Posts Tagged ‘abiotic stress’

Hail Hammers Corn and Soybean Fields – Do I Replant?

Friday, June 19th, 2009

Richard Taylor, Extension Agronomist; rtaylor@udel.edu

Over the past few weeks, a number of hail storms have impacted corn, soybeans, and small grains on Delmarva. In some of the wheat fields I’ve visited, the field sometimes appears to have heads remaining although when closely examined little grain actually remains while other fields appear to have been previously combined with a stripper head leaving the stem upright but little to no grain on the head. Barley fields have faired even worse with some flattened so badly that they appeared to have been previously combined with the straw baled off even though this was not the case. In most cases, these fields will be total losses; and if the rains continue, double-cropping to soybeans may not be possible. If any of the fields are successfully planted to soybeans, be aware that volunteer barley or wheat will be a major problem.

The real dilemma growers face is whether to replant corn and soybean fields that have been hard hit with hail. For corn, the impact of hail damage really depends on the type and severity of damage and the growth stage of the crop. Since all our corn is still in the pre-tassel stage, I’ll concentrate on that aspect. Keep in mind that if the damage is restricted to leaf shredding, grain yield reductions are not directly proportional to the amount of leaf area loss since there is an increase in dry matter production in the remaining leaf area and movement of dry matter from other plant parts later to the developing ear. Very young corn if able to grow through the damaged top will produce a fully functioning plant since many of the lowest leaves are lost to shading and leaf aging before the plant even tassels or silks.

Leaves beginning with the first rounded tip leaf are counted as each collar region becomes visible. Little yield loss occurs before about the 7th leaf stage (although many of the corn hail damage estimate charts actually count the upper most leaves as long as about 50% of the leaf is exposed from the whorl and the leaf tip points below a horizontal line). At this stage, which should equate to five to six leaves with collars visible, a one percent yield loss can occur if 40 to 45% of the leaf area is missing or dead but even at 100% leaf loss the yield loss will only be about nine percent. As another example at the 10 leaf stage which is about the size of the largest corn I saw with damage, yield loss is one percent at 25% leaf loss, six percent at 50% leaf loss, nine percent at 75% leaf loss, and 16% at 100% leaf loss (see photo 1).

hail damaged cornPhoto 1. Hail damaged corn with an estimated leaf loss of >50%.

An added complication occurs when the growing point is above ground and the hail damages the stem below the growing point (Photos 2 and 3). If the hail impacts the stem causing minor injury (Photo 2), the leaf loss tables from charts assessing hail damage to corn can be useful by themselves but if the hail either breaks the stem below the growing point (Photo 3) or causes such severe injury that disease issues become important, another factor must be considered. This added factor is the impact of stand reductions on yield losses. Many of the available fact sheets on assessing hail damage include this type of information and the two charts must be combined to estimate yield losses.

hail damaged cornPhoto 2. Hail damaged corn with injury to the stem from the impact of the hail but without clipping the stem (note that the plant was bent over to allow a better photo of the injury).

hail damaged cornPhoto 3. Hail damaged corn where the stem has been clipped below the growing point.

One of the most difficult decisions to make is when to evaluate a field to see if it will grow out of the hail damage. In most cases, in 7 to 10 days after the hail you should be able to see renewed growth and estimate whether the new leaves will successfully emerge. This is especially critical on very young (less than five leaves emerged) corn that has been totally flatted or clipped by hail. In older corn where only the leaves have been shredded (Photo 1), new growth can often be identified in as little as 3 to 5 days but wait about a week to get a better assessment.

Should the corn be replanted is the question most frequently asked and the answer almost always is no unless the stand loss is nearly 100%. The reason is that replanting corn in our area this late in the growing season seldom results in enough yield to justify the expense of more seed, more fertilizer, and more labor and time to plant. With the added delay of waiting to evaluate regrowth and, this year, for the field to dry enough to replant, I doubt if any replant decision will result in making you money.

What about soybeans that have been damaged by hail? In most cases, yield loss from hail will be primarily due to stand reductions. Generally, within 5 to 10 days after the hail damage occurs you can make an assessment of the recovering stand to estimate yield loss (Photo 4). In almost all cases, unless the stand has fallen well below about 75,000 plants per acre (one plant per foot of row on 7 inch drilled rows), replanting will not be profitable. The combination of yield loss from a delay in planting of several to many weeks from the ideal time plus the ability of soybeans to compensate in yield potential for low populations will make replanting unnecessary and unprofitable. Although I did see some plants clipped off below nodes where secondary buds can develop, many plants were pock marked from the hail damage and will quickly recover (photo 5).

soybean regrowth after hailPhoto 4. Hail damaged soybean in double-cropped barley showing bud development at the cotlyledonary nodes about 5 days after hail.

soybeans with leaves damaged by hailPhoto 5. Note pock marked (holed) leaves from hail damage in double-cropped soybeans.

Hail Damage to Agronomic Crops

Friday, June 12th, 2009

Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu

There was heavy hail damage in the northwest area of Kent County on June 9. Of course, small grains will have large yield losses. Corn that is 10 leaf stage or younger may have limited yield losses.

 hailwheat1Hail damage to wheat

hailwheat2 Hail damage to wheat.

hailbarley1Hail damage to barley.

 hailbarley2Hail damage to barley.

hailcorn1 Hail damage to corn.

hailcorn2Hail damage to corn.

hailcorn3Hail damage to corn.

The following is information from the National Corn Handbook (http://www.extension.iastate.edu/Publications/NCH1.pdf) on assessing losses due to hail in corn.

1) Assess stand losses. Wait about a week and then go out into the field and check for plants that have died or where the growing point is dead. Split suspect plants open and check to see if the growing point is light in color (still alive) or dark in color (is dead or dying).

2) Assess the loss of leaf area.

The following tables from the National Corn Handbook are used to estimate yield losses to stand loss and leaf loss. (Click picture to see larger version.)

haildamage12


haildamage2

 The following information is from Iowa State University on hail damage in corn:
http://www.ipm.iastate.edu/ipm/icm/2004/5-31-2004/hail.html
http://www.extension.iastate.edu/CropNews/2008/0607LoriAbendrothRogerElmore.htm

In contrast to soybean, corn has an advantage early season when hail damages the aboveground plant, because its growing point remains below ground until approximately the sixth-leaf stage. The sixth-leaf stage of the ISU leaf-collar system correlates to the seventh-leaf stage used by hail adjusters. Several fields that received hail damage are beyond this point, with the growing point at soil level or above.

Two different methods exist for assessing damaged fields based on the developmental stage of the crop when it incurred the damage:

In fields where the corn was at the fifth leaf or smaller, regrowth is expected and yield impacted negligibly. This is true regardless of the amount of defoliation.

In fields where corn was near or beyond the sixth leaf stage, evaluate injured plants to determine whether the growing point is viable. Make assessments of plant survival three to five days after the storm so that surviving plants have a chance to recover. If weather is not conducive for plant growth for a prolonged period after the storm, assessing the remaining stand may require waiting up to a week. It may take that long before it is clear which plants will survive and which will not.

Assessing a damaged field requires that the growing point is located and evaluated. Use a sharp knife and cut lengthwise down the stem in order to cross-section the stem. Assess the viability of the growing point; it should have a white to cream color. Plants with a healthy growing point should survive, especially if the growing point lies below the soil surface.

If most of the corn has not reached the V5-V6 growth stage yet this is good news because the growing point is still below ground and even if the leaves have been destroyed or the plant has been cut off, re-growth from the growing point below ground will occur. The loss of those early leaves will reduce growth rate following the damage but will not affect the overall yield significantly. Corn that had reached the V6 or more advanced growth stages may not be viable due to the growing point having moved above ground. At these growth stages, the plant will continue to grow if only the leaves have been knocked off or shredded and the stem has not snapped. When the stems have snapped at the base of the plant, the plant should not be considered viable. Leaves on the plant may have been shredded, but as long as they are connected to the stem they will continue to be an energy source for the plant and plant growth will therefore continue. Defoliation should not be considered a problem until later growth stages, approximately V7 or greater.

Unlike soybean, corn can do little to change its growth pattern to take advantage of increased space in reduced plant populations. A low plant population of corn will mean fewer ears on an area basis, resulting in a yield reduction. Therefore, stand loss is more of a problem in corn, making estimation of viable plants very important.

See the following for how insurance adjusters evaluate hail damage:
http://www.rma.usda.gov/handbooks/25000/2007/07_25080.pdf

Soybeans were also damaged in the recent storms. The following is information from the Integrated Crop Management Newsletter from Iowa State University

Soybean differs from corn in that as soon as the plant emerges the growing point is above ground and is extremely sensitive to adverse weather events such as hail or frost. In the case of hail, the plant is considered dead if it is in the cotyledon stage and is cut off below the cotyledons, or if it is damaged by hail to such a degree that they have no green leaf tissue or re-growth. The reason is that nutrients and food reserves in the cotyledons supply the needs of the young plant during emergence and for about seven to 10 days after emergence, or until about the V1 stage (one fully-developed trifoliolate leaf). Cotyledons are the first photosynthetic organs of the soybean seedling and are also major contributors for seedling growth. Unlike corn, whose growing point is below ground until it reaches V5-V6, the growing point for soybean is between the cotyledons and moves above the soil surface at emergence. This makes soybean particularly susceptible to damage from hail, frost, insects like bean leaf beetles, or anything that cuts the plant off below the cotyledons early in its life. Stand reductions are likely to follow hailstorms. After V1, photosynthesis by the developing leaves is adequate for the plant to sustain itself. It is important to remember that defoliation during the vegetative stages will seldom have a large impact on yield. However, it is a whole other story during the reproductive stages.

Salt Injury from Starter Fertilizer

Friday, June 5th, 2009

Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu

I recently looked at several snap bean plantings with symptoms of salt injury from starter fertilizer. Leaves had large areas that were dried from the margin inward, other areas were light green and showing signs of dessication. Symptoms were field wide and did not show up until after the plants had germinated and emerged. It was likely that fertilizer salts had moved toward the seedlings with water from rain and irrigation in high enough concentration to cause the injury. The grower had changed starter fertilizer to a higher analysis from previous years. Other crops were not affected. Caution should be taken with starter fertilizers, especially in crops that are sensitive to salts, such as beans. Choose low salt index fertilizers and limit the total amount of nitrogen and potassium (a general guideline is no more than 80 lbs total of N + K). Adjust fertilizer applicators to deliver the band no closer than 2″ to the seed and 2″ deep. If higher amounts of starter are required, move the fertilizer band farther from the seed.

Pictures from Suspected Lightning Strike to Cantaloupe Field

Friday, June 5th, 2009

Emmalea Ernest, Extension Associate – Vegetable Crops; emmalea@udel.edu

Folks at the Carvel Research and Education Center spent a few days this week puzzling over a section of dead plants discovered on Monday in the cantaloupe variety trial. The early theory was that there was some sort of herbicide carryover issue but that didn’t make sense with the field history and some of the symptoms/evidence. After ruling out disease, aliens and sabotage we now suspect that the field was struck by lightning in the violent thunderstorm Georgetown got on Sunday morning.

Both cantaloupe plants and yellow nutsedge in the affected area showed symptoms (Figure 1) – making disease an unlikely explanation of the problem. The affected area is circular and approximately 50′ in diameter (Figure 2). Plant damage decreases as you move away from the center. At the center of the affected area the plastic mulch was damaged and the drip tape was split for approximately 30 ft (Figure 3). Cantaloupe and nutsedge plants near the center of the affected area were completely dead. Cantaloupe plants that were less affected have necrotic stems and necrotic patches on the leaves (Figures 4 & 5). The roots are partially or totally dead. Nutsedge plants had necrotic leaf tips and roots were partially or totally dead (Figure 6).

The cantaloupe trial will be replanted.

lightning struck lope and nutsedgeFigure 1. Affected cantaloupe and nutsedge plants.

 circle of destructionFigure 2. Circular area of damage in the field. Note damaged plastic at the center of the circle and that plant damage decreases toward the perimeter of the circle.

split drip irrigation lineFigure 3. Split drip tape and damaged plastic (replacement tape is beside the split tape).

 cantaloupe line-upFigure 4. Cantaloupe plants with varying levels of damage. Plants to the left are from the center of the affected area. The right-most plant is from outside the affected area.

lightning struck cantaloupe plantFigure 5. Close up of lightning damage to a cantaloupe plant. Note necrosis from the soil level, up the stems and petioles and out the leaves – presumably the path of the electric current through the plant vascular system.

nutsedge line-upFigure 6. Three yellow nutsedge plants from the affected area and one from another part of the field. Note damaged roots and burnt leaf tips on the three plants on the left.