REINBECK - A small portion of Iowa's soybean crop still needs to be planted, but farmers and agronomists are already worried that a familiar pest may devastate yields.

Crop experts say soybean aphids are poised to make a big comeback in Iowa later this summer. Four years ago the pests, along with dry weather, cut yields in half - especially in fields not treated or sprayed a timely fashion - throughout most of the state.

Monday's U.S. Department of Agriculture Crops and Weather Report indicates 87 percent of the state's beans are in the ground and only 47 percent have popped out of the soil. Yet, experts say it's good to be prepared for aphids to avoid a repeat of 2003.

"You have to keep an eye on them. If they get too bad, spray," said Robert Blohm, a grain and cattle farmer near Reinbeck. "If they come, they come. We sprayed and got on top of them (in 2003) and our yields weren't that much different than normal."

Unfortunately, many Northeast Iowa farmers can't say the same thing. Soybean yields ranging from 20 to 30 bushels per acre were common four years ago when aphids attacked plants, sucking nutrients that curtailed development and yields.

No major aphid infestations have occurred the last few years, but Travis Kriegshauser, a senior research associate with Pioneer Hi-Bred International in Waterloo, says that could change. He said aphids are more predominate during odd years and a large number survived the winter.

"Illinois and Minnesota reported a particularly high counts of overwintering soybean aphids," Kriegshauser said in a press release. "At this point, it is important to prepare for the possibility of significant soybean aphid populations and anticipate the need to scout for this pest beginning in late June through August.

"Scout at least 80 percent of the field," he continued. "Select 20 to 30 plants in 10 random areas of the field. If you count 250 or more aphids per plant and populations are on the increase, it's time to spray."

Only 2 percent of Iowa's corn crop needs to be planted as of Monday, equal to the five-year average. Eighty-six percent of the corn is emerged, one day behind last year's progress and one day ahead of the five-year average.

The report said crops weakened by cold temperatures in April are fighting weeds while wind and moisture limited application of herbicides. Blohm was spraying post-emergence herbicide on corn on Monday.

"Nothing out of the ordinary, just a few broadleaf weeds and grass," he said.

The state's corn is rated 3 percent poor, 17 percent fair, 59 percent good and 21 percent excellent.

Soybean emergence is 3 percent behind last year, but 5 points ahead of the five-year average. The crop is rated 2 percent poor, 20 percent fair, 62 percent good and 16 percent excellent.

None of the state's corn or soybeans are in very poor condition.

More rain during the middle of last week halted field work, the report said. More moisture helped soften hard soil to aid emergence of crops, but it also caused flooding of replanted fields.

Livestock are reported in good condition statewide.

Contact Matthew Wilde at (319) 291-1579 or matt.wilde@wcfcourier.com.