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).

 

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.

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.