Number of moths trapped per day is increasing. Numbers are higher in areas where crop diversity is higher. I haven't seen any worms yet, but they are expected by the end of the month. At this point, moths may be mating and laying eggs on weeds and other plants in the area, including rice. This week I received a picture from a PCA of what seemed to be armyworm eggs laid in a rice seedling. No worms are expected on rice until late June or early July. In 2016, worms were observed in fields only after catches were around 20 monts/trap/day.
I have set up seven armyworm pheromone traps in the Sacramento Valley, and Michele Leinfelder-Miles is monitoring one trap in the Delta. Last year the traps showed a distinctive peak mid August, when worms started causing problems during heading. This year, we will start monitoring earlier and so we will try to identify the peak that corresponds to when worms start feeding on foliage in late June - early July.
I will publish the results of the monitoring weekly or biweekly on the UC Rice On-line website and I will sound the alarm when monitoring efforts need to be increased to make sure infestations don't go unnoticed.
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.
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
Earlier this week, I received reports of two fields near Willows that showed evidence of armyworm feeding and very small worms in the plants. Today, I sampled a field that had some severe armyworm affected areas last year. At first sight, there was no evidence of injury. However, when looking closely, some of the bottom leaves in the plants showed evidence of armyworm feeding.
This is a 40-day old field, drained for propanil. When I shook the injured plants a bit, a small worm fell to the ground half the time. The worms were hard to notice; they were small, and their color ranged from yellow to dark green. Most of the injured plants and all the worms I found were in the corners of the field and next to levees, where the plants showed symptoms of N deficiency because the aqua rig couldn't reach.
The larvae I found ranged from first to early third instar. It is the fifth and sixth instars that will cause yield reductions (look at the red line in the graph below). It should take between 127 and 268 degree days (above 50 and below 84.2 oF) for the larvae in the field I sampled to reach the fifth instar. Using average temperatures for the past 10 years, I calculated that we should be seeing fifth instar larvae between June 15 and June 21. Those dates are really close to the dates when we saw the armyworms causing problems last year.
For information on thresholds, see the UC IPM website.