By: Barbara Ziesman Provincial Specialist, Plant Disease A.Ag, PhD
As mentioned in the blog article titled “Getting familiar with plant diseases”, I will be writing a series of blog articles focused on specific plant pathogens and the diseases that they cause. The first article in this series focused on the basics. This article is second in the series and is focused on Fusarium species
Fusarium species are fungal pathogens that cause a range of different diseases in many crops. Many crops grown in Saskatchewan are susceptible to various Fusarium species, including (but not limited to) Fusarium graminearum, F. avenaceum, F. acuminatum, F. culmorum, F. equiseti, F. oxysporum, F. poae, F. solani, and F. sporotrichioides. For the purpose of this article, the individual pathogens will not be discussed in detail. For simplicity, fusarium root rots, seedling blights and fusarium wilt will be discussed in this article and fusarium head blight will be discussed in the January article.
Fusarium root rots and seedling blights
Management of these diseases needs to take place prior to seeding and seedling emergence. The main recommended strategies are to follow good agronomic practices, use disease-free seed and treat seed with a registered seed treatment. Good agronomy is very important to reduce the risk of seedling diseases, since a stressed or slow-growing plant is going to be more susceptible to infection than a healthy, vigorous plant. Using high-quality and disease-free seed, and seeding at the optimal seeding depth and into warm, well drained soil, while minimizing seed damage during seeding will help to maximize seedling health and stand establishment.
Fusarium species can cause root rot and seedling blight diseases in most of the cereal, oilseed and pulse crops that we grow in Saskatchewan. However, root rots in these crops can also be caused by other pathogens including Rhizoctonia species, Pythium species and Aphanomyces eutieches (pulse crops). This group of pathogens is often referred to as the root rot complex; it is common to have more than one species present within a field or even within a single infected plant. Depending on the environmental conditions, one pathogen may be more prevalent due to differences in optimal conditions for the different root rot and seedling blight pathogens. Infection by Fusarium species is favoured under wet conditions and a wide range of temperatures.
Seed treatments are a valuable tool that can help to protect seedlings from diseases caused by Fusarium species. The decision to use a seed treatment should be based on the level of seedling infection, field history, seed quality information and the environmental conditions at seeding. Fungicide seed treatments can protect seeds and developing seedlings from the infection by both seed-borne and soil-borne organisms, as well as protect seedlings that are germinating in less than optimal conditions. Seed treatments will only provide control early in the season while the seed treatment is active and will not protect from later infections. Fungicide seed treatment can be beneficial in poor seed lots, but it is important to remember that seed treatments provide protection but will not rescue dead or damaged seed.
To help with the decision of whether or not to use a seed lot or to apply a seed treatment, the seed should be tested for germination and disease levels at a seed testing lab. Information on seed treatments, including the crops they are registered for and the pathogens they are effective against, can be found in the Guide to Crop Protection.
For cereal seed, it may be tempting to estimate Fusarium infection levels based on fusarium damaged kernels (FDK). This is not recommended and will likely result in an underestimation of Fusarium infection levels. Later infection of cereal heads may result in infected kernels without any physical damage to the seed and, as a result, later infection will not be represented by FDK levels. This indicates the importance of a disease test when deciding whether or not to use a seed lot. Information on recommendations for using fusarium-infected seed can be found on our Fusarium Head Blight page.
Fusarium wilt is known to occur in canola, mustard, flax and pea. Fusarium wilt is primarily caused by F. oxysporum, with F. avenaceum being a potential causal agent in canola and mustard. Compared to the other diseases caused by Fusarium species, there is limited information on fusarium wilt and its disease cycle. This disease is often associated with wilting symptoms, foliar discolouration and stunted growth. In flax, early infection may result in the death of seedling before or shortly after emergence.
Fusarium wilt is best managed through the use of resistance varieties. A diverse crop rotation with cereals may also be beneficial to reduce pathogen levels in the field.