The big news for crop production in Iowa this week has been the colder temperatures. Frost in some areas of the state last weekend has raised injury concerns for emerged corn and soybean seedlings and for forage crops. In the following report, check out what ISU Extension field agronomists are seeing and hearing around the state for field conditions and planting progress.

Now is the time to start evaluating corn and soybean fields to see how the emerging crops and young seedlings are recovering. Are crops showing signs of frost injury? Also, watch for signs of insect pests in fields. Alfalfa weevils, both adults and larvae, are being observed in some alfalfa fields across Iowa this week. If you have crop questions, consult your local ISU Extension field agronomist. Their contact information is at here.

Rainfall totals for the past week in various areas of Iowa are at this National Weather Service. A map showing low temperatures across the state of Iowa from May 8-12 is at Iowa Environmental Mesonet.

Northwest

Joel DeJong, Region 1. “We had several nights with lows around 30 degrees F in northwest Iowa but not much below that. Crop injury was limited, it appears, although you can find an occasional corn plant that had tissue killed by frost. The growing point looks good on the plants I cut open, so I suspect most will resume growth once it warms up again. Not many soybeans are emerged, and those I found look as if they survived the frost OK in the area. While looking, it was easy to find some emerged grasses along field edges, mostly woolly cupgrass. Scouting for weeds escaping reemergence herbicides might be more important this year.

“Soybean planting slowly progressed even with the cold temperatures last week. We are likely approaching the 80% range of soybeans planted, with almost all the corn in the ground. It’s been a long time since a good rain shower, so one good rain in conjunction with warmer weather, and a resumption of good planting days will get us wrapped up soon. Alfalfa measurements on May 11 for using the PEAQ method to determine when to take the first cutting of alfalfa were from 14 to 17 inches in height. That growth, too, will resume rapidly with the forecast for much warmer temperatures early next week. I found no alfalfa weevil issues yet.”

COLD SYMPTOMS: Corn plants retain a yellowish color after several mornings of temperatures in the low 30 degrees F.

Paul Kassel, Region 2. “This week has been quiet. Corn planting and soybean planting is mostly complete, but there are still a few soybean acres to be planted. Preemergence herbicide applications on soybeans is also nearly complete. While there was a lot of concern about frost injury to both the corn and soybean crops, at this time it appears that the injury is limited. There were relatively few soybean fields with emerged plants. Nevertheless, farmers and agronomists are advised to check and assess corn and soybean fields. The next big fieldwork activity will be postemergence herbicide applications to corn. However, currently there is not much urgency because of the slow development of both the corn and the weeds.”

North central

Angie Rieck-Hinz, Region 3. “Planting progress continued last week, and the May 11 USDA Crop Report showed north-central Iowa at 97% of the corn planted and 85% of soybeans planted with 5.3 days suitable for fieldwork. Conditions remained ideal for planting, and in most places, the top 1 to 2 inches of soil is relatively dry. Cold temperatures on the morning of May 9 hovered around 28 degrees at my house, 25 degrees in Webster City and 26 degrees at Hampton.

“Later that afternoon when the front pushed through Iowa, we experienced blowing soil. Water erosion is not the only kind of erosion we have here in Iowa. I’ve received very few calls about freeze or frost-damaged crops, but I took pictures showing the varying degrees of freeze-injury to corn on May 11 near Kamrar. Other phone calls of concern this week include slow growth of pastures, management of pasture and post-applied nitrogen for corn.”

Northeast 

Terry Basol, Region 4. “This past week had good planting conditions to help growers in my area either finish with both corn and soybean planting, or get very close to finishing. According to the May 11 USDA Crop Progress Report, farmers in north-central and northeast Iowa have 97% and 88% of the corn acres planted. The report said 85% and 76% of the soybeans were planted, respectively. Both corn and some soybeans have begun to emerge from the early planting dates. We did get a little dust settling from a weather system that came through on May 5, giving us an average of a half-inch of rain.

“Record lows were recorded for this area on May 9, with Waterloo getting down to 25 degrees and the ISU Northeast Iowa Research Farm getting down to 23 degrees. Corn should be fine, as the growing point is still below the soil surface. Most emerged soybeans would be at VE growth stage (cotyledons emerged through the soil surface). And although the growing point is aboveground, the cotyledons are resilient to cold temperatures. Nevertheless, it will be important to scout and assess the corn and soybean fields that had emerged at the time of these low temperatures. Do the scouting three to five days or more after cold temperatures strike to be able to assess living versus damaged or injured plant tissue.”

Central

Meaghan Anderson, Region 7. “The big news was the cold temperatures that came through Iowa this past weekend. Low temperatures were below freezing for a short time across part of central Iowa, and with our early planting this spring, many crops were already emerging. Later this week (May 13-16 or so) will be an excellent time to scout and observe recovery of plants that may have suffered frost damage.

WEEDS EMERGING: Velvetleaf seedlings are up and growing in a crop field in central Iowa on May 7. (Photo courtesy of Meaghan Anderson)

“While we’ve received some rain (and expect more this week) and our PRE herbicides are hopefully working effectively now, keep an eye out while scouting emerged crops for weeds that may have snuck through the preemergence herbicide during the dry period in April. I’ve noticed velvetleaf and grasses (likely giant foxtail) surviving in fields. Questions I’ve received have been primarily about managing cover crops, herbicide restrictions to planting, and what will happen with cold temperatures and crops.”

Southwest and West central

Mike Witt, Region 6. “Corn and soybeans are emerging across west-central Iowa. Corn planting is over 90% complete and soybeans over 70% for the area. With the early planting and colder temperature, many farmers are reporting yellow-looking corn. These plants need a little warmth and sunlight to perk up. There were patchy areas of frost last weekend. I’ve had few reports of widespread frost damage in west-central Iowa. All crops should recover if they were damaged, but it’s important to scout your fields and do stand assessments.

“Also, check weed pressure in these areas as herbicides do their best work on growing weeds, and frosted or slow growth will mean slower herbicide interactions. While scouting, early-season pests to be on the lookout for include true armyworm, black cutworm, bean leaf beetles and alfalfa weevils. Pained lady butterflies (adult thistle caterpillars) have been found in Iowa. Rain in the forecast for the end of this week in west-central Iowa should give farmers a small break to get ready for the next round of field activities.”

Aaron Saeugling, Region 10. “Cool temperatures and scattered light rain occurred over the past week. However, portions of Pottawattamie and Cass counties are abnormally dry. With limited rainfall, pastures and newly seeded alfalfa need a soaking rain. Pasture growth and winter small-grain growth is slow this spring. Most all the corn is planted, and perhaps 80% of the soybeans have been planted. Cool conditions nipped emerged corn and soybean plants last weekend. Most spraying is on schedule. Expect some preemergence weed escapes on herbicide applications due to lack of soaking rains and slow crop growth.” 

East central, Southeast and South central

Rebecca Vittetoe, Region 8. “While rain the past week was welcome, the colder temperatures and frost over the weekend were not welcome. Corn planting is winding down, and two-thirds to three-quarters of the soybeans have been planted across my region. Many farmers have finished planting. For the crops that have emerged, corn is mainly VE to V1 growth stage and soybeans mainly VE. The cold temperatures caused frost injury to emerged crops and forages; however, it is important to be patient and wait three to five days after the frost to really evaluate how plants are recovering.

“So far corn and alfalfa seedlings I've looked at appear to be coming out of it just fine. For alfalfa fields, scout for alfalfa weevils. I found a few adults and larvae in an alfalfa field in Washington County. I took a PEAQ measurement and the alfalfa averaged between 16 to 17 inches in height. Common questions this past week have been on weed identification, herbicide considerations (mainly on dry conditions earlier and PRE’s or spraying after the frost), replanting considerations, black cutworm predicted cutting dates, and cold weather [and] frost concerns.”

Virgil Schmitt, Region 9. “Rain in the last week has generally been light with under 1 inch of precipitation reported nearly everywhere in the counties I cover. The weather allowed for planting and spraying. About 90% of the corn is planted and two-thirds of the soybeans in my area. It appears that with the cold temperatures the past weekend, there was some frost damage to emerged crops. Herbicides, herbicide drift and soybean populations dominated calls last week.”

Josh Michel, Region 11. “Some welcomed rain slowed down fieldwork for a couple days across most of my region last week. Most areas received anywhere from 0.25 to 0.5 inch of rain. Although the rain will help alfalfa fields and pastures continue to grow, much of the region could use some additional moisture. Many farmers have either completed planting for the year, or they hope to finish within the next couple days. Corn and soybeans planted at the end of April are at VE to V1 and VC to V1 growth stages, respectively.

“There are some concerns about recent cold temperatures and possible frost injury to crops and forages. Some areas experienced freezing temperatures for up to three hours. Farmers should wait to scout these areas. Do it later this week to know what the impact was for sure on crops. Recent calls have included alfalfa weevils, forage management, weed identification and herbicide applications.”