Stephen J. Toth, Jr. and Thomas A. Melton, editors
Volume 18, Number 17, August 8, 2003

Field and Forage Crops

From: Jack S. Bacheler, Extension Entomologist

Our unusually large plant bug populations appear to be hanging around in high enough levels in many Bollgard fields to trigger dirty bloom and/or internally damaged small boll thresholds. The need to treat for plant bugs can be helped by observing nymphs (often in blooms) finding blackened squares, and by using drop cloths in some fields. Bidrin, Orthene and Vydate at rates in the 0.4 pound of active ingredient per acre range are all active against plant bugs, though these materials have little or no activity against bollworms and other caterpillars. Because bollworms are often present at this time of year and because most pyrethroid insecticides are reasonably active against plant bugs, pyrethroid insecticides are often a good choice for controlling both pests at medium to high rates.

Although stink bugs can theoretically occur any time after bloom initiation, in reality gradual migration from fruit, nut, weed, and cultivated hosts during the month of August account for most of our economic damage to bolls. Unlike our high stink bugs levels in 2001, stink bug pressure has been more similar to 2002 so far. However, populations will inevitably build in some cotton fields in the next few weeks, and the routine examination of quarter-sized bolls is suggested at least weekly in all Bollgard fields.

For most of the state, this week marks about the mid-point of the major late season bollworm control period, with situations ranging from some growers making their initial spray decisions to those who have completed two pyrethroid insecticide applications on their conventional cotton. Some replanted cotton fields are just now beginning to set bolls, while other fields are starting to cut out, some prematurely due to unrecognized nitrogen loss.

For the many cotton producers, the insect management season may still run another 2 to 3 (or even 4) weeks. Bollworm moth flights for the most part remain strong, resulting in heavy egg pressure in some areas but very light in others with bollworm moths sometimes being attracted back into our late, still-green corn fields.

The European corn borer is another potentially boll-damaging pest that could make it's presence known over the next 4 weeks, particularly on later and/or ranker conventional cotton. Although the European corn borer has not be an economically widespread boll damaging pest, we appear to have a very large moth flight just beginning to emerge from field corn and other hosts. Petiole and main stem penetrations in cotton, although seldom of economic concern, is may signal the beginning of upcoming more serious establishment on bolls of all sizes. We will have information on managing European corn borers in the coming weeks.

From: Stephen R. Koenning, Extension Plant Pathologist, and Ronnie W. Heiniger, Extension Crop Science Specialist

Ordinarily southern rust of corn is of little concern to North Carolina growers because spores arrive so late in the season that little or no impact on yield occurs. In 2003, however, there is some concern because much of the corn was planted late and many hybrids have inadequate resistance to this disease.

The fungicides Tilt or Quadris (Syngenta) are registered for use on corn to control rusts and may also provide control of gray leaf spot. Fungicide sprays on corn are not generally recommended for use in North Carolina. Because some corn was planted late, applications of Tilt or Quadris may prove beneficial this year, especially with the prospect of continued high humidity and rainfall. Tilt sprayed field corn should not be harvested within 30 days after the last application, and should not be sprayed after silking. Quadris may be sprayed within 7 days of harvest. Preliminary results from tests conducted in Georgia indicate that Quadris may have performed better than Tilt. We have no thresholds for southern rust on corn or data on the efficacy of fungicides for controlling this disease. The following guidelines are suggestions for factors that need to be considered in making a decision to apply a fungicide.

1. Corn within two weeks of black layer is unlikely to benefit.

2. Estimate yield potential – spraying corn with a yield potential of less than 100 bushels per acre is unlikely to provide a profitable return.

3. If more than 1 to 2 percent of the leaf area is affected, spraying may increase yields.

4. Continued warm humid weather may cause disease to accelerate in susceptible hybrids.

5. The labeled rate for control of rusts for Tilt is 4 fluid ounces per acre and for Quadris is 6.2 to 9.2 fluid ounces per acre.

6. Cost of fungicide and application is likely to be $15.00 to $20.00 per acre, thus a 10 bushel increase is needed to pay for treatment costs.

7. The 4 fluid ounces Tilt per acre rate should also provide some control of gray leaf spot, but higher rates of Quadris are recommended for control of this disease. Gray leaf spot is generally more of a problem in no-till corn that is not rotated.

For more information on corn diseases, visit the following web sites or contact your county extension staff:

http://ipm.ncsu.edu/corn/diseases/corn_diseases.html

http://www.cropsci.ncsu.edu/CSArea.asp?Subject=COMMODITY+PRODUCTION+AND+MANAGEMENT&Topic=Corn&Info=Com%5FCorn&fmtinfo=1,400,133

Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age or disability. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

Last modified on August 11, 2003 by Stephen J. Toth, Jr.