By Angie Peltier
In a September, 2015 Plant Health Progress article entitled, "Timing and Efficacy of Fungicide Applications for Diplodia Ear Rot Management", Purdue Plant Pathologist, Dr. Kiersten Wise and graduate student Martha Romero Luna, summarize a series of field and lab-based experiments in which they investigate fungicides to manage this disease.
What did they do? In field environments over five site-years, the researchers studied the effect of two fungicide products labeled either for Diplodia ear rot or other ear rotting pathogens: azoystrobin plus propiconazole (Quilt Xcel) or prothioconazole (Proline 480 SC), respectively.
They studied grain yield and disease suppression in the field in untreated control plots or plots in which plants were treated with a fungicide at one of three corn growth stages at which fungicides are commonly applied: V6 (6 visible leaf collars), VT/R1 (tasseling/silking) and R3 (early dough). To each fungicide treatment was added an inoculum treatment where they either relied upon natural inoculum or added Stenocarpella maydis, the fungus that causes Diplodia ear rot, into the whorl of each plant.
What did they find? By growing field-collected isolates of S. maydis in the lab on growth medium amended with fungicides, the researchers confirmed that the fungicides were capable of inhibiting growth of the fungus. In the field, however, they found that when compared with untreated controls, fungicide treatment did not consistently increase grain yields. This same trend was observed in every year and with every fungicide application-timing in plots with plants that were both inoculated in-whorl and infected naturally.
Luna and Wise theorize that perhaps the fungicide is physically unable to reach the fungus to inhibit growth and infection. Infection takes place between the ear shank and the stalk, an area that is conversely both favorable for fungal growth and physically shielded. They also theorize that at silking, the humid conditions within the husk favor both growth of the fungus and the degradation of the fungicide.
How might these results affect management recommendations? Luna and Wise conclude that "The absences of consistent yield improvement with fungicide application does not likely justify the use of these fungicides even when environmental and field conditions favor Diplodia ear rot, and producers should focus on other management methods, such as crop rotation and tillage, to reduce severity of this disease."