UC Cooperative Extension has augmented efforts to monitor armyworm populations in rice fields since 2015 when we observed large populations earlier in the year (June) than previously observed. Here in San Joaquin County, we began monitoring in Delta rice fields a couple weeks ago. We are cooperating with rice farm advisors in the Sacramento Valley to get a more comprehensive assessment of the populations. Figure 1 shows moth counts from last week. The Delta count is the single orange data point at about 36 moths/day. Compare that to the Sacramento Valley where there have been similarly high moth catches in Colusa and Glenn counties.

These counts illustrate that it is important to be monitoring fields for worm feeding. The UC IPM guidelines for monitoring and treatment are excerpted below. In general, at the foliar stage, if half of the sampled plants have at least 25 percent defoliation from feeding, and worms are visible, then treatment is probably warranted. At the panicle stage, if 10 percent of the panicles are damaged and worms are present, then treatment may be warranted.

Armyworm larvae will grow to full size and pupate in about 3 to 4 weeks. That said, it is important to monitor fields now and later in the summer in case the current generation reproduces and a new generation develops when panicles are present.

In 2016, UC Cooperative Extension worked with the California Rice Commission to get an emergency approval for the use of Intrepid 2F (methoxyfenozide) in affected rice counties, including San Joaquin County. The 2017 application has not yet been approved, so we do not currently have this product available for rice. Please see the UC IPM guidelines for a list of registered products. I will provide an update on future moth trapping counts and product approvals as the information becomes available.

From UC IPM: Rice Armyworm Monitoring and Treatment

Foliar Injury: Monitor for foliar injury from panicle differentiation to heading by looking for signs of armyworms feeding on leaves. Once you begin to observe injury, start taking samples twice a week until grain start maturing or larvae are no longer present. 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. Record your observations on a monitoring form. Repeat this procedure every 5 to 10 feet (1.5–3 m) 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.

Panicle Loss: Monitor for panicle loss after panicle emergence by checking for entire panicles or parts of panicles that have turned white; these indicate armyworm feeding. Be sure to differentiate this injury from stem rot, which may kill the entire panicle and darken the stems. Once you begin to observe armyworm injury to the panicle, take samples twice a week to determine the need for treatment. Use a sampling ring made of plastic tubing that encloses 1 square foot. Select your sampling sites in parts of the field with white panicles. Drop the ring at your side without looking. Examine all the plants within the ring down to the water level for armyworms; at the same time check for stem rot. Record the number of panicles and the percentage of them that are white and the presence or absence of armyworms within the ring. Move on 5 to 10 feet and repeat the procedure until 10 samples have been taken. Move to another area of the field with signs of panicle injury and take 10 more samples. Repeat the 10-sample procedure until you feel that you have a good estimate of the field condition.

Treatment Decisions: From panicle differentiation through heading, treat for foliar damage only in those areas of the field where 5 or more of the 10 samples taken have over 25% defoliation and armyworms are present on the plants. If you observe a few or no armyworms, come back at night to check for the larvae, which are more active after dark. Do not treat if armyworms are not present, especially during late August, because they have probably completed development.

From panicle emergence to grain maturity, treat for panicle loss if 10% of the panicles in the area sampled are damaged and armyworms are observed. If armyworms are not observed but panicle loss is 10% or more, check for the larvae at night. If larvae are not found, do not treat because they have probably pupated and will do no further damage. Limit treatments to those areas of the field with economic damage.

1. Register for the Weedy Rice Workshop

UC Cooperative Extension and the California Rice Commission are sponsoring this workshop to update growers and consultants on the current weedy rice situation in California and on research that is being conducted by the University of California. Additionally, guest speaker, Dr. Nilda Burgos from the University of Arkansas, will be presenting on weedy rice management, lessons from the southeastern U.S.  Two workshops will be held:

• August 9^th, 9:00am – 12:00pm, New Earth Market Harvest Room, 1475 Tharp Road, Yuba City
• August 10^th, 9:00am – 12:00pm, Colusa Casino, 3770 Hwy. 45, Colusa

There is no cost to attend, but on-line registration is required. Enrollment per workshop is limited to 50 people, so please enroll early. Lunch is included. Applications for DPR and CCA CE hours have been submitted.

Information on weedy rice in California is also available from this website, which was developed by UC Cooperative Extension and the California Rice Commission.

2. Armyworm Update

We continue to monitor armyworms in Delta rice fields. Moth trap counts were high at the end of June, but the count did drop during the first week of July. We encourage growers and consultants to continuing monitoring this pest, particularly in late-planted rice. Keep an eye out for a another generation of worms that may become evident when panicles have emerged. UC IPM has the following guidelines for monitoring and treatment. The E.P.A. has granted an emergency approval of Intrepid 2F (methoxyfenozide) in rice growing counties. Please contact the County Agricultural Commissioner's office for more information.

The 2017 UCCE grain corn variety trial was planted on May 9^th, almost two weeks later than the trial was planted in 2016, due to the wet winter and spring. The trial is located in the Sacramento County Delta. Three replicate blocks of fifteen varieties were planted by air planter. This year, the varieties represent both conventional and RR varieties, as indicated in Table 1. Stand counts were made approximately two weeks after planting, and bloom was assessed over the week of July 10^th. While bloom occurred later this year due to the later planting, the number of days to bloom was less than in 2016. Across all varieties, the average number of days to bloom was 65, compared to 70 in 2016. Over the remainder of the season, we will also evaluate disease pressure (fusarium ear rot, head smut, and common smut), lodging, ear height, grain moisture, and yield. Results from previous years are available from my website. 

Table 1. Corn varieties planted in the 2017 UCCE grain corn variety trial.

 

We are continuing a trial that we began last year to evaluate optimum seeding rates for grain sorghum. UC research on sorghum has increased over the last few years, primarily in the southern San Joaquin Valley, to evaluate grain and silage sorghum for its adaptability to drought and low-input conditions. This seeding rate trial complements those efforts to provide management information for California growers. The 2017 trial was planted on May 25^th, approximately 5 days later than last year's trial, in the Sacramento County Delta. The variety is Eureka Seeds 3325W. The trial consists of five replicated blocks of five treatments: 5, 6, 9, 12, and 15 pounds per acre. These treatments correspond to approximate plant populations of 68,000, 81,600, 122,400, 163,200, and 204,000 plants per acre, respectively. (This takes into account the 85 percent germination for the variety.) To date, we have taken stand and weed counts and have been monitoring bloom (Fig. 1). On average across treatments, bloom occurred 70 days after planting, compared to 71 days last year. At the end of the season, we will measure grain moisture and yield in an effort to better understand optimum seeding rates. Results from last year's trial are available from my website.