Fungicide Application: Is it worth it to spray?

Jun 28, 2023

Written By: Kerry Gerein

Fungicide Application: When should you spray?

Our team at Simplot Grower Solutions is here to help you find solutions and make decisions that fit your farm. One of the decisions that we are faced with every year – is a fungicide application going to be worthwhile? There are a variety of factors to consider when it comes to a fungicide application including circumstances such as a healthy, lush crop canopy with moisture and temperatures that are ideal for disease development. In this article, I will touch on some of the common diseases found in the North region of our trade area.
Cereals – Leaf Diseases & FHB
The development of leaf disease in cereals can impact the yield and quality of the crop, which is why it’s important have a chat with your Crop Advisor to ensure you stay on top of diseases as they may develop. The upper leaves in cereals contribute over 50% towards total yield for the plant. There are a wide range of leaf diseases that can affect cereals including: Powdery Mildew, Rusts, Septoria Leaf Blotch Complex, Spot Blotch, Tan Spot, and Net Blotch.
For Tan Spot to develop, the leaf must remain damp for a minimum of 6 hours for the fungus to infect the leaf tissue with ideal temperatures for disease development ranging from 20-28°C. Conidia are produced in old lesions on wet leaves in the spring and they become airborne as the leaves dry out. Ascospores and conidia are then carried by the wind to young plants. There can be several cycles of conidial production in a growing season. Symptoms will begin as small, dark brown to black spots on the lower leaves which will develop into tan, oval lesions with a dark spot in the center. Sometimes, there may also be a chlorotic halo that develops around the lesion. With favorable moisture and temperatures, these lesions will come together and form irregular blotches. At this point, it will look very similar to Stagnospora/Septoria leaf blotches; however, tan spot lesions do not develop pycnidia. Oat and barley are resistant, but not immune.

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Conditions favourable for disease development of Septoria Leaf Blotch Complex includes wet, windy weather with temperatures ranging from 15-27°C. The fungi can be both seed borne and can overwinter on crop residue. Spores are dispersed into the crop by rain splash. Septoria symptoms will first appear as yellow flecks on the lower leaves, especially leaves that are touching the soil. They develop into yellow, greyish/white, or brown blotches on all above ground plant parts. The lesions on the leaves will have a yellow border. Small, dark pycnidia will develop in the blotches and can result in shrivelled grain, leading to yield loss.


Fusarium head blight (FHB) is a fungal disease that can affect cereals including wheat, barley, and oats and causes a reduction in both yield and quality. The fungi will overwinter as spores or mycelium on seed and crop residue. At least 12 hours of high humidity or precipitation is required for spore germination and infection, temperatures favorable for infection range from 16-30 degrees celsius. These spores are then spread onto the crop from wind and rain splash when they come into contact with the open florets. In addition to the flowers, the fungus can also infect the plant through any type of wound including hail or insect damage. With warm and moist conditions, the pathogen can continue to spread to other kernels and produce high levels of mycotoxins. Symptoms of FHB will appear towards to end of July and into August when one or more spikelets will be bleached, and the base of the glumes will be brown with orange spores visible at the base. There could be some unfilled spikelets above the infection or there could be thin, chalky white, ‘tombstone’ kernels. During the fungal infection there can be toxic, secondary metabolites produced called mycotoxins. DON (deoxynivalenol) is the most common mycotoxin for FHB in Canada. Important management practices of FHB include crop rotation and stubble management, getting seed tested and sourcing new seed if necessary, variety selection, using a seed treatment, and applying a fungicide at proper timing. The most ideal timing is when flowers are first visible, which is a very narrow window. There are also FHB risk maps produced by SaskWheat based on the weather to assess the risk of disease development.

Some important management practices of cereal leaf diseases in general include ensuring that you have an adequate crop rotation, selecting resistant varieties, and applying a foliar fungicide at the appropriate time. The ideal timing for a foliar fungicide application is when the flag leaf is fully emerged, or the penultimate leaf with barley. However, the application can be done earlier if there is some disease developed early-on.
Canola - Sclerotinia Stem Rot
Sclerotinia stem rot is a disease caused by the fungus Sclerotinia sclerotiorum. The disease is heavily influenced by environmental conditions leading up to and during flowering of canola including temperatures, rainfall, and high humidity. If high inoculum levels are present and the crop canopy is dense, then sclerotinia can cause greater than 50% yield loss in canola.
Sclerotinia fungus spends most of its life cycle in the soils as a resting structure called sclerotium. These sclerotia are resilient to adverse conditions and can survive in the soil or plant tissue for 3 or more years. Sclerotia germination results in the formation of mushrooms called apothecia which usually takes 2-3 weeks and occurs under prolonged conditions of moisture at the soil surface (at least 10 days) and temperatures of 11-15°C. Apothecia function for about 5-10 days and during that time they can release up to 2 million tiny airborne spores, called ascospores. The majority of ascospores land within 100-150 m from their source, but spores that are picked up by wind currents can be dispersed for several km. Apothecia can begin to appear in June and can continue to develop until late September. However, the critical period when they cause the most damage is between early crop stages to full bloom. Ascospores use flower petals as a food source to establish an infection followed by infected petals dropping into the canopy and infecting leaf and stem tissue. Lesion development is favored by humid or moist conditions and temperatures between 20-25°C. Dry conditions can slow or stop infection and lesion development. Two to three weeks after infection, soft watery lesions or areas of very light brown discoloration become visible on the leaves, main stem, and branches. These lesions become bleached and infected plants will ripen prematurely, containing small, shriveled seeds. Sclerotia develop within or on diseased plant tissue and are returned to the soil with crop residue or are harvested with the seed.  
Disease management practices for Sclerotinia include a proper crop rotation to reduce sclerotia buildup in the soil, controlling susceptible weeds, removing crop residue if possible, choosing varieties with improved sclerotinia tolerance, and apply a foliar fungicide at proper timing. The most ideal timing for a foliar fungicide application is at about 30% flower, which is before too many of the flower petals have dropped. We can also assist you with Sclerotinia petal testing (a rapid DNA test for in crop sclerotinia stem rot risk) to help you make informed choices in your decision to spray. Other factors to also consider are the crop density, canola price, and the moisture conditions.
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Pulses – Leaf Diseases
There are many different diseases which can affect pulse crops including: Ascochyta, Anthracnose, Downy Mildew, Grey Mould, Powdery Mildew, and White Mould. Chocolate spot is a disease which is specific to faba beans.

Mycosphaerella Blight is a common disease in field peas. This is one of the Aschochyta diseases and it can result in yield losses as high as 80%. Cool, wet conditions are ideal for disease development with the fungi being seed, stubble, and soil borne, meaning it can survive for many years. When the seed is disease borne, the pathogen will grow from the seed into the stem. With stubble and soil borne, the infection will happen when seedlings come into contact with resting spores. The spores can be spread by both wind and rain splash. Lesions from Mycospaerella Blight can occur on the leaves, stems, flowers, and pods and symptoms begin as small, purple spots on the leaves with irregular margins. These lesions can enlarge and merge together, which will result in the leaf tissues drying up, flower petals may drop if they are infected. Lesions on the stem can lead to foot rot. Peas in the diseased pods may show no symptoms or they will be shrunken and discolored. Important management practices include using disease free seed, grow peas once over 4 years, use a seed treatment, and apply a foliar fungicide. The most ideal timing for a foliar fungicide application is at first flower, before the rows close over. This application can be done earlier if there is disease found.


For more information about diseases and fungicides, please reach out to your local Simplot Grower Solutions Crop Advisor, we are happy to assist you in any questions you may have in making your decision to spray.  

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