CORN
Crop Observation and Recommendation Network

October 13-19, 2003
C.O.R.N. 2003-35

In This Issue:

A) Purple Corn at Harvest
B) Fall Sampling of Slugs
C) Give Winter Wheat a Head Start Over the Weeds
D) Time to Begin Fall Herbicide Applications

A) Purple Corn at Harvest - Thomison CORN Questions

Some growers are reporting reddish-purple plants as they harvest corn this year. This purpling has often been attributed to European corn borer (ECB) injury. However, other factors can cause purpling of corn plant tissues late in the season. Purpling will occur when plants cannot utilize all the sugars that the plant is producing . Excess sugar produced by photosynthesis accumulates in the leaf tissue, husk tissue, parts of the stalk, and triggers formation of the red pigment anthocyanin. This is basically the same process responsible for the purpling we sometimes see in the spring when young corn plants turn purple, especially under cool conditions. At harvest, the purpling is often most pronounced in barren plants or plants from which ears have been removed prematurely or reduced in size (with markedly reduced kernel numbers per ear) due to some environmental stress. When raccoons remove ears from corn plants, purpling often occurs. Similarly when corn borers burrow in stalks and ear shanks they often disrupt and prevent the normal redistribution of sugars from the stalk into the developing kernels. This damage results in a buildup of sugars in the leaves and stalks triggering anthocyanin production and the appearance of purple plants. Purpling is also associated with plants producing "beer can" ears. In this case, these stunted ears with limited numbers of kernels cannot use all the sugars being produced by the plants, so sugars accumulate and plants turn purple. Traces of purpling on plants, which appear healthy, with normal ears, also occur. Perhaps given very favorable growing conditions, these plants produce more sugars than even a normal ear can use? The extent to which plants turn purple is also influenced by hybrid genetics with some hybrids more inclined to purple than others when some stress disrupts the flow of sugar from leaves and stalks during grain fill.

B) Fall Sampling of Slugs - Hammond & Eisley CORN Questions

Sampling this past week revealed relatively large populations of adult gray garden slugs in a number of no-till fields. Although these fields had significant slug injury last spring, most had not been treated. Slug counts under roofing shingles following the first 24 hour period ranged from 2 to 6 per trap, with many more found underneath other coverage. The next month is a good time to determine the relative size of the slug population in fields. As crops are removed, traps should be placed in the field and left for a few weeks. Traps should be checked at least weekly if not every few days to get an idea of the slug numbers in your fields. Growers are also advised to look underneath the leaves of larger weeds that are covering the ground. Numerous slugs were found in those situations. Although no thresholds are available, fields with large numbers of slugs should be monitored more closely next spring.

C) Give Winter Wheat a Head Start Over the Weeds - Stachler and Loux CORN Questions

Now that much of the wheat has finally been planted, we wanted to remind you to apply glyphosate before the wheat emerges in order to control dandelion and other winter annual weeds. In previous CORN Issues (Sept. 15th, Issue 31 and Sept. 2nd Issue 29), we discussed the reasons for a burndown herbicide program in winter wheat and what rates to use. There are no consistently effective herbicides available to control dandelion in the fall after the wheat has emerged.

D) Time to Begin Fall Herbicide Applications - Stachler and Loux CORN Questions

The time has come to begin fall herbicide applications. Scout fields and determine whether you need an application, because not all fields need an application. However, to determine the full potential of winter annual weeds you must get on your hands and knees to find them, because they are still germinating and are hard to see. Previous newsletter articles (Sept. 29th, Issue 33 and Sept. 2nd, Issue 29) have addressed how to control marestail (horseweed) and dandelion with fall applications. Below are some additional points to consider:

• We now believe glyphosate-resistant marestail is as far north as U.S. Rt. 36 and as far east as U.S. Rt. 23! We will have to wait for results from greenhouse studies to confirm how widespread it is, but for now anyone south of U.S. Rt. 30 (possibly the entire state) should manage marestail as if it is glyphosate-resistant. Therefore all fall applications should contain 2,4-D ester in order to improve marestail control.
• If you are targeting marestail and/or dandelion, you will also control most of the winter annual species. The only exception is 2,4-D ester applied alone, in which case chickweed will not be controlled. In this situation, add glyphosate or Express to the 2,4-D to control the chickweed.
• It is PREFERRED to apply herbicides on days when the morning low is greater than 35 degrees Fahrenheit. The BEST control will be when the morning lows of the days preceding and following application are greater than 35 degrees. Applying herbicides on days when the morning low is below 35 degrees does not mean you will loss all herbicide activity, but you should not expect complete control when spraying at low temperatures. If temperatures stay cool, go ahead and spray as some control is better than NO control.
• Herbicides with little or no residual activity, such as 2,4-D and glyphosate, that are applied now may not control all of the winter annual weeds, as more may germinate after application. Germination may continue until the ground is frozen for more than 24 hours. Therefore you may want to wait a couple more weeks before applying. Residual herbicides such as Canopy XL and Backdraft may be more suited to being applied now, because they will control later emerging winter annuals.

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Past versions of C.O.R.N. can be found on the World Wide Web at: http:/www.ag.ohio-state.edu/~corn/archive/

C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

Editor: Barry Ward        Web Editor: Nathan Watermeier

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

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Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

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