CORN
Crop Observation and Recommendation Network

June 30 - July 6, 2003
C.O.R.N. 2003-20

In This Issue:

A) Wheat Head Scab Update and Harvest Recommendations
B) Septoria Brown Spot on Soybeans
C) Potato Leafhopper in Alfalfa
D) Hail Injury to Corn
E) Reminder on OSU Weed Science Field Day

A) Wheat Head Scab Update and Harvest Recommendations - Lipps and Mills CORN Questions

The wheat crop is rapidly maturing throughout the state and wheat harvest will begin in southern Ohio this week. Reports from county agents throughout the state have indicated levels of head scab are quite variable. The incidence of scab has ranged from 0 to about 20% in fields indicating that some fields will likely have economic levels of scab, but the overall yield loss caused by scab on a state wide basis will likely be relatively low.

At this point we are not so much concerned with the effect of scab on yield, but more importantly we are concerned with the possible effect of having scabby seed contaminating the harvested grain with DON. DON is a mycotoxin also known as vomitoxin. This mycotoxin is commonly associated with scab-infected seed. Those seed that are shriveled and white to pink in color are potentially contaminated with DON. In areas of the state that have received persistent rain showers during the past couple of weeks as the crop was maturing, it is highly likely that diseased seed will have some level of DON.

Fields with scab-infected heads should be harvested as soon as possible and the grain dried to prevent continued accumulation of DON. We advise that combines be adjusted to blow out as much shriveled and lightweight grain as possible in order to achieve higher test weights. Since DON is generally associated with the lighter weight seed, removing these diseased seed will also reduce the level of DON in the harvested grain. The best thing that could happen to the wheat crop at this point is to have dry weather throughout the harvest season. Wet conditions will cause more shriveling of the grain and low test weights.

B) Septoria Brown Spot on Soybeans - Dorrance CORN Questions

Several phone calls and a sample to the clinic - indicate that we have early season Septoria again this season. Septoria is a fungus that survives on soybean straw left on the soil. In rainy weather, these are splashed onto the lower leaves of the plants, where reddish-brown spots will form. They are somewhat irregular in shape and vary in size from minute flecks to approximately 1/4 in in diameter. Infected leaves will turn yellow quickly and drop. This disease is particularly worse in continuous soybean production fields. For pictures and more information about Septoria check the web site: http://www.oardc.ohio state.edu/ohiofieldcropdisease/. for foliage diseases.

C) Potato Leafhopper in Alfalfa - Eisley and Hammond CORN Questions

Potato leafhoppers (PLH) numbers in alfalfa 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.

For additional information about potato leafhopper on alfalfa see the June 2-8 CORN newsletter: http://corn.osu.edu/archive/2003/jun/03-16.html#linkf

D) Hail Injury to Corn - Thomison CORN Questions

Over the weekend, severe thunderstorms accompanied by hail caused considerable damage to crops in parts of central Ohio. In corn, the impact of hail damage is largely dependent on the crop's stage of development. Hail affects yield primarily by reducing stands and defoliating plants. Defoliation usually results in most of the hail damage. The corn plant is generally little affected by hail prior to the 6 to 7 leaf stage because the growing point is at or below the soil surface and in the leaf whorl. However, once the growing point is elevated above the soil surface due to inter-node elongation, the plant grows rapidly and becomes increasingly vulnerable to hail damage with the tassel stage/pollen shedding stage (VT) being the most critical period.

Severe hail damage prior to the 6 to 7-leaf stage can also result in "twisted" or "tied" leaf whorls as injured plants recover and new leaves try to unroll; however, most plants will grow out of this problem and tied whorls seldom cause major yield loss.

Leaf damage by hail usually looks much worse than it really is, especially during the early stages of vegetative growth. Shredded leaves still have some capacity to contribute to plant growth. Plants not killed outright by hail usually show new growth within 3 to 5 days after injury occurs (i.e. if damage occurs prior to tasseling). For this reason, estimates of hail damage should be delayed several days to allow for this period of re-growth.

The hail insurance adjustor's growth staging system counts leaves beyond the last visible collar to the uppermost leaf that is 40-50% exposed whose tip points downward - usually this results in a leaf stage that is numerically 2 leaves greater than the "leaf collar method" (e.g. a V6 plant according to the leaf collar method would probably correspond to a 8-leaf plant according to the hail adjustor's method).

How do we estimate the potential yield loss from recent hail storms? Presently corn growth stages in central Ohio vary considerably depending on planting date, early season growing conditions, production environment, etc. As of 6-30-03, most of my corn plots in central Ohio planted in late April are in the 11- to 12-leaf stage range (or about V9 to V10 according to the leaf collar method). Based on estimates of the National Crop Insurance Association (see table below), at the 11-leaf stage (or about V9) if 50% of the leaf tissue is destroyed by hail, a corn plant loses only 7% of its yield potential; if 100% defoliation occurs, a corn plant loses 22% of its yield potential. At the 14-leaf stage (or about V12), a corn plant may lose up to 44% of its yield potential with 100% defoliation. The slower development of this year's corn crop may have actually limited yield loss to hail.

Percent yield loss in corn based on growth stage & defoliation
(adapted from NCIA Corn Loss Instructions, rev. 1984)

For more detailed information on evaluating hail injury in corn, consult "Assessing Hail Damage to Corn" National Corn Handbook Chapter 1 (NCH-1)." Available on-line at http://www.agcom.purdue.edu/AgCom/Pubs/NCH/NCH-1.html

E) Reminder on OSU Weed Science Field Day - Loux CORN Questions

The OSU Weed Science field day is Wednesday, July 9 at the OARDC Western Branch in South Charleston, OH. The field day starts at 9 am, and is the usual self-directed tour of our research plots. Drinks and plot maps will be available free of charge. We will have lunch available for a small fee, and would appreciate an RSVP if you plan to purchase the lunch (614-292-9081 or loux.1@osu.edu) Directions to Western Branch: From I-70, take SR 41 south approximately 4 miles. The branch is on the right side of the road. After coming in the main driveway, follow the road around to the right of the large white barn and park near the pine trees.

Readers can subscribe electronically to this newsletter by sending an e-mail message to: corn-out-on@postoffice.ag.ohio-state.edu. A successful subscription message will receive by an automatic reply from the listserv. Contact your local Ohio State University Extension Office or e-mail labarge.1@osu.edu if you have problems subscribing.

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: Clark Hutson        Web Editor: Nathan Watermeier

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

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Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868

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