This week precipitation has been mixed in northeast Illinois, areas north of the Rte. 80 corridor have received multiple rainfall events while areas south have received limited to no precipitation. Soy continues to progress, reaching R5, beginning seed stage. Depending upon variety maturity and planting date, most corn fields visited were R3-R4 to R4-R5. An unwelcome discovery this week was significant Tar spot symptoms in several corn fields. The decision on using a fungicide treatment is difficult in later maturity stages, especially when we are near R5, the dent stage. A reminder that grain fill in the dent stage often extends to 30 days or more. However, with declining commodity prices farmers need to consider their ROI (return on investment) when considering a or additional fungicide applications. A tool available to aid in the decision making is the Corn Fungicide ROI Calculator from the Crop Protection Network. The purpose of the Corn Fungicide ROI Calculator is to share results from university uniform corn fungicide trials conducted in the United States and Canada and allow farmers and others in the agricultural industry to calculate the potential return on investment (ROI) for corn fungicide application across a variety of user-defined factors, which is based on research data included in this calculator. The two variables needed are expected corn yield and marketing price. The calculator can be accessed at https://cropprotectionnetwork.org/fungicide-roi-calculator

Crops across Logan, Menard, and Sangamon counties continue to grow and develop nicely, thanks to last week’s rain showers. Despite having high winds during some storms, there does not appear to be any wind damage to the crops. Many soybean fields are in the R4 stage, with some earlier planted fields beginning to develop seeds (R5). Much of the same can be said for the corn crop as well. Most fields are in the R4 dough stage, with some of the earlier planted fields beginning to dent (R5). The alfalfa across the area has grown back nicely as well, with last week’s rains and this week’s cooler temperatures helping. Most fields look to be in Stage 3 (early bud).

This past week has brought some drier weather to east central Illinois than the week prior. In the eastern half of McLean County, soil moisture conditions looked good, overall, during my survey. Most fields have started to dry in the top couple of inches of the soil profile, but some parts of low-lying and/or poorly drained fields still had soils that were at field capacity. Compared to some of my surveys in recent weeks in neighboring counties, I saw very few soybean fields showing spots of plant stress due to waterlogging and/or soil-borne pathogens. A few of the corn fields I visited were showing early signs of stalk rot in some plants, although this seemed to be largely limited, at this time, to those wetter fields I mentioned earlier. Something else I saw in several of these wetter corn fields was corn ears containing both brown, senesced silks and unpollinated silks. The tassels in these fields did not appear to be shedding any viable pollen, which may mean it’s too late for these silks/ovules to make grain. Most corn was in the late R3 (milk) to early R4 (dough) range, but I did find one field at early dent (R5) and another still at blister (R2). Soybeans ranged from R3 (beginning pod) to late R5 (beginning seed), with most falling in the latter half of that range.

The season is winding down but diseases seem to be flaring as previously applied fungicides fade. Tar spot is gaining ground with cooler temps. It will flourish on corn that is in later growth stages. As corn approaches R5, many may choose not to spray. Downy mildew appeared in soybeans. Fungicides are useless against it. Overall, crops appear in good shape with April corn still looking better than Mid-May planted corn.

The last few mornings have brought significant rainfall across Logan, Menard, and Sangamon counties. High winds have accompanied this rain, but no crop damage has been observed or reported. While this rain has replenished some drier areas, it has caused a lot of standing water in the low-lying areas. The forecast for the next couple of days looks to be much of the same: rain in the morning with high temps and humidity in the afternoon. Crop progress remains steady. While these rains are beneficial, these humid and hot days are perfect conditions for crop diseases to flourish. No reports of diseases have been made in this area, but producers are keeping a close eye on their fields.

As July ends warmer temperatures and humidity returned to NE Illinois. While some appreciate seeing a sunrise mist with morning coffee, I think of extended leaf wetness on crops and that it often favors fungal leaf diseases. Despite these occurrences, I continue to see very limited leaf disease symptoms in corn or soy. From a maturity standpoint in fields visited, corn is transitioning from R3 (milk) to R4 (dough) stage. The starch within the kernel is converting from a liquid to a pasty consistency. R4 is often the shortest reproductive stage dependent on environmental conditions. Soy has reached R4 or the full pod stage. At this stage a ¾ inch (2 cm) pod can be found on one of the 4 uppermost nodes on the main stem. R4 through R6 (full seed) is a critical time for the soybean plants exposed to environmental stresses. Issues at this time can cause more significant yield decreases than other growth stages.
Recently Dr. Doris Lagos (USDA-ARS) at the University of Illinois reported finding corn aphids in the suction trap network https://suctiontrapnetwork.org/data/ and in fields. Several have corroborated finding corn aphids and suggested treating specifically for the pest. In my scouting visits I am finding corn aphid populations where I often find them, on plants at or near field edges, and at very low densities (random mostly singular plants).