Stephen J. Toth, Jr., editor
Volume 20, Number 22, September 9, 2005

Field and Forage Crops

From: Jack S. Bacheler, Extension Entomologist

Of the 50 or so cotton fields that I have evaluated in the past week as part of our project's annual damaged boll survey, no significant ongoing insect infestations were present.

So far it looks like stink bug damage is down considerably from 2004. However, bug damage to bolls will likely be at higher levels than from 1996 to 2003. Bug pests will demand increasing attention in the coming years if the newer, more worm-proof Bt cotton is more readily adopted.

From a very late, rugged start, this cotton crop in general has made significant progress since spring, and many growers could harvest good to exceptional yields if we can match last year's weather patterns during the upcoming harvest season. Over the short run, most producers could use some rainfall.

From: Rick L. Brandenburg, Extension Entomologist

The current and upcoming weather continues to allow spider mites to remain. There are quite a few out there in a number of fields. The cooler nights are helping and I certainly would not encourage any wholesale spraying, but with forecasts in the 90s for mid September, we need to watch for them. They can result in a rapid leaf shed at this time of year. Remember that both Danitol and Comite have 14-day restrictions. Also, remember that at this time of year we are moving toward a caterpillar threshold of 12 per row foot. That is a level we don't often see.

From: Stephen R. Koenning, Extension Plant Pathologist, and James E. Dunphy, Extension Soybean Agronomist

Sentinel plots continue to be monitored weekly and several samples from kudzu (taken in the southern part of the state) were submitted to the lab for examination. All were negative for Asiatic soybean rust and rust has not been found in North Carolina thus far. Frogeye leaf spot and target spot are quite common in susceptible varieties this year and these diseases warrant fungicide application if soybeans are at the R5 stage or earlier. The current pattern of dry weather, however, minimizes the chance of an economic return. Southern stem canker has been found in North Carolina for the first time.

A sample submitted to North Carolina State University's Plant Disease and Insect Clinic by Cooperative Extension Service agent Josh Beam of Lincoln County was diagnosed as Southern soybean stem canker caused by the fungus Diaporthe phaseolorum var meridionalis. This disease has not been recorded in North Carolina previously. Southern stem canker causes substantial yield losses in susceptible varieties in the Mid-South and Delta. Infection generally takes place early in the season, usually when soybeans are still in the vegetative stages. Management of this disease is through rotation and the use of resistant or tolerant varieties. Fungicides have rarely been effective in controlling southern stem canker.

Most full-season North Carolina soybeans and much of the late planted crop should be safe from rust at this point. Nevertheless, Asiatic soybean rust is 50 miles closer to North Carolina because of recent finds in South Carolina and Georgia. The most recent find is in Calhoun County, South Carolina which is about 150 miles from Wilmington and about 100 miles from Lumberton and Charlotte. An increasing number of commercial Georgia soybean fields are being found infested with soybean rust and this increases the chances for the discovery of soybean rust in North Carolina this year. Recent dry weather has lowered the potential for soybean rust to damage our soybean crop this year. Crop advisors and producers, however, need to remember that this is an active hurricane season and historically most hurricanes that strike North Carolina occur in September.

The current pattern of dry weather makes the probability of an economic return on fungicide application at this time fairly small. Soybeans are unlikely to benefit from fungicide application beyond the R5 stage. Soybeans will not replace foliage lost to disease after R3, and all fungicide labels restrict application to R5 or earlier. While there are soybeans that could still be legally sprayed with fungicide, please consider the following:

1. Consider the yield potential of late planted soybeans before making a decision to apply fungicides. The yield increase, if any, is likely proportional to the yield potential. Ten percent of 60 bushels is 6 bushels which will cover fungicide and application costs, whereas 10 percent of 20 bushels is 2 bushels which may not cover costs.

2. Soybeans maturing in mid to late October typically experience cooler and drier weather. Disease in these soybeans are usually (with the possible exception of soybean rust) minimal. Yield losses due to poor seed quality and weathering at this time are usually very small.

3. While it seems likely that we will detect Asiatic soybean rust in North Carolina this year, it is probably too late to experience significant yield losses.

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 September 12, 2005 by Stephen J. Toth, Jr.