NDSU Crop and Pest Report

Plant Science

ISSUE 6   June 10, 2004


Each year we get some hail damage in various crops in North Dakota, with 2004 being no exception. A fairly extensive hail storm hit last Sunday evening, June 6 in Minot, ND. and surrounding growing regions to the south and west.

Flax: Up to the sixth leaf stage, the flax plant is very susceptible to hail damage. Plants cut off below the cotyledonary leaves during this period do not produce new growth and are considered lost. It will recover from hail if green material remains above the area of the first leaf. Buds along the stem will re-grow following destruction of the terminal growing point. After the sixth leaf stage a more fibrous stem develops and the plant becomes increasingly less susceptible to hail injury. Hail injury at full flower and at boll setting time can be very injurious to flax as well as once bolls are fully developed.

Delay in maturity is also a factor in final yield. Flowering time will be delayed somewhat due to delayed recovery time. In addition stand counts maybe reduced thus each plant will need more time to branch and flower. Hot temperatures during the critical flowering time will reduce number of bolls set and total yield potential.

Soybean & Dry Bean: The growing points of beans are located in the top of the plant and in leaf axils. Growing points of beans are easily damaged by hail soon after emergence. Regrowth will not occur if hail stones cut the stem off below the cotyledonary node. If the top of the plant is damaged, regrowth can occur from one or more axillary buds. Bean stems may be bruised or broken. The damage may not be severe enough to kill the plant. However, the plant may lodge later as the callus tissue is weak and cannot support the pod weight. Reduction in soybean stands to four plants per linear foot of row can still produce fair yields.

Sunflower: Sunflower may be more tolerant than beans, but the degree of hail tolerance depends on the intensity of the hailstorm and the stage of growth. Sunflower is least tolerant during the seedling and budding stages, and most tolerant after flowering. Hail damage may be direct or indirect. Direct damage results from stand reduction, loss of recoverable heads because of severely bruised or broken stems, and head shatter at later stages. Indirect damage results from defoliation and disease infestation to injured plant tissue. Research conducted on simulated hail losses in sunflower indicated that a one to one relationship does not exist between seedling stand reduction and yield loss. A 50% stand reduction resulted in only a 28% yield reduction. Defoliation of sunflower by hail was reported to be most damaging during the bud stage. Defoliation of 80% at the bud stage resulted in yield reduction of 53%. Whereas 80% defoliation at the 50% mature stage resulted in only a 12% yield loss.

Canola: Plantings in seedling stages can have stands reduced by 50% and still produce acceptable yields. An average stand of 11-12 plants/ft2 can be reduced to 4/ft2 before yield losses exceed 10 percent. Prior to bolting and flower development, canola can withstand hail without much economic loss. Canola with leaves that are torn and shredded suffer only partial loss, while leaves bruised on the main vein or torn and broken will be lost. Leaf area destroyed will result in seed yield loss. Seed yield losses in canola is approximately 25 percent of leaf area lost. If leaf defoliation is 50 percent, then yield loss would be approximately 12.5 percent. Canola plants injured in late bolting or early flowering stages seldom die. The well developed root systems and ability to rebranch and develop secondary flower clusters help the plants recover. When buds or flowers are destroyed, the canola recovers rapidly by development of flowers which normally would have aborted. New branches also develop from growth buds lower down on the plant. Seed yield loss will depend on both percent leaves and branches lost. For example, if canola has 60 percent lost branches 7 days into flowering, seed yield loss is estimated at 18 percent, whereas 21 days into flowering, yield loss would be an estimated 60 percent. If hail strikes late, such as during pod filling or ripening, plant recovery is not possible. The time needed to develop new growth, flowers and mature is limited before a killing frost. Canola seed yield loss if injury occurs at the ripening stage depends directly on the loss of branches, individual pods and seed knocked out of pods. Severe hail losses have occurred in canola swaths in past years.

Corn: The growing point remains below ground 2 to 3 weeks after the plant emerges (up to 6-leaf). If the growing point is not damaged, corn will recover and perform better than replanted corn. Split the stalk down the center and inspect the growing point. If normal, it will appear white in color and firm in texture. Injured growing points will appear brown or discolored 2 to 3 days following the hail. Complete loss of leaves early to corn when small usually does not greatly affect grain or silage yields.



Most years in North Dakota, a number of sunflower fields are planted late or replanted. This cold and wet (in some areas) spring of 2004 will go down as one of the more difficult years of planting late season broadleaf crops such as sunflower, soybean, and dry beans. For sunflower it is not recommended to plant non-oilseed sunflower (confectionary) beyond June 1. The primary reason is because of quality problems. Oilseed sunflower can be planted to early maturing hybrids up until mid-June with less risk. In addition if one is to plant NuSun sunflowers into June, the earliest hybrids available should be selected. Several seed companies now have early maturing NuSun hybrids now that were not available several years ago. Research on late planted sunflower has been conducted at various North Dakota NDSU Research Center sites.

Table 1. Sunflower yields* (lb/A) as influenced by planting dates at Prosper and Carrington, ND.

Approximate planting date


% oil



June 1




June 15




June 30




July 15




* Average 3 years, 2 locations
** Sunwheat 101 - early semi-dwarf sunflower

Table 2. Sunflower oilseed yields*-Early vs. late planting.

Planting time





Mid May





Early June










* 5 year ave. Yields - lbs/A

When planting sunflower late (after June 7) itís suggested to plant early maturing hybrids. Selection of short season sunflowers will increase the chance of reaching maturity in the northern areas of North Dakota and Minnesota. Once again, planting of non-oilseed or confectionary sunflower is discouraged in June.



Soybean seed can begin germinating when the seed has absorbed enough water to equate to about 50% of the dry seed weight. So under adequate soil and air temperatures plus good soil moisture, soybean can germinate in just one day under ideal conditions. Emergence from soil seeding depths may take an additional three to four days, depending on growth conditions. Like corn, soybean yield is affected by temperature or moisture stress especially if it occurs during flowering and pod fill. However, unlike corn, soybeans produce excess flowers on the plants. Usually only 34 to 40% of the plantís flowers develop into mature pods with the remaining 60 to 66% of the flowers or pods aborting and never contributing to yield. Day-length also affects most soybean varieties grown in North Dakota and Minnesota so that late-planted soybean may hasten their development toward maturity with less yield loss than other late-planted crops. Early maturing soybeans can still be planted up until June 15 with some limited risk. It is just not advisable to plant corn for grain beyond the 1st week of June in most areas of North Dakota.

Duane R. Berglund
Extension Agronomist



The heavy rains of the past two weeks in eastern North Dakota have resulted in flooding, ponding in low spots and saturated soil conditions. In my most recent travels in southeastern ND, I saw many corn fields with ponding. In these fields corn was somewhere between just emerging to about the 3 leaf stage of development depending on when it was planted. Water-logging (ponding, saturated soils) affects a number of biological processes in plants and soils and can be damaging to crop growth. The extent of yield loss caused by excessive moisture, however, cannot be easily generalized as it is influenced by a number of factors.

Effect of water-logging on the developing plant

The primary cause of damage of water-logging to corn plants is oxygen deprivation. Oxygen is needed for cell division, growth and the uptake of nutrients by roots. When soils become saturated, the amount of oxygen available to plant tissues below the surface of the soil (or water level if ponding occurs) decreases rapidly as plants and microorganisms deplete what is available. The movement of oxygen from the air into water/saturated soil is much slower than in a well aerated soil and much less than is needed by the various organisms in the soil. The rate of depletion of oxygen in a saturated soil is dependant on a number of factors, but temperature is the most important and predictable factor; the higher the temperature the faster the rate of oxygen depletion. Generally, the oxygen level in a saturated soil reaches the point that is harmful to plant growth after about 48 hours. In an effort to survive, tissues growing under reduced oxygen levels use alternate metabolic pathways that produce by-products, such as lactic acid, that at elevated levels reduce the ability of a cell to function normally.

Since the growing point is below or near the soilís surface until about the 5-6 leaf stage, corn is quite sensitive to water-logged conditions during the early spring. Young corn plants can be killed if soils are saturated beyond 48 hours, particularly when soil temperatures are high (i.e. above 65 degrees) Water-logged conditions also reduce root growth and can predispose the plant to root rots later in the season, so the ultimate effect of excess moisture may not be known until late in the season. To determine if plants have been killed by ponding, wait 3 to 5 days after the excessive moisture has drained through the soil and check to see if there is any visible regrowth.

Effect of water logging on the soil

Water-logging can also indirectly impact corn growth by affecting the availability of nitrogen in the soil. Excessive water can cause leaching of nitrate nitrogen beyond the rooting zone of the developing plant, particularly in lighter textured soils. Furthermore, when oxygen levels become depleted, soil microbes extract oxygen from the nitrate molecule, causing nitrogen to be converted to a gaseous form that is lost to the air. This process is called denitrification. The amount of N loss through denitrification depends on the amount of nitrate in the soil (the ammonium form of nitrogen is not lost through denitrification), soil temperature, and the length of time that the soil is saturated. Research conducted in other states has found losses between 1 and 5% of the nitrate N lost for each day that soils remain saturated. Adding additional nitrogen to fields that have had significant N losses, once they have dried can remedy these losses. However, before adding extra nitrogen to fields that experienced water-logging, you should first consider the likely yield potential of the crop that has probably already been damaged. Additionally, N losses are not likely to be uniform throughout the field and additional N may only be needed in low spots where losses were the highest. If you do decide to apply some additional N, you should consider varying the rate to target those areas in the field where N is likely to be the most limiting. For additional details and links on applying supplemental nitrogen after excessive moisture I would recommend the following article:


Joel Ransom
Extension Agronomist - Cereal Crops

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