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For Week of June 22-28, 1998
C.O.R.N. 98-15
In This Issue:
A) From Deserts to Lakes: Injury to Corn From Flooding And Ponding
B) First Brood Corn Borer Nearly Non-Existent
C) No-Show of Potato Leafhopper Nymphs in Alfalfa
D) What to do With Large Grass in Corn
E) Where to Find Problem Weeds
F) Utilizing Late Cut Forage
Although recent rains brought much needed relief to drought stressed crops in NW Ohio, excessive rainfall in parts of southern Ohio caused periods of flooding and ponding in many corn fields.
The extent to which flooding injures corn is determined by several factors including: (1) plant stage of development when flooding occurs, (2) duration of flooding and (3) air/soil temperatures. Prior to the 6-leaf stage (measured by visible leaf collars) or when the growing point is near or below the soil surface, corn can survive only 2 to 4 days of flooded conditions. The oxygen supply in the soil is depleted after about 48 hours in a flooded soil. Without oxygen, the plant cannot perform critical life sustaining functions; e.g. nutrient and water uptake is impaired, root growth is inhibited, etc. If temperatures are warm during flooding (greater than 77 degrees F) plants may not survive 24-hours. Cooler temperatures prolong survival. Once the growing point is above the water level the likelihood for survival improves greatly. Corn in southern Ohio that had not yet reached the 6-leaf stage, had great potential for flooding and ponding injury.
Even if flooding doesn't kill plants outright, it may have a long term negative impact on crop performance. Excess moisture during the early vegetative stages retards corn root development. As a result, plants may be subject to greater injury during a dry summer because root systems are not sufficiently developed to access available subsoil water. Flooding and ponding can also result in losses of nitrogen through denitrification and leaching.
If flooding in corn is less than 48 hours, crop injury should be limited. To confirm plant survival, check the color of the growing point. It should be white to cream colored, while a darkening and/or softening usually precedes plant death. Also look for new leaf growth 3 to 5 days after water drains from the field.
Certain disease problems which may become greater risks due to flooding and cool temperatures are corn smut and crazy top. The fungus that causes crazy top depends on saturated soil conditions to infect corn seedlings. There is limited hybrid resistance to these diseases and predicting damage is difficult until later in the growing season.
Efforts to locate first brood European corn borer (ECB) activity to date are indicating very low levels of infestation, which can only be found in early planted fields. As indicated in previous newsletter reports, corn having delayed development will not likely attract or support first brood ECB. In addition, the periodic rains, which have been rather heavy at times, have probably drowned ECB larvae where they occurred. A walk through a stand of knee high corn will likely detect some early foliar feeding, but close examination of the whorls will often detect very few ECB larvae.
During the past week, adult potato leafhopper (PLH) activity has increased significantly in alfalfa. However, PLH nymphs are lacking in the sweep net collections. In general, PLH nymphs will be absent on alfalfa during the first week or two of regrowth after cutting, but during the past week PLH nymphs have also been absent in 2nd growth alfalfa that is approaching harvest height.
In our PLH treatment trials over the past eight years at the O.A.R.D.C. Western branch station, we have often observed that PLH impact is most severe when PLH nymphs are present in abundance. In contrast, in years when PLH nymphs were lacking, significant differences in yield among treatments were minimal.
The recent increase in adult PLH activity may indicate forthcoming change in PLH activity, but if PLH nymphs are lacking and alfalfa growth is vigorous and near harvest, treatment may not be warranted despite levels of adult PLH activity that may be above threshold.
Additional reading information is available through the Field Crops Pest Management Circular #33, Potato Leafhopper on Alfalfa, Ohio Pest Management and Survey Program.
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Potato Leafhopper nymph. |
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Potato Leafhopper adult. |
There are not many options for control of large annual grasses in corn. Accent is the most effective post-emergence herbicide for control of annual grasses in corn, and it is more effective on giant foxtail than most other annuals. The Accent rate is 2/3 oz per acre for control of foxtails, barnyardgrass, and fall panicum up to 4 inches tall. The label allows a rate of up to 1 1/3 oz per acre for control of grasses larger than 4 inches, and also allows sequential applications (total rate not to exceed 1 1/3 oz per acre). Control of large grasses will vary with environmental conditions, becoming more difficult as conditions get drier. Use of a methylated seed oil may improve control of large grasses, especially under dry conditions. Be cautious of corn height when applying Accent this late in the season, and especially at rates higher than 2/3 oz. Broadcast applications are allowed until corn is 20 inches tall or in the V6 stage, whichever comes first. Use a directed spray with drop nozzles for corn up to 36 inches tall or the V10 stage. It can be difficult to achieve the proper height above the corn whorl when applying broadcast to large corn. If the height is too low, the spray pattern will not be uniform and excessive herbicide may be directed down the whorl. This will increase the risk of corn injury. In some cases where large grasses are treated with Accent, the corn will appear yellow and stunted as the grasses slowly die. This is generally NOT due to Accent injury, but is the result of competition between the crop and weeds. This will be more severe under dry conditions and dense grass populations.
This is a reminder about the section of the OSU Weed Control Guide titled, "Control of Problem Weeds" (This may seem redundant, since weeds are by definition a problem). This section provides recommendations for perennial and problem annual weeds that may require special control measures, and gives more information than can be provided in other parts of the guide. Look for this section in pages 110-119.
We have received some questions regarding options for producers who harvested a late first crop, or who have not yet been able to harvest their first crop due to rainy weather (especially in SW Ohio). Needless to say, the forage quality of this late cut forage will be poor. Below are listed some options for utilizing this forage.
1. Have the forage quality tested, so you know the quality parameters you are dealing with. Consult a nutritionist for advice before feeding this forage to animals with high nutrient requirements.
2. Feed the lower quality forage to livestock having lower nutritional requirements (eg. heifers, dry cows, etc.).
3. If adequate supplies of corn silage are available, feed more corn silage and reduce the amount of low quality forage fed. For example, feed only 4 to 5 pounds of dry matter per day of the low quality forage to lactating dairy cows.
4. Anhydrous ammonia can be used on the forage if it is put up as hay. DO NOT APPLY ANHYDROUS AMMONIA TO HAY CROP SILAGE. Anhydrous ammonia may improve digestibility of hay by 5 to 8 percentage units and crude protein by 2 to 3 percentage units for dry hay and 3 to 4 percentage units for wet hay (bailed between 22% and 30% moisture). Application of anhydrous to hay should be done carefully, as there is risk of injury if proper procedures are not followed. Directions for application are given in AGF-015, Improving Lower Quality Forages by Ammoniation. DO NOT USE THE RATES SUPPLIED IN THAT PUBLICATION FOR LEGUME HAY, THE RATES GIVEN IN AGF-015 ARE FOR STRAW, MATURE GRASS HAY, AND CORN STOVER. Apply anhydrous ammonia to legume or grass-legume hay at no more than 2% of the dry matter tonnage of the hay.
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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.
Contributors to C.O.R.N. this week include: State Specialists: Pat Lipps and Anne Dorrance(Plant Pathology), Hal Willson (Entomology), Peter Thomison (Corn Production), Mark Loux (Weed Science), Mark Sulc (Forage Production) and Bill Weiss (Animal Science); District Specialist: Curtis Young (IPMP); Extension Agents: Clark Hutson (Seneca), Dave Jones (Allen), Larry Lotz (Fayette), Barry Ward (Marion), Howard Siegrist (Licking), Steve Prochaska (Crawford) and Dennis Baker (Darke).
Editor: Curtis Young Web Editor: Nathan Watermeier
Information presented above and where tradenames are used, they are supplied with the understanding that nodiscrimination 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.
All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.
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.
TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868
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