Integrated Crop Management News

Links to these articles are strongly encouraged. Articles may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If articles are used in any other manner, permission from the author is required.

Updates on Chlorpyrifos Uses in 2022

Chlorpyrifos (e.g., Lorsban and Warhawk) is an organophosphate (Group 1B) insecticide that has been used for many important field crop pests in the United States. In the past 15 years, chlorpyrifos, like many organophosphates, has come under scrutiny due to acute toxicity concerns to humans, especially children. In an effort to protect all ages of humans and the environment, EPA began the process of phasing out many uses of organophosphates. On August 18, 2021, the EPA announced their decision to revoke tolerances for chlorpyrifos.

2021 Summary of Foliar Fungicide Applications on Corn in Iowa

Corn foliar fungicide trials done at six locations in Iowa in 2021: ISU Northwest Research and Demonstration Farm (NWRF), Sutherland; Northeast Research and Demonstration Farm (NERF), Nashua; Northern Research and Demonstration Farm (NRF), Kanawha; Southwest Research and Demonstration Farm (SWRF), Lewis; Southeast Research and Demonstration Farm (SERF), Crawfordsville; and the Ag Engineering and Agronomy Farm (AEA) near Boone.

SCN-resistant Variety Trial Information Estimated to Have Provided Over $200 Million in Value to Farmers from 2011 to 2016

Almost all soybean varieties resistant to the soybean cyst nematode (SCN) have been developed from a breeding line named PI 88788. The amount of SCN control varies among the varieties because they have different numbers of copies of the single SCN resistance gene. The Iowa State University SCN-resistant Variety Trial Program evaluates hundreds of commercially available resistant varieties for yield and SCN control each year. In a recently published journal paper, ISU agricultural economists estimated that information from the ISU SCN variety trial provided as much as $205 million of economic value to farmers from 2011 to 2016. This finding underscores the value of selecting and growing SCN-resistant soybean varieties that offer high yields and effective control of SCN.

Substantial Yield Suppression from SCN Seen in Soybean Varieties with Resistance from PI 88788 in 2021

The SCN-resistant Soybean Variety Trial Program at Iowa State University assesses the yield performance and SCN control provided by hundreds of SCN-resistant soybean varieties each year. Variety trial experiments are conducted annually in each of Iowa’s nine crop reporting districts. Harvest of the 2021 experiments was completed in late October, and processing of soil samples from the research plots to determine end-of-season SCN egg population densities is ongoing. The SCN data from one experiment, in Fruitland, Iowa, have become available. The results provide an eye-opening look at how much SCN reproduction occurred in 2021 as well as how control of SCN numbers can affect soybean yields.

Soybean Varieties for Iowa in 2022 with SCN Resistance Different from PI 88788

There are several different breeding lines, called sources of resistance, that are available to develop soybean varieties that are resistant to the soybean cyst nematode (SCN). More than 95% of the resistant varieties available to Iowa farmers in the last 15 years have had resistance from the breeding line named PI 88788. As a consequence of continuous widespread use of this resistance, SCN populations in many fields throughout Iowa now have increased reproduction on varieties with resistance from PI 88788. Farmers are advised to grow soybean varieties with SCN resistance from other genetic sources in rotation with high-yielding varieties with PI 88788 SCN resistance. This article lists 36 varieties available for Iowa soybean farmers in 2022 in maturity groups I, II, and III with SCN resistance from two sources of resistance different from PI 88788.

SCN-resistant Soybean Varieties for Iowa in 2022

Growing resistant varieties in rotation with nonhost corn and using nematode-protectant soybean seed treatments is recommended for integrated management of the soybean cyst nematode (SCN). ISU compiles a list of soybean varieties with resistance to SCN each year. This year’s publication was recently completed and is available online. There are 872 varieties in the publication, 96% with resistance from PI 88788, which has been used almost exclusively for 15 years. Due to prolonged widespread use of PI 88788 SCN resistance in Iowa, SCN populations have developed increased reproduction on varieties with PI 88788 resistance and SCN is causing increasing yield losses. This article discusses the situation and gives guidance on how farmers should manage SCN with so few choices of resistance genetics available.

Pasture Weed Control

Fall is one of the best times for managing perennial and biennial weeds found in pastures or other areas maintained in perennial grass. As perennials prepare for the upcoming winter, they move energy reserves from shoots to their perennial vegetative reproductive structures (e.g. rhizomes, perennial rootstocks).

Give Careful Consideration to Likely High Soil and Cornstalk Nitrate Levels This Fall

The 2021 cropping season had variable rainfall across Iowa. Since crop harvest began, rainfall also has been variable, and temperatures have generally been above normal. Therefore, it is not surprising to hear of variable but often higher than normal end-of-season cornstalk nitrate test levels and postharvest soil nitrate levels. Farmers and crop consultants should use caution in interpreting these results for N fertilization of next year corn.

End-of-season cornstalk nitrate test

Soil-Test Interpretations for Fall Fertilization and Liming Decisions with High Fertilizer Prices and After Highly Variable Rainfall and Crop Yields

Net returns to P or K fertilization of corn and soybean for different soil-test levels

The 2021 cropping season had very variable rainfall across Iowa with either drought or excessive rainfall. Highly variable landscape and soil moisture retention capacity in many fields also may cause high within-field yield variability. Reduced potential income due to low yield in some areas combined with currently very high fertilizer prices are creating significant uncertainty among producers about P, K, and liming decisions for the 2022 crop season. Several factors need to be considered.

Fall is the Perfect Time to Collect Soil Samples for SCN

The soybean cyst nematode (SCN) is a major yield-reducing pathogen of soybeans throughout Iowa and many other states. SCN-resistant soybean varieties have been used for decades to produce profitable yields and keep SCN numbers in check, but most resistant varieties have lost much of their effectiveness. Also, SCN reproduction in fields where soybeans were grown likely was much greater than normal in 2021 due to hot, dry weather. Collecting soil samples in the fall is advised to determine the SCN situation in fields. This article outlines guidelines for sampling fields for SCN, gives information on where to send SCN soil samples, and provides guidance on managing fields that are infested with SCN.

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