- Author: Luis Espino
- Author: Michelle Leinfelder-Miles
This year, with the help of Dow AgroSciences, UC farm advisors will increase the number of armyworm traps that they will monitor in rice fields. The idea is to give growers and PCAs more localized information so that they can have a better idea of what's going on near them, and when to increase their monitoring efforts. Weekly trapping numbers will be posted on the UC Rice Online website, http://rice.ucanr.edu/armyworm_traps/.
Luis Espino will be sending a weekly “armyworm alert” email once the trap numbers are updated on the website. The e-mail will go out to those who are subscribed to one of our electronic newsletters (Rice Briefs, Rice Leaf, or Field Notes). If you receive the armyworm email but are not interested, just click on the unsubscribe link at the bottom of the email. For those who do not receive our newsletters electronically, you can subscribe to the alert email in the armyworm website: http://rice.ucanr.edu/armyworm_traps/.
I will also keep you updated through this blog, specifically on Delta trap counts.
Here are a few articles, written by UC Cooperative Extension colleagues, that may be of interest to readers of this blog:
From the UC Rice Blog:
Armyworm vs. High Temperature Blanking - by Luis Espino, Farm Advisor, Colusa County
From the UC Dry Bean Blog:
UC Davis Dry Bean Field Day Announcement - by Rachael Long, Farm Advisor, southern Sacramento Valley
From the UC Small Grains Blog:
Start Planning Your Nitrogen Management Strategy for Fall-Planted Wheat Now - by Mark Lundy, Small Grains Specialist, UC Davis and Konrad Mathesius, Farm Advisor, southern Sacramento Valley
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 9th, 9:00am – 12:00pm, New Earth Market Harvest Room, 1475 Tharp Road, Yuba City
- August 10th, 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.
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.
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.