CORN
Crop Observation and Recommendation Network

October 2 - October 8, 2000
C.O.R.N. 2000-33

In This Issue:

A. Phomopsis seed decay and Soybean viruses - Will this season ever end?
B. Corn Ear Molds and Potential Mycotoxin Problems
C. ALS-Resistant Weeds - What to do?
D. Weed Control in Wheat Stubble

A) Phomopsis seed decay and Soybean viruses – Will this season ever end?- Anne Dorrance CORN Questions

Seed decay--We received several reports from the south, west, central and northwest regions of the state last week of seeds harvested with “the white fuzzies, the brown fuzzies and the purple streaks”. This includes one of my Cobra plots in Morrow County (no, Cobra did not reduce the incidence of seed decay). The fuzzies are mycelium, the body of the fungi that cause Phomopsis seed decay. The purple streaks, commonly called purple seed stain, are caused by a different fungus called Cercospora kikuchii.

White fuzzies - Phomopsis seed decay is one of the most common seed diseases of soybeans. There are three fungi involved, Phomopsis longicolla, Diaporthe phaseolourm var. sojae and Diaporthe phaseolorum var caulivora. All three of these fungi overwinter on the soybean straw and these fungi can be carried on the seed. This fungus is also responsible for poor germination of seed the following spring. Infections occurred on flowers and young pods earlier in the season during the rainy weather. The fungi remain latent on the pods until they begin to mature or turn yellow. These fungi then colonize the seeds and pods during periods of high moisture. Heavily infected seed are badly cracked, shriveled, and moldy. Lightly infected seed appear normal, however these seeds will not germinate or will be weak and rot soon after.

Management of Phomopsis seed decay - harvest soybeans in affected fields as quickly as possible to prevent more soybeans from becoming diseased. If the seed is to be saved for next year, be sure to run a germination test on the seed. If seed lots have a germination of less than 70%, reject the seed lot. Treat seed with germination between 70% and 90% with fungicides that are active against Phomopsis (See seed treatment bulletin 639A, http://ohioline.ag.ohiostate.edu/b639/b639_17.html).

For the fields where the incidence of Phomopsis is high (>30%). The soybean residue in this field will serve as the source of inoculum until it becomes broken down. For no-till production fields, the only option is to rotate until the inoculum levels are reduced. This fungus will look like small black dots in rows on the soybean stems and pods. Otherwise plowing the residue under in the fall should enhance the decay of the soybean straw.

Brown fuzzies. There are several fungi, mainly Alternaria spp. that can infect and colonize seeds. If the infections are severe, they will also reduce germination. Seed generally appear normal, but we have isolated Alternaria from some seeds that are mottled and have black streaks. Infected seed is often the result of physiological damage and weathering that occurred during the production season.

Purple streaks. This is caused by another fungus which overwinters on the soybean debris and soybean seed. This fungus grows on the seed in humid weather and the infections also occurred at flowering. The fungus grows into the seed through the hilum to the seed coat where it produces the characteristic purple streaks. This disease does not affect seed quality, but it will affect food grade beans because of discoloration. For management, no-till fields require rotation and otherwise plow down the residues.

Soybean Viruses. As many of you are aware from articles in Soybean Digest, two soybean viruses appear to be increasing in incidence and at economically damaging levels in some fields throughout the north central region. These have also been referred to as green stem syndrome. The pods are brown, the beans are rattling inside the pods but the stems are still green. In some cases we have collected samples where there are no pods or if they are present they are turned upside down and the whole plant remains green with leaves. Last year we identified two viruses associated with this phenomenon in Ohio, soybean mosaic and bean pod mottle virus with the help from the University of Wisconsin. These viruses can be spread with the feeding of the Bean Leaf Beetle but not Japanese Beetle. Seed transmission, alternate weed hosts and where these viruses overwinter are big unknowns at this time. Because the seed transmission is such a big unknown, the seed from these fields should not be saved. Also, bean leaf beetle should be managed in these areas next year to prevent further spread of these viruses.

B) Corn Ear Molds and Potential Mycotoxin Problems - Pat Lipps CORN Questions

The cool wet weather during the late whorl, silking and pollination growth stages of the corn crop has caused some potential problems with several different ear molds. Corn producers are advised to examine ears to determine the presence of ear molds and to make preliminary assessments of the damage caused in each field. Take notes on which ear rots are present in the field and which hybrids have the greatest amount of ear rots. Make future hybrid choices based on this information. Ears that have had significant bird damage are prone to fungal invasion of kernels.

We have many reports of Diplodia ear rot throughout the state. Incidence in the field has ranged from a few ears scattered in the field up to 35% of the ears damaged in some fields. Diplodia causes a thick white mass of mold to grow on the ear, usually initiating from the butt of the ear and growing toward the ear tip. There have been no reports of Diplodia producing mycotoxins that are harmful to animals in Ohio, but animals may refuse to eat grain with high levels of damaged kernels. Additionally, severely affected grain has low nutritional value. It would be wise for animal producers to correct any ration with Diplodia damaged grain to ensure proper nutritional value.

Gibberella ear rot, is common in some fields. This fungus enters the ear tips through the silk channel. Ears with visible white to pink mold covering the ear tip or more of the ears is characteristic of Gibberella. Gibberella ear rot is generally most severe when rain and wet weather is prevalent during the 7 to 10 days after silking is initiated. Certain hybrids are more susceptible to this ear rot than others. The Gibberella fungus is capable of producing mycotoxins that are harmful to animals. These include deoxynivalenol (Vomitoxin) and zearalenone and T-2 toxin, all of which can cause detrimental effects on livestock. It is advisable to have suspect grain tested for these mycotoxins by chemical analysis before attempting to feed. As a general rule do not feed any grain with 5% or more Gibberella moldy kernels. Hogs and young animals are particularly sensitive to these mycotoxins.

Fusarium ear rot is also common, especially in fields with bird or insect damage to the ears. Affected ears usually have infected kernels scattered over the ear among healthy appearing kernels or are confined to kernels that are damaged. The fungus appears as a white mold and infected kernels sometimes develop a brown discoloration with light colored streaks. Several different Fusarium species are frequently involved, but one common one produces a toxin called Fumonisin. Horses are particularly sensitive to Fumonisin, but cattle and sheep are comparatively insensitive.

When attempting to manage mold affected grain it is very important to be conservative and have the grain tested for the presence of mycotoxins. Some mycotoxins are harmful at very low levels (a few parts per million). There are a number of laboratories that conduct these tests. Knowing which toxins are present and the amount there will help in making decisions of how best to use the grain.

If you observe significant amount of mold in the grain during harvest, your next step should be to prevent further mold growth. Immediately dry the corn to 15%, but if it is going to long-term storage dry it to 13-14% moisture. Keep the grain cool (35-40F) as much as possible. Inspect the grain frequently to monitor moisture levels and any insect problems. Any grain that is to be fed on the farm should be tested for mycotoxin levels if you feel the grain has a mold problem. Dilute contaminated grain with good quality grain and other feed stuffs to meet nutrition requirements and to dilute out mycotoxins. Avoid feeding contaminated grain to the most sensitive animals.

C) ALS-Resistant Weeds - What to do? - Jeff Stachler CORN Questions

We are observing and hearing about reports of ALS-resistant common and giant ragweed in fields throughout Ohio. If you believe that you have any other weeds resistant to ALS-herbicides please contact us, so that we can visit the field and collect seed. We suspect shattercane and eastern black nightshade as being ALS-resistant. The only way to verify the presence of ALS-resistant weeds is to collect seeds, grow plants in the greenhouse, and apply ALS-herbicides to the plants. If you want to have common and giant ragweed tested for ALS-resistance, we will be willing to test some samples. We will accept up to 4 samples per person and will make sure that at least two samples per person are tested in the event that too many are sent to us. The procedure for collecting ragweed seed is as follows: 1. Harvest 6 HEALTHY (no injury or at least very little injury) plants; 2) Harvest at least 80 %, preferably 90 % of each plant; 3) Only harvest the plants when at least 70 %, preferably 90 %, of the seeds are completely brown in color (the seeds are located at the nodes of stems, carefully look for this otherwise they will not grow); 4) Harvest plants that were definitely sprayed and not from the field edge; 5) Harvest plants by cutting them into pieces and placing them in large grocery-sized paper bags (2 bags per sample)(Do not include parts of the stem that do not have seeds); 6) Label the bags with farmer name and/or field name, size of field and date of harvest; 7) Make sure that each bag for each sample is properly identified, so that we can track individual fields; 8) Keep the bags open to dry, but do not allow seeds of one location to get mixed with another location; and 9) Once the samples have dried for at least 3 days they may be shipped. There are some ragweeds that could be harvested at this time, but most will not be ready until the end of this week or next week. Ship samples to Jeff Stachler, The Ohio State University, 223 Kottman Hall, 2021 Coffey Rd., Columbus, Ohio 43210. If you have questions you may contact me at 614-292-1393.

D) Weed Control in Wheat Stubble- Jeff Stachler CORN Questions

Now is the time to begin spraying wheat stubble fields, but the decision to spray should be based upon several things.

• Decide what are the most important weeds to be controlled in the wheat stubble and spray at the right time to achieve maximum control of those species.
• If hemp dogbane, common milkweed, honeyvine milkweed, hedge bindweed, field bindweed, big-root morningglory, johnsongrass, other warm-season perennials, or summer annuals are the target weeds, then get these fields sprayed before a frost occurs, but preferably during a warm-spell.
• For best control of Canada thistle, quackgrass, Canada bluegrass, other cool season perennials, or biennials apply herbicides in mid- to late October, but during a warm-spell. One to two days straight of a light frost usually does not affect the control of these species as long as the herbicides are applied during a warm-spell.
• When targeting winter annuals wait until the beginning of November. The later the better, but extended periods of freezing conditions during most of the day may limit control.
• For maximum weed control, make sure the day before, of and after application is sunny and warm. Preferably have night-time temperatures above 50 degrees F and daytime temperatures above 65 degrees F. Temperatures lower than this, especially at night and with cloudy conditions the day of spraying, can cause reduced control.
• When targeting Canada thistle, quackgrass, Canada bluegrass, johnsongrass and other perennial grasses, control may be reduced when 2,4-D is added to glyphosate products, especially Canada thistle.
• Maximum control of perennial weeds will only be possible if they have reached a certain size. This is variable between species, but 8 to 12 inches in height is the best target.
• To control hedge bindweed, field bindweed, honeyvine milkweed, common milkweed, hemp dogbane, wild four-O’clock, bigroot morningglory, wild carrot, velvetleaf (over 15 inches in height), morningglory and other hard to control weeds apply a glyphosate product equivalent to 2.0 quarts per acre of Roundup Ultra and add 2,4-D ester at 1.5 pints per acre.
• Always add ammonium sulfate (AMS) to glyphosate products to maximize weed control.
• When using glyphosate products other than Roundup Ultra, read the label concerning the addition of a surfactant.

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: Barry Ward         Web Editor: Tom Rosati

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.

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

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

  | C.O.R.N. | Newsletter | Archive | Search | Questions? | Ohioline | Publications |