After the Flood: Row Crop Replanting

The U.S. Army Corps of Engineers estimates floodwaters covered approximately 185,000 acres of row crops in the Mississippi Delta during late May. As the water recedes, producers are facing decisions about how to manage their cropland the rest of the 2011 growing season.

Mississippi State University Extension Service agronomic crop specialists and Mississippi Agricultural and Forestry Experiment Station researchers have compiled the following information on late season planting and crop management. Also included is post-flood crop insurance information.

Post-Flood Soil Fertility

The bioavailability of most plant nutrients is very dynamic as soils transition from flooded to normal conditions. Soil testing remains the foundation of nutrient management.

Since the flood has produced and altered farming landscape, soils from these fields should be tested before the 2012 growing season even if they were tested going into 2011. The sampling should be done after the soils have dried sufficiently to allow good sampling. Previous soil test results can support fertility management for crops planted this summer.

Nitrogen: It is likely that most of the nitrogen (N) fertilizers applied prior to the flood have been lost except in some special situations. Soybean seed planted after flooding should definitely be inoculated, regardless of whether soybeans have previously been grown.  If nodulation is hindered or delayed, relatively small N applications may provide a temporary supply.  However, proper nodulation is necessary for soybean nitrogen fixation and normal plant growth. 

Phosphorus:  Phosphorus (P) deficiencies in fibrous rooted crops such as corn are often seen in post-flood soils, regardless of high soil test levels. These P deficiencies are caused by several factors including less soluble iron and aluminum phosphates in post-flood soils, and diminished activity of mycorrhizal fungi that are essential in P nutrition and uptake. These fungi colonize the roots of the host plants, and greatly increase the nutrient and water uptake of the plant.  Tap-rooted crops such as soybeans and cotton grown in the same situations are affected less, but the same principles apply.  Soils will  recolonize with the fungi in the first few weeks after the flooding subsides. Therefore, if soil test P levels were adequate for soybean prior to flooding, they should remain adequate after the flood. If soil test P was low or unknown prior to the flood, P fertilization should be considered.

Potassium:  Flood related potassium (K) issues are rare, although K may leach in sandy, low cation exchange capacity (CEC) sandy soils during the flood. If the CEC of the soil is 8 or less, K fertilizer may be beneficial.

Other Nutrients:  Sulfur (S) may also leach in sandy soils. However, S will mineralize and become available from the soil organic matter in the drying soils. Micronutrients should not be an issue as the soils dry, and in fact some may be more bioavailable in the soil following the usual shift of soil pH toward 7.0 during the flood.

Crop/Residue Management after Floodwater

Most crops in fields inundated with floodwater for a week or more will likely die.  However, early-planted corn which attained considerable height prior to the flood could live, if water does not submerge plants.   Prolonged flooding will likely stunt growth and severely reduce potential corn productivity, depending on the duration of flooding, air temperatures (high temperatures increase stress), and corn growth stage. Ear size determination begins during mid-vegetative stages and grain yield is extremely sensitive to any stress during pollination.  Considerable root damage will likely occur, which may further jeopardize plant health when soils dry.  Large corn or wheat which remains after water recedes could restrict fieldwork and replanting of subsequent crops.  Live or upright corn stalks could be mowed and allowed to dry for several days.  Dry corn, wheat or other residue remaining in fields could then be burned, if necessary.  Burning would promote quick, efficient planting of another crop, particularly for dryland fields which may not require tillage or raised bed reconstruction.  It could also save valuable soil moisture, compared to multiple primary tillage operations, such as disking.  All weeds should be killed with either herbicides or tillage prior to planting.

Potential for Crop Damage from Herbicide Carryover in Soil

It is difficult to accurately predict the potential for crop injury associated with herbicide carryover in flooded soils. In general, most herbicides degrade fastest in warm, moist soils where microbial activity is high.  In oxygen-limited (anaerobic) conditions, as occurs in soils inundated for several days, herbicide degradation often slows, increasing carryover potential. For example, this occurs with products containing the active ingredient atrazine.  Other herbicides, such as those containing trifluralin, may actually degrade faster under flooded conditions, while degradation rates of products containing rimsulfuron (Resolve^®) appear to be unaffected by flooded conditions.  Less is known about the increased carryover potential under flooded conditions of products containing mesotrione (Callisto^®), such as Halex GT^®, Lexar^® or Realm Q^®. Anecdotal reports from flood-prone areas along the Ohio River in Illinois observed no atrazine or mesotrione injury in June-planted soybean following flooded corn. Consider each field and cropping situation individually. However, it should be noted that herbicide labels and restrictions apply whether or not flooding has occurred. If any residual herbicide was applied prior to flooding, label restrictions and plant back intervals will need to be adhered to when replanting crops. 

Chemical analysis of soil can help determine if a herbicide is present at a detectable concentration, but most laboratories cannot tell if a detection will necessarily result in crop injury. The most straight-forward approach to test for potentially harmful herbicide residues is to perform an in-field bioassay.  Producers in flood-prone areas report successfully performing in-field bioassays to answer replant questions. To conduct the bioassay, hand-plant some seeds as soon as water recedes, even while lower portions of the field remain flooded.  As the field dries over the next 7 to 14 days, look for herbicide injury, and successful emergence. Emergence failure or chlorosis in the first true set of leaves likely suggests herbicide carryover. For further assistance, contact your county Extension agent or the appropriate agronomic crop agent.

Effect of Growing Season Length on Cropping Decisions

Cropping decisions after this season’s floodwater may be limited by the length of growing season, depending on when water recedes from fields and they are ready to plant.   Although southern growers rarely have problems with this issue since we are blessed with long growing seasons, frost occurring prior to crop maturity can drastically limit productivity and commodity quality. 

The first fall frost at Yazoo City has a 10% probability level of occurring on October 30 and reaches 50% probability by November 14. Thus, crops with long growing season requirements, such as corn, cotton and rice, may not be practical options at late planting dates.  Also, late fall crop harvest could hamper grain drying and rut fields, if conditions are rainy and fields are muddy at harvest. This outcome could restrict fall tillage operations and damage fields, prohibiting implementation of stale seedbed systems or other reduced tillage systems which we use to promote timely spring planting.  As a result, a late crop this season could also have lingering harmful effects on next season’s crop.

Evaluating Crop Options

SOYBEAN 

Soybean is likely the best post-flood cropping option because the growing season generally fits and soybean has a proven track record when planted late, for double-cropping and after floods. Soybean is also the most common crop grown on flood-prone soils. Planting after a major flood is a unique situation where soybean historically has been rather productive. This response is largely dependent on moisture from the floodwater fully-charging the soil profile, which enhances moisture availability well through the season.  The soybean tap root system likely enhances its ability to utilize this soil moisture as well. Soybean grows and flowers quickly in warm, summer temperatures and when  planting after a flood, may yield about 80 percent of normal plantings (35-55 bu/a).  Soybean is not particularly sensitive to high night time temperatures, compared to corn, so it is capable of maintaining productivity relatively well when high temperatures persist during reproductive development.  Maturity Group V and VI soybean varieties are generally more productive when planted in June, compared to earlier varieties.  However, group V and VI varieties require nearly 120 days to mature, so you may need to consider group IV varieties, if planting is delayed into July.

Management Tips for Late-Planted Soybean

•  Planting soybean in narrow rows will likely increase productivity in a post-flood cropping system because it will promote quicker canopy closure, help control weeds, and improve light interception. 
• Late planted soybean seeding rates should be increased 10 percent above normal rates. This will account for potential losses from seedling disease, increased insect pressure and shorter soybean plants. 
• Rhizobium inoculation of soybean planted following flooding is strongly suggested. 
• A seed treatment fungicide should be applied since flooding may increase Pythium populations. Choose a seed applied fungicide that is compatible with the soybean inoculant.  For a table of compatible seed applied fungicide and inoculant combinations please refer to the Mississippi Crop Situation Blog.
• Floodwater may increase the possibility of new weed infestation. Many weed species, including pigweed, have seeds that float, increasing the likelihood of movement with floodwater. This makes a sound resistant-weed management program extremely important. A list of recommended herbicide programs for managing glyphosate- and ALS-resistant pigweed in soybeans is available at http://msucares.com/crops/weeds/pigweed.pdf. 
• An R3/R4 fungicide application could be beneficial on post-flood soybeans, due to late-season diseases such as Cercospora and soybean rust.  A full rate of a strobilurin (6 fl oz/A) may be more beneficial than the 4-ounce rate that is typically applied in our production area.  In addition, a 6 oz rate applied at approximately R4 will likely provide disease prevention through R5.5 or R5.7, which may be long enough to prevent the need for a second fungicide application.

Insect Management Considerations for Post-flood Soybean:  Insect pest pressure will likely be much higher than normal on post-flood planted soybean. This alone should not deter post-flood soybean planting, but it will require more intense management.  It is highly recommended that a consultant monitor these crops at least weekly to scout for insect pests.  Most insect pest problems can effectively be managed on post-flood planted soybean with little loss of yield, but scouting frequency may need to be increased if other than routine outbreaks of a specific pest occur.

• Soybean Loopers:  For many years Mississippi has missed the bulk of the problems from soybean loopers by simply planting early group IV varieties early and maturing the bean crop before loopers arrived in the state.  On soybean planted after June 15 (post-flood) many acres may require more than one application.  Fortunately, we have several choices of insecticides that provide excellent control with long residuals for soybean loopers.  Although populations are expected to be much higher on very late planted soybeans, they can be managed effectively.
• Stink Bugs:  Studies at Stoneville show stink bug numbers tend to reach their highest points September 15-25 each year.  Anything we do to expose soybean during this period will likely result in higher stink bug numbers.  Because a large portion of the Mississippi crop is planted in early group IV soybeans, many acres will be maturing when the post-flood soybeans are still very green.  This creates “green islands” across the landscape that are highly attractive to stink bugs. Plan at least 2 applications for late-season stink bug control.  Stink bugs can be managed effectively on late-planted crops, but reinfestations will likely be common.
• Velvetbean caterpillar:  Problems with velvetbean caterpillars are usually in the hills, but we do occasionally see outbreaks in extremely late-planted fields in the Delta.  Velvetbean caterpillars are very easy to control with foliar insecticides, but you must scout for them frequently. 
• Corn Earworm:  It is difficult to predict whether or not corn earworm will be a problem in post-flood soybean since their occurrence has been sporadic most years. However, this pest does need to be monitored closely throughout the reproductive period. Consider budgeting at least one spray application for this pest.
• Bean Leaf Beetle:  Bean leaf beetles should be monitored closely. If treatment is required, use tank mixes or premixed products with more than one mode of action.  Pyrethroids alone are not recommended in the Delta due to confirmed resistance to this class of chemistry.
•  Insecticide seed treatments:  Insecticide seed treatments are still a viable option to help reduce risk, even if you are trying to cut input expenses on late-planted soybean.  Recent studies conducted in Starkville, Stoneville, and Verona showed a similar response of 2.7 bu/a on soybean regardless of planting date or maturity group.  Insecticide seed treatments will also help protect against early-season threecornered alfalfa hopper damage as long as 24-28 days after planting.

CORN

Irrigated corn yields expectations for mid to late June plantings decline considerably (about 2 bu/a/day).  They will likely be no more than 50% of normal plantings (110 bu/a) and can be far less.  Yield expectations for dryland corn are much lower (<60 bu/a) and much more volatile than where irrigation can temper drought and heat stress.  Corn hybrids maturation is directly related to heat unit accumulation which is represented as growing degree days with a 50° F base level or GDD50’s.  Corn hybrids adapted to Mississippi require 2,800-3,000 GDD50’s to reach physiological maturity, and this requirement cannot normally be achieved planting after July 1 at Yazoo City.  Corn (and sorghum) grain moisture at physiological maturity is approximately 30%, which is not acceptable for long-term storage.  As a result, additional time and/or artificial grain drying ability needs to be factored into practical growing season requirements for all crops.  Also, field drying of corn will be very slow when temperatures cool and humidity and rainfall increase during the fall.  In summary, grain drying and general harvest conditions, particularly if we have abundant fall rainfall, will be far less desirable than normal. 

Management Tips for Corn

• Resist the natural temptation to plant early-maturing corn hybrids when planting late in order to make up for lost time.  Early corn hybrids are bred for much milder climates, and although they may perform well when planted early, they must endure extreme heat and humidity when planted late.  This can contribute to poor performance or failure.
• Insect pests, including corn borers, armyworms, and earworms are more likely to infest late-planted corn in high numbers and cause heavy crop damage.  Hybrids containing multiple Bt traits, such as VT3Pro or Viptera, are strongly preferred.  However, these specific traits require a 20 percent non-Bt refuge, which has the potential to be a catastrophic loss, given intense insect pressure.  
• Southern rust will likely be a substantial threat to late-planted corn.  Southern rust is an aggressive disease that traditionally infects Mississippi corn in late July.  However, it doesn’t normally doesn’t reduce yield much because corn is nearly physiologically mature.  Late-planted corn is considerably more vulnerable, particularly since the corn hybrids planted in our production system are not known to possess resistance to Southern rust.  Plan to closely scout the crop closely and apply a fungicide if disease threatens.  Since corn’s reproductive growth stages span about 60 days and this is an aggressive disease, a single “automatic” fungicide application at tassel stage will likely not protect the crop.  Frequent field scouting and potentially multiple fungicide applications could be necessary to moderate a heavy Southern rust infection.

GRAIN SORGHUM

Grain sorghum is an alternative crop that may be better suited than corn for late planting because it is earlier maturing and much more heat tolerant.  It is best suited for late June through mid-July plantings, particularly when grown in dryland culture.  Using earlier-maturing grain sorghum hybrids for planting after July 1 is necessary because full-season hybrids require nearly 120 days to mature.  Growing earlier-maturing sorghum hybrids should be feasible, especially compared to corn, because grain sorghum is routinely evaluated for heat tolerance and is grown in environments as far south as coastal regions in Texas.  Yield expectations for post-flood dryland grain sorghum are likely about 75 percent of normal or about 60-80 bu/a.  However, numerous insect problems, including chinch bugs, fall armyworm, corn earworm and sorghum midge, can cause severe damage and will require diligent management.  Transgenic herbicide and/or insect resistant traits are not available for grain sorghum, so growers must rely upon conventional herbicide and pest management strategies. As always use good pesticide stewardship, especially regarding sensitive crops.  Another potential pitfall with grain sorghum is that it is prone to kernel sprouting when rainy or humid weather persists during the drydown period prior to harvest.  Thus, the ability to harvest quickly and dry grain using commercial drying equipment could be very beneficial.  Production expenses are about 40% lower for grain sorghum than for dryland corn.  Therefore, for dryland fields planted after mid-June, grain sorghum offers higher potential profitability and lower risk than corn.  However, marketing options are more limited, so investigate opportunities and secure an outlet before planting.

Management Tips for Grain Sorghum

• Plant about 60,000 seeds/acre.  This moderate rate will limit interplant competition between plants and promote better plant health. 
• Use very conservative nitrogen rates (50-80 lbs. N/a).  Mid-summer conditions should minimize nitrogen loss normal with earlier plantings and your yield goals are more moderate.   
• Use herbicides prior to crop emergence to kill existing vegetation and provide residual weed control, because few quality postemergence options exist.  
• Insect pest pressure will likely be much higher than normal on post-flood planted sorghum. Plan to dedicate considerable scouting efforts to monitor insect pests, and budget more pesticide applications than normal. Potential insect problems include chinch bugs, fall armyworms, corn earworms and sorghum midge. 

RICE

Rice yields will typically decline approximately 0.5 percent a day when planting past May 1.  Yield losses associated with late planting can be significantly higher, especially if temperatures are high during heading. Rice that emerges by June 20 will be ready for harvest around October 21 in the south Delta region.  Rice planted after this time period may not have enough heat units to fully mature before harvest.

Management Tips for Rice

• Reduce nitrogen to a total of 150 lb N/a since high yields may not be achievable.
• Destroy all existing vegetation from prior crops ahead of planting. 

COTTON

Cotton yields typically begin declining when cotton is planted after May 15 in Mississippi.  Although some growers have been successful planting cotton up to June 1, the likelihood of success when planting after this date is greatly diminished.  In addition to potential yield reductions, crop and pest management costs must be considered.  Cotton planted June 20 will likely not fully mature, which will result in yield losses.  Production costs, including irrigation and insect management, are also likely to be higher due to the delayed planting date.  Due to time required for full maturity, cost of production, and potential yield losses, planting cotton in mid-June following flooding is not recommended. 

Management Tips for Cotton

• Plant an early maturing variety. Although the difference in relative maturity of cotton compared to some other crops is not as wide, managing for earliness is essential.
• Plant a two-gene Bt variety that also is resistant to either glyphosate or glufosinate.
• Scout for and control early season insect pests and mites to improve early square retention and boll set. Even with Bt varieties, scout thoroughly for worms.
• Do not over fertilize with nitrogen. Do not exceed 100 lbs of actual N per acre.  Consider reducing this rate to 80 pounds or less when following soybean or corn, which leave significant amounts of N in the soil.  Research has shown that excess N can delay maturity.
• Be timely with plant growth regulator applications.
• Irrigation may be initiated earlier than normal due to hot, dry conditions typically encountered in June, July, and August.
• Be proactive with regard to weed management. Mississippi is home to several glyphosate-resistant weed species. Once these species emerge, management is glyphosate-resistant cotton become extremely difficult. The use of residual chemistry is encouraged to prevent potential losses due to competition from weeds.
• Initiate defoliation when the topmost boll you realistically expect to harvest resists being cut with a knife and has seed coats beginning to turn dark. Defoliation applications should be considered when cotton is 40 – 60 percent open, depending on weather conditions.

Crop Insurance Considerations after Flooding

Important prevented planting provisions:

• No prevented planting coverage under GRP or GRIP policies.
• Prevented planting payments equal 60 percent of the production guarantee for timely planted crops, unless a higher option was selected at signup.
• If a producer does not plant a second crop, he or she may collect all of prevented planting payment for the first crop.
• If a second crop is planted, a producer may collect 35 percent of prevented planting payment for the first crop and pays 35 percent of original premium.

Planting a second crop after losing first crop

• A producer can plant a second crop on the same acreage, not insure it, and get all of the prevented planting payment on first crop.
• A producer can plant and insure a second crop and collect a premium equal to 35 percent of the prevented planting payment for first crop while paying 35 percent of original premium.
• If the second crop does not suffer an insurable loss, the producer can collect the remaining 65 percent of the prevented planting payment for first crop but must pay the remaining 65 percent of the original premium.

Note:  These situations do not apply to double cropping.

Producer options regarding prevented planting provisions (with examples)

1.  Plant during the late planting period, generally 25 days after final planting date.

• For cotton and rice, the final planting date was May 25. A producer can plant cotton or rice until June 19 and still be covered.
• For soybeans and grain sorghum, the final planting date is June 15. A producer can plant soybeans or grain sorghum until July 10 and still be covered.

Note: For most crops, the timely planted production guarantee is reduced one percent per day after the final planting date.

2.  Plant after the late planting period and receive an insurance guarantee equal to the prevented planting guarantee

• If crop is planted more than 25 days beyond the final planting date, the insurance coverage level is reduced by 40 percent (or 60 percent of the original coverage level) unless a higher prevented planting option was selected at signup.

3.  Idle acreage and receive a full prevented planting payment.

• Producer can leave field idle and receive 60 percent of the original coverage level guarantee, unless a higher level was selected at signup.

4.  Plant a cover crop and receive a full prevented planting payment.

• Same as above, with the exception that a cover crop is planted. The cover crop CANNOT be utilized until after November 1 (for most crops) and CAN NEVER be harvested. If cover crop is utilized or harvested, the payment is void and other penalties could be incurred.

5.  Plant a second crop or cover crop after the late planting period and receive a prevented planting payment equal to 35 percent of the prevented planting payment.

• The prevented planting reduction (40 percent of original coverage level, unless a higher level was selected at signup) is reduced by another 65 percent.
• Example: Corn crop is lost and soybeans are planted after the prevented planting period of July 10 (for soybeans), the corn insurance payment will be: original coverage level x 60% x 35%.

If planting soybeans before the 25-day late planting period expires, see “Planting a second crop after losing first crop” section above.

Notes: These options are only applicable AFTER the final planting date.

Final planting dates*

• Soybeans following another crop: 6/25/11
• Soybeans not following another crop: 6/15/11
• Cotton: 5/25/11
• Corn: 4/25/11
• Grain Sorghum: 6/15/11
• Rice: 5/25/11

*Applicable for Bolivar, Claiborne, Issaquena, Sharkey, Warren, Washington, and Yazoo Counties for the Yield Protection, Revenue Protection, and Revenue Protection with Harvest Price Exclusion policies.

Reference

USDA Risk Management Agency. “Prevented Planting Insurance Provisions—Flood.” Program Aid 2020. May 2011. Available from: www.rma.usda.gov/pubs/rme/ppflood.pdf

Acknowledgement

Thanks to all who contributed to this effort.  For a complete list of contributors and the publication version, see http://msucares.com/pubs/publications/p2680.pdf.