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.
Please see this article on the UC Rice Blog for an update on armyworm populations. We will continue to monitor traps in the Delta through mid-September, and we will plan to monitor populations next season.
I was recently contacted by a PCA who was observing armyworm feeding in Delta rice fields. Over the last two years, both locally and in the Sacramento Valley, armyworms have been striking rice fields earlier in the season and in greater numbers. This has been described by farm advisors in the UC Rice Blog. Armyworms are generally a summer pest of rice, spending spring and early summer months on other plants, but over the last two years, armyworm feeding has been detected in June. Armyworms generally only have one generation in rice later in the season, but last year, earlier infestations caused concern for there to be two generations. This was not generally observed, but PCAs should keep this in mind again this year as they scout throughout the summer.
Armyworm defoliation is most deleterious during stem elongation and grain formation and is observed as angular cut-outs from the leaves (Figure 1). UC IPM guidelines state that yield may be affected if defoliation is greater than 25 percent of the plant at two to three weeks before heading, and they provide the following monitoring instructions.
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 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.
It is important to monitor throughout the season in order to detect damage severity, and thus, know when to treat. Later in the season, damage may also occur on the panicle rachis. UC IPM guidelines recommend treatment when, in the vegetative stage, at least half of the plants sampled have at least 25 percent defoliation and armyworms are present. When the panicle has formed, UC IPM guidelines recommend treatment if 10 percent of the sampled panicles are damaged and armyworms are present. Armyworms are generally more apparent at night or in the cooler morning hours; thus, monitoring should occur when worms are active and apparent.
Early season management of armyworms includes weed management around the perimeter of fields. Registered chemicals are limited but include certain pyrethroids, which have not always proven efficacious, and carbaryl, which cannot be used within two weeks of a propanil application. The carbaryl label also includes precautionary language regarding bees, so it would not be recommended when rice is neighbored by insect-pollinated crops, like melons.
This year, the California Department of Pesticide Regulation has issued a crisis exemption under the US EPA Section 18 to allow for the use of Intrepid 2F (methoxyfenozide) on armyworms in certain rice growing counties, including San Joaquin County. The emergency exemption is valid until September 30, 2016. Please contact the county Agricultural Commissioner's office for more details.
Tables 1 and 2, respectively, show the results of the 2015 San Joaquin County rice variety trial and a 5-year yield summary of very early maturing commercial varieties. The statewide trials are a cooperative effort of the California Cooperative Rice Research Foundation, Inc., the United States Department of Agriculture, and the University of California. The trials compare advanced breeding lines with commercial varieties. The San Joaquin County test site is located in the Delta. It is a test site for very early maturing varieties because San Joaquin County is cooler than other rice growing regions of the state. The varieties were drill-seeded on April 29th at a rate of 140 lbs/acre and harvested on October 13th.
When interpreting the results, consider the following. The mean represents the average of all varieties. The CV, or coefficient of variation, is a measure of variability of the data in relation to the mean. The LSD (.05), or least significant difference at 95%, is used to compare means of different varieties. When the difference between two varieties exceeds the LSD value, we are 95% certain that the two varieties performed differently; the results are not due to random chance. For example, the LSD of the grain yield at 14 percent moisture is 640. This means that if the yields of two varieties differ by at least 640 lbs/acre, then we can conclude that the two varieties yielded differently. In this case, the top six varieties in Table 1 had statistically similar yields. In Table 2, yield means are averaged across all locations and years and compared to M-104, a standard very early variety. Over the five years, and across the four very early variety locations, M-206 – a common variety in this area – yielded 2.2 percent higher than M-104.
UC Cooperative Extension annually sponsors four rice grower meetings in the Sacramento Valley. This year, the meetings will be held on Tuesday, January 19th and Wednesday, January 20th. The schedule and locations are as follows:
Richvale: Tuesday, Jan. 19, 8:30 am, Evangelical Church, 5219 Church St., Richvale
Glenn: Tuesday, Jan. 19, 1:30 pm, Glenn Pheasant Hall, 1522 Highway 45, south of Glenn
Colusa: Wednesday, Jan. 20, 8:30 am, CIP Conference Room, 100 Sunrise Blvd., Colusa
Yuba City: Wednesday, Jan. 20, 1:30 pm, Veterans Hall, 1425 Veterans Memorial Circle, Yuba City
Doors open at 8:00 am and meetings start at 8:30 am at Richvale and Colusa. Doors open at 1:00 pm and meetings start at 1:30 pm at Glenn and Yuba City.
8:00 a.m. (1:00 p.m.) Doors open, sign-in, coffee
8:30 a.m. (1:30 p.m.) Call meeting to order - Rice Research Board Nominations – Dana Dickey, Rice Research Board
8:35 a.m. (1:35 p.m.) Rice Pesticide and Regulatory Update – County Ag Commissioner
8:50 a.m. (1:50 p.m.) Irrigated Lands Program: Farm Evaluations and Nitrogen Management Plan – Roberta Firoved, California Rice Commission
9:05 a.m. (2:05 p.m.) Year in Review – Cass Mutters, UCCE
9:35 a.m. (2:35 p.m.) Nutrient Management in California Rice Systems – Bruce Linquist, UCCE
10:15 a.m. (3:15 p.m.) — BREAK —
10:30 a.m. (3:30 p.m.) Impacts of Irrigation Price Hikes & Cutbacks on Water Management and Wildlife – Nathan Van Schmidt, UC Berkeley
10:45 a.m. (3:45 p.m.) Red Rice Update – Timothy Blank, California Crop Improvement Association
11:00 a.m. (4:00 p.m.) 2015 Armyworm Outbreak – Luis Espino, UCCE
11:30 a.m. (4:30 p.m.) Weed Management Update – Kassim Al-Khatib, UCCE
12:00 p.m. (5:00 p.m.) — ADJOURN —
At the Richvale meeting, there will be a slight change, as follows:
10:45 a.m. New methods, models and surveys to evaluate the value of rice lands to waterfowl – John Eadie, UC Davis (Richvale only)
11:00 a.m. Red Rice Update – Timothy Blank, California Crop Improvement Association
11:15 a.m. 2015 Armyworm Outbreak – Luis Espino, UCCE
Please contact your local farm advisor with questions.