By Kent Thiesse
Mother Nature seems to throw a new twist into the situation just when crop conditions are looking near perfect as they did in portions of Minnesota. A timely planting season and favorable growing conditions during May and most of June resulted in good-to-excellent corn and soybean crop conditions in many areas. However, severe storms in Minnesota and other the Upper Midwest States during July have caused significant crop damage in some locations and raised questions about the final quality of the 2020 crop.
The severe storms in July have caused widespread wind and hail damage to crops across Minnesota and portions of Wisconsin, Iowa, North and South Dakota. The wind damage to crops resulted in leaning and flattening in cornfields and caused lodging in small grain crops. There may be minimal loss of yield potential, depending on the severity of the wind damage; however, there will be some harvest challenges and potential for further yield loss closer to maturity. The wind damage may have also caused some “green snap” damage in certain corn hybrids, which would likely result in more significant yield reductions.
The most considerable crop damage from the recent severe storms was due to significant hail damage across Minnesota and the surrounding States. The hail damage hit at a particularly vulnerable stage of development for corn in many locations. Much of the corn across the Upper Midwest was tasseling and silking from July 6-20. The tasseling and silking process must be completed to ensure good pollination to produce a viable ear of corn on a plant. If severe hail damage prevents the completion of the pollination process, it can result in significant yield loss in severely damaged corn. According to data from the University of Minnesota, corn that is 60 percent defoliated by hail at the time of tasseling will have a 42 percent or more loss of yield. If the hail damage was light to moderate, it is best to wait 7-10 days to evaluate the extent of the damage fully.
The soybean crop also received severe hail damage in some areas, with some soybeans being completely destroyed. Like corn, it is best to wait seven to ten days on soybeans that were partially damaged by the hail to evaluate the hail loss and final yield potential. Soybean plants that are still producing auxiliary buds may have some re-growth of the plant after hail. At certain stages of development, soybeans can adjust to reduced stands, with limited loss of production potential. In the early stages of growth, soybean stands can be reduced by up to 50 percent and have less than a 25 percent yield reduction. However, as the soybeans reach the blooming stage, as many soybeans have this year, and there is significant defoliation and stand reductions, the yield loss from hail can increase.
There could be further losses that result from the hail damage later in the growing season. Many times, soybean plants have bruises and stem damage from hail, which can result in plants breaking over prior to harvest. Similarly, corn can have stalk damage from hail that leads to stalk diseases, stalk breakage, and corn lodging at harvest time. Farm operators with significantly damaged corn and soybean fields may want to adjust harvest schedules to combine them as soon as they reach maturity to avoid further harvest losses.
Producers who had significant hail damage should contact their crop insurance agent before destroying the crop. Farmers that do need to destroy hail-damaged crops may want to consider seeding a cover crop to protect against soil erosion and control weed populations. Livestock producers may also be able to plant a cover crop that can provide them with additional forage this fall. The University of Minnesota Extension has some useful resources on hail damage and cover crops.
Portions of Minnesota and the surrounding States have received nearly double the normal precipitation amount in late June and the first three weeks of the month – five to eight inches per storm. Very hot and humid weather across the Upper Midwest also raised dew points to extremely high levels creating numerous thunderstorms with excessive rainfall amounts. Rainfall has caused substantial drown-out damage in corn and soybean fields and saturated soil conditions that are not conducive to crop growth. Observers are concerned that excessive rain will result in low levels of nitrogen for the rapidly growing corn. Producers should evaluate crop conditions before deciding to invest in supplemental nitrogen in the late 2020 growing season.
Many corn producers are now applying fungicide to their cornfields to reduce losses from corn diseases. Farmers with hail-damaged corn should thoroughly evaluate yield potential following a hail storm. They should do this before investing in fungicide for the corn. Fungicide treats corn for leaf fungal diseases. It will not be effective in controlling stalk rot and other stalk diseases that resulted from the hail, which are bacterial type diseases.
In areas of Minnesota and many portions of the Upper Midwest that have not been impacted by the severe storms, crop conditions have been quite favorable. Corn and soybean development for 2020 in most areas of Southern Minnesota are seven to ten days ahead of normal. Adequate soil moisture, together with the warmer than average daytime and night-time temperatures in late June and the first three weeks of July, has resulted in rapid growth of the corn and soybean crop in the region. The accumulation of growing degree units (GDUs) at the U of M Southern Minnesota Research Center totaled 1,306 GDUs from May 1 through July 15, 2020, which is about 10 percent ahead of normal GDU accumulation for that date. This accumulation is a big improvement from 2019 when the GDU accumulation at Waseca was only 1,132 on July 15.
The Minnesota crop ratings in the weekly USDA Crop Progress Reports have remained fairly steady in recent weeks. The July 13 report indicated that 85 percent of the corn and 83 percent of the soybeans in Minnesota were rated “good” to “excellent,” with only 3 percent of both crops rated “poor” or “very poor.” By comparison, at this same time in 2019, only 58 percent of the corn and 60 percent of the soybeans were rated “good” to “excellent.” As of July 13, other States reported “good-to-excellent” corn ratings; they were: Iowa at 83 percent, South Dakota at 82 percent, Wisconsin at 81 percent, Nebraska and North Dakota at 70 percent. On July 13, the following states reported “good-to-excellent” soybean ratings: 83 percent in Iowa and Wisconsin, 77 percent in South Dakota, 73 percent in Nebraska, and 67 percent in North Dakota.
Nationally, in the July 13 USDA report, 69 percent of the corn and 68 percent of the soybeans were rated “good” to “excellent.” The lowest crop ratings in the Eastern Corn Belt, where “good” to “excellent” ratings for both crops were near or below 60 percent. There is a growing concern with dry soil conditions and moderate drought in portions of the Eastern Corn Belt and Western Iowa and parts of the Plains States. A year-ago in mid-July, USDA rated 58 percent of the U.S. corn crop and 54 percent of the soybeans as “good” to “excellent.”
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