- 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
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
Planting is starting to pick up now that water allocations are known. One of the first pest problems one is going to find in recently flooded rice fields is tadpole shrimp (TPS). Most of the time, when muddy water or uprooted plants are observed, it means the TPS are large and probably already done quite a bit of damage. Young TPS are hard to detect; because of their size they might not cause mudding of the water. However, look carefully to see if you can spot them. Small TPS, when their shell is about half the size of a rice seed, can injure rice roots as they emerge from the seed; they have a hard time chewing on the coleoptile that emerges first from the seed. Larger TPS, when their shell is about the size of a rice seed, are capable of feeding on the coleoptile and roots, and can dislodge seedlings easily.
Look carefully, there are other bugs that can be confused with small TPS, such as small beetles and clam shrimp. Small TPS look just like fully grown TPS. The very first TPS instars do not look quite like TPS, but those are really hard to spot, and do not feed on rice seedlings anyway. Here's a few images.
TPS eggs
TPS first instars next to eggs
Second or third TPS instar
Small TPS
TPS mandibles
TPS mandibles
- Author: Luis Espino
Stored Product Insect Pest Management in Rice Mills and Storage Facilities
Workshop
Optimizing Insect Control and Grain Quality
Sponsored by University of California Cooperative Extension and Lundberg Family Farms
April 7, 2015
9:00 am – 3:00 pm
Lundberg Family Farms
5311 Midway
Richvale, CA 95974
We would like to invite you to attend an exciting and informative workshop on rice storage and mill insect pest management. The workshop is organized by the research team of the Post-Harvest Grain Management Project, which was funded by the United States Department of Agriculture, National Institute of Food and Agriculture Grants Program. The team consists of several scientists with many years experience in the subject of pest management in stored grains and storage and milling facilities.
The workshop will focus on pest management in rice mills as well as in storage bins. Major topics include: 1) Current status and challenges of rice grain insect pest management; 2) Integrated pest management programs; 3) Monitoring and dynamics of storage insect pests inside and around rice mills; 4) Structural treatments, residual insecticides, and aeration; 5) Economics of storage rice insect pest control; and 6) Integrated storage rice insect pest management and tool delivery.
Register on-line at http://ucanr.edu/2015ricemillworkshop
Registration is free. Please register before April 1st to ensure participation. Seats will be filled on a first-come basis. Lunch will be provided.
****Applied for DPR CE credits****
For more information, contact Luis Espino, University of California Cooperative Extension (530-458-0578, laespino@ucanr.edu) or Jim Stewart, Lundberg Family Farms (530-538-3500).
- Author: Luis Espino
In early 2012 UCCE conducted a survey of rice storage facilities (on and off-farm) to see what research and extension needs the rice industry had in this area. The results of the suvey have been published in the journal California Agriculture, and if you are interested, the article can be accessed on the web here: http://californiaagriculture.ucanr.edu/landingpage.cfm?article=ca.v068n01p38&fulltext=yes
The survey showed that storage facilities are users of IPM: most operations rely on monitoring, thresholds, sanitation and aeration to manage pest problems.