Be a fun guy and reduce your fun-gal infections through crop rotations

By Brett Rumpel, BSc. (Agr.), Plant Health Technician, and Alireza Akhavan, PhD, AAg, Provincial Specialist-Plant Disease, Crops and Irrigation Branch, Regina

Crop rotations are used by a large population of Saskatchewan producers. Crop rotations benefit soil nutrition due to the different nutrient requirements between crop species. Changing the crop species annually breaks up the natural cycle and reduces the incidence of weeds, insects and diseases that affect yield. This also means there’s less reliance on pesticides. Longer crop rotations are also an inexpensive management tool for plant pathogens.

In order for crop rotations to be a successful management tool against pathogens, it is important to know how long the pathogen can survive in the soil, if there are alternative host species that can be infected and how the pathogen can spread or get reintroduced.

Longer crop rotations are a proven successful tool to reduce the populations of pathogens in the soil. Diversity is key when developing a crop rotation. A longer rotation with a larger rest period of three or more years between each species is the most effective in reducing the pathogen load in the soil. Pathogens overwinter in the soil or in plant material as spores and quickly repopulate when they infect host plants; therefore, continuous cropping of host species allows for the pathogen population to accumulate.

An important factor to consider when making decisions on crop rotations is the alternative hosts of the pathogens. Choosing species that are closely related leads to a larger pathogen presence.

For example, Fusarium spp. (the casual pathogen of fusarium head blight) can infect wheat and barley plants, so it is beneficial to have a break between them in a rotation. Many diseases that are specific to only one type of crop; for example, staghead (also known as white rust) commonly only occurs in polish canola and brown mustard. Lengthening your rotations to have a three or more-year break can significantly decrease the risk of infection.

Many pathogens can remain dormant for long periods of time. However, the longer the rotation, the more resting spores deteriorate.

Some plants that are non-host crops also suppress pathogens. These plants suppress the pathogens by stimulating beneficial organisms in the soil or by producing toxic chemicals. Including legumes such as peas and beans in your rotation stimulates soil microbes and increases the soil nitrogen levels. Members of the mustard family produce isothiocyanates during decomposition which work as a biofumigant. While legumes and crucifers may be beneficial in reducing the population of a pathogen, they can also promote the growth of pathogens that can infect them if these crops are grown in a tight rotation.

Scouting for disease symptoms in your crops is always the first step in managing pathogens. Effective crop rotations are a beneficial tool in reducing your pathogen populations and preventing yield loss. The Saskatchewan Ministry of Agriculture performs a number of surveys that monitor crop pests, including diseases.