a 15 year period shows a benefit of Gaucho or Cruiser seed treatment on wheat of about 3 bushels per acres. Again, this is statistically significant when analyzed across 40 experiments from 1993-2007 (t-Test Value = 4.21; df = 39; P < 0.01).
Soybean are one of the least responsive crops that I deal with in regards to insecticide seed treatments. The normal response is no response, but I’ve still observed statistically significant yield responses in Tennessee as high as 6-8 bushels/acre. I’m in the midst of a “meta-analysis” of multi-year, regional testing of commercially available IST in soybean. Although a variable and not overly impressive, these data show an average increase from a neonicotinoid IST of about 2 bushels/acre across the Mid South (and again significantly significant). However, several of my counterparts and I have observed situations where these treatments did or would have prevented replanting.
Growers tend to place more value to risk management than we do in science. Just a few experiences of substantial yield loss (or perceived losses) resulting from seedling insect pests will often result in their unilateral use. This may not always be the right decision, but it is also amazing how many time rare occurrences occur when millions of acres are being planted. I do not suggest using ISTs on every crop all the time, but there is no question that neonicotinoid seed treatments routinely increase yields in many crops in the South.