By Jonathan Zettler CPA, CMA, CCA-ON and Patrick Lynch CCA-ON

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Weather

Weather (PJL)

There are several ways to track weather. The most common way is Growing Degree Days. GDD is used to track things like insect development and crop stages. The GDD system is widely used. The other system is Crop Heat Units. In Ontario this was developed to track corn development. We called it corn heat Units. I am giving you both

GDD = ((Daily Maximum Temperature + Daily Minimum Temperature) / 2) – Base Temperature. This calculation is performed for each day.

To illustrate, consider a day with a maximum temperature of 25°C and a minimum temperature of 15°C, with a crop having a base temperature of 10°C. First, average the daily maximum and minimum temperatures: (25°C + 15°C) / 2 = 20°C. Next, subtract the base temperature from this average: 20°C – 10°C = 10 GDD. This value represents the accumulated GDD for that single day.

CHUs The formula used to calculate tor a day is:

(1.8 × (Minimum Temperature − 4.4) + 3.33 × (Maximum Temperature − 10) − 0.084 × (Maximum Temperature − 10) ²) ÷ 2.0

I will publish CHUs from the start of the year to current date until about 50% of the corn is in the ground. Then I will publish CHUs from that date until current date.

Crop Conditions

Crop conditions; not a lot done last week. Some drone application of N on wheat. One grower said he applied 310 lbs of product on 100 acres at a cost of $22 an acre. Across the province there is very little N on wheat. Estimates range from 5-25% of wheat acres having some N applied. This week will be busy with N on wheat, manure applications, maybe even planting some crops. Right now, consider planting soybeans or corn on whichever ground is fit. Forages more fields showing winterkill. Some years we lose more forages in April than in February. Thawing and freezing can cause heaving. And wet saturated soil is not good for the roots. Generally, there is a significant shortage of forages east of highway 400 and other areas in western Ontario.

Things to do This Week

1.     Check all wheat fields for winter kill. Everything that is alive now should make it. Consider broadcasting red clover into kill out spots in winter wheat.

2.    Check alfalfa fields for winterkill. Patch up any dead areas with an annual rye grass.

3.    Get ready to spray wheat. (See Issue 10 March 24, 2026, for weed control in winter wheat for various weeds).

4.    If you don’t have your pre-emerge herbicides on hand, get them now.

5.    If you are a no-tiller, make sure the openers are set to run deeper than the coulter. Or better yet, take them off and just run sharp openers.

6.    You can start to do burndown walks to determine weed spectrum. The product rate and selection are determined by the winter annuals and perennials that will already be emerged. The exception would be to glyphosate resistant annual broadleaves weeds that are just emerging.

7.    Update your YEN cropping information on the CropTrak portal.

Cereals

How many heads can I expect based on the number of tillers? (JZ)

Generally speaking once you get over 20-25 plants per foot of row the number of tillers reduces to 1-2 per plant.

A review on Winter Wheat Staging and Growth Stages

A common question is what stage is my wheat at?

When it comes to crop management, we can approximate crop stage to the following timings.

T0 – Herbicide timing – i.e., Zadok’s 22 – 2 tillers
T1 – Fungicide/growth regulator timing – Zadok’s 31 – 1st nodeT2 – Fungicide timing at flag leaf – Zadok’s 39 – Flag leaf fully emerged
T3 – Fusarium Head Blight timing – Zadok’s 61 – Flowers emerged on head

Wheat Response to Fungicide Use (JZ)

Winter Wheat Response to Fungicides (JZ)

Attached are the 2025 OCCC trial results for area 1 and area 2 when it comes to response to fungicide by wheat variety. I have also attached the disease ratings by variety for area 2.

Rules of Thumb for N on spring cereals (JZ)

For best yields you need to plant early, make sure you have enough nitrogen and sulphur, and apply fungicides twice. The further north your location, the higher the N rate you should consider. Consider credit off these values for manure and alfalfa. With growth regulators, consider stepping up your cereal management with the use of these tools, especially on oats.

If planting oats after corn vs soybeans, you will need higher amounts of nitrogen and sulphur due to residue tie-up.

Weed Control

Question - How long do I really have to wait between spraying glyphosate and working the ground? (PJL)Answer It is really species dependent. Perennials, and biennials will take longer to kill than annuals. Weeds with a bigger root system like Canada thistle, bindweed take longer. Individual species can be very sensitive to glyphosate. Winter wheat is very sensitive to glyphosate. If wheat is sprayed on a warm day, there will probably be enough glyphosate translocated in the first couple of hours to kill winter wheat. The other thing is that the longer you wait the better the kill on most weeds. So, in the case of perennials you need the full 48-72 hours or so for maximum kill. But even if you wait a few hours, you will get some kill. The objective is to wait as long as possible for best kill. If you feel you will not get planting done before the next rain it is better to accept less than 100% efficacy and get the seed in the ground. Another factor is weed size. Weeds like big dandelions will not be killed in the spring no matter how long you wait. Experience has also shown that weeds like the lamb’s quarters, and   its’ sort of lookalike spreading Atriplex are hard to kill once they get over 2-3".

Corn

Corn (Darel Walker CCA Indiana)

It takes about 110-120 GDU for corn emergence. Corn will germinate if placed in soil that is 50 degrees (10 degrees C) or warmer and we want that first drink of water to be warm to avoid stress. When contemplating early corn planting we can do a 10-day GDU prediction and estimate days to emerge. Emergence taking longer than 10 days is risky because it increases the odds of insect damage, seedling blight, and cold shock damage. Our Indiana Lead agronomist, Dan Emmert, recommends that nighttime air temperatures be above 40 degrees (4.4 degrees C) for the first 5 days after planting to avoid chilling injury and ruptured coleoptiles. He also recommends high temperatures above 60 degrees (15 degrees C) for the first 5 days. If the 10-day prediction is above 80 GDU, corn can be planted with good prospects for emergence.

(PJL comment) This is the science behind getting best yields. I believe you should put the thermometer somewhere that you can’t read it and if soil is fit start planting. Too often I have seen planting delayed because the soil was too cold and then planting was delayed and the last planted yield poorly. But each to their own. But if you are in a yield competition or putting out hybrid plots consider checking soil temperature.

Forages

Q Can I spray Eragon for fleabane control before seeding alfalfa peas and oats? (PJL)

Ans No. The peas and oats are safe but not the new alfalfa seeding. BASF trials show there is a chance of damage too many times. Same with Elevore, too much damage. Liberty is not an option since weather is too cool. Options now are 1) mould board plough. Secondary tillage with a cultivator or disc will just move them around. 2) Spray Eragon and Merge and glyphosate now. Plant the peas and oats now, and seed alfalfa after peas and oats are harvested.

Q I have an alfalfa field with a lot of dandelions. Is there anything I can spray to get rid of them?

Ans (PJL)

For years growers have been trying to do this. Years ago, Prof Bob Fulkerson at U of G researched this problem. Not sure what product(s) he used. I think he also hand hoed to remove dandelions. But I do remember the results. When he was able to reduce the stand of dandelions the total yield of alfalfa plus dandelions was lower than where there was no reduction of dandelions. Make sense, you have a thin stand of alfalfa with dandelions. If you can remove the dandelions now you have a thin stand of alfalfa with no dandelions. I remember his comments. “Dandelions do have some feed value” Final solution, you need to control dandelions before you plant. Then using Embutox can control those coming from seed. Then you need to aggressively manage alfalfa with fertilizer. The other option is HarvXtra alfalfa and then use glyphosate.

Fertility

Reading tissue sample results (JZ)

I have picked up the following over the last number of years from reading tissue tests and wanted to share how weather conditions, crop growth and the soil can influence what shows up on the lab test. A key item is that a tissue test result does not necessarily correlate with potential for a strong yield. It can only report on what nutrients the plant has been able to take up and diluted through biomass. Many times, lower tissue sample nutrient levels end up having higher yields than those with high levels. The plants simply had more biomass relatively the amount of nutrient concentration, so the nutrients got diluted compared to the poor plant. The 2^nd take away is that looking at the relative amount of nutrients to each other within the plant is or possibly more important than looking at the absolute value of each nutrient individually. If you are reading a tissue test from Honeyland Labs (i.e. the YEN reports), they report on the plant’s nutrient balance, this can help pick up on any outliers when everything else seems in balance, however this still may not correlate with an increase in yield if you try and address it.

Business Matters

Writing and reading scout reports (JZ)

Writing a detailed scout report is part art, part science. Trying to paint a picture of the field variability can be challenging which is where learning to use descriptive and qualitative words is key to making a quality report. See below for examples.

Poor – Field has winter kill. Average population – 13 plants per foot of row.

Good – Field has winter kill in the depressions. – 7 plants per foot of row in the depressions, 15-20 plants per foot of row in other areas.

Better – Field has moderate amounts of winterkill in the depressions7 plants per foot of row in the depressions, 15-20 plants per foot of row in other areas.

Best – Overall field has 5% winterkill, mainly located in the depression areas, with 7 plants per foot of row remaining. Remainder of field consistently has 15-20 plants per foot of row, with a slight reduction in stand on top of the old corn rows.

Writing a strong report takes practice, keep at it when working on writing descriptive reports.

The way I see it, if you want the rainbow, you gotta put up with the rain.

-Dolly Parton