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.
The last couple of weeks we had some unusually cold weather. Some days, daytime temperature was 20 degrees below the average for this time of the year. The graph below compares average maximum daily temperatures with actual 2011 maximum daily temperatures during April and May in Colusa County.
Because of the cold weather, rice seedlings aren't growing much. Growth is very slow, and plants seem to lag behind. However, don't think that just because the rice is not growing, other organisms are also slowed down. I've been hearing of shrimp in several fields, and saw some in a field that was planted two weeks ago. Look at the size of the shrimp and the size of the seedlings in the pictures below.
Tadpole shrimp can grow very fast. A few days with water temperatures between 60 and 84 can promote egg germination and shrimp development. Since the rice is growing slower than normal because of the cold weather, it is under more risk of being injured by shrimp. Monitor your field closely during seedling development, and worry about shrimp only until the rice breaks the water surface. Once the rice is out of the water, shrimp will not cause damage. A lengthy discussion of the biology of the tadpole shrimp was included in the May issue of the Rice Briefs newsletter, available at the Colusa County Rice Program website: http://ucanr.org/sites/colusa/rice/Newsletter/
For monitoring and treatment recommendations, go to the UC IPM website: http://www.ipm.ucdavis.edu/PMG/selectnewpest.rice.html