Mycotoxin Outlook for 2026 Harvest – Part 2
19 Oct 2026
Animal Nutrition & Health
It seems as though within the recent past that each year has seen a “new” pathogen or pest making its first appearance or spreading to a new region in crops within North America. Unfortunately, this year is no different. There are various rumblings in the field of new or growing disease and pest pressures across multiple regions. This article will provide a high-level overview of some of the concerns that are being discussed in 2026 crops and the potential implications that they may have on the occurrence of mycotoxins. In terms of mycotoxins being tied to these primary issues, there are many unknowns at this time. This article is an attempt to bring awareness to several crop challenges that are being reported in the field and as such, many articles will be referenced to provide additional outlets for more in-depth education and awareness on these topics.
Most mycotoxin-producing molds live in the soil and can survive on crop residues as their primary purpose in life is to break down organic material. Mold spores can be transferred to plants via wind, splashing water, or by vectors such as insects or wildlife. Soilborne spores can also infect plants via uptake by the roots. Damage or lesions from insects, wildlife, hail, wind, or other mechanical injury can also provide a pathway for molds to colonize the plant as damage to the plant increases susceptibility to disease and often enhances the ability of molds to colonize the plant.
Many plant pathogens have not been associated with production of mycotoxins, including most foliar diseases. However, such non-mycotoxigenic pathogens can reduce yield and quality, as well as stress the plant which in turn can increase the risk for secondary disease by molds that can produce mycotoxins. Although contamination in the grain portion of crops like corn and wheat is often the primary concern when it comes to mycotoxins, several of the troublesome mycotoxigenic fungi can cause stalk rot and root rot and infect a wide range of crops. Thus, making mycotoxins a bigger problem than in just corn and wheat grain. In addition to highlighting some different plant diseases and issues, this article intends to feature some additional crops which should also be considered as potential sources of mycotoxins beyond just corn.
Moldy Beans – A Frequently Overlooked Risk for Mycotoxins?
Locally grown soybeans are often thought to be a low-risk matrix for mycotoxins in North America. Recent wet conditions in some areas, Iowa included, have created the opportunity for some fungal diseases to develop in soybeans. There is much to be learned about some of these fungal diseases and their potential for mycotoxins. While mycotoxins might not ultimately be a concern, yield losses and discounted quality are frequent concerns. Two primary seed diseases have been identified in the field that are worth discussing although they’re not necessarily new, perhaps just more severe this year.
Purple Seed Stain
• General information: Again, this is not a new issue, but producers are reportedly seeing more of this characteristic purple discoloration in soybeans. Cercospora flagellaris and other Cercospora species are associated with purple seed stain, and these are the same fungi that cause the foliar disease Cercospora leaf blight (CLB). Although the same fungi cause both of these issues, no consistent relationship has been described among purple seed stain and CLB. Warm and wet weather conditions are conducive to infection and disease development. Although yield is not generally reduced, the value of the crop may be reduced through dockage. Cercospora is a widespread plant pathogen found in a variety of crops beyond soybeans including corn and tobacco.
• Potential Link to Mycotoxins: Cercospora species of fungi have been shown to synthesize mycotoxins including cercosporin. Cercosporin is a toxic red pigment. Unfortunately, toxins like cercosporin are not routinely screened for and such analysis is not readily available at commercial laboratories. So, the occurrence is not well known. Similarly, the toxic effects in livestock have not been widely studied so the risk this toxin may present is not well-characterized. From a potential mode of action standpoint, it is photoactivated and generates reactive oxygen species (ROS) which can indiscriminately attack and damage cell membranes, proteins, lipids, etc. This could cause a broad range of toxic cellular effects and subsequent damage in tissues that could harm animal health and performance. The true impact on livestock is not well-understood at this time.
• Purple Seed Stain / Cercospora / Cercosporin Resources:
Daub and Chung. “Cercosporin: A Photoactivated Toxin in Plant Disease.” American Phytopathological Society (APS) Education Contributed Content, 2007. Retrieved November 6, 2026, from https://www.apsnet.org/edcenter/apsnetfeatures/Pages/Cercosporin.aspx
Crop Protection Network: https://cropprotectionnetwork.org/encyclopedia/cercospora-leaf-blight-of-soybean
Crop Protection Network: https://cropprotectionnetwork.org/publications/an-overview-of-cercospora-leaf-blight-of-soybean
Iowa State University Extension and Outreach – Integrated Crop Management: Soybean seed quality issues during a wet fall | Integrated Crop Management
Newman and Townsend. “Molecular Characterization of the Cercosporin Biosynthetic Pathway in the Fungal Plant Pathogen Cercospora nicotianae”. J Am Chem Soc. 2016 Mar 30;138(12):4219-28. Retrieved November 6, 2026, from https://doi.org/10.1021/jacs.6b00633
Science Societies: Identifying and managing Cercospora leaf blight in soybean: From scouting to best management practices | Science Societies
Soy Checkoff – Science for Success: Purple Seed Stain on the Rise in 2026
Diaporthe (formerly Phomopsis) Seed Decay
• General information: Yet another issue that isn’t technically new but is seeing renewed pressure this year due to warm and humid, wet weather conditions in some areas of the Midwest is Diaporthe seed decay (DSD). Multiple species of Diaporthe fungus can cause DSD, but the main pathogen in the USA is Diaporthe longicolla which can be visualized as a chalky, white mold that can result in cracked and shriveled seeds. Infected seeds can appear healthy if the disease is not extreme, visual identification can be challenging. Delays in harvest can increase disease severity. Shifts between wet and dry weather can cause pods to be compromised and split, creating an entry point for Diaporthe into pods where it can then infect mature seeds.
• Potential Link to Mycotoxins: Diaporthe fungi has not been directly linked to mycotoxin production, so this disease is not expected to lead to mycotoxin contamination directly. However, compromised plant health may increase the risk for opportunistic mycotoxigenic molds to also colonize plants and cause contamination.
• Diaporthe Seed Decay Resources:
Bayer Crop Science United States: Diaporthe Soybean Disease Identification & Management | Crop Science US
Crop Protection Network: https://cropprotectionnetwork.org/publications/new-fungi-discovered-causing-phomopsis-seed-decay-of-soybean
Crop Protection Network: https://cropprotectionnetwork.org/encyclopedia/phomopsis-seed-decay-of-soybean
George et al. “A diagnostic guide of diseases caused by Diaporthe species in soybean.” American Phytopathological Society (APS) Online Publications, 2025. Retrieved November 8, 2026, from https://apsjournals.apsnet.org/doi/10.1094/PHP-03-25-0096-DG
Iowa State University Extension and Outreach – Integrated Crop Management: Soybean seed quality issues during a wet fall | Integrated Crop Management
NC State Extension Publications: https://content.ces.ncsu.edu/seed-decay-and-pod-blight
New Foliar Disease Identified - Phaeosphaeria leaf spot (PLS) aka Maize White Spot (MWS)
Although Phaeosphaeria Leaf Spot was first identified in corn in the continental USA in the 1990s, this year the fast-spreading disease has been observed or is suspected in Michigan, Pennsylvania, New York, and northern Indiana. Testing is on-going and university plant pathologists are looking to source samples to try to determine if the fungus found in the Great Lakes region is the same as what was first found in Florida over 30 years ago. The signs in the field appear to be the same and initial laboratory testing has identified isolates as a phomoid fungus, but researchers are trying to determine if this is a new pathogen or a dormant disease making a resurgence.
• General information: This is considered a major disease in tropical and subtropical parts of the world including in African regions. The disease is often found in areas with high rainfall and moderate temperatures (especially at night) such as India where it was first identified and Brazil. One challenge so far this year is that the lesions can be misdiagnosed either as chemical burn / herbicide damage or fertility deficiencies. Plant pathologists are concerned about fungal residues overwintering in fodder left in the field after harvest. A lot of work in on-going as there are many uncertainties related to this emerging disease, so it is recommended that you stay updated by reading the latest publications and articles especially if you live in the Great Lakes region.
• Potential Link to Mycotoxins: Phaeosphaeria maydis and related phomoid fungi have not been associated with mycotoxin production. As with other foliar diseases, however, it’s plausible that maize white spot could predispose plants to secondary mycotoxigenic fungi although this relationship has not been explicitly studied or found thus far with PLS.
• Phaeosphaeria leaf spot Resources:
Adam et al. “Detecting the early stage of Phaeosphaeria leaf spot infestations in maize crop using In Situ hyperspectral data and guided regularized random forest algorithm.” J Spectrosc. 2017. Retrieved November 8, 2026, from https://doi.org/10.1155/2017/6961387
American Phytopathological Society (APS) – APSnet: https://www.apsnet.org/publications/PlantDisease/BackIssues/Documents/1991Abstracts/PD_75_968E.htm
Farm Progress – MichiganFarmer: New fungal disease could rival tar spot’s devastating impact
Goncalves et al. “Etiology of Phaeosphaeria leaf spot disease of maize.” J Plant Path. 2013, 95 (3), 559-569. Retrieved November 8, 2026, from https://www.researchgate.net/publication/255711372_Etiology_of_Phaeosphaeria_leaf_spot_disease_of_maize#fullTextFileContent
Hooser Ag Today: https://www.hoosieragtoday.com/2026/09/28/maize-white-spot/
Michigan State University – MSU Extension Corn: https://www.canr.msu.edu/news/emerging-leaf-spot-disease-of-corn-under-investigation-in-michigan
Successful Farming: https://www.agriculture.com/first-cases-of-maize-white-spot-suspected-in-2026-michigan-corn-crops-12185494
Invasive Pest Identified in Florida
Pasture mealybugs (Heliococcus summervillei and H. novovillei, PMB) are small, white, oval-shaped insects which have a fuzzy and fluffy-looking appearance. These invasive insects have been identified in several southern states (Texas, Louisiana, and Georgia) and were first detected in Florida in May 2026. As this invasive pest continues to spread, surveillance work is being conducted to understand where and how this insect is expanding as it causes severe dieback of pastures and grasses and devastated much of this year’s sugarcane crop.
• General information: Pasture mealybugs are currently primarily affecting warm-season perennial grasses in pastures and rangeland as well as hay fields, but are also impacting sugarcane, and turfgrass or ornamental grass across the southern USA. The indications of PMB infestation can appear within a week. They are typically found feeding on the underside of grass blades. Some signs of PMB infiltration include yellowing to red or purple discoloration (especially in sugarcane), what appears to be drought-stress despite recent rain, overall stunting and poor root development, subsequent senescence and ultimately death of the plant. Adult PMB reproduce in the thatch or soil and can produce multiple generations per year. Warm conditions support population growth and PMB can move deeper into the soil during drought or other unfavorable conditions.
• Potential Link to Mycotoxins: As an insect, PMB are not a direct source of mycotoxins themselves. However, there is a two-fold concern of how PMB could become associated with mycotoxins: (1) as these invasive insects feed on plants, they will create feeding injury which can increase risk for mycotoxigenic molds to also infect the plant and (2) the insects themselves can potentially act as a vector to spread mold spores from infected plants or soil. As a new threat in Florida, there are many unknowns in general, but also more information is needed to determine what potential impact PMB may have on the presence of mycotoxins.
• Pasture Mealybug Resources:
Florida Department of Agriculture and Consumer Services: Pasture Mealybug - Florida Department of Agriculture & Consumer Services
University of Florida IFAS Extension: Pasture Mealybug Detected in Florida Pastures - UF/IFAS North Florida Research and Education Center
University of Florida IFAS Extension: Pasture Mealybug Update: What Have We Learned in Florida? - UF/IFAS North Florida Research and Education Center
University of Florida IFAS Extension: Pasture Mealybugs - Pasture Mealybugs - University of Florida, Institute of Food and Agricultural Sciences - UF/IFAS
United States Department of Agriculture – Animal and Plant Health Inspection Service (USDA-APHIS): Pasture Mealybug | USDA APHIS – Grass & Crop Pest Threat
If you live in an area which is impacted (or suspected to be afflicted) with any of these issues, especially the emerging foliar disease Phaeosphaeria Leaf Spot or the spreading pasture mealybug, please consult your state Department of Agriculture or local land grant university to potentially submit samples for testing and surveillance. If you are curious about the potential impact such issues may have on mycotoxins, please contact you dsm-firmenich representative to learn more about what mycotoxin analytical services we can offer as support.
09 November 2026
19 Oct 2026
11 Sep 2026
17 Aug 2026