Optimum and Last Planting Date, Minimum Stands, Crops Loss from Frost or Hail for Small Grains

Optimum and Last Planting Date

Seeding rates should be increased by 1% for each day planting is delayed up to a maximum rate of 1.6 million seeds per acre. Delay in planting reduces yield potential and tiller development. On average, yield loss of 1% per day occurs after optimal planting dates.

Minimum Stands

Optimum plant populations for 30 to 32 plants per square foot for spring wheat.  For thin stands, tillering can fill in and reasonable yields can be obtained with populations of 14 plants per square foot.  Replanting costs must weighed against a later maturity crop with less yield potential (1.5% yield loss per day), moisture loss from soil disturbance, seed and operating inputs.  

If the reduced stand is uniform (no skips or holes), keep stands of 15 plants per square foot.

If skips are large (3 to 6 ft.) or holes are 4 to 6 ft. in diameter and the stand is 18 plants per square foot or less, replant if moisture is adequate.

After June 1 in North Dakota, replant with a crop other than wheat or barley since yields are reduced by about 50 percent.

Source: The Small Grains Field Guide A-290, J.J. Wiersma and J.K. Ransom, 2005.

1. Replant
2. Replant for use as silage or grazing forage.
3. Replant with earlier-maturing varieties.
4. Use alternative crop with shorter maturity
5. Replanting using higher seeding rate (1.3 to 1.6 million plants/acre)
6. No not replant

Source: Replanting or Late Planting Crops (A934)

Crop Loss from Frost or Hail

Plant damage is dependent on crop stage, duration, and intensity of a frost or hail event.  Additionally for hail, the direction of hail fall and size of hail stones can increase crop loss. 

Spring frost damage appears as water-soaked leaves which turn dark green.  The injured leaves dry out and quickly turn brown. If the crown was not exposed to freezing temperatures, plants will quickly recover.  Several frost events will greatly weaken plants and may result in yield loss.  Plant hardening via low day and night temperatures can deter actual frost damage.

Wait to assess damage until a couple of days after the event.  Look for regrowth at uninjured growing points (see illustration below). If frost damage occurs prior to jointing, new growth will come from the growing point beneath the soil surface.  At jointing, the growing point is above ground and thus, more sensitive to frost injury.  Locate the growing point by splitting the wheat stem vertically above the uppermost node to expose the tiny developing head.  A frost injured growing point will be dull white or brownish and water-soaked. The injured plant will develop tillers from the crown as regrowth. Uneven maturity and moderate to severe yield loss will occur.

The hail impact on yield is dependent on the severity of plant injury and stand loss.  Like frost, early-vegetative hail loss can stimulate regrowth of additional tillers.  Yield loss is proportional to foliage loss.  Pre-boot stage hail damage can result in partially exposed twisted heads. By boot stage, hail can cause severe losses and severity yield loss can continue through the milk stage. Hail damage can produce poor floret development and lack of grain fill. Broken over stems will give shriveled kernels unless mature.  Hail can also knock kernels out of head. Severely hailed wheat stands may be used as a “green manure” or can be used as hay, silage or bedding for livestock. The hailed crop can have a slight risk for nitrate accumulation which is detrimental for livestock.  Nitrate risk increases in oat hay or high-N fertilized stands.

Crop damage provides opportunities for disease infection and greater weed competition. Damaged plant stands usually grow slowly until they are recovered.  Herbicide crop injury is more likely to occur with herbicides that normally stress the crop and spraying should be delayed. Alternately, generally crop-safe herbicides can be applied when needed.

Source: Replanting or Late Planting Crops (A934), G. Endres et. al.; Wheat Production Handbook C-529, Kansas State Research and Extension, J.P. Shroyer et. al, 1997.; Nitrate Poisoning of Livestock V-839, C. Stoltenow and G. Lardy, 2015. Reviewed May 2017.