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WEEKLY UPDATES |
Weekly Soybean Field Crop Report - June 7, 2007
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Posted on
June 11, 2007 at 08:47:27
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Soybean
Soybeans are in excellent condition other than a few exceptions on heavier soils planted between May 8th and 15th, some of which have been replanted. Plants range from the VE (vegetative emergence) to V3 (third fully developed trifoliate) leaf stage. Early season competition from weeds significantly reduces yields when left uncontrolled. Yield losses from late herbicide applications are irreversible. To minimize yield losses from weeds, soybeans should be kept weed free from the 1 to 3 trifoliate leaf stage. Weeds emerging after the 3rd trifoliate stage generally cause less then 5% yield loss.
Focus on weed leaf stage when making herbicide applications. Control of weeds, most notably lamb’s-quarters, is dramatically reduced as they get bigger. Table 11-5 of OMAFRA Publication 75, lists the maximum weed leaf stage at which post-emergent soybean herbicides will provide effective control.
Rolling fields to level the soil and push rocks into the ground usually occurs immediately after planting although, some does happen after emergence. Research has shown that rolling soybeans after emergence does not reduce yields. If rolling is delayed until after soybean emergence, be aware that:
1) Rolling during the heat of the day ensures that soybeans are limp. Soybeans are the most turgid (stiff) during the morning hours, and rolling at that time will result in more plant injury.
2) Do no roll soybeans that are in the hook stage as they are more vulnerable to stem breakage. Wait until all soybeans have fully emerged before rolling.
3) The optimum time to roll soybeans is during the unifoliate stage since all beans will have emerged by then. Rolling can occur successfully until the second trifoliate leaf stage although, waiting beyond the first trifoliate stage will increase plant losses.
Bean leaf beetle adults are active in many soybean fields including ones much further north than usual. Be aware that seedling plants can tolerate 30-40% defoliation as long as significant plant clipping is not occurring. Seed, IP or food grade beans are most at risk. The threshold is 16 beetles per foot of row (4-5 beetles per plant) before the V3 stage or if extensive clipping is observed. Once plants reach the V3 stage they usually can outgrow the beetle feeding.
Soybean aphids were found in a few fields scattered across Ontario last week along with sites in the Midwest US and Quebec. Populations are very low but scouting should begin to monitor aphid numbers, especially in fields with buckthorn nearby. OMAFRA will be monitoring sites across Ontario with results being reported weekly on the Ontario Soybean Growers (www.soybean.on.ca) and USDA PIPE websites (www.sbrusa.net).
-Submitted by Horst Bohner, OMAFRA Soybean Specialist
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