Phomopsis in Soybeans

October 6, 2021

Phomopsis is a fungus that can cause yield loss and significantly reduce seed quality. In this article, we tell you how to detect Phomopsis and give you some tips to manage it.

Detecting Phomopsis in soybeans

Phomopsis is a fungus that belongs to the genus Diaporthe. It normally occurs in soybeans when (1) susceptible varieties have been planted and (2) rainfall is above normal during growth stages R6 to R8.

Phomopsis-infected soybean seeds are typically cracked and shriveled and usually covered with a chalky, white mold. Infected seedlings have reddish-brown pinpoint lesions on the cotyledons or reddish-brown streaks on the stem near the soil line.

Disease cycle

Phomopsis infects soybean plants early in the season and can be introduced via previously infected seed or spread by surrounding weeds such as velvetleaf and pigweed.

The fungus generally infects pods between the R5 and R6 growth stages.

Soybean seeds will not become infected with Phomopsis when seed moisture drops below 19%. However, seed infection and colonization can continue or resume if moisture increases to more than 19%.

The effects of Phomopsis in soybean crops

Decreased seed quality and reduced vigour, germination and emergence are the main impacts of Phomopsis in soybeans.

Yield losses from Phomopsis can be significant, but depend on the cultivar’s susceptibility and the weather during maturity. Damage and yield loss will be higher when rainy, wet conditions persist from early to mid-season.


If you detect Phomopsis in your soybean crop, reduce the amount of inoculum in an affected field by planting fewer susceptible crops and rotating with a non-host such as corn or a grain.

Don’t delay harvest, as it increases exposure to cool, wet conditions that favour the development of the disease. Harvesting at the right time helps reduce the risk of seed damage and maintain crop quality.

Infected seed can be treated with fungicides, which are usually effective against Phomopsis. These products increase germination and emergence.

Another tip: Don’t use seed lots with more than 20% Phomopsis, because severely infected or moldy seed will not germinate even after being treated.

Phomopsis in soybeans and your crops

And there you go! Now you know a bit more about Phomopsis in soybeans. We hope you enjoyed this article and found these tips helpful.

To learn more about the soybean world, visit the Blog section of our website or contact us.

Have a great harvest!