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July 28 to August 3, 2001
C.O.R.N. 2001-24
In This Issue:
A) Was Pollination Affected By Dry Weather?
B) Soybean Aphid And Management Considerations
C) Two Spotted Spider Mites
D) Late Season Soybean Weed Control
E) Yellow Beans, Short Beans And Ugly Beans B
F) Precision Agriculture Guidance Demonstrations And Information
At Farm Focus- August 7th And 8th
Hot, dry weather can interfere with pollination. Drought conditions often slow growth of silks which can result in failure of silks to emerge in time to receive pollination.
Two techniques are 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 10 to 14 days 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 if 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. Recent studies indicate that silks can remain receptive to pollen up to 5 to 6 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.
The general thought among researchers in the Midwest is that it will take 1000+ or more aphids per plant, and a lot of plants with this number of aphids throughout the field, before treatment should be considered. There are apparently some thresholds being mentioned in the Midwest that suggest treatment should occur at 50 or more aphids per plant. There is no research we know of that supports this low threshold. There is some information out of a Midwestern state from last year suggesting 80-100 per leaflet, but remember that means almost 300 per leaf (a single leaf that is heavily infested will not cause a loss). This would probably get into the 1000+ aphid category.
There are a number of factors that growers should consider before applying an insecticide for aphid control. The first is that most fields do not have these large populations. Also, our experience so far suggests that beneficial insects are doing an outstanding job in helping to keep the aphid numbers down. In fact, experiments at Wooster are a failure because the lady beetles are thick in the plots and not allowing the aphids to build up. Information coming from other states also suggest that beneficial insects are going an outstanding job.
The other consideration related to taking action comes from experiences in
other states that have larger populations and have done some insecticide work.
Other states have observed aphid populations at higher densities in treated
plots compared with check or control plots that were not sprayed, where beneficial
insects were allowed to feed. Insecticides will not kill 100% of the aphids,
there are just too many of them. An effective insecticide killing 90% of the
aphids still will allow 100+ aphids on the
plant. However, these insecticides do a very good job at greatly reducing the
beneficial insects, and thus, eliminating a natural aphid control. The thought
is that insecticide use might allow for the resurgence of aphids because of
the destruction of the natural enemies.
In terms of insecticides that should be used, information being provided by
other states suggest that some of the organophosphates might be more effective
against the aphids than the newer pyrethroids. Some of our northern neighboring
states have had larger populations and have been able to conduct insecticide
studies (our fields we had set up appear to be going down in aphid populations
rather than up, most likely because of the beneficial insects). Thus, a decision
to treat should not be taken lightly. You should have a significant infestation,
where yellowing is perhaps occurring throughout the field, most plants having
large numbers of aphids, and beneficial insects not doing the job. In the fields
found in Summit, the decision was made NOT TO SPRAY. Even though aphids were
numerous, the heaviest infested areas had large numbers of beneficial insects,
and some areas appeared to have aphids going down in numbers. Remember that
there are lady beetles, minute pirate
bugs, and lacewings to name a few that are feeding on aphids, plus there are
fungal pathogens which will help to reduce aphid populations.
A list of criteria for treatment, suggested by Michigan State, includes the
following. These factors are based on their experiences with the aphid from
last year and this year.
An additional suggestion being mentioned throughout the Midwest is to leave unsprayed strips as a refuge for beneficial insects. This will allow the lady beetles and other "good" insects the chance to repopulate the field and continue to help control the aphids.
The warm weather and continued lack of rainfall in some areas of the state have increased two spotted spider mite (TSSM) populations, and we are beginning to experience outbreak situations. Large TSSM populations are being reported, and treatments are being required. Growers should inspect their fields for the mite and take action if treatment is warranted. Last week's CORN newsletter gives information on when to take action. If TSSM problems are occurring on the edge of the field, a treatment of the border rows might be possible. However, if TSSM are occurring throughout the field, the entire field should probably be sprayed. Remember that if soybean aphids are present, fields should be watched for possible flare-ups of aphid populations.
Weeds are starting to show up over the top of soybean canopies and people are wondering whether herbicides should be applied. If soybeans are over 12 inches in height and weeds are only now coming out over the canopy, then these weeds should not reduce yield. There are certain weeds such as eastern black nightshade, morningglories, and burcucumber that are a real problem at harvest time and may need to be controlled at this time. However there are several products that should not be used any more this season due to harvest restrictions. Products that should not be applied any more this season because the harvest restriction is 85 days or greater are Backdraft, Extreme, Flexstar, Fusilade, Fusion, Pursuit, Raptor, Reflex, and Scepter. The products listed below have the following harvest restrictions based upon the label:
As can be seen, early-planted, non-Roundup Ready soybeans can only be sprayed with Galaxy, Storm, Ultra Blazer, Cobra, or Basagran. The Roundup Ready soybeans have greater flexibility in that they may be sprayed with glyphosate up to 7 or 14 days before harvest, depending upon the product.
With the warm weather forecasted for this week, if small (late-planted) soybeans need to be sprayed, we suggest using herbicides and or adjuvants that are the least injurious to the soybean. Injury at this time of the year to small soybeans can cause yield loss, especially if your area is dry.
Some soybean fields in the state this year have areas with yellow plants. Do not assume what may have caused the yellowing. Take the time to get an accurate diagnosis of the problem. Numerous factors can cause yellow beans; Soybean Cyst nematode (SCN), Phytophthora root rot and stem canker, root rots in general, Sudden Death Syndrome (SDS) as well as nutrient deficiencies and environmental stresses. August is a good time to begin digging up beans with symptoms to take a look to see what the problems are.
SCN is present in all counties where soybeans are produced. This nematode can be present at low numbers, but with continuous soybeans and shorter rotations, population levels can increase dramatically. Target locations with early maturing beans, areas where there has been movement of equipment. Dig up the beans and look for the female cyst on the roots.
Phytophthora stem canker symptoms begin as a wilt, followed by overall yellowing as the canker moves up the stem. Target low areas of the field, this will be especially prevalent in areas of the state that have received rains which saturated the soils.
Poor root development due to early infections caused by a number of pathogens during the May rains will continue to plague some fields. These fields should be considered for tiling to increase water drainage and possibly deep cultivation to alleviate soil compaction. Few roots will be present on plants in these fields and plants will be stunted.
SDS is quite prevalent in fields in states to the west of Ohio, however in Ohio, we have only confirmed its presence in approximately 300 acres. All of the locations in Ohio had very high SCN populations. One of the most striking symptoms of SDS is the yellow spotting on upper leaves which then turns to brown areas between the veins. Yellow spots can also be indicative of brown stem rot another soybean disease. Take the time to look at the roots for SCN.
All of these pathogens are in the soil and they possess very good survival strategies. The best management tactic, host resistance through variety selection, can only be effective if problems are identified in a field this year so a resistant variety can be chosen for that field the next time it is planted to soybeans.
Custom applicators, farmers and interested persons in precision agriculture can drive demonstration vehicles that will have one of the current guidance systems that are available on the market today. There will be guidance systems from John Deere, Mid-Tech, RHS Outback, Satloc, Smucker and Trimble. In addition to the demonstration area there will be a precision agriculture information tent. Precision ag. specialists from Ohio State University Extension, Agri-Tech and Agro-Chem will be available to answer questions.
Farm Focus will be held August 7th and 8th in Van Wert County.
For more information on Farm Focus visit http://www.farmfocusshow.com
or call 419-238-1214. For more information on the GPS guidance program at The
Ohio State University contact Matthew Sullivan at Sullivan.64@osu.edu
or 614-247-6286.
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.
State Specialists: Pat Lipps, Ann Dorrance, and Dennis Mills (Plant Pathology), Jeff Stachler and Mark Loux (Weed Science), Ron Hammond and Bruce Eisley (Entomology), and Peter Thomison (Corn Production), Matt Sullivan (Ag Engineering). Extension Agents: Steve Prochaska (Crawford), Dennis Baker (Darke), Howard Siegrist (Licking), Roger Bender (Shelby), Ray Wells (Ross) and Barry Ward (Champaign).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.
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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.
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