ISSUE 7 June 16, 2005
HAIL DAMAGE IN OILSEED & ROW CROPS
Hail damage to crops occurs somewhere in the state every year. Reports have already been made last week and this week of hail in some areas of the state. When hail damage occurs on corn, soybean, dry bean and sunflower early in the growing season, replanting is possible; but deciding whether to replant is usually difficult. Total stand reduction, leaf loss, stem injury, weed control, and calendar date are factors to consider when making this decision. At this time (Mid-June) its too late to consider a replant.
Corn: The growing point remains below ground 2-3 weeks after the plant emerges (5-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_3days following the hail. Complete loss of leaves early to corn when small usually does not greatly affect grain or silage yields. Corn in the silking and tasseling stage when damaged by hail can result in severe yield losses.
Soybean and Dry Bean: The growing points of beans are located in the top of the plant and in leaf axis. 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 tip 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 in 30 inch row spacings can still produce fair yields. For dry beans one can get down to two plants per foot of row and still get 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 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/sq. ft. can be reduced to 4/sq. ft. 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.
ANALYZING AND EVALUATING CROP PROBLEMS
Persons working in crop production are often called upon to trouble-shoot in situations involving suspected crop injury from herbicides. These situations require careful analysis and scouting before judgements are formulated. For purposes of this article, I would like to define "injury" as stunting, delayed development or malformation of plant tissues which may or may not affect yields. Herbicide injury may result from applications to the crop, from residues in the soil or from drift.
When evaluating crops involved in suspected herbicide injury, keep in mind that some other factors may have caused the observed effects or the herbicide may be only one of a combination of several casual factors. Look for other possible causes. Are there holes in the leaves or stems or pruned roots from insect damage? Has there been severe weather - wind, drought, hail, flooding, frost, high temperatures, etc. - that could have caused damage, Flooding damage in crops which recently occurred in June, greatly compounds the diagnosis. Could a disease be involved? Could it be excessive or misplaced row fertilizer or a nutrient deficiency? Or is the effect resulting from a combination of causes?
Look for patterns of injury in the field. Herbicide injury is often in a pattern associated with soil types or movement of application or incorporation equipment. Observe other susceptible crops or weeds in the area for herbicide effects. For comparison, try to find a check area where no herbicide was applied in the same field.
If you conclude that herbicides are the probable cause of crop injury, try to determine why the injury occurred. Limited crop tolerance to certain herbicides is sometimes a problem especially under heavy rainfall or sandy soils or on dry, loose soil. Miss use high rates, wrong chemical, contaminated spray tank, improper method of application, nonuniform application, overlaps, improper applicator adjustments and tillage operations that concentrate the chemical - are some reasons for herbicide injury. Some varieties/hybrids are more susceptible than others. Weather and soil conditions that cause plant stress may make the crop more susceptible to herbicide injury.
Don't be too hasty to evaluate the effects of herbicide injury. Give the plants a chance to recover. Check growing points to see if the plants have potential for recover. Compare injury effects and weed control benefits. Stand counts and injured plant counts are important considerations. Unbiased yield checks later in affected and unaffected similar areas of the same field are the best estimates in damage losses.
CHECK YOUR SOYBEANS FOR NODULATION
Soybean plants that are five to six inches tall should have their first unfolded leaflets (V2 stage). Nodulation, the symbiotic relationship of bacteria on the soybean roots, can be seen shortly after emergence, but the plant is not actively fixing nitrogen until the V2 to V3 stages. The number and nodules formed on the soybean roots along with the amount of nitrogen fixed increases until the R5.5 stage. Nodules actively fixing nitrogen for the plant are pink or red inside. White, brown or green nodules indicate that nitrogen-fixation is not occurring. Nitrogen fertilization after planting (other than pop-up or early, limited fertilization) is not recommended as nitrogen fertilizer applied to active nodules will render these nodules inactive or inefficient, depending on the amount of nitrogen applied. Soil nitrogen is utilized over fixed nitrogen, if available in large amounts. Check the health of your soybean nodules and check root proliferation. Soybean roots should be dug up to check nodules and not pulled from the soil. The pulling action tends to slough off nodules and results in an inaccurate assessment. At V2, soybeans should be rooting down six inches into the soil and by V5 will completely reach between 30-inch rows, making any cultivation at V5 needing to be very shallow.
Duane R. Berglund
CEREAL CROP GROWTH IN SATURATED SOILS
With the nearly continuous rains of the last few weeks, soils have become saturated. Ponding is so common in parts of the state that ducks have a nearly endless supply of places in which to paddle. Waterlogging (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.
The primary cause of damage to cereal crops by waterlogging is oxygen deprivation The rate of oxygen depletion 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. Fortunately, up until now temperatures have been moderate which have helped slow the deleterious effects of waterlogging. Generally, the oxygen level in a saturated soil reaches the point that is harmful to plant growth after about 48 to 96 hours.
Effects on Corn - Much of the corn in the state is currently at or near the 4 leaf stage. The growing point of the corn plant remains below the surface of the soil until the 5-6 leaf stage and is quite sensitive to waterlogged conditions at this stage. Young corn plants can be killed if soils are saturated beyond 48 hours, particularly when soil temperatures are high (i.e. above 65 degrees) Waterlogging also reduces root growth and predisposes the plant to root rots later 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 then check to see if there is any visible re-growth.
Effects on small grains - Depending on planting date, small grains currently vary from the 4 leaf stage to heading.
Barley is reported to be more sensitive to temporary waterlogging than is wheat. Furthermore, varieties vary considerably in their response to waterlogging, though I am not aware of any data on how varieties commonly grown in North Dakota respond. Sensitivity to waterlogging generally decreases with age with spike size and tiller numbers being the yield components most affected. Though leaf yellowing is common in small grains after soils have been waterlogged, yield loss can occur, even if these visible symptoms are not observed. Effects on the soil - Water-logging can also indirectly impact cereal crop growth by affecting the availability of nitrogen in the soil and by reducing root development. 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, nitrate nitrogen is converted to a gaseous form that is lost to the air. Research conducted in other states has found losses between 1 and 5% of the nitrate N lost for each day that the soil remains saturated. Corn responds to additions of N when N is limiting up to the beginning of grain filling. Consider side-dressing N to corn fields with good stands where excess water caused be economical once that this year. In small grains, in order to impact yield, additional N should be applied prior to the 6 leaf stage. Additional N, after this stage, however, does have the potential to increase protein levels. See Dave Franzen's article in last week's Crop and Pest Report for more details.
NDSU Extension Agronomist