CORN
Crop Observation and Recommendation Network

July 17 - July 23, 2000
C.O.R.N. 2000-22

In This Issue:

A) Soybean Defoliation Assessment - Hal Willson CORN Questions

Many soybean fields have reached the early bloom stage of development which is stage of growth that is most susceptible to defoliation by foliar feeding insects. During the pre-bloom stages of growth, soybeans were able to tolerate up to 30% levels of defoliation. However, from bloom to pod-fill, defoliation by insect pests should not be allowed to exceed 15%.

At the present time, adults of the 1st generation of bean leaf beetles are becoming active, outbreaks of Japanese beetles have been reported, and grasshoppers mostly in the nymph stage appear to be more abundant than normal. The combined effect of such a complex of insect defoliators may cause levels of defoliation that exceed the 15% action threshold and may warrant application of a rescue treatment.

Where one or more pest populations are causing economic levels of defoliation, the bottom line for deciding whether a rescue treatment is warranted or not depends on an accurate assessment of defoliation. It is relatively easy to overestimate insect defoliation. Thus, it is important that defoliation assessment be based on a random sampling procedure that reduces the possibility for error.

A minimum foliar sample should include the collection of trifoliate leafs from the top, middle and lower portions of 10 randomly selected plants. From each trifoliate one should discard the most and least damaged leaflets. At this point one should have 30 leaflets upon which the defoliation estimate should be based. The process may be repeated in various locations of a large field if defoliation appears to be significantly different from one area of a field to another. It is important that one not sample from the perimeter of a field where Japanese beetle and grasshopper activity tend to be high. Illustrations of insect defoliation levels are presented in various Extension publications such as the OSUE Field Crops Pest Management Circular #22 on Soybean Insect Defoliation Assessment, which can be retrieved from the Ohioline website or from the OSUE Corn, Soybean, Wheat and Alfalfa Field Guide (Bulletin 827).

B) Field Crops Day at the Northwestern Branch - Ed Lentz CORN Questions

OARDC's Northwestern Branch, 4240 Range Line Rd., Custar, Ohio 43511, will host a Field Crop Day on Tuesday, July 25, 2000, from 6:00 to 9:00 p.m., at the research farm. Wagon tours promptly at 6:00 p.m.

Program topics and Speakers include: "Nitrogen Management Effects on Nitrate in Tile Effluent," Don Eckert, OSU; "Exploring Market Opportunities: How can we add value?," Mark Koenig, OSUE Sandusky County; "Comparing Tillage Costs," Robert Fleming, OSUE Farm Management Specialist; and "Is strip tillage a viable option for Northwest Ohio corn production?," Alan Sundermeier OSUE Henry County.

C) . Late Summer Forage Establishment - Mark Sulc CORN Questions

Late summer can be an excellent time to establish forage crops. The most critical factor to successful summer seeding is having adequate moisture and planting early enough to ensure good stand establishment before a killing freeze. It is very risky to place seeds into bone-dry soil and hope for rains to come. But if moisture is available and seedings are made early (late July to mid August), seedlings emerge rapidly and become well established before winter. Successful summer seedings can provide yields the following year of nearly full yield potential of established stands.

The following steps will improve the chances for successful stand establishment:

1. Soil test and apply needed lime and fertilizer and control problem perennial weeds ahead of seeding. A preplant incorporated herbicide is usually not required when using tillage to prepare seedbeds. Post-emergence herbicides can be used in late fall if winter annual weed problems develop.
   
   
2. Prepare a very firm seedbed if using tillage. A loose seedbed dries out quickly. Avoid deep tillage right before seeding, but complete it several weeks ahead of seeding so there is a greater chance for rainfall to settle the soil before final seedbed preparation. A cultipacker or cultimulcher is an excellent last-pass tillage tool. The soil should be firm enough for a footprint to sink no deeper than 3/8 to 0.5 inch.
   
   
3. Plant seed shallow and in firm contact with the soil. Drills with press wheels usually provide the greatest success in the summer. Broadcasting seed on the surface without good soil coverage and without firm packing is usually a recipe for failure in the summer.
   
   
4. No-till seeding is an excellent way to conserve moisture, provided weeds are controlled prior to seeding. No-till also saves time and fuel. Remove all straw after small grains. Any remaining stubble should either be left standing, or clipped and removed. Do not leave clipped stubble on the field as it will form a dense mat that will prevent good emergence. CAUTION: No-till or reduced-till summer seedings of legumes are at risk of infection by Sclertotinia crown and stem rot, especially in fields where clover or alfalfa were present recently. Planting from mid- to late-August will dramatically increase the risk of damage by this disease compared with planting earlier, so plant legumes as early as possible and do not no-till where clover was grown recently.
   
   
5. Use high quality seed of known varieties. Cheap seed often results in big disappointments and shorter stand life. Make sure legume seed is inoculated with the proper rhizobium inoculant. If the seed is already inoculated in the bag, make sure it was stored in a cool environment, otherwise you should re-inoculate the seed to ensure viable rhizobium. Some reports have shown positive results from coated seed, especially under less than favorable conditions, but other reports have shown no benefit to coated seed.
   
   
6. Seed when soil moisture is adequate for germination and early seedling growth, or a strong rain system is in the forecast. Do not seed into a very dry seedbed, as there may be just enough moisture to germinate the seed but not enough for seedling establishment.
   
   
7. Do not use a companion small grain crop, as it will compete for moisture. If seeding on erosion prone soils, consider no-till seedings.
   
   
8. Seed early. Seedlings require 6 to 8 weeks of growth after emergence to have adequate vigor to survive the winter. Seed no later than August 15 in northern Ohio and by September 1 in southern Ohio. Slow establishing species like birdsfoot trefoil or reed canarygrass should be planted in early August or late July. Fast establishing species like red clover, alfalfa, and orchardgrass can be seeded up to the dates listed above if moisture is present. Kentucky bluegrass and timothy can actually be seeded 10 to 15 days later than the dates listed above. Keep in mind that the above dates assume sufficient moisture to establish the crop. Dry soils conditions and much delayed emergence will in essence provide the same risks as late plantings.
   
   
9. Scout new summer seedings for insects and weeds that will compete with seedling establishment. Watch carefully for any insect damage on legumes soon after emergence.
   
   
10. Do not harvest new summer seedings this fall. The only exception to this rule is perennial ryegrass. If perennial ryegrass has tillered and has more than six inches of growth in late fall, clip it back to 3 to 4 inches before snowfall.
    
    
11. Scout new seedings for winter annual weeds in October to November, and apply herbicides as needed. Winter annual weeds are much easier to control in late fall than in the spring.
    
    
12. Summer-seeded fields should be harvested a little later than established stands next spring. This will allow plants to become well established and build root reserves for strong regrowth.

D) Evaluating Defoliation Damage in Corn from Hail at Pollination (Thomison) CORN Questions

I've received several reports that over the weekend hail storms caused localized damage to crops in western Ohio. Severe thunderstorms accompanied by hail and strong winds have the potential to cause considerable damage to corn. The extent of the damage is dependent on the corn crop's stage of development. Hail affects yield primarily by reducing stands and defoliating plants. Defoliation usually results in most of the damage. The corn plant is generally little affected by hail prior to the 6 to 7 leaf stage because the growing point is below the soil surface and in the leaf whorl. However, once the growing point is elevated above the soil surface due to internode elongation, the plant grows rapidly and becomes increasingly vulnerable to hail damage up through the tasseling stage which is the most critical period.

The table below indicates the range of yield losses that can be expected due to defoliation. Based on estimates of the National Crop Insurance Association, if 100% of the leaf is destroyed by hail at the 17-leaf stage, which occurs shortly before tasseling, a corn plant may lose up to 72% of its yield potential. At tasseling a corn plant may lose 100% of yield potential with 100% defoliation. Once past tasseling, hail causes progressively less damage throughout grainfill.

Leaf damage by hail usually looks much worse than it really is. 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 occurred (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 regrowth.

For more information on evaluating hail injury, consult p. 47 in the OSU Extension IPM Corn, Soybean, Wheat, and Alfalfa Field Guide (Bulletin 827).

Estimates of percent yield loss in corn due to leaf defoliation (adapted from National Crop Insurance Association's "Corn Loss Instructions.")

E) Assessing Success of Pollination in Corn - Peter Thomison CORN Questions

There are two techniques commonly used to assess the success or failure of pollination. One involves simply waiting until the developing ovules (kernels) appear as watery blisters (the "blister" stage of kernel development). This usually occurs about 1 " weeks after fertilization of the ovules. However, there is a more rapid means to determine pollination success.

Each potential kernel on the ear has a silk attached to it. Once a pollen grain "lands" on an individual silk, it quickly germinates and produces a pollen tube that grows the length of the silk to fertilize the ovule in 12 to 28 hours. Within 1 to 3 days after a silk is pollinated and fertilization of the ovule is successful, the silk will detach from the developing kernel. Unfertilized ovules will still have attached silks. Silks turn brown and dry up after the fertilization process occurs. By carefully unwrapping the husk leaves from an ear and then gently shaking the ear, the silks from the fertilized ovules will readily drop off. Keep in mind that silks can remain receptive to pollen up to 10 days after emergence.

The proportion of fertilized ovules (future kernels) on an ear can be deduced by the proportion of silks dropping off the ear. Sampling several ears at random throughout a field will provide an indication of the progress of pollination.

F) Organic Corn Variety Trials - Phil Rzewnicki CORN Questions

Twelve corn varieties are being grown in a multi-farm testing program across the state this year. The project is being sponsored by a North Central SARE producer group grant. Some support is also being provided by OARDC's Organic Food & Farming Organic Research and Education (OFFER) program. The twelve varieties were selected by growers with long term experience in certified organic grain production. Test strips are located side by side on 14 participating organic farms and 4 OSU conventional corn performance test sites.

The purpose of the project is to select varieties possessing characteristics that perform well within typical organic growing conditions. These include such factors as marginal nitrogen environments and mechanical weed control. Early season data are already showing distinct differences among the varieties for germination, days to emergence, plant height and rate of growth. Participating farmers are collecting time sensitive data themselves such as emergence dates, tasseling dates and silking dates.

The twelve varieties include feed grade hybrids, food grade hybrids and two open-pollinated varieties. The corn at all the sites is performing well. It appears the project will produce some interesting and useful data for the increasing number of organic grain producers present in Ohio. Additional data to be collected will be leaf tissue analysis, grain quality, corn/ear height ratios, leaf angle and the usual harvest time performance data.

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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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