What are minimum germination temperatures?

Soil temperature is a useful gauge for timing when crops are seeded.  Table 1 shows the minimum germination temperatures for various crops.  These values should be regarded as approximate since germination depends on several factors.  If the soil is too cool, germination can be delayed which can result in uneven or inadequate seedling emergence.

How do I measure soil temperature?

Determine how deep you will be seeding. Then place your soil thermometer at that targetted depth. Take two measurements throughout the day: one in the morning (8am) and one in the early evening (8pm) . Average the two readings to determine the average soil temperature.

MAFRD recommends that you take readings for two to three days to establish a multiple day average, and reminds you to measure temperature in a number of locations in the field, to account for field variability.  Still not sure, see soil temperature data for various locations across Manitoba is available from MAFRI’s Ag-Weather Program:  http://tgs.gov.mb.ca/climate/SoilTemp.aspx.  This can be used as a guideline for an area, but in-field measurements are going to tell you what is actually going on in your field!

Table 1: Minimum Germination Temperatures for Various Crops

Crop Temperature (°C)
Wheat 4
Barley 3
Oats 5
Corn 10
Canola 5
Flax 9
Sunflower 6
Edible Beans 10
Peas 4
Soybeans 10

Sources: North Dakota StateUniversity Extension Service, Alberta Agriculture & Rural Development and Canola Council of Canada

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Manitoba Sclerotinia Risk Assessment Update

MAFRI currently does not produce sclerotinia risk maps like we do for Fusarium Head Blight, as we do not have a proven and consistent model to forecast sclerotinia risk. 

Since Manitoba producers grow multiple sclerotinia susceptible crop (canola, soybean, sunflower, dry bean, etc.), the inoculum is present in the environment, but risk and disease development is dependent on a combination of inoculum as well as day/night temperature, precipitation, crop canopy and soil moisture, which can vary from field to field.

 Scout and monitor your fields, you may be at greater risk and require a fungicide application if you have the following conditions:


  • Ground is damp to wet and,
  • Canopy is moderately closed to closed (i.e. you cannot see the ground through the leaves), and
  • Canopy is still damp to wet when walking through the field at 10am (i.e. your pants are wet), and
  • Field is at 20 – 50% flowering (you are wanting to cover the petal so when it falls into a humid canopy, it won’t be a viable food source for the sclerotinia to start on).

 Conditions can change throughout flowering.  If the canopy is somewhat open and dry at 20% flower you may not feel that you need to spray, but if there is a rainfall event and the canopy is wet at 30 – 40% flower, you may want spray then.

 Dry Bean:

  • Ground is damp to wet and,
  • Canopy is moderately closed and is continuing to close, and
  • 50 – 80% of the Field has started to flower (at least one open flower per plant)
  • Dry bean may require a second application at full flower, depending on the precipitation, temperature and canopy moisture

 Sunflower (for Sclerotinia Head Rot only) :

  • Ground has been damp to wet for the past week, and
  • Plants are at R5 (sunflower face is open with ray petals out, but pollination has not yet started)

Spraying for sclerotinia in soybean is not being considered at this time as flowering has not yet occurred. Damage and economic loss in soybean has only occured in one growing season on record. Sclerotinia development can occur under extreme wet and cool conditions, or the crop is significantly lodged and further information will be posted if these conditions do occur later on in the 2013 growing season. 

Canola Council of Canada July 3, 2013 New Release – Moisture Raises Sclerotinia Stem Rot Risk  http://canolacouncil.org/news/moisture-raises-sclerotinia-stem-rot-risk/                                                    

NSDU Sclerotinia Risk Map http://www.ag.ndsu.edu/sclerotinia/.  Please note this is based on temperature and precipitation only and is not based on individual field conditions


Prepared by:  Anastasia Kubinec – MAFRI Oilseed Crop Specialist  and  Holly Derksen – MAFRI Field Crop Pathologist

Have a follow-up question?

Most of my beans are dry but there are some pods in the field where the seed is still green. What % of green can I have in my sample before it is a concern?

You may be better off to wait a few days before harvesting to allow those beans to mature in the field if it is a high percentage.  

Companies who buy beans say that if the sample  has more than 2.5 % green seed  you could be down- graded.

If however it is just the odd green seed in the sample then it should change in the bin.

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Could Potash Deficiency Show Up in Soybean Field This Late in Season? Symptoms are showing up on the newest trifoliate.

Reports of symptoms on soybean in the Beausejour, Plum Coulee areas and in dry beans near Gladstone (see photo “Potash Deficiency in Dry Bean”) that have Potash deficiency are showing up between previous crop swaths.

It can be difficult to diagnose Potash deficiency but the coincidences are strong when symptoms start showing up on the newest leaves when crops found occurring on lighter textured soils and during pod filling, as the leaves move Potash out of leaves into pods.  Potash starved leaves are quick to show symptoms once Potash is mobilized out of them. Potash deficiency in the late season is most seen in the upper leaves. 

 Other causes of late season yellowing:

  • Senescence – which we are seeing in some dry beans now
  • Drought – sandy soils may be worst – but these are also soils most likely low in K
  • Salinity – this is probably bigger than people recognize – seeing soybeans yellowing NOT in the lowest part of the field, but adjacent to these areas – typically where salinity rises out of the subsoil.  Likely these soils are not bone-dry – the plant just cannot squeeze any water out of saline soil
  • Iron chlorosis – which normally we see under excessively wet conditions.    

For the future, soil test and /or tissue test and compare good vs. poor areas and look at the levels of  Potash to determine if more is needed for future crops or early in the season to help the present crop.

Have a follow-up question?