Illinois Crops Update 7.8.22

Each week, I put out a request to crops educators and specialists from the University of Illinois to compile an update to share with the entire state. We hope you find this information useful. If you have any questions or suggestions about the format or any feedback in general about these updates, please email me (harbach2@illinois.edu).

Aaron Hager, Extension Weeds Specialist, University of Illinois

We received multiple reports of poor waterhemp control following application of postemergence soybean herbicides. Several callers have asked about testing waterhemp plants for resistance to growth regulator herbicides (i.e., 2,4-D, dicamba) and/or glufosinate. We do not have laboratory techniques nor molecular assays to determine resistance to herbicides from these two classes. Greenhouse experiments currently are the only method available to confirm resistance to these herbicides. These experiments utilize plants generated from seed collected from the putative resistant female waterhemp that survived the herbicide.

Nick Seiter, Field Crop Insects Extension Specialist, University of Illinois

I have not received many reports of insect pest activity, other than the ongoing emergence of Japanese beetles and corn rootworm beetles in much of the state. Hot dry conditions during pollination might make an insecticide for silk clipping insects tempting; keep in mind that it takes relatively large amounts of silk clipping (to within 1/2″ of the tip of the ear) throughout the field (including the field interior) while silks are still actively growing to impact pollination – a rare combination in Illinois.

Emerson Nafziger, Agronomy Extension Specialist, University of Illinois

Illinois crop rating slipped a little more in the first week of July, with Good + Excellent ratings on July 3 at 65% for corn, down from 70% a week earlier, and at 62% for soybean, down from 66% the week before. This is mostly due to continuing dryness: the US drought map released on July 7 has 50% of f Illinois rated as abnormally dry, 15% in moderate drought, and 3% in severe drought (3%). The severe drought area includes most of Champaign, Douglas, and Piatt Counties. The good news is that this area got some rain on July 7, and more might be coming on July 8. This should do a lot to restore growth rates and yield potential of corn, although it’s doubtful that fields where leaves have curled daily for the past three weeks will be able to recover to produce full kernel numbers. Four percent of the Illinois corn crop had pollinated by July 3, and most of the rest should pollinate over the next two week. Fields planted after May 15 are behind in their development, and that may enable them to respond a little more to stress-relieving rain. As long as it doesn’t turn dry again, rain should restore soybean yield potential.

Dennis Bowman, Digital Agriculture Specialist, University of Illinois Extension

Until the last 2 days, Central Illinois had not received much additional rainfall. However,  rains on Wednesday and Thursday provided much-needed relief. Double crop soybeans planted two weeks ago in Macoupin county had emerged by the Fourth of July. A Thursday trip to northern Illinois indicated wheat harvest had extended at least as far north as Pontiac. Tassels are starting to emerge in the earliest fields.

Phillip Alberti, Commercial Agriculture Extension Educator, Northern IL

Significant rainfall events in consecutive weeks have come at a great time in the northwest corner of the state. Coming out of a very dry June, the corn (V5-V7) and soybean (V4-R1) crops are in a much better place after the first week of July. Earlier planted crops do seem to have a sizeable advantage compared to their later planted counterparts which struggled to weather the dry heat. Weather reports indicate that July will be another dry month overall, so the rain events that are expected to close out the week will be a welcome sight.

Talon Becker, Commercial Agriculture Extension Educator, South Central IL

Much of the southern Illinois region received rain over the past weekend, although with variable reported rainfall totals ranging from 0.1″ to almost 2″.  Some pop-up showers also moved through the south-central region Tuesday afternoon, delivering another tenth or two where the rain did fall.  These rains have helped keep soil moisture at a good level, but with the hot temps, slightly rolled corn leaves and limp soybean leaves are visible in the hottest afternoon hours.  Some of the earliest corn will likely start to flower in the next week or two, and I have seen a few soybean flowers starting to open in some of our earliest planted soybean plots.  Double crop soybeans are emerging, at or near VC in most fields.  So far, stands look pretty good in the fields I have seen.

Chelsea Harbach, Commercial Agriculture Extension Educator, Northwestern IL

I have received a few reports through Ag Pest Monitor of tar spot incidence in corn across Illinois in the past week-and-a-half; however, the reports did not include any photos so I was unable to confirm whether the reports were accurate. I know tar spot has been observed in Iowa, and so it is most likely out there in our Illinois fields. Incidence to date is low, but with some wetter, more humid, and slightly cooler forecasts, the opportunity for this disease to take off is there. We are approaching the timeframe for fungicide applications, which may yet have some efficacy. However, remember that there is a 14-day latent period between infection and symptoms for tar spot… so it is a bit difficult to say what the real disease potential is right now prior to sprays. Best to be scouting for this disease now as well as after fungicide applications to observe spray efficacy in your fields. As we’ve received rains in western Illinois, it seems like we flipped a switch from diseases unlikely to diseases likely in both corn and soybean. Now is the time to scout for both. I will be working on a write-up about tar spot reporting in corn that I’ll publish here on CropCentral within the week. That will help guide you on how to report and use/interpret the tar spot map on corn IPM Pipe or Ag Pest Monitor.