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.

Start scouting for armyworms. Begin in the areas where plants are light green because of N deficiency (corners, levees). Small larvae do not cause yield reductions, but once they reach a large size, they can defoliate rice quickly. Additionally, the larger the worms are, the harder to kill with an insecticide. If you find small worms, it does not necessarily mean that they will reach economic levels. There are many natural enemies in rice that can reduce armyworm populations, such as spiders, wasps, and plant bugs. Weather can also affect the development of the worms. Monitor the field closely. Once defoliation is noticeable, plan a treatment soon while the worms are still small if you feel you are at risk of reaching the threshold.

For information on thresholds, see the UC IPM website.

An exciting opportunity for rice growers to create on-farm habitat will have a final enrollment opportunity on July 29^th. A Regional Conservation Partnership Program (RCPP) supports practices in the Waterbird Habitat Enhancement Program (WHEP) and provides incentives to farmers to voluntarily modify their field management in small ways to benefit birds that are also compatible with farming. Rice provides critical food and other resources for many species of waterbirds year-round. Small changes to farm management, as supported by this program, can increase the value of rice fields as resources for birds.

We strongly encourage new growers/landowners who have not enrolled in WHEP or RCPP in the past to apply. New applicants will be preferentially ranked for acceptance into the program. However, we anticipate that quality proposals from past WHEP-RCPP participants will also be considered for funding. Practices available through the RCPP-WHEP include:

• Two weeks of continuous shallow flooding August-October
• Variable drawdown of winter-flooded fields in February
• Planting and maintaining cover crops for nesting birds
• Nesting islands for safe breeding habitat
• Postponing decomp activities until January

No long-term commitment is required in this program. EQIP-eligible producers in Butte, Colusa, Glenn, Placer, Sacramento, Sutter, Yuba, and Yolo counties can apply. For more information about this program or to schedule a farm visit to discuss this program, join us at a free workshop about the program June 7^th 10:30am at the Colusa Casino OR contact Khara Strum at Audubon California, kstrum@audubon.org OR Paul Buttner at the California Rice Commission, pbuttner@calrice.org.

I have received an update from the Butte County Ag Commissioner's office regarding winged primrose willow. Germinating seedlings have been detected recently. At this point, the seedlings are very small and would be very difficult to notice. Scouts were able to find them in places where the weed had been seen in the past. But this is a good indication that conditions are now good for germination. Growers and PCAs in risk areas should be on the alert. Larger seedlings will probably be visible in 30 days.

For more information and pictures, visit the UC Rice On-line winged primrose willow page.

Photo by Evan Padgett, Butte County Agricultural Commissioner Department

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
Control	60
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.