Field Notes addressed delayed planting concerns

 Phyllis Bongard, Educational content development and communications specialist

The cool, wet spring has led to significant planting delays in several parts of the state. Others are dealing with flooding after planting. How are management decisions impacted by these situations? Extension agronomists Jeff Coulter, Jochum Wiersma and Seth Naeve joined moderators Anthony Hanson and Dave Nicolai, Extension crops educators, for the May 25th Field Notes session to help sort through the issues.

Small grains

In the central and northern parts of the state, planting has been significantly delayed due to wet conditions. According to Wiersma, producers are switching between crops and picking off fields as they can get them planted. The question he gets most frequently is whether growers should still plant wheat or oats. High commodity prices and crop insurance planting deadlines make the question a tricky one to navigate. The spring wheat planting deadlines for full coverage are May 15, May 31, and June 5 for southern, northern, and far northern Minnesota, respectively.

Losing full insurance coverage is part of the equation, but yield potential is also impacted by planting delays. When spring wheat is planted beyond the optimum planting dates, reductions of approximately 0.5 to 1 bushel per day can be expected. This currently translates to about half to two-thirds of the 2022 crop. However, final yields will heavily depend on weather conditions throughout the rest of the season.

If late planting is combined with a warmer summer, the risk of the crop developing Fusarium head blight is greater. This combination seems to synchronize spore development with heading dates, increasing the risk for disease development. To access risk models, visit the Fusarium Risk Tool or the NDAWN Center.

When spring wheat planting is delayed, is there a need to switch varieties? Because most varieties are daylight insensitive, their growth is driven by heat units. As a result, their development gets compressed with warmer temperatures, so there’s little incentive to switch varieties. Even if the crop is planted mid-late June, the crop should mature, but the concern becomes whether the crop will dry down in time. For more information, see Does it make sense to switch to earlier maturing wheat varieties?

What about oats? Oat is more daylight sensitive than wheat, so it would make sense to switch to an earlier variety, if one is  available.

Corn

Corn planting has progressed in southern Minnesota, but there are still pockets where it has been delayed, particularly in the central and northern parts of the state. Based on UM planting date trials, corn planted by May 25 still has a yield potential of 94 to 96%. That potential drops to 91 to 93% for corn planted between May 26 and 30. The greatest impact on corn yield will be the soil moisture and weather during the critical period from 12 days before tasseling to 14 days after tasseling.

The latest recommended planting dates for corn grain are June 10 in southern Minnesota and June 5 in the central and northern parts of the state. Corn grown for silage can be planted until about June 20 in southern Minnesota and June 12 in central and northern Minnesota.

When should I switch relative maturities?

Through May 28, switch to corn hybrids that are 5 to 7 relative maturity (RM) units shorter than the full-season hybrids for your area. Between May 29 and June 4, look at hybrids that are 8 to 15 RM units shorter and from June 5 to 10, choose hybrids that are 15 or more RM units shorter than the full-season hybrids.

If growers typically order hybrids that are a couple of RM units earlier than full-season hybrids grown in their area, that provides something of a cushion with later planting.

What about planting depth and population?

Two inches is the standard planting depth, according to Coulter. He doesn’t recommend planting any shallower and notes that there’s no need to plant deeper when surface soils are not excessively dry. The corn should emerge relatively quickly since temperatures are warming.

Optimum planting populations don’t change with delayed planting, so there’s no need to modify planting rate decisions.

What about flooded fields?

Some producers were able to plant right before the derecho on May 12 and now have flooded fields. As a result, there are a few things producers should keep an eye on. First, dig up seeds and seedlings and look for healthy tissue. Orange to brown discoloration is a sign of diseased or dead tissue.

Check the field for soil crusting. If a hard crust is present and hard enough to restrict emergence, rotary hoeing may be beneficial.

In fields that have had ponding, some applied nitrogen (N) fertilizer will be lost to denitrification. While recent cool temperatures would have slowed denitrification losses compared to losses when temperatures are warmer, there still will be some N loss. The supplemental nitrogen worksheet for corn is helpful when considering whether a sidedress application might be needed.

Are N rate adjustments needed?

Coulter suggests that there’s no need to adjust N rates with later planting. But if preplant N still needs to be applied, the late-planted crop will be highly efficient at using it because the crop will grow rapidly, resulting in better synchrony between N application and crop uptake.

Soybeans

Planting delays also affect the yield potential of soybeans. While there’s no penalty for most of May, yield potential does start to tick down the last week of May and into early June. Even with late planting, Naeve states we could see very good yields, depending on late summer and early fall weather. As of May 25, yield potential for soybeans was still about 90%.

What about changing maturity groups?

If growers plant varieties in a conservative maturity group, there’s no need to change varieties through mid-June. For growers that push the long season varieties, they may want to consider changing to an earlier group. However, there’s no urgency to make any changes until June 10.

Bottom line

Naeve urges growers to continue to use the good management practices that they’ve fine-tuned over the years. The practices normally used for early planting will be fine for late planting.

Emerging crops and delayed preemergence herbicide applications

Preemergence (PREs) herbicides are very effective and provide a strong foundation for the growing season. However, there are several products that should not be applied to emerging crops, due to the potential for severe crop injury. Dr. Aaron Hager, Extension weed specialist at the University of Illinois, recently published a helpful summary of active ingredients that should not be applied over the top.

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Thanks to the Minnesota Corn Growers Research and Promotion Council and the Minnesota Soybean Research and Promotion Council for their generous support of this program!