Blog: Agronomy & Extension

Flax Diseases: A 2025 Overview

Coles Ag on October 1, 2025

Crop disease surveys are performed for several reasons. MCA looks to this project as being useful for extension purposes, as well as providing data to support research priorities in Manitoba.

The disease survey is conducted each August – September, depending on maturity. Eight to ten fields are scouted, primarily for pasmo incidence and severity, but also for Alternaria, aster yellows, fusarium, powdery mildew, rust and sclerotinia. These are all uncommon in Manitoba, and considering only 100 plants are being rated for the above diseases, it is rare to have incidence of anything other than pasmo and aster yellows reported. The last time aster yellows were reported in the flax disease survey was 2023, when incidence was relatively high in a small number of tested fields. Since then, there has been low incidence but it can still be found on the odd plant. Mainly because it is easy to identify and the infected plants stick out among “normal” plants.

In the 2025 flax disease survey, 10 fields were surveilled, which equivalates to one field for every approximately 2,800 acres of flax. For larger acreage commodities, there would typically be one field surveyed for every 5,000 acres in a Rural Municipality.

Due to dry weather conditions in 2025, disease incidence was very low to zero for every pathogen looked at. In fact, only three of the 10 fields scouted showed signs of pasmo in the 100 sampled plants. In those three fields, incidence was 10%, 14% and 2%, which is to say that only 10, 14 and two plants in the 100 plants sampled in each field had pasmo present. Severity refers to the total area on the plant that is infected with pasmo, expressed as a percentage. In the three fields with pasmo present, severity ranged from 1% to 30% on the plants affected. Overall, incidence and severity were both lower than normal; likely an effect of dry conditions early in the season. Pasmo, like several other pathogens, spreads rapidly in high temperature, damp conditions.

Pasmo is a fungus that attacks above-ground parts of flax and overwinters in the soil on infected flax stubble. Flax is most susceptible to pasmo in the ripening stage. Pasmo can cause defoliation, premature ripening and can weaken the infected pedicels resulting in heavy boll-drop by rain and wind. Depending on the earliness and severity of the infection, pasmo reduces the yield as well as the quality of seed and fibre. Most commercial varieties lack resistance to this fungus. Pasmo is characterized by circular and brown lesions on the leaves and by brown to black infected bands that alternate with green and healthy bands on the stem. The best control is achieved by early seeding at the recommended rates to avoid high moisture conditions in the fall, using clean seed, treating seed with a fungicide, controlling weeds, and following a rotation of at least three years between flax crops.

Pasmo-infected flax stalk.

Aster Yellows is a very random disease, infecting plants that have been fed on by aster leafhoppers that are specifically infected by the aster yellow phytoplasma. Aster yellows affect many different crops, with canola being the most economically significant in Manitoba. Aster leafhoppers are sucking insects that transmit aster yellow phytoplasma directly into the phloem of a healthy flax plant, thereby infecting that plant. Damage is evident in misshapen or unproductive bolls.

Flax aster yellows.

In preparation for the 2026 flax crop, farmers will want to follow some key tips for disease prevention:

  • Use clean seed
  • Diversify crop rotation
  • Use seed treatments
  • Keep fields weed-free

For more information on:

Emergency Use Registration: Avian Control For Use as Blackbird Deterrent in Sunflower

Morgan Cott on September 2, 2025

Manitoba Agriculture, Manitoba Crop Alliance and Avian Enterprises® are pleased to announce that Avian Control® Bird Repellent has been approved for use to deter blackbird feeding in sunflowers in Canada.

The need for a product used to deter blackbirds from feeding on sunflower crops has been identified as a need in Manitoba due to the significant losses recorded by farmers. Sunflower seeds are particularly vulnerable to predation by blackbirds due to the high nutritional value and easy accessibility.

After nesting, blackbirds form large flocks and begin feeding in grain fields nearby. Feeding begins in sunflowers soon after petal drop and most of the damage occurs during the following three weeks. Peak concentrations of blackbirds occur in mid-September, coinciding with the crop reaching physiological maturity.

Farmers have alternative options to applying a deterrent, like Avian Control ®. Alternate practices include planting far away from roosting areas, like cattail marshes and woodlots, or planting at the same time as neighbours to spread feeding damage over more acres during seed maturity. Insect and weed control will reduce the pre-season food source for blackbirds before the crop reaches a susceptible stage for feeding. Delaying cultivation or harrowing of crop stubble in neighbouring fields increases alternate feeding area for hungry birdlife. Desiccation to advance harvest and getting the crop harvested as soon as possible also reduces exposure.

Another effective management practice is to control cattail production areas, which reduces nesting sites for blackbirds. Managing cattails does take a significant amount of time and should be a collective project for local farmers to deter blackbirds from roosting in a large geographic area, to be effective. Scare methods, like bangers or sound devices, to frighten birds away from the area have achieved different levels of success, but birds tend to start tolerating certain tactics after a period and return to host crops.

How does Avian Control work?

The active ingredient in Avian Control is methyl anthranilate. This active irritates a bird’s trigeminal nerves, which are sensitive to smell and taste, and causes a temporary, non-harmful, but unpleasant sensation to the affected bird’s eyes, beak and throat. The first birds to visit the treated field associate this discomfort with that location and communicate this information to the rest of their flock, instructing them not to feed there.

Methyl anthranilate is a food-grade additive, naturally derived from Concord grapes. It is a non-toxic, non-lethal and humane repellent, recognized as safe for humans and other animals. Due to the nature of this product, it does breakdown on surfaces much quicker than pesticides and will likely need to be applied more than once for continued efficacy.

Crop Specific Instructions for Avian Control

  • Apply Avian Control to ripening sunflowers before damage by blackbirds begins to occur
  • Do not apply when crop is wet or rain is expected
  • Repeat treatment at 6 – 8 day intervals if significant crop damage from blackbirds begins to occur
  • Avian Control may be applied up to the day of harvest
  • Use with non-ionic surfactant at 0.06 – 0.25% v/v
  • DO NOT exceed 5 applications per year

For full Avian Control label on sunflowers, click here.

Please contact Avian Enterprises for more information on Avian Control and product orders:

Jon Stone
President, Avian Enterprises
1 (888) 707-4355
https://aviancontrolinc.com/products/avian-control/ 

Sunflower Survey 2025

Morgan Cott on June 30, 2025

In partnership with National Sunflower Association, every other year Manitoba Crop Alliance and Agriculture and Agri-Food Canada participate in a Sunflower Survey. The collaboration includes several states in the U.S. where sunflowers are grown, so participation in Manitoba is beneficial to the dataset. 

Some of the factors included in the survey are:

  • Field analysis: population, head size, seed fill, yield calculations
  • Weed pressure: weed prevalence
  • Insect Pressure: insect incidence and damage severity
  • Disease Pressure: disease incidence and severity
  • Blackbird Presence: percent blackbird damage estimate
  • Other Limiting Factors: environmental, uneven growth, herbicide damage, plant spacing, and more.

Sunflower diseases make up the bulk of the survey since, agronomically, they are the greatest concern to the crop. The requirements are to assess ten diseases in incidence (number of plants) and severity (% damage to affected plants) of sunflower rust, specifically. 

MCA is funding the participation of AAFC’s oilseed and Pulse Crop Pathologist, Dr. Ahmed Abdelmagid, on this project. Dr. Abdelmagid participates in the field survey and also analyzes stalk disease samples from each field to determine various strains present in Manitoba sunflowers.

This survey is important in a “minor” crop for Manitoba in order to help farmers understand the specific pressures they are working against. Together with AAFC and Manitoba Agriculture, we can use the survey data to create extension for farmers and agronomists that will strengthen the crop’s success on the Prairies. Paired with the U.S. data, we are able to make fair comparisons and and identify Manitoba’s successes and areas that need improvement. This leads to more directed research projects in the future and extension work with farmers on specific topics.

The 2025 Sunflower Survey will begin in late August. MCA is looking for several sunflower fields across the province to include. Please contact Morgan Cott at morgan@mbcropalliance.ca or 204-750-2489 if you or someone you know would like to be contact this summer to be involved in the survey. This tends to be a quick visit to collect data on all points mentioned above and the farmer will be kept informed throughout the short process.

Managing Bt Resistant European Corn Borer

Morgan Cott on April 3, 2025

European corn borer larvae

European corn borer (ECB) has long been a pest of Manitoba corn crops, but it is not only a nuisance to corn – crops like potatoes and hemp are affected as well. The larval stages of the insect are most economically significant due to their tunneling (boring) capabilities which disrupt the flow of nutrients and water, and the integrity of the stalk. Yields can certainly be affected by ECB presence, around 3-5% yield decrease being possible in standard incidences (5-9 bu/acre in a 175 bushel crop) and increasing in more significant infestations.

Until Bt (Bacillus thuringiensis) traits were introduced to corn in Canada and the United States in 1996, corn farmers would rely on cultural practices and insecticidal control when economic thresholds were met. Cultural practices include crop rotation, residue management – destroying stalks where larvae overwinter successfully, and tillage that buries residue deep enough that larvae cannot survive. Insecticidal control is difficult due to timing between egg hatch and the boring phase. Diligent scouting to monitor egg hatch progress is extremely important to time when most eggs have hatched and larvae have not begun entering the stalk tissue yet. Once larvae reach the 3rd instar stage (7-10 days following hatch), they begin to bore into the stalk, and rarely resurface, rendering insecticide applications ineffective.

The introduction of Bt hybrids allowed farmers to not rely so heavily on residue management and insecticide application. Farmers were able to choose a fitting Bt-traited hybrid for their farm and had to match that hybrid with a refuge, or non-Bt, hybrid in 20% (or more) of the field in a block, strip or perimeter method. In more recent years, seed companies have come out with a 5% refuge system, called refuge-in-a-bag, making the system a lot easier for farmers to adhere to.

Unfortunately, non-compliance with pesticide requirements weakens the system and creates an opening for resistance. While the Bt trait is very strong, there is a small portion of the ECB population that are naturally resistant to the trait that controls the rest of the population. If farmers were to plant 100% Bt hybrids, those resistant populations would thrive and reproduce, eventually being the only population remaining.

BT CORN 101 - Manage Resistance Now
BT CORN 101 – Manage Resistance Now
HOW RESISTANCE DEVELOPS - Manage Resistance Now
HOW RESISTANCE DEVELOPS – Manage Resistance Now
HOW TO MANAGE INSECT RESISTANCE IN YOUR BT CORN - Manage Resistance Now
HOW TO MANAGE INSECT RESISTANCE IN YOUR BT CORN – Manage Resistance Now
MANAGING INSECT RESISTANCE VIA REFUGE PLANTING - Manage Resistance Now
MANAGING INSECT RESISTANCE VIA REFUGE PLANTING – Manage Resistance Now

Managing resistance on-farm can feel daunting, but it is very straightforward. Best management practices to avoid European corn borer resistance to Bt traits include:

  • Scout for pests and damage
  • Rotate crops and traits
  • Plant a refuge
  • Manage with insecticides
  • Keep accurate records

If there is a suspected case of ECB resistance in a Bt corn field, the following should be monitored to identify the issue:

  • Scout – both Bt and non-Bt corn for damage
  • Field Investigation – verify trait(s) present, evaluate presence and damage caused by ECB, rule out external reasons for damage
  • Contact Seed Company – seed company representative must be informed if ECB damage is found in Bt-traited crop, where it is determined the pest is resistant
  • Best Management Practices
  • Collect Insects – the seed company will likely arrange for live ECB samples to be taken from affected field(s)
  • Resistance Mitigation – if resistance is confirmed, farmer will be notified of next steps (see Managing Resistance in your Bt Corn)

Resources have been developed to help farmers, agronomists and seed companies identify issues in Bt corn fields as resistance incidents have occurred in Canada. Canadian Corn Pest Coalition is a group of industry members that work to develop extension and support to Canadian farmers and industry as insect issues arise. The CCPC has extensive resources available on their website on this specific topic, as well as other insect pests in corn. It is important for members of the corn industry to be educated on pest pressures that could turn into serious resistance incidents. Together we can improve the longevity of Bt traits so farmers can continue to use them safely and effectively.

Act Now ECB Campaign – Canadian Corn Pest Coalition

Contact your provincial Extension Entomologist (John Gavloski, Manitoba Agriculture) or MCA’s Agronomy Extension Specialist – Special Crops (Morgan Cott) for further information on European corn borer resistance, what to do to avoid it, and how to determine if you see possible resistance.

New, promising flax varieties for Manitobans

Morgan Cott on March 4, 2025

Manitoba flax farmers (and upcoming flax farmers) will soon have full access to a new flax variety, CDC Esme. As of spring 2025, CDC Esme is available to seed producers across the province, as long as they have been able to access it from seed dealers. 

As stated in the Secan Technical Bulletin for the variety, CDC Esme is a large seeded, high yielding brown seeded flax variety with good lodging resistance and late maturity. Esme proves to be a strong yielder in MCVET trials across several site years, with oil content similar to check varieties. Statistics show an average of 2 cm shorter than CDC Glas, which is a beneficial trend in Manitoba, where farmers are trying to reduce flax straw and residue. 

Dr. Bunyamin Tar’an and his team at the Crop Development Centre in Saskatoon developed CDC Esme and have several more flax lines that have strong potential for registration on the Canadian Prairies. Most recently, Tar’an had an experimental flax line that has been recommended for registration via Canadian Food Inspection Agency. This line, currently named FP 2608, will undergo a registration process and could likely be available for seed production in the next two years. 

FP 2608 has been a promising yielder in the Flax Co-op trials performed in Manitoba and is a consistently strong yielder. It appears to be quite tolerant of pasmo infections in past reports, and oil content and yield has been ranked very high amongst other varieties and lines. Tar’an has noted that FP 2608 had considerably strong performance in the more northern Co-op trials in Manitoba, which perhaps displays its ability to thrive in less diverse rotations.

MCA is very proud of our relationship with Dr. Tar’an and are very excited about his future work in flax breeding. Some new work that he is working on includes “Accelerated Breeding Strategy for Flax Improvement” which looks at developing inbred populations in a shorter term than is current reality. This would mean that future varieties could potentially be brought to the market more quickly and readily than they have in the past. Another highlight of Dr. Tar’an’s work is that he is committed to reducing straw content while increasing seed production in future varieties. He has had to delve back in time and use flax’s wild ancestor, Linum bienne. By using historial genetics, Tar’an can benefit by breeding their old, shorter varieties with new modern varieties that have bushier plant structure, therefore, higher yielding qualities and improved harvestability.

Flax can have a strong future on the Prairies and Manitoba Crop Alliance is supporting that possibility for our farmers. It is a crop that requires patience and consideration, which we believe Manitoba farmers are great at and can help us solidify the flax industry on the Prairies. Discussions with farmers that have been growing flax successfully for several years tell us that it is one of the top most profitable crops on their farms because they are willing to put an extra effort in to the crop. In this case, it doesn’t mean inputs, directly. These farmers are treating flax like the special crop that it is; slowing down and using precision and sustainable practices to support the germination of a tiny seed into a beautiful and profitable crop.

Please contact the MCA’s Agronomy Extension Specialist for Special Crops if you are considering growing flax or currently work with flax and are interested in more agronomic information. 

Lambda-cyhalothrin update – March 2025

Morgan Cott on March 3, 2025

Lambda-cyhalothrin insecticide – a fast-acting stomach and contact insecticide that provides control of several foliar pest in various crops. It is a synthetic pyrethroid and group 3A insecticide.

In April 2021, the PMRA published and announced that lambda-cyhalothrin and all associated end-use products underwent a re-evaluation decision. As is well-known, the final decision at the time was to cease all sales of lambda-cyhalothrin products in Canada. Another re-evaluation in 2023 determined that the insecticide could only be used on crops not being used, in any form, for human or animal feed consumption.

Health Canada’s PMRA made the most recent update on February 3, 2025, which appears to be a generous re-evaluation of lambda-cyhalothrin to reinstate certain feed uses of the product. Several livestock feed uses have been re-instated, which are generally grain, meal and by products. Feed uses not re-instated are several silages, stover, forage, hay and straw products, plus some others. The full list can be found in the latest publication here.

Unfortunately for confection sunflower farmers, lambda-cyhalothrin has not been re-instated for the control of lygus bugs. Products for direct human consumption do not appear to have potential for reinstatement on the insecticide’s label. Oilseed sunflowers are not affected as readily by lygus bug damage because their impact to the oil content of the seed is not as detrimental as quality is to confection sunflowers.

Lygus nymph and adult.

Manitoba Crop Alliance has worked together with Manitoba Agriculture and FMC Canada in 2023 and 2024 to ensure confection farmers have Carbine (R) insecticide available for use on confection sunflowers to control lygus bug. This occurred via a 12-month Emergency Use Registration. The current EUR is valid until July 2025, so the three groups are working on another 12-month EUR and FMC Canada is making efforts toward a permanent registration of the product via the PMRA.

Carbine (R) Insecticide is a group 29 insecticide that is an “ideal partner in integrated pest management (IPM) – has minimal impact on beneficial insects and pollinators when applied according to the label,” and “has no known cross-resistance to other active ingredients,”  according to FMC Canada.

Additional Information: Lygus bugs are a major pest of sunflowers because they can cause kernel brown spot, which is a small brown to black spot on the blunt end of the seed. The industry standard allows for a maximum of 0.5% kernel brown spot in confection sunflowers marketed for human consumption. The economic threshold for lygus but in confection sunflowers is one bug per 9 sunflower heads. Each adult lygus bug is capable of damaging as many as 35 seeds per head.

Control of lygus bug is very limited and insecticides (lambda-cyhalothrin) are the most effective option in sunflowers. Cultural options are even more limited. When planning sunflower acres, it is recommended to avoid planting near adjacent canola fields since they are both favourable host crops to lygus bug. Canola does have limited insecticide options available for lygus bug, so in canola-lygus infestation and insecticide application scenarios, those neighbouring lygus bugs will attempt to move out and find another host crop, like sunflowers.

Some environmental and biological control factors from Manitoba Agriculture include:

  • Weather: Heavy rainfall may reduce levels of early-instar nymphs of lygus bugs. A study in alfalfa found heavy rainfall reduced first generation nymphs of Lygus lineolaris by 50%.
  • Biological Control: Nymphs of Lygus bugs may be killed by parasitic wasps in the genus Peristenus (Hymenoptera: Braconidae); with parasitism being common in weedy alfalfa stands or uncultivated weedy sites but very low in canola. Damsel bugs, assassin bugs, lacewing larvae, big-eyed bugs and crab spiders can prey on lygus bugs. Protecting these natural enemies by avoiding unnecessary insecticide applications may also help to reduce the impact of lygus bugs.

Research on the Farm: Flax Plant Population Trials Summarized (2022 – 2024)

Morgan Cott on February 5, 2025

Manitoba Crop Alliance’s Research on the Farm program looks at common agronomic, crop-specific concerns on field-scale, replicated trials in commercial fields. 2024 saw the flax plant population trials completed with 19 site-years of data.

The objective of this specific trial was to quantify the agronomic and economic impacts of various plant populations in flax production in Manitoba. A lack of genetic improvements in flax varieties in recent years raises the question of whether farmers can either increase or decrease their planting populations with improvements in quality and/or yield. Farmers took to the field to make that final decision.

Figure 1: MCA Research on the Farm: Flax Plant Population Trial locations from 2022 – 2024

Tone Ag Consulting performs MCA’s Research on the Farm trials in all 6 of our crop-types. In this specific trial type, they are helping the farmer with planting and harvest of the plots, plus taking some key information during the growing season. This includes soil sampling in the spring followed by growth stage notes and precipitation data during the season.

Table 1: Three-year summary of flax plant population trial for 19 site years. Zero of the 19 site-years contributed statistically significant yield differences which would provide profit for the farm, based only on seed prices.

When looking at this full data set, it doesn’t necessarily give a farmer the details they are looking for. At the end of the day, they want to know the ROI for each treatment, which includes spring seed costs and flax prices off the combine. Simply stated, if the “high” planting rate outyielded the “low” and “check” planting rates, it may have only been marginally, therefore the higher seed cost of planting at a high rate was likely not the economical choice.

Table 2: Three-year economic summary of flax plant population trial for 19 site years. Net profit per acre was calculated using estimated seed cost in spring 2024 and contract pricing in fall 2024.

According to this small data set in Manitoba, farmers appear to seed on the heavier side of what is necessary for their management practices. Experience determines what works best on any given field, in addition to being mindful when it comes to general flax management. It is a special crop and requires a certain amount of care and precision to achieve profitable yield, but it absolutely is realistic in Manitoba.

Planting populations are reasonably simple to set up on-farm and MCA recommends farmers make the effort to periodically do this same testing. 2022 and 2023 were dry years in areas of Manitoba and 2024 had much more precipitation. It is important to continue to collect data in years of varying precipitation to determine planting rates that work better on your farm in all environments.

Tone Ag Consulting carries out MCA’s ROTF trials in all six of our crop-types. They assist the farmer with plot planting and harvesting, then capture key information throughout the growing season. This includes soil sampling in the spring, followed by growth stage notes and precipitation data during the growing season.

Phantom Yield Loss

Morgan Cott on December 4, 2024

Phantom Yield Loss – A phenomenon related to yield loss with little to no explanation why, aside from letting the grain dry naturally, prior to harvest.

Farmers who have to pause harvest, after opening a field, do record decreased yields when they return to continue combining. A few things come to mind when considering what the losses are a result of. Could it be ear drop? Or lodging is a common occurrence, the longer the crop stands in the field and is exposed to wildlife, snow, or wind. Another consideration is that as the grain dries in the field, it does loosen from the cob and can fall to the ground when disturbed. Low moisture grain is also susceptible to cracking or breakage at harvest, resulting in losses.

Speaking to Manitoba farmers, it appears that phantom yield loss is caused by none of the above. All the obvious culprits (ear drop, lodging, kernel shattering) can be accounted for and there are yield penalties beyond these factors, still.

Purdue University performed research on this topic in the early 90’s – before the phenomenon even had a name. The project looked at three hybrids over the course of four years and measured kernel dry weight until physiological maturity and again after maturity until they were ready for harvest. The study found that kernel dry weight increased until reaching physiological maturity, which occurred at about 25% moisture for all three hybrids. Following maturity, during the dry down period, kernel dry weight decreased by an average of 1.1% for every one per cent decrease in grain moisture content. This is an average across three hybrids in the four years of study. There was one year where none of the hybrids experienced any significant changes in kernel dry weight. The “bottom line” of the project is that there is a potential average 1% yield loss per point decrease in grain moisture content. That is to say that if a field is left to naturally dry down 5 moisture points following physiological maturity, there is a potential +/- 5% yield loss.

So, how does this occur and why? We now know that this is part of the drying process, but why is so much dry matter being lost as the grain dries a small amount?

Quite simply, physiological maturity occurs and each kernel develops a “black layer” where it connects to the cob and had gained access to nutrients and water throughout the season. Once black layer is achieved, grain continues to use up the starch and sugar reserves, which decreases kernel dry weight and quality. Grain is typically alive following black layer until it has dried down to around 15% moisture, so it is not surprising that this process results in loss of dry matter.

Unfortunately, it is impossible to predict losses as a result of this phenomenon. Factors affecting losses include harvest timing, soil type, hybrid/genetics, and of course, environmental factors. That being said, it is difficult to predict what genetics are most susceptible to respiration losses following black layer, so that isn’t something that would normally factor into hybrid choices. Earlier harvest timing is the best way to avoid significant losses, in this case. As mentioned, losses are impossible to predict, but measuring drying costs against the alternate potential yield loss is key in finding the best management practice for your farm.

Holcus Spot

Morgan Cott on November 8, 2024

What is holcus spot?

Holcus spot on corn leaf

Holcus spot on corn leaf

A bacterial leaf disease affecting mainly corn crops, though it can overwinter in both monocot and dicot species. Holcus spot begins as a water-soaked spot on lower leaves and develops into small (1/4 to 1/8 “ in diameter), circular to elliptical, white to tan lesions. Lesions commonly develop a brown margin and sometimes a light halo is visible around the lesions. In severe infections, holcus spot can cause significant lesions on plant leaves, though it is more common to have minor spotting, covering less than 5% of a single leaf’s surface.

Conditions for Development

Holcus infections follow typical Manitoba spring conditions. This includes high winds and heavy rains, followed by extended moisture and warm summer temperatures (24C – 30C). The bacteria is interesting because it infects the leaf via wounding, but it doesn’t need a wound for development. The pathogen also does not spread from an infected leaf to a healthy leaf, as in many other leaf diseases. 

Disease Management

The holcus spot pathogen lives and overwinters on crop residues. Best management practices to gain control of the pathogen are crop rotation and tillage. As a bacterial pathogen, fungicides will have no effect on the disease.

Fortunately, holcus spot affects a very small area of each infected leaf and photosynthesis of the green leaf material is still very effective. This is a concern in more disruptive leaf diseases or killing frosts that affect large areas of each leaf and photosynthesis is allocated to a small area or none at all. As a result of the small area affected, yield is not penalized and holcus spot is more of an aesthetic disease than a concern for farmers. 

Don’t get confused…

Holcus spot infections are relatively uncommon. It is easy to see them and be unsure of what it means because lesions are most often minute and don’t draw attention. 

In the rare occasion that the disease does grab attention, lesions can be confused with drift of a contact herbicide, like diquat (image below), or fertilizer burn. Key tips to determine if it could be fertilizer injury would be to ask the farmer or applicator if anything was applied recently or in the sprayer tank. If there is a possibility of herbicide drift, there will be a clear pattern in the area that would have gotten “hit”. The lesions would likely be worst along the outer rows and lessen the further into the field you look.  Early in the season, injury would not grow with the plant and new leaves would be injury-free. 

Diquat drift on corn leaf

Diquat drift on corn leaf

Ear Moulds in Corn

mca2022dev on July 29, 2024

Not every growing season brings a high risk of ear moulds in corn, but it certainly can be an issue every once in a while. It is crucial to scout for ear moulds of all kinds every fall to determine risk and harvest order. Upright ears, tight husks, high humidity, precipitation, insect feeding and very slow drying conditions are all factors that contribute to mould development and spread. Severity and mould types will vary, so scouting is recommended, regardless of environmental potential.

There are several types of mould that can grow on corn, and three that are typical in Manitoba:

  1. Gibberella Ear Rot
  2. Fusarium Ear Rot
  3. Diplodia Ear Rot

Gibberella ear rot

Gibberella ear rot occurs via an infection of the fungus Gibberella zeae, the same fungus that causes Fusarium head blight in cereals and overwinters on corn and wheat residues. Infection occurs when spores are splashed by rain or carried by wind, and settle on corn silks or the base of the ear. Silks are vulnerable to infection for the first week after emerging, during the pollination period of corn. Further in the season, during grain fill, ear rot is known to start becoming visible and worsening when conditions are cool and wet at this time. 

Gibberella ear rot is characterized by a pink or red colouring of the mould, most commonly at the ear tip. High amounts of mould can make the ear bond to the husk and become hard to pull away from the ear. It can produce the toxins Deoxynivalenol (vomitoxin or DON), Zearalenone (ZEN) and T-2 toxin.

Fusarium ear rot

Fusarium ear rot infections peak when areas are highly affected by grain-feeding insects, such as European corn borer or corn earworm, coupled with warm and wet conditions prior to harvest. Identification is different from Gibberella ear rot in that it occurs in individual kernels or in patches on the ear, based on insect feeding. Infected kernels may appear white to pink-coloured, which is the visible fungal growth. Some affected kernels may be a tan to brown colour. In the event that the pathogen is growing underneath the seed coat, the kernels may show a white starburst or streaking pattern.

There are three common fungi species that cause Fusarium ear rot, but only Fusarium verticillioides and Fusarium proliferatum produce fumonisins, which can be toxic to livestock. If infections are visible, species testing needs to be performed in a laboratory and Fusarium contamination can be determined at that point.

Diplodia ear rot

Diplodia ear rot is less common in Manitoba. It may be visible in continuous corn fields or fields with short rotation and that are managed by reduced tillage practices. Infected ears will have mould growth starting at the base of the ear that will begin as a white to gray colour and will be growing both between and on the kernels. With further maturation of the fungus, the mould could turn to a darker gray to gray-brown colour.

Infection occurs via spores being splashed onto developing ears. Spores infect the ear shank during silking, then move into the ear shank to the cob and can progress outward via the kernels, then becoming visible in the mouldy appearance of the ear. Due to infection timing, corn ears are most susceptible to Diplodia infection around silking and the threat becomes less as the crop matures.

Corn yield can be affected simply by any three of these fungus-related moulds taking over several kernels and spreading throughout a cob. Affected kernels likely disintegrate or pass right through the combine at harvest. Kernels can be successfully harvested but cracked or damaged. Finally, harvest may be a total success, only to learn there are high mycotoxin levels (most concerning being vomitoxin or DON – Deoxynivalenol) in the grain, deeming it unsaleable. Husky Grain states that they buy grain with only a maximum level of 1 ppm of vomitoxin.

If a producer is unsure of their risk this year, the first step will be to scout their corn and identify any moulds occurring. Vomitoxins are primarily produced by Gibberella or Fusarium ear moulds, so if either of these are identified or suspected, the risk is increased. Mycotoxins cannot be identified visually, so a representative sample needs to be sent for analysis, if suspected. Samples in Manitoba can be sent locally to Central Testing Laboratory Ltd. in Winnipeg.

Gibberella Ear Mould

Figure 1. Gibberella Ear Mould

Fusarium Ear Rot

Figure 2. Fusarium Ear Rot

Ear Moulds OMAFRA

Figure 3. (L to R) Gibberella, Penicillium/Trichoderma and Diplodia Ear Rot. Photo Credit: Ontario Ministry of Agriculture, Food and Rural Affairs.

Fields with high incidence of moulds of any kind should be harvested first, where possible. Affected kernels should be harvested and dried as soon as possible to minimize spread and further degradation. High temperature drying (anything above 30oC) will stop mould growth and mycotoxin production but will not reduce mycotoxins already present. See OMAFRA’s article on Harvest Tips for Mouldy Corn for more information that may benefit corn harvest this year.

Corn Ear Mould Identification Article – Ontario Ministry of Agriculture, Food and Rural Affairs

Field Drydown

We are often quite fortunate with drying weather for natural grain dry down in the field. Manitoba Agriculture has an article indicating speed of natural drying in the field, in October and November. It also touches on artificial low temperature versus high temperature drying, estimating drying costs, in-storage cooling and much more. It is a great reference to bookmark.

More great articles on field dry down, natural air drying and storage of grain corn:

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