Late Season Rains Slow Harvest And Could Cause Disease
LAMAR, MO.
Phomopsis seed rot occurs when harvest is delayed due to rainy, wet weather or when soybeans mature during wet weather. Seed infection may reduce seed quality, vigor, and viability.
“Severely diseased seeds appear moldy, may be graded lower and docked at the elevator,” said Jill Scheidt, agronomy specialist with University of Missouri Extension.
Symptoms of Phomopsis seed rot, pod and stem blight are apparent after the plants reach maturity. Dead petioles, stems, and pods may be covered with small black specks, which are the fruiting bodies of the fungus (pycnidia). The pycnidia are parallel along the stem, usually on the lower portion, or scattered on pods.
Affected seeds are usually cracked, shriveled, and covered with white mold. Severely infected seeds rarely germinate when planted.
Phomoposis-Diaporthe fungi overwinter as pycnidia on previously infected soybean residue. Pods may become infected at any time, but most seed infection occurs after the yellow pod stage (R7). Prolonged wet periods after flowering and pod set favor the infection and development of pod and stem blight.
“As pods mature, the fungus grows from the wall of the pod to the seed. Seed infection is greatly increased if harvesting of the crop is delayed during warm wet weather,” said Scheidt.
Scheidt does have some recommendations for the management of pod and stem blight and phomopsis. First, harvest when seed reaches 13 percent to 16 percent moisture regardless of stem conditions. Remember to use rotation with wheat or corn. Tillage is important, and fungicides applied to pods at midflowering to late pod stage may reduce the incidence of disease. ∆