C.O.R.N. Newsletter 2007-19

Comparing Soybean Aphids to Other Soybean Leaf Insects

Authors: Bruce Eisley, Ron Hammond

Growers often have difficulty correctly identifying soybean aphids when only a few are present on the leaves. There are often numerous other insects present that can confuse them. In last week’s Purdue University’s, Pest & Crop News Letter, our entomology colleagues wrote an article on Soybean Aphid Look-Alikes that contains outstanding close-up pictures not only of soybean aphids, but of the other insects that are similar in size and appearance. For help in identifying aphids, see their article at http://extension.entm.purdue.edu/pestcrop/2007/issue13/index.html for great pictures.

Significant Armyworm Moth Numbers

Authors: Bruce Eisley, Ron Hammond

Although we have mentioned armyworms in the past few weeks and the need to monitor for them, we felt the need to again call your attention to armyworm moth densities that have become extremely high in some states surrounding Ohio. Although wheat is far enough along in development so as not to be a concern, adjacent corn fields or corn having significant grassy weed densities, especially no-till fields, should be checked for possible larval buildups.

Scouting for Corn Rootworms

Authors: Bruce Eisley, Ron Hammond

With the hot and dry weather that Ohio experienced the past two months, corn rootworm larval development has proceeded very quickly. Numerous states in the Midwest have already begun seeing adults emerge. Assuming this is also the situation in Ohio, we feel that the next couple of weeks will be a good time to check for corn rootworm larval feeding injury. Growers should check their corn fields where corn follows corn or those fields in NW and west central Ohio where corn follows soybeans to determine the possibility of first year corn damage. The coming weeks will be the time to root sample because the maximum larval feeding injury will be during this time and larval feeding will be ending as the larvae pupate and new adults begin to emerge. After larval feeding has ended, the roots on some hybrids will begin to regenerate and when this happens, rootworm larval injury is more difficult to detect.

We suggest the following method to check for rootworm injury:

1. Carefully dig plants, don’t pull them, from the field taking as much soil as possible with the plant.

2. Carefully remove as much soil as possible from the plant without damaging the roots and also look for any larvae that might still be in the soil or on the roots. Rootworm larvae are white, about 1/2 inch in length when full grown with a brown head and brown plate on the tail http://ohioline.osu.edu/icm-fact/images/43.html (see picture).

3. If there is still soil on the roots you can either soak the root system in a bucket to loosen this remaining soil or you can spray the root system with a hose to remove the remaining soil.

4. After the soil has been removed, check the roots for feeding injury, either roots chewed back to the stalk or tunneling in the roots.

Root systems can be rated using the 0 to 3 scale. The scale indicates the amount of damage to the root system and can be used to determine if economic injury has occurred.

Modified Node-Injury Scale.
 

Sentinel Plot Update for June 25

Authors: Anne Dorrance

Twenty sentinel plots were examined last week as we continue to gear up for the flowering stages. No additional reports of frogeye leaf spot. Severe dry weather in some parts of the state is most likely contributing to this. In the one field that I did visit this last week, soybean residue was beneath the leaves that had the leaf spots. We will continue to monitor this situation, especially if the rains return.

Soybean rust was found in 2 soybean sentinel plots in Louisiana that were 80 miles north of the positive kudzu patches. In one plot the incidence was low, the second it was high but the level of disease was still low. Inoculum in the south is still very low and with only 8 weeks of time left for potential infections to impact Ohio crop – this risk is getting lower and lower and lower.

Hail Injury Evaluations Yield Loss in Corn

Authors: Peter Thomison

Popup thunderstorms accompanied by hail can caused damage to corn in localized areas. 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 with most of the damage resulting from defoliation. Corn becomes increasingly vulnerable to hail damage at later vegetative stages of development with the tassel stage/pollen shedding stage (VT) being the most critical period.

Leaf damage by hail usually looks much worse than it really is, especially during the early stages of vegetative growth. Shredded leaves and plants with broken midribs 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 V9 plant according to the leaf collar method would probably correspond to a 11-leaf plant according to the hail adjustor's method).

How do we estimate the potential yield loss from recent hail storms? Corn growth stages will vary considerably depending on location, planting date, etc.. But this year in many corn fields, it’s not unusual to see corn differ by three or more growth stages because of uneven emergence and development. I suspect most corn in Ohio has not progressed much beyond the V10 stage (as of 6-18-07). Based on estimates of the National Crop Insurance Association, at the 11-leaf stage (or about V9) if 50% of the leaf tissue is destroyed by hail, a corn plant loses 7% of its grain yield potential; if 100% defoliation occurs, a corn plant loses 22% of its yield potential.

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 (verified 6/18/07)

Wheat Harvest Tips and Conditions

Authors: Jim Beuerlein, Pierce Paul, Dennis Mills

The wheat crop is drying down very fast and harvest has already begun in some parts of the state. As harvest continues over the next few weeks, growers should keep their eyes on the weather and the moisture content of the grain to ensure good quality wheat.

Wheat grain is about 30 percent moisture when it reaches physiological maturity and can be harvested efficiently and easily when the grain moisture is between 14 and 20 percent. Harvesting above 20 percent grain moisture increases kernel damage, and reduces storability, test weight and germination percentage. Delaying harvest past the time that grain reaches 14 percent moisture reduces yield about one-fourth bushel per acre per day, increases cutterbar loss, and decreases test weight each time the grain is wetted by rain or very heavy dew.

Exposure of the grain to rain after maturity may lead to sprouting and mold development. Also, the risk of loss by bird and rodent feeding increases as does the potential loss due to fire, hail, high wind, and other weather factors. Yield, test weight, germination percent, grain quality, and harvest efficiency are greatest when the grain moisture is between 14 and 20 percent moisture at harvest. Within that range wheat grain moisture decreases about one percentage point per day with normal weather conditions.

Plan to complete harvest before the grain moisture drops below 14 percent and before it starts raining. Assuming that ideal harvest conditions last for six days enables one to estimate the moisture level at which harvest must start. If the crop can be harvested in two days, harvest can be delayed until the grain reaches 16 percent moisture. For a crop that will require six or more days to harvest, threshing should start when the grain reaches 20 percent moisture.

Check combine thoroughly for worn or broken parts that should be replaced and then lubricate according to the operators’ manual. Adjust cylinder speed, concave clearance, fan speed, and screens for wheat. Service the motor and remove any combustible material from the motor compartment to make the machine field ready so harvest can start on time and at the proper grain moisture content.

Wheat is unusually short this year due to the low temperatures during the stem extension phase (jointing through head emergence). Plant height varies across most fields and the grain table will need to be very low. The secondary tillers are always shorter than the main tiller, so it is prudent to check their height and be sure they are collected in to the grain table.

 

Three Southern Ohio Crop Events for July 10th & 11th

A Soybean/Wheat Clinic will be held on July 10th from 9-12 at the Fayette County Demonstration Farm, 2770 SR 38 in Washington Courthouse, OH 43160.

The program will include Fungicide Control for Head Scab and Intensive Management Programs by Dr Pierce Paul, Hessian Fly and Other insect pest of Wheat with Dr Ron Hammond, Foliar Feeding Soybeans with Dr Robert Mullen and Soybean Insect Pest with Dr Hammond.

The program is free and open to everyone. Pre registration can be made by calling 740-335-1150 by July 2nd.

The Western Agricultural Research Station Agronomy Field Day in South Charleston, Tuesday, July 10, from 2-5 p.m. Talks will be given while touring research plots, allowing participants to discuss with state specialists exactly what the crop has suffered through so far this year. Certified Crop Advisor CEUs will also be available at this event.

Topics include:
• Phosphorous and potassium management and nitrogen use requirements from Robert Mullen, OSU Extension, state Soil Fertility Specialist.
• Corn weed control issues from Mark Loux, OSU Extension, Weed Control Specialist.
• Foliar disease of corn and foliar fungicides from Pierce Paul, OSU Plant Pathologist for corn and wheat.
• Corn insect update from Bruce Eisley, OSU Extension Research Associate, Department of Entomology, corn insect specialist.
• Emerging Corn Production Issues from Peter Thomison, OSU Extension, Corn Production Specialist.

For more information contact Harold Watters, OSU Extension in Champaign County at 937-484-1526, watters.35@osu.edu or Joe Davlin, Research Assistant, Western Agricultural Research Station, 937-462-8016, davlin.1@osu.edu.

The Western Agricultural Research Station is located at 7639 South Charleston Pike, just south of I-70 on SR 41 between Springfield and South Charleston in Clark County.

The OSU Weed Science Field Research Tour will be held at the OARDC Western Agricultural Research Station on Wednesday, July 11. The tour, which is self-directed in nature, starts at 9 am and runs until noon. OARDC Western Agricultural Station is north of South Charleston on State Route 41, approximately 5 miles south of Interstate 70.