Late Summer is Time to Watch Insect Pressure

Cultivating a successful crop while relying so heavily on the whims of the weather is an amazing feat in itself. Unfortunately weather is only one of the variables faced by soybean farmers who plant millions of seeds in the ground each spring in hopes there will be no interference in the growing season. In the late summer months, Ohio farmers need to be watching for tiny uninvited visitors who enjoy munching on their growing plants.

While slugs can be problematic in no-till fields with a wet spring, the majority of insect pests found in soybean fields in Ohio arrive in late July or early August. In the last 10 years, the soybean aphid has made a name with farmers and remains a top insect threat to soybean fields.

While it may be hard to imagine the tiny yellow aphid could have much of an impact on a fairly established plant, they are able to reproduce at amazing speeds. They are not a major concern until the population reaches levels that can have an impact on yields and in turn profit.

“If you have one adult aphid on a plant, by the end of the day you could have three small aphids. They reproduce that quickly,” said Andy Michel, a state extension specialist in Field Crops Entomology at the Ohio Agricultural Research and Development Center (OARDC) in Wooster, Ohio.

“We have thresholds for soybean aphids; we recommend treating when populations reach 250 per plant. That can usually occur in mid-August. There are also some aphid resistant varieties, Ohio Soybean Council (OSC) and soybean checkoff has helped with research on these, but there’s not a lot of availability yet,” said Michel.

They have also seen some patterns emerging with aphid populations seeming to be larger in odd numbered years, so producers may see an increased presence compared to last year.
As pods begin to fill out in August, stink bugs also make an appearance in Ohio soybean fields, including a newer invasive species – the brown marmorated stink bug. While finding a few of them in fields each year is not unusual, in the past three to four years Michel reports having fields every year that reach economic levels that should be treated.

“Stink bugs have a relatively low threshold of around two bugs per foot of row, which can be quite significant in a field,” said Michel. “We recently had a field in Wooster with a stink bug presence and saw about a 30% yield loss in the field just from stink bugs.”

Hotter and dryer weather tends to encourage the stink bug population with 2012 seeing some rather significant numbers compared with other years.

Bean leaf beetles are another insect that frequently shows up in soybean fields. While they maintain a presence throughout most of the season, recent years have seen them feeding on pods as they begin to fill out.

“We’ve seen significant pod feeding in recent years, and with prices where they are, losing one or two seeds per plant can lead to a potential economic loss. They not only chew quite heavily on the pods, but the bite marks leave plants susceptible to pathogen outbreaks,” said Michel.

Another pest on the radar at OARDC is the kudzu bug which was found in Georgia in 2009 and is currently being monitored for in Ohio with support from the Ohio soybean checkoff.

“A couple counties in Kentucky is as close as it is to Ohio. There is not a strong insect presence in southern Ohio, but I know there are some kudzu patches. It likes kudzu, but later in the season it also feeds on soybeans. Wherever we see patches of kudzu, we run the risk of having high kudzu bug infestations,” said Michel. “We’ll be looking to see what the range is this year in June and July. The expansion so far seems to be in the Gulf Coast and Mid-Atlantic states.”

While there are likely some insects feeding on soybeans throughout the growing season, fields with good canopy closure and no stress factors should have an easy mid-season. Pest activity increases when the pods come on because they insects want the same thing producers do – a high quality soybean. Scouting fields and monitoring insect pressure as pods fill out will go a long way in making sure any unwanted visitors are dealt with before they impact yields.

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