C.O.R.N. Newsletter 2006-25

Soybean Aphid Update

Authors: Ron Hammond, Bruce Eisley

Although aphid numbers are starting to slightly increase in Ohio and surrounding states, they remain greatly below the economic threshold level of 250 aphids per plant. They are easier to find both in numbers of plants with aphids, and the density of aphids on any single plant. Hopefully we should be out of the woods within the next few weeks as soybeans enter the later growth stages of pod fill and seed development. As always, keep scouting to prevent isolated problems. But remember, the threshold, or the time to take action, is 250 aphids per plant with a rising population. This threshold has been established to keep the aphids from reaching much higher numbers that can go into the 1000s per plant. You should NOT spray to keep from reaching the 250 aphid threshold; you use the 250 threshold to keep the aphids from reaching those larger densities! A level of 250 aphids per plant will NOT cause a yield reduction.

This late summer increase in aphid populations was expected, and is similar to what we saw two years ago in 2004 during the last “low” aphid year. These are the aphids that will produce further generations leading to the overwintering generation in the fall. We will plan on monitoring aphid flights this fall and subsequent aphid colonization on buckthorn, the aphid’s overwintering host to determine the potential for problems next summer. Although there is not much buckthorn in Ohio and thus, we assume little overwintering, we do know of a few locations where the plant exists that we can determine the insect’s overwintering potential. Stay tuned!

The Late Season Diseases are Making an Early Appearance

Authors: Anne Dorrance

Phytophthora, SDS, Diaporthe stem canker AND Sclerotinia were all identified in soybean fields in Ohio last week. From the windshield these four diseases can all look very similar, below is an easy checklist on how to tell many of these apart. Pictures and links to factsheets can all be found at www.oardc.ohio-state.edu/ohiofieldcropdisease/.

Phytophthora stem rot, plants will first turn yellow, sometimes unevenly and wilt, at the base of the plant, a chocolate brown canker will colonize from the base of the plant up the stem. The roots will be very rotted.

Diaporthe stem canker, again the plants will turn yellow, leaves may turn necrotic between the veins, very similar to Brown stem rot and sudden death syndrome, but it is a paler yellow. At the base of the stem, there will be canker, usually at the 2, 3 or 4 node of the plant. On this canker, it will have a black scurfy appearance or with a hand lens you will see black dots.

Sudden death syndrome – This disease has a striking pattern in the leaves, necrosis (browning) between the veins which is surrounded by yellow. The key to diagnosing this disease is that the roots are rotted and if you cut open the base of the plant, the crown, it is typically a gray color, not bright white. The pith is white and in good shape up the plant. This disease is caused by a fungus that colonizes the base of the plant and produces a toxin. It is the toxin that causes those symptomatic changes in the leaves.

Brown stem rot – which we have not found, yet; has foliar symptoms very similar to SDS. There is more necrosis, browning of the leaves and the pith turns chocolate brown, this pith browning does not necessarily develop from the base of the plant up the stem.

Sclerotinia – this was bound to make a reappearance at some point and this may be the year. Fields that had canopy during flowering are the ones that have the highest likelihood of this occurring. The tops of the plants will wilt, sometimes it will be yellow first, then a gray color, but some place on the stem or side branch there will be a canker. If the conditions in the field are wet, it will be white and fluffy. If the conditions in the field are dry, it will be a pale white color, the stem will be hollow and there may be black hard structures, look similar to mice droppings on the surface or inside the stem.

All of these diseases can be managed, first with resistance in the variety, by improving soil drainage and/or rotation.

Warm Nights Reduce Grain Yield Potential

Authors: Peter Thomison, Jim Beuerlein

High night temperatures (in the 70s or 80s) can result in wasteful respiration and a lower amount of dry matter accumulation in plants. The rate of respiration of plants increases rapidly as the temperature increases, approximately doubling for each 13 degree F increase. With high night temperatures more of the sugars produced by photosynthesis during the day are lost; less is available to fill developing kernels, thereby lowering potential grain yield. Past research at the University of Illinois indicates that corn grown at night temperatures in the mid 60s outyields corn grown at temperatures in the mid 80s. Corn yields are often higher with irrigation in western states, which have low humidity and limited rainfall. While these areas are characterized by hot sunny days, night temperatures are often cooler than in the Eastern Corn Belt.

Low night temperatures accounted in part for Ohio’s record high corn yields in 2004. During most of the 2004 growing season, temperatures were below normal. From late June through most of August, a period of time that included most of the grain fill period in corn, weekly temperatures were cooler than normal - as much as 4 to 7 degrees below normal in August. Cool night temperatures in 2004 reduced respiration losses during grain fill. The absence of moisture stress was especially important during grain filling. In parts of the Ohio where rainfall was below average during grain fill in July and August, cooler than average temperatures also minimized moisture stress.

Comments about Weed Control in Soybeans

Questions have been coming in about still spraying for weeds in soybeans. Most April and early-May planted soybeans are beyond the R3 stage of development and some are at the R6 stage which are only about 40 days from harvest. Therefore, it is too late to spray most early and mid-planted soybeans, including Roundup Ready. The Roundup branded products are not to be applied to soybeans beyond the R2 stage of development, which has been exceeded in most fields. http://corn.osu.edu/index.php?setissueID=140#E of the C.O.R.N. Newsletter for more details. Other reasons for not applying any more herbicides to soybeans this season include decreased soybean yield due to herbicide injury, decreased yields from driving over the soybeans, and increased risk of selecting for herbicide resistant biotypes because the weeds are too large for the amount of herbicide that can be used.

For those fields that have weeds coming out over the canopy at this time, weed seeds will be returned to the seedbank. Therefore, mark these fields and plan a weed control program next year to maximize weed control. A planned three-pass herbicide program may need to be used for the next two to four years to get the population back into check. A harvest-aid application may need to be used in these fields, especially if harvest will occur before a hard freeze.

The only soybeans that could still have herbicides applied are those planted after mid-June. If late-planted soybeans have not been sprayed yet, please do so immediately to reduce yield loss potential due to injury (absolutely the case for non-GMO soybeans) and competition and to maximize weed control. For Roundup Ready soybeans planted after wheat, that have not been sprayed, apply at least 1.1 pounds acid equivalent/A of glyphosate and preferably 1.5 pounds acid equivalent/A of glyphosate to maximize weed control and decrease the selection for hard to control biotypes.

Twospotted Spider Mites on Soybean

Authors: Ron Hammond, Bruce Eisley

Although most of Ohio has good soil moisture levels, it has come to our attention that there are isolated dry areas around the state because of spotty rainfall. During our sampling last week in north central Ohio, we came across some of these areas and easily found hot spots of twospotted spider mites. Although this would not be a widespread problem, growers in dry areas might want to check their fields for possible mite infestations, especially around the field edges.

Bean Leaf Beetle on Pod Feeding

Authors: Ron Hammond, Bruce Eisley

Although we mentioned soybean defoliators in last week’s newsletter, we wanted to bring up another concern in fields with high numbers of bean leaf beetle. What you are seeing are adult, first generation beetles; there is a good possibility that these same fields might experience high levels of pod feeding when the second generation arrives later this month or early September. Now is a good time to locate fields having high adult numbers that should be watched for pod feeding. This does not mean other fields, especially later-planted fields, will not have significant pod feeding. But it does help to identify those fields that need extra monitoring over the next month. This need is especially important for food grade soybeans where seed quality is more of an issue. We will have further information on pod feeding in a later article.

Determining Proper Moisture for Corn Silage

One of the key steps to producing high yielding corn silage with excellent quality is harvesting the crop with the proper moisture.

Checking corn plant moisture while harvesting a field would be ideal to ensure optimal material is harvested, but not always practical. As an alternative, the kernel milk line method can be used to approximate whole plant moisture. On examining the cross-section of an ear, one will see the starch/milk separation line appear after denting. As the plant matures, that line will move toward the bottom of the kernel. Once the milk line is at the halfway point in the kernel, 90% of the final dry weight is accumulated and the moisture level should be somewhat close to the acceptable range for harvest.

Abnormal weather conditions and hybrid selection may affect the exact moisture content of the plant in relation to milk line position by as much as 2 to 3%. A more accurate test may be in order using a microwave to drive moisture off of a known mass of chopped corn. Dividing the dry weight by the wet weight yields the percentage of dry matter as a decimal. Subtracting that decimal from 1.0 will equal percent moisture in the sample. One way to predict harvest date is to test corn plant moisture at full dent and consider that drydown occurs from 0.5 to 0.75 percentage units every day following. The actual range of ideal moisture desired is determined by the type of storage structure.

Optimal Silage Moisture Content by Silo Type
(from Ohio Agronomy Guide, 14th ed.):

Bunker or Trench: 65 to 70%
Silage Bags: 60 to 70%
Upright Concrete: 62 to 68%
Sealed Upright: 55 to 60%

Silage with moisture levels higher than 70% can cause problems with seepage and the formation of foul-smelling butyric acid, ammonia, and carbon dioxide. Feed quality and palatability will decrease and dry matter losses will increase. Silage leachate has a very high biochemical oxygen demand, that is, it is very efficient at removing dissolved oxygen from surface water. If leachate were to reach streams via ditch or waterway, fish kills could result.

Silage that is too dry is not likely to pack, ferment, and heat adequately, and may result in increased dry matter losses. Total digestibility will decline as plant moisture decreases in the field. Drier materials are better suited to upright silos rather than bunkers or bags.

Silage should be chopped from 5/8 to 3/4 inch lengths, but if the crop is drier than desired, smaller lengths may promote better packing and oxygen exclusion. Very fine particles made with a recutter may pack more dry material in a silo, but palatability decreases as a result.

Unwanted Farm Pesticide Disposal Collection

Authors: Glen Arnold

The Ohio Department of Agriculture, in cooperation with Ohio State University Extension, will be conducting the Clean Sweep Program at three locations in Ohio to collect old or unwanted farm pesticides.

The collections are for only farm pesticides. No paint, antifreeze, solvents, household pesticides, or other non-farm pesticides will be accepted. Farmers and landowners with old, unwanted pesticides (insecticides, fungicides, insecticides, rodenticides and herbicides) are encouraged to dispose of them.

The three sites for collecting pesticides are:

August 16, 2006
Fayette County Airport, Washington Courthouse
9:30 a.m. - 3:30 p.m.
In conjunction with Southwest Ohio Corn Growers Field Day

August 24, 2006
Putnam County OSU Extension Office, Ottawa
9:30 a.m. - 3:30 p.m.

August 31, 2006
OARDC, Wooster
9:30 a.m. - 3:30 p.m.

No pre-registration is required for farmers to bring farm chemicals for disposal and there is no charge. For more information, contact the Ohio Department of Agriculture, Pesticide Regulation Section, at (614) 728-6987.

Western Ohio Agronomy Field Day

The Ohio State University Extension, and Stillwater Watershed and A.C.E. (Agriculture for a Clean Environment) groups are co-sponsoring the Western Ohio Agronomy Field Day on August 9, 2006. The field day will be held at the Darke County Research Farm located at 5105 County Home Rd. Greenville, Ohio (the farm is located at the southwest corner of St. Rt. 127 and St. Rt. 49, just south of the Darke County Jail). Register by calling the OSU Extension Office at 937 548-5215 or email: foster.99@osu.edu.

The program will start at 6:30 p.m. with a discussion of general pesticide application issues which will include drift reduction, calibration and record keeping. A tour of the research test-plots will follow, which includes: Soybean seed treatment plots, and Corn production demonstration plots. In addition, a first year corn rootworm survey study will be on going, participants will be able to observe the procedures for monitoring the corn rootworm in soybean fields and to discuss the economic importance of such a survey.

Presentations will also be given on the following topics:
- Crop Insect Up-date, presenter, Dr. Ron Hammond, IPM and Entomology Specialist, OSU Extension.
- Weed Control Up-date, presenters, Harold Watters and Roger Bender, OSU Extension Agents.
- Soybean Rust and other Disease Up-date, presenter, Dennis Mills, Extension Pathology Program Specialist, OSU Extension.

This educational program is open to the public. CCA credits for Certified Crop Advisors and Pesticide Applicator credits (Core & category 1) will also be provided. For more information contact the Darke County OSU Extension office at (937) 548-5215 or email foster.99@osu.edu.