C.O.R.N. Newsletter 2012-27

Dates Covered: 
August 21, 2012 - August 27, 2012
Editor: 
Rob Leeds

Weather models indicate dryness and heat will increase going into late August and early September

Drought conditions improved across Ohio in the last month thanks to beneficial rainfall and cooler temperatures. However, going into late August and early September, weather models indicate dryness will increase along with more heat. The outlook calls for below normal temperatures to continue this week with a return to above normal temperatures after that into early and mid September with periods of 90s possible for highs. At the same time, rainfall will be below normal. This will likely increase drought conditions as we go into September but not to the extent that it was this summer. It is not uncommon when you have had a drought and are on the road to recovery you will see improvement and worsen going back and forth with the overall trend to improve. Normal rainfall through September 4 would be about 1.4 inches. Weather models indicate there is a 60% chance of 0.50 inches of rain through then, a 25% chance of 1.0 inches of rain and only a 5% chance of 2 inches. The main message is, anyone who gets normal rainfall from now to early September should consider themselves lucky.

The Stress Degree Days (SDDs)  which is the departure of the maximum daily temperature from 86 accumulated over the growing season has risen to 329 as of August 19. This is in line with 1988 and 1934 but well behind 1936. Above 140 degrees is consider the point where corn yields fall below trend line.

Even though we are expecting a warmer than normal fall, at least through September and early October, with drier than normal soils, we expect a normal frost period. Dry soils promote cool nights. As we get closer to the frost season the National Weather Service Ohio River Forecast Center will update this forecast.

Finally, in the coming weeks, with the low dewpoints and moisture levels, we expect some major swings from morning to afternoon in temperatures sometimes on the order of 30-40 degrees between low and high temperatures.
 

Stink Bugs in Soybeans

Stink Bugs in Soybeans

Last week we mentioned to be on the lookout for the brown marmorated stink bug, although we did not expect it to be a concern.   That thought has changed somewhat over the past week in regards to this potential pest and the rest of the stink bug complex that occur in soybeans.   We have become aware of some soybean fields with much higher numbers of stink bugs than are normally seen, with some fields reaching a level that might need treatment.  Since the article last week, we have had reports of brown marmorated stink bug from a few of fields. With support from the Ohio Soybean Council, scouting trips have confirmed brown marmorated stink but in soybean.  At this time only adults are being seen, but observations last year suggest that larger numbers of nymphs will start occurring within a few weeks.  But we are also seeing greater numbers of the green stink bug and a smaller stink bug that is also green but with a reddish shoulder, this latter one being called the red shouldered stink bug.  This is a new stink bug that has not been seen very much in Ohio.  It is not the red banded stink bug that is causing significant concern in southern states, but it nevertheless might be a potential problem.  At this time, little is known about its damage potential.  For the time being, we recommend grouping all stink bugs together for determining the need for treatment.  Through Ohio Soybean Council support, we will expand our sampling for stink bugs over the next few weeks across the state.

To sample for stink bugs, take multiple 10-sweep samples with a sweep net in multiple locations throughout the field. Average the number of stink bugs in the 10-sweep samples. The threshold to treat is 4 or more stink bugs, adults or nymphs. If soybeans are being grown for seed, the threshold can be dropped to 2 or more stink bugs.  Pods should still be green.  We would mention that we have already been in fields that meet this criterion.  Because stink bugs often occur mainly on the field edges, especially next to woody areas, we suggest sampling both field edges and within the field to determine which parts of the field might require treatment.  See the soybean insect images page, http://entomology.osu.edu/ag/pageview3.asp?id=1152 , on our web site for pictures of the various stink bugs.  The ones most likely to be in Ohio soybean fields include the brown marmorated stink bug, the green and red shouldered stink bugs, the brown stink bug (with rounded shoulders) and the spined soldier beetle (with pointed shoulders), this last one actually being a beneficial predator.

Soybean Yield Estimates

With hot and dry weather conditions, many growers are curious about soybean yield potential.  It is difficult to accurately predict soybean yield because of plant variability, but estimates become more accurate as the growing season progresses.  Soybean yield will be influenced by rainfall (or lack of rainfall) through August as seeds are filling. 

To estimate yield, four soybean yield components need to be considered: plants per acre, pods per plant, seeds per pod, and seeds per pound (seed size).  A printable worksheet to estimate soybean yield can be found by clicking here. (http://agcrops-cms.cfaes.ohio-state.edu/links/Estimating%20Soybean%20Yield%20Worksheet.pdf/view)

1. To calculate plants per acre, count the number of pod-bearing plants in 1/1,000th of an acre.  In 7.5-inch row spacing, count the number of plants in 70 feet of row.  In 15-inch row spacing, count the number of plants in 35 feet of row.  In 30-inch row spacing, count the number of plants in 17.5 feet of row. 

2. To estimate pods per plant, count the number of pods (containing one or more seeds) from 10 plants selected at random.  Divide the total number of pods by 10 to get the average number of pods per plant.

3. To estimate the number of seeds per pod, count the number of seeds from 10 pods selected at random.  Generally, the number of seeds per pod is 2.5, but this number can be less in stressful environmental conditions.  Divide the total number of seeds by 10 to get the average number of seeds per pod.

4. To estimate the number of seeds per pound (seed size), assume that there are 3,000 seeds per pound.  If the soybean plants experienced stress, seed size will be reduced, and it will take more seeds to make one pound.  Use a seed size estimate of 3,500 seeds per pound if smaller seeds are expected because of late season stress.

Using the above estimates, the following formula is used to estimate soybean yield in bushels per acre:bushels per acre = [(plants/1,000th acre) x (pods/plant) x (seeds/pod)] ÷ [(seeds/pound) x 0.06]

Farm Pesticide Disposal

The Ohio Department of Agriculture will be sponsoring a pesticide collection and disposal service for farmers wishing to dispose of unwanted pesticides. Be aware that the collection is for farm chemicals only. Paint, antifreeze, solvents, and household or non-farm pesticides will not be accepted.

The collection will take place on Aug. 27, 2012 from 10:30 a.m. to 2:30 p.m. at the parking lot of the Wood County Junior Fair Building, 1380 W. Poe Road, Bowling Green, OH 43402.

To pre-register, or for more information, contact the Ohio Department of Agriculture at 614-728-6987.

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About the C.O.R.N. Newsletter

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.