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Update on the Efficacy of Fungicide Programs on Charcoal Rot Development
Tue - December 20, 2016
by Kiersten Wise, Soybean Plant Pathologist, Purdue University

Charcoal rot, caused by Macrophomina phaseolina, is a fungal disease of growing importance in the north-central region of the U.S. and Canada. The disease is more severe when plants are stressed by heat and dry conditions. With unpredictable weather patterns from year to year, there is the potential that charcoal rot could increase, especially in hot, dry years.

Our current understanding of charcoal rot management comes mostly from studies conducted in the southern United States, where the disease has been more prevalent. Efforts to identify resistance to charcoal rot have focused largely on soybean varieties adapted to the southern U.S. (maturity group IV and later). Partial resistance to the charcoal rot pathogen has been identified in southern soybean varieties, and evaluation of commercial varieties and northern breeding lines for partial resistance to charcoal rot is underway.

New seed and foliar fungicide programs and fungicide products have been marketed to protect soybeans against soil-borne diseases and plant stress. In a recently-completed project, funded by the North Central Soybean Research Program, soybean plant pathologists in six mid-western states conducted a regional evaluation of these products to determine their impact on charcoal rot development and yield.

In the first year (2014), we determined that foliar fungicide applications had no effect on reducing infection by the charcoal rot pathogen and had no effect on yield at any application timing. The effects of seed treatments and in-furrow fungicides on charcoal rot development were mixed, with seed treatments reducing final levels of charcoal rot in two of six states. In-furrow fungicides did not reduce charcoal rot, but did improve yield in some trials.

The seed treatment and in-furrow fungicide experiments were repeated in 2015. Charcoal rot levels were low across trial locations due to excessive rainfall in many locations. However, charcoal rot was present at high levels in Kansas. In the Kansas studies, seed treatments and in-furrow fungicides did not reduce disease severity or fungal growth in soybean. In-furrow fungicides improved yield in some locations.

We conclude from these studies that foliar fungicides applied to reduce plant stress and manage charcoal rot does not provide an economic benefit to farmers. Currently available fungicide seed treatments and in-furrow applications will not consistently reduce charcoal rot in soybean, and the effect on final yield is inconsistent.

To learn more about charcoal rot biology, scouting, and management, please see our 8-page, full-color publication Charcoal Rot. We have also produced a series of videos about charcoal rot which you can view on the SRII YouTube channel.

Read or download Charcoal Rot (pdf) >
View charcoal rot videos >