Tar Spot Of Corn: What To Know And New Research

by: Dan Quinn and Darcy Telenko, Purdue University

Due to its relatively recent U.S. discovery and its ability to cause significant production and economic losses, tar spot is often a topic of angst and anxiety amongst corn farmers and agronomists in Indiana. For example, a severely infected field can reach yield losses upwards of 60 bushels per acre! Yield losses are often a result of reduced photosynthetic capacity (green leaf area) of the corn plant during grain fill resulting in poor grain fill, kernel abortion, and reduced kernel weight. In addition, severe infection can reduce corn stalk integrity and cause significant lodging later in the season. Tar spot was first confirmed in northwest Indiana in 2015 and the first significant yield-reducing event of the disease was observed in 2018. Similarly, severe outbreaks and large areas of infection of this disease were observed in Indiana in 2021. Tar spot is caused by the fungus known as Phyllachora maydis and can be identified by small, raised black and circular spots present on corn leaves, stalks, and husks (Figure 1). These black and circular spots are known as fungal fruiting structures called stromata, each of which can produce thousands of spores. Overall, tar spot infection and severity can vary based on environmental conditions, the total amount of the pathogen present in the field, and corn hybrid chosen.

What Conditions Cause Tar Spot? Continue reading

Double-Crop Soybean Weed Management

by: Dr. Mark Loux, OSU Extension

It’s been a tough summer in parts of Ohio to do anything on a timely schedule and there are some weedy fields.  The best advice we have for big weeds in full-season soybeans is to increase rates and the complexity of POST herbicide applications, while still adhering to cutoffs for the application of certain herbicides as much as possible.  Dicamba products, XtendiMax, Engenia, and Tavium, cannot legally be applied to Xtend and XtendiFlex soybeans after June 30.  This cutoff date pertains to use in double-crop soybeans also.  If you are planning on planting Xtend or XtendiFlex soybeans in double-crop fields and using dicamba as a burndown, apply before Friday.  There isn’t a cutoff date for most other POST soybean herbicides – it’s based on either crop stage (eg R1) or days before harvest.

Double crop soybeans usually need some type of weed control program, although how weedy they get depends upon weeds surviving down in the wheat that can take off once they receive light; how much rain we get in July, which drives additional weed emergence and rate of soybean growth; and how fast the soybeans grow and develop a canopy.  Control can occur via the use of pre-plant/preemergence burndown herbicides, followed by POST as needed.  It’s also possible to accomplish this with one early POST application in Enlist soybeans, using Enlist Duo or a combination of Enlist One with glyphosate or glufosinate.  And also in LLGT27 soybeans with a combination of glyphosate and glufosinate.  Herbicides need to address marestail in many fields, which is often lurking in the wheat ready to regrow.  Marestail that are taller and get cut off by the combine will be more difficult to control than the smaller intact ones below the cutter bar.  Herbicide options vary depending upon the weeds and what type of soybeans are planted.  More effective options include:

  • Glyphosate or glufosinate + Sharpen (1 oz) + MSO – any soybean, prior to emergence
  • Glyphosate or glufosinate + 2,4-D – any soybean, at least a week before planting
  • Enlist Duo; glyphosate or glufosinate + Enlist One (Enlist soybeans) – PRE or POST, no wait to plant
  • Glyphosate + XtendiMax or Engenia (Xtend or XtendiFlex soybeans) – PRE, apply by June 30
  • Glyphosate + glufosinate – PRE in any soybean, PRE or POST in LLGT27 soybean

​​​​​​​It is possible to include residual herbicides with a PRE burndown treatment, but their value in this situation is questionable.  Residual herbicides with long recrop intervals to corn should be avoided.  POST options in double-crop include glufosinate, glyphosate, Enlist One/Duo, and conventional herbicides, depending upon the type of soybean planted.  One caution here is to avoid excessive injury to soybeans that slows growth and development since this is likely to reduce yield due to the short season.  Weed emergence is reduced and variable in July compared with May and June.  Where burndown herbicides are used, but there is still a need for POST herbicides to control a flush of late-emerging weeds, consider reduced rates.  Research we conducted back in the 1990s demonstrated that weeds up to 2 inches tall can usually be controlled with half of a typical labeled rate.  When we planted soybeans in early June, the single application of a half-rate provided adequate control, versus early May when a second application was needed.  So this should be a suitable approach for double-crop soybeans.  Just be sure to start with an effective burndown at planting, and apply when weeds are well within the 2-inch size.

Ohio Department of Agriculture Reminds Pesticide Applicators of June 30 Cutoff Date for Dicamba Products

The Ohio Department of Agriculture (ODA) is reminding pesticide applicators of the June 30 cutoff date for over-the-top dicamba products to soybeans. No additional applications can be made to this year’s crop after this date, regardless of growth stage.

Dicamba is an herbicide used to help limit unwanted weeds around crops. In 2018, the Environmental Protection Agency (EPA) designated new dicamba products as restricted use, meaning they can only be used by certified applicators.

In December 2021, the EPA released its 2021 incident report, which indicated that across the United States “more than 1 million acres of non-dicamba-tolerant soybean crops were allegedly damaged by off-target movement of dicamba.” In Ohio, there were 34 reported incidents involving dicamba.

If you have questions or concerns about dicamba please contact the Division of Plant Health’s Pesticide & Fertilizer Regulation Program at (614) 728-6987 or Pesticides@agri.ohio.gov.

Striped Cucumber Beetles Already Active

Originally posted on the May 16, 2022 OSU VegNet Newsletter – posted By Jim Jasinski

My Extension colleague in Pickaway County sent me a quick note and picture over the weekend that the Striped Cucumber Beetle is actively searching and feeding on transplanted or emerged cucurbit crops. Given how cool the temperatures have been the past few weeks I thought it was a bit early but these past few days of 80+F have certainly activated them out of their overwintering locations and into nearby fields. Like the canary in the coal mine, this pest alert from southern growers should help growers in central and northern Ohio prepare to scout and manage transplants or emerged seedlings of cucumber, squash, zucchini, pumpkin or melon.

Continue reading

Rainfast Intervals, Spray Additives, and Crop Size for Postemergence Soybean Herbicides

Mother nature is finally cooperating, allowing us to get some corn and beans in the ground.  Later this summer it will be time for postemergence herbicide applications.  The table below from the “2022 Weed Control Guide” lists important information on rainfast intervals, spray additives and crop size  for soybean postemergence applications.Click on the table to print a camera ready copy

 

Rainfast Intervals, Spray Additives, and Crop Size for Postemergence Corn Herbicides

Mother nature is finally cooperating, allowing us to get some corn and beans in the ground.  Later this summer it will be time for postemergence herbicide applications.  The table below from the “2022 Weed Control Guide” lists important information on rainfast intervals, spray additives and crop size  for corn postemergence applications.

 

 

Click on each page to print a camera ready copy