Tag Archives: double crop

It’s Time to Increase Soybean Seeding Rates

Wheat harvest has begun.  Remember that soybean yield potential declines with delayed planting date.  During the first two weeks of June, this decline is barely noticeable.  After mid-June, expect yield to decline about ½ bushel per acre per day.  So to minimize soybean yield loss due to late planting, immediately (or as soon as you can) plant.  I like to see the combine and the planter or drill in the field at the same time.

Soybean planted after mid-June will not always develop enough leaf area to capture 90-95% of the available sunlight by early pod development (R3).  Only if four layers of leaves are formed by that time will yield not be affected.  Of course the growing season makes a difference.  Last year in many parts of Virginia, even the latest-planted soybean were able to produce enough leaf area.  But, on average, June- or July-planted soybean are unable to do so.  Therefore it’s important to take actions to minimize this decline.

First, plant as soon as possible.  With the recent rains, soil moisture should not be a problem.  Even if the soil is dry on top, I suggest to go ahead and plant.  You may have to plant a little deeper to hit moisture (don’t plant much deeper than 1.5 inches), but planting depth is not as big of an issue with double-cropped as with full-season soybean.

Second, narrow your row spacing.  Narrow rows will produce more leaf area and canopy over faster.

Finally, increase your seeding rates gradually as time goes on.  I’m suggesting the following plant populations for Virginia in 2013:

  • June 2-8 – 120,000 plants/acre
  • June 9-15 – 140,000 plants/acre
  • June 16-21 – 160,000 plants/acre
  • June 23-29 – 180,000 plants/acre
  • June 30-July 5 – 200,000 plants/acre
  • After July 5 – 220,000 plants/acre

See the seeding rate chart below to determine the seeds per foot of row needed to obtain a certain number of plants per acre.  Note that these seeding rates assume 80% emergence.  For different emergence assumptions, divide your desired plant population by the percent emergence that you expect.

 

Desired Plant Population

Row Width

Early-June Planting Date

Late-June/Early July Planting Date

120,000

140,000

160,000

180.000

200,000

220,000

 

(Seed per foot of row assuming 80% emergence)

20

5.7

6.7

7.7

8.6

9.6

10.5

18

5.2

6.0

6.9

7.7

8.6

9.5

15

4.3

5.0

5.7

6.5

7.2

7.9

10

2.9

3.3

3.8

4.3

4.8

5.3

7.5

2.2

2.5

2.9

3.2

3.6

3.9

As planting is delayed, increase seeding rate.

Use lower seeding rates on more productive soils.

Calculation: Desired Plant Pop. ÷ (43,560 sq. ft./acre ÷ row width in ft.) ÷ % emergence

Example: = 180,000 ÷ (43,560 ÷ (15 ÷ 12)) ÷ 0.80 = 6.5 seed per foot of row

In addition to planting date, I’ve found that more productive soils will tolerate lower seeding rates, and less productive soils need higher seeding rates; a more productive soil will produce more leaf area than a less productive soil over the same time period.

Marestail Management in Wheat (Chris Drake, Southampton County Agent)

Over the last couple weeks, I am seeing a lot of Marestails poking through the top of wheat fields throughout the county. This is a major concern for the farmers that have to manage this weed in their bean crops. Once these weeds get the point of being 30 inches or greater in height, control is difficult with any herbicide.

There are a couple options for control after the wheat harvest. One is the use of mechanical cultivation prior to planting beans. Disking, turbo-tilling, or running a dyna-drive will eliminate these weeds that are present. This option does not appeal to many producers due to moisture loss and conservation tillage program payments. The second option is using glufosinate (Liberty formerly called Ignite). An application of Liberty should control or suppress these weeds, but at these sizes two applications may be necessary for complete control. A second application of Liberty will not be possible unless Liberty Link beans are planted. In either scenario, the use of a residual material at planting such as Envive, Prefix, or Boundary is strongly encouraged.

What is causing these escapes? Two things are the likely culprit. One is the lack of use of a burndown/ tillage before planting wheat and two is inadequate weed control in the growing season. Harmony is widely used for weed control in wheat but is not a great product on Marestails. Many applications were made after the weeds were 8 inches in height or greater. Harmony will simply not control this species at this height.

So, what do we do next year to prevent these problems? BURN DOWN the land before planting wheat if you don’t till before planting. Also, in season Marestail control can be obtained using 2-4D after wheat is fully tillered but before jointing. Scouting your fields in late February or early March when you start to see winter annual weeds may be necessary to determine if control measures are needed.