What’s New in Plant Pathology

2019 Crop Production Clinic Proceedings

What’s New in Plant Pathology January 9, 2019

Extension Soybean Pathologist Position

On September 1, 2018, Extension soybean pathologist Loren Giesler became head of the Department of Plant Pathology at UNL. Responsibility for soybean disease programming will be covered by Tamra Jackson-Ziems until the position can be refilled.

First Report of Fusarium boothii on Wheat in the United States

In 2015, widespread epidemics of Fusarium head blight (FHB) occurred in wheat in Nebraska. During a wheat disease survey, symptomatic wheat heads were collected from the major wheat growing regions in the state. Twenty-three single-spored isolates were obtained from wheat kernels from the collected wheat heads and identified using traditional and molecular methods. Three isolates, two from Chase County in the southwest and one from Box Butte County in the northern Panhandle were identified as Fusarium boothii. This identification was confirmed by APHIS.

The F. boothii isolates were inoculated onto wheat heads in the greenhouse and caused typical FHB symptoms. The remainder of the isolates were identified as F. graminearum which until now was the only known cause of FHB in the United States. This is the first documented record of F. boothii causing FHB of wheat in the United Sates. F. boothii has been reported in Texas on corn and as the cause of FHB of wheat or Gibberella ear rot of corn in several countries, including Mexico and South Africa. To date, F. boothii has not been confirmed on corn in Nebraska.

Plant and Pest Diagnostic Clinic Update

Depending on location, 2018 was too hot, too cold, too wet, and/or too dry. These fluctuating environmental stresses weakened plants, making them more susceptible to many diseases throughout the season.

Table 1. P&PDC’s 3 Most Commonly Identified Wheat, Corn, and Soybeans Diseases*
March – MayJune – AugustSeptember – October
Corn
  1. Fusarium root rot
  2. Pythium seedling blight and root rot
  3. Rhizoctonia seedling and root rot
  1. Bacterial leaf streak
  2. Rust diseases (commonA, southernB)
  3. Northern corn leaf blight
  1. Fusarium stalk and ear rot
  2. Anthracnose stalk rot
  3. Gray leaf spot
Soybeans
  1. Rhizoctonia Damping off
  2. Pythium Damping off
  3. Phytopththora root and stem rot
  1. Phytophthora root and stem rot
  2. Frogeye leaf spot
  3. Stem canker
  1. Pod and stem blight
  2. Anthracnose
  3. Charcoal rot
Wheat
  1. Bacterial stripe/black chaff/Wheat streak mosaic virus
  2. Bacterial stipe
  3. Fungal leaf spots (SeptoriaA, tan spotB)
  1. Bacterial stripe/black chaff
  2. Rust diseases (leafA, stripeB)
  3. Fungal leaf spots (SeptoriaA, tan spotB)
* Confirmed via microscopic, serological, or molecular techniques
A Identified most often
B Identified second most often
Moldy Soybean Seed

There was an increase in late-season soybeans that came in due to darkened stems, damaged pods, moldy/discolored seed, and decreased yields. In many cases this was the result of adverse weather in addition to fungal pathogens while many soybeans were at early- to mid-reproductive stages. This caused a lot of fields to have aborted and/or small seed size. In some cases diseases such as pod and stem blight (Phomopsis seed decay) or purple seed stain were responsible; however, in other cases weak pathogenic fungi and secondary fungi that were only able to colonize the seed and stem due to the unique environmental conditions late in the season caused the moldy seed and darkened stems.

Credit Cards and Sample Fees

The P&PDC will begin accepting credit card payment in 2019. Due to the associated fees, there will be an increase in fees with a basic diagnosis now costing $20. If specialized tests are required, additional fees are assessed that typically range $10 to $40. (See Diagnostic Service Fees.)

Services Provided

The P&PDC is set up to diagnose

  • diseases caused by both living (fungi, bacteria nematodes, viruses) and non-living factors (environmental stress, nutrient deficiencies, etc.),
  • identify insects, mites, or other arthropod pests, and
  • identify unknown weeds.

Herbicide injury is determined solely on a visual inspection and no chemical analysis is performed. The clinic is not able to provide soil nutrient testing or pesticide residue analysis.

Jim Kalisch, our entomology diagnostician, retired at the end of 2018. Insect and arthropod pests may still be submitted; however, there may be a delay in turnaround time until the new diagnostician is in place.

New and Updated Product Labels for Disease Management

The Disease Management Section of the 2019 Guide for Weed, Disease, and Insect Management in Nebraska underwent a few changes this year. Several minor formatting changes, updates to price estimates, and annual updates to the efficacy and product tables were made. In particular, a column of new content has been added to the corn product table indicating the types of “Labeled Corn,” i.e. field/dent, popcorn, seed corn, and/or sweetcorn, for which each product is registered. Three tables of products for disease management in potato (seed-, soil-, and foliar-applied) were added, and several products were added to existing tables, including several additional modes of action. We gratefully acknowledge the new contributions of team members Amy Timmerman and Sarah Sivits who have been added to the list of section authors. Because of the size limitations of the publication, lengthier versions of the Corn and Potato Disease Management products, including more generic products, are now on the CropWatch website at:

Most changes to the Disease Management section are summarized in the tables below.

Table 2. Modes of action added to the “2019 Guide for Weed, Disease, and Insect Management in Nebraska.”
FRAC CodeCode NumberMode/Site of ActionCommon Name/Chemical Group
Group 2 MAP/Histidine Kinase in osmotic signal transduction Dicarboximides Chlozolinate, dimethachlone, iprodione, procymidone, vinclozolin/dicarboximides
Group 9 Methionine biosynthesis AP (Anilino-Pyrimidines)/amino acides and protein synthesis Cyprodinil, mepanipyrim, pyrimethanil/ aniline-pyrimidines
Group 21 C4 complex III: cytochrome bc1 (ubiquinone reductase) Qi site QiI (Quinone inside Inhibitors)/respiration Cyazofamid/cyano-imidazole
Amisulbrom/sulfamoyl-triazole
Group 28 F4 cell membrane permeability, fatty acids (proposed) Carbamates/lipid synthesis or transport/membrane integrity or function Iodocarb, propamocarb, prothiocarb/carbamates
Group 40 H5 cellulose synthase CAA (Carboxylic Acid Amides)/cell wall biosynthesis Dimethomorph, Flumorph, Pyrimorph/cinnamic acid amides, valinamide carbamates

Table 3. Foliar disease management products for disease control that were updated in the “2019 Guide for Weed, Disease, and Insect Management in Nebraska.”
trade nameActive Ingredient(s)Fungicide ClassChange(s) made
Delaro SC Prothioconazole (16.0%) + Trifloxystrobin (13.7%) Mixed Modes of Action
(Groups 3 +  11)
Added to Wheat  table

Table 4. Biological products for crop disease management that were updated in the “2019 Guide for Weed, Disease, and Insect Management in Nebraska.”
Trade nameCode NumberMode/Site of ActionCommon Name/Chemical Group
PRESTOP WG Gliocladium catenulatum J1446 (93%) Greenhouse or field grown vegetables, ornamentals, cereals, legumes, fruits, and turf Foliar spray, drench, and mixing with growth substrate. Rates may vary, see label Biofungicide against seed-borne fungal diseases including damping-off, root and stem rot, and wilt