Diseases & Disorders

All Diseases & Disorders Content

Left: Green soybean plants covered with yellow and brown spots indicative of frogeye leaf spot infection. Right: Green soybean trifoliate that is covered in brown spots.

Deciding on Fungicide Application to Manage Mid-Late Season Soybean Leaf Fungal Diseases

Soybean leaf diseases can develop in some soybean fields to reach yield-reducing levels. The question that growers often ask is whether it is profitable to apply a fungicide to soybeans at the R3/R4 growth stage in South Dakota.

A mostly green corn leaf that is in brown to yellow markings caused by southern rust.

Is a Fungicide Applied at Tasseling Profitable in Corn?

Corn is currently at tasseling/silking across the state. This is usually the growth stage when a fungicide is applied to control fungal diseases.

Two photos of oat plants exhibiting fusarium root and crown rot. Left: An oat tiller with pinkish color on the crown and first node indicative of Fusarium root and crown rot. Right: Green oat plant with yellow, dry markings throughout indicative of Fusarium root and crown rot.

Fusarium Crown and Root Rot Observed in Oats

Some oat fields are showing plants wilting with tillers dying prematurely and heads looking bleached. Inspecting the crown and sub-crown area reveals the discoloration and rotting and sometimes a pinkish color can be observed. These are typical symptoms of Fusarium root and crown rot.

Green soybean plant with white mold present on the stem and pod.

Start of Flowering Is the Ideal Time for White Mold Management in Soybeans

Some early planted soybeans are starting to flower (R1 growth stage). One soybean disease that needs to be managed at this growth stage is white mold.

Map of South Dakota showing Fusarium head blight risk. Green indicates low risk, yellow moderate risk, and red high risk. Most of the state is green except for scattered, yellow areas within Edmunds, Faulk, Hyde, Hand, Buffalo, Jerauld, Brule, Aurora, Turner, Lincoln, McCook, Lake, Brookings, and Kingsbury counties. Some red, high risk areas are in Buffalo, Brule, Hyde, and Minnehaha counties.

Fusarium Head Blight Predicted Risk for Spring Wheat

Most of the spring wheat is at or will soon be at flowering. One disease that can develop in wheat at this growth stage is fusarium head blight (FHB or scab).

Yellow and brown streaks on a winter wheat leaf indicative of bacterial leaf streak symptoms.

Bacterial Leaf Streak Developing at Low Level in Winter Wheat

A few winter wheat fields were found with bacterial leaf streak starting to develop at low levels. Bacterial leaf streak is usually observed starting from flag leaf growth stage. It can be severe on the upper leaves when there is prolonged leaf wetness resulting from frequent rains.

A few wheat plants showing heavy yellowing mosaic symptoms due to Wheat streak mosaic virus.

Wheat Streak Mosaic Disease Developing in Winter Wheat

Although the majority of winter wheat in the state is rated good to excellent in the recent USDA-NASS report, a few winter wheat fields in Central South Dakota have been diagnosed with wheat streak mosaic disease (WSMD) caused by wheat streak mosaic virus (WSMV).