Will rice escape tadpole shrimp injury? Here’s how to tell

By Luis Espino —

tadpole shrimp feeding on a rice seedling

In fields where flooding takes several days, tadpole shrimp will have a head start and may reach the injurious size before the seedlings reach the first-leaf stage — photo by Luis Espino

Tadpole shrimp (TPS) are starting to pop up in rice fields. A grower asked me when is the period when rice is “safe” from TPS. He is seeing very small shrimp, and seedlings are already past the first-leaf stage of rice (lsr).

To determine if rice is going to escape TPS injury, two things need to be considered: the rice seedling stage and the size of the TPS.

It is difficult to determine the size of TPS, but if you pull one out of the water and its shell is smaller than half the size of a medium grain rice seed, then it won’t injure a germinating seed. TPS larger than that will readily feed on germinating seeds and seedlings.

TPS will feed on seedlings until they reach the first leaf (when the spike is well developed). TPS don’t seem to like feeding on the green tissue. However, they will feed on roots. If the main root is exposed, seedlings are still at risk of TPS injury.

Use this guide when scouting:

tadpoll shrimp scouting guideOne more thing to considering when scouting. If rice escapes injury and TPS are not treated, they will lay eggs that will stay in the soil and hatch next season.

When it comes to TPS management, fields that can be flooded quickly have an advantage over fields that take several days to flood. A quick flood followed by timely seeding will result in seedlings that can reach the first-leaf stage rice before the TPS grow too large.

In fields where flooding takes several days, TPS will have a head start and may reach the injuring size before the seedlings reach the first-leaf stage rice.

Dr. Luis Espino is a University of California Cooperative Extension farm adviser and county director for Colusa County. He may be reached at laespino@ucanr.edu