Integrated Pest & Crop Management Newsletter University of Missouri-Columbia Vol. 16, No. 14 Article 1 of 3 July 28, 2006 Corn Growers-Don't Let Aflatoxin Ruin Your 2006 Corn Harvest By Allen Wrather, Professor, University of Missouri-Delta Center This is a warning. Corn harvest will soon begin in Missouri, and producers should take precautions to avoid aflatoxin contamination. Aflatoxin is a poison to humans and animals and is produced by a mold which grows on corn kernels in the field and on high moisture kernels stored in a truck or trailer or in a grain tank for a few days, especially drought-stressed corn damaged by earworms. Because of the toxicity of aflatoxin, grain buyers will reject truck loads of corn containing 20 parts per billion. Aflatoxin contaminated corn has not yet been found in any of this year's deep south harvested corn, but Missouri producers should not relax. Corn producers can reduce the risk of aflatoxin by properly irrigating corn and by drying wet, freshly harvested corn to 15 percent moisture within 24 hours. Producers that planted Bt varieties may have fewer problems with aflatoxin because these varieties often have less damage due to earworms than non- Bt varieties. Yes, you did see this story in the newspaper last year, the year before that, and the year before that. I publish something about aflatoxin each year before corn harvest starts to warn producers about it because most problems due to this potent toxin can be reduced. To reduce the risk of aflatoxin, producers should irrigate properly and dry wet, freshly harvested corn to 15 percent moisture within 24 hours. Some aflatoxin may be produced by this mold on kernels in the field, but much more will be produced by this mold growing on wet, warm corn kernels stored on a truck or in a grain tank for several days. The mold grows best when 18 percent moisture corn is stored at 86 degrees. Never store wet corn (greater than 15 percent moisture) for more than one day. Many producers in south Missouri experienced problems with aflatoxin contaminated corn in 1993 and in 1998. Drought and earworms damaged the corn these years, and that damage enhanced growth of the mold that produced the toxin on corn kernels in the field and in especially on wet corn kernels in storage. Corn producers that irrigated their corn this year and planted Bt varieties will experience fewer problems with aflatoxin than others. But, all producers should still beware of this problem and always dry their corn to 15 percent moisture within 24 hours of harvest. Yes, I already stated four times in this article that corn should be dried quickly after harvest, and I did that because it is very important to avoid this problem. Following these suggested procedures will give corn producers a better chance of producing aflatoxin-free corn. This has been brought to you by University of Missouri Extension through the College of Agriculture, Food, and Natural Resources. More information about aflatoxin is available at http://aes.missouri.edu/delta/croppest/aflacorn.stm. Allen Wrather 573-379-5431 ##################################################################### Article 2 of 3 Field Crop Disease Update- July 24, 2006 By Laura Sweets Corn We have not had many reports of diseases showing up on field corn. Anthracnose, gray leaf spot and rust are present in low levels in some fields. For the most part these foliar diseases are primarily in the lower portion of the canopy and the ear leaves are relatively disease free. Soybean Soybean rust continues to spread very slowly in the southern United States with only a few new reports of finds on kudzu, still only three finds on soybeans in sentinel plots and no reports from commercial soybean production fields. The risk of soybean rust in Missouri remains low. We have been receiving leaflet samples from the 25 sentinel plots throughout the state of Missouri. Soybean rust has not been found on any of these samples. Septoria brown spot, downy mildew and bacterial blight have been present on samples from most regions of the state. However, none of these foliage diseases appear to be present at damaging levels. A reminder seems in order about the use of foliar fungicides for "Plant Health" or for yield boost in soybean production. Quadris, Headline and several products containing chlorothalonil (ex. Bravo Ultrex, Bravo Weather Stik, Echo 90 DF, Echo 720, Equus DF, etc.) do have full federal registrations and are labeled for use on soybeans for a number of diseases in addition to soybean rust. The section 18 fungicides such as Bumper, Domark, Folicur, Headline BSR, Laredo, Orius, PropiMax, Quilt, Stratego, Tilt and Uppercut, have quarantine exemption labels for use on soybeans only if there is a threat of soybean rust and only for management of soybean rust. These section 18 fungicides are not labeled for general plant health or for the control of other soybean foliage diseases. The use of section 18 fungicides in the absence of threat of soybean rust is a misuse of those products and could jeopardize future section 18 requests. We have received numerous calls and samples related to "yellow beans". Patterns in the field range from scattered yellowed plants to distinct circular to elongate patches of yellowed plants. Yellowing may be occurring in the lower canopy or the upper canopy. Finally the pattern of yellowing on individual leaflets may vary greatly. In some cases the yellowed plants have poor root systems. The roots may be very shallow or crooked which could be the result of low soil moisture, compaction or a similar environmental factor. Many of these plants are also showing symptoms of either Fusarium root rot or Rhizoctonia root rot. Fusarium root rot is more likely to cause a general rotting and deterioration of the main taproot while Rhizoctonia root rot causes a reddish discoloration of the stem at the soil line. Phytophthora root rot may cause entire plants to turn off-color, yellow, wilt and die. A key symptom of Phytophthora root rot is the dark brown discoloration of the main stem from the soil line up the stem and even out the lower side branches. The high temperatures of the last week have caused many plants that were showing initial wilting due to Phytophthora to die. These dead plants are harder to find in the field as the canopy closes and hides the dead plants. Initial symptoms of sudden death syndrome SDS are showing up in some fields in central Missouri. The light yellow blotches between the veins of leaves in the mid to upper canopy, is a key symptom of this disease. Soybean cyst nematode continues to be a major problem on soybeans in Missouri. Damage from SCN can be more severe when plants are under moisture stress. If beans are slow to close, if plants seem stunted or unthrifty or if yields are below expectations, it would be wise to collect soil samples for SCN analysis. Bean pod mottle virus has been more prevalent this season than for several years. This virus is spread by the bean leaf beetle so high populations of bean leaf beetle can lead to an increase in bean pod mottle. Symptoms of this virus disease are most evident on the upper leaves and include a mottling of the leaf tissue. Leaflets may also be smaller in size and have a bumpy appearance. Laura Sweets 573-884-3707 ##################################################################### Article 3 of 3 Weather data for the Week Ending July 24, 2006 By Pat Guinan -------------------------------------------------------------------------------- | Monthly | Growing Weekly Temperature (deg. F) |Precip (in.)|Degree Days^ -----------------------------|------------|------------ Ext- Ext- Depart| Depart|Accum Depart Avg.Avg. reme reme from |Jul 1 from |since from Station County Max.Min. High Low Mean avg. |Jul 24 avg. |Apr 1 avg. ------------------------------------------------------|------------|------------ Corning Atchison 90 67 101 59 79 +2 | 2.07 -2.16 | 2220 +437 St. Joseph Buchanan 88 69 98 62 79 +2 | 3.84 +0.16 | 2150 +333 Brunswick Chariton 91 68 99 60 79 +2 | 3.63 +0.58 | 2146 +285 Albany Gentry 90 67 101 59 79 +1 | 1.71 -2.6 | 2032 +210 Auxvasse Audrain 90 68 100 61 78 0 | 4.01 +1.17 | 2103 +237 Columbia Boone 91 68 100 62 79 0 | 2.36 -0.69 | 2151 +211 Sanborn Field Boone 92 71 101 64 81 +2 | 2.68 -0.39 | 2305 +323 Williamsburg Callaway 92 67 101 60 78 0 | 3.78 +0.94 | * * Novelty Knox 88 67 96 61 77 -1 | 2.44 -0.56 | 1957 +131 Linneus Linn 89 68 96 61 78 +1 | 2.89 -0.72 | 2003 +230 Monroe City Monroe 90 67 97 60 78 0 | 2.09 -0.85 | 2024 +151 Versailles Morgon 95 69 107 61 82 +3 | 1.53 -1.78 | 2315 +339 Green Ridge Pettis 94 69 105 61 81 +3 | 2.07 -1.66 | 2235 +409 Lamar Barton 92 68 102 57 80 +1 | 1.88 -2.01 | 2309 +256 Cook Station Crawford 94 64 103 56 78 0 | 1.18 -1.55 | 2051 +40 Alley Spring Shannon 92 64 97 56 77 -1 | 3.90 +0.98 | 2022 +120 Round Spring Shannon 92 64 98 57 77 -1 | 3.76 +0.84 | 2046 +143 Delta Cape | | Girardeau 90 66 98 58 78 -2 | 4.05 +1.57 | 2262 +2 Cardwell Dunklin 91 67 97 59 79 -2 | 0.86 -1.52 | 2626 +171 Clarkton Dunklin 92 68 98 61 80 -1 | 3.94 +1.7 | 2543 +122 Glennonville Dunklin 92 68 98 61 80 -1 | 3.78 +1.47 | 2524 +112 Charleston Mississippi 90 68 97 60 79 -1 | 2.91 +0.07 | 2403 +186 Portageville- | | Delta Center Pemiscot 91 70 98 63 80 -1 | 2.54 +0.35 | 2631 +224 Portageville- | | Lee Farm Pemiscot 91 69 97 62 80 -1 | 4.32 +2.02 | 2634 +245 Steele Pemiscot 92 69 98 61 81 0 | 3.10 +0.66 | 2735 +329 -------------------------------------------------------------------------------- * 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