Tadpole shrimp are pests of water-seeded rice fields. Sexually mature tadpole shrimp are found as early as 9–12 days after floods are established; therefore, rice plants have <9 days to break the surface of the flood (i.e., the time at which rice is no longer vulnerable), before tadpole shrimp are large enough to uproot seedling rice. This is particularly important during periods of flooding like we are experiencing now. Farmers, who decide water-seeding is the only option, may be planting in fields with mature tadpole shrimp that can damage rice. These farmers need to be on the lookout! However, rice planted by dry-seeded methods should have periods of time when the field is dry and unable to support this aquatic critter. When the field is permanently flooded, plants should have an adequate root system to prevent stand loss. Therefore, tadpole shrimp are not pests in normal dry-seeded systems. If a farmer drill-seeded is rice, and rain flooded the field before the rice emerged and it remained flooded for a long period, tadpole shrimp may damage rice in that scenario. This should be the only scenario when dry-seeded rice is at risk. Once rice is no longer vulnerable to tadpole shrimp damage (i.e., breaks the water surface), tadpole shrimp may serve as a biological control agent for mosquitoes and/or weeds.
Lower seeding rates are more susceptible to tadpole shrimp damage than higher seeding rates. For example, losing 10% of a stand planted at 30 lbs/A is more detrimental than losing 10% of a stand planted at 90 lbs/A.
Where are tadpole shrimp found in Missouri?
We developed a method of sampling for tadpole shrimp after harvest when conducting a distribution survey. Results showed tadpole shrimp are widely distributed; however, not every field within an area is infested. Additionally,most of the fields that were positive for tadpole shrimp are east of the Little River Drainage District. Tadpole shrimp are transferred from field to field via floodwaters, wind, birds and other wildlife. They are also likely transferred via equipment used in an infested field as well as transferred on the soles of boots when walking in and infested field and then walking in a non-infested field. The latter two mechanisms of transfer could be avoided by adopting better sanitary practices when moving between rice fields.