Hurricane Matthew and Soybeans

— Written By

As flood waters recede across North Carolina, disaster assessment begins. For soybean farmers one of the first things is to attempt to estimate crop damage. Unfortunately, this can be a difficult task. The extent of damage is dependent on a number of factors including plant growth stage, depth of flood waters, days of flooding, and weather conditions after the flooding.


Due to seed damage in 2015, an unusual portion of the acreage was planted in early maturing varieties. Some of these early varieties that were ready to harvest when the Hurricane Matthew came through will be affected more by the rainfall and wet conditions that may cause delayed harvest and damage like shattering. Some of the later maturing varieties may be more affected by grain quality reductions, sprouting, and diseases.

Floods waters can have significant damage on both immature and mature crops. For fields that were totally submerged it appears that insurance policy allows for appraisal at zero value due to the potential for toxins in the floodwaters. Check with your insurance adjuster to confirm.

Immature Crops

Yield Losses – In fields that had not yet reached maturity, damage to the plants could limit or stop seed development. The good news is Dr. Dunphy estimates it takes three to four days underwater for plants to not recover. Fields where the water receded quickly are therefore in better shape. If plants at the R6 stage (full seed stage, approximately a month from maturity) are underwater for more than four days a significant yield loss would be expected.


Types of Flood Damage on Soybeans

Soybeans are very susceptible to flood damage with lodging, shattering, and low quality grain being the most likely issues. Yield may be reduced by each of these problems.

  • Lodging – Soybeans have little resistance to flowing water, so lodging is a likely result where water rapidly enters or leaves the field. Even non-flowing water can kill or weaken roots and leave soybeans susceptible to future lodging.
  • Shattering – When soybeans are mature, splitting of pods and loss of seeds (“shattering”) increases with repeated cycles of wetting and drying. Prolonged wetting due to submersion may amplify shattering losses.
  • Grain Quality Reductions – As we’re all too familiar with after the 2015 season, periods of prolonged moisture are not good for soybean grain quality. Prolonged moisture creates an ideal environment for disease development and just like last year, seed diseases such as Phomopsis, downy mildew, and purple seed stain will be common. The good news is hopefully the low humidity and drying conditions we saw following the storm will help many fields. Although less likely than disease, sprouting will be an issue if soybeans seeds dried below 50% moisture before the flooding and then flood waters and rain caused them to increase back to above 50% .


  • Management of Flooded Soybeans
  • Scout fields thoroughly to identify the type and extent of flooding damage. Continue monitoring fields closely through the pre-harvest period to optimize harvest timing and minimize yield and quality losses.
  • Manage field areas separately – Most fields will not be uniformly affected by flooding. Where practical, consider harvesting flooded and non-flooded field areas separately, as one harvest date may not be optimal for the whole field.
  • Separate grain from flooded and non-flooded fields or field areas, as quality, storage life and marketing channels may be very different from these sources.
  • Early harvest – Fields with severe flooding damage will likely benefit from early harvest to avoid further shattering, lodging and quality problems.
  • Storage and Marketing – Keep grain from flooded and non-flooded fields separate as the quality, storage, and marketing of these groups will likely be different.
    Clean bins and grain handling equipment before putting damaged grain in storage to help prevent contamination and extend storage life.
    Bring a sample of damaged grain to your local elevator or the state grain grading office to determine marketability. Work with your elevator to discuss discounting and delivery options.
    Monitor grain closely while in storage and eliminate hot spots by stirring or removing grain from the bin.
 frost-damage-R6  Stage R6 – Full Seed Stage

  • “Green bean” stage – bean fills pod cavity
  • Seed Moist. ~75 – 80%
  • ~25 days remaining until full maturity
  • Yield Loss ~ 20 – 35%


 frost-damage-R65 Stage R6.5 – Mid-way from Full Seed to Maturity

  • Pod/seed color between green and yellow
  • Seed Moist. ~65-70%
  • ~16-18 days remaining until full maturity
  • Yield Loss ~ 10 – 15%


 frost-damage-R7 Stage R7 – Beginning Maturity Stage

  • All green color lost from seeds and pods
  • Seed Moist. ~55 – 60%
  • ~8 – 10 days remaining until full maturity
  • Yield Loss ~ 0 to 5%


Future Concerns

While dealing with the current soybean crop is the greatest priority, there are likely to be other issues in flooded fields over the next few years.

The major concern is weed pressure. Flood waters likely washed soil away, uncovering old weed seeds that were buried by deep tillage and brought weed seeds from upstream into a field. Growers could potentially see a whole new set of weeds in these fields. In the coming season, scout often to quickly identify weed species present and adjust your weed management plans to deal with these species.

Another concern is soil fertility and soil health. Flood waters could have easily changed both the landscape and nutrient profiles of your fields. Soil testing will be critical for determining the actions that should be taken to correctly fertilize these fields for next season.