Hail and flooding hit fields hard in some areas of Iowa late last week and over the weekend. With hail-damaged corn and soybean fields, the question is: Should you tear up the remaining stand and replant? How much will the stand recover? What’s the yield potential of a hail-damaged field vs. replanting it at this later date?
This week — the week after the storms — is a good time to evaluate how crops are recovering from the injury, so you can determine what concerns may exist for yield and the remaining stand for the rest of the season. Meaghan Anderson, an Iowa State University Extension field agronomist, offers the following guidelines to help farmers assess hail-damaged fields.
Corn: Evaluate damage
The growing point, located inside a corn plant, reaches ground level around V6 growth stage. Most corn is currently between V5 and V8 stage of growth (using the leaf collar staging method). Corn that’s been cut off at or slightly above ground level is likely no longer a viable plant — if the plants were this tall when hail cut them off. Corn that’s cut off higher on the plant should continue producing new leaves and trying to outgrow the old, damaged tissue.
Corn with an intact and healthy growing point will survive, but there are several things to consider for the rest of the season, Anderson says.
• Yield potential of original stand. When figuring out yield potential, consider the original stand and planting date. This is not how many seeds per acre you planted in the field, rather it’s what the stand was, or the established stand before the hail hit. Next step is to take several stand counts across the damaged field to evaluate stand loss. Use this information, along with guidelines and resources listed in this article to determine the loss in yield potential.
• Questionable corn plants. Some plants may be in a “questionable” category for survival and production of a harvestable ear. This might include plants caught up in old, damaged tissue or those with deep bruises on stems.
• Check for signs of bruising. Plants with exposed stalks that are damaged (not shallow leaf sheath bruising) may suffer from stalk rot or standability issues later in the growing season. These plants should be monitored closely to determine whether early harvest is necessary.
• Defoliation of surviving plants. Check for tissue that’s dead or lost from the plants. If the tissue is still green, then it is still photosynthesizing to help the plant grow.
When using Figure 6 in the publication “Hail on Corn in Iowa,” you should add approximately two leaves to your “leaf collar estimate” of stage of growth, says Anderson. For example, if your corn had seven collars (V7), use growth stage V9 for your potential yield loss estimates in Figure 6. This is because those figures use crop insurance staging which counts more leaves on a plant than the collar method.
• Taller corn considerations. For nine-leaf corn (about V7 growth stage by collars) it should withstand up to 25% defoliation without yield loss.
Additional resources to help you when assessing hail damage in corn:
1. Hail: Deciding to keep the stand or make other plans
2. Evaluating Hail Damage on Corn
3. Estimated Percent Corn Yield Loss Due to Defoliation at Various Growth Stages Chart
4. Hail on Corn in Iowa
5. Corn Loss Adjustment Standards Handbook
BEAN INURY: Soybean plants should begin producing new leaves at the buds within a week following hail injury, if they are to recover.
Soybeans: Evaluate stand
The growing point of soybeans is aboveground as soon as the plant emerges, says Anderson. “At each location on the stem where a leaf attaches, an axillary bud exists that can grow if the top bud is broken off the plant. Thus, soybeans have an incredible ability to recover from lost tissue if an axillary bud still exists on the plant. If soybean plants are cut off below their cotyledons, they will not survive.”
Should you replant the entire field? Or just fill-in the damaged areas of the field? Significant damage to soybean stands often makes the replant and fill-in question more difficult than with corn. “With significant defoliation, soybean plants are slower to recover,” Anderson says. “That makes stand evaluation more difficult without giving the plants some more time to resume growth of axillary buds. Waiting seven to 10 days should be enough to see if regrowth is occurring or if plants are dead.”
• Estimate potential maximum yield. Compare potential yield from the original final stand and planting date to potential yield from replanting beans at the later date. Again, this isn’t the 150,000 soybean seeds per acre you may have originally planted; rather, it’s the final stand you had in the field.
Keep in mind soybean yield loss can come from stand loss, defoliation on plants, and loss of nodes or breaking of stems on individual plants.
Vegetative stage soybeans are considered to have zero percent loss in yield potential from even total defoliation. With soybean plants, the concern is about significantly thinned stands and nodes lost from plants. Damage to stems is difficult to quantify, but may result in lodging problems later this season.
• How to evaluate a soybean stand. Count the number of plants in a known length of row in several areas (at least 5 areas) across the field or in the hail damaged area. “You could do a small area like 3 feet of row or evaluate the full length of a thousandth of an acre” says Anderson. “The more counts you make will result in a more accurate assessment.”
Separate the plants into “will survive” and “won’t survive” and “questionable” categories. These categories can help in estimating a percent stand loss from the original final stand in the field.
Plants should begin producing new leaves at axillary buds that will be visible within the week following the hail injury.
Soybean stands need to be below 75,000 evenly spaced plants in mid-to-late May and 50,000 to 60,000 evenly-spaced plants in mid-to-late June to get a potential yield increase from replanting. Soybean plants have an incredible ability to make up for stand loss.
If many of the surviving plants fall into the “questionable” category, replanting the beans may pay from a yield perspective. “Using the information resources listed at the end of this article can help you estimate potential yield loss from stand loss and node loss on soybean plants,” says Anderson. “However, you can’t easily assess the potential for lodging issues to occur, due to stem damage.”
• Check stems carefully when evaluating plants. Look for bruising or potential for lodging later in the season. Also, the value of having a good, uniform soybean canopy to help suppress and shade-out late-season weed pressure is also not easily quantified. Hail, of course, damages the canopy and it lets in light which helps weeds grow. Soybean fields should be monitored for weed emergence that requires control.
If replanting soybeans, don’t bother tearing up the current stand, but do try to plant across rows (at an angle or perpendicular to rows) and try to increase the stand closer to 140,000 plants per acre (that is, don’t plant a full rate).
“We often use mid-June as the date for switching to a shorter maturity group soybean variety for replanting in Iowa,” says Anderson. “In other words, we will likely be okay sticking with a full-season bean unless replant occurs after June 15 to 20. If you are planting after that date then switching to a shorter maturing soybean variety, perhaps a variety that is 0.5 to 1.0 MG (maturity group rating) shorter than a variety that is normally well-adapted for your area, may be a good idea,” she adds.
Additional resources to help you when assessing hail damage in soybeans:
1. Evaluating Hail Damage on Soybeans
2. Hail on Soybeans in Iowa
3. Soybean Loss Adjustment Standards Handbook
Fungicide application to hailed crops
Some farmers ask whether hail damage on corn and soybean crops should alter the decision-making process for fungicide application. In short, the answer is, “No.” “Fungicide application decisions should be made in the same manner as if no leaf tissue had been damaged,” says Anderson. “It’s important to remember that while the cost of fungicide per acre doesn’t change, yield potential of the replanted crop has likely been reduced.”
Except for smut on corn, fungal diseases usually don’t enter a plant through open wounds; the diseases enter the plant in other ways. Also, no fungicides claim efficacy on smut. ISU has done several hail/fungicide studies in corn and soybeans. Check out this video to learn more about the results. Foliar diseases will influence yield response to fungicides much more than hail damage. “So, you should make fungicide application decisions in the same manner as if the tissue had not been damaged,” she says.
However, if a fungicide is applied to corn, waiting at least a week after the weather event may be more beneficial than an immediate application, adds Anderson. Read more about the ISU study results at Would a fungicide benefit hail-damaged crops?, an article written by ISU Extension plant pathologists Daren Mueller, Alison Robertson and Adam Sisson.