I visited a field with leafhopper damage. What was interesting about this field, is that the leafhopper causing the problem was not the aster leafhopper, which is the common one we have in rice. It was a different, green leafhopper that I have seen around in the past, but I have never paid much attention to. I don't even know what its name is (yet). It is green, larger than the aster leafhopper, and moves quite fast. We could not get a picture of it on a rice leaf, so here it is on a weed.
The damage was similar to what I have seen when aster leafhopper feeds on rice. The tip of the leaves get yellow and eventually burned. In this case, the damage was limited to a cold water check, so no treatment is needed.
Another interesting thing is that we found the eggs laid on watergrass plants around the field. Rice did not have any of the oviposition marks. They don't seem to like rice to lay their eggs. That is good because the lesions created due to the egg laying were quite large.
Tadpole shrimp (TPS) are starting to pop up in rice fields. A grower asked me when is the period when rice is “safe” from TPS. He is seeing very small shrimp, and seedlings are already past the first leave stage of rice (lsr).
To determine if rice is going to escape TPS injury, two things need to be considered, the rice seedling stage and the size of the TPS. It is difficult to determine the size of TPS, but if you pull one out of the water and its shell is smaller than half the size of a medium grain rice seed, then it won't injure a germinating seed. TPS larger than that will readily feed on germinating seeds and seedlings.
TPS with a shell size about half the size of a rice seed feeding on developing root.
TPS will feed on seedlings until they reach the first leave (when the spike is well developed). TPS don't seem to like feeding on the green tissue. However, they will feed on roots. If the main root is exposed, seedlings are still at risk of TPS injury.
TPS feeding on exposed roots of 1 lsr.
Use this guideline when you scout:
|If TPS shell size is...||And the rice stage is...||Risk of injury is...|
Smaller than half the size of a medium grain rice seed
|smaller than 1 lsr||LOW at this point, but may increase as TPS grows|
|Smaller than half the size of a medium grain rice seed||1 lsr or larger||LOW|
|Larger than half the size of a medium grain rice seed||smaller than 1 lsr||HIGH|
|Larger than half the size of a medium grain rice seed||1 lsr or larger||LOW, but check the main root. If exposed, it can be consumed by TPS|
One more thing to considering when scouting. If rice escapes injury and TPS are not treated, they will lay eggs that will stay in the soil and hatch next season.
When it comes to TPS management, fields that can be flooded quickly have an advantage over fields that take several days to flood. A quick flood followed by timely seeding will result in seedlings that can reach the 1 lsr before the TPS grow too large. In fields where flooding takes several days, TPS will have a head start and may reach the injuring size before the seedlings reach the 1 lsr.
This year, with the help of Dow AgroSciences, I will increase the number of armyworm traps that I have been monitoring. 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 our website, UC Rice Online, http://rice.ucanr.edu/armyworm_traps/
I will be sending a weekly “armyworm alert” email once the trap numbers are updated on the website. The email 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 was evaluating armyworm injury in plots and noticed there was quite a bit of panicle blanking not caused by armyworms. When armyworms injury panicles, they feed on the rachis of panicle branches, causing those branches to dry out. Sometimes the kernels in those branches may be partially filled, but since they stop receiving nutrients and water due to the biting injury of the armyworm, they dry and turn straw colored. Most of the time, the branches brake off at the point of injury and can be seen hanging on the panicle. If you look closely at where the rachis is broken, you can see the biting mark of the armyworm.
The other blanking I was noticing was a little different. It was mostly on the panicles under the canopy, although some could be seen in the panicles on top. Blanked branches turned white, almost as if bleached, and kind of translucent. This might be because these panicles were young. Most likely they will dry out and also turn straw color. None of these injured branches were hanging on the panicle and no biting marks could be noticed. I suspect this blanking was caused by high temperatures. Temperatures above 104 F during flowering dry the germinating pollen tube before fertilization and cause blanking. It seemed that some areas in the field were more affected than others.
Going back to armyworms, I found very little injury in my Butte County trial. Two trials in Colusa had no injury. The number of armyworm moths caught in the traps as of 8/24 have come down again. I suspect we won't see the numbers climb up again, therefore the risk of armyworm injury now is very low.
Click on the images below to see a close up of armyworm injury (left) and high temperature blanking (right).
For two years in a row I have received a report from a PCA in Yuba County of conchuela stink bugs on rice. This is very unusual; I have never seen these stink bugs on rice before, and I'm not very familiar with them. A quick on-line search shows that they are common on the western US; they can be a pest of cotton, alfalfa seed and sorghum, but it has a wide host range. Our UC IPM webiste only lists them as a pest of apple and pear, so I don't know how prevalent they are in agronomic crops in the Sacramento Valley.
Last year they did not affect yield or quality in the field where they were detected. I am not considering these bugs a pest; just incidental at this point. I'd love to hear from other PCAs or growers if they have noticed them in their rice.