Integrated Pest & Crop Management Newsletter University of Missouri-Columbia Vol. 15, No. 12 June 17, 2005 Diagnosing Herbicide Drift Injury on Corn By Kevin Bradley I've received several calls recently regarding corn that has been injured as a result of drift from a herbicide application made on a nearby field. Due to the widespread use and adoption of Roundup Ready soybean, most of these cases involve glyphosate injury to non-Roundup Ready corn hybrids. However, there are a variety of other herbicides that can cause significant injury on corn if drift occurs. The following article provides some tips for diagnosing injury to corn as a result of drift from other non-labeled herbicides. Overall, corn that has been injured as a result of glyphosate drift or tank contamination will usually have a stunted appearance with chlorotic areas on the newest emerging leaves. Perhaps the most characteristic symptom of low levels of glyphosate drift or tank contamination is distinctive chlorotic "bands" on the newest corn leaves emerging from the whorl. This is a result of glyphosate coming into contact with these leaves while they are rolled up within the corn whorl. Once these leaves emerge from the whorl, these bands can usually be observed in a distinctive pattern around the plant. These bands also reveal where and when the glyphosate contacted the plant. Depending on the severity of the glyphosate dose received, a variety of injury symptoms may be observed. For example, in some cases the whorl and newest leaves may be bleached to the point of being white. Additionally, glyphosate may cause some "purpling" of the corn leaf midribs under certain conditions, but does not typically cause entire leaves or leaf margins to turn purple as is the case with phosphorous deficiency. In cases where glyphosate tank contamination has occurred, injury symptoms may be Diagnosing Herbicide Drift Injury on Corn especially variable as several herbicides (including small amounts of glyphosate) and modes of action have been applied at the same time. The degree and significance of the corn injury may be determined by noting the amount of chlorosis in the newest leaves emerging from the corn whorl. Although it is much less common, corn may also be injured as a result of drift or tank-mix contamination of glufosinate, which is sold as Liberty or Ignite. On non-Liberty Link corn varieties, glufosinate injury will appear within a few days after application. Very small, water-soaked lesions may be observed within just one day after application. Affected plants will turn yellow and then necrotic depending on the severity of the drift or tank-mix contamination. Corn leaves often have bleached white striped areas that may sometimes be confused with frost damage. Corn may also show signs of injury as a result of drift from paraquat, which is sold under the trade name of Gramoxone Max, Cylcone Max, and Boa. This typically occurs on emerged corn in areas where a burndown application of paraquat has been applied to a nearby field that will be no-till planted to corn or soybean. Initial symptoms of paraquat injury can be observed within a few hours after application especially during hot sunny days. Paraquat destroys cell membranes so within a few hours after contact with paraquat, corn leaves will have indiscriminate, grayish water-soaked lesions that are a result of the cellular constituents leaking out of the plant cell membranes. Within a few days after application, these lesions will progress and appear as bleached white or necrotic spots wherever the herbicide came into contact with the corn foliage. The severity of the injury will be dependant on the degree of paraquat drift that has occurred, but this "speckling" is usually minor and yield reductions will only occur under severe cases. Another class of herbicides that may cause injury to corn as a result of drift from a nearby soybean field is the graminicides, or grass herbicides. These include the herbicides fluazifop-P (Fusilade), quizalofop-P (Assure II), fenoxaprop (in Fusion), clethodim (Select), and sethoxydim (Poast Plus). These products have 'regained' some of their usefulness in recent years due to the emerging problem of controlling volunteer Roundup Ready corn in Roundup Ready soybeans. All of these products have a similar mode-of-action and will cause essentially identical symptoms on affected corn plants. Corn that has been injured as a result of drift from one of these herbicides will have newer leaves that become distinctly reddish in appearance. Another key symptom is that new leaves in the whorl will separate easily from the remainder of the plant and will become necrotic and rotten at the point of the leaf attachment. For more information and pictures pertaining to the diagnosis of corn injury symptoms as a result of drift, tank contamination, or misapplication of herbicides, see the MU Herbicide Symptomology website at [http://www.psu.missouri.edu/agronx /weeds/Web%20Resources/herbinjsymptoms/muhrbinj.html]. Kevin Bradley 573-882-4039 Plan Now to Attend the MU Weed and Pest Management Field Day on July 14th The annual Weed and Pest Management Field Day will be held this July 14th at the Bradford Research and Extension Center near Columbia, Missouri. As in recent years, we have expanded the focus of this field day to include a variety of pest management topics that are of interest to agricultural industry representatives, agrichemical dealers, Extension specialists, and producers. Some of the research topics and trials that will be on display at this year's field day include corn rootworm transgenics, soybean aphid thresholds and control tactics, fungicides for soybean rust, insecticide and fungicide combinations on soybean, glyphosate and fungicide tank-mix evaluations, planting date and maturity group interactions with soybean rust, herbicide-resistant weed biotypes in Missouri, fall herbicide applications, and much more. As usual, you will also have the opportunity to view plots that showcase a wide variety of herbicide treatments and weed management systems for use in either corn or soybean. The program will begin at 8:30 a.m. and will include guided wagon tours with stops that feature presentation of results and talks by MU weed scientists, entomologists, plant pathologists, and agronomists. There will be a $20 registration fee collected at the time of check-in. This will cover costs associated with lunch and will provide each attendee with a tour booklet that describes the layout and location of each experiment. After lunch, you are welcome to spend the afternoon browsing the plots on your own. For certified crop advisors, 2 CEU credits for the field day are pending. If you plan on attending the field day, you must pre-register before July 8 by calling 573-884-7593 or by sending an e-mail to liji@missouri.edu. The Bradford Research and Extension Center is located 7 miles east of Columbia, off of highway WW. For more complete directions call 573-884- 7945 or visit http://aes.missouri.edu/bradford/index.stm. Update on Soybean Aphid By Wayne Bailey Soybean aphid can be a problem early in the spring as overwintering eggs hatch on buckthorn (Rhamnus) and winged soybean aphids move to soybean fields. Aphids produced during early spring are usually not a problem in Missouri, although this year an infestation was found in Nodaway County in NW Missouri. Infestations were light with most aphids possessing wings suggesting they recently migrated from buckthorn to the soybean fields. Young aphids born from the winged form of the soybean aphid are usually non-winged and may colonize soybean plants if conditions are suitable. Of much greater concern is the potential for late July migrations of soybean aphids into Missouri from more northern states. At present, entomologist from Canada, Wisconsin, Minnesota, Michigan, Ohio and New York are reporting moderate infestations of soybean aphids on seedling soybean. Numbers range up to 50+ aphids per seedling plant in some areas of these northern regions. If these populations continue to grow as expected in these areas, then the potential for heavy migrations of the aphid into Missouri during the 3rd and 4th weeks of July is increased. Field conditions, weather patterns, and beneficial insect populations will all influence aphid population growth and help determine whether Missouri will receive aphid migrants during July. We will continue to monitor aphid reports from states in the north central region of the U.S. and provide early warning as to whether the aphid will be a problem in Missouri during the 2005 growing season. Wayne Bailey 573-882-2838 office or 573-864-9905 cell Weather Data for the Week Ending June 7, 2005 By Pat Guinan -------------------------------------------------------------------------------- | Monthly | Growing Weekly Temperature (deg. F) |Precip (in.)|Degree Days* -----------------------------|------------|------------ Ext- Ext- Depart| Depart|Accum Depart Avg.Avg. reme reme from |Jun 1 from |Since from Station County Max.Min. High Low Mean avg. |Jun 7 avg. |Apr 1 avg. ------------------------------------------------------|------------|------------ Corning Atchison 82 63 90 58 72 +5 | 1.87 +0.95| 853 +257 St. Joseph Buchanan 80 63 87 58 71 +4 | 3.25 +2.43| 776 +135 Brunswick Chariton 84 61 89 54 73 +5 | 2.64 +1.54| 850 +185 Albany Gentry 82 61 88 52 71 +3 | 1.86 +0.90| 755 +128 Auxvasse Audrain 86 61 92 57 74 +6 | 0.34 -0.55| 825 +163 Columbia Boone 85 62 91 59 74 +5 | 0.31 -0.72| 831 +120 Sanborn Field Boone 86 63 92 60 75 +6 | 0.61 -0.43| 898 +168 Novelty Knox 84 60 88 54 72 +4 | 2.30 +1.45| 744 +103 Linneus Linn 83 59 88 52 71 +4 | 1.72 +0.74| 746 +129 Monroe City Monroe 85 61 91 56 73 +5 | 1.04 +0.09| 787 +111 Versailles Morgan 86 63 91 59 74 +6 | 0.60 -0.33| 899 +138 Green Ridge Pettis 85 63 90 57 73 +6 | 0.78 -0.62| 867 +235 Lamar Barton 84 64 87 60 74 +4 | 0.95 -0.06| 885 +93 Cook Station Crawford 86 58 91 48 73 +4 | 0.55 -0.47| 781 -22 Delta Cape | | Girardeau 86 65 94 60 74 +2 | 0.13 -0.68| 911 -23 Cardwell Dunklin 89 65 97 58 77 +3 | 0.00 -0.89|1095 +35 Clarkton Dunklin 88 65 97 58 76 +2 | 0.21 -0.65|1028 -9 Glennonville Dunklin 88 66 96 59 76 +2 | 0.10 -0.72|1033 -1 Charleston Mississippi 85 64 95 59 74 +2 | 0.47 -0.42| 973 +68 Portageville- | | Delta Center Pemiscot 86 68 97 62 76 +2 | 0.59 -0.43|1086 +63 Portageville- | | Lee Farm Pemiscot 86 67 96 61 76 +3 | 1.07 +0.07|1088 +77 Steele Pemiscot 87 68 98 61 77 +3 | 1.37 +0.34|1127 +97 -------------------------------------------------------------------------------- *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