- Author: Luis Espino
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.
- Author: Luis Espino
Finally, the armyworm season seems to be over. Moth trapping shows that the numbers are decreasing to the lowest levels of the season. Additionally, most fields are ripening and therefore less susceptible to armyworm injury.
Overall, armyworm infestations were not as severe as last year. At the beginning of the season there were some very early infestations; however, those infestations may have been detected early because growers and PCAs were scouting closely after last year's outbreak. In most cases, the early infestations that were brought to my attention consisted of small worms, which usually go unnoticed until a few weeks later in the season.
In late August, a second infestation peak occurred. However, this infestation was similar to what we see in normal years. Nevertheless, I saw some injury that might have been approaching treatment levels.
The armyworm moth trapping conducted this year started a little later than I wanted. Next year I hope to start trapping in late May or early June so the first armyworm peak can be detected timely. Number of moths trapped remained low until August, when they started to increase and reached a peak in all locations in the Sacramento Valley. The moth peak observed in early to mid August corresponds to the increased injury observed in late August, when eggs laid by those moths reached the 3rd and 4th instars.
- Author: Luis Espino
This year, armyworm infestations were not as severe as last year. Populations did not reach the very high numbers of 2015, but they were early. Growers and PCAs were scouting diligently, and were able to recognize infestations when the worms were small. This gave growers the upper hand and many were ready to make a treatment decision if necessary. Intrepid was used in some fields successfully.
We are not totally off the hook yet. We usually get a second peak of armyworm activity during the late boot and heading stages. UCCE is monitoring moth populations in several areas of the valley using pheromone traps. The traps were set up in early July, and the trapping numbers will be shared in this blog and the UC Rice On-line website.
So far, moth numbers are low, averaging 2.5 moths/trap/day during the week of July 11. Numbers have decreased since the previous week, when the average was 4.3 moths/trap/day. The location with the highest moth numbers is near Knights Landing, averaging 9.2 moths/trap/day. Previous work done by Larry Godfrey, UC Davis Extension Entomologist, found that peaks of 20-40 moths/trap/day might indicate an armyworm larvae peak 7 to 10 days later.
Number of moths/trap/day captured in armyworm pheromone traps across the Sacramento Valley
- Author: Luis Espino
Before the weekend I got reports of two fields where defoliation was over threshold and worms were big. As predicted, we are now seeing armyworms at fifth and sixth instar. These are the worms that will cause noticeable defoliation. The timing of infestation is similar to last year's.
I scouted a field in Colusa on Friday. Defoliation was limited to corners, and even though it was over threshold at some spots, the field was not at risk. However, it is important to keep scouting because there are still small worms that will continue to develop and can potentially cause more defoliation.
Intrepid is not available for use yet. Hopefully we will be hearing from EPA and DPR soon.
I also noticed a heavy infestation of caterpillars on the cattails. I don't know what these caterpillars are, but they are not armyworms. The cattails were heavily damaged, but not the rice. There were several of these caterpillars resting on rice, but they were causing very little defoliation. I suspect these are Simyra insularis, the cattail caterpillar (very appropriate name).
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- Author: Luis Espino
In the past week, many growers and PCAs have identified fields infested with armyworms. The size of these worms is small, ranging from first to third instars. The amount of defoliation they cause at these stages is small. However, once these worms reach the fifth instar, they will consume a lot more foliage and have the potential to cause yield reductions.
Last year, infestations sneaked up on us and were difficult to control because of the number of worms and their size. Older worms are much harder to kill than younger worms. This year, the fact that many growers and PCAs have noticed the infestations early gives us the upper hand. Nevertheless, I would not recommend treating until you notice defoliation is approaching the threshold.
Many factors affect the survival of armyworm larvae in the field. There are many natural enemies that will consume the larvae, such as spiders, plant bugs, beetles, frogs, etc. Additionally, weather can also play a role. Humid conditions can promote the development of armyworm diseases. Cold weather will slow down their movement, making them more susceptible to attack by natural enemies.
Research has shown that rice can withstand up to 25% defoliation before a yield reduction occurs. Most of the time, defoliation is limited to discrete areas of the field. Monitor for foliar injury by looking for signs of armyworms feeding on leaves. To sample, choose a part of the field where you have observed injury. Select a plant at random and pull it up or move all the surrounding foliage away and check for defoliation. Check the plant from the top of the leaves to the base of the plant and the water surface for armyworms. Determine if 25% or more of the foliage has been removed by armyworms; also note if you find armyworms on neighboring weeds or rice plants. Repeat this procedure every 5 to 10 feet across a transect until 10 plants have been examined. Move to a different part of the field where feeding is evident and examine 10 more plants in the same manner. Repeat this procedure at several areas of the field until you are confident that you have an estimate of the average field condition.
Keep in mind that warm weather speeds up armyworm development, and therefore, defoliation will occur faster. Once you are approaching treatment levels, make the decision to treat so that there is enough time for the application to go out before the threshold is reached. Windy days and applicator backlog can delay the treatment date.