Late season weed escapes, off-target herbicide movement, sightings of soybean aphids, and a little bit of frogeye leaf spot were some of the common issues that Iowa State University Extension and Outreach field agronomists saw in fields across the state this past week. Read on for more information about crop conditions and what’s happening in crop fields across the state.
Paul Kassel (Region 2): “Some of our corn and soybean fields continue to look excellent. The early planted corn looks good and is entering the R4 (dough) stage of development. The later planted corn did not withstand the waterlogged conditions of late June as well and does not look as good. In fact, some of the later planted corn has lower leaves that are beginning to fire. The corn acres that received added nitrogen in early July have regained their green color. However, these acres are behind in development and are in various stages of pre-tassel or early tassel stages. Some of the early planted soybean fields look excellent. The mid- May planted soybean fields are in the R5 (beginning seed) stage. Soybean aphid numbers are so far staying at low levels; however, continue to keep scouting for this pest. The treatment threshold for soybean aphids is 250 aphids per plant on 80% of the plants. Alternatively, you can use the "speed scouting" method, which can be found here. There have been a few more reports of dicamba off-target movement.
North Central Iowa
Angie Rieck-Hinz (Region 3): “Corn averages from R2 (blister) to R4 (dough); however, I have even seen a few fields planted mid-April at early R5 (dent). In many places corn is firing pretty high up the stalk—mostly due to lack of nitrogen and now again, lack of water across the southern part of my area. Maintaining stalk quality will be a challenge this year to get us to harvest. Soybeans are R3 (begin pod) to R5 (begin pod fill). I have had a few reports of aphids. I continue to receive phone calls regarding off-target herbicide movement in soybeans. North Central Iowa received less than a half inch of rain for the past week, with the exception of Northwood, which received 0.79 inches.
Terry Basol: (Region 4): "The recent weather has provided a nice low stress environment for both the corn and soybeans. According to the Iowa Mesonet, we received about 1.2 inches of rain from July 15 through July 31 at the NE IA Research and Demonstration Farm near Nashua. Corn ranges mainly from the R2 (blister) to R3 (milk) stage with some fields in the southern edge of my region being at R4 (dough). Soybeans range from R3 (begin pod) to R4 (full pod); however, there are some acres in the far northern area of my region that are just in the early reproductive stages (R1 or R2). Overall, there has been low levels of foliar diseases in both corn and soybeans. I've found some gray leaf spot in corn and Septoria brown spot and frogeye leaf spot in soybeans. On the insect side, soybean aphid levels continue to remain very low for NE Iowa, although It’s important to continue scouting as the recent weather that we’ve had is conducive for population increase of this pest. There have been cases of Bt resistant issues in corn fields with corn rootworms that are being investigated. Other insects that have been found in fields include Japanese beetles, Bird Cherry-Oat aphids in corn, and second generation true armyworms."
Southwest and West Central Iowa
Mike Witt (Region 6): “West Central Iowa received little to no rainfall over the last week. Crops are still doing well, but they could use rain and are starting to show signs of water stress or leaf rolling in lighter soils. If this trend of limited moisture continues and the heat of summer returns there is potential for stress issues. Corn is mainly at the R3 (milk) stage. There is the beginnings of nitrogen stress and firing of leaves in the lower canopy of some fields depending on maturity and nutrient availability. Soybeans are in the R3 (begin pod) to R4 (full pod) stages of pod development with a few fields hitting R5 (begin seed). There have been a few reports of soybean aphids around the area. None of the reports or numbers have hit economic thresholds for spraying, but scouting should continue for this pest. Corn rootworm beetles and Japense beetles can also be commonly found in fields. Disease pressures have been limited this year in West Central Iowa with many different diseases present but very few reaching levels that required a fungicide application. It's easy to spot waterhemp and other weeds emerging above the soybean canopy. Take some time now to scout fields for herbicide effectives and for potential weed resistance issues. A trusty hoe is your best bet at this stage of the season for weed control."
Central, East Central Iowa, Southeast, and South Central
Virgil Schmitt (Region 9): “In an unusual turn of events, the area that most needed rain in the last seven days received the most, with the driest area (southwest Lee County) receiving between 1.5 and 2.0 inches of rain with progressively lesser amounts to the north, with areas north of Highway 34 generally receiving less than 0.5 inches of rain. Corn is mostly late R3 (milk) and is generally looking good. Gray leaf spot continues to generate calls and field visits. Soybeans are mostly R4 (full pod) and also looking good. Frogeye leaf spot is showing up. Gray leaf spot, Japanese beetles, and weed escapes dominated calls last week.”
Josh Michel (Region 11): “Scattered light showers brought some minor drought relief to some areas, but unfortunately many areas across my region didn’t receive any rainfall. Extreme drought (D3) conditions have now been expanded into three counties in my region (Davis, Van Buren, and Appanoose) according to the most recent drought monitor (released July 26). Pastures, hayfields, and corn fields are really showing signs of drought stress. Most corn fields are at R3 (milk) and R4 (dough). Most soybean fields are at R3 (begin pod) to R4 (full pod), and overall are looking good despite the lack of precipitation. The majority of my calls last week consisted of drought stressed corn, drought stressed hayfields, gray leaf spot, frogeye leaf spot, Japanese beetles, and off target herbicide damage in soybeans.”
Check out the map below to find your local ISU Extension and Outreach field agronomist and find their contact information here!