C.O.R.N. Newsletter 2005-20

Dates Covered: 
July 5, 2005 - July 12, 2005
Editor: 
Jim Skeeles

Drought of 2005

Authors: Harold Watters

For the second week in a row much of the CORN conference call discussion centered around rain. From most reports, the rains over the last week were spotty. Only two agents felt that their rainfall needs had been met, other areas had from 0.2 inches to 2 inches last week – but widely scattered.

Several of us sat down this spring to try and answer the question, “What is the best scenario for a perfect crop year in Ohio?” Most of us agreed that a dry spring followed by a cool, moist summer would make for excellent yields. We have the first half of our perfect season, now we need to move on to the cool and moist phase.

During our last drought in 2002, the Agronomic Crops Team and others assembled a very good resource page for drought information and that web page is still available: http://corn.osu.edu/drought02/

For those of you who have adequate moisture, count yourself lucky. Others may want to review the 2002 Drought webpage for advice and suggestions categorized by crop, livestock and marketing in a drought situation. State specialists will be updating the 2002 Drought website shortly and as needed. Please check back as your needs change.

For those looking for a good crop moisture map, this from NOAA combines several predictors to create a short-term drought indicator map: http://www.cpc.ncep.noaa.gov/products/predictions/experimental/edb/sbfinal.gif

Follow Up to Aphids and Mites

Authors: Ron Hammond, Bruce Eisley

The past week has brought some needed moisture to many locations in the state, along with slightly cooler temperatures. How much impact this will have on soybean aphids and twospotted spider mites is unknown. Hopefully the rainfall and cooler temperatures will lower mite populations. However, growers should continue to monitor for possible mite buildups in their fields, especially in those locations that remain dry. Growers should also be aware that soybean aphids are now being found in most fields, ranging in populations that are very low and hard to find to densities where aphids are easily found on all plants. Of significance, we did find the first soybean field that required treatment in northern Wood County, well beyond the threshold of 250 aphids per plant. As with twospotted spider mites, growers should continue to monitor aphid build up in their fields.

Lodged Corn

Authors: Bruce Eisley, Ron Hammond

It is possible to see lodged corn at this time of year especially if the corn is in an area that received one of the storms that moved through Ohio last week. Corn lodging can be caused by a number of things including:

Less than adequate root system due to by environmental conditions (compaction, cold soils earlier, etc.) are possible causes for lodging because the root system is not able to anchor the plant and especially when heavy rains and winds move through the area.
OR
Corn plants with adequate root systems can also lodge under the right conditions. If a 2 to 3 inch rain moves through a field, the soil becomes saturated and then it doesn’t take much wind to blow the plant over.
OR
Damage caused by rootworm larval feeding can also cause plants to lodge when high winds move through the area. There is an article in this newsletter that gives information on how to sample, identify and rate rootworm injury in corn.

The important thing to remember about corn lodging is to check the root system by digging some roots and checking the root system to see if the problem can be identified.

Rootworm Larval Feeding Evident

Authors: Ron Hammond, Bruce Eisley

We are finding rootworm larvae feeding on corn roots in research plots in central Ohio at this time. The next couple of weeks will be a good time to check for corn rootworm larval feeding injury. Cornfields to check include fields where corn follows corn or those fields in NW and west central Ohio where corn follows soybeans and where damage from the western corn rootworm variant might be a problem.

The reason to check in the next couple of weeks is because the maximum larval feeding damage will be during this time, with larval feeding ending as the larvae pupate and adults begin to emerge. After larval feeding has ended, the roots on some hybrids will begin to regenerate and when this happens, rootworm larval injury is more difficult to detect.

We suggest the following method to check for rootworm injury:

1. Carefully dig plants, don’t pull them, from the field taking as much soil as possible with the plant.

2. Carefully remove as much soil as possible from the plant without damaging the roots and also look for any larvae that might still be in the soil or on the roots. Rootworm larvae are white, about 1/2 inch in length when full grown with a brown head and brown plate on the tail: http://ohioline.osu.edu/icm-fact/images/43.html (see picture).

3. If there is still soil on the roots you can either soak the root system in a bucket to loosen this remaining soil or you can spray the root system with a hose to remove the remaining soil.

4. After the soil has been removed, check the roots for feeding injury, looking for either roots chewed back to the stalk or tunneling in the roots.

Root systems can be rated using either a 1 to 6 or 0 to 3 scale. In both ratings, the scale indicates the amount of damage to the root system and can be used to determine if economic injury has occurred.

Iowa 1 to 6 Scale (Economic injury normally occurs at a rating of 3 to 3.5)

Rating by damage to roots:

1. No damage to the roots.
2. Slight feeding scars present.
3. One root chewed to within 1-1/2 inch of the plant.
4. One node of the roots destroyed.
5. Two nodes of the roots destroyed.
6. Three nodes of the roots destroyed.

Modified Node-Injury Scale

Rating by damage to roots:

0 = no visible damage to roots
0.05 = slight scarring
0.08 = moderate to severe scarring, no roots chewed to 1.5 inches of stalk
0.1 = one root chewed to 1.5 inches of stalk
1 = one node of roots destroyed
2 = two nodes of roots destroyed
3 = three nodes of roots destroyed

European Corn Borer (ECB) Larval Feeding in Some Fields

Authors: Bruce Eisley, Ron Hammond

We observed some ECB larval feeding injury in some central Ohio cornfields last week. The corn had been planted in early May and was about waist high in height. Slight feeding damage (< 5% of the plants) was observed in this field. The worms were small, about 3/8 inch in length, and feeding on the leaves in the whorl. This would be a good week to check fields for ECB feeding.

Rust Update for July 3

Authors: Anne Dorrance

Two changes this past week for soybean rust. The first is that soybean rust was found in Alabama. Before you get excited, it was on 2 plants in a sentinel plot. They are continuing surveys this week, but again the soybean rust inoculum levels are very, very low. What is great about the sentinel plot and spore monitoring efforts is that we are able to detect these very, very low levels of disease in these intensively surveyed plots. Interestingly as well, many of the soybean fields in this region are at the stage where the southern soybean producers begin to spray for their “other diseases”. There are a number of foliar pathogens in the south, Frog-eye leaf spot and purple leaf stain, which are very rare in the north. For those fields that were sprayed, this will also slow down the rate of inoculum build-up. Two tropical storms are predicted for later this week. Again, these will be tracked and our sentinel plot scouting will increase about mid-July to determine if anything got moved this way. But at this point – there just is NOT a lot to move.

Another soybean fungicide was granted a Section 18 exemption last week. EPA has granted emergency use status for Uppercut, active ingredient, tebuconazole to DuPont. Other products containing tebuconazole include Folicur and in a mixture Headline SBR. Tebuconazole is a triazole, which has curative activity. Curative activity means that this works primarily on the growing mycelium of the fungus. The best timing for these materials is right before spores are deposited on a majority of the plants in the fields. Section 18 emergency use materials are only to be used in Ohio and only when the risk of rust is predicted to be high.

Archive Issue Contributors: 

State Specialists: Anne Dorrance and Dennis Mills (Plant Pathology), Peter Thomison (Corn Production), Mark Loux and Jeff Stachler (Weed Science), Bruce Eisley (IPM) and Ron Hammond (Entomology) Extension Educators: Roger Bender (Shelby), Steve Foster (Darke), Greg La Barge (Fulton), Howard Siegrist (Licking), Dusty Sonnenberg (Henry), Keith Diedrick (Wayne), Gary Wilson (Hancock), Jim Skeeles (Lorain), Harold Watters (Champaign), Alan Sundermeier (Wood), Bruce Clevenger (Defiance) and Steve Prochaska (Crawford) and Glen Arnold (Wood)

About the C.O.R.N. Newsletter

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.