Since early August, farmers and consultants have been reporting what they believed were potassium (K) deficiency symptoms in soybean leaves located in the middle or upper canopy. This is not surprising in fields or portions of fields with soil-test values in the very low or low K interpretation categories. Moreover, K deficiency symptoms could develop at these growth stages with drought conditions, even in fields with adequate soil-test K levels. Sometimes symptoms occur in late summer with rainfall events after a dry period.
Integrated Crop Management News
Links to these articles are strongly encouraged. Articles may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If articles are used in any other manner, permission from the author is required.
I have been reluctant to provide estimates of soybean acres damaged from dicamba applied to Xtend soybean due to the difficulty in developing a realistic number of affected acres. While there has been a significant number of acres damaged by dicamba, I am sure it is less than five percent of Iowa’s nearly 10 million soybean acres. Due to this relatively small number of acres affected (in relation to total soybean acres), dicamba injury will not significantly impact Iowa’s productivity in 2018.
Iowa State University Extension and Outreach field agronomists have reported the appearance of frogeye leaf spot in soybeans as much of the crop across Iowa enters the R3-R5 growth stage.
Soybean aphid is the most important insect pest of soybean in Iowa. Foliar insecticides, mostly pyrethroids and organophosphates, have been the primary management tactic for soybean aphid in Iowa since 2001. Regular scouting and timely treatments will protect yield. Our research and extension program at Iowa State University (ISU) is focused on evaluating insecticide efficacy for soybean aphid on a wide range of products. We are also screening soybean aphid populations for pyrethroid resistance in northern Iowa.
According to the U.S. Drought Monitor, southeastern and south central Iowa are experiencing prolonged heat and moisture stress. In early August, there were twospotted spider mites detected in corn and beans. I recommend scouting corn and soybean fields for mite infestations this month, especially in these areas.
The activities of the soybean cyst nematode (SCN) are significantly affected by environmental conditions. Greatest SCN reproduction occurs during hot, dry conditions. SCN development likely is accelerated this season, and hastened development could result in greater-than-normal increases in SCN numbers. Every year, as fall approaches, patches of early-maturing plants will begin to appear in soybean fields. Early-maturing patches in soybean fields can be an indirect symptom of SCN damage. Farmers are encouraged to have fields soil sampled to determine SCN population densities prior to growing soybean crops and to take an active, integrated approach to managing the nematode.
Since 2010, aphids have been colonizing corn later in the summer and are building up to striking levels in Iowa. They can be found at the base of the stalk, around the ear and sometimes above the ear leaf. It seems these aphids have been sighted in corn again this summer (Photo 1).
In 2016 and 2017, there were isolated reports of soybean injury by soybean gall midge in northwest Iowa. Confirmations were reported in 2011 from Nebraska and in 2015 from South Dakota. In 2018, the distribution in Iowa has spread to twelve Iowa counties (Figure 1). This article hopes to raise awareness about a new soybean pest and confirm any additional infested Iowa counties.
While off-target dicamba injury to soybean has dominated the news the past year, it is important to recognize that dicamba is not the only Group 4 herbicide (HG4) capable of injuring soybean. These herbicides mimic the activity of indole acetic acid (IAA), a hormone that regulates the activity of numerous genes involved in plant growth. IAA also is referred to as auxin. HG4 products can induce plant responses at lower doses than most other herbicide groups, thus off-target injury has been a problem since their introduction in the 1940’s. This article will discuss some of