Integrated Pest & Crop Management Newsletter University of Missouri-Columbia Vol. 16, No. 10 June 2, 2006 Article 1 of 4 June 2, 2006 Soybean Rust Update By Laura Sweets The soybean rust sentinel plot system is up and running for the 2006 season (www.sbrusa.net). Missouri is again cooperating in this effort. Right now it looks as though there should be 26 sentinel plots located throughout the soybean producing areas of the state. Some sentinel plots have plants in the early vegetative stages and have been scouted for soybean rust. The procedure this season is for 100 terminal leaflets from the lower canopy to be submitted for microscopic examination for soybean rust. Foliage samples submitted from Pemiscot County and Scott County were negative for soybean rust. Scouting has been intensive in the southern states, first on kudzu and now on kudzu and soybeans, especially soybeans planted in sentinel plots. Rust has been confirmed in five counties in Alabama, eleven counties in Florida, four counties in Georgia and one county in Texas. Most of these finds have been on kudzu. There are no current reports of soybean rust on newly planted soybean in 2006 including volunteer soybean plants. Several of the southern states are reporting hot, dry weather that is not conducive to the development of soybean rust. In their latest reports both Louisiana and Florida mentioned that periodic rains, extended dews and high humidity are maintaining moisture in the canopy which could be more favorable for the development of foliage diseases including soybean rust. Sentinel plots are being scouted on a weekly basis. Although soybean rust appears to be slow in developing or moving in the south, it is still early in the season. It is very important to keep up-to-date on the occurrence of the disease and changes in weather patterns in the southern states. Laura Sweets 573-884-7307 ********************************************************************* Article 2 of 4 June 2, 2006 Missouri Cotton Growers - Beware of Root-Knot Nematodes By Allen Wrather Crop-threatening levels of root-knot nematodes are present in some, but not all, cotton fields in southeast Missouri. During a recent survey of Missouri cotton fields by University of Missouri scientists, root-knot nematodes were found in 20 percent of the New Madrid County fields, 27 percent of Pemiscot County fields, and 43 percent of Dunklin County fields. This nematode is also present in some Scott County fields. These nematodes can cause severe injury to cotton and will reduce yield. The symptoms of root-knot nematode injury will initially be visible 6-8 weeks after planting. Most years, the symptoms are visible during early- to mid-June. Unfortunately, cotton planting this year has been delayed for some producers due to wet weather and symptoms may not be visible until late-June to early-July. The symptoms of root-knot nematode injury are stunted cotton plants and these plants may wilt more quickly than healthy plants during a hot afternoon. Plants injured by these nematodes will also have galls; swollen areas visible on infected roots. Be cautious about diagnosing the cause of stunted cotton because other factors such as low soil pH and drought may cause plants to be stunted. Ask your scout to tell you about areas in your fields where they observe this symptom and then determine the cause of the stunting. Growers suspicious of nematode problems in their cotton should dig up roots soon after harvest and the stalks are shredded and look for galls on the roots. Nothing can be done this year to protect cotton against these nematodes, but growers can take precautions to avoid this problem next year. There are no cotton varieties highly resistant to root-knot nematodes, but Stoneville 5599 is tolerant. These nematodes will reduce yield of this variety but not as much as they reduce yield of other varieties. Growers should consider planting Avicta Complete Pak treated seed or using Temik at 3.5-5.0 pounds per acre in furrow when planting this or any other cotton variety. Following these suggested procedures will give cotton farmers a better chance of producing higher yields and greater profits. For more information contact Allen Wrather at the University of Missouri Delta Center (Phone: 573-379-5431, E-mail: wratherj@missouri.edu) or check the Delta Center Webpage (aes.missouri.edu/delta). Remember, the University of Missouri-Delta Center Field Day is August 31, 2006. Dr. Allen Wrather Professor, University of Missouri ********************************************************************* Article 3 of 4 June 2, 2006 Field Crop Disease Observations- May 30, 2006 By Laura Sweets Corn With the recent swing to above normal temperatures, young corn plants have taken off and are looking much better in both color and size. Much of the yellowing and stunting of corn plants that had been reported over the last week was related to below normal temperatures and correspondingly cool soil temperatures. Anthracnose may be evident on the very lowest leaves of plants as brown to reddishbrown elliptical lesions. These areas may expand along the margin of the leaf and can be mistaken for herbicide injury. Stewart's bacterial wilt is also showing up in very low levels. Right now Stewart's wilt would be evident as long, pale green to yellow green streaks that tend to follow the veins of the leaf. As the lesions mature they will turn a lighter brown or papery brown in color. Crown decay has not been as widespread nor severe as might have been expected from the vacillating weather conditions in much of the state this spring. Still when trouble shooting in corn fields with uneven stands or stunted plants, it would be prudent to split plants open and look for signs of discoloration or decay of the lower crown tissues. Healthy plants should be white to light cream in color and have a solid texture in the lower crown. With crown decay, the lower crown tissues may be spongy or pithy and may range in color from light brown to dark brown or almost a blackish-brown. Soybeans Thus far there have been few questions or problems on soybeans. A few scattered plants are showing single lesions of Septoria brown spot or frogeye leaf spot. If Pythium and/or Phytophthora root rot are going to be problems this season, I would expect to see symptoms developing over the next few weeks. Wheat Wheat across the state ranges from good to not so good. Barley yellow dwarf has been quite prevalent in almost all areas of Missouri this season. The purple to pinkish-red discoloration of the flag leaves is still quite evident in some fields. However, in other fields the shift to higher temperatures has caused barley yellow dwarf infected plants to fire and leaves are drying out and turning brown prematurely. Septoria leaf blotch, leaf rust and stripe rust are being reported in scattered fields throughout the state. In most cases these diseases have come in late enough in the season that they should not have a major impact on yield. Areas which had rain or extended periods of overcast weather with frequent rains as the wheat crop was flowering may be seeing symptoms of scab or Fusarium head blight on heads. Symptoms of Fusarium head blight are most evident during the grain fill stages before heads normally begin to turn. Scab would be evident as bleached areas anywhere on the head. Areas of pink mold growth may be obvious at the base of glumes. Laura Sweets 573-884-7307 ********************************************************************* Article 4 of 4 June 2, 2006 Weather data for the Week Ending May 30, 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 |May 1 from |since from Station County Max.Min. High Low Mean avg. |May 30 avg. |Apr 1 avg. ------------------------------------------------------|------------|------------ Corning Atchison 88 66 93 56 77 +11 | 1.95 -2.38 | 756 +293 St. Joseph Buchanan 86 66 90 61 76 +11 | 1.66 -3.06 | 717 +213 Brunswick Chariton 89 67 92 61 78 +12 | 3.47 -1.67 | 758 +237 Albany Gentry 88 64 92 55 76 +10 | 0.70 -3.89 | 652 +174 Auxvasse Audrain 89 66 92 61 77 +11 | 1.90 -2.97 | 735 +217 Columbia Boone 89 66 91 60 77 +10 | 1.15 -3.78 | 754 +190 Sanborn Field Boone 90 69 93 65 79 +12 | 2.24 -2.74 | 832 +250 Novelty Knox 88 64 93 60 76 +11 | 2.29 -2.52 | 638 +143 Linneus Linn 88 65 92 57 76 +11 | 2.35 -2.54 | 657 +182 Monroe City Monroe 89 66 93 60 77 +12 | 0.60 -4.31 | 681 +156 Versailles Morgon 88 67 91 61 77 +10 | 2.35 -2.76 | 820 +200 Green Ridge Pettis 89 66 91 57 77 +11 | 0.66 -4.78 | 781 +289 Lamar Barton 88 67 90 63 78 +10 | 5.39 -0.17 | 878 +243 Cook Station Crawford 88 62 89 57 75 +8 | 4.32 -0.34 | 747 +103 Alley Spring Shannon 88 60 92 56 74 +7 | 6.27 +1.57 | 755 +167 Round Spring Shannon 89 61 93 57 75 +8 | 5.54 +0.84 | 756 +167 Delta Cape | | Girardeau 90 65 92 60 77 +7 | 5.32 +0.54 | 835 +83 Cardwell Dunklin 93 71 96 65 81 +9 | 2.72 -2.40 | 1078 +215 Clarkton Dunklin 92 70 97 62 80 +8 | 4.39 +0.20 | 984 +142 Glennonville Dunklin 92 70 95 63 80 +8 | 3.39 -0.64 | 992 +150 Charleston Mississippi 90 66 93 60 78 +9 | 6.72 +2.14 | 913 +189 Portageville- | | Delta Center Pemiscot 91 71 96 66 80 +9 | 4.70 +0.16 | 1037 +199 Portageville- | | Lee Farm Pemiscot 92 70 96 64 80 +9 | 5.44 +0.85 | 1042 +215 Steele Pemiscot 92 71 98 65 81 +9 | 4.86 -0.20 | 1110 +270 -------------------------------------------------------------------------------- ^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