Each Monday Iowa State University Extension field agronomists report what’s going in in Iowa corn and soybean fields in the areas of the state they cover. Here’s a look at this year’s crop progress as of July 25, along with weather conditions and problems such as diseases and insects showing up in Iowa corn and soybean fields.
Northwest—Joel DeJong: In the northwest corner of Iowa, the corn is in the R2 (brown silk) stage for the most part. Soybeans are fully blooming, and some of the earliest fields are close to R3 (small pods at the top four nodes of the plants). There isn’t much disease pressure, and soybean aphid numbers remain low. Corn rootworm beetles can be found in continuous cornfields quite easily, and at heavy populations at times. Grasshoppers are getting abundant in some field borders.
Rainfall in the counties along the Big Sioux River has been quite limited for the past few weeks. That area could use a rain since all they seem to pick up is a 10th or two at a time. Although not on the U.S. Drought Monitor yet, I suspect that area and southeast tip of South Dakota, could get added soon if rain does not arrive in the near future.
Northwest—Paul Kassel: My area of northwest Iowa has received adequate rainfall this past week with a lot of the area receiving about 4 inches of rain or more for the month of July. There continues to be a wet area in northern Clay County and a large part of Dickinson County which has resulted in a fair amount of acres that have drowned out and are stunted due to the excess rainfall.
Corn is mostly pollinated and is in the blister stage. The replanted corn—planted the week of May 16—is pollinated also and looks good. Fungicide applications are occurring on corn although there is little corn leaf disease present in the fields. The soybean crop is at R2 and R3 stage of growth. Fungicide applications are occurring on soybeans. Soybean aphid numbers have been very low to date although many farmers are checking their fields for this insect.
North Central—Angie Rieck-Hinz: Soybeans are at R3 to R4 stage of growth. I have seen a few fields with aphids but at very low levels and also a few fields with bacterial blight. Producers should be scouting for aphids. Corn is R1 to R3 growth stage. So far I have seen very few corn rootworm beetles. I did put out traps on July 18 and will continue to monitor for the next few weeks.
There are fungicides going on in corn and soybeans but I have seen no fields with disease pressure that warrants any application. The only disease I have seen is common rust which is pretty much in every field but this is to be expected and rarely do we treat for common rust.
Northeast—Brian Lang: Beetle emergence has begun. High corn rootworm beetle population fields might cause silk clipping. Scout to make certain there is at least ½ inch of silks out to receive pollen. Finding five or more beetles per plant under drought conditions might be enough to keep silks trimmed back too far, but under “normal” conditions as many as 15 beetles per plant could be tolerated.
If silk clipping is a threat before pollination is complete, respond quickly with insecticide to still allow time for silk emergence and reception of pollen to fertilize the kernels. Once pollination has occurred, it no longer matters if the silks are fed on by insects.
Current soybean aphid trends are tracking just a bit ahead of those in 2014 and 2015 near Decorah (view 2014 and 2015 trends here). We usually find a couple of populating outbreaks in some fields ahead of trendline so start speed scouting fields now. Speed scouting is the easiest/best/quickest way to scout for this pest. You can download a speed scouting card here: Speed Scouting for Soybean Aphid.
Central—Mark Johnson: My area of central Iowa received anywhere from 0.7 inches to well over 3 inches of rain over the last week with some spots even getting 4 inches or more. I didn’t receive many calls for diseases or insects in corn or soybeans this past week. I did notice some fields had some bean leaf beetle feeding. Much of the corn in my area is R2 to R3 stage of growth and soybean fields are also R2 to R3.
West Central—Michael Witt: The west central Iowa area got around 1 to 2 inches of rain over the last week based off of ISU Mesonet sites. Corn is, on average, around R2 to R3 growth stage with some of the later planted corn hybrids earlier in maturity. Soybeans are also around R2 to R3 stages of growth with pod formation just beginning. The upcoming weather this week looks very good for continued development of plants.
Disease pressure in crops has been low this year but it can change rather quickly if environmental conditions allow. Insects of interest that have been reported are Japanese beetles, grasshoppers and corn rootworm (CRW) beetles. Both Western and Southern CRW beetles were observed at the Western Research Farm in Castana in western Iowa on Wednesday this past week (July 20). Overall, crop conditions are good across the area with the crops responding well to the intense heat. Scouting for insects and disease is important at this time of year to make sure you identify possible problems before economic thresholds are reached. Proper identification of defoliation or infestation amounts is also important to determine insect and disease pressure.
South Central, Southeast—Rebecca Vittetoe: Last week was a hot one in south central/southeast Iowa but we received some rainfall throughout the week. Rainfall totals seem to range from just over 0.5 inches to over 3 inches in some areas. Check out the U.S. Drought Monitor.
Corn is mostly around R2 (blister) growth stage but some is getting close to R3 (milk stage). Soybeans are at R2 (full bloom) to R3 (beginning pod). From a disease and insect perspective, things are still pretty quiet. I have been seeing small amounts of gray leaf spot, common rust and holcus spot corn diseases and I’ve spotted some adult corn rootworms flying around in cornfields.
Southeast, East Central—Virgil Schmitt: In the last week, my area in east central/southeast Iowa received 1 to 5 inches of rain with most areas receiving at least 2 inches and an area in Des Moines County receiving over 5 inches. Corn is R2 to R3 stage of growth and soybeans are at R2 stage. There probably are some R3 soybeans, but I haven’t seen any. Japanese beetles and bean leaf beetles are the topics of discussion regarding crop pests. Aerial applicators are spraying both corn and soybean.
Find your local ISU Extension and Outreach field agronomist here!