Integrated Pest & Crop Management Newsletter University of Missouri-Columbia Vol. 16, No. 7 Article 1 of 6 April 28, 2006 Glyphosate-Resistant Weeds: Pay now or Pay Later. Which is Better? By Kevin Bradley and Ray Massey Perhaps no single event in the history of agriculture has changed weed management to the extent that Roundup Ready crops have. In 2005, 89% of the soybean acreage in Missouri was planted with Roundup Ready soybean varieties while approximately 15% of our corn acreage was planted with Roundup Ready corn. Many have speculated that our Roundup Ready corn acreage will continue to increase in the next few years, which would place much of our acreage in a Roundup Ready soybean-Roundup Ready corn rotation. And, even though most growers will be applying a preemergence herbicide treatment in corn (hopefully), it’s probably safe to assume that the vast majority of the postemergence applications in either Roundup Ready corn or soybeans will involve glyphosate. This scenario represents a tremendous selection pressure that will be placed on weeds to develop resistance to glyphosate. In fact, in recent years a number of glyphosate-resistant weed biotypes have already been identified. These resistant species have been identified primarily in locations where a Roundup Ready crop, such as soybean or cotton, has been planted continuously without rotation and where repeated applications of glyphosate have been made year after year. Some of the more recent examples of these species include a number of glyphosate-resistant horseweed biotypes located throughout the central and eastern United States (including sites in southeastern Missouri), a glyphosate- resistant common ragweed biotype discovered in Missouri and Arkansas in 2004, glyphosate-resistant palmer amaranth biotypes discovered in Georgia, Tennessee, and North Carolina in 2005, and glyphosate-resistant common waterhemp biotypes that we discovered in two separate locations in northwestern Missouri also in 2005. Although we are just beginning our field research on these populations and these biotypes are not "officially" confirmed resistant yet, all research that we have conducted thus far leads us to believe that these waterhemp populations are indeed resistant to standard and even fairly high rates of glyphosate (Figures 1 and 2). The identification of these glyphosate-resistant waterhemp populations in Missouri should be viewed as a big, flashing "WARNING" sign to growers who have been planting a continuous Roundup Ready crop like soybeans for many years in a row or even to growers who are planting a Roundup Ready soybean-Roundup Ready corn rotation. The last thing we need in our corn and soybean production systems is to lose the profitability of our current weed management programs as a result of the development of glyphosate-resistant weeds. In our view, two alternatives to this problem exist. Farmers can manage the development of resistance by not spraying glyphosate continuously in the same area over time and by rotating to herbicides with other modes-of-action (proactive resistance management), or farmers can choose to deal with a glyphosate-resistant weed once it occurs by using more expensive weed control measures at that time. The question boils down to: "do I pay a slightly higher price today for weed management strategies that delay or prevent glyphosate resistance or do I pay a much higher price in the future when a glyphosate-resistant weed requires me to use more expensive control measures?" Costs in the long term (e.g. more than 5 years) do not really cost as much in today’s dollars as costs incurred in the near term (e.g., within 5 years). Discounting all expenses back to today’s dollar allows for a comparison of the cost of managing resistance versus the cost of having resistance. Recently, some of our colleagues have published an interesting study which attempts to address many of these important issues1. In this study, the authors determined that if it took common waterhemp 29 years or less to develop resistance to glyphosate, then it would be better economically to proactively manage resistance 1 or use alternative weed control strategies now in an effort to delay resistance. On the other hand, the authors found that if it took more than 29 years for common waterhemp to develop resistance to glyphosate, then it would be better from an economic standpoint to just continue to use glyphosate without rotation (use the tool until it breaks strategy). This study made a necessary assumption that could affect the predicted costs of developing glyphosate resistance. They assumed that herbicide prices before and after glyphosate resistance develops will be the same. A more likely scenario is that once glyphosate resistance develops, the price of alternative herbicides will increase because the demand for them increases. Such increases in alternative herbicides would make dealing with resistance even more expensive and give added incentive to managing resistance proactively. Another important aspect of this study is that this was written prior to our discovery of glyphosate-resistant common waterhemp in Missouri. Given that we now have a real-world scenario and glyphosate resistance has been discovered in common waterhemp after about 8 or 9 years of continuous glyphosate use, it seems clear to us that growers should consider adopting some of these proactive weed management strategies in order to prevent higher costs in the future. Some examples of proactive strategies for the management of common waterhemp, for example, would be to: 1) Rotate to conventional corn hybrids and get out of a continuous soybean rotation if at all possible. 2) Use conventional preemergence and/or postemergence herbicide programs that are effective on common waterhemp in corn, given that most producers will plant Roundup Ready hybrids and utilize glyphosate as the sole herbicide for weed control in soybean. 3) In Roundup Ready soybean, first consider the use of preemergence herbicides that have good activity on common waterhemp (Valor, Spartan, Dual, Intrro, etc.). The use of an effective postemergence (Phoenix, Cobra, Reflex, Flexstar, Ultra Blazer) herbicide other than glyphosate either applied alone or as a glyphosate tank-mix partner is also an option, but these products are generally more expensive than some of the preemergence options like Valor listed above. 1 Mueller, T. C., P. D. Mitchell, B. G. Young, and A. S. Culpeper. 2005. Proactive versus reactive management of glyphosate-resistant or -tolerant Weeds. Weed Technology 19:924-933. Kevin Bradley 573-882-4039 Ray Massey 573-884-7788 ********************************************************************* Article 2 of 6 April 28, 2006 Troubleshooting Field Crop Problems By Allen Wrather Producers will experience problems with crops in many Missouri fields this year. I don’t know what types of problems will develop in each field, but I do know they will occur; not in every field but it many. The problems will most likely be due to too much or too little fertilizer, too much or too little water, insects, diseases, herbicide drift or carry over, and the damage to the crop may be mild or severe. Producers should get the cause of each problem diagnosed so action can be taken to prevent spread of the problem this year, if it is spreading, or prevent it from developing next year. Diagnosis of crop problems can sometimes be easy, but it is more often difficult. This article is a brief summary of the material in University of Missouri Extension Guide G4050 that describes a six step process to help farmers and crop consultants diagnose the cause(s) of field crop problems. This guide, Troubleshooting Field Crop Problems, was written by Laura Sweets, Andy Kendig, and me. For the novice, troubleshooting can be intimidating in the absence of a systematic process. For those with experience, a systematic process to troubleshooting can help prevent the bias of looking only for the familiar and thwarting the investigative process. First, determine the variety and the age of the plant. An investigator should identify the plant variety so that a basis exists for defining its normal appearance. In addition, the variety should be noted because some are more resistant or susceptible to certain diseases, insects, or herbicides, and this information may be very useful when diagnosing the cause of the problem. Second, identify all the symptoms affecting the leaves, stems, roots and fruit. An investigator should observe all parts of abnormal plants when troubleshooting a field crop problem including the leaves, stems, fruit and roots as well as the tissue inside roots and stems. Frequently, the point of injury to the plant is not where the symptoms appear. For example, leaves on one or several branches may be discolored and withered because of a canker on a lower branch or a borer in the stem. Nutritional deficiencies and injuries from herbicides may damage both roots and leaves. Examine individual plants in detail and determine the location of symptoms on the plant. Are symptoms on old or young leaves, upper or lower stems, or perhaps on one side of the plant? Look for insects and insect feeding damage. Cut stems to check for discoloration inside the stem and for insect feeding. Hold leaves up to the light to check for mosaic, other viral symptoms, or the presence of webbing and mites. Investigators should look for leaf abnormalities in color, size, shape and texture. Also, carefully dig up roots and examine them. Check for galls, rot, abnormal root color and feeder root condition, and assess root growth. While probing the soil, check for soil compaction, soil structure, texture and organic matter, and the presence and depth of hardpans. Also take note of odors, insects, fertilizer placement and the depth of planting. Third, estimate the percentage of plants damaged in the affected part of the field and the severity of damage. Do you observer damage on all plants in an area or only 10 percent? Symptoms of injury due to insects and disease may appear on every plant in an area, but this is unusual. Symptoms of injury due to herbicides or inadequate fertilizer will usually appear on every plant in an area. Fourth, determine the distribution or pattern of the problem in the field. Look at the entire field to determine where the problem appears. Determine the distribution of the problem in the field as it relates to field characteristics such as areas with light soil, and drainage patterns. Is the problem only in wet areas? Take notice of whether the problem is associated with certain rows or areas of lower or higher elevation. Fifth, evaluate whether all plants (crop and weeds) in the field share similar symptoms. Examine the weeds in the area where the crop is injured and in nearby fence rows. Symptoms caused by nutritional disorders are usually not plant specific. For example, low-pH soils will cause stunting of most plants in the field, including crops as well as weeds. Leaf spots caused by drifting droplets of a contact herbicide (e.g., paraquat) are not plant specific, and several plant types in the area may show similar leaf spotting due to paraquat drift. However, diseases are usually plant specific, and weeds in the area are normally not affected by the same diseases that can attack corn or soybean. Sixth, determine the history of the problem. Ask when the problem was first noticed, and whether crop problems were observed in the same area during previous growing seasons. The answers may provide a clue that could be useful in diagnosing the cause of the problem. Extension Guide sheet G4050 gives more details about troubleshooting field crop problems. Following these suggested procedures will give field crop consultants and producers a better chance of diagnosing the cause of field crop problems. Some information that may help with troubleshooting will be presented during the 2006 Delta Center Field Day on August 31. Allen Wrather Professor Division of Plant Sciences ********************************************************************* Article 3 of 6 April 28, 2006 Black Cutworm Moth Captures Remain High in Central Missouri By Wayne Bailey Numbers of moths captured in pheromone traps in central Missouri remain high (see http://www.ipm.missouri.edu). Moth captures in other locations throughout the state are much fewer in number, although windy conditions may be limiting moth flight and subsequent capture. Using the IPM Black Cutworm Predictive Model, first cutting by 4th instar black cutworm in central Missouri counties is predicted for May 9, 2006. Corn producers in the central Missouri region are encouraged to begin scouting for this pest around May 1 and continue for the next few weeks. The predictive model is based on 30-year average temperatures and may either under or over estimate the time of first cutting by black cutworm larvae depending on current weather conditions. In other regions of the state where moth captures have been limited, producers still are encourage to scout for foliar feeding and cutting from black cutworm larval. Moth captures do not always accurately reflect actual moth activity in a specific area of the state. Fields with winter annual weed cover prior to planting, heavy crop residue levels, or late planted corn are at higher risk of BCW egg laying and subsequent damage from larval feeding. It is unknown what effect dry field conditions in central Missouri may have on BCW larval populations. Seed treatments will help reduce BCW larval number, although trials conducted in Missouri suggest control to be 50 percent at best. If a rescue insecticide application is necessary for management of BCW larvae in field corn, one of the following insecticides is should be selected. Insecticides Labeled for Black Cutworm Insecticide Rate of formulated Placement Comments Common Trade material per acre Name Name permethrin *Ambush 6.4 to 12.8 fl oz Broadcast Apply as a esfenvalerate *Asana XL 5.8 to 9.6 fl oz postemergence cyfluthrin *Baythroid 2 0.8 to 1.6 fl oz rescue treatment bifenthrin *Capture 2EC 2.1 to 6.4 fl oz when 2-4% or more chlorpyrifos *Lorsban 4E 1 to 2 pt of plants are cut zetacypermethrin *Mustang Max 1.28 to 2.8 fl oz and larvae are chlorpyrifos *Nufos 4E 1 to 2 pt present. permethrin *Pounce 3.2EC 4 to 8 fl oz gammacyhalothrin *Proaxis 1.92 to 3.2 fl oz lambdacyhalothrin *Warrior 1.92 to 3.2 fl oz * indicates Restricted Use ********************************************************************* Article 4 of 6 April 28, 2006 Pea Aphid Problems Continue in Alfalfa By Wayne Bailey The pea aphid, Acyrthosiphon pisum (Harris), is the most common of several aphid species found in Missouri alfalfa. Pea aphids are light green in color, about 1/8th inch in length, with long legs, a pair of antennae with dark bands located at the tip of each antennal segment, two cornicles or "tailpipes" projecting from the rear of the abdomen, and green to pink eyes. This aphid possesses piercing-sucking mouthparts used to remove sap from stems and terminal leaflets of alfalfa. Heavy infestations of pea aphid on alfalfa may result in wilted plants, deformed leaflets, and a shiny coating of sugary aphid waste called "honeydew". This waste material often attracts other insects such as ants, bees, or flies, which use the honeydew as a food source. The honeydew may support the growth of molds resulting in the plants taking on a dark color, whereas cast skins produced when aphids grow in size may give plants a white coloration. Weather and beneficial insects are major factors affecting pea aphid populations in this state. Cool springs with moderate to high relative humidity often favor pea aphid population growth, whereas, beneficial insects effectively reduce pea aphid numbers in most years. Common natural enemies of pea aphid include several species of ladybird beetles, lacewings, damsel bugs, syrphid flies, bigeyed bugs, and species of parasitic wasps. Management of pea aphid may be needed on seedling alfalfa when 5 or more aphids are present per stem and alfalfa is less than 3-inches in height. In established alfalfa the economic threshold for pea aphid is 50 or more per stem on alfalfa less than 10-inches in height. In alfalfa 10-inches or greater in height the threshold increases to 75 or more aphids per stem. If alfalfa is under drought stress, it is appropriate to reduce these thresholds as the alfalfa is less able to withstand aphid infestations. Early harvest of infested alfalfa (7-10 days prior to 1/10th bloom) is an effective management techniques for this aphid. In more western states, pea aphid outbreaks often occur following insecticide applications for alfalfa weevil, which reduce beneficial insect numbers and allow for a surge in pea aphid populations. A common question asked by alfalfa producers this past week was whether it is necessary to manage pea aphid infestations at this time in the season. To determine whether to treat with an insecticide, early harvest, or to do nothing really depends on the unique condition in each alfalfa field. In several fields I scouted this past week, pea aphids were present but in numbers approaching or below the economic threshold. Beneficial insect numbers were relatively high in number, alfalfa weevil larvae were low in number due to the presence of the fungal pathogen, and most alfalfa stems were 10-inches or greater in height. Given these factors, an insecticide application for control of pea aphid would not be justified. An exception might be if the alfalfa was under severe drought stress or exhibiting damage symptoms associated with aphid feeding. Early harvest of alfalfa may be an appropriate management strategy for some fields, but early harvest reduces beneficial insect populations along with pea aphid numbers. Each producer must assess their field conditions and determine an appropriate management strategy for this occasional pest of alfalfa. Other aphids commonly collected from Missouri alfalfa fields include the cowpea aphid, spotted alfalfa aphid, and to a lesser extent, the blue alfalfa aphid. The following insecticides are labeled for management of pea aphid in alfalfa Chemical Name Product Name Rates Preharvest Amount of Product Interval (PHI) Cyfluthrin Baythroid 2* 2.8 fl oz/acre 7 days Methyl Parathion Chemnova Methyl 4EC* see specific label 15 days Chlorpyrifos Lorsban 4E* 1 to 2 pts/acre 14 - 21 days Chlorpyrifos Nufos 4E* 1 to 2 pts/acre 14 - 21 days Chlorpyrifos several formulations* see specific labels see specific label Malathion Malathion 1 lb a.i./acre See specific label for rates/ PHI Zeta-cypermethrin Mustang Max* 2.24 to 4.0 fl oz/acre 3 days Gamma-cyhalothrin Proaxis* 2.56 to 3.84 fl oz/acre 1 day forarage, 7 day hay Lambda-cyhalothrin Warrior* 2.56 to 3.84 fl oz/acre 1 day forarage, 7 day hay Lambda-cyhalothrin several formulations* see specific labels see specific labels * indicates Restricted Use a.i. = active ingredient Wayne Bailey 573-864-9905 ********************************************************************* Article 5 of 6 April 28, 2006 Seed Decay and Seedling Blights of Corn By Laura Sweets Some years, early season stand establishment problems are widespread and, in some cases, severe- especially in early planted field corn. The weather pattern during and immediately after planting is a major factor contributing to those problems. Corn planted before extended periods of cold, wet weather in late April and May tends to show damage from saturated soils, cold soil temperatures, frost injury, herbicide injury, nitrogen deficiencies, seed decay and seedling blights. In some fields the seed decay and seedling blight may progress into crown decay resulting in even more severe stunting and yellowing of plants. If weather patterns are favorable for germination and emergence of corn and not as favorable for development of corn seed and seedling diseases, there will be a substantial reduction in seed decay and seedling blight problems in corn. A significant number of corn acres have been planted across the state and many are emerging. The early hot, dry weather would not have favored the development of seedling blight diseases such as Pythium seed decay and seedling blight but may have stressed germinating seedlings. Now the weather pattern seems to have shifted slightly to cooler, slightly wetter weather, so it will be "interesting" to see what types of seed decay and/or seedling blight problems develop on corn this season. Certainly weather conditions over the next several weeks will be a key factor in which early season corn diseases develop and how serious these diseases are. Seed decay and seedling blights of corn are generally caused by soil-inhabiting fungi such as Pythium, Fusarium, Diplodia, Rhizoctonia and Penicillium. These fungi may rot the seed prior to germination or cause preemergence or postemergence seedling blight. Affected seeds are usually discolored and soft and may be overgrown with fungi. Rotted seed may be difficult to find because they decompose very rapidly and because soil adheres fairly tightly to the decomposing seed. With preemergence seedling blights, the seed germinates but the seedlings are killed before they emerge from the soil. The coleoptile and primary roots are usually discolored and have a wet, rotted appearance. With postemergence seedling blights, the seedlings emerge through the soil surface before developing symptoms. Seedlings tend to yellow, wilt and die. Discolored, sunken lesions are usually evident on the mesocotyl. Eventually the mesocotyl becomes soft and water soaked. The root system is usually poorly developed, and roots are discolored, water soaked and slough off. If the primary root system and mesocotyl are severely affected before the nodal or permanent root system has developed, the plants have little chance of surviving. The Pythium, Fusarium, Diplodia, Rhizoctonia and Penicillium species which cause seed decay, seedling blight and crown decay are common in soils throughout the state. If conditions are favorable for germination and emergence, these fungi may not have the opportunity to invade seed, germinating seed or young seedlings so seed decay, seedling blights and crown rot will not be significant problems. On the other hand, conditions that are not favorable for germination and emergence, give these soil fungi more time to attack the seed and developing plants. Numerous other factors also contribute to early season corn establishment problems. Insect damage, nutrient imbalances, herbicide injury, soil conditions and environmental factors, especially saturated soil conditions and oxygen depravation, may also cause or contribute to early season corn establishment problems. Corn seedling blights are more severe in wet soils, in low lying areas in a field or in soils that have been compacted or remain wet for an extended period of time. Low soil temperatures (50-55 degrees) and wet soil conditions especially favor Pythium seed decay and seedling blight. Disease severity is also affected by planting depth, soil type, seed quality, mechanical injury to seed, soil crusting, herbicide injury or other factors which delay germination and emergence of corn. Planting high quality seed into a good seedbed when soil temperatures are above 50 degrees will help minimize these early season problems. Virtually all field corn seed comes with a fungicide seed treatment. Hopper box treatments can be used to supplement the existing seed treatment. Laura Sweets 573-884-7307 ********************************************************************* Article 6 of 6 April 28, 2006 Weather data for the Week Ending April 24, 2006 By Pat Guinan -------------------------------------------------------------------------------- | Monthly | Growing Weekly Temperature (deg. F) |Precip (in.)|Degree Days^ -----------------------------|------------|------------ Ext- Ext- Depart| Depart|Accum Deprt Avg. Avg. reme reme from |Apr 1- from |since from Station County Max. Min. High Low Mean avg. |Apr 24 avg. |Apr 1 avg ---------------------------------------------------------|------------|------------ Corning Atchison 75 45 79 35 60 +5 | 1.21 -1.32 | 271 +271 St. Joseph Buchanan 74 49 83 43 61 +5 | 1.71 -1.25 | 267 +267 Brunswick Chariton 77 48 85 40 63 +6 | 1.07 -1.53 | 290 +290 Albany Gentry 74 44 79 35 59 +4 | 1.57 -1.49 | 232 +232 Auxvasse Audrain 76 50 83 46 63 +6 | 0.64 -2.39 | 294 +294 Columbia Boone 76 51 84 46 64 +7 | 0.88 -2.37 | 302 +302 Sanborn Field Boone 78 52 85 46 65 +7 | 0.65 -2.60 | 334 +334 Novelty Knox 74 44 78 41 60 +4 | 0.75 -1.93 | 237 +237 Linneus Linn 74 45 86 38 60 +4 | 1.06 -1.68 | 245 +245 Monroe City Monroe 75 46 79 42 61 +4 | 0.29 -2.49 | 255 +255 Versailles Morgan 78 51 90 47 65 +6 | 0.97 -2.55 | 336 +336 Green Ridge Pettis 77 50 90 43 64 +8 | 1.00 -2.02 | 304 +304 Lamar Barton 81 53 94 45 67 +8 | 1.87 -1.54 | 360 +360 Cook Station Crawford 81 49 91 42 65 +6 | 2.05 -1.16 | 320 +320 Alley Spring Shannon 83 50 92 39 66 +8 | 1.07 -2.19 | 316 +316 Round Spring Shannon 83 52 92 41 66 +8 | 1.39 -1.87 | 319 +319 Delta Cape 79 55 87 45 67 +7 | 1.02 -2.05 | 320 +320 Girardeau | | Cardwell Dunklin 83 59 96 52 71 +9 | 1.73 -2.07 | 417 +417 Clarkton Dunklin 81 59 94 53 69 +7 | 1.57 -1.62 | 386 +386 Glennonville Dunklin 81 58 92 51 70 +8 | 0.85 -2.28 | 393 +393 Charleston Mississippi 78 58 88 49 68 +8 | 2.20 -1.23 | 358 +358 Portageville- | | Delta Center Pemiscot 81 61 91 53 70 +8 | 1.99 -1.76 | 404 +404 Portageville- | | Lee Farm Pemiscot 82 60 92 52 70 +8 | 1.61 -2.13 | 411 +411 Steele Pemiscot 83 61 95 54 72 +10 | 1.04 -2.66 | 438 +438 -------------------------------------------------------------------------------- * Complete data not available for report ^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