Replanting After Early Season Crop Injury
A-934 (Revised), June 1997
Michael D. Peel, NDSU Extension Small Grains Specialist
Greg Endres, Area Extension Agronomist
Crop damage and stand reduction early in the growing season presents farmers with decisions on replanting. Replanting decisions are complicated by not knowing what future seasonal growing conditions will occur. Decisions should be based on historic trends plus current environmental and economic conditions. Questions that should be addressed when considering replanting include: is there an economic advantage to replanting? Should the same crop be replanted? The advisability of replanting must be carefully considered, keeping in mind that the cause and severity of injury, soil moisture, cost of replanting, previous herbicide use and the date of replanting all influence whether a crop should be replanted or a different crop should be planted.
The final decision on replanting should be based on sound agronomic and economic information. Injury to the original stand must be accurately determined, including crop uniformity and overall plant health. The critical question is whether keeping the original stand or replanting will result in greater net income.
Appraising Crop Injury, Stand Reduction and Yield Potential
Evaluating crop injury and estimating potential crop yield is the first step in determining if a crop should be replanted. The best possible evaluation of the surviving stand is needed because the critical yield comparison ultimately will be between the sub-optimal stand from the original planting date versus a full stand from a later than optimum planting date. During the seedling stage, injury that results in stand reduction will cause the greatest yield reductions. Leaf loss or leaf burn during early stages has a minimal effect on yield; however, as the crop approaches reproductive developmental stages, leaf damage or loss is more damaging to yield.
An assessment of potential plant stand soon after crop injury occurs is critical to avoid delays if replanting is necessary. An accurate determination of the existing stand must be made. Stand counts should be taken at random from several areas in damaged portions of the field. Determining stand level may be more complicated than simply counting plants. If seedling emergence is uneven, an evaluation of potential late emerging plants should be made. If areas in a field are not damaged they do not need to be considered for replanting.
In early plant development a few key structures are indicators of potential plant survival. In addition to a reasonably healthy radicle and seminal roots, seedling emergence requires mesocotyle and coleoptile elongation or hypocotyl elongation, depending on the type of emergence. If these structures appear normal and seed depth is not excessive there usually is a good chance emergence will occur when soil moisture is adequate.
Figure 1. Effect of injury
on grassy crops at
different growth stages
and on broadleaf crops.
Click here for a full size
version of this illustration.
(16KB b&w illustration)
Destruction of leaf area on young plants is seldom as serious as appearances may indicate. If the growing point of small grain is not damaged and the stem is not broken below the cotyledonary node of pulse, bean or oil seed crops, the plants will likely recover
During early growth stages, most North Dakota crops can sustain some stand loss without experiencing significant yield reduction. Crops compensate for stand reduction through tillering, secondary branching or increased head number, and increased ear or seed size. Comparison of the estimated yield of the injured crop with expected yield of an alternative crop minus reseeding costs most often indicates crop stands should be left, even with substantially reduced populations. Table 1 shows the population levels of several crops that should be considered minimum stands when deciding whether to replant, assuming the plant population is relatively uniform in distribution. As the season progresses the yield potential of a newly planted crop is reduced (Table 2); therefore, the lower minimum stand values from Table 1 should be utilized as the season progresses.
Table 1. Minimum stand levels of several crops that should be considered
acceptable before replanting is done.---------------------------------------------------- % of Normal Crop Stand Minimum Stand ---------------------------------------------------- Small Grains 30-40 8-14 plants/ft2 Flax 20-40 20-35 plants/ft2 Soybean 25-50 37,500-75,000 plants/A Sunflower 50-60 8,000-11,000 plants/A Safflower 40-50 2-2.5 plants/ft2 Dry Bean: Navy 50-60 45,000-60,000 plants/A Pinto 40-50 28,000-35,000 plants/A Field pea 40-70 3-5 plants/ft2 Corn: Irrigated 70-75 See A-1130* Dryland 60-70 See A-1130* Crambe 15-20 4 plants/ft2 Canola 25-50 4 plants/ft2 ---------------------------------------------------- * Varies with region, see NDSU Extension Service bulletin A-1130.
Table 2. Expected yield reductions when planting after
May 15 in North Dakota.--------------------------------- Crop % Yield Loss/Day --------------------------------- Wheat 1.5 Barley 1.7 Oat 1.2 Soybean 0.8 Irrigated Corn 1.2 Dryland Corn 1.0 Flax 2.3 Dry Bean 0.3 Crambe 0.9 Canola 1.9 ---------------------------------
Cereal Crops
During early development the growing point of cereal crops is below the soil surface, making it less susceptible to injury. With this protection, plants can suffer loss of above ground foliage without dying. When hail, frost or similar types of injury cause severe foliar damage, it is advisable to wait several days after the injury occurs to make an accurate determination of stand reduction. After this period, new growth on plants with uninjured growing points can be observed as in Figure 1. If no regrowth is observed, the stem of the plant may be split to inspect the growing point. The growing point should be white or cream colored. Darkening or softening of the growing point usually precedes plant death. When the growing point moves above the soil surface at jointing in small grains and the sixth-leaf stage in corn, it becomes more vulnerable to physical damage.
When hail severely injures small grain cereal crops after jointing, plants still have potential for recovery by initiating new tillers. Precipitation that usually accompanies hail storms will help stimulate tillering. Potentially, tillering can restore yields to acceptable levels. The number of head bearing tillers is determined before heading, so injury that occurs after heading in small grains is the most damaging to yield.
Broadleaf Crops
The initial growing point on most broadleaf crops is at the plant tip (pea and lentil are exceptions) which increases susceptibility to injury early in the season. Stem breakage or damage below the cotyledons (Figure 1) will result in plant death. However, buds form in the leaf axils later in the development of broadleaf plants, unlike small grains. After loss of the main stem from injury, these buds can begin growth with secondary branching replacing the loss of the main stem. When this occurs, yield reduction will result from leaf loss only, rather than a combination of stand and leaf loss.
In sunflower, secondary stems developed from buds in the leaf axils will not compensate for loss of the main stem. These secondary stems will not produce viable seed heads, so loss of the main stem growing point results in the loss of the plant's yield potential. In addition, injured plants with secondary stems compete with healthy plants, further reducing yield.
Indirect Effects of Injury
In addition to the direct effect of leaf loss or stand reduction, other indirect effects of crop injury should be considered, such as increased weed competition and increased disease potential. Damaged crops usually grow slowly until they have recovered, which provides the potential for greater weed competition. Loss of leaf canopy allows additional sunlight for previously shaded weeds and may result in additional weed flushes. Wounds from hail, insect or wind injury provide opportunities for pathogens to infect the plant. Resulting diseases may directly reduce yields or grain quality.
Previously applied herbicides may have little remaining activity to control new flushes of weeds. Use of post emergence herbicides (particularly those that normally stress the crop) to control new weed flushes should be delayed on visibly weakened crops until the crop has an opportunity to recover. Otherwise, herbicides that are relatively safe on the crop should be used to control new weed flushes when weeds are likely to become too large to control by waiting for the crop to recover.
Replanting Decision
The decision to replant must ultimately be made by comparing the estimated yield of the injured crop to that of a replanted crop. This is quite subjective and each case must be individually considered in terms of time of year, alternate crop choices, previous herbicide use and other related factors. Crops replanted late in the season will almost always yield less than those planted at an optimum time. Table 2 shows approximate yield reductions that may be expected from late planted crops. The remaining growing season may be too short for some crops. Table 3 shows options for replanting and the dates by which most North Dakota crops can be safely planted and still produce a useful or marketable product. These dates will vary somewhat depending on the region of the state.
Residues from previously applied herbicides may restrict some crops from being used as a replant crop. Table 4 shows crops that, under normal conditions, can be safely planted on soils previously treated with a given herbicide(s).
The decision to replant is both an agronomic and economic one that requires careful assessment of crop injury, yield potential, alternate crop choices and cultural practices related to crop growth and development. Each case of injury must be considered thoroughly and individually.
Table 3. Field crop replanting suggestions for North Dakota when soil moisture is not
limiting.
------------------------------------------------------------------------
Wheat
Durum
Replanting Oats Sun- Soy- Dry
Date Corn Rye Barley flower beans Flax Beans
------------------------------------------------------------------------
May 1-10 --- 1 1 1 --- 1 ---
May 11-20 1 1 1 1 1 1 1
May 21-31 3 1,5 1,5 1 1 1 1
June 1-10 2,3,4 2,3,4,5 1,3,5 3 3 3 3,5
June 11-20 2,4 2,3,4 3,4,5 3,4 3 3,4 3,5
June 21-30 4 2,4 2,3,4 4 4 4 4
July 1 & thereafter 6 2,6 2,6 6 6 6 6
------------------------------------------------------------------------
Replanting Saf- Buck
Date flower Lentils Millet Wheat Canola Mustard
------------------------------------------------------------------------
May 1-10 1 1 --- --- 1 1
May 11-20 3 1 --- --- 1 1
May 21-31 4 3 --- 1 3 3
June 1-10 4 3,4 1 1 4 4
June 11-20 4 4 1 1 4 4
June 21-30 4 4 3,4 1 4 4
July 1 & thereafter 6 6 6 2,6 6 6
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1. Replant.
2. Replant for use as silage or grazing forage.
3. Replant with earlier maturing varieties/hybrids.
4. Use alternative crop with shorter maturity )Be aware of possible
herbicide residue restrictions).
5. Replant using higher seeding rates (1.3 to 1.6 million plants/acre
for small grains).
6. Do not replant.
Table 4. Crop choices for replanting fields previously treated with herbicides that have
crop rotation restrictions.
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Herbicide Used
on Initial Crop Crop Choices for Replanting*
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Accent Field corn, soybean (15 day interval)
Ally HRW and spring wheat (1 month interval)
Amber HRS wheat and durum
Assert Barley, HRS wheat, and durum
Atrazine Corn and sorghum
Banvel/Banvel SGF See label
Basis Field corn, soybean (15 day interval)
Basis Gold Field corn
Broadstrike + Dual Field corn and soybean
Broadstrike + Treflan Soybean
Buckle Barley, durum, field pea, and HRS wheat
Canvas Barley and wheat
Curtail Wheat, barley, oat, grasses, and corn
(30 day interval)
Far-Go Barley, HRS wheat, durum, triticale,
field pea, chickpea and lentil
Finesse Wheat, rye, and triticale (soil pH <8)
Harness Corn
Hornet Corn
Lexone/Sencor See label
Lightning See label
Matrix Corn and potato
MCPA See label
Peak Barley, oat, wheat, rye, and triticale
Permit Field corn and grain sorghum
Prowl Dry bean, potato, soybean, and sunflower
Pursuit Soybean
Scorpion III Field corn
Sonalan Dry bean, field pea, soybean, and sunflower
Stinger Barley, corn, oat, sugar beet, wheat, and grasses
Surpass Corn
2,4-D See label
Tordon See label
Trifluralin Alfalfa, canola, crambe, dry bean, field pea, flax,
lentil, potato, safflower, soybean and sunflower
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* For additional information refer to the North Dakota Weed Control Guide,
Circular W-253
A-934 (Revised), June 1997
