SOY NUGGETS Prepared by the UGA Soybean Team

Transcription

1 SOY NUGGETS Prepared by the UGA Soybean Team July 12, EMERGENCE ISSUES IN JUNE PLANTED SOYBEAN 1 DISEASE MANAGEMENT CONSIDERATIONS FOR JULY 2 BEAN PLATASPID INFESTING SOYBEANS IN NORTHEAST GEORGIA 3 WARRANT HERBICIDE 5 REFLEX + CLASSIC TANK-MIXES 6 SOYBEAN GROWTH STAGES AND PRODUCTION DECISIONS 6 EMERGENCE ISSUES IN JUNE PLANTED SOYBEAN (Whitaker) Although too late to help us in 2010, I think it s worthwhile to talk about issues with soybean emergence late in the planting season. For many growers soybean emergence was less than perfect, especially during June plantings. I m sure we all can recall that the month of June was a hot one. If not for the pleasant July 4 th weekend, we all may have melted away. Nevertheless, many of the instances where soybean emergence was poor occurred during a period of high temperatures. These somewhat unseasonable high temperatures may have contributed to inadequate stands. Heat stress is often the suspected culprit for poor late-season soybean stands, and for good reason. A study conducted in Clemson examined the emergence of soybean in high temperatures and demonstrated that emergence dropped off dramatically with soil temperatures over 100 F (Figure 1) (Wallace, S.U Soybean seedling emergence at high temperatures. Plant and Soil 109: ). Additionally, this study determined that varieties respond differently to high soil temperatures (Figure 2). It should be noted that this experiment was conducted in the late 80 s with dated varieties, but I believe this study illustrates an important message. Poor stands may result from high soil temperatures and should be avoided if possible. Although there may be differences in soybean emergence in high temperatures related to variety, we don t have good grasp on this phenomenon regarding more current varieties. It should also be noted that many other factors may contribute to poor soybean stand other than variety, including seed lot, tillage situation, planting depth, soil crusting, etc. Therefore, it is our recommendation that soybean planting should be postponed when 2-inch soil temperatures peak out at 100 F, regardless of variety. 1

2 Figure 1. Emergence (%) of soybean seedlings as influenced by temperature. Data averaged over two cultivars, Bragg and Cobb. Figure 2. Emergence of three soybean cultivars seeded in three soil temperatures. DISEASE MANAGEMENT CONSIDERATIONS FOR JULY (Kemerait) As of July 12, 2010 Asian soybean rust hast NOT yet been observed in Georgia. Very small amounts have been found on kudzu in Alabama (near Mobile) and in Florida in Jefferson County (immediately south of Thomas and Brooks Counties). The rust at both locations is developing 2

3 very slowly. Recent weather in southern Georgia, with sporadic rainfall and storms, could allow soybean rust to develop in the near future. Growers, consultants, and agents should continue to monitor the detection and spread of Asian soybean rust on the web at Current disease recommendations: Growers should begin to consider the need for the use of fungicides to protect their soybean crop from Asian soybean rust and other diseases (especially Phomopsis pod and stem blight and anthracnose) once the crop reaches full bloom (R2) and early pod set (R3). Though an automatic fungicide application at this timing is not absolutely essential for all soybean producers; the R2-R3 growth stages start the window where management of disease becomes more important. The growers who are most likely to benefit from an early fungicide application include those who are planting soybeans behind soybeans (thus increasing the risk to Phomopsis pod and stem blight and anthracnose), those who are in extreme southwestern Georgia (where rust is likely to occur sooner rather than later), and those growers who have had excellent growing conditions and sufficient rainfall or irrigation. Growers least likely to benefit from an early fungicide application at this time include those with poor yield potential, poor growth, good crop rotation, and fields further removed from southern Georgia. We have a number of very good (and excellent) fungicides for managing Asian soybean rust. Tebuconazole is a good product, but is not as strong on rust as are some other products like Domark or Topguard. Also, tebuconazole may not have the depth of a broad-spectrum activity against other diseases as would fungicides like Headline and Quadris. In selecting a fungicide for use on soybeans, remember that tebuconazole is a good fungicide and reasonably priced, but it may not be the best product for the grower s needs in a specific field. BEAN PLATASPID INFESTING SOYBEANS IN NORTHEAST GEORGIA (Roberts) The Bean Plataspid, Megacopta cribraria (Hemiptera: Plataspidae), has recently been observed infesting soybeans in NE Georgia. On July 1, 2010, Dr. John All, UGA research entomologist, and Bobby Smith, CEC Morgan County, observed Bean Plataspids infesting soybeans in Oconee and Morgan counties. This insect is not native to Georgia or the U.S. and was first observed last fall aggregating on homes and other structures and feeding on kudzu in several NE Georgia counties. The pest is native to India and China, where it feeds on kudzu. It has also been reported as a pest of numerous legume crops, including soybeans. To date the furthest south the bug has been observed is in Putnam County (communication with Dr. David Buntin, UGA research entomologist). The bug has also been observed in Hart and Elbert Counties. Since its detection in soybeans, we have been actively searching the literature for additional information on the pest status and management of the Bean Plataspid in soybeans. Unfortunately we have found minimal information on management and control. 3

4 Bean Plataspid adults on soybean stem. Bean Plataspid adults on soybean leaf. The majority of soybeans we have observed which are infested with Bean Plataspids are vegetative or in early bloom. Adults have been observed feeding on the main stem of plants and on foliage. We are not sure if vegetative soybeans are being economically damaged but high populations have been observed feeding on plants in some fields. There appears to be a significant edge effect with higher populations be observed on edges compared with the inner portions of fields. It will be important for growers to monitor fields infested with the bug when pods begin forming. If feeding is occurring on pods or blooms, treatment with insecticide would be recommended based on available information. We have observed a single Group IV soybean field in Hart County which had begun settings pods and did not observe the bugs feeding on pods. Based on limited observation, pyrethroids and Lorsban appear to have insecticidal activity on the Bean Plataspid. Bean Plataspid eggs hatch in 4-5 days and the nymphal stage will likely be days. We will continue to provide updates as we learn more. Bean Plataspid adults on soybean leaves. 4

5 Bean Plataspid adults on soybean stems. Bean Plataspid eggs and early instar nymphs. WARRANT HERBICIDE (Prostko) Monsanto recently announced the release of a new herbicide, sold under the trade name of WARRANT, for use in cotton and soybeans. Warrant has been tested under the name of MON The active ingredient of Warrant is acetochlor. Acetochlor has been sold for numerous years under the trades names of Harness or Surpass. The only thing new about Warrant is that it is an encapsulated formulation. Encapsulation is the incorporation of the herbicide into very small capsules or polymer shells, generally 10 µm or less. Encapsulation has the potential to extend the period of weed control of an herbicide. An example of how encapsulation works is illustrated in Figure 1. Figure 1. Herbicide encapsulation. 5

6 I have only had the opportunity to conduct 1 weed control trial with Warrant. For all intents and purposes, Warrant performs much like Dual Magnum (S-metolachlor). This makes sense since they both are members of the same herbicide family (chloroacetamide). A copy of the Warrant label can be obtained from the following link: REFLEX + CLASSIC TANK-MIXES (Prostko) Over the last few days or so, I have received many questions about tank-mixing Reflex + Classic. This mixture could be warranted in soybean fields that contain pigweed and sicklepod (coffeeweed). Here is what I know: 1) Both the Reflex label and Classic label indicate that these products can be tank-mixed. 2) A single application of Classic would rarely provide acceptable control of sicklepod. A sicklepod management program must include the use of a residual herbicide such as Python (flumetsulam) or metribuzin applied at planting. 3) I would anticipate significant soybean injury in the form of leaf-burn and stunting from this tank-mix. Check out Figure 2. Figure 2. Soybean response to an application of Reflex (16 oz/a) + Classic (0.5 oz/a) + Clethodim (20 oz/a) + 80/20 (0.25% v/v). Pictures taken 3 days after application. SOYBEAN GROWTH STAGES AND PRODUCTION DECISIONS (Whitaker) Since much of the crop will or has started flowering, many growers will consider applying fungicides for soybean rust, spraying insecticides for stinkbugs and lepidopteron pests, making Dimilin and boron applications, and determining irrigation regimes. Proper identification of reproductive growth stage will be a critical part of making these production decisions in an effective manner. Soybean development can be divided into vegetative (V) and reproductive (R) stages. The beginning of each stage starts when at least 50% plants are at that stage. Vegetative growth stages start with soybean emergence and reproductive growth stages start with the first flower. The following is an explanation of soybean reproductive growth stages. 6

7 Reproductive Growth Stages: The reproductive stages in soybean start when at least one flower is present on the plant (R1) (Table 2). These stages refer to bloom development (R1 and R2), pod development (R3 and R4), seed development (R5 and R6), and maturity (R7 and R8). Table 2. Reproductive (R) soybean growth stages. Reproductive Stages Description R1 R2 R3 R4 R5 R6 Beginning bloom Full bloom Beginning pod Full pod Beginning seed Full seed One flower present on the plant, which will generally appear towards the bottom of the plant. Flower present at a node immediately below the uppermost node with a fully unrolled leaf. Usually occurs 1 day after R1. Pods (¼ inch in length) can be observed at any one of the four uppermost nodes. Typically occurs 10 to 12 days after R2. Pods at any one of the four uppermost nodes are ¾ inch long. Typically occurs 8 to 10 days after R3. Seeds in the pods are 1/8 long at any one of four uppermost nodes (can be felt when the pod is squeezed). Typically occurs 9 to 11 days after R4. Pod containing full size green seeds at one of the four uppermost nodes (seed are likely touching in the pod). Typically occurs 13 to 17 days after R5. R7 R8 Beginning maturity Full maturity At least pod can be found on the plant which is mature (brown or tan in color). Pods and leaves beginning to yellow during this stage. At this point the plant has reached physiological maturity. Typically occurs 17 to 21 days after R6. 95% of pods mature (brown or tan in color). Typically occurs 9 to 11 days after R7. Beans are close to being harvest ready. Acknowledgements: This section on soybean growth stages was adapted from the 2009 edition of the South Carolina Soybean Production Guide (Soybean vegetative and generative growth stages, Pawel Wiatrak) published by Clemson University Cooperative Extension Service and the 2004 edition of PM 1945 Soybean Growth and Development published by Iowa State University Extension. Original descriptions of soybean growth stages were developed by Fehr, W.R., C.E. Caviness, D.T. Burmood, and J.S. Pennington Stage of development descriptions for soybeans, Glycine max (L.) Merr. Crop Science 11:

8 Contributions by: Jared Whitaker, Extension Agronomist Bob Kemerait, Extension Plant Pathologist Eric Prostko, Extension Weed Specialist Phillip Roberts, Extension Entomologist Your local County Extension Agent is a source for more information on these subjects Edited by: Jared Whitaker, Extension Agronomist 8