CORN
Crop Observation and Recommendation Network

October 16 - October 29, 2000
C.O.R.N. 2000-35

In This Issue:

A. Will the Soybean Aphid be Your Next Pest Nightmare?
B. More on Phomopsis Seed Rot, Seed Quality and Germination Testing
C. Grazing Alfalfa in the Fall

A) Will the Soybean Aphid be Your Next Pest Nightmare? - Ron Hammond CORN Questions

A regional meeting on the soybean aphid, a new soybean pest that has been found in the Midwest, was held in Chicago last week. Although only reaching economic levels in Minnesota, Wisconsin, and Michigan, the soybean aphid has been found throughout most other Midwestern states. The aphid was found south into Kentucky and Missouri, and west into central Iowa. The biggest question is what will happen next year and in the following years. The answer is, we do not know. Being a new insect pest in this country, there are more questions than answers. Where and how will it overwinter? What are the treatment thresholds? How can we control it? Under what environmental conditions will the aphid reach economic populations? These are the immediate questions that will be explored in the coming years. The first question will be its capacity to overwinter in the Midwest. The aphid’s overwintering host might be Rhamnus species, probably Rhamnus cathartica, the common buckthorn. We will be examining this species next spring to determine if the soybean aphid has overwintered on it. We will also be conducting surveys next spring to determine the aphid’s spread in Ohio. You can find information along with pictures of the aphid at the following two web sites:

http://www.agric.nsw.gov.au/Hort/ascu/insects/aglycin.htm and
http://www.msue.msu.edu/ipm/CAT00_field/FC08-17-00.htm#1

For more information about the aphid in Ohio, contact Ron Hammond at 330-263-3727 or hammond.5@osu.edu.

B) More on Phomopsis Seed Rot, Seed Quality and Germination Testing – Anne Dorrance and Jim Beuerlein CORN Questions

We have received several questions this week on how to store and manage soybean seed for replanting next spring. For conventional soybeans, select only the best, disease-free fields for seed to be used next spring. Phomopsis is a fungus that will colonize seed giving it a white fuzzy appearance. Infections can range from heavily colonized seed which is already dead, to seed that has a small amount of infection but will die when planted next spring. If this seed is stored overwinter under adequate moisture conditions, the fungus will continue to colonize the seed, and killing more seed. If the seed is stored at less than 14% moisture – the fungus will no longer grow because the moisture conditions are not favorable.

For the highest quality seed follow these guidelines -

1. Select the best, disease-free fields for seed
2. Clean the seed prior to storage
3. Store the seed under cool dry conditions and maintain moisture at 14% or below.
4. Control the moisture in seed throughout the winter by aeration as needed.
5. Complete a germination test on the seed, late March or early April prior to planting.
6. Be sure to handle seed gently and as little as possible to avoid mechanical injury. Seed that is very low moisture (below 12%) is prone to splits and mechanical damage. For example: augers should be full and run at slow speed to avoid mechanical injury.

Finally, seed lots with Phomopsis will most likely need a fungicide seed treatment next spring to ensure good stands.

There are several types of seed germination tests. Each type of test focuses on a different problem. A warm germination test is all that is needed for Phomopsis. The following is excerpted from our seed treatment bulletin which can be found on the web at GOTOBUTTON BM_1_ http://ohioline.ag.ohiostate.edu/b639/b639_2.html.

Seed Germination Tests:

The warm germination test reflects the stand producing potential of a seed lot under ideal planting conditions. Usually 400 seed from each seed lot are placed under moist conditions on blotters, rolled towels, or sand and maintained at 77 degrees F for about seven days. At the end of this period the seedlings are categorized as normal, abnormal, or diseased, and dead or hard seeds. The percentage germination is calculated from the number of normal seedlings from the total number of seeds evaluated.

The cold germination test is designed to measure the ability of seeds to germinate under high soil moisture content and low soil temperature. This vigor test simulates early season adverse field conditions and usually represents the lowest germination that would be expected from a seed lot planted under such conditions. Actual field germination would normally fall between the cold test result and that of the warm germination test. Seeds are planted in a sandsoil mix at high moisture content and maintained at 50 degrees F for seven days. The test is then placed at 77 degrees F for four days. The percentage of healthy seedlings that emerge at least one inch above the soil is reported.

The accelerated aging test estimates the carryover potential of a seed lot in warehouse storage. The seeds are exposed to high temperatures and high relative humidity for short periods of time that cause seed deterioration. Seed are suspended over water in a chamber for 72 hours then tested in a standard warm germination test. This test only would be used on seed whose longevity was in question.

If growers wish to use binrun seed and have not had a germination test conducted by a competent laboratory, they can get an approximate germination test using the following procedure in their own home.

Place two paper towels in the bottom of a dish or tray, one on top of the other; wet the towels thoroughly and tilt the tray up on one end so that excess water runs off the tray. Select a random sample of 100 seeds from the seed lot and place them in between the moist paper towels. Put the tray in a plastic bag and tie the end shut to prevent the towels from drying out. Place the tray in a location of diffuse, not direct light, such as a north window. The location should be warm enough (75 to 85 degrees F) for good plant growth. An ideal location is with well growing house plants. After five to seven days, open the plastic bag and count the number of germinated seed with intact tap roots and shoots. Do not count moldy seed or diseased seedlings. Testing 400 seeds in this way will give a good indication of the germination percentage.

C) Grazing Alfalfa in the Fall - Mark Sulc CORN Questions

Grazing alfalfa in the fall is of interest because of its high quality and the fact that making hay is difficult this time of year. Producers must weigh the opportunity for gain with fall grazed alfalfa against the risk of subsequent stand injury. Anytime alfalfa is defoliated in the fall there is increased risk of winter injury. How much risk is dependent on many variables. Physiologically, alfalfa needs a fall rest period to accumulate carbohydrate and energy reserves for the winter. Complete defoliation during the critical fall period (mid September to a killing frost) interrupts this process and can be very harmful to the stand. Grazing can be controlled so alfalfa plants are grazed lightly, which should allow photosynthesis and energy reserve accumulation to continue. Some studies have demonstrated that light fall grazing is less harmful than complete defoliation.

If grazing alfalfa during the fall, make sure that at least 8 inches of active growth remains at all times. To accomplish this, rotate animals more frequently or reduce stocking rates. With top grazing, animals will be consuming lush, high quality forage. Precautions against bloat are even more important than when the whole plant is grazed. To maximize energy reserves in alfalfa, allow a fall rest period and only graze alfalfa after mid to late October. Better yet, wait until after a killing frost. A killing frost for alfalfa is 25 F for several hours, and often for two consecutive nights. But late fall grazing is not without risk. Removal of plant cover by close grazing can dramatically increase the risk of plant heaving in late winter on heavy soils. Leave at least six inches of stubble going into the winter.

Anytime alfalfa is grazed, and especially during the fall, make sure soils are dry and firm. Grazing alfalfa when soils are soft and wet is a sure recipe for severe damage to crowns and subsequent stand loss over the winter. Frosted and frozen alfalfa does not contain toxic compounds. It is likely, however, that a slightly higher potential for bloat exists for one or two days after a frost or freeze. The safest management is to wait a few days before grazing after a killing freeze, when the forage begins to dry. Always use good bloat management practices whenever alfalfa is being grazed.

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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: Barry Ward         Web Editor: Tom Rosati

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