While on a farm stop last week to evaluate pollination success of some corn planted in early April, I saw what I thought was a lesion of northern corn leaf blight (NCLB) on the ear leaf of a couple of plants.
Long elliptical lesions crossing the leaf veins were a certain identification. The field had fungicide applied a few days prior at the tassel silking stage, but these plants were near a field border, so I thought they could’ve been present prior to application or not treated during the field application.
I sent the diseased leaf samples to the plant disease diagnostic lab at the Grain and Forage Center for Excellence at Princeton. To my surprise, the lab confirmed the plants were infected with diplodia leaf streak, not NCLB.
Diplodia leaf streak has become more prevalent over west Kentucky during the past few years. In fact, you may have mistaken it for NCLB as I did.
Small, dark, round, brown-to-tan lesions are first observed on the leaves. Dark concentric rings, giving the appearance of a bulls-eye target, may be observed in the center of early lesions at the infection site on the leaf.
Those lesions expand lengthwise from the infection and form elongated, elliptical lesions nearly identical in appearance to NCLB. In severe cases, lesions can enlarge, merging to kill large areas of infected leaves.
Symptoms can be observed on any leaf but are often first observed in the mid to lower canopy. Small, dark, spore-producing fungal structures can be seen quite easily throughout the lesion. The presence of these structures are what distinguish diplodia leaf streak from NCLB.
The fungus that causes diplodia leaf streak overwinters in Kentucky on plant residue. The pathogen infects corn during hot, humid weather and can affect corn at any time during the growing season. The word diplodia can make the hair stand up on the neck of a corn grower.
Diplodia ear rot, the white cotton-like substance that can envelope entire corn ears prior to harvest, destroying quality and test weight, is a concern. Likewise, diplodia stalk rot can infect corn late in the season and predispose it to lodging; the worst recent year for this was in the late 1990s.
Fortunately, diplodia ear and stalk rots are caused by a different fungus. But the fungus that causes diplodia leaf streak can also infect ears and stalks, and the signs of these two fungi are impossible to tell apart. It is currently unknown how diplodia leaf streak incidence and severity affect the incidence of diplodia ear rot in Kentucky.
Currently, diplodia leaf streak is not reported to cause yield loss, and management is often not necessary. Residue management through crop rotation or tillage can reduce the amount of fungus that overwinters.
There are no foliar fungicides currently labeled for diplodia leaf streak, and there is little efficacy data available. It is also unknown if hybrids vary in susceptibility to the disease. Research is ongoing to determine the impact of this disease in Kentucky.
Upcoming Virtual EventsThe Cooperative Extension Service remains closed to large group gatherings during the COVID-19 pandemic, but we are doing our best to continue sharing information and providing resources to our community. One way is through virtual learning opportunities. Two are planned this week.
The Grain Production Field Day held at the Grain and Forage Center of Excellence at Princeton each year is being split into a two-day, virtual format shared through Zoom, which can be easily downloaded to a smartphone or computer. The first session is Tuesday from 8 a.m. to 10 a.m. central time. Email me at chardy@uky.edu, and I’ll get you registered.
The second meeting this week begins a series which I would like to personally invite you to consider participating in, called “Crossing Through This: Managing Farm and Family in 2020.” 2020 has affected each of us physically, mentally, and financially in different ways, but I suspect each of you and your families will benefit from taking an hour a week, beginning this Thursday, at 6 p.m. for this program. It will also be conducted through Zoom and is limited to 300 people, so sign up early at https://bit.ly/2020FarmFamily.
July 19, 2020 at 12:08PM
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