Mississippi County Soybean Update

Tuesday, August 20, 2013

Soybeans

The stage of soybean development across the county varies from fields just now reaching R-2 (or early R-3) to fields that are approaching R-6. Several of the early planted soybeans are getting close to R-6 while many of the double crop soybeans are just starting to flower.

Disease

We have had several questions about fungicide applications and the need for insecticide applications for stink bugs. There is a misconception that soybeans at the R-3 stage of growth should receive an automatic fungicide treatment. The University of Arkansas Division of Agriculture recommends the use of a fungicide only if a disease is present in the field. Unwarranted applications of fungicides are an added expense to production and will contribute to the development of resistance. Timing fungicide applications to crop growth stage instead of disease presence in the field may also result in the need for additional applications if diseases develop later in the season. Based on scouting our verification fields and "spot" checks around the county, disease pressure does not appear to be heavy and is not consistent across the county. Fields should be scouted for disease and treated only when necessary. Additionally, host plant resistance should be considered. Many of the soybean varieties today have good resistance to some of the diseases common to Arkansas and therefore may be less likely to require a fungicide application.

Insects

We have also been hearing reports of soybean fields being treated for stink bugs. Again, insecticide applications should be made only when fields reach economic thresholds. University of Arkansas recommendations are to treat fields for stink bugs when the field is averaging 9 stink bugs/25 sweeps. Insect resistance to insecticides is a major concern when applications are made without justification. Insecticide applications can reduce the population of beneficial insects and may lead to the buildup of worm pests and other secondary pest problems. Moth trap catches in the county have shown an increase in bollworm moth numbers over the past week. Preserving beneficial insect populations may help prevent worm populations reaching an economic threshold in the coming weeks.

Irrigation Termination

Irrigation termination should be a field by field decision. The variability of the crops growth stage across the county will make irrigation termination decisions more difficult. Based on University of Arkansas recommendations, irrigation can be safely terminated once 50% of the pods have soybeans that are touching and there is adequate soil moisture. Rains over the past 2-3 weeks have helped carry some of the early planted soybeans a long way toward maturity. Producers/scouts should check fields at the R-6 stage of growth and time irrigation termination based on crop development.

For additional information on any of the topics discussed in this article please feel free to contact the Mississippi County Extension Office at (870) 762-2075 or via email at rbenson@uaex.edu.

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