Abundant Insects Could Mean Trouble

for Ohio Soybeans

08/28/2003

Abundant Insects Could Mean Trouble for Ohio Soybeans

Writer:

Candace Pollock
pollock.58@osu.edu
(614)292-3799

Source:

Ron Hammond
hammond.5@osu.edu
(330)263-3727

WOOSTER, Ohio Ohio soybeans are being overrun by insects, and the verdict is still out as to how much the crop will be impacted come harvest.

Ron Hammond, an Ohio State University entomologist, said that soybean aphids have been found in abundance throughout Ohio with some fields registering thousands of insects per plant. The high levels of feeding could damage the crop, causing a drop in yields, and could potentially spread diseases.

We are where we do not want to be right now said Hammond, a professor at the Ohio Agricultural Research and Development Center in Wooster, OhioGrowers are spraying a lot of acres. We are talking about hundreds of thousands of acres if not more

The soybean aphid, practically nonexistent in soybean fields last year, has shown up in full force the latter half of the growing season for reasons researchers have yet to figure out. Where the threshold for treatment was set at 250-300 aphids per plant during flowering and pod development, some fields now have upwards of 2,500 aphids per plant.

When you get populations that high there is a concern about what kind of damage thas going to do to the crop said Hammond, adding that based on reports from other states, yield losses from aphid feeding can run as high as 15 bushels per acreIn July, the aphids weret in most fields so we didt think it was going to be exceptionally bad. But over the past three weeks, a lot of fields have had heavy populations, especially in late-planted fields

Researchers speculate that late-planted soybeans may be one contributing factor to the high aphid numbers and their extended stay in Ohio.

In 2001, when we also had high aphid populations, we had the soybean crop in early. The aphids had migrated and were greatly reduced by August said HammondThis year, because of the later planted fields, most of the problems are occurring in August. If we had everything planted early, we might have had the problems like in 2001

Cooler-than-normal summer temperatures may also be a reason for this yeas high soybean aphid numbers.

In 2001, it was a cool summer. Last year, when we hardly had any aphids at all, it was really hot. And this year is another cool summer said HammondA number of us think that the weather has a lot to do with aphid populations The soybean aphid is a northern climate insect, having been reported in Canada, and other states such as Minnesota, Wisconsin, Michigan, Iowa, Indiana and Illinois.

Another insect giving soybean growers headaches is the bean leaf beetle. The insect is showing up in high numbers in many fields. But, unlike the soybean aphid, its presence didt come entirely as a surprise.

High populations of bean leaf beetles overwintered in Ohio, so we were actually predicting high populations this summer said HammondBut I havet seen such large populations in the state in years

One issue associated with high soybean aphid and bean leaf beetle populations is the potential transmission of diseases. The soybean aphid, like other aphids, can transmit soybean mosaic virus, while the bean leaf beetle is a vector for bean pod mottle virus. Growers wot know until harvest whether or not the crop was affected by either disease.

Soybean mosaic virus ist that big of a problem because is seed transmitted. So if you are planting seed that is free of the disease, then the chances of picking it up from other sources is going to be very low said HammondBut bean pod mottle virus is more of an issue

But the biggest concern agronomists have right now is treating fields with insecticides so close to harvest.

Most insecticides have a harvest interval. That is, you have to wait a certain period of time after spraying before you can harvest your crop said HammondSome insecticides have a 60-day interval, others 45 days, others two weeks. If a grower uses an insecticide with a 45-day harvest interval now, hs not going to be able to harvest until mid-October

Hammond recommends that for the soybean aphid, in this stage of the game, growers should think seriously before spraying unless they have very large populations, well over 2,000 aphids per plant. He said that in most other states aphid populations are crashing either through migration, beneficial insects or pathogens. Ohio should not be far behind.

For the bean leaf beetle, that insect will begin feeding on pods and growers should watch their fields closely so that pod feeding remains at low levels. If pod feeding becomes more common, Hammond recommends treatment with an insecticide with a short harvest interval.