Del Voight – Penn State Extension
There seems to be a notion that each time a producer crosses a field there needs to be products in the tank to address every pest that might be in the field at the time. Certainly there are times that I recall that through scouting I had justified a three way to avert disease, insect and weed issues in small grains. But this is not a clear case for Corn or Soybeans or alfalfa. From the economic side for the inexpensive cost of the products many producers elect to simply put it in for insurance reasons. The risk is clearly resistance issues among the pests to some of our best proven insecticides and fungicides. We do not need to look far to see the affects of resistant pathogens. Our counterparts in both vegetable and fruit crops are in a constant state of rotating modes of action to fight against resistant populations of pathogens. Further in soybeans States to the west have confirmed resistance of frog eye leaf spot to strobularin fungicides. Things are shaping up in field crops that we should be managing these products not from the economic side and insurance but the keep the technologies effective.
For Corn some companies are promoting foliar fungicide use on corn at early growth stages, such as V5 or V6 (when five or six leaf collars have developed). It does allow growers to use their own equipment to apply the products. This timing also affords the grower the ability to combine a clean up trip with a herbicide, however this early application may not provide any advantage in disease control. Further some hybrids may or may not have differing responses to fungicides applied this early.
University of Illinois Extension Plant Pathologist Carl Bradley wrote about this last year in his Crops Bulletin and he relates that the most important reason to apply a fungicide is to control disease. However, at the V5 or V6 growth stage, most foliar diseases frequently observed in Pennsylvania would not be present yet.
In an interview with Corn and Soybean Digest Dr. Bradley states “Unfortunately, few replicated field research trials have been conducted to evaluate these early growth-stage timings of foliar fungicides on corn,” he says.
In the Spring of 2011, Dr. Bradley requested results from the University of Wisconsin, Purdue University, Iowa State University, the University of Nebraska and the University of Illinois regarding the yield responses of corn with early fungicide applications.
Based on the responses he received regarding products currently registered for corn, only Headline fungicide (BASF) had been evaluated at early timings in more than two trials. In these trials, yield responses to Headline applied at either V6 or tassel emergence/silking varied. The overall average yield response across all trials was 1.5 bu./acre with V6 applications and 8 bu. with tassel emergence/silking applications. The level of disease pressure varied by trial and location; for instance, a high level of southern rust was present in some of the Nebraska trials.
“Overall, the tassel emergence/silking timing appears to be more advantageous for disease control and yield response compared to the V6 application,” Bradley says. “The biggest yield responses with foliar fungicides on corn will be observed in fields that have the highest risk of foliar diseases. Disease risk increases with more susceptible hybrids and in corn-on-corn situations.”
What about early and late applications???
So what about insects? There are a number of insects that attack corn this early in its lifecycle. I am not aware of Extension research projects aimed at health applications of insecticides in corn without the presence of a pest in the field. I can think of a few cases where a Bt corn was not used that had insect pressure early (armyworms corn borer and other cutworms) but unless an insect threat is observed I am relatively confident this treatment would do more long term harm to beneficials and hasten potential resistance issues. In this case it is highly advisable to walk the fields and determine if any pests are active and at what level.
For Soybeans the cases is not as clear. There are numerous early season insect pests that can become issues at the final herbicide timing. I am not aware of any research in the tank mixing of insecticides however there are numerous insects that may be present in the field at this time. A check for bean leaf beetles and or other defoliators, aphids etc. will easily make the decision clear for the inclusion of an insecticide for management. The Pa Soybean board provided 4,000 copies of managing pests in soybeans to growers that contain thresholds and products.
Early season fungicide applications typically do not result in yield enhancement. Most research supports the R3 timing as the highest yield benefit timing. In our Pa On Farm Research trials over the last two years we have seen a 3.5bu/acre advantage from a R3 timing of a fungicide. This would suggest the arbitrary inclusion of a fungicide at V6 soybeans would not be advantageous. Again this also may aid in the resistance issue as well.
Alfalfa has a label for both Headline and Quadris fungicides and it is now feasible to apply those particular products on almost all crops across the board. A trial was conducted during the summer of 2011 at Waseca, MN, (IMPROVING ALFALFA AND OTHER FORAGE CROPS FOR BIOENERGY, LIVESTOCK PRODUCTION, AND ENVIRONMENTAL PROTECTION, Samac, Deborah) to evaluate the performance of Headline to control leaf diseases in alfalfa and measure the impact on yield and forage quality. For each of the three cuttings, treatment with Headline or Headline plus Warrior significantly reduced leaf spots and increased yield compared to the untreated control or the treatment with Warrior alone. Another study in Wisconsin Extension compared Quadris + Warrior to Headline plus Respect and found significant differences between untreated and treated but both companies products performed equally well. I could not find references within the Mid Atlantic Region however I would expect results similar to these.