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A number of things are showing up in the corn patch, now that corn is actively growing and farmers/agronomists are scouting for emergence, growth and weeds.
To see pictures and find out what is causing them see corn-concerns-curiosities (PDF 1.88MB)
Submitted by Anne Kirk, Cereal Crop Specialist, Manitoba Agriculture
Hail has been reported in several areas of Manitoba, and due to the size of the hail and duration of the storm, crops were affected in some areas. Assessments of damage will occur over the next few days. The amount of loss expected from a hail event depends on the severity of hail, crop type, and the growth stage of the crop.
Spring Wheat – is least susceptible to hail damage prior to stem elongation since the growing point is below the soil surface and will likely not be damaged. Hail damage during jointing or in the boot stage is difficult to assess. Spikes can still pollinate and fill, and regrowth from new tillers can occur. The more advanced the wheat is at the time of hail the greater the yield loss. The greatest yield reduction from hail occurs in the milk stage.
Oats and Barley – will tiller and recover better from hail than wheat, especially prior to the boot stage. Grower experience has demonstrated that barley hailed severely in the boot stage has recovered to produce 70-80% of normal yield. Crop hailed prior to the boot stage should be left if stems or green tissue remains.
Corn – early season hail occurring when the growing point is still below the soil surface will result in very little yield loss. At the 6 leaf stage the growing point is above ground, but leaf loss without damage to the growing point has a small impact on yield. Yield loss as a result of hail can be estimated by determining percent leaf defoliation (Table 2). Leaf area removed and leaf necrosis need to be considered, while damaged green leaf tissue should not be included. Assess leaves 7-10 days after a hail event, so that living and dead tissue can be easily distinguished.
Assessing Damage – New growth should be evident within a few days after a hail event. Assess crop to evaluate new crop growth. Yield potential of a damaged crop will depend on rainfall and temperatures in the next 30 days after hail damage.
Submitted by Anne Kirk, Cereal Specialist, Manitoba Agriculture
For more information see Manitoba Corn Growers newsletter for Growth Stage Information for Herbicide Application
When applying post-emergent herbicides, proper corn growth staging is extremely important. Herbicide labels may refer to plant height, crop growth stage, or both when listing crop stage timing. Farmers and agronomists need to accurately stage corn plants to ensure that herbicides are being applied at the correct stage. Some common methods of determining corn growth stage are listed below.
Corn Height Method – Measure from the soil surface to the highest point of the arch of the uppermost leaf whose tip is pointing down. Don’t measure to the “highest point” on the plant, which is often the tip of the next emerging leaf above. Refer to Figure 1/2 on how to correctly determine the height of a corn plant. Corn height varies due to growing and crop management conditions, and is not the most accurate way to stage corn.
Leaf Over Method – Count the number of leaves, starting from the lowest (the coleoptile leaf with a rounded tip) to the last leaf that is arched over (tip pointing down). Younger leaves that are standing straight up are not counted. In Figure 1/2, the corn plant would be at the 4 leaf stage using the leaf over method.
Leaf Tip Method – Count all leaves, including any leaf tips that have emerged from the whorl at the top of the plant. In Figure 1/2, the corn plant would be at the 6 leaf stage using the leaf tip method.
Leaf Collar Method (V-stage) – Count the number of leaves with visible collars, starting from the lowest (the coleoptile leaf with a rounded tip) and ending with the uppermost leaf with a visible leaf collar. This method is the most common staging system and involves dividing the plant development into vegetative (V) and reproductive (R) stages. The leaf collar method is generally also the easiest to use, and related better to the physiological stage of the plant and therefore to the effects of herbicides. In Figure 1/2, the corn plant would be at 3 leaf stage (V3) using the leaf collar method.
See Dry Weather Weed Control on Manitoba Agriculture website for more details and complete recommendations and cautions.
Dry weather means both weeds and crops shift gears. Weed spectrums can be different, post-emergent herbicides can be less effective because weeds may have smaller leaves and/or thicker cuticles (waxy layer) that slows the penetration of herbicides.
Some herbicides withstand dry weather better than others so choose your product carefully. Here are some general guidelines on weed control during a dry period.
1. Remove weeds early.
2. Know your crop stage.
3. Review the “Effects of Growing Conditions” section of each product in the Manitoba Agriculture Guide to Field Crop Protection to determine likely outcomes.
4. High Daytime temperatures can trigger crop injury in some herbicides.
5. Use full rates of herbicide.
6. Use higher water volumes.
7. Use split applications of broadleaf and grassy herbicides rather than tank mixing if the Guide to Field Crop Protection warns that antagonism can occur.
8. Check the forecast for rain – shallow, stressed crops roots may be impacted by herbicides moving into the root zone.
9. Compare the risk of crop injury to the risk of yield loss due to weed pressure.
Submitted by John Heard, Soil Fertility Specialist, Manitoba Agriculture
Registration is now open for the 2018 Crop Diagnostic School in Carman, MB.
School dates are July 10-13 and 17-19.
Topics this year will include insect scouting, dicamba drift, pea disease & soil erosion damage mitigation and others.
For more information see Crop Diagnostic School webpage
Registration can be called into 204-745-5663.