The frequency of heavy precipitation in the US has increased over the past few years and is projected to continue increasing for the unforeseeable future. In fact, ‘torrential rain’, ‘downpour’, and‘flash flood’ are common terms used in weather alerts that help the public prepare for potential flooding. For farmers, the threat of flooding is unwelcome because that means there is the potential for the loss of crop yield. Furthermore, the occurrence of floods complicates weed management.

Every once in a while, a crop growing season may be very wet due to excessive amounts of rainfall, or perhaps fields may be flooded. Whether this phenomenon is common or not, when there is excessive wetness crop growers must adapt to the conditions to ensure that their crop-growing enterprise does not fail. If the field is flooded, the crop producer is faced with several challenges related to crop yield and weed management.

To most, there is a wet season and a dry season that occurs every year. The wet and dry seasons are spread over winter, spring, summer, and fall seasons. Sometimes, the seasons are simply referred to as either cold, dominated by cold temperatures and high amounts ofprecipitation, or warm, which is dominated by high temperatures and little precipitation.

The wet season

The wet season, or rainy season, is the part of the year when a region’s average rainfall occurs. Lasting at least a month, the wet season helps sustain vegetation growth which leads to crop yields late in the season. In addition, during the wet season, air and freshwater quality improves.

When there is excessive moisture duringa wet season, it could lead to (i) soil erosion or (ii) the overflow of water bodies and flooding.

1. Soil erosion, a form of soil degradation, is the destruction of the upper layer of soil,often caused by flowing water especially when the moisture is excessive. The wind is the other agent of soil erosion.
2. Overflow of water bodies leads to flooding which causes the affected inhabitants of the flooded area to retreat to higher ground. Those unable to retreat, like plants, will likely succumb when the ground is flooded.

Flooding

Excessive rainfall that leads to flooding is something that happens in the US each year. In 2022, there have been several incidences of excessive rainfall and accompanying floods. For example, incidences of flooding in Texas, Eastern Kentucky, Arizona, Nevada, and Yellowstone Park, Montana have dominated the news in 2022.

What happens when crop fields are flooded?

Flooding in agriculture has become very common. Whether it is linked to climate change or just normal weather patterns, flooding can lead to losses in many ways. For example, the occurrence of floods can:

• Make fields unsuitable for planting for part or all of the season.
• Ruin crops already planted.
• Ruin harvested grain that has been stored in silos. Food that has been in contact with flood water is considered to be unfit for human consumption by the US Food and Drug Administration (FDA).
• Complicate weed management.

How does flooding complicate weed management?

The occurrence of a flood can complicate agricultural operations in many ways. In crop production, complications in weed management may arise due to the circumstances surrounding the flooding event. For example:

1. Abundant weed growth:
   1. Ifa crop survives flooding, recovers, and continues growing, it likely will be stunted and less competitive against weeds. Weeds often thrive following a flood and must be controlled to allow the crop to maximize its yield.
   2. If crops are damaged and not worth harvesting, weeds that grow in the field must be managed to prevent them from producing seed which would replenish the seedbank. Mechanical methods, such as mowing can be used if the field is not excessively wet. Otherwise, applying herbicides may be the best control option if the field is too wet for mechanical methods to be used.
2. Introduction of new weeds: Someweed seeds may be carried into the field by floodwaters and present weed control problems in subsequent years. Sometimes, new weed problems emerge the year after a flood. A continual assessment of weed populations in a field after a flood will help managers keep track of new weeds.
3. Limited feasibility of herbicide use: If the crop recovers from flooding and weeds growing in the crop must be removed, itmay not be safe to apply some herbicides especially if the “window” for safe applicationin a crop has passed.

References

• Bradley, K., and M.D. Bish. Weed Management Issues Related to the Flooding and Wet Conditions in Missouri. Missouri IPM Publ., Aug. 2019. (Accessed, August 28, 2022).
• Mississippi State Univ. Extn. Serv. Weed Management after a Flood. The Disaster Handbook, 1998. Info. Sheet 1734. (Accessed, August 28, 2022).