CORN
Crop Observation and Recommendation Network

August 14 - August 20, 2000
C.O.R.N. 2000-26

In This Issue:

A) Wheat Seed Treatments and Wheat Seed Quality
B) Diagnose What's Wrong with Those Soybeans - Now!
C) Continue Monitoring Adult Corn Rootworm
D) Impact of Root Lodging on Corn Yield
E) Time to Park the Sprayers
F) Request for Weed Seeds

A) Wheat Seed Treatments and Wheat Seed Quality -Pat Lipps CORN Questions

Most wheat producers were very happy with their yields this year, but most were disappointed with the test weights of harvested grain. Wet periods during grain maturation caused several cycles of wetting and drying of the grain. This process causes shriveling of the kernels and low test weights. In some areas of the state, the wet conditions also favored the development of certain diseases that directly affect the seed. These included Stagonospora glume blotch and Fusarium head scab. Fortunately head scab was not severe this year, but some fields had up to 5% of the heads affected by the disease. Stagonospora glume blotch was severe in some fields with up to 80% of the heads being affected. The fungi that cause both of these diseases can invade developing kernels and cause grain shriveling. Seed germination is not greatly affected by shriveling due to wet/dry cycles, but shriveling due to diseases can reduce germination and affect plant stand and/or vigor of the crop in the fall. Early reports of germination rates from the 2000 crop indicate that germination rates are excellent (92-95% germination). However, some lots of seed do have evidence of both Fusarium and Stagonospora seed infection. Seed treatments will improve germination and stand establishment if low germination is due to disease. Additionally, reducing seed infection by using an effective seed treatment is a major management practice to limit development of Stagonospora leaf and glume blotch in the spring.

In Ohio, it is highly recommended to treat winter wheat seed for control of several seed-borne diseases including loose smut, common bunt, Stagonospora glume blotch and Fusarium scab. The seed treatments Dividend XL, Raxil - Thiram, Raxil-XT and Raxil MD contain systemic fungicides that have excellent activity against both loose smut and common bunt at low usage rates. These products appear to have somewhat different efficacy for control of diseases other than the smuts and bunts. Dividend XL is effective in controlling seed-borne Stagonospora, but it is more effective against seed-borne scab at the higher rate (1.0 fl. oz./cwt) than at the lower rate (0.5 fl. oz./cwt). Products containing Raxil are effective against seed-borne Stagonospora and have relatively good activity against seed-borne scab.

To provide effective control of severely scab damaged seed both Dividend and Raxil should be combined with another companion fungicide. The thiram component in Raxil-Thiram improves control of seed-borne Stagonospora and scab. TBZ, sold as LSP Flowable Fungicide by Gustafson, provides excellent control of seed-borne scab. When head scab has caused damage to a wheat crop for seed production, the seed processor should add TBZ to the treatment slurry to improve control of seed-borne scab. Gustafson's LSP material should be used at the 0.25 fl. oz/cwt when used in combination with another seed treatment product for seed-borne scab control. Dividend XL is a combination of Dividend (difenconazole) and Apron XL (mefenoxam) for added protection against Pythium damping off. Raxil XT and Raxil MD contain metalaxyl, the active ingredient in Arpon and Allegiance, and provide control of Pythium damping off. Following is a table listing the relative effectiveness of these products available on wheat:

Table 1. Efficacy of Wheat Seed Treatments
Pythium
Active Common Loose Stagonospora Fusarium damping
Product ingredient bunt smut nodorum (Scab) off
========= ========== ====== ===== ============ ======== =======
Agrosol T Thiram, G N F G F
TBZ

Allegiance Metalaxyl N N N N E

Apron FL Metalaxyl N N N N E

Apron XL Mefenoxam N N N N E

Dividend Difenoconazol, E E E F E
XL Mefenoxam LSP

Thiabendazole N N P G N
Flowable (TBZ)
Fungicide

Raxil- Tebuconazole, E E E G F
Thiram Thiram

Raxil XT Tebuconazole, E E E G E
Metalaxyl

Raxil MD Tebuconazole, E E E G E
Metalaxyl

RTU Carboxin, G G F G F Vitavax- Thiram Thiram
Vitavax Carboxin, G G F G F 200
Thiram
______________________________________________________________________
Efficacy based on labeled rates of active ingredient for each material.
Efficacy rating schedule: E=excellent; G=good; F=fair; P=poor; N=no activity, ND=no data.

B) Diagnose What's Wrong With Those Soybeans - NOW! -Anne Dorrance CORN Questions

This is a great year to look at variety performance under high disease pressure. Plants continue to die throughout those areas which were hit early with Phytophthora. Now is the best time to identify Phytophthora stem rot because it is the only soybean pathogen that will colonize stems from below ground up the stem. You need to get off the 4-wheelers to find the chocolate brown lesions in early dying plants!

We have received many samples of soybeans where the plants are yellowing, the pith tissue is degraded, when you squeeze the stems, they are soft and collapse. There are few if any roots, but the crown appears healthy. We have isolated a number of weak pathogens from these roots at this point, Pythium and Fusarium spp. mainly. The common denominator in all of these samples is that they are from areas of the fields that have remained wet. These plants are most likely suffering the effects of flooding injury and have not had time to re-root. Make note of the variety, some varieties do withstand flooding conditions better than others.

We will begin to see "road-side" symptoms of Sclerotinia stem rot, Diaporthe stem canker, Soybean Cyst Nematode, Brown Stem Rot and Sudden Death Syndrome. Sclerotinia stem canker is beginning to colonize stems, this is the white fluffy mold found on stems. Diaporthe stem canker will appear as a lesion on the 2nd or 3rd node, which girdles and kills the top of the plant. This has rarely reached economically damaging levels, but it's one we like to keep our eye out for. Brown Stem Rot and Sudden Death Syndrome, look very similar, yellow spots, on leaves which will fall of the plants. If you split the stems, brown stem rot, will have a chocolate brown pith, most of the time. This pathogen doesn't always follow the book and we have isolated both fungi from the same plant. Please visit the following websites for more information:

Soybean Disease On-line factsheet available at
==================================================================
Sclerotinia http://ohioline.ag.ohio-state.edu/ac-fact/0045.html
Brown Stem Rot http://ohioline.ag.ohio-state.edu/ac-fact/0035.html
Sudden Death http://ohioline.ag.ohio-state.edu/ac-fact/0044.html Syndrome

C) Continue Monitoring Adult Corn Rootworm -Hal Willson CORN Questions

It is mid-August and field personnel monitoring adult corn rootworm activity in soybean fields on a biweekly schedule should be replacing yellow sticky traps at this time to detect potential movement of adult rootworm beetles from corn in which silks are drying to soybean fields that may be attractive egg laying rootworm adults. If traps are not
employed for monitoring rootworm activity, corn fields may be visually inspected to detect unusual levels of rootworm activity and soybean fields may be sweep net sampled to detect rootworm activity.

A first year corn field that is not impacted with first year corn rootworm will generally exhibit minimal adult rootworm beetle activity if a field is not late planted and no continuous corn is in the immediate vicinity. In general, a first year corn field with above normal rootworm beetle activity can be readily identified by casual walk into the field. If rootworm activity is minimal, one will have to inspect a number of plants closely to find the adults. If rootworm activity is high, one will quickly see the beetles flying about before a visual count is initiated. If significant rootworm activity is detected in a first year corn field, one should make a visual count of beetles per plant to get a fix on rootworm abundance and randomly inspect some root systems for the presence of rootworm feeding injury. Given the favorable growing conditions this season, detection of lodging due to rootworm may be minimal due to root system regeneration following injury.

Sweep net sampling of soybean foliage may provide an indication of potential first year corn rootworm activity. Although the use of yellow sticky traps is regarded as the optimal procedure for monitoring adult rootworm activity in soybeans, a sweep net catch may serve as a useful indicator of rootworm activity where traps have not been deployed. In general, a sweep net sampling of soybeans collects very few adult corn rootworm beetles. However, if a sweep net sample from soybeans averages one or more adults per sweep, such a catch may indicate a potential problem. Since bean leaf beetle activity should be monitored at the present time to detect potential pod injury problems, sweep net sampling of soybeans will provide an indication of both bean leaf beetle activity and first year corn rootworm activity in soybeans. (The issue of bean leaf beetle and pod injury will be addressed in next week's issue of CORN).

Reports have been received from the field that captures on yellow sticky traps in soybeans are running relatively low compared to that of the previous year on some farms. It should be noted that rootworm populations rise and fall from year to year. Furthermore, it should be recognized that the occurrence of economic rootworm injury in continuous corn or areas of first year corn rootworm is more often the exception than the rule in Ohio.

In a few weeks, we anticipate that data on rootworm trap captures will be forthcoming as the six week monitoring survey for first year corn rootworm is concluded. By mid-September, I expect that we will be able to report some initial results on the status of first year corn rootworm in Ohio.

D) Impact of Root Lodging on Corn Yield -Peter Thomison CORN Questions

Strong winds (as high as 50-60 mph in some areas) and heavy rains associated with thunderstorms last week (Aug. 7) caused varying degrees of lodging in northern Ohio corn fields. Although these lodging problems may be related to rootworm injury in some cases, early season saturated soil conditions and soil compaction may have inhibited good nodal root formation and predisposed corn plants to such wind injury. Strong winds can pull corn roots part way out of the soil, a condition referred to as root lodging. If root lodging occurs before mid-grainfill, plants usually recover at least partly by "kneeing up." This results in the characteristic goose-neck bend in the lower stalk with brace roots providing above ground support. Plants exhibiting these symptoms are sometimes referred to as "sled runners."

Although hybrids differ in their ability to resist root lodging, the major factor influencing yield response to root lodging is the developmental stage during which the root lodging injury occurs. If this stalk bending takes place before pollination, there may be little effect on yields. If it occurs later in the season, there may be some yield decrease due to partial loss of root activity.

According to University of Wisconsin study, hand harvested yield reductions were generally 10% or less when wind lodging was simulated at or before the mid-vegetative growth stages, but losses increased up to 15-30% with lodging at late vegetative or early reproductive stages. Combine harvest speed may also need to be reduced to minimize harvest losses if the root lodging occurred after tasseling when stalk curvature will likely be more pronounced and ear heights reduced.

E) ) Time to Park the Sprayers -Jeff Stachler CORN Questions

If non-Roundup Ready soybeans will be harvested in September, then no herbicides can legally be applied now. Roundup Ultra can be applied to Roundup Ready soybeans as long as they are still flowering. Late applications of herbicides in soybeans may cause some slight yield reduction due to direct damage from application equipment. For late planted/double crop soybeans, there are some herbicide options available yet, but any injury to the soybeans now will more than likely cause yield loss. Products that can be used on soybeans if they are harvested after October 18th (65 days before harvest) include: Basagran, Blazer, Cobra, FirstRate, Pinnacle, Resource, Roundup Ultra, Select, Touchdown and 2,4-DB. Roundup Ultra, Touchdown and Gramoxone Extra can be applied as harvest aids for all soybeans.

F) Request for weed seeds -Jeff Stachler CORN Questions

Anyone having some eastern black nightshade, common lambsquarters or shattercane in their crop fields or a non-cropland area that has NEVER or RARELY had Scepter, Squadron, Steel, Detail, Pursuit, Pursuit Plus, Raptor, Pinnacle, Synchrony STS, Beacon, Exceed or Spirit applied to these weeds, please contact Jeff Stachler at 614-292-1393. We are looking for ALS-sensitive eastern black nightshade, common lambsquarters or shattercane in order to test for ALS-resistance in these species. Also, if anyone believes they have ALS-resistant eastern black nightshade, common lambsquarters, shattercane or any other species, please contact Jeff Stachler at 614-292-1393.

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: Andy Kleinschmidt         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 |