NDSU Crop and Pest Report

Plant Science

ISSUE 4  May 22, 2003


A heavy frost and freeze has hit some areas of the state mainly in the west and certain northern areas. Luckily, not many susceptible crops were emerged when the frost occurred. Temperatures Tuesday morning, May 20 were as low as 20 degrees F. Some reports of temperatures below 25EF for a period of 4 to 6 hours and had many growers concerned.

Frost damage what to look for?

Small Grains:

Are very tolerant to temperatures as low as 20E F and keep in mind that the growing point is below the soil surface until the 5 Ĺ leaf stage to jointing. The only significant damage that could occur would be that if the frost was hard enough to collapse the stem, which would cause the plant/stem to wilt and most likely die. In most instances, wilted, dark green and discolored leaves will be the normal appearance. Recovery usually is quick with a new leaf emerging from the stem within 2 to 3 days with a normal green color.

Winter wheat/jointed (5/12 leaf):

The extent of time that the plants were subjected to the cold temperatures will be the issue. The worst case scenario would be that the developing spikelets were injured to where no kernels will develop in those spikes. This usually will be the top of the head and that area will be white in color along with the awns.


Early Season _ when early frost kills corn leaf tissue, producers worry about whether or not corn plants will recover. The key to assessing corn seedling viability is to find and observe the "growing point". The growing point is where all new tissue originates, and is protected below ground until the plants reach the V_5 stage. That is when corn has five true leaves. It is usually about 6-8 inches in height. Removal or death of leaf tissue above the growing point has only a small effect on corn growth and yield at these early stages. It may set the growth and development back slightly.

The growing point can be found by pulling the entire corn plant, including roots and splitting lengthwise the entire plant. If the growing point was below ground, white or creamy in appearance then injury didn't occur. Observations of frost damage are best made by waiting at least 2 or 3 days after frost occurred. If the growing

point appears healthy, white to light yellow color several days after frost, full plant recovery is likely. Plants with extensive leaf tissue damage will likely recover if the growing point is not injured by early frost. New leaves should appear within 3_4 days if growing point is uninjured.

Canola, Flax, Mustard:

These crops can handle a frost of 24 degrees for a short time with Canola the most tolerant to the cold temperatures. Frosted leaves/plants will have a dark green or black in color. If discolored or injured we need to wait at least 2 - 3 days before any decisions are made to see if the growing point is alive. Within 3 days, there should

be a new leaf emerging from the growing point located in the center of the plant. The best indication that the plant has been killed by a frost is the stem. If the stem below the cotyledons is wilted and doesn't straighten out within 48 hours of the frost, the plant is most likely dead.

Pulse crops ( field peas, lentils and chickpeas):

Similar to small grains, the growing point is below the soil surface to the fifth node stage or about the 4 inch height stage. If the stem is collapsed, wilted on the soil surface for 48 hours and regrowth has not occurred, that plant has most likely been killed. Recovery is usually quick with the newest leaf emerging from the stem within 3 days.


When in the cotyledon stages can withstand temperatures in the 25-26 F range for short periods of time if they are just emerging from the soil. Sunflower true leaves in the 2, 4 or 6 leaf stages become more sensitive with each development stage and the terminal bud can be permanently damaged. Its believed that when sunflower are in the V2 stage then the lower limit would be 26-27 F, whereas if sunflower are in the V4 or V6 stages then the lower limit would be 28-29 F. If sunflowers become brown or blackened and the terminal bud is damaged then the plants will not recover.

Kent McKay
Area Agronomy Spec. Minot REC Center

Duane R. Berglund
NDSU Ext. Agronomist



Wet soils and recent rains have led to questions of whether soil crusting will be a problem in various area fields. Itís always best to wait at least 5 days to a week after a crop is beginning to emerge to determine what percentage of the stand will be established. If a heavy crust does occur, a harrow or rotary hoe will be the best option. Before deciding to harrow, be sure that seedlings are unable to emerge through the crust. Harrowing can break off an emerging coleoptile or hypocotyl resulting in more damage than good. It is not advised to harrow canola, flax, mustard or crambe as seedlings are small and near the soil surface.

If the plant is leafing out under the crust layer and the stand is poor, then breaking the crust layer is recommended. A harrow, rotary hoe or any empty press drill has been used successfully to break up a crust.

Light, spring tooth harrows should be set shallow (1/2 inch deep) and angled back to reduce the potential of going too deep. Harrowing at a right angle to the rows and driving as slow as possible will also reduce the injury potential to the crop that has emerged.



Populations of shallow emerging weed seedlings such as green and yellow foxtail, kochia, Russian thistle, pigweed and certain nightshades can be severely reduced by timely harrowing. Harrowing wonít reduce wild oat, volunteer grains or sunflowers and perennial weeds very much due to their deeper emergence. However control will be higher if they have not yet emerged and are near the soil surface. Extremely wet soil conditions will not allow good weed kill by harrowing.

Harrows should be set shallow and angled back to reduce the potential of crop injury. Light spring tooth type harrow should be used and not the heavy harrows designed for vigorous tillage operations.

Itís best to harrow wheat and barley at the two leaf stage and no later than the three leaf stage to minimize injury potential. Wheat can be harrowed twice while barley should be harrowed only once. Corn can be harrowed between the one and four leaf stage, and sunflower, 2 to 6 leaf stage. Soybeans and dry beans can be harrowed between the 1 to 2 trifoliolate stage. Itís advised not to harrow canola, mustard, crambe or flax seedlings before or after emergence.

Duane R. Berglund
NDSU Extension Agronomist



The 2002 USA Sunflower Survey showed that growers lost hundreds of pounds of yield due to poor stand establishment. Poor stand establishment was a close second to drought as the number one yield robber.

Sunflowers will compensate if you have both even emergence and plant spacing in your field in spite of having several thousand less plants. Fields that have plants emerging for several weeks with skips and doubles can decrease yields by 400 to 500 lbs.

Planter Adjustments

Your planter is like a machine gun. It has to shoot out 13.5 seeds/second, if you have an eight row planter seeding 20,000 seeds at 5 mph. Sunflower seeds have more variation than most other seeds. That is why it is so important to clean and adjust your planter before planting your sunflowers. Also use the recommended plates, fingers and air pressure to help avoid skips or doubles. Run your planter at recommended speeds.

Woody Hull

Sunflowers have evolved in the High Plains over thousands of years. One survival mechanism is its woody hull which prevents germination during dry conditions. To insure even germination, seed must be placed in soils with adequate soil moisture and good seed to soil contact.

Seed Depth

Sunflower seed needs to be planted at depth of 1.5 to 2.5 inches and into moisture.

Furrow Closing

Sunflower needs to have excellent seed to soil contact. Again because sunflowers have a woody hull, closure of the furrow becomes more important than for corn and most other crops.

Soil Temperature

Soil temperature needs to be at 50įF or more at seed depth (1.5 to 2.5 inches). Planting sunflower seed into cold soils may cause seed to go into dormancy and can delay germination.


Insects like wire worms and cutworms can drastically reduce stands. Use approved chemicals to control insects.

Weed Control

Satisfactory weed control is essential. Use labeled products and apply them as recommended. Know the fieldís weed history and control accordingly.


Sunflowers have a deep rooting taproot but will not penetrate a hardpan. Break up any hardpan prior to planting.

Max Dietrich
National Sunflower Association



Several reports of alfalfa fields exposed to 20 to 26EF air temperature have occurred. Whether this will kill the alfalfa or not depends on many factors including the maturity of the alfalfa, duration of the freezing temperature, soil water level, etc., but generally it takes a colder temperature to kill an alfalfa stem. I have seen alfalfa survive a 14EF frost with less than 30% stem kill here on the campus.

When frost occurs, wait until the air temperature recovers, generally that same afternoon. A hard frost will cause the alfalfa stems to either "shepherd hook" or act as a lazy stem. If after a warming period the stems straighten back up, the stem is uninjured and will resume growth as if no frost had occurred.

If the stem does not straighten up following a frost, it has been killed and will start to dry out. The frost may also cause alfalfa nearing harvest to turn a whitish color. If the stem is killed or whitened, the alfalfa should be harvested assuming enough growth has occurred to justify a harvest. If the alfalfa growth it too short to justify a harvest (less than eight inches), nothing needs be done. The alfalfa will recover from the crown or active axillary buds on the lower portion of the plant. Do not recommend to clip the alfalfa. Clipping will not hurt the plant, but it will not help it either.

If the stand is a grass-alfalfa mixture, the decision to harvest must be based on the percent of dry matter coming from alfalfa. If the alfalfa component is less than 30%, wait for the proper stage for the grass and disregard the alfalfa. If the alfalfa component is greater the 50% and some stems (say 30 to 40%) are uninjured, I would also wait for the grass. If alfalfa is the dominate component, then handle like an alfalfa field.

Dwain Meyer
NDSU Professor, Forage Management



In last weekís Crop and Pest Report, I expressed my concern that planting of cereal crops not already in the ground could be delayed beyond their optimum dates if rains continued. The heavy rains during the past week have in fact delayed or stopped planting in a wide area of the state. We are now at the point in the season where any new plantings or replantings of cereal crops will be "late". Late planting will almost always result in reduced yields. The optimum window for maximum yield in barley and spring wheat is between the middle of April and the middle of May. Delays in planting small grains generally result in a 1% reduction in yield for each day delay after May 15. The optimum planting date for corn is around the 1st of May for North Dakota. Not only does the yield of corn decline after this date, but moisture content at harvest increases and test weight decreases if full season hybrids are planted. In this issue, I will briefly describe potential options for managing the problems associated with late plantings.

Late Planting of Small Grains

The yield reduction associated with late planting small grains is largely a result of the higher temperatures during early plant growth causing accelerated plant development which reduces tillering and head size. When seeding rates below 900,000 seed per acre were planned, the lower yield potential of late planted small grains can be partially offset by increasing the seeding rate. For every 10 days delay beyond May 15, increase your seeding rate by 5 to 10% up to a maximum of 20%. There is probably little advantage at this point in changing varieties to one that is earlier or to one with known tolerance to late planting unless you already have it on hand. You should avoid planting varieties developed for Canada, as they tend to be more photo period sensitive and typically do poorly when planted late. Although there is urgency in getting the crop in, it will probably pay to exercise some patience, as working a wet field can result in clods, compaction and potentially poor emergence.

Late planting often results in higher protein. You should adjust nitrogen applications to more closely match the lower yield potential of your delayed plantings. This is particularly important in barley that is intended for malt, where high protein may result in the loss of malt quality.

Late Planting of Corn

Full season corn varieties planted near May 1st are the most productive. A full season hybrid will almost always out-yield a earlier hybrid. In late planting situations, however, a full season hybrid has a high probability of having high moisture content and low test weight at harvest. The cost of drying a full season hybrid planted late should be considered before deciding on whether or not to stay with a full season hybrid. Data from a hybrid trial conducted in Carrignton in 2002 demonstrates the effect of pushing the maturity of a hybrid beyond the heat units required for it to fully mature and dry down before harvest (see Table 1). These data demonstrate the potential yield advantage of a later maturing hybrid, but they also show that the value of the crop, even if yield is greater, can be less due to the cost of drying the extra moisture from the grain. Earlier hybrids can often be more profitable to produce than later ones, particularly for late plantings.

Table 1. The effect of corn hybrid maturity on grain moisture content at harvest, yield, and market value, Carrrington, 2002 growing season.

Relative Maturity

Moisture Content at Harvest (%)

Yield (bu/A)

Value+ ($/A)

















+ Value after drying to 15.5% assuming a drying cost of 3 cents per percent moisture per bushel and a corn grain price of $2/bu.

It is recommended that when corn planting is delayed beyond the 20th of May that you switch to a 5 to 7 day earlier hybrid in order to avoid excessive drying costs and discounts for low test weight after harvest. Plant population does not interact strongly with planting date, so you should stay with your planned seeding rate. Although there is a temptation to plant shallow to achieve faster emergence in late plantings, especially after a wet period, planting to a depth of 1.5 to 2 inches is still recommended to ensure good germination and emergence.



In addition to what has already been mentioned in this issue relative to frost damage, I will add some additional information on frost damage to small grains and corn. With the exception of winter wheat, the growing points of emerged cereals are currently still below the surface of the soil and are well insulated from short periods of freezing temperatures. The growing points of spring wheat and barley remains below the soil surface until jointing starts, usually around the 5 to 6 leaf stage. Similarly, the growing point of corn remains below the soil surface until the 5 or 6 leaf stage. Earlier this week in parts of the state, the frost was quite severe. These low temperatures will no doubt cause some damage to the emerged leaves. When temperatures are cold enough (the temperature varies depending on the tissue, crop, and other environmental factors) the contents of cells freeze, causing small ice crystals to form and pierce through cell membranes. The allows the cellís contents to leak resulting in cell death. Damaged leaf tissue first appears water soaked, and eventually turns brown. Usually within one or two days new leaves will start to emerge from the whorl. Slight damage to the leaves will have little or no effect on yield or plant development. Severe leaf damage may reduce yields slightly and delay the development of the plant. If you suspect that the plant has been killed (the growing point damaged) by the frost, you can cut the plant in half vertically and check the growing point. A healthy growing point will have a bright white to cream colored appearance. Darkening tissue or a watery appearance usually indicates that the growing point was damage and that it will soon die.

There can be large differences between small grain varieties to frost, but information on the currently produced spring wheat and barley cultivars is lacking. Research in growth chambers indicate that spring wheat tends to be more tolerant to frost than barley. When growth staging a frost damaged crop, you should continue counting leaves as though the plant had not been damaged. For example, if your barley plant has 3 leaves that were damaged by frost, the next leaf that emerges will be the 4th leaf (not the first leaf). Generally a severe frost will only delay the normal development of the crop by a few days at most.

Winter wheat is just starting to joint throughout much of the state. This means that the growing point is no longer below the surface of the soil and is now susceptible to frost damage. The growing point is the most susceptible part of the plant to frost and can be injured even though the leaves show little signs of damage. Occasionally the main stem can be damage while the tillers survive, resulting in uneven maturity of the crop. Frost during the jointing stage of winter wheat can have a moderate to severe impact on yield.



In the southeastern region of the state, early planted corn should now be emerged. The corn I planted on May 1st in Fargo began emerging on Monday (May 19th). As of May 20th (assuming a May 1 planting date), the southeastern corner of the state had accumulated about 150 growing degree days (GDDs), while GGD accumulations for most locations in the rest of the state were at about 100. Since corn generally emerges after about 125 GDD, most corn that was planted on or before 1 May should emerge before the end of the week. On average, and as you well know using averages for spring weather in North Dakota can be fraught with problems, about 10 corn GGDs accrue daily during the last 10 days in May.

Joel Ransom
Extension Agronomist - Cereal Crops



Generally wheat grain yield will be reduced a minimum of 0.5 bu/a each day past the optimum planting date. In the northern part of North Dakota, the optimum planting date is before May 20. Usually wheat will take 50 to 55 days to head when planted in late May. This means grain fill will occur during the warmest part of the growing season and for a cool season plant like wheat it results in smaller kernels and reduced yield potential. What options do growers have when faced with a late season planting?

Are there varieties that have more tolerance to heat stress? Yes, varieties like Ingot, Russ, and Alsen seem to handle heat stress during grain fill better than, for example, Gunner, Marshall, and AC Barrie. Research at Langdon has shown that planting Gunner and AC Barrie late will result in a larger decrease in grain yield relative to varieties like Ingot and Russ. Leaf rust damage potential increases in late plantings. In sensitive varieties like Ingot and Russ, a fungicide to protect from leaf rust should be strongly considered or plant a leaf rust tolerant variety.

The Langdon Research Extension Center had a late planting trial in 2000 and 2001. The two average yield for AC Barrie was 26.6 bushels per acre while Gunner averaged 30.9 bu/acre. All other varieties in the trial average yields were at 40 bu/acre or above. The varieties Alsen, Russ, and Parshall had average yields of 43 bu/acre. In a similar trial planted the first week of May, Gunner, and AC Barrie had yields similar to the other varieties.

When should one consider switching varieties? While each year is different, general farmer experience and research data suggest that Gunner and AC Barrie and perhaps varieties with similar genetics should not be planted after May 20 in northern North Dakota/Minnesota and perhaps earlier in southern portions of North Dakota. If planting is delayed into June, consider planting an earlier maturing variety if an earlier choice is available. A week earlier heading can make a difference of two weeks or more when the variety is maturing in September. The risk of frost and sprout damage increases as maturity occurs in September.

Will an adjustment in seeding rate help reduce losses to late planting in wheat? Bryan Hanson, Agronomist at the Langdon Research Extension Center conducted two three year planting date and rate studies in the mid 1980's with a semi-dwarf durum, Cando and Robust barley. Seeding rates of 0.5, 1.0, 1.5, and 2.0 million seeds were used at three dates of late April, mid May and early June. There were no significant differences among seeding rates for planting dates for any measured trait. It did not help to increase seeding rate as planting date changed. However, these trials and trials with Grandin wheat in the early 1990's did show that seeding enough seed to establish a minimum of 17, 27, and 26 plants per square foot of barley, durum and spring wheat, respectfully, maximized yields. Establishing these minimums for any seeding date should be a producers goal.

Terry Gregoire
Area Extension Specialist
Cropping Systems

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