IPM NEWSLETTER Update for Field Crops and Their Pests

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1 The University of Tennessee IPM NEWSLETTER Update for Field Crops and Their Pests West TN Research and Education Center 605 Airways Boulevard Jackson, TN No. 15 July 15, 2005 Past Newsletters and other information can be found at CONTENTS (links): Cotton Update - Insect Issues - Soybean Rust Update - Area Report - Moth Traps Upcoming Events: UK Agricultural Field Day, July 28, 8:00 AM - 3:00 PM, Princeton, KY (link to Flyer and Program) 2005 Midsouth AgTechnology Field Day, July 28, 7:00 AM - 1:30 PM, Agricenter International, Memphis, TN (link to Flyer) Cotton Crop Update (Chism Craig, Cotton Specialist) The Tennessee Ag-Statistics Service reports that 27% of the crop is blooming compared to 26% last year and the five-year average of 23%. Rain has fallen in most areas and the crop has really responded. Cotton is growing extremely rapidly in some cases and growth control is necessary. Cotton that is growing very rapidly often takes on a lighter shade of green and often appears to be deficient in some nutrient. Many times an application of a plant growth regulator will make this cotton turn a darker shade of green. In the last week, I have had several phone calls about the mottling of leaves (chlorosis between the leaf veins) (Figure 1). When I first observed this characteristic, the first thought that came to mind was potassium deficiency. In many cases, the cotton was not yet blooming and I was confused as to why we might begin seeing this deficiency so early. The mottling was most apparent in fields with rapidly growing plants that had outgrown previous mepiquat treatments or fields that had not yet been treated. Owen Gwathmey, our cotton physiologist, has also observed this mottling and feels that potassium is indeed the culprit. Now, does this mean that we are totally deficient in potassium? I don t think so. We have pulled some tissue samples and hope to find out the exact cause of this chlorosis. If this is indeed potassium, I think this particular deficiency will be transient and go away as growth slows down and mepiquat applications are made. The rapid growth probably leaves the plant unable to keep up with the demands at this particular point in time. Is this transient deficiency going to translate into lower yields and poor fiber quality? I don t think so at this point but on the other hand I don t know. So what do we do? As with any deficiency, tissue analysis is first and foremost on the list. We need to verify the actual deficiency and the severity of the deficiency. Secondly, mepiquat applications made this week and next will probably make the crop look a good deal better. Addition of a foliar K source would probably not hurt as well. I hope to get some treatments out on some of these spots and see what we can do. The bottom line is we don t need to panic. Some drier weather and sunshine along with some mepiquat will probably make the cotton look much better. 1

2 Figure 1. Early season leaf mottling. One thing that shouldn t be confused with K deficiency is Verticillium wilt. Many producers may have seen it already and I would suspect that we will see some of it in the coming weeks. Symptoms found later in the season exhibit a mottling on the lower leaves first (Figure 2.), and then move toward the top of the plant as the season progresses. The disease can only be verified through laboratory testing but slicing stems and observing discolored vascular tissue gives a pretty good indication of Verticillium wilt (Figure 3.). In severe cases, affected plants shed all their leaves and most of their young bolls. The disease is more prevalent during periods of cool, wet weather. In Tennessee, the disease is more common on heavier soils, particularly in bottomland areas. Control measures include avoiding excess nitrogen, applying sufficient K, long term crop rotation and planting resistant varieties. However, when the wilt occurs, nothing can be done for affected plants. Isolated spots in the field will probably not hurt yield but some fields with uniform distribution of the disease will suffer yield loss. Below are some pictures from fields observed in Tennessee last year. Figure 2. Verticillium wilt symptoms on PM 1218 BG/RR in Haywood, Co. 2

3 Figure 3. More Verticillium wilt symptoms in cotton. DD60 accumulation to date for eight West Tennessee locations. Location April 24- May 2- May 8- May 16- May 22- Ames Plantation Brownsville Covington Dyersburg Huntingdon Jackson Memphis Milan Cotton Insect Issues (Scott Stewart, IPM Specialist) Overall, the crop condition looks very good with no widespread insect problems. Calls about spider mites are still leading the pack. We are finding a few mites on soybeans as well, although I have not seen or heard of any requiring treatment. The rain has certainly taken some stress off the cotton plants, but I m still finding live mites in many fields. My recommendations have not really changed. Kelthane MF (32-36 oz/a) and Comite II (24 oz/a) are my first choices when treatment is necessary. Product availability remains an issue, maybe even for Zephyr (for which we just received a 24C label). Folks are hoping that the mite fungus (Neozygites floridana) will knock back populations, and it sometimes does, particularly following rains. There are reports of this occurring in Mississippi and Arkansas. However, if a field justifies treatment now, this fungus is too unpredictable to wait on for more than a few days. Tip: Carry a hand lens and make sure live spider mites are present before making a treatment. Plant bug and stink bug populations continue to be generally light to moderate but are on the rise, with an occasional field requiring treatment. So far, the highest populations have been in the most mature fields. I usually switch to the drop cloth at this time of year because it is better at sampling immature plant bugs. Nymphs often become more common than adults as the season progresses. I may not carry a drop cloth into every field, but I certainly use it when I see plant bugs, stink bugs or injury (dirty blooms, etc.) in a field. Reminder: Dropping fruit retention, particularly 2-3 weeks into bloom, is common and often is not the result of insect injury. Be realistic! Plants can not turn every square into a harvestable boll. The highest yielding fields may average 10 harvestable bolls per plant. Nodes

4 will produce a total of 22 fruiting sites on the 1 st and 2 nd positions. The point - if you are running over 80% fruit retention on positions 1 and 2, expect some fruit shed regardless of how much insecticide you spray. A few tobacco budworm and bollworm eggs and larvae are being found, and some non-bt cotton fields have recently been treated. I think we are still a good 7-10 days away from our big bollworm flight, but continue to scout fields regularly for these pests. Pay special attention to non-bt cotton, and at this time of year, early planted fields. Also remember that bollworms often lay their eggs deeper in the canopy on square and boll bracts, stems and on bloom tags (pictured). Small larvae may be found under bloom tags. Once again, this is a reason to consider coverage when making insecticide applications. I ve included some data from Jeff Gore (USDA ARS Research Entomologist in Mississippi). Dr. Gore did some experiments contrasting insect control using low drift (A111002) and hollow cone (TX12) nozzles. All tests were done at 9.4 GPA, 40 PSI and 5 MPH. Treatments were sprayed, insects were caged on plants, and mortality was rated after 48 hours. This kind of test is not necessarily designed to compare among insecticides or indicate actual field performance, but it does show how the quality of an application can impact efficacy. Impact of spray tips on insect mortality (J. Gore, USDA ARS) Insect and Spray tip Treatment Rate % Mortality Tarnished plant bug Hollow cone Centric 40WG 0.05 lb ai/acre 96.4 Low drift Centric 40WG 0.05 lb ai/acre 75.8 Untreated N/a N/a 14.5 Tarnished plant bug Hollow cone Orthene 0.5 lb ai/acre 65.3 Low drift Orthene 0.5 lb ai/acre 49.5 Untreated N/a N/a 18.7 Bollworms Hollow cone Karate lb ai/acre 54.0 Low drift Karate lb ai/acre 27.0 Untreated N/a N/a 0.0 4

5 Soybean Rust Update (Angela Thompson, Extension Soybean Specialist) Soybean rust was observed in a 60 acre commercial soybean field in Baldwin County Alabama on July 12. The field is approximately 1 mile NE of the soybean sentinel plots that were observed to have rust on June 28. Disease incidence within the field was estimated at 20%, with low disease severity, and the field is at the R4-R5 stage of development. The field had been sprayed with Stratego on June 26. Product rate used, application and row spacing information is not available at this time. More scouting was done on nearby kudzu and soybean. Rust was not found on kudzu patches in the area, including patches located approximately half-way between the sentinel plots and the commercial field. No rust was detected in three other commercial soybean fields with 10 miles of the positive sentinel plot. These were late planted soybeans at the V2 growth stage. Area Report for Dyer, Lake, Gibson, Lauderdale, Obion, Weakley and Crockett Counties (Gene Miles, Area Plant & Pest Management Specialist) Cotton: Much needed rain and cooler temperatures were well received in the area this week. 12 or 16 oz. applications of mepiquat are being put on more growthy cotton varieties like DP444BG/RR and ST 5599BR which are approaching the 36 inch height and still have plenty of horsepower. The rainfall, cooler temperature and recommended insecticides have had a positive affect on reducing spider mite infestations. All reports this week regarding this pest have indicated only light infestations. Above threshold levels of clouded and tarnished plant bug populations (4.2 per 6 row feet) are being reported from the delta area of Lauderdale County in some fields of blooming cotton. Square retention in prebloom cotton this week ranged from %. Stink bug numbers are being found above the threshold level (1.0 per 6 row feet) in taller, growthy cotton fields where reports range up to 1.2 per 6 row feet. Aphid infestations are being noted in the light category at the present time. Grasshoppers and snails also have been noted in the area this week, causing no economic problems. Bollworm/tobacco budworm reports have indicated 1 worm (less than 1/4 inch) in Bt cotton this week. Beneficial counts range up to 3.8 per 6 row feet. Soybeans: Frog-eye leaf spot is being noted in varieties which are susceptible to this disease. Recommended fungicides are applied at the R3 growth stage where this disease is being noted. Stink bug numbers range up to 2 per 25 sweeps in the bloom to mid-podfill growth stage, with the threshold being 3 per 25 sweeps at this stage of maturity. 5

6 Tennessee Pheromone Moth Trapping Summary (Week 10, Ending ) Number of Moths Trap location Tobacco Corn Earworm Budworm (Bollworm) Beet Armyworm Madison (South) 0 * --- Madison (North) 0 * 0 Madison (Exper. Stn.) Hardeman (Bolivar) 0 * 0 Fayette (Oakland) 0 * missing Fayette (Somerville) 0 * --- Haywood (Brownville) 1 * 0 Haywood (West) 1 * --- Tipton (Avreet) 0 * --- Tipton (Mt. Carmel) 0 * 0 Lauderdale (Hwy 19) 0 * 0 Crockett (Maury City) 0 * --- Crockett (Alamo) 0 * 0 Carroll (Atwood) 0 * 0 Gibson (Milan) 0 * 0 Gibson (Kenton) 0 * --- Dyer (Dyersburg) 0 * --- Dyer (Newbern) 0 * 0 Lake (Ridgley) 0 * 0 * Traps were baited with wrong pheromone. DISCLAIMER STATEMENT Pesticides recommended herein were registered for the prescribed uses when this publication was printed. Should registration be canceled, the University of Tennessee will immediately discontinue its recommendation of the pesticide. Use of trade or brand names in this publication is for clarity and information; it does not imply approval of the product to the exclusion of others that may be of similar, suitable composition, nor does it guarantee or warrant the standard of the product. The Agricultural Extension Service offers its programs to all eligible persons regardless of race, color, national origin, sex religion, disability or veteran status and is an Equal Opportunity Employer. COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS. The University of Tennessee Institute of Agriculture, U.S. Department of Agriculture and county governments cooperating in furtherance of Acts of May 8 and June 30, Agricultural Extension Service, Charles L. Norman, Dean. Scott D. Stewart (editor), Extension Cotton IPM Specialist 6