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.
- Author: Larry Godfrey
Large RWW flight at RES (Biggs, CA) night of April 30. We got over 2100 RWW which exceeds the total number captured the entire season in 2011 (a record low with only 415) and rivals the seasonal total for any year of the last 10 (except 2009 which was over 6000). The night of April 29 appears to have over 500 adults as well (have not counted them yet). The environmental conditions for flight did not appear ideal during those nights but I guess it was “good enough”. Am I predicting a heavy weevil year? It seems the infestation patterns are very localized now as opposed to coming from long-range flights so a prediction is hard to come up with. But this pest is certainly “out and about” and waiting for flooded conditions.
I've been receiving reports of high armyworm populations this summer. You can always find some armyworms in rice fields, but I have rarely seen fields that needed a treatment due to armyworm injury.
Defoliation caused by armyworms is not uncommon. However, rice plants have abundant foliage and can take quite a bit of defoliation.
UC guidelines recommend a treatment only if more than 25% of the foliage has been consumed and you still see armyworms in the field.
It can be challenging to find armyworms in a rice field. They usually feed at night. During the heat of the day, they hide at the base of the plants where it's cooler. To monitor for armyworms, open the canopy and look down near the water level. Spend a minute or two looking; small armyworms can be hard to see.
Alternatively, you can shake the plants and observe for worms falling into the water. This is especially effective for large larvae.
Panicle damage can be severe. Armyworms can feed on developing panicles causing whole panicles or panicle branches to become blank.
Observe closely where the panicle branch breaks or becomes blank and you will see chewing marks.
UC guidelines recommend a treatment if more than 10% of the panicles are affected and you still see worms in the field. If you can't find them during the day and are still in doubt, come out during the evening and see if you see any worms in the panicles.
Those fuzzy white cocoons you find at the base of the plants are pupal cases of the parasitic wasp Apanteles militaris. The wasp lays its eggs inside the armyworm, wasp larvae develop and when they are ready to pupate they leave the armyworm and form the white cocoons. This, of course, kills the armyworm.
It's important to remember that armyworms pupate in the soil. In a rice field, when they are ready to pupate, they usually drop to the water and drown. Some may pupate in the foliage at the base of the plants, but there they are easy prey for their natural enemies. If you see injury but the worms are gone, there is no need to worry about the next generation of armyworms.
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
I was looking for weevils today, so I visited a field with a history of weevil problems. The field was seeded 3 days ago, and there were no plants (rice or weeds) in the field yet. Levees were clean, the borders were weedy.
First, I looked at the grassy weeds around the edges of the field, and found some fresh feeding scars. Evidence that weevils were around.
Then I looked at some of the weeds that ended up under water after the flood.
After a few minutes searching, I found some weevils.
Rice water weevils come out of their overwintering sites in March-April and start feeding on grassy weeds. This allows them to regenerate their wing muscles and fly to flooded rice fields. Water seems to be the main attractant. Once there, they can feed on grassy weeds until rice seedlings start developing.
Looking for feeding scars and weevil adults will help you decide if you need a treatment. Remember that weevil infestations tend to be higher near weedy borders and levees.
While you are out there, also look for midge larvae and tadpole shrimp. Inspect the seed for midge injury and silken tubes. Tadpole shrimp eggs hatch after 3 days of flooding, but young tadpole shrimps are very small and hard to see. You will start seeing tadpole shrimp adults 8-12 days after flooding.
For more information and management options, consult the UC IPM Management Guidelines: Rice.