Weed Control Advice for Dry Conditions

Early weed removal recommended under dry conditions, especially in thin crop stands that are less competitive.

Different crops have different critical weed free periods, usually from emergence to 4 leaf stage. During this time, it is important to minimize weed competition to. The herbicide label is important for the appropriate crop stage, but also for weed size, so read carefully.

Weed control and crop tolerance can also be affected by dry conditions. see FULL ARTICLE

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Effect of Spring Frost on Emerging Crops

Submitted by Anastasia Kubinec, Manitoba Agriculture

Originally posted May 8th and 30th, 2015…..re-post May 13, 2016 and now May 27, 2019.

Don’t assume because there is frost (or snow) on the ground, that your emerging crop in dead!

With the drop in temperatures in the past couple of days, there are a few things to keep in mind if the mercury dips below 0°C. The temperature is the instigator for causing frost, but whether it is -0.1°C or -4°C the damage inflicted is highly influenced on these other factors:

  1. Duration
    • Short frost = < 2 hours,  may not cause much damage if frost is light (above -1 to -2°C), crop type and staging is tolerant, conditions wet and crop has become acclimatized.
    • Short frost = < 2 hours, but hard frost (lower than -2°C), crops like canola are more sensitive to longer frost vs. cereals, damage can be variable in field and across area.
    • Long frost = > 2 hours, whether frost is light or hard the longer the negative temperatures the more time for damage to happen.  Tolerance by crop type varies.
  2. Other Environmental Conditions
    • Cloudy and wet – prior to a frost, cool temperatures slow plant growth and ‘hardens’ plants off, which will help them tolerate a frost.  Also wet soil helps buffer the cold air effects on the plants, as wet soils change temperature slower than dry soils.
    • Sunny and dry – The combination of a  dramatic drop in air temperatures when plants are actively growing then a brilliant sunny day after the frost event is where we have seen the most damage.  Scouting after the frost (24 and 48 hours) is very important though to assess extent and percentage of field injury.
    • Field trash cover – increased trash in fields was seen to increase frost damage on very susceptible crops in the 2009 June frost
  3. Crop Type
    • Spring Cereals – more tolerant than other crops types, can tolerant to temperatures as low as -6°C as growing point below ground until the 5 leaf stage.
    • Winter Wheat – can withstand very low temperatures for a short period of time (-11°C for less than 2 hours) up until the tillering stage.
    • Corn – smaller then V5, will recover from light frost as growing point below ground. Leaves probably will be killed, but plants will recover if the growing point ok.
    • Oilseeds – environmental conditions impact frost severity on susceptible canola and flax cotyledons. Resiliency increases at the 3-4 leaf stage (canola) or 2nd whorl (flax).  Sunflowers are fairly tolerant  up to the V4 stage.
    • Pulses – peas are most tolerant, then soybean, edibles bean are very susceptible even before emergence.   Field pea crops are rarely lost to frost. Soybean are more sensitive, but the smaller the soybean plant the more tolerant they are  – from emergence to cotyledon can withstand short light frosts.

Scouting After a Frost

Scouting should start 24 – 48 hours after the frost and continue for the 5 days following the frost event.  Look for leaves wilting, looking “water-soaked” or see “frost banding”.  Watch for new growth in the plant.  You do not want to see plants wilted and not perking back up or pinching off on the stem near the growing point (canola, flax, soybeans).  Also assess the area affected by frost, small areas or a few plants damaged are ok, as other plants emerged (or just emerging) will fill in those spaces.  Large dead areas may need to be re-seeded.

If in doubt of what look for, call your local agronomists, local FPE Specialist with Manitoba Agriculture or the Crop Industry Branch.

For more specific details on what actually occurs to plants with a frost and crop specific details and symptoms to look for (and how long after a frost to do assessment) see Manitoba Agriculture’s Spring Frost Damage Bulletin.

 

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What Does Seedplaced Fertilizer Injury Look Like?

Submitted by John Heard, Soil Fertility Specialist, Manitoba Agriculture

Already we are hearing of spotty emergence with cereal crops in Manitoba.  Possible culprits may be dry seedbeds, poor quality seed, seed depth, herbicide residues, or seed placed fertilizer injury.Past Prairie studies suggested a 15% stand reduction was tolerable for cereals since surviving plants tillered and filled in the stand.  But maturity is less uniform and is delayed up to 4 days.
How might one confirm seedplaced fertilizer injury?  Close inspection can show a range of symptoms:
1.        Seeds that imbibed water but did not develop any root or shoot
2.       Seeds that developed shoots but no roots
3.       Seeds that developed root and shoot but leafed out below ground
4.       Those that did germinate and emerge (about 44%) were ½ to 1 full leaf stage behind normal seedlings in the low fertilizer strip.
In other crops injury can show as:
Canola – seeds just do not germinate and remain intact.   Fields simply appear to have very poor crop establishment.
Soybeans – stands may be injured, especially with wider row spacing and on sandy soils under dry conditions.
For more information, see the full .pdf document on Manitoba Agriculture Current Crop Topics – What Does Seedplaced Fertilizer Injury look like in Cereals
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Volatilization of surface applied urea/UAN

Submitted by: John Heard, Manitoba Agriculture, Soil Fertility Specialist
Surface broadcasting of nitrogen (N) fertilizers has become popular to increase operational efficiency – increasing the speed of seeding and reducing risk of seed injury.  But, in a dry spring with limited rain prospects, growers may choose not to till and avoid further drying out seedbeds.  Then growers must consider the risks of nitrogen volatilization loss and take precautions when risk is high.
Volatilization of ammonia (NH3) from urea or the urea portion of UAN (28-0-0) affected by several factors and can be increased under specific situations.
For more details on the risk factors and ways to minimize losses, see full .pdf 
More topics on soil fertility can be found on Manitoba Agriculture’s Soil Fertility webpages.
 
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Spring Preplant Banded nitrogen Too Hot for Corn in Dry Springs!

Submitted by: John Heard, Manitoba Agriculture, Soil Fertility Specialist
There is no single best way to fertilize corn in Manitoba.  The 4 most common N application methods are spring broadcast and incorporated, fall banded, banded at seeding and preplant banded.
In a dry spring like 2019 (similar to 2018),  broadcasting and incorporating fertilizer before seeding, risk drying out the seedbed.  Many farmers, especially on clay-textured soils prefer not to disturb their seedbed in the spring and so prefer to fall band their N.  And although spring preplant banding is a very efficient way to place nutrients for a corn crop, it comes with some particular cautions – thinning and seedling injury.  
More detailed information and analysis in full .pdf
More topics on soil fertility can be found on Manitoba Agriculture’s Soil Fertility webpages.
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Can Sidebanded Nitrogen Cause Injury in a Dry Year?

Submitted by: John Heard, Manitoba Agriculture, Soil Fertility Specialist

With a lack of seedbed moisture, there are justified concerns about seedplaced fertilizer injury to canola and other crops.  How safe is sidebanded nitrogen? Research studies by  Dr. Cindy Grant documented considerable canola stand thinning when high rates of sidebanded urea or UAN solution were applied.  Agrotain (AT) served to reduce stand injury, but is no longer supported for this use by the manufacturer. 

Points:
  • Stands were thinned at even modest N rates, on a clay loam soil.  At high rates stands were reduced to 50%
  • Crop growth compensated for reduced stands and generally produced as good a yield as the Agrotain protected stands, except at the highest rate.
For more detailed analysis and discussion on the issue see the full .pdf
More topics on soil fertility can be found on Manitoba Agriculture’s Soil Fertility webpages.
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Seed Placed Fertilizer Cautions for Canola

Submitted by: John Heard, Manitoba Agriculture, Soil Fertility Specialist

Spring 2019 (like 2018) has brought many questions about seedplaced fertilizer rates for canola.  Several factors are causing concern:

  • Drier soils – which increase the risk of seed toxicity
  • Desire to apply sufficient P to meet crop removal – since many fields have seen decreasing P levels due to high yield.  P removal is about 1 lb P2O5/bu, so high yield potential fields are looking at high P replacement rates.
  • Increased use in low disturbance, low seedbed utilization (SBU) drills.  Many new openers are arriving on the scene, which are “close-to-seed” sidebanding for which one may need to consider as seedplaced.
  • Desire by growers to reduce seeding rates for cost savings.  Most research studies investigating seedplaced fertilizer injury were seeded at some 150 seed/m2, about double what some farmers are now targeting.
For more detailed analysis on the issue, see the full text in .pdf format 
 
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Crop Germination – What Soil Temperatures are Needed?

Soil temperature drives germination and seedling emergence, so how cold is too cold?  What is your soil temperature at your targeted seeding depth….today? Finally, when should you be measuring the soil temperature?

The following are the minimum temperatures needed for germination to begin in various crops.  These values should be regarded as approximate, since germination depends on factors other than just temperature.  But, if soils are too cool, germination will be delayed and cause uneven or poor seedling emergence.

 

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 State University Extension Service, Alberta Agriculture & Rural Development and Canola Council of Canada

Getting an accurate measure on soil temperature

Determine how deep you will be seeding. Then place your soil thermometer at the targeted 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. The recommendation is to take readings for two to three days to establish a multiple day average and to measure at a number of locations in the field, to account for field variability.

Still not sure and short on time?  See the soil temperature data for various locations across Manitoba from the MB Ag-Weather Program: https://www.gov.mb.ca/agriculture/weather/soil-temperature.html.  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!

 

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How Longer Can Winter Wheat Survive under Flooded Conditions?

Flooding tolerance of crops is impacted by a lot of things, but the main ones are: crop type, length of time under water and the temperature.

A couple of things that winter wheat has going for it is that is may not have yet broke dormancy when the water arrived and with relatively cool soil temperatures and cold water, things slow down for biological activities.  One report from North Dakota indicates that winter wheat could withstand flooded conditions for up to 3 weeks, but source is anecdotal https://www.ag.ndsu.edu/news/newsreleases/2009/april-20-2009/flooding-impacts-winter-wheat/

With all water-logged crops, once water has receded, inspect the crown to see if there are any signs of life. As weather warms and if soils remain saturated, there is still risk of oxygen deprivation in the plants and potential for seedling death.

 

General information on crop tolerance to flooding: https://www.gov.mb.ca/agriculture/crops/crop-management/seed-survival-flood-conditions.html

Impact of Flooding on Soil Fertility in Red River Valley: https://www.gov.mb.ca/agriculture/crops/crop-management/impact-of-flooding-soil-fertility.html

Forage Stands – Assessing Flooding Injury: https://www.gov.mb.ca/agriculture/crops/crop-management/forage-stands-assessing-flooding-injury.html

 

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How Much Nitrogen Do I Use to Fertilize my Fall Hybrid Rye?

Submitted by John Heard, Crop Nutrition Specialist, Manitoba Agriculture

Interest and acreage of fall rye has grown substantially in Manitoba. Hybrid rye has about a 20% yield advantage over traditional open pollinated (OP) varieties and are expanding onto more productive soils than rye’s historic range on the droughty sands.

With increased yield potential comes the question about nitrogen rates to sustain that higher yield. The hybrids are shorter and more lodging tolerant, so one might suspect they can tolerate more nitrogen, and hence respond to more nitrogen. Very few studies have looked at nitrogen rates of the open pollinated versus hybrid varieties. Three Saskatchewan studies provide the extent of the data. From this data we observe the substantial yield increase of the hybrids over the open pollinated variety but that similar rates of nitrogen are required to optimize yield of each.

Read the whole story here (PDF 325KB): hybrid-rye-fertilization-rates

 

Visit our website at www.manitoba.ca/agriculture

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