These three photographs show herbicide injury related to application problems. The variety is CL161 which has excellent herbicide tolerance. The field had been sprayed with a mixture of Newpath, Permit, and Grasp plus a crop oil. From an undetermined cause the herbicide application was uneven with some areas getting too much herbicide resulting in the pattern shown in the top photo. The bottom left picture is of plants in the affected area. The bottom right photograph compares the root systems of affect plants on the left and “normal” plants on the right. Clearly there is reduction in root mass. This is NOT root pruning. The affected roots are not short and stubby, there are just less of them and those present are not as long as the unaffected. True root pruning results in damage to the root tips where growth occurs. The consequence is a short, stubby root or a root obviously missing the root tip. The first type of pruning can happen when herbicides containing pendimethalin (Prowl, Stealth) contact the root. The second type of purning usually is the result of insect feeding as in the case of rice water weevils or disease such as root rots or hydrogen sulfide toxicity. Twenty or thirty years ago most herbicides had a 2X measure of safety built into them, but today’s herbicides do not. It was already a pretty hot mixture and overlapping the pattern caused injury.
Below are two photographs taken in Vermilion parish. Dr. Groth had earlier examined leaves collected from the same field and suspects the disease is brown spot. Interestingly, the spots were mainly on the lower leaves indicating the environmental conditions favorable for the development of this weak pathogen were no longer present.
Above is a photograph of Creeping Rivergrass with spots on the leaves. The disease causing them is blast, the same disease found in rice. In this instance it actually behaves as a mild herbicide slowing down the growth of the plants. I have seen the disease on many grasses over the years and this one has been confirmed by Dr. Groth who was able to isolate blast spores from the lesions a couple of years ago.
Below are two photographs of another member of the genus Echinochloa. The reason the photograph was taken was not to identify the plant, but to show what the unseasonably warm weather (the hottest March and April on record according to meteorologists) is doing to some plants. This plant is already producing an inflorescence with enough detail that a pretty good identification could be made. The second picture shows the inflorescence up close. The long awns projecting from each seed indicate this is probably Echinochloa walteri. So we have another close relative of barnyardgrass which can hybridize with barnyardgrass and might even key out that way. I suspect E. walteri because it was in Cameron parish where this species is pretty common. The awns alone are not enough to separate it from barnyardgrass because sometimes barnyardgrass has awns too and certainly hybrids of the two species will have everything from very short to very long awns. Later on a more typical plant may provide more definitive information. I found two common names for this grass; Coast Cockspur Grass and Walter’s Barnyardgrass.
The two photographs below demonstrate the first time I have had an herbicide help in identifying a plant. The bottom photograph was taken several years ago to show the diagnostic purple bands that appear only on Jungle Rice, Echinocloa colona, a close relative of barnyardgrass. In fact, members of the genus Echinochloa are known to cross amongst themselves producing hybrids that are difficult to identify. When the purple bands appear on what looks like a barnyardgrass seedling it is Jungle Rice. However, frequently the purple bands do not show up. If you look carefully at the plant in the top photograph the green leaves do not show the purple banding. Only the leaves where the chlorophyll has been affected by an application of Command herbicide show the purple bands in a very striking way.
Below are a series of photographs of a plant brought in for identification. The person who collected it noted that it was scattered around and not likely to be a problem, but because he had never seen it before he was curious. I had not seen it before either, but because of its unique features it was relatively easy to identify. Overall appearance resembles sedges, the inflorescence spike rush and the stem is nearly square in cross section. The scientific name is Eleocharis quadrangulata. The genus puts it in with spike rush. The species name describes the 4 angled stem. In my field notes I did not have a common name, but have since found one in the USDA Plants Database; it is appropriately called Squarestem Spikerush.
This blog was originally post at the Louisiana rice insects blog.
A Section 18 request has been approved by EPA for the use of Tenchu 20SG on up to 100,000 acres of Louisiana rice to control rice stink bugs. Click here to read about biology and management of rice stink bugs. This product will provide an alternative mode of action to the pyrethroids that are currently registered for use in Louisiana. The exemption expires October 31, 2012. The distributor in Louisiana is Mr. Michael Hensgens with G&H in Crowley. According to Mr. Hensgens, the suggested retail price is $24.30 lb at ½#per acre = $12.15/ac.
Rate and restrictions: Please contact your local County Agent for a copy of the Section 18 registration before using this product. Remember that the label is the law! The registered rate is from 7.5 to 10.5 oz of product per acre. A maximum of two applications can be made per acre per season. A seven day pre-harvest interval must be observed. Be aware that this product is toxic to honeybees – read the Section 18 registration for precautions to avoid bee injury.
Treatment threshold:We do not recommend treating until you exceed the recommended thresholds as described on the Section 18 label (the current label reads that you should follow the Texas guideline – this has been amended to reflect LSU AgCenter recommendations in pub 2270). To scout for rice stink bugs in the field, use a 15-inch diameter sweep net, take 10 sweeps at 10 different areas around each field. Count the number of bugs collected after every 10 sweeps and then treat if they exceed the threshold as described in LSU AgCenter Publication 2270. During the first two weeks of heading, treat when there are 30 or more stink bugs per 100 sweeps. From the dough stage until 2 weeks before harvest, treat fields when there are 100 stink bugs per 100 sweeps.
Before we consider applying for an emergency exemption next field season (should we feel it is warranted) we need to gather some specific data. We need your assistance gathering this information.
1. Resistance. Please notify us if you believe that you have a stink bug population that is resistant to pyrethoids. We will gather insect samples to run laboratory bioassays to screen for insecticide resistance.
2. Efficacy. If you use Tenchu 20SG we would appreciate any data you gather on residual efficacy of the product. Data from Texas has indicated that it provides a longer window of activity than pyrethoids. This will potentially result in a reduction of the number of insecticide applications to a field in one season. We will be conducting efficacy trials in Louisiana to measure residual efficacy when compared to pyrethoids. If you’d like to participate in a field demo, please contact your local County Agent and they can work with me to make arrangements.
3. Milling. We also need your assistance in gathering data on milling quality of rice. Specifically, we need more data on reductions taken at the mill in the form of peck and broken grains which is attributed to Rice stink bug feeding injury. Any information you can provide on grade reductions attributed to rice stink bug feeding injury will be appreciated.
For more information, please contact Natalie Hummel, Associate Professor, LSU AgCenter at email@example.com or 225-223-3373.
Above are two photographs. The first one appeared in an earlier edition of Field Notes showing Command injury to Cheniere. The second one was taken Thursday in the same field. While there is a little stand loss most of the rice has recovered very well. If the entire field had been affected the same way some yield loss could have been expected, but not in this instance.
Late one afternoon this week I got a call to look at some “rice that looks like it is dying.” From a distance there were apparent rust colored areas of the field that corresponded to areas of the field that had remained dry longer than they should have. Close-up views exhibit one of the worst cases of blast I have seen since 1995 when it ripped through many Bengal fields. The variety here is CL261. We know it is susceptible to blast and have documented it in this variety since its release, but this is the worst case I have seen. The plants have about 3 crown nodes so it is much too early to apply any fungicide. Two more factors complicate the issue: first, it is a seed rice field; second it is in a field where soybean samples were shown to have aerial blight that is resistant to Quadris. In this case the preferred fungicide would be Gem applied at heading to control blast. Because Gem and Quadris are so closely related chemically something else will have to be applied to control sheath blight. A section 18 for a new fungicide has been applied for, but not granted yet. A few seasons ago a similar outbreak occurred in another variety because the field had dried out. This always aggrevates blast problems. A good deep flood is one of the best managerial things that can be done to at least lessen blast disease. It will not prevent it or control it, but it sure makes a difference in the severity of the disease.
Below is a picture of yellow nutsedge exhibiting two characteristics that contribute to its ability to be a serious pest. The “nut” part of its common name is derived from the structure shown at lower left. It is not a nut, but is actually a tuber, an enlarged part of the rhizome. The white, root-like structures are also rhizomes which are underground stems. If the stems were above ground they would be called stolons. These structures are underground and well protected from herbicide sprays. To really get to them requires a good translocated herbicide. If you plow and cut the tuber off from the main plant it just produces a new plant from the tuber. The plant can also produce lots of viable seed enabling it to survive by more than one method. One way to distinguish yellow nutsedge from purple nutsedge is to cut the tuber and smell it. If it has a petroleum odor it is purple nutsedge. Purple nutsedge also has a more blunt leaf tip than yellow nutsedge. The tubers of purple nutsedge are hairy compared to the fairly smooth yellow nutsedge tubers. Yellow nutsedge is actually sold as Chufa to be used in wildlife food plots. Apparently turkey will scratch up the tubers and eat them. One biologist said he found the crop of Teal killed in a rice field full of the tubers. If they would leave the rice seeds alone and selectively consume the tubers it sure would help.