Farmers in the Midwest may be concerned about white mold (also called Sclerotinia stem rot) in soybean this year. The disease, caused by the fungus Sclerotinia sclerotiorum, is not common every year, but farmers who have battled the disease in the past will want to assess the risk of white mold development as soybeans approach flowering (growth stage R1 – plants have at least one open flower at any node).
Grasshopper activity has been noted this week in Iowa. These insects feed on grasses and weeds, and can become field crops pests. In corn and soybean, feeding is frequently, but not always, restricted to field edges. When crop injury does occur, it usually is related to drought conditions due to a reduction in natural vegetation.
Since 2000, soybean aphid has been the primary soybean insect pest in Iowa. Infestations are sporadic and unpredictable, but this insect has the ability to cause significant yield loss during periods of optimal reproduction. Several notable infestations have been reported, particularly in north-central Iowa, this week, and therefore scouting to determine population densities is strongly encouraged. Fields that have a fairly uniform infestation with low densities (e.g., 50% of plants infested with an average of 40 aphids per plant) should be closely monitored in August.
The lack of reliable traits to distinguish Palmer amaranth and waterhemp during vegetative stages complicates efforts at stopping the spread of Palmer amaranth across the state. However, both plants should be in full reproductive mode at this time, greatly simplifying the identification of the two amaranths.
While most agronomists and weed scientists prefer to identify weeds using vegetative traits, the small bracts (modified leaves) associated with flowers of Palmer amaranth and waterhemp are the most, if not only, reliable way to differentiate the two species. Palmer amaranth has relatively large, green bracts that extend well beyond the other flower parts, whereas on waterhemp the bracts are similar in length to the tepals surrounding the seed capsule. On close examination, Palmer amaranth’s bracts on mature female plants are easily seen protruding from the plant’s seedheads without the use of a hand lens. Redroot and smooth pigweed also have large bracts; however, these species have hairy stems in contrast to the smooth stems of Palmer amaranth and waterhemp.
The Integrated Crop Management Conference offers over 30 different seminars and workshops focusing on the latest in crop production technology. Experts from Iowa and surrounding states will provide research updates and results in soil fertility, soil and water management, crop production and pest management. Attendees can choose from up to 5 topics each hour. This format allows you to customize your conference experience to meet your interests and CCA credit needs. Click HERE for more information.