Crop issues as the 2024 season winds down
The 2024 growing season was somewhat unusual in Illinois, with overall conditions good enough to produce record-high corn and soybean yields. The September estimate of corn yield in Illinois is 222 bushels per acre, down three bushels from the August estimate. Soybean yield is projected to be 65 bushels per acre, one bushel less than the August estimate. These declines may reflect the increasing dryness in the state over the past weeks. With early-planted corn and soybean at or near maturity, dryness will affect mostly late-planted crops. High temperatures and low rainfall over the next week could further diminish yields of late-planted crops, including those of doublecrop soybean.
Although crop condition ratings have remained high since June, we continue to hear concerns about the 2024 crop, with advice to keep scouting, and to take notes so problems spotted can be corrected next year. As a general principle, adjusting management for what might happen next year is not a very sound approach—we have no reason to expect that the weather next year will duplicate the weather in 2024.
Some of the issues that have come up over recent weeks are presented as questions below, with commentary.
Q: Is lodging in corn a serious concern this fall?
While there has been a lot of rain in places this year, there has been little damage from high winds and hail across the state. Above-normal rainfall in many areas in July produced rapid corn growth, and good growing conditions continued into August, with outstanding canopy color in most fields. When this happens, today’s hybrids are able to build stalk strength by depositing lignin in the stalk rind. Stalks strengthened like this remain supportive even if the soil dries and leaves lose their green color before maturity, and even if ears are heavy. Stalk strength is probably as high now as it has ever been as the crop matures. Although very high windspeeds could still break stalks over, nothing in the forecast is for such conditions. Stalk strength could be an issue in areas where dryness persisted until mid-July, and in late-planted fields where dryness caused loss of leaf color before maturity. In general, though, if stalks are not easy to break by pushing on them, they will likely hold up well until harvest.
Q: Does having corn leaves turn yellow as the crop nears maturity mean that the field did not get enough nitrogen?
Although river nitrate levels showed that some fall-applied N likely left fields following heavy rainfall last spring, most N deficiency in 2024 resulted from problems with N uptake, not from inadequate N in the soil. Standing water wasn’t widespread in 2024, but there was some in late May and some during wet periods in July, which may have showed up as N deficiency later in the season. Some fields showed yellowing of lower leaves during the dry period in June, but July rainfall restored leaf color of the important leaves above and below the ear. If canopy color was good in early August, we can be confident that loss of color beginning in late August was from dry soil conditions. When dry soils restrict water uptake, N uptake is also low: water and N from near the roots gets depleted, then uptake of both decline as soils dry. The crop also matured starting in late August in early-planted fields, and mature plants have no need to take up more N. If husks were drying before leaves lost their color, it is likely that kernels filled fully.
Q: Was this a season when most fields needed foliar fungicides?
Dry weather during June limited the buildup of fungal disease inoculum, so although July was wet, most reports during grainfill were that fungal diseases were limited. An exception in some areas was tar spot disease. If the TS-infected crop matured while it still had a considerable amount of green leaf area, it likely filled kernels with little loss from the disease. Applying fungicide probably made leaves healthier, but may or may not have increased yield enough to pay for treatment. We can only know if it did if we have a way to compare treated and untreated corn.
Soybeans, like corn, showed very good canopy cover and color going into podfilling, and although lower leaves may have lost color due to their being shaded, there were few diseases reported that would have responded to foliar fungicide. The process of leaf drop seems somewhat “ragged” this year, with some petioles staying on the stem, leaves drying instead of dropping, and a mixture or green and yellow leaf area. Some of this may have resulted from the large fluctuations in temperatures over the past month. Having green leaf area remaining on plants as pods begin to turn color might result in some green stems at harvest. We don’t think this will be more than a minor nuisance during harvest, but can’t rule out the possibility of delayed harvest in fields with a lot of green stems.
Q: How much will late dryness lower yields of late-planted corn and soybeans?
Both corn and soybean had considerable acreages planted in late May or in June this year. The photos in Figure 1 are of corn and soybeans planted on June 4 near Urbana. From planting to September 12, 14.6 inches of rain and 2,308 growing degree days accumulated. The corn canopy remains healthy and kernels are about one-fourth milkline down. Ears show some tipback, but kernel numbers are not much different than those on April-planted corn. With warm weather forecast for next week, this crop may reach maturity by the end of September. We expect good yields given how late planting was.
Soybean pod numbers are fair, seeds are not yet filled completely, and the canopy is incomplete. These point to the likelihood of modest yields, and also that 2024 will end up as a season in which early planting was very helpful to soybean yields. How the late-planted, doublecrop soybeans do in Illinois will depend on how far along seedfilling is now, when the last rains fell, how dry it is now, and how soon rain falls. The US Drought Monitor this week shows abnormal dryness over most of Illinois, and moderate drought (level D1) in the southernmost part of the state, with some chance of relief from the remnants of Hurricane Francine over the next few days there. In fields with pods still filling and leaves still green, that may help recover some yield.
