The Uncommon Becomes Common - Cladosporium Ear RotA hot topic during corn harvest is always ear moulds and this year is no exception especially if you are a producer near London or in the surrounding U.S. Great Lake States. Actually the southwest has been the pleasant surprise with less ear mould then I expected based on the weather but that is not to say we have none. As with any year there are fields or hot spots which develop in the province but considering the weather conditions late in the season, those ear moulds (Gibberella, Fusarium and Diplodia) we normally would be concerned with have been about par with other years. Others such as Cladosporium which is a minor nuisance most years has been widespread but unlike Gibberella and Fusarium, Cladosporium does not produce any mycotoxins. That is not to say we don't have any Gibberella or Fusarium which are often worse in a wet fall or in fields which have considerable insect injury, bird damge, poor pollination and other factors such as a highly susceptible hybrid. Hybrid genetics (remember some hybrids are more susceptible then others and as in any year, you should know how you hybrids performed) and the local environment play an important role in ear mould development. In Ontario the three primary ear moulds are Gibberella, Fusarium and Diplodia Ear Rots and to a lesser degree Penicillium and Cladosporium. Colour and distribution on the ear makes it relatively easy to identify these moulds. For instance, although both Gibberella and Fusarium produce a white colour mould which makes it difficult to tell them apart - Gibberella has a characteristic red or dark pink almost purple in colour which starts at the ear tip whereas Fusarium infection produces a white to pink or salmon-coloured mould with a "white streaking" or "star-bursting" appearance on infected kernels which are scattered around the ear. Gibberella, (Gibberella zeae) is the most common and important ear mould in Ontario followed by Fusarium ear rot. Although many Fusarium species cause ear rot symptoms, the primary species we are concerned about in Ontario is Fusarium verticillioides (formerly Fusarium moniliforme). Both Gibberella and Fusarium are our most important moulds because they have the potential to produce mycotoxins so if you are planning to feed your grain a mycotoxin test should be a standard practice. Refer to Table 1 for a list of testing laboratories. Table 1. Moulds and Mycotoxins Laboratories Offering Mycotoxin Analysis
Diplodia is the least common of the three primary ear rots that occur in Ontario and it produces a white mould that begins at the base of the ear and will eventually cover and rot the entire ear. Mould growth can also occur on the outer husk which has small black bumps (pycnidia) embedded in the mould. These reproductive structures are where new spores are produced. Unlike Gibberella and Fusarium, Diplodia does not produce any known toxins. Four other fungi cause storage moulds in Ontario. Penicillium, Aspergillus, Cladosporium and Alternaria and they can be found in varying amounts each year. Penicillium and Aspergillus produce a green to blue-green moulds whereas Alternaria and Cladosporium produce a black mould and are considered "opportunist" fungal pathogens. Cladosporium in particular has been the prominent ear mould around London and to the north this year. The delayed harvest, in conjunction with premature crop death from frost, has contributed to the Cladosporium issue. Cladosporium as well as the other storage moulds grow mainly on the kernel surface (surface colonizers) or between kernels and therefore, are not great colonizers. Basically as the corn dries you could expect the fungal mould to dry as well and some friction such as combining will remove it to some degree. It is important to know your storage moulds since they can reduce feed value, marketability as well as lower germination, discolour the seed, cause caking, heating and bin-burned corn. And as mentioned, some of these fungi (Fusarium, Gibberella) can produce certain toxins and pose a risk to livestock. If you are storing your corn remember it is critical to aerate, maintain proper temperature and moisture content, control insects, minimize mechanical injury, and clean the bin. Regular inspections and removal of broken kernels or fine grain particles will help reduce further mould growth in storage. Fines and broken kernels are ideal locations for mould growth to begin and subsequently spread to the healthy grain. For more on the judicious management of fines, refer to Helmut Spieser's CropPest article titled Get the Fines Out of 2009 Corn.
Figure 2- "White streaking" or "star-bursting" appearance on kernels with white to pink mould scattered around ear typical of Fusarium ear rot. (OMAFRA- Tenuta)
Figure 3- Diplodia begins as white mould at the base of the ear and may eventually cover the entire ear. (OMAFRA- Tenuta)
Figure 4-Penicillium and Aspergillus produce a green/blue-green mould. (OMAFRA-Tenuta)
Figure 5. Cladosporium Ear Rot infection could be seen as a black mould on kernel surface. (Photo courtesy of DG White, University of Illinois).
Figure 6. Cladosporium infection (black mould growth) can be seen around the ear and on the kernel. (Photo Courtesy of Gary Munkvold, Iowa State University)
Figure 7. Cladosporium growth often occurs between the kernel as a black
mould.
For more information: Toll Free: 1-877-424-1300 Local: (519) 826-4047 E-mail: ag.info.omafra@ontario.ca
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