C.O.R.N. Newsletter 2007-25

Soybean Aphid is Hitting Northeast Ohio

Authors: Ron Hammond, Bruce Eisley

After a waiting game to see if the soybean aphid would occur at economic levels in Ohio, it has finally happened. As discussed in the “pest alert” we placed in the C.O.R.N. newsletter last Thursday, the soybean aphid has reached or gone over threshold is many fields in extreme northwest Ohio and in the north central counties bordering Lake Erie. Having received word last week that outbreaks were occurring in Ashtabula County, we made a visit on Thursday to look at the situation. Indeed, a few fields were found with populations well above threshold. These fields had honey dew and sooty mold already covering the plants, some fields at or just above threshold, and other fields with moderate aphid populations. Counties surrounding Ashtabula also had significant populations. The next day we also received word of aphid populations above threshold in northern Erie and Lorain Counties. As of this week, counties in western, northwest, and central Ohio were not seeing these high of numbers, although aphids were easier to find.

Why in northeast Ohio, and not elsewhere? In discussing this situation with our colleagues in Michigan and Canada, our hypothesis is that a storm front that went through our area around July 24 might have been the culprit. Although the storm was moving from west to east, its circulation was counter-clockwise. We believe that during that time, the eastern edge, was passing over areas with heavy aphid populations (eastern Ontario, Quebec, New York), and was picking up winged aphids and depositing them on the back edge of this front, which just so happened to include northeast Ohio. While only a hypothesis, it does make sense why economic populations are only being seen in the northeastern part of Ohio.

For growers in north central and northeast Ohio, we do recommending scouting for soybean aphid as soon as possible to determine the need for action. While not all fields will require an insecticide treatment, this is a critical time to prevent losses. In other parts of Ohio, we continue to recommend scouting to determine the current level of soybean aphid. Remember that the threshold for treatment is 250 aphids per plant with a rising population.

Regarding plant growth stage, this threshold holds for soybeans through R5, which is during seed fill when beans can be felt within the pod. As the plants reach R6, or full seed stage, the level when you should spray is higher. Although an accepted threshold at R6 has not yet been determined, we would recommend NOT spraying unless the population is going much higher; probably well above 500 aphids per plant or with the plants under stress. At this time, most fields are no farther along than early R5. Many fields in northeast Ohio were just beginning R3 and R4 growth stages.

Check for insecticide use in the current Corn, Soybean, Wheat and Alfalfa Field Guide (Bulletin 827) available from your local OSU Extension office or the on-line soybean aphid pest recommendation factsheet: http://entomology.osu.edu/ag/545/sisa.pdf. If you also notice twospotted spider mite buildup in any field, remember that the product of choice should be chlorpyriphos (Lorsban, Yuma, Nufos). It is the only material with good efficacy against both soybean aphids and twospotted spider mites.
 

Late season diseases: A diagnostic guide

Authors: Anne Dorrance

Soybean cyst nematode has done very well this year in Ohio, much to the detriment of some soybean fields. Areas of some fields are stunted and when the plants are dug up, lots of pearls or cyst females can be seen along the roots. Other fields have no above ground symptoms, and there are reports coming from across the mid-west that soybeans which are cyst resistant (PI88788) now have high cyst populations on the roots. This is a good year to monitor these fields.

Symptoms of sudden death syndrome (SDS) and brown stem rot look very much alike. The leaves will have browning (necrosis) surrounded by yellow in between the veins. To tell these two soybean diseases apart, dig up the plants and first look at the roots. If the plant has SDS, the root system will be heavily damaged (SDS is a good root rotter). Brown stem rot tends to colonize the pith – so the pith will have a chocolate brown appearance but the tap root and outside of the pith will appear healthy. For SDS the tap root will be blue-gray (unhealthy looking) but the pith will be white. Examine plants that the stems are still green, you can’t tell anything when the plants are totally dead. If you are really lucky and it is about a day or two after a rain, SDS will sporulate on the tap root. When the plants are dug up there will be blue-green spores on the root surface.

White mold looks quite different from the above two diseases mentioned, random plants will be dying in the field, turning yellow, then tan. When the plants are examined, the mycelium which is white and fluffy will be on the stem. Despite the dry weather, there are some reports of this. Phytophthora has a late season phase as well, in this case, a chocolate brown canker will appear at the base of the stem and grow up the stem girdling the plant.

The one drought linked disease that I am surprised has not been reported is charcoal rot. Plants will die prematurely and in the stem tissue will be black dots (microsclerotia embedded in the tissue).
For pictures and more information on all of these late season diseases – examine the field crop disease website at http://www.oardc.ohio-state.edu/ohiofieldcropdisease/; or the soybean disease bulletin 895 at http://ohioline.osu.edu/b895/

Fertilizer Price Outlook

Authors: Robert Mullen

Short-term forecasts for nitrogen fertilizer shows that the high prices experienced this past spring are likely to be evident again this fall and winter; due to increased natural gas costs and increased demand both domestically and globally. Prices will in all likelihood be lower than they were this spring, but do not expect prices similar to those paid in the winter of 2004 or 2005. Natural gas prices are projected to be up 3.7% in 2008 which is lower than the 9.2% increase projected for 2007 hopefully meaning less volatile nitrogen prices next spring. Nitrogen fertilizer demand is also projected to increase because of greater demand for ethanol resulting in more corn acres keeping prices high. Potassium and phosphorus prices are also projected to stay high this fall due to increased global demand.

Fungicides should only be applied to a few fields

Authors: Anne Dorrance

Frogeye is present in a few fields and is building in the top canopy following the last few rains. Again, there are a few highly susceptible varieties out there that this affects. Most of the varieties have very effective resistance so fungicides are not needed. How do you determine if you need to spray – here are some questions to ask yourself and recommendations.

1. Is Frogeye present? if not - go fishing – check out a ball game, enjoy the summer.

2. How is the field doing, is the field under drought stress or are mites present? – Fungicides should NOT be applied. In this case they will aggravate the mite situation, due to killing off of the beneficial fungi plus the fungicides will not help plants that are under severe drought stress.

3. If Frogeye is present, the next question to ask is where is it in the canopy and how widespread is it in the field.
a) If it has stayed in the bottom canopy and is at very low incidence (you have to hunt for it) – and the field is post R4, there will probably not be any benefit to spraying. The plant resistance levels are holding and there will not be any economic return to spraying.

b) If it can be found in the upper canopy and the field is between R3 to mid-R5 producers might see a benefit to fungicide application. With a new disease, we don’t have any data on Ohio soybean varieties. So be sure to leave at least 3 check strips in the field to help you determine if this was the way to go.

The risk of soybean rust continues to be very, very, very low for 2007. The reports from the southeast are all negative from Georgia, northern Alabama, Mississippi and the Carolinas. Texas seems to be the hot spot this year with reports coming from Oklahoma and Arkansas. We should begin to see Kansas, Northern Arkansas begin to have finds within a few weeks, based on wind and rain patterns. A note to remember, these counties are turned red with the first pustule on the first leaf. It often takes another 3 weeks for the rust to sporulate, re-infect and sporulate again to build up enough inoculum to spread to the next field. It has a long way to go to reach Ohio this year.

Soil Quality Workshop

Authors: Alan Sundermeier

On August 28 there will be a Soil Quality Workshop conducted near Bowling Green, Ohio. With the theme - Managing pests by linking plant health to soil health - this hands-on workshop will instruct farmers, crop consultants, NRCS, SWCD, and Extension Educators on the benefits of achieving healthy soils. Certified Crop Advisor credits - 5.0 hours Soil & Water category. Registration of $25 needed by August 18. Refer to this news release for more information. http://www.ag.ohio-state.edu/~news/story.php?id=4218 A duplicate workshop will be held at Wooster, Ohio on September 27.

Wheat Varieties Suitable for 15-inch rows and for Relay Intercropping

Authors: Rich Minyo, Jim Beuerlein

Some Ohio wheat producers are interested in producing soft red winter wheat in 15-inch rows which allows them to remove a grain drill from their machinery inventory and because production in wide rows reduces their seed cost by half. Other producers are interested in wide rows for the purpose of relay intercropping soybeans. We have evaluated wheat varieties in 15-inch rows for several years and have learned that some varieties will produce about as much yield in 15-inch rows as in narrow rows. For example, in 2001 six of 23 varieties in 15-inch rows produced a yield between 99 percent and 105 percent of the yield in 7.5-inch rows. That capability is due primarily to their growth habit, i.e. plant height and erectness of growth. Varieties with medium height and a very erect growth habit are needed for relay cropping and tall varieties with a non-erect growth habit perform well in 15-inch rows where intercropping is not planned.

We evaluated 57 varieties that were entered in the 2007 Ohio Wheat Performance Trial for plant height and growth habit and developed two lists. As seen in Table 1, only six of the 57 varieties were found to be suitable for relay intercropping and another 22 were found to be suitable for wide-row (15 inch) production (Table 2). For wide-row production, wheat should be planted as soon as possible after the fly safe date, and the most profitable seeding rate is 20-25 seeds per foot of row. An application of 25 pounds of Nitrogen should be made at planting.


Table 1: Varieties suitable for relay cropping

Table 2: Varieties suitable for 15-inch row production