Integrated Pest and Crop Management Newsletter Vol. 17, No. 6 April 20, 2007 ********************************************************************** Finishing off that Damaged Wheat Stand By Kevin Bradley The temperatures we have experienced over the past week and the resulting injury to some wheat fields have led many to consider killing off the current wheat crop in order to plant corn or soybeans. There are many factors that should be considered before this decision is made but once it has been made, there are two additional questions you should ask yourself. First, are the herbicides that I used in my wheat crop going to carryover and harm my corn or soybeans? And second, what are the options for killing my current stand of wheat in order to plant my new crop? As far as the possibility of herbicide carryover, the table below shows some of the more common wheat herbicides that are used in winter wheat production in Missouri and the rotation intervals to corn and soybeans after applying these herbicides. For the most part, the majority of wheat fields in Missouri are treated with either 2, 4-D or Harmony Extra. As you can see from the table below, if you have treated your wheat crop with either of these herbicides, carryover to corn or soybeans should not be much of a concern. One caveat to this statement is that the previous Harmony Extra label had a 45 day requirement between application and planting of corn or soybeans. Recently, a new supplemental label for burndown use of Harmony Extra in corn or soybeans has been approved which allows for an interval of 14 days between application of this herbicide and planting. I have talked with DuPont about the "burndown" terminology on this new supplemental label in contrast to the use of Harmony Extra in the existing wheat crop, and they have assured me that this 14 day interval is still appropriate for our current situation. If you have applied one of the other products in the table below like Olympus, Olympus Flex, Osprey, etc., then herbicide carryover may be much more of an issue and rotating to corn or soybeans may not be possible at this time. Finally, if you have made the decision to kill off your wheat crop and herbicide carryover is not a concern, then the good news is that killing your current crop should not be that much of a problem. One of the most obvious options is tillage. However, if you wish to stay with a no-till system, then any of the brand name or generic glyphosate products will provide good control of wheat, even at this stage in the game. Most of the glyphosate labels indicate that 12- to 18-inch tall wheat will be controlled with 1 lb of glyphosate per acre (1 quart/acre of most generics; 22 fl ozs/acre of Roundup WeatherMax or Roundup OriginalMax), and that poorer control should be expected if wheat is in the boot stage of growth. Based on my experience with killing wheat, I would agree with this recommendation. Additionally, in one of the few studies that I have found published on this topic (Weston, L. A. 1990. Weed Science 38:166-171), the author observed essentially complete control of wheat with glyphosate at either 1.0 or 2.0 lb a.i. per acre and therefore increasing the rate of glyphosate above 1.0 lb a.i. per acre was not warranted. Perhaps the most important factor to consider when making a decision about rate selection, however, is the condition of the wheat at the time of the glyphosate application. For optimum control, it will be important to make sure you delay the glyphosate application until after the wheat has resumed active growth. Making a glyphosate application to injured wheat stands that are not actively growing in the cool, wet conditions we are currently experiencing will more than likely not provide good results and if you have no other alternative than to spray under these conditions, then increasing the glyphosate rate above 1.0 lb a.i. per acre would be a good idea. Another option for killing your wheat in areas where corn will be planted is to apply paraquat (Gramoxone Max, Gramoxone Inteon, etc.) plus atrazine. As paraquat is a contact herbicide, applications of paraquat alone will more than likely not provide suffi cient wheat control, but the combination of paraquat and atrazine should provide good control as both foliar and root uptake will occur with this combination. Kevin Bradley 882-4039 BradleyKe@missouri.edu ********************************************************************** Killing Frost-Damaged Corn - It's Not as Easy as it Sounds By Kevin Bradley According to the National Agricultural Statistics Service, about 12 percent of the corn was planted in Missouri prior to the freezing temperatures experienced last week. Because of this, I have already received a few calls pertaining to the options for killing out these frost-damaged fields of corn and planting a new stand of corn back into these areas. First, one of the most obvious options is tillage. Many growers are not willing to resort to this, but this is a viable option and the costs of a tillage operation should be weighed against the cost of the available herbicide options before this possibility is ruled out. If the decision has been made to use a herbicide to kill out the frost-damaged corn stand, then the type of corn that was planted will be very important in determining which herbicide should be chosen. If the frost-damaged corn was not a Roundup Ready variety, then any of the generic or brand name glyphosate products will provide good control. If the frost-damaged corn was a Roundup Ready variety, then eliminating the corn stand will be much more diffi cult and costly. This has been an issue of increasing importance over the past several years, and will continue to be a big issue for growers who plant continuous Roundup Ready corn. The problem with eliminating frost-damaged Roundup Ready corn is that there are few herbicides that will provide good, consistent control of Roundup Ready corn and at the same time will allow for corn replanting in a short period of time. Last year it appears that some of the Roundup Ready corn acres in other states were treated with postemergence grass herbicides like Select Max, Assure II and Fusilade, which are commonly used in soybeans. The problem with this is that these herbicides are not registered for this use and in some cases, injury to the developing corn crop can occur due to residues of these herbicides in the soil. The one exception to this may be with the active ingredient in Select Max (clethodim), which has a soil half-life of just three days. As a result of several studies conducted last year, we are currently pursuing a Section 18 label in cooperation with Valent for the use of Select Max on frost-damaged Roundup Ready corn in Missouri. This application use for Select Max has already been submitted to the EPA by Valent for a full federal label (expected next year), but due to the conditions we have experienced in Missouri, we are now pursuing this emergency label. This label, if obtained, would allow for the application of Select Max at 4 fluid ounces per acre for the control of Roundup Ready corn and for replanting of the subsequent corn stand as soon as four or five days after application. In research conducted last year, we observed 95 percent control of four-inch Roundup Ready corn with applications of Select Max at this use rate and 92 percent control of eightinch Roundup Ready corn. Let me be clear; this is NOT a legal use of this product at the time of this writing, but we hope to obtain this label soon for the problem we have encountered in Missouri. If granted, it would provide one of the cheapest options for eliminating damaged Roundup Ready corn stands (Table 1). Contact your regional Extension agronomist or retailer before applying this product in order to ensure that the Section 18 label has been approved for Missouri. As far as the currently-labeled options, applications of Liberty have provided inconsistent control of Roundup Ready corn in our research. In one of the trials we conducted last year, we observed very poor control of one- to three-inch Roundup Ready corn with applications of Liberty at 32 ounces per acre. This is due to the contact nature of Liberty and the likelihood that the growing point remained below ground at the time of these applications. In this same study, we observed much higher levels of control with applications of Liberty to Roundup Ready corn that was four to six inches in height, but the overall control was still only about 85 percent. This means that some frostdamaged corn survivors will be present to compete with the subsequent crop. However, if the replanted corn is a Liberty Link variety, then it is likely that these initial survivors can be controlled with a subsequent in-crop Liberty application. Another thing to keep in mind is that if the initial corn was stacked with Herculex, then this variety also has resistance to Liberty and therefore applications of Liberty would provide no control of the frost-damaged corn. Our research has also shown poor results with applications of Gramoxone (paraquat) alone. Regardless of the rate or timings evaluated in our studies, we observed less than 40 percent Roundup Ready corn control with this treatment. However, we have observed good results with applications of Gramoxone in combination with either Sencor or Linex. In our research, Gramoxone Inteon at 2¼ pints per acre plus Sencor at 3 ounces per acre or Gramoxone Max at 2¼ pints per acre plus Linex at 1 pint per acre both provided greater than 95 percent control of one- to three-inch or four- to sixinch Roundup Ready corn 30 days after treatment. Both of these treatments will also allow for corn planting anytime following application. At this time, however, the amended Linex label for this new use pattern has been approved at the federal level, but is still pending state registration for use in Missouri. One of the drawbacks of either of these treatments is the cost in comparison to the proposed Select Max use (Table 1), but until this label is approved, Liberty or Gramoxone plus Sencor appear to be the only legal options for frost-damaged Roundup Ready corn control in Missouri. Table 1. Approximate costs of herbicide programs for Roundup Ready corn control ####################################################################### # Herbicide Program Rate Approximate Cost # # -- Product / Acre -- -- $ /Acre -- # # Liberty 32 fl ozs 15.87 # # AMS 3 lbs 0.52 # # 16.39 # # Gramoxone Inteon 2.25 pts 7.73 # # Sencor 3 ozs 2.63 # # Crop Oil Concentrate 1 pt 0.67 # # 11.03 # # Gramoxone Inteon 2.25 pts 7.73 # # *Linex 1 pt 7.70 # # Crop Oil Concentrate 1 pt 0.67 # # 15.40 # # *Select Max 4 fl ozs 3.57 # # Non-ionic Surfactant 0.25 percent v/v 0.58 # # AMS 2.5 lbs 0.43 # # 4.58 # # # # *Indicates products with labels pending for this use in Missouri. # ####################################################################### Kevin Bradley 882-4039 BradleyKe@missouri.edu ********************************************************************** Crop Insurance and Freeze Damage to Wheat By Ray Massey Wheat farmers are closely watching their crop to see what damage was done by the record low temperatures during April 4 - 9, 2007. Missouri has just over one million acres planted to wheat; of that 575,303 or about 55 percent is covered by crop insurance. The predominant crop insurance form is Actual Production History (64 percent of acres), followed by Revenue Assurance (18 percent), Crop Revenue Coverage (15 percent) and group risk plans (4 percent). If a farmer believes that his wheat suffered damage, they need to contact their insurance agent to have an adjuster appraise any damage. If damage is high, farmers may consider whether or not to destroy the crop and plant second crop - either corn or soybeans. Of greatest importance is that farmers communicate with their insurance agent before they take any action on their existing wheat acres. This is the case regardless of the type of insurance they purchased on their wheat. If a decision to destroy the existing wheat crop and plant second crop is made, farmers may be asked by their crop insurance company to leave a strip of wheat until maturity so that an accurate assessment of the damage can be made. The crop insurance company will initially pay only 35 percent of the indemnity due to a damaged crop if a second crop is planted and insured on those acres. The remaining 65 percent of the indemnity will be held until the harvest of the second crop. If the second crop has no problems requiring an indemnity, the farmer will receive the 65 percent of indemnity that was held back. If the second crop does earn an indemnity, the farmer will need to choose whether to receive the indemnity on the second crop or the remaining 65 percent of the wheat indemnity. They will not be able to get both indemnities. This will be an interesting year to see how the group risk plans perform. Group risk plans are best suited for widespread disasters such as this freeze rather than for local disasters such as a hail storm or flooding of lowlands. If, in fact, damage is widespread from this freeze, the group risk plans may pay well this year. Ray Massey MasseyR@missouri.edu ********************************************************************** Alfalfa Weevil Populations After the Freeze By Wayne Bailey Although alfalfa plants were frozen and collapsed to the soil surface in many of the states alfalfa fields, alfalfa weevil larvae appear to have survived the cold conditions without experiencing much mortality. Weevil numbers vary around the state and from field to field. In general, southern Missouri fields have all sizes of larvae present with new adults emerging from pupal cases in some areas. This range in size of larvae and the presence of new adults indicate that a minimum of two peak egg hatches occurred this season. In central Missouri adults, weevils have not yet emerged, although larvae of all sizes are present in most central Missouri fields. In those fields where plants are still standing, larvae can be found feeding on plant foliage whereas in fields where the alfalfa has collapsed due to freezing, the larvae are present in the plant debris at the soil surface. Small first and second instars are present in most north Missouri alfalfa fields. These surviving populations of alfalfa weevil larvae and adults have the potential to cause significant damage to the alfalfa plants as new tillers grow from plant crowns. In 1987 similar problems occurred when alfalfa plants in the southern part of the state froze and collapsed to the ground. As the new tillers emerged, larvae quickly fed upon them and limited tiller growth. Without the canopy competition from the tillers, numerous weed species (non host plants of the alfalfa weevil) grew and eventually caused mortality of the alfalfa plants resulting in significant stand reductions. Alfalfa producers are encouraged to scout alfalfa fields to determine whether larvae or adult weevils are present and at what levels. Regardless of whether the alfalfa foliage has been harvested or remains, the potential for feeding on emerging alfalfa tillers exists for both larvae and adult weevils. Surviving weevils should be inspected to see if any are infected by the fungal pathogen which turns these larvae from their normal light green/lime green color to a pale yellow color. If several weevil larvae are found to be infected by this pathogen, then treatment with an insecticide may not be necessary. In those fields where larvae are numerous and remain their normal color, then an insecticide application may be necessary to prevent substantial damage to the alfalfa plants. Similarly, in fields where adult weevil numbers are high, an insecticide application may be needed to prevent the adult weevils from girdling the new stems and limiting tiller growth. Several insecticides are labeled for control of alfalfa weevil larvae, but not all are labeled for adult weevil control. Most insecticides labeled for adult control will also control larvae. If adult weevils are high in number, be sure to select an insecticide which is labeled and effective on the adult stage of this pest. ################################################################################################################ # # # Recommended Insecticides for Larval Alfalfa Weevil Management - 2007 # # Insect Pest # # Alfalfa Chemical name Common name Rate of Formulated Rate of Active # # weevil Material Ingredient (a.i.) # # Larvae: Beta-cyfluthrin *Baythroid XL 1.6 to 2.8 fl oz/acre 0.0125 to 0.022 lb a.i./acre # # Carbofuran *Furadan 4F 1/2 to 2 pts/acre 0.25 to 1 lb/acre # # Chlorpyrifos 4E *Lorsban 4E 1 to 2 pts/acre 0.5 to 1 lb/acre # # *numerous products see specific labels see specific labels # # Methyl Parathion *Chemnova Methyl 4EC 1 pt/acre 0.5 lb a.i./acre # # Gamma-cyhalothrin *Proaxis 2.56 to 3.84 fl oz/acre 0.02 to 0.03 lb a.i./acre # # Phosmet Imidan see specific label see specific label # # Zeta-cypermethrin *Mustang Max 2.24 to 4.0 fl oz/acre 0.014 to 0.025 lb a.i./acre # # Carbaryl Sevin 4F 1.5 qts/acre 1.5 lb a.i./acre # # Carbaryl Sevin XLR Plus 1.5 qts/acre 1.5 lb a.i./acre # # Lambda-cyhalothrin *Warrior 2.56 to 3.84 fl oz/acre 0.02 to 0.03 lb a.i./acre # # *Numerous products see speciic labels see specific labels # # # # Read and follow all label direction, precautions, and restrictions. # # * Designated a restricted use product. # # # ################################################################################################################ ####################################################################################################### # # # Recommended Insecticides for Larval Alfalfa Weevil Management - 2007 # # Insect Pest # # Alfalfa Chemical name Common name Rate of Formulated Rate of Active # # weevil Material Ingredient (a.i.) # # Adults: Carbofuran *Furadan 4F 1 to 2 pts/acre 0.5 to 1 lb/acre # # Chlorpyrifos 4E *Lorsban 4E 1 to 2 pts/acre 0.5 to 1 lb/acre # # *numerous products see specific labels see specific labels # # Methyl Parathion *Chemnova Methyl 4EC 1 pt/acre 0.5 lb a.i./acre # # Phosmet Imidan see specific label see specific label # # Read and follow all label direction, precautions, and restrictions. # # Be aware of preharvest restrictions following insecticide application to alfalfa crop. # # * Designated a restricted use product. # # # ####################################################################################################### Laura Sweets 573-864-7307 SweetsL@missouri.edu ********************************************************************** Fate of wheat crop may take until week's end; corn, too, may have been injured by frosts By Greg Horstmeier COLUMBIA, Mo. - Missouri's frosted crops need to revive before they will reveal the extent of damage from the Easter weekend's record low temperatures. "We need warmer temperatures and some sunshine before plants will regrow, and we can see how much damage was done," said Bill Wiebold, University of Missouri Extension agronomist. Wiebold and other MU crop experts discussed damage during a weekly teleconference, April 11, with extension specialists from around the state. Most specialists reported area wheat fields were showing frost-damaged leaves. While only a fraction of the state's corn crop has been planted, it too may have been damaged by temperatures that caused soils to freeze down to a 2- inch depth in places. Plant stems and leaves turned dark and limp due to the heavy frost, Wiebold said. This indicates cell death, and the affected portion of plant will not survive. "Patience is essential," he said. "We need some heat units for the damage symptoms to show up." He suggested specialists and farmers wait until the end of the week, which promises some chance of sunshine, before trying to assess the fate of fields. Wheat, typically a frost-hardy crop, was in an extremely vulnerable condition, Wiebold said. Near-record warm temperatures in March pushed the young wheat plants to grow ahead of schedule. Plants were well past jointing in central and south Missouri. Jointing is the stage where the stem begins to elongate, and the immature head is pushed above ground although still hidden by the leaves. "Minimum temperature records were set throughout the state during the April 8-9 weekend," said Pat Guinan, MU Extension climatologist with the Commercial Agriculture Program. "The state witnessed an unprecedented climatic event over a three-week period when an unusually warm two-week period beginning March 21 abruptly transitioned to a record six-day cold wave beginning April 4," Guinan said. A map of low temperatures for the weekend shows a smattering of 17- to 20-degree temperatures, deadly to tender crop plants. Only the Bootheel region was spared lows 20 degrees or lower. To check wheat spikes, or the stem containing the tiny, immature wheat head, Wiebold said to slit the main plant stem from the soil to the tip. When healthy, the tiny wheat head and nodes will appear white to light-green and be firm and moist. Damaged heads and nodes will appear dark and mushy. Corn fields also were in a vulnerable stage. At this point in the season, corn that has been planted and emerged has its growing point one-half inch or so below the soil surface, Wiebold said. Freezing temperatures below that point could likely have killed the growing point. Sprouted, but not yet emerged, corn kernels could also have been killed in soil that froze into the 1- to 2-inch depth. Wheat has secondary tillers that, if they survived, can produce wheat heads, though yields will not be as high as from the primary spike. Corn has no secondary, or "backup," growth point. As with wheat, Wiebold recommended waiting a few more days for temperatures to get back to more normal conditions, then checking corn plants and sprouted seeds for the mushy, dark appearance that signals plant death. Source: Bill Wiebold, 573-882-0621 Greg Horstmeier News Director 573-884-1846 horstmeierg@missouri.edu ********************************************************************** Weather Data for the Week Ending April 16, 2007 By Pat Guinan -------------------------------------------------------------------------------- | Monthly | Growing Weekly Temperature (deg. F) |Precip (in.)|Degree Days^ -----------------------------|------------|------------ Ext- Ext- Depart| Depart|Accum Depart Avg.Avg. reme reme from |Apr 1 from |since from Station County Max.Min. High Low Mean avg. |Apr 16 avg |Apr 1 avg. ------------------------------------------------------|------------|------------ Corning Atchison 56 36 77 34 46 -6 | 1.60 -0.07 | 34 +21 St. Joseph Buchanan 53 37 73 33 45 -9 | 1.06 -0.72 | 32 +4 Brunswick Chariton 54 36 73 31 45 -8 | 1.16 -0.57 | 34 +7 Albany Gentry 54 33 74 30 44 -8 | 0.83 -1.12 | 21 +6 Auxvasse Audrain 54 36 72 33 45 -8 | 1.80 -0.19 | 39 +10 Columbia Boone 53 37 72 33 45 -10 | 2.25 +0.08 | 40 -7 Sanborn Field Boone 54 37 73 35 46 -9 | 1.89 -0.28 | 46 -6 Williamsburg Callaway 54 37 73 34 45 -8 | 2.95 +0.65 | 43 +13 Novelty Knox 54 34 73 30 44 -9 | 2.19 +0.41 | 27 +5 Linneus Linn 54 33 72 29 44 -9 | 1.01 -0.70 | 28 +9 Monroe City Monroe 54 34 72 29 44 -10 | 1.96 +0.03 | 33 +1 Versailles Morgon 54 37 75 32 45 -11 | 2.50 +0.08 | 49 -18 Green Ridge Pettis 53 35 70 31 44 -9 | 2.60 +0.48 | 39 +15 Lamar Barton 55 37 71 32 45 -11 | 2.05 +0.02 | 45 -23 Cook Station Crawford 54 36 76 33 45 -12 | 2.58 +0.55 | 44 -29 Alley Spring Shannon 56 36 78 29 46 -10 | 2.22 +0.18 | 39 -22 Round Spring Shannon 56 36 78 30 46 -10 | 2.72 +0.67 | 38 -24 Delta Cape | | Girardeau 57 39 73 36 48 -10 | 2.61 +0.65 | 51 -42 Cardwell Dunklin 59 43 72 39 50 -10 | 2.65 +0.22 | 63 -62 Clarkton Dunklin 59 41 73 38 50 -10 | 1.79 -0.20 | 59 -60 Glennonville Dunklin 58 41 74 38 50 -10 | 2.05 +0.15 | 62 -60 Charleston Mississippi 58 41 72 37 49 -8 | 2.31 +0.11 | 62 -33 Portageville- | | Delta Center Pemiscot 59 42 73 40 50 -9 | 2.50 -0.02 | 68 -53 Portageville- | | Lee Farm Pemiscot 59 42 73 39 50 -9 | 2.56 +0.13 | 70 -49 Steele Pemiscot 60 43 72 40 51 -8 | 2.92 +0.48 | 69 -48 -------------------------------------------------------------------------------- ^Growing degree days are calculated by subtracting a 50 degree (Fahrenheit) base temperature from the average daily temperature. Thus, if the average temperature for the day is 75 degrees, then 25 growing degree days will have been accumulated. -------------------------------------------------------------------------------- Pat Guinan Commercial Agriculture Program 573-882-5908 GuinanP@missouri.edu