Is PI 88788 Working in Your Soybean Fields?

Soybean Cyst Nematode (SCN) is the number one yield-reducing pest in soybeans. Potential yield loss to SCN is expected to rise as more and more populations of SCN overcome the PI 88788 source of resistance. The Peking source of SCN resistance is not near as common as the PI 88788 source but is used in several soybean varieties.

If you want to see how the SCN resistance source in your soybeans is holding up this growing season, you can do an early and late SCN soil test. If the egg count increases substantially between the early and late SCN sample, your SCN resistance source is likely failing.

Here are the 4 steps to this simple test:

Early SCN sample (June): 

  1. Choose a spot in a current soybean field
  2. Collect 8 to 10 0-6″ soil cores taken within the soybean row at that spot
  3. Mark that spot with a flag or GPS so you can get back to that spot to sample later in the season

Late SCN sample (mid to late August): 

4. Go back to the same spot you collected a soil sample from in June and repeat step #2

Once you’ve conducted this simple test, you will get an idea of whether or not the SCN resistance source in your soybean variety is holding up or if it is time to change the resistance source in next year’s varieties. AGVISE completed a field project using a similar procedure in 2019 and 2020. The data showed that the PI 88788 trait was not preventing SCN populations from increasing in some field sites tested in Minnesota. You can read more about our project here.


Data from the AGVISE SCN field project, 2019-2020

A silver bullet for managing SCN does not exist and will likely never exist. Do your due diligence and figure out if your SCN resistance source is working in your own fields.

You can order SCN submission forms from our online supply store here.

Additional resources:

SCN in Iowa: A Serious Problem that Warrants Renewed Attention

Iowa State University – SCN Resources

 

 

 

Soybean cyst nematode: Failing resistance traits, increasing SCN populations

Originally featured in the Winter 2020-2021 AGVISE Laboratories Newsletter

In 2019, AGVISE Laboratories investigated if popular soybean varieties with PI88788 or Peking SCN-resistance traits were effectively providing protection from soybean cyst nematode (SCN) and found that a number of the varieties failed to do so. We expanded the project in 2020 with cooperation from agronomists in west-central Minnesota.

For over 20 years, PI88788 has been the primary SCN-resistance trait in over 95% of soybean varieties. In the past few years, university research is showing that PI88788 is losing its effectiveness at controlling SCN. Detecting SCN-resistant trait failure with the naked eye is impossible, unlike the detection of failed pesticide control, where you can still see a herbicide-resistant weed that is growing vigorously. Therefore, we wanted to demonstrate how you can measure SCN resistance with soil sampling, even though you cannot see it with your naked eye.

In the project, we had 41 soybean fields with SCN-resistant varieties, 35 with the PI88788 trait, and 6 with the Peking trait. In each field, a location was flagged and soil sampled for SCN egg count in early (June) and late (September) parts of the growing season. From June to September, the SCN egg count increased by 4.9 times on average across all 41 soybean fields (individual field reproduction factor ranged from 1.2 to 12.9). In some fields, the high SCN reproduction rate shows that SCN were successfully reproducing on soybean plants and the SCN resistance trait is failling. We also learned that soybean varieties with the Peking trait had much better control of SCN than those with the PI88788 trait. One cooperator from Benson, MN grew both PI88788 and Peking soybean varieties on his farm. He noted a 2.5 bu/acre soybean yield advantage with the Peking soybean variety (56.5 bu/acre) over the PI88788 soybean variety (54.0 bu/acre).

The project showed that SCN soil sampling in the early vs. late growing season was a simple way to detect a failing SCN resistance trait. The simple protocol only takes a big flag to mark the spot, then a set of soil samples in June and September to compare the SCN egg count results.

 

Copper for Small Grains

Among crops grown in the northern Great Plains, small grains (cereals) are the most susceptible to copper deficiency. Copper (Cu) is an essential micronutrient required in small concentrations for plant growth and reproduction. Copper deficiency symptoms in cereals include pale yellowing, wilted and twisted leaf tips, and malformed seed heads. Severe copper deficiency will stop plant growth and kill plants during tiller formation. During pollination, copper deficiency will cause florets to remain partially open. This creates a vulnerable period for diseases, such as Fusarium head blight (head scab) and ergot, to infect the seed head and reduce grain yield.

Small grains sensitive to copper deficiency include barley, oat, rye, triticale, and wheat (including durum, spring, and winter types). Copper deficiency is most common on soils with less than 0.5 ppm Cu. Soils with low soil test Cu frequently include sandy soils with low organic matter (<3.0%) and organic soils (peat) with very high organic matter (>10%). Between soil and plant analysis, diagnosing copper deficiency with soil analysis is the most predictive. Plant analysis is less helpful because the plant Cu concentrations in sufficient and deficient plants are very close.

The most effective strategy to build soil test Cu on mineral soils is to broadcast-incorporate copper sulfate (25% Cu). building soil test Cu for many years. Do not mix copper sulfate with seed-placed dry fertilizer blends for air drills; copper sulfate is a hygroscopic (water holding) material that makes blending difficult and bridging is a concern. For seed-placed copper, use a liquid copper source injected in furrow. Liquid copper sources include dissolved copper sulfate and various chelated Cu products.

On organic soils, soil test Cu is difficult to build as copper readily forms complexes with soil organic matter. To reduce copper complexation, apply seed-placed liquid copper at planting and follow with foliar copper in the first herbicide application. Liquid copper sources include dissolved copper sulfate and various chelated Cu products.

Prevented Planting Acres in 2020: Maximizing Cover Crop Effectiveness

In 2020, there are again widespread acres of Prevented Planting (PP) in North Dakota and northwest Minnesota. Farmers are now making plans to plant cover crops on unplanted cropland in the next few weeks. It is important to establish cover crops on PP fields because growing plants help reduce the chance these fields will be PP fields again next year.

Let’s look at the major reasons why cover crops are valuable tools on Prevented Planting acres.

Soil Water Use

A field without any growing plants is a fallow field. Before no-till, summer fallow was a widespread soil water conservation strategy in dryland agriculture. Actively growing plants transpire (use) a lot more water than evaporation from the soil surface alone does. Cover crops help fill the water-use void by transpiring a lot of water, helping to dry the soil surface and lower the water table before the following year. This also opens space in the soil profile for summer and fall rains to leach soluble salts from the soil surface and reduce salinity in the root zone.

Soil Erosion Control

Tillage is a popular weed control tool, but it also destroys crop residue and leaves soil exposed and vulnerable to water and wind erosion. Planting cover crops protects the soil surface from rain and wind, keeping soil firmly in place. Just because you cannot grow a cash crop on the field this year, you should not let your soil blow into the next field, letting your neighbor farm it next year.

Weed Control

An established cover crop can compete with weeds, helping suppress weed growth and weed seed production. For fields with problematic broadleaf weed histories, a cover crop mix containing only grass species is preferred. In grass cover crops, you can still use selective broadleaf weed herbicides to control the problematic broadleaf weeds of conventional or no-till systems such as Canada thistle, common ragweed, kochia, volunteer canola, and waterhemp while not killing the grass cover crop. For fields with low weed pressure, a cover crop mix containing grasses, brassicas, and legumes will provide more soil health benefits.

Soil Biological Activity

Have you heard about “fallow syndrome” before? Fallow syndrome is an induced nutrient deficiency, often seen in corn following fallow, when the population of mycorrhiza fungi is insufficient to colonize plant roots and help them acquire water and nutrients. Mycorrhizae are especially important in plant uptake of phosphorus, so plants with fallow syndrome often show phosphorus deficiency symptoms. Fallow syndrome is a major concern in corn following summer fallow or Prevented Planting without cover crop.

During the Prevented Planting year, it is important to include grass species in the cover crop mix to support and maintain the mycorrhiza population through next year. Brassica species, like radish and turnip, are often included in cover crop mixes for their deep taproot architecture and high forage value for grazing livestock, but brassicas do not support mycorrhizae. You do not want a cover crop mix consisting of brassica species alone because fallow syndrome might occur next year.

 

In June 2020, excessive rainfall slammed some parts of the upper Midwest and northern Great Plains, drenching soils with 3 to 15 inches of rain over a couple days. On summer-flooded fields, cereal rye is an attractive soil management tool. You can plant or fly on cereal rye well into August or mid-September, and it will continue to use soil water through late summer and fall. Next spring, the overwintered rye will grow again, using more soil water and maintaining soil structure, providing you with a much better chance to plant the field. If soybean is the next crop, you can plant glyphosate-tolerant soybean into green cereal rye then terminate the cereal rye with glyphosate later. This practice has become more and more popular on difficult fields.

Do not forget about soil fertility and plant nutrition for cover crops. A modest application of nitrogen will help cover crop establishment, plant water use, and competition with weeds, as cover crops with adequate nitrogen will grow faster and larger than those without nitrogen. Around 46 lb/acre nitrogen (100 lb/acre urea, 46-0-0) should be enough to establish nice cover crop growth. Prevented Planting fields, being wetter than those successfully planted in spring, lost some, if not most, soil nitrogen via nitrate leaching or denitrification. Although additional nitrogen may have mineralized from soil organic matter during May and June, excess precipitation in June may have caused additional soil nitrogen loss. The best way to know is collecting 0-12 or 0-24 inch soil samples for nitrate-nitrogen analysis.

As you choose the appropriate cover crop mix on Prevented Planting fields, you must consider the pros and cons of each cover crop species and how each will help accomplish your goals. These are some helpful resources that will provide additional information on what cover crop options will work best on your fields.