Early Season Soybean Diseases

May 7, 2020

When we talk about early season soybean diseases, we are referencing soybean root pathogens that can affect the health of the plant early on in its growth from first imbibition - the seed’s first taste of moisture, to germination, through emergence and the early vegetative stages of the plant.

There are four major pathogenic fungi that can be hazardous to a young soybean causing seed rot, seedling mortality, and root and stem decay. These pathogens are Pythium, Fusarium, Rhizoctonia, and Phytophthora. While most early season soybean diseases do occur in cool and wet soils, some pathogens thrive in warm and dry soil conditions.

Both Pythium and Fusarium are more active in cooler and wetter environments. Pythium is most likely to occur in moist soils with temperatures ranging from 50-59°F (Pythium ultimum*). One of the more common species of Fusarium is most active in moist soils with temperatures ranging from 57-73°F (Fusarium oxysporum sp.*).

On the other end of the spectrum, Rhizoctonia and Phytophthora are two pathogens that tend to prefer warmer soils. One strain of Rhizoctonia (Rhizoctonia solani*) is most detrimental to soybeans when soil temperatures are in the 77-85°F range and can be active in dry soil conditions. The fourth major pathogen in this group, Phytophthora, is one of the leading yield robbing pathogens in soybeans and is most active in warmer soil environments ranging from 77-86°F (Phytophthora sojae*)  

Disease pathogen growth stage symptoms
Seed Rot Pythium Phytophtora VO–VE Soft decay of seed; missing seedlings in row
Seeding Mortality  Phytophthora Rhizoctonia Pythum VE–V4 Yellow writing leaves, followed by necrosis; leaves remain attached to stem
Root and lower stem decay Rhizoctonia Fusarium Phytophthora VE–V6 Reddish-brown lesions on taproot and hypocotyl; usually superficial. Phytophthora causes brown lesions on stem above soil line


Your crop’s highest potential starts with the seed. Good planting practices that minimize stress and the use of seed applied fungicides are the best ways of managing early season soybean diseases. Once the seed is in the ground, not much can be done to defend against them.

Hoegemeyer’s LumiGEN™ seed treatment provides a comprehensive portfolio with industry-leading and proven fungicide components to protect against all these pathogenic fungi. Protect your seed’s potential and your bottom line by protecting your crop with LumiGEN.