Battle for the Belt: Season 2 Episode 7- Soybean & Weed Competition

Episode 7 of Battle for the Belt is now available: https://www.youtube.com/watch?v=F1FZlpe_QK8 
In Episode 7, Dr. Eugene Law, a new Assistant Professor of Weed Ecology in the Department of Horticulture and Crop Science at Ohio State, discusses early season weed competition in soybean.

Early season ragweed competition
In the video from April 25, we are in the field at the Western Agricultural Research Station in an early planting weed control study observing seedling giant ragweed (Ambrosia trifida) establishment in March 25th planted soybeans. The ragweed at this point is outgrowing the soybean crop (Figure 1). Ragweed is resistant to many herbicides including ALS inhibitors, which are some of the best residual pre-emergence herbicides. The issue here is that ragweed seedlings have a greater tolerance to environmental stress compared to the soybean seedlings, and ragweed seedlings are coming up at the same time as the ultra-early planted soybeans. The resilience of ragweed is showcased by the frost conditions a few weeks ago (April 22), where the soybeans were heavily damaged in this field and the ragweed exhibited no injury. Early emerging weeds are generally adapted to colder and wetter conditions than crops, giving issues with early-season weed control if the weeds are resistant to or otherwise escape the herbicide programs being used. 

Figure 1. Ragweed seedling and frost-injured soybeans on April 25^th at the Western Agricultural Research Station three days after initial frost.

What can we do to manage weed competition?

When soybeans are planted early, the normal burn down is applied even earlier and may not control the initial emergence of ragweed. Early planted soybeans can also have a reduced plant population due to frost, water damage, disease, or a combination of abiotic and biotic factors. Over time, the soybean can compensate for a low plant population with branching and does not always cause yield decline (depending on how severe stand loss is) but canopy closure takes longer and that is a major factor in the weed vs crop competition. Cultural practices that can be used to combat these issues include narrow row spacing or increasing seeding rate, to increase the speed of canopy closure to shade out the weeds. Another option is cover cropping, which provides a mulch that can slow down or prevent germination of weeds giving the soybean a head start if cover crops are managed properly.

What’s happening in the field?

Last week at the Western location, bean leaf beetle damage was found in the soybeans planted on March 25, but minimal damage was observed for the soybeans planted on April 16. Bean leaf beetle is common early in the growing season. For more information about bean leaf beetle in Ohio, please see this FactSheet: https://ohioline.osu.edu/factsheet/ENT-23#:~:text=The%20bean%20leaf%20beetle%20(BLB,found%20feeding%20on%20soybean%20nodules. The Western location received rain after planting the third date on Monday, May 6 (Table 1). Corn is at the V3/V4 growth stage and V2 growth stage for planting date 1 (March 25) and planting date 2 (April 16), respectively. Soybean is at V1 and VC for the first and second planting date, respectively. The fourth planting date is expected to occur in about 1-2 weeks.

Figure 2. Bean leaf beetle at the Western location in March 25^th planted soybeans.

The Wooster location had a little over two inches of rain last week. The stages for planting date one (April 22) were V1 for corn and VC for soybean. Planting date two (May 3) was germinated but has not yet emerged (https://www.youtube.com/shorts/IWS-309H-sw). Planting date three in Wooster will happen in the next 5-10 days.

At the Northwest location, no planting has occurred due to wet conditions. We will plant when soil conditions become adequate, hopefully very soon. A summary of all planted sites and weather is presented in Table 2.

 Table 1. The planting date conditions for planting date three at the Western Location, 2024.

Table 2. Weekly weather conditions for planting dates one, two, and three at the Western location and planting date one and two at the Wooster Campus, with day of planting, soil, air temperature averages, and growing degree days (GDDS) from May 6 to May 12. Information from CFAES Weather System (https://weather.cfaes.osu.edu/).