Crop Report – Week of June 26th, 2023

Tar spot injury on corn

Corn Tar Spot Watch Begins!

Tar spot has now been established in the midwestern US for almost a decade and is an annual concern in many Midwestern states like Illinois, Indiana, Iowa, Michigan, and Wisconsin. While tar spot was not as yield-limiting in these areas in 2022, it continued to expand its range across the corn belt, as far west as Kansas and South Dakota, and as far east as New York, Maryland, and Pennsylvania. Ontario joined the tar spot group in 2020 and is well established in the southwest and mid-central regions of the province especially along the north shore of Lake Erie (Essex through Haldimand-Norfolk). As with the US, 2022 was much different than 2021 and shows the importance of environmental conditions on tar spot disease development. Remember, this holds true for any disease!

If 2023 goes the way of the past 2 years, tar spot will most likely be confirmed in southwest Ontario during the first 2 weeks of July. Farmers, consultants, agribusiness, and others are encouraged to scout for the disease and be aware of reports of tar spot in the province. As of June 28, tar spot has been detected in Iowa, Missouri and Kansas. The drought conditions in states such as Michigan, Indiana, Illinois and Wisconsin which have potential to impact Ontario’s risk to the disease has been very dry but the most recent rain in these areas will help the crops but likely tar spot as well. The fungus which causes tar spot favours dry and wet environmental cycles like those we have had in the southwest the past few weeks.

What can you do:

  • Be alert to tar spot movement in Ontario and your area by tracking the disease in real-time on the corn ipmPIPE website at
  • Talk to your local agronomist/consultant, retailer, neighbours and OMAFRA specialists
  • Scout fields for the presence of tar spot symptoms (Figures 1 & 2)
  • If needed, a well-timed fungicide application has shown to provide good control of tar spot. There are many registered products available to farmers that have demonstrated good tar spot control.

Current Ontario and U.S. data indicates that fungicides applied between tasseling (VT) and silking (R1) provide optimum control of tar spot when the risk of infection is high. Fortunately, this is also the optimum application timing for other common leaf diseases like northern corn leaf blight and Giberella ear rot (DON).

Figure 1. Tar spot symptoms on leaf (closeup image)

Figure 1.Tar spot symptoms on leaf (closeup image)

Figure 2. Tar spot injury on corn

Figure 2.Tar spot injury on corn

There are many other corn diseases that are annually important and may require management, and the diseases that could potentially impact corn in 2023 will depend on environmental conditions at critical points in the growing season. Check out all of the corn disease resources available on the Crop Protection Network website ( as well as OMAFRA and be ready for whatever 2023 brings!

Now is Time to Check for Soybean Cyst Nematode (SCN)

Have you thought “I really don’t need to scout for SCN since I planted a resistant variety?” It is still important to evaluate cyst reproduction of your soybean variety because no two fields have the same mix of SCN types (what we used to call races but now referred to as SCN Types). Another reason to check is there are differences between the SCN resistant varieties. So, dig plants with a shovel and gently remove soil and examine roots for the presence of the small white to yellow cysts (Figure 3.). If you see no or very few cysts on the roots this is a good indication you have a low population or a highly resistant variety for your SCN population. But if you have 50 or more cysts, you are looking at a less tolerant variety or your SCN population is changing to SCN types that can reproduce on the PI88788 or Peking SCN resistance source depending on the variety. When it comes to SCN, remember SCN can steal yield every year. If anything, SCN is consistent and that is why it is called the “silent yield robber.”

Figure 3. Do not confuse SCN cysts with nodules

Figure 3.Do not confuse SCN cysts with nodules

Ontario Nematode Survey Can Help Track SCN!

One important way to get SCN populations down or delay shifts is to take a SCN soil test to monitor nematode populations. A new OMAFRA SCAP (Sustainability Canadian Agriculture Partnership) funded nematode survey targeting field crops (grain, oilseed, forage) and horticultural crop fields across the province can help. Nematodes present a significant and ongoing threat to plant health in Ontario and can result in significant economic and production losses. The primary survey objectives are to update provincial nematode distribution maps and establish baseline data for six different nematode species including soybean cyst nematode, root lesion or other nematode species. The survey results will support the enhancement of current nematode Best Management Practices for field and horticultural crop farmers, helping to improve the economic and sustainability of crop production in Ontario.

Participating in the survey is FREE and easy. Soil samples can be collected specifically for nematode testing such as SCN or alternatively, soil samples collected for soil fertility can be split, with subsamples submitted for nematode testing. If you would like more information on the Nematode Survey, please contact Albert Tenuta (, Katie Goldenhar ( or your local agronomist.

Weather Data – June 19 – 25, 2023

LocationYearHighest Temp (°C)Lowest Temp (°C)Rain (mm)Rain (mm) April 1stGDD 0C April 1stGDD 5C April 1stCHU May 1st
10 YR Avg. (2011-20)26.815.125.326211937651158
10 YR Avg. (2011-20)
10 YR Avg. (2011-20)26.413.828.125010906711052
10 YR Avg. (2011-20)26.213.919.424810916711047
10 YR Avg. (2011-20)25.112.325.4246963557919
Mount Forest202327.812.531.92111007618866
10 YR Avg. (2011-20)24.812.638.1248946548911
10 YR Avg. (2011-20)25.810.718.6234975569926
10 YR Avg. (2011-20)26.312.219.82361021616982
10 YR Avg. (2011-20)24.59.420.1200755433765
10 YR Avg. (2011-20)24.910.720.7218824479823
Thunder Bay202327.88.027.1157782450743
10 YR Avg. (2011-20)22.97.733.4212683350645
Fort Frances202333.011.520.8136961622973
10 YR Avg. (2011-20)
Report compiled by OMAFRA (Ontario Ministry of Agriculture, Food and Rural Affairs) using Environment Canada data. Data quality is verified but accuracy is not guaranteed. Report supplied for general information purposes only. An expanded report is available at

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