Each year we conduct white mold fungicide efficacy trials. We examine old and new fungicide products, fungicide timing and application techniques. The two following graphs are snapshots from individual trials conducted over the last two years at the MSU Montcalm research station. We conducted these trials in 15” rows at a population of approximately 160,000 plants per acre, in irrigated fields with a history of white mold. The soybean variety used was moderately susceptible to white mold.
Note, the amount of white mold that developed in the trial is expressed as the disease severity index (disease severity x disease incidence) and is shown in blue, while the respective yield (bu/A) of each treatment is shown in red. Disease severity index or yield that is different between treatments is indicated with different letters. Also take note of the different application timings that are indicated such as R1 (beginning of flowering – plants have at least one flower on any node), R2 (full flowering - there is an open flower at one of the two uppermost nodes), and R3 (beginning pod - pods are 3/16 inch at one of the four uppermost nodes).
In addition to conducting these trials, we also collaborate with colleagues in states across the north central region allowing us to collect data on product performance over multiple environments. The fungicide efficacy table is a consensus of product performance for white mold and other soybean diseases and can be found here:
In addition to making the decision of what to apply, the “how” of fungicide application is also very important. For ground rig applications the following considerations should be made
A helpful article discussing these points in more detail can be found here: https://www.canr.msu.edu/news/equipping_and_operating_sprayers_to_control_insects_and_diseases_in_soybean
Martin Chilvers, Associate Professor and Field Crop Pathology Specialist, Jill Check, PhD candidate, Austin McCoy, postdoctoral associate, Mike Staton, MSUE soybean educator
The answer to this question will depend upon three factors that must come together, the prevailing weather, presence of the white mold fungus and susceptibility of the soybean variety.
White mold of soybean is an annual problem for some producers and can be particularly severe when conditions are cool and wet during flowering. This disease is often most problematic in soybean fields having productive soils, planted at a high population with narrow row spacing (<30 inches). Canopy closure provides a humid, shaded environment that is conducive to white mold apothecia (mushroom) formation and plant infection, especially in cool, wet years. No soybean variety is completely resistant to this disease, however, as shown in the figure below, even within a company there are varieties which are far more tolerant and perform better under white mold disease pressure. Selecting a variety that is tolerant to white mold, as well as planting lower soybean populations and utilizing wider row spacing can help manage the severity of this disease. Company catalogues do provide white mold ratings, but it is always wise to check with your seed dealer, especially if you have had issues managing white mold in the past. Knowing variety susceptibility can also help inform in-season management decisions such as fungicide applications.
The weather that we receive shortly before and into July will heavily dictate the degree of white mold disease that develops later in the season. A cool (<85o F), wet July means favorable conditions for the white mold fungus to produce apothecia (mushrooms) that release spores and infect the plant primarily through the flowers or fallen flower petals. Disease won’t be readily apparent until August when cottony mycelia of the white mold fungus start to be produced from infected plants and plants begin to wilt. In addition, producers that irrigate will be at increased risk of white mold and should consider less frequent but heavier waterings. Irrigators should also hold off watering as much as possible until the R3 growth stage (one pod 3/16” long on the upper four nodes of the main stem having a fully developed leaf node).
Finally, the third in the trifecta of white mold disease development is the presence of the white mold fungus. Unfortunately, the white mold fungus can survive for many years in the soil as sclerotia. Seed lots can also be infected or infested with the white mold fungus and can act as another source of inoculum. White mold inoculum typically does not move very far from the source. However, in the white mold epidemic of 2014 it did appear that the excessively foggy, wet, and cool July may have seen dispersal of white mold spores into fields with no previous inoculum source. Tillage can also play an important role in inoculum movement and survival. Tilling fields will bury the sclerotia resting bodies where they are more likely to survive and then germinate once brought to within the top inch or two of the soil profile. Sclerotia buried deeper are unlikely to be able to produce an apothecia (mushroom) on the soil surface. Under no-till systems there is evidence that sclerotia do not survive as well on the soil surface.