Farm Talk

August 27, 2013

To spray or not to spray, that is the question

Josh Coltrain

Parsons, Kansas — Even though I grew up in Southeast Kansas, and have recently moved back, I have to admit that the weather has not seemed too familiar. My colleagues ensure that in my time away from the district this was not the norm. Recent rains have taken our soybean crop from a possible total failure of poorly palatable hay to what could be a great yielding crop. Along with that rain came cool temperatures which are the ideal growing conditions for fungus. The question that many producers are facing is whether or not to apply foliar fungicide, and according to a group of K-State Research and Extension specialists, the answer is: possibly.

Doug Shoup, Southeast Area Crops and Soils Specialist, Stu Duncan, Northeast Area Crops and Soils Specialist, Doug Jardine, Plant Pathologist, and Jeff Whitworth, Entomologist recently reported on foliar fungicide use in soybeans. They tested fungicide application at R2 (full bloom) through R4 (full pod formation) across many locations in central and eastern Kansas from 2007 to 2012. They readily admit the data is not cut and dry with occasional results of large increases (greater than 5 bu./acre) or no response at all (or even a negative yield affect). Complicating the matter was the fact that the yield responses don’t always seem tied to visual presence of the diseases.

If producers decide that they want to apply fungicide, the type of fungicide is very important. Most of the yield increases within the trials were found when stobilurin containing fungicides (Headline, Priaxor, Quilt XCEL, Quadris, Stratego YLD, Approach, and others) as opposed to the less expensive triazole containing fungicides. However, the specialists pointed out that one side effect of apply strobilurin containing fungicides is that they often delay maturity. Compounding this is the fact that many beans were planted later than intended this year so producers must factor that into their decisions.

R3 (beginning pod formation) is a very important stage for determining yield. At this stage and beyond, producers need to scout for pod-feeding insects like corn earworm (called podworm when found in beans), stinkbug, and bean leaf beetle. Because of producer interest, the specialists included the added variable of insecticide application at R3. The economic threshold for stink bug and bean leaf beetle the threshold is 1 insect per three feet of 30 inch row, and for corn earworm is 1 worm per foot of 30 inch row (although it could be argued that finding any earworm in beans would justify spraying). The specialists found no statistical difference between the untreated check and the plots where insecticides were applied. They did grant, however, that the insect pressure was far below the recommended thresholds so this result was not terribly surprising.

In summary, the decision rests solely on the producers shoulders. It is a gamble so to speak. The application and product may cost the producer $20 or so per acre, and even at today’s good bean prices ($12 or even more), a return 1 and 2/3 bushel would be the breakeven point. Frankly, there is no guarantee of garnering a return from the spray, but when is there ever a guarantee in agriculture? Interestingly, the recent stretch of warmer, drier temperatures may take care of the fungal issues for producers without the need for spray.

If you have questions or would like more information, please call me at the office 620-724-8233, or e-mail me at, or visit the Wildcat Extension District Website at £