CORN
Crop Observation and Recommendation Network

June 25 to July 1, 2002
C.O.R.N. 2002-19

In This Issue:

A) Wheat Harvest Started In South: Make Preparations To Insure Quality Grain.
B) "Rootless Corn Syndrome" In Late Planted Fields.
C) When Is Corn Ear Size Determined?
D) Weed Control Reminders.
E) Controlling Wild Carrot.
F) Insect Update.
G) Soybean Aphid.

A) Wheat Harvest Started In South: Make Preparations To Insure Quality Grain - Pat Lipps and Dennis Mills CORN Questions

Wheat is Ohio's number one food grade crop. Growers are encouraged to take care of the grain just as they would any food crop. Growers should do everything possible to insure harvest of quality grain. This includes getting into the wheat fields as soon as possible to prevent weathering of the crop. The highest test weights and best grain quality is seen after the first dry down of the crop. If wheat stands in the field after this time and is rewetted from rain or heavy dew, the wheat grain shrivels more and test weights are reduced. To avoid dockage from reduced test weight, wheat producers should begin harvest as soon as possible once the grain reaches 20 percent moisture if they can dry the grain. Growers that do not have the possibility of drying grain should watch the moisture level in the crop closely and harvest as soon as possible. Keeping track of the 5 day weather forecast will also help plan harvest to prevent wetting and drying of the grain in the field. Visit field prior to harvest to note any significant problems like head scab, freezing injury or lodging.

Wheat harvest has begun in southern Ohio and the warmer weather over the past weekend will cause wheat to ripen quickly in more northern areas of the state. Diseases frequently cause special problems to wheat during harvest. However, the dry conditions that have prevailed over the past two weeks limited the development of most head and grain diseases. Head scab is generally at low levels throughout the state (trace to 5% incidence), with only a few locations having as high as 10% of the heads affected. Growers should adjust the combines to allow for maximum cleaning of the grain when harvesting fields with head scab. Higher blower speeds will eliminate most of the small, shriveled diseased seed that significantly reduce test weight. These shriveled seed may be contaminated with vomitoxin, a toxin associated with head scab. Grain with high test weight generally has little, if any, vomitoxin. Fields with the higher levels of scab should be harvested first and immediately dried to 14% moisture to prevent additional accumulation of vomitoxin. Grain can be further cleaned to remove the shriveled kernels and improve grain quality. Screenings from the cleaning process should not be used for animal feed unless they are subject to a mycotoxin analysis. This test in needed to determine the possible level of vomitoxin in the grain that could affect livestock. A list of laboratories that will do mycotoxin analyses can be obtained at http://www.oardc.ohio-state.edu/ohiofieldcropdisease/. A little preparation now as the harvest begins will pay the grower later when grain is delivered to the elevator.

B) "Rootless Corn Syndrome" In Late Planted Fields - Peter Thomison CORN Questions

As the weather conditions turn hot and dry, it's likely that some corn fields, especially later planted fields, will experience "rootless corn syndrome". Rootless corn syndrome (or "rootless corn") occurs when there is limited or no nodal root development. Plants exhibiting rootless corn symptoms are often leaning or appear ready to lodge. Affected corn plants may only be anchored in the soil by seminal roots or by a single nodal root. This condition is generally observed in plants from about the three leaf stage to the eight leaf stage of development. Before the problem is evident, corn plants may appear vigorous and healthy, but after a storm with strong winds, plants will fall over because there is a limited number or no nodal roots supporting them. Leaning and lodged plants (sometimes referred to as "floppy corn") may also be wilted. When affected plants are examined they are found to lack all or most nodal roots. The nodal roots present appear stubby, blunt, and unanchored to the soil.

Rootless corn problems are usually caused by weather related conditions that coincide with development of the permanent (or nodal) root system and environmental factors. These include shallow plantings, hot, dry surface soils, compacted soils, and loose or cloddy soil conditions. Excessive rainfall and shallow plantings may cause erosion and soil removal around the crown region that can result in rootless corn. Nodal root development is inhibited by hot, dry compacted soils. The force of strong winds can break off secondary roots and inhibit establishment of a permanent root system.

The nodal roots develop above the seed and comprise the permanent root system of corn. The nodal roots, not the seminal roots (associated with the seed), are important in providing the water and the mineral nutrients that the corn plant needs for normal growth and development. If corn seed is planted 11/2 to 2 inches deep, then the nodal (or crown) roots begin develop at about 3/4 inches below the soil surface. However, if seed are planted shallower (1 inch or less), then the nodal roots may form near or at the surface where they are more exposed to fluctuations in soil moisture and temperature. Nodal root growth is very sensitive to high temperatures (w/ root growth slowing or stopping at soil temperatures exceeding 86 degree F ). When unshaded surface soil temperatures reach the mid 90's or higher on hot days, the nodal root growth of shallow planted corn may stop. Plants are forced to rely on the seed root system or limited nodal root growth until more favorable temperatures and moisture conditions allow nodal root growth to resume.

Although certain types of herbicide injury (e.g. 2,4-D, Banvel) and insect feeding (e.g. corn rootworm) may cause lodging to occur in corn plants during vegetative development, there is generally little evidence of their involvement in these rootless corn problems. Nevertheless, there may be situations where insect feeding and/or herbicides may be a contributing factor to the problem.

Poor root development may also occur in no-till fields that were planted when soils were too wet. In addition to likely compaction-induced root problems, abnormal root development may also occur because the furrow walls may have been smeared during the planting operation, preventing good seed-soil contact. If conditions turn dry, the walls of the furrow become hard and act as a barrier to root development. Roots growing in such an environment often appear flattened and under extreme conditions may result in plants' breaking and falling over during wind storms.

Can rootless corn recover? Yes, after plants lodge, adequate rainfall will promote crown root development and plants can recover. Cultivation to throw soil around exposed roots may aid the corn's recovery. Of course, this is difficult to do in a no-till situation or when the soil is hard and dry. Since affected corn is likely to be vulnerable to potential lodging problems at maturity, it should be harvested as soon as grain moisture conditions permit.

C) When Is Corn Ear Size Determined? - Peter Thomison CORN Questions

There is considerable variability in corn growth and development across the state - with some of the early corn (planted in April) at V12 or later, and corn planted in late May/early June at the V4-5 stage. During the rapid phase of corn vegetative growth, now evident in the early planted corn, ear yield components are now being determined. Kernel row numbers per ear are generally established by about V12 (the 12 leaf collar stage). Kernel row number is generally less affected by environmental conditions than by genetic background. Corn hybrids characterized by "girthy" ears exhibit more kernel rows (e.g. 18 or 20 rows) than hybrids with long tapering ears (e.g. 14 or 16 rows). Determination of kernels per row (ear length) is usually complete about one week before silking (R1) or about the V17 stage. Unlike kernel rows per ear, kernels per row can be strongly influenced by environmental conditions, so severe stress such as a drought occurring the two weeks prior to pollination can reduce kernels per row and ear length.

D) Weed Control Reminders - Jeff Stachler CORN Questions

The weather is not our friend this season! Now that we are hot and dry in many areas of the state herbicide activity can be affected. The hot, humid conditions will make corn more sensitive to injury to growth regulator herbicides, so be cautious. Carefully scout fields and correctly determine the corn growth stage and apply herbicides accordingly. If weeds are showing signs of drought stress herbicide activity may be reduced. In these circumstances, spray fields in the morning when weeds are under less water stress.

E) Controlling Wild Carrot - Jeff Stachler CORN Questions

Some questions have been coming in about controlling wild carrot. In corn, use Spirit, Exceed, Beacon, Hornet, Permit, or Accent. Dicamba will not control wild carrot. In non-Roundup Ready soybeans, use Classic at 0.75 oz/A with MSO and 28% Nitrogen. In Roundup Ready soybeans, use glyphosate at least at 1.2 lbae/A (40 oz/A of Roundup UltraMax and 48 oz/A of other glyphosate formulations). The addition of Classic at 0.67 oz/A with the glyphosate may allow a lower rate of glyphosate.

F) Insect Update - Bruce Eisley & Ron Hammond CORN Questions

Potato leafhopper - Potato leafhoppers (PLH) numbers have exploded during the past week. Fields that did not get sprayed are showing considerable yellowing and hopper burn at this time. A rescue treatment is warranted on alfalfa for PLH when the number of adults and nymphs exceeds the height of the alfalfa in inches. For example, if more than 6 leafhoppers were collected per 10 sweep sample on 6 inch alfalfa, a rescue treatment should be considered. If fields are too severely damaged by PLH, then early cutting may be necessary. If early cutting is used for control, be sure to check the next cutting for PLH after a week or so of regrowth has occurred.

G) Soybean Aphid - Bruce Eisley & Ron Hammond CORN Questions

Although we have not yet observed the soybean aphid in Ohio, reports from surrounding states indicate that the aphid is starting to occur in soybeans. Thus, everyone should start checking their fields over the next few weeks for their presence. When the soybean aphid begins to occur in larger numbers, most people will have no problem making the correct identification. It will be the only aphid colonizing soybeans. However, at the early stage of infestation when only a few aphids might be on the plant, care needs to be taken that they are correctly identified. This might take examining the aphid underneath a microscope or magnifier to ensure it is truly an aphid. Remember that soybean aphids are similar in size to small potato leafhopper nymphs, although the leafhoppers are usually more active. You should also not confuse the aphids with other small critters such as thrips, and the other small invertebrates that might be on the leaf. Thus, the reason for using a microscope. If soybean aphids are located, please send an email to hammond.5@osu.edu with the date and location. Thank you!

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Past versions of C.O.R.N. can be found on the World Wide Web at: http:/www.ag.ohio-state.edu/~corn/archive/

C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

Editor: David A. Jones        Web Editor: Tom Rosati

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