In the last post I described some experiments I was conducting to determine if the redshouldered stink bug could be the cause of some "mysterious" cases of pecky rice. The result is clear: when caged on heading rice plants, this stink bug can definitively feed on developing kernels and cause peck.
Does this mean this insect is a pest of rice? NO. The redshouldered stink bug has been rarely found feeding on rice. This may explain some cases of pecky rice, but the redshouldered stink bug is not common in rice fields.
Every year for the past 3 or 4 years I've been hearing of rice that is graded No. 2 because of "peck". It's always been just a few isolated cases, except in 2011 when we had some early rains during harvest. The free water on the surface of the the grains may allow fungi to grow and stain the kernel. Here's what water staining looks like:
Pecky kernels are damaged kernels that have one or more black, brown, red, or other discolored spots or areas on them caused by fungus growth or insects. In the southern rice producing states, the occurrence of peck is common because of the rice stink bug. This insect feeds on developing grains and causes peck. Here's what typical rice stink bug injury looks like:
The rice stink bug is not present in California. Some of the pecky rice reported from California could be just kernels that have been damaged by water (I suspect that rice that lodges while the field is still flooded is susceptible to discoloration). In the end, when making the grade determination, it doesn't matter if the discoloration was caused by insects or water, discolored kernels are all classified as "damaged kernels".
However, in some cases, water damage can be ruled out and the reason for the peck is unknown. In trying to solve this mystery, Larry Godfrey, UC Davis Extension Entomologist, and I sampled a field last year where peck had been reported before. We found a couple of redshouldered stink bugs (Thyanta spp.). I also collected this bug from rice in Glenn and Yolo counties. Even though we found just a few bugs, we wondered if this stink bug could cause peck. There is a 2007 report from Mississippi that claims this stink bug causes damage in rice. Here's what the redshouldered stink bug looks like:
We are currently doing some experiments with the redshouldered stink bug. We collected some of these bugs from weeds and infested panicle and whole plant cages. So far, it seems that these bugs can feed and survive on rice. After harvest we will be able to tell if the redshouldered stink bug is capable of causing peck. I will update after harvest.
In the meantime, if your rice is graded No. 2, and peck or damaged kernels seem to be the reason, let me know (email@example.com; 530-635-6234).
Japanese millet is not a weed of rice in our area. However, a PCA recently noticed it in an organic rice field. Japanese millet is in the same genus as our common watergrasses, and looks similar, but is much more robust. It seems to grow well under flooded and dry conditions.
The presence of this plant in the organic rice field was puzzling. Then the PCA learned that the field had been in pasture the year before. Most likely, the Japanese millet was part of the mix of grasses seeded as pasture and produced seed that survived the winter and germinated in the flooded rice field.
Unusual find, hopefully we won't see it ever again!
RICE FIELD DAY
Wednesday, August 28, 2013
Rice Experiment Station, Biggs, CA
The annual Rice Field Day will be Wednesday, August 28, 2013, at the Rice Experiment Station (RES), Biggs, California. You and your associates are cordially invited to join us for this event to observe and discuss research in progress at RES. Rice Field Day is sponsored by the California Cooperative Rice Research Foundation (CCRRF) and University of California (UC), with support from many agricultural businesses. Following is a brief outline of the Rice Field Day program (updated program here).
7:30 - 8:30 a.m. Registration
Posters and Demonstrations
8:30 - 9:15 a.m. General Session
CCRRF Annual Membership Meeting
D. Marlin Brandon Rice Research Fellowship
California Rice Industry Award
9:30 - Noon Field Tours Of Rice Research
Insects and Control
Weeds and Control
The program will begin at 8:30 a.m. with a General Session that serves as the Annual CCRRF Membership Meeting. Posters and demonstrations will be in place during registration until after lunch. Field tours of research will emphasize progress in rice variety improvement, disease, insect, and weed control. The program will conclude at noon with a complimentary lunch that includes rice. The RES is located at 955 Butte City Highway (Hwy. 162), approximately two and one half miles west of Highway 99 north of Biggs, California.
This is the first time since I moved to California that I've seen leafhoppers actually injuring rice. Leaf tips turned yellow, and from the road it looks like salt injury, but once you get in the field you can see leafhopper nymphs and adults jumping and flying around.
What we have is aster leafhopper. They are reported to feed on broadleaf weeds and rice. I have some research plots in this field, with some areas where rice was not planted between plots. Weeds grew on the open areas, and after a propanil application that killed the weeds the leafhoppers might have moved to the rice.
From the UC IPM: Rice website: "Although leafhoppers can be present in fields during most of the growing season, the heaviest populations usually occur from early July through mid-August. Leafhoppers feed on rice plants by sucking up plant fluids through their long, piercing mouthparts. Although they are not known to vector of any rice pathogens in California, leafhoppers may occasionally occur in sufficient numbers to cause damage by their feeding. Injury associated with leafhoppers include stippling, yellowing, and drying leaves. Leafhoppers prefer senescing leaves, and symptoms usually occur on older leaves first. Leafhoppers are very mobile; adults fly and nymphs jump. Thus, infestations are rarely localized but appear generally throughout the field."
We haven't treated this field yet. There are still plenty of leafhoppers, but the plants are growing fast and putting out new leaves. If the leafhoppers remain and start injuring the flag leaf, a treatment might be appropriate.