During our Jan 2017 winter meetings, I conducted a short clicker survey about how bad tadpole shrimp (TPS) has become in the past few years. There were a couple of technical difficulties, and attendees to the Richvale meeting didn't get to see the answer to the questions. I thought it would be a good idea to share the results of the survey here. The results were very similar for all meetings, so I have aggregated all the answers.
Q1: In your opinion, compared to 10-15 years ago, TPS problems are currently:
Total respondents: 109
About half of respondents thought TPS problems are the same than 10-15 years ago and almost 40% thought problems were somewhat or much worse. This seems to indicate that TPS problems are slowly becoming worse. It might have to do with the fact that copper sulfate is more expensive, less effective against algae, and therefore less used; and pyrethroids don't seem to be working as well as before (see question 2).
Q2: Have you noticed a reduction in the efficacy of pyrethroid insecticides controlling TPS?
Total respondents: 119
A third of respondents have noticed a reduction in pyrethroid efficacy for TPS control. This is alarming. Last year, TPS from two fields were confirmed as tolerant to pyrethroids. Responses to this question indicate that there might be way more fields with tolerant TPS out there.
Q3: If you treat for TPS, do you:
Total respondents: 90
A bit over half of respondents scout their fields before doing a TPS treatment (wait), and 40% schedule treatments. In my opinion, both approaches are valid. TPS develops very fast, specially in late planted fields, and in problem fields, they will show up no matter what.
Responses to the questions indicate that we need new alternatives for TPS control and tools to make scouting easier. Some of the work being done to address these questions was presented during our last winter meetings. The presentation is posted on-line on the UC Rice On-line website.
I have been alerted of three instances where pyrethroid applications for TPS control have failed. One field had been treated with a pyrethroid two times, and TPS were still alive in great numbers. I collected some of these surviving TPS and run a quick test to see if they would survive exposure to lamba-cyhalothrin or copper.
|Treatment rate||% survival after 24 h exposure|
|Lambda-cyhalothrin 1 mg/lt||70|
|Lambda-cyhalothrin 2 mg/lt||0|
|Copper sulfate 4.5 mg/lt||0|
The lamda-cyhalothrin 1 mg/lt concentration is roughly equivalent to 5 times the field rate applied to a 4 inch flood. It is remarkable that TPS were able to survive this concentration. The copper concentration is equivalent to a 5 lbs/a rate. In another test, I had TPS survive the equivalent of half and double the rate of a lambda-cyhalothrin application. I'm currently testing the TPS collected from a third field.
Make sure your TPS treatments are being effective. If TPS are surviving a pyrethroid treatment, use copper sulfate to kill survivors. We need more testing to figure out what is going on, but it is a good idea to prevent surviving TPS to lay eggs that may create more problems next year.
If you notice TPS surviving a pyrethroid treatment, contact me. At this point the issue seems to be in only a few fields, but it is important to learn of any other instances of control failure.
Planting is starting to pick up now that water allocations are known. One of the first pest problems one is going to find in recently flooded rice fields is tadpole shrimp (TPS). Most of the time, when muddy water or uprooted plants are observed, it means the TPS are large and probably already done quite a bit of damage. Young TPS are hard to detect; because of their size they might not cause mudding of the water. However, look carefully to see if you can spot them. Small TPS, when their shell is about half the size of a rice seed, can injure rice roots as they emerge from the seed; they have a hard time chewing on the coleoptile that emerges first from the seed. Larger TPS, when their shell is about the size of a rice seed, are capable of feeding on the coleoptile and roots, and can dislodge seedlings easily.
Look carefully, there are other bugs that can be confused with small TPS, such as small beetles and clam shrimp. Small TPS look just like fully grown TPS. The very first TPS instars do not look quite like TPS, but those are really hard to spot, and do not feed on rice seedlings anyway. Here's a few images.
TPS first instars next to eggs
Second or third TPS instar
I was asked the other day what do immature tadpole shrimp (TPS) look like. Young TPS look pretty much like the older ones, just smaller. The very first instar, which remains inside the egg for a few hours, looks somewhat different, but you are not going to see this instar in the field with the naked eye. A few hours later they molt and look more like regular TPSs. Here's a picture of a few of them a few days later swimming belly up. Notice the rice grain floating next to them for size comparison.
We received several reports of tadpole shrimp (TPS) problems this year. One field I visited had to be replanted due to TPS damage. Flooding of this field took a long time, resulting in checks that were flooded for more than 10 days before the field was seeded. This might have allowed enough time for the shrimp to develop and reach high numbers by the time seeds were starting to germinate. The grower drained to field and this killed the TPS, but after reflood, we saw a second TPS hatch. A pesticide had to be used to protect the replant.
My theory is that the dry winter is to blame for the spike in TPS activity this year. Fields were really dry and flooding took longer than usual. Additionally, because everyone was trying to flood at the same time, in many areas there wasn't enough water for a fast flood. As in the field described above, some checks were flooded for several days before seeding, giving the TPS an advantage.
I'm conducting an experiment with an experimental compound for TPS control. So far, it looks promising, but we'll have to wait some time before we can draw any final conclusions.