Waterhemp in soybean field

CORN to Go

Managing your soil seedbank

By Stephanie Karhoff

Achieving clean, weed-free fields next spring requires acting now to prevent seed from being deposited into the soil seedbank. The weed seedbank is the reservoir of seeds in the soil that will serve as the source for seedlings next season. Exhausting this reserve of seeds can help prevent rapid population increases and slow herbicide resistance development.

Our most problematic weed species are prolific seed producers. Waterhemp can produce over a million seeds per plant if plants emerge early in the season and have adequate resources. Meanwhile marestail can produce about 200,000 seeds per plant.

Weeds that have either escaped POST herbicide applications or emerged afterwards are currently developing mature seeds. If we assume that one single waterhemp plant can produce 1 million seeds, and 20 percent of these seeds are viable, and only 25% germinate, 50,000 plants are generated in the span of one year from that single escape. Even with 99% control, that equals 500 plants, half of which are female and can produce the next generation of seed. The ability to produce large volumes of seed and replenish seedbanks is one reason why waterhemp populations can rapidly increase.

Fortunately, the majority of waterhemp seeds cannot survive in the soil after a few years. About 80% of seeds will not be viable after one year, and only approximately 5% will remain viable after three years (Figure 1).

Figure 1. Effect of time and burial on viability of waterhemp seed. Source: Korres et al, Weed Science, 2018.

This short-lived seedbank is the “Achilles’ heel” or point of weakness in the waterhemp life cycle. Focusing efforts on eliminating seed production for 3 to 5 years will dramatically lower populations.

Preventing weeds from setting seed is the best way to manage your soil seedbank. At this point in the year, that may mean scouting and hand-pulling weeds. Also factor in weed infestations into your harvest sequence and logistics, leaving weedy fields or infested areas within a field last. If you are planting a cover crop this fall, be sure to buy weed-free seed. Growers can mail seed samples to the Ohio Department of Agriculture, Grain, Feed & Seed Program for purity testing to ensure there are no noxious weeds present. If you are interested in submitting a sample, instructions can be found at https://go.osu.edu/seedsampletesting.

Harvest Weed Seed Control (HWSC) is another tactic to reduce the soil seedbank by using the combine to remove, concentrate, or kill weed seeds harvested along with the crop. You can learn more about this emerging weed management tool by accessing a recent article in the Crops and Soils Magazine (highlighted by Greg LaBarge in the January issue of Ohio’s Country Journal) at https://go.osu.edu/combineweed.

I invite you to learn more about weed control and ecology with Weed Science Extension State Specialist Dr. Alyssa Essman at the 2023 Farm Science Review Agronomy College on September 12, co-hosted by Ohio State University Extension and the Ohio AgriBusiness Association. To register, please visit https://go.osu.edu/FSRAgronomyCollege.

Laying the foundation for high-yielding wheat

By Greg LaBarge

Making sound agronomic decisions give wheat a well-established root system as a foundation to maximize yield. Wheat is an annual crop, but there are ten months between planting and harvest. Here are seven practices to establish your wheat for its long growing season.

  1. Variety selection is of utmost importance. The Ohio State University Wheat Performance Trials shows yield and other important agronomic data for 74 varieties at four sites at https://www.oardc.ohio-state.edu/wheattrials/ with an average yield of 107.9. Company trials are another information source. The more information you look over, especially from your region, the higher your confidence will be about your choice.
  2. Plant a high-quality seed and use a seed treatment. You take on that responsibility if you plant saved seed from the farm. Unfortunately, we often get calls about head scab, loose smut, and Stagnospora that tie back to farm-saved seed. Purchasing new fungicide-treated seed would solve many of these problems.
  3. Crop rotation would solve many of Ohio’s crop insect and disease problems. Wheat following soybean is optimal for breaking disease cycles and timely planting. There are documented benefits to corn, soybean, and wheat rotation for all three crops.
  4. The planting date depends on where you are in the state. Suggested dates start after September 22 (Northernmost counties) to October 5 (Southernmost counties). These dates are used to avoid Hessian flies, but the Hessian fly-free date is also beneficial to reducing other pests and is agronomically sound to attain good yields. Earlier planting dates can result in excessive growth and increased concerns about fall diseases and aphid injury. The best planting period is ten days after your county’s fly-free date.
  5. Seeding practices help wheat become well-established in the fall. Don’t plant too wet. Aim for a planting depth of 1.5 inches. Choose an optimum seeding rate of 1.2 to 1.6 million seeds per acre. If planting three to four weeks after your fly-free date, increase seeding rates to 1.6 to 2 million seeds per acre. Avoid planting by a bushel measure due to seed size variability. Wheat has a tremendous capacity tiller, fall through early spring, increasing the headcount per acre. Get the drill calibrated to plant the targeted number of seeds per acre for your situation.
  6. Row width is also essential to achieving high yields. We get the highest yields in 6 to 8-inch rows. However, other cropping system goals may dictate different row spacings. For example, relay inter-cropping soybeans into wheat is popular in some areas. These growers are planting in 15-inch rows and returning with the planter in May to seed soybeans between the wheat rows. Wheat varieties that do well in wider rows tend to be tall by nature, with a non-erect growth habit that allows them to fill in row middles. Likewise, a variety that tillers well will achieve higher yields in wide rows. Typically 15-inch row wheat yields 5% to 15% less than 7-inch rows, but tall plant height and tillering can help overcome that reduction.
  7. Good fertility levels also get wheat off to a good start. First, apply 20 to 30 pounds of nitrogen at planting to stimulate fall growth. Then, use a soil test to determine P and K needs. If soil test P levels are less than 30 ppm or soil test K is less than 100 to 120 ppm, apply fertilizer since the risk of yield loss when the soil test is below these numbers.
  8. Plan for spring 2024 disease control. The Ohio wheat performance trial includes disease ratings for all varieties. Noting disease risk is essential in the spring for planning disease control strategies, including what fungicide is needed and the application timing.

C.O.R.N. to Go is a supplement to the OSU Extension Agronomic Crops Team Online C.O.R.N. Newsletter. This version for Ohio’s Country Journal is by Greg LaBarge, OSU Extension Agronomy Field Specialists, labarge.1@osu.edu or 740-956-5047 and Stephanie Karhoff, OSU Extension Agronomy Field Specialist, karhoff.41@osu.edu or 567-376-4019.

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