- Author: Luis Espino
In the past two weeks we saw very high armyworm populations in rice. Many fields had to be treated. However, the pyrethroids, common insecticides used against armyworms, did not provide good control. Applications of carbaryl did not reduce populations either.
Most likely, these products failed to provide good control because of the very high populations. In an average year, when an insecticide treatment is needed, the number of armyworms in the field is much lower than this year, and therefore control is much easier to achieve. Achieving good control with an insecticide application under very high population pressure is difficult, even with effective insecticides.
Another factor that contributed to the lack of control this year is the size of the worms. As with most moth larvae, the smaller the worm, the easier it is to kill it. However, targeting small worms in rice can be challenging.
After hatching, armyworms go through six instars, or stages, before pupating and turning into moths. Each stage occurs when the worms outgrow their skin, and need to molt so that growth can continue. The first two instars stay hidden in leaf sheaths or inside furled leaves, where they feed. These worms are really small, eat little and are hard to find. The third instars start feeding on leaf blades, but the amount of tissue they consume is small and the injury difficult to notice (see Table 1 below). It is during the last two instars, fifth and sixth, when armyworms consume the most foliage. Usually this is when the injury and worms are noticeable. Unfortunately, these worms are the hardest to kill.
Table 1. Time to develop and rice foliage consumption by each armyworm instar
|
Instar |
Duration of instar (days) at 70o F |
Leaf area consumed per instar (square inches) |
Leaf area consumed (% of total consumed per larvae) |
|
First |
3.9 |
0.06 |
0.15 |
|
Second |
3.1 |
0.12 |
0.29 |
|
Third |
3.1 |
0.36 |
0.87 |
|
Fourth |
2.9 |
0.90 |
2.18 |
|
Fifth |
3.8 |
9.23 |
22.25 |
|
Sixth |
6.3 |
30.81 |
74.26 |
At 70o F, it takes 13 days from hatching for worms to reach the fifth instar. With the warm weather experienced in the past weeks (average daily temperature for the last two weeks of June was 75o F in Willows), armyworm development must have occurred somewhat faster. Infestations probably started in the early part of June and went unnoticed until the worms reached a large size.
Fifth or sixth instar armyworm feeding on rice leaf.
Populations are now dwindling. In most areas worm density is decreasing or have disappeared all together. A second infestation might occur sometime around the boot and heading stages. The second infestation does not originate from the one we just experienced. Armyworms pupate in the soil, but in rice fields, when they drop to find a suitable place to pupate, they drown. This means that the worms seen earlier do not produce the moths that will lay eggs in rice later in the season. Nevertheless, we might see another severe outbreak if the conditions that favored the previous outbreak continue. Growers and PCAs should remain vigilant and try to identify infestations early to avoid direct panicle injury, which can occur during the armyworm second infestation.
- Author: Luis Espino
UCCE Rice Production Workshop
An in-depth workshop that covers the principles and practices of rice production
Friday, July 24, 2015
The Refuge Restaurant
1501 Butte House Road
Yuba City, CA 95993
Program:
8:30 Sign in, pick up class materials
9:00 Introduction and Workshop Overview
9:10 Rice Growth and Development
9:30 Land Formation, Water Management
9:50 Tillage, Planting and Stand Establishment
10:10 Break
10:30 Variety Selection
11:00 Invertebrates
11:30 Diseases
12:00 Lunch
1:00 Fertility
2:00 Weeds
3:00 Adjourn
Enroll on-line at http://ucanr.edu/2015riceworkshop
Prepaid enrollment ($100) is required, and enrollment is limited to 75 people. Please enroll by July 21st to ensure your participation. Seats will be filled on a first-come basis.
DPR (2.5 Other) and CCA (1 Nutrient Management, 2 IPM, 1 Crop Managment) continuing education credits available.
For more information, contact Cass Mutters (530-538-7201), Luis Espino (530-458-0578), or Michelle Leinfelder-Miles (209-953-6120), Farm Advisors, UC Cooperative Extension.
- Author: Luis Espino
I recently visited a couple of fields in Glenn County with severe armyworm injury. It seems somewhat early to be seeing this type of injury. Application of pyrethroids are not controlling these really high infestations. Fortunately, the really heavy injury is confined to corners and borders of fields.
The challenge with armyworms is to detect them early. Usually, the presence of worms is not noted until severe defoliation is observed. By this time, the worms are large and hard to kill with any insecticide. The fields I visited were about 45 days, and had large worms in them, which means that the infestation probably started at least 2 or 3 weeks ago.
Keep in mind that at this stage, rice can take quite a bit of defoliation before a yield reduction or delay in maturity is observed. If defoliation is higher than 25%, a treatment is warranted. Also, most of the armyworms you observe in the field now will drop off the plants to try to pupate in the soil, but will drown. So they won't be a source of moths for the infestation we see around heading. But the earliness and high pressure of armyworms now is an indication that growers need to be on the alert near the boot and heading stages to try to detect early armyworm infestations at that point. During booting and heading, armyworm injury can cause more damage because they can feed on the flag leaf or directly on the developing panicle.
For more information, visit the Rice IPM Guidelines here.
- Author: Luis Espino
The 2015 Rice Production Workshop will be held on July 24th, at The Refuge Restaurant, 1501 Butte House Road, Yuba City, CA. The Workshop, organized by University of California Cooperative Extension (UCCE), aims to present current and potential growers, pest control advisers, industry representatives, regulatory agencies and other interested parties with a broad view of the California rice production system and the most up to date research findings.
Information will be presented by UC Davis and UCCE scientists and extension personnel with many years experience working in California rice. Topics include land preparation, varieties, rice growth and development, water management, crop fertility, and pest management.
Prepaid enrollment ($100) is required, and enrollment is limited to 75 people. Please enroll by July 21st to ensure your participation. Seats will be filled on a first-come basis. The registration fee covers lunch and workshop educational materials.
Register online at http://ucanr.edu/2015riceworkshop
For more information, contact Cass Mutters (530-538-7201), Luis Espino (530-458-0578), or Michelle Leinfelder-Miles (209-953-6120), Farm Advisors, UCCE. Remember that space is limited, so register early!
- Author: Luis Espino
The University of California Cooperative Extension Rice site (UC Rice On-line) has been updated with a new look and a lot of new information which we think you will find useful.
Thanks to support from UC ANR and UC Davis (Department of Plant Science), we have been able to hire a webmaster to develop this site and keep it maintained. On this site you will find rice management guidelines (variety selection, nutrient and pest management, water use, straw management), presentations from recent meetings, production costs, links to the UC Rice Blogs and newsletters, dates and venues for upcoming meetings, contacts, and links to other important rice sites.
We invite you to visit the site and take a look. We want to make sure this site is relevant and meets your needs, so your comments are more than welcome. Just click on the "Click to tell us!" button and leave your thoughts. The address for the site is http://rice.ucanr.edu/; however, if you use the old address you will still be directed to this site.
