Brought to you by: Jonah T. Johnson, MS, CPAg, CCA - Sales Agronomist, PCT | Sunrise

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June 4, 2019: Should I increase my soybean seeding rates? Be on the lookout for BCW!

Should I increase my soybean seeding rates?

We are all aware that some growers are progressing with #plant19, and some are unfortunately not. Planting date is major factor in setting the yield potential of soybean. We typically see our greatest yields with late April to early May planting, which are long passed. In a given year, the yield potential will often decline roughly 0.4 bu/ac/day beyond mid-May. As we turn the calendar into June now, we need to consider making some amends to our soybean seeding rates as well as our variable rate seeding prescriptions. Many seeding rates were determined in the late winter or early spring, so here are some tips to help your growers.

You need to consider your seeding rates, row width and maturity group. Soybeans trip their reproductive trigger (flowering) as the day length shortens, which occurs much quicker with delayed plantings.

 

SEEDING RATE: Planting in the first weeks of June require roughly 10% increase in seeding rates (10,000 to 15,000 seed/acre increments for each week of delay). The higher seeding rates will help to facilitate quicker row closure and higher pod height with fewer days to flowering.
 
General starting recommendations for normal planting operations in April and May are: 120,000 to 140,000 seeds/acre for planters (15 to 30”), 140,000 to 160,000 seeds/acre for air seeders (~15”), and 160,000 to 180,000 seeds/acre.
 
If you typically plant 140,000 seeds/acre in 15-inch rows, you need to bump the seeding rate to 150,000 to 155,000 seeds/acre in the first week of June then to 165,000 to 170,000 seeds/acre in the second week of June, so forth and so on. Soybeans will produce fewer main-stem nodes (attachment points of trifoliates and ultimately pods) as planting is delayed, so the increasing seeding rates will also help to overcome the shortfall in node production.

ROW WIDTH:  If you plant 30-inch rows, you need to look into the possibility of planting narrower rows with the limited time to flowering. We typically see a yield advantage of 5 to 10% for soybeans planted in narrow rows (15 inches or less) compared to 30-inch rows, and this difference will be even more prominent in late planting situations. Wide rows (30-inch) take nearly 25 days longer and 40 days longer to canopy compared to 15-inch and 7.5-inch rows, respectively. This delay will certainly decrease the yield potential as canopy closure would occur well after reproductive initiation.

MATURITY GROUP:  Full-season varieties for your respective regions should be planted until June 15 for the northern third, June 20 for the central third and June 25 for the southern third of Ohio. Varieties should be dropped a half maturity group after these dates and planted for another two weeks before we consider other alternatives. If you are in a very late planting situation, I suggest back-dating 90 days from the typical fall freeze in your region to determine if you have enough growing season to mature a soybean crop.

Resource: Purdue University

 

Be on the lookout for BCW!

The last two weeks has proven that Black cutworm (BCW) is very present in some area of Ohio. Last week we were scouting south of Columbus and BCW was very evident and warranted an insecticide application. Loss of stand prior to emergence or due to above-ground cutting or below-ground tunneling injury often indicates presence of black cutworm. Adult moths of the BCW overwinter in the south and migrate north with the prevailing spring weather fronts. The intensity and distribution of the migratory BCW flight may differ from year to year due to this migration. Some regions such as the Ohio River valley often exhibit higher levels of BCW activity than other regions such as the areas bordering the Great Lakes. Within a region, migrating BCW moths tend to be attracted to fields having a significant ground cover of winter annuals such as chickweed at the time of peak migratory flights. Since the accumulation of winter annuals is often associated with reduced tillage or no-tillage systems, the incidence of BCW infestations tends to be linked to tillage practices and weed management. Late tillage prior to corn planting may not reduce BCW infestations if significant weed cover was present at the time of peak egg laying by migratory BCW moths.

Thus, reduced tillage or no-tillage corn may be equally susceptible to BCW infestation if the corn crop follows a no-tillage corn or soybean crop that enabled development of a significant stand of winter annuals, which are attractive sources for egg laying by migratory BCW moths. In terms of weed management, fall tillage can give growers a start in providing weed-free fields in the spring.

 
Scouting for BCW:  To scout for black cutworm injury, walk along rows of corn at several locations in a field looking for feeding on corn leaves and missing plants. Small larvae will feed on the edges of leaves before they get large enough to cut corn plants. Cutting may not happen for several days after the first leaf feeding is observed. If leaf feeding is observed, begin looking for missing (cut off) plants. Sort through soil near the surface in the area of missing plants while looking for cutworm larvae. 

Widely accepted thresholds are 2, 3, 5, and 7 cut plants per 100 for seedling, V2, V3, V4, and V5 stage plants, respectively. Some lines of transgenic Bt corn, particularly those expressing the Cry1f toxin (e.g., Herculex® lines), can provide some protection against black cutworm as can higher rates of neonicotinoid seed treatment, though no rates appear to be completely effective. 
 
Larvae must consume plant tissue to eventually succumb from the Cry1f protein.  If you have high numbers of BCW, especially 4^th and 5th instar larvae, plants can be cut very aggressively.


Examples:

1. You scout a corn field and find V2 corn, and within 100 plants you find 2 plants cut.  This would warrant an insecticide application.
2. You scout a corn field and find V5 corn, and within 100 plants you find 7 plants cut.  This would warrant an insecticide application.

Resource: The Ohio State University & Penn State University
Photos: Jonah Johnson