Our Wayne County Integrated Pest Management (IPM) Program has been hard at work, covering many acres and farms in Wayne and surrounding counties. Throughout our scouting activities, we evaluate crops and field conditions, looking for disease and pest pressure, presence of problematic weeds and crop health concerns. We also keep an eye out for the good things happening in these fields. Integrated pest management places a significant amount of value on biological pest control, so accordingly, many of the observations that we make and report on are beneficial insects, and this week, we observed some of our strongest surges of beneficial insects that we have observed in a long time.
Corn leaf aphids had a rapid increase in population throughout the summer last year, and we saw a similar increase in population this year. Last year, after some time, lady beetle populations eventually grew to levels that were able to help manage the corn leaf aphid. This year looked to be following a similar trajectory. Our weekly scouting found increasing levels of corn leaf aphids, slowly being worked on by increasing counts of lady beetle adults and larvae. We soon noticed a consistent presence of another beneficial insect: syrphid flies.
Syrphid flies, also known as hover flies (often mistaken as sweat bees), are beneficial insects in multiple regards. Adults are commonly found around flowers, feeding on pollen and nectar while serving as important pollinators. Adult females may deposit several hundred eggs throughout the summer. As these eggs hatch, the larvae feed on pests such as aphids, caterpillars, leafhoppers, planthoppers, mealybugs and thrips.
What we observed in some sweet corn and field corn this week was remarkable. Thousands, likely hundreds of thousands (in reality, probably even more) of syrphid fly larvae were decimating the corn leaf aphid populations. So much so, that they had eliminated the aphid populations, demonstrating their ability to provide near complete control of aphid infestations. Each larva can consume between 100-600 aphids throughout its lifetime. Now consider this feeding ability, multiplied by thousands of active, hungry syrphid fly larvae, with multiple generations throughout the growing season. Not to leave out countless other beneficial insects that we are currently observing such as lacewings, lady beetles, ground beetles, predatory stink bugs, parasitic wasps and numerous others. The corn leaf aphids stood no chance where the army of natural enemies were allowed to thrive and provide biological pest control services. Remember, the goal of integrated pest management is to reduce reliance on chemical controls, reduce input costs and promote ecological balance. Getting to see the outcome of having these practices implemented can be very rewarding, and a great reminder of just how powerful some of our IPM tools are. These corn leaf aphids were controlled entirely by natural enemies. No insecticides sprayed, no money spent and no negative impacts on our biological natural enemy populations.
Cucurbit Downy Mildew Now in Ohio
Cucurbit downy mildew has recently been confirmed in Ohio, specifically in Fulton County. Growers who have cucumbers and cantaloupes in their fields should be aware of the nearby presence. Cucurbit downy mildew is best managed with preventive applications before infection takes place. Once visual symptoms appear, control becomes increasingly difficult, and yield reductions may occur. In conditions that are favorable for disease development and without effective, timely management, cucurbit downy mildew can cause rapid decline of the plant, severe defoliation and ultimately plant death in just a matter of days. Disease development is favored by rainy, humid conditions — relative humidity greater than 85% — and cooler temperatures of 60-70 F.
According to research trials completed in Ohio, Michigan, and other states and provinces around the Great Lakes region, the best fungicide options are as follows: Orondis Opti (FRAC 49+M05), Ranman (FRAC 21), Omega (FRAC 29), Previcur Flex (FRAC 28) and Elumin (FRAC 22). These should be tank mixed with chlorothalonil (Bravo, Equus, et cetera) or mancozeb (Dithane, Manzate, et cetera). Orondis Opti is a premix already containing chlorothalonil, but at a reduced rate. Fungicides have restrictions on how much product can be applied and how often, so follow the label. Always follow all label directions; The label is the law. Fungicide products with higher efficacy ratings should be rotated to avoid resistance development in the pathogen. Please note, the inclusion of any pesticide name is for educational purposes and does not imply endorsement of that product. We do not attempt to give specific chemical recommendations, but we do summarize research, efficacy trials and basic concepts and principles for growers to use when considering the use of pesticides.
Growers in Ohio also should intensify scouting of cucumbers and melons. Look for yellow or tan angular lesions delimited by veins on the top surface of leaves and fuzzy gray/brown growth on the undersides of the lesions. With a good hand lens or a smartphone camera with high magnification, you may be able to see small dark brown/purple spots within the fuzzy growth. These are the spores of the downy mildew pathogen.
If you suspect downy mildew in cucumber or melon, submit samples to the C. Wayne Ellett Plant and Pest Diagnostic Clinic for confirmation. Instructions for sample submission are on their website. Call or email Dr. Francesca Rotondo at 330-263-3721 or rotondo.11@osu.edu with any questions. You also can work with your county extension educator to get samples submitted to the lab. Another helpful resource is the Cucurbit Downy Mildew IPM PIPE (cdm.ipmpipe.org), where you can track Cucurbit Downy Mildew progress county by county and sign up to receive real-time alerts when new cases are found.
A major “thank you” to Dr. Rotondo and her staff in the Plant and Pest Diagnostic Clinic and Dr. Andres Sanabria-Velazquez and the Vegetable Pathology Lab for their critically important work. Also, thanks to financial support from the Ohio Produce Growers and Marketers Association’s Ohio Vegetable and Small Fruit Research and Development Program, there is no fee for this service for Ohio vegetable growers.
Frank Becker is the Agriculture and Natural Resources Extension Educator with Ohio State University Extension – Wayne County, and a Certified Crop Adviser, and may be reached at 330-264-8722 or becker.587@osu.edu
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This article was previously published in The Daily Record.