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July 23 - July 29, 2002
C.O.R.N. 2002-23
In This Issue:
A) Harvesting Drought Stressed Forages
B) Late Summer Forage Seedings
C) Firing On Lower Leaves Of Corn
D) Understanding Corn Crop Water Needs: Available Soil Moisture
E) Defoliation On Soybeans
F) Rootworm Beetles & Silk Clipping
G) Controlling Weeds In Wheat Stubble
H) Soybean Growth And Dry Weather
I) Field Crops Day To Have Drought Emphasis
Forages are under drought stress in many parts of the state. New seedlings are most severely affected, especially late planted fields. New alfalfa seedings that have been harvested are regrowing very slowly. They should survive the drought stress and initiate more vigorous growth once moisture returns. In established grass stands, growth has been slow at best. Established grass stands can survive through severe drought conditions and regrow once rains return.
Deep-rooted established legumes such as alfalfa have the best capacity to continue growth under dry conditions, but in the driest regions, alfalfa growth is limited. Alfalfa and birdsfoot trefoil have good drought tolerance, while red clover stands can be reduced during severe drought and heat stress. Therefore, harvest management strategies are different for these legumes.
Alfalfa, unlike birdsfoot trefoil and red clover, can actually maintain production during short periods of dry weather (provided the soils allow development of a deep taproot). But some regions have experienced an extended period of drought and high temperatures, and the alfalfa very short and is in the bloom stage. Cutting alfalfa under these stressful conditions usually does not harm the plant or cause stand reductions. If moisture is lacking after cutting, alfalfa plants go dormant until sufficient moisture is again available for regrowth.
During the initial phases of moisture stress, alfalfa stems stop elongating, but the plant continues to manufacture carbohydrates. These carbohydrates are stored in the root system since they are not being used for top growth. These energy reserves are available for regrowth after cutting and when soil moisture is recharged.
So if there is enough harvestable forage to economically justify a hay cutting, then go ahead and harvest it. You still should maintain about a 30- to 35-day interval from the last harvest. Even though the plants may be in full flower, the forage will probably be higher in quality than normal growth in full bloom. If fencing is available, controlled grazing of drought-stressed alfalfa stands is a very economical way to utilize the forage that is present, but bloat prevention strategies should be employed.
Red clover is not as tolerant to the combined effects of drought and heat stress as alfalfa. Cutting during periods of hot and dry weather CAN WEAKEN RED CLOVER PLANTS and may cause stand reductions. If feed is badly needed, red clover stands can be lightly grazed during drought stress.
When cutting or grazing birdsfoot trefoil during periods of heat and drought stress, be extra careful to harvest when plants are at least in mid-bloom stage and leave a 3-inch stubble. Birdsfoot trefoil maintains relatively low levels of reserve carbohydrates in the roots and crowns during the summer. Cutting or grazing when plants are well into bloom stage and leaving sufficient leaf area will improve its regrowth potential.
1. Apply lime and fertilizer according to soil test and control problem perennial
weeds ahead of seeding.
2. Prepare a firm seedbed if using tillage. Loose seedbeds dry out very quickly.
Deep tillage should be completed several weeks ahead of seeding so rains can
settle the soil before final seedbed preparation. A cultipacker or cultimulcher
is an excellent last-pass tillage tool. The soil should be firm enough for a
footprint to sink no deeper than 3/8 to 0.5 inch.
3. No-till seeding is an excellent way to conserve moisture, provided weeds
are controlled prior to seeding. Remove all straw after small grains. Any remaining
stubble should either be left standing, or clipped and removed. Do not leave
clipped stubble in fields as it forms a dense mat that prevents good emergence.
CAUTION: No-till or reduced-till summer seedings of legumes are at risk of infection
by Sclertotinia crown and stem rot, especially in fields where clover or alfalfa
were present recently. Mid- to late-August plantings dramatically increase the
risk of damage by this disease compared with planting earlier. It is best to
avoid no-till where clover was grown recently.
4. Seed when soil moisture is adequate or a good rain system is in the forecast. It is very risky to place seeds into dry soil, as there may be just enough moisture to germinate the seed but not enough for seedling establishment.
5. Seed as early as possible. Seedlings require 6 to 8 weeks of growth after emergence to have adequate vigor to survive the winter. Seed by August 15-20 in northern Ohio and by September 1 in southern Ohio. Slow establishing species like birdsfoot trefoil or reed canarygrass should be planted in early August. Fast establishing species like red clover, alfalfa, and orchardgrass can be seeded up to the dates listed above if moisture is present. Kentucky bluegrass and timothy can actually be seeded 15 days or more later than the dates listed above. Keep in mind that the above dates assume sufficient moisture to establish the crop. Planting later than the dates mentioned above is sometimes successful depending on fall and winter weather patterns, but there is increased risk of failure and reduced yield potential for the stand as planting is delayed.
6. Plant seed shallow and in firm contact with the soil. Carefully check seeding depth, especially when no-tilling. Drills with press wheels usually provide the greatest success in the summer. Broadcasting seed on the surface without good soil coverage and without firm packing is usually a recipe for failure in the summer.
7. Use high quality seed of known varieties. Cheap seed often results in big disappointments and shorter stand life. Make sure legume seed has fresh inoculum of the proper rhizobium.
8. Do not harvest new summer seedings this fall. The only exception to this rule is perennial ryegrass. If perennial ryegrass has tillered and has more than six inches of growth in late fall, clip it back to 3 to 4 inches before snowfall.
9. Scout new seedings for winter annual weeds in October to November, and apply herbicides as needed. Winter annual weeds are much easier to control in late fall than in the spring.
Moisture stress conditions, in combination with other factors such as soil compaction and limited root growth, are resulting in nutrient deficiencies in some Ohio cornfields. The following information is adapted from a recent Penn State Field Crop newsletter article by Dr. Doug Beegle that addresses these drought-induced deficiencies.
There have been a number of questions and reports lately about firing on the bottom leaves of corn plants. The two most common nutritional causes of lower leaf firing are nitrogen (N) and potassium (K) deficiencies. While both of these show up on the lower leaves, it is very easy to tell them apart.
Nitrogen deficiency will start as yellowing at the tip of the leaf and then go back the middle of the leaf. Potassium will also start at the tip of the leaf but the yellowing will go down the edge of the leaf. The symptoms will start at the bottom of the plant and go up as the deficiency becomes worse. Eventually they may cover the entire leaf and the leaf may die. Thus, the higher up on the plant symptoms are observed, the worse the deficiency.
There are several possible causes for these deficiencies. Most obvious is the lack of N or K in the soil. For N, either not enough was applied or a significant amount may have been lost after application. This year, the early dry weather could have resulted in significant losses of N by volatilization if urea or urea ammonium nitrate solution (UAN) was applied early and not incorporated. If we did not lose the N by volatilization then we could have lost it later by leaching and denitrification when we got into the wet weather pattern. If you have access to high clearance equipment, there will probably still be a benefit to applying some N to fields showing deficiency at this time of year.
For K, look at the soil test. If the soil test is low then this is likely the cause of the deficiency. Probably there is not much we can do about this at this point. Just be sure to apply the recommended amount of K as fertilizer or manure before the next crop. However, K deficiency can show up even with optimum or high soil test levels. This is usually due to the plant not being able to take up the K that is in the soil. Anything that limits root growth can cause this. Common problems to look for include: compaction, low pH, root injury by pesticides, and root feeding insects. Compaction is a very common cause of this problem. One recent report of serious K deficiency problem occurred on a high K soil but with severe sidewall compaction. Again, there is not much we can do about this at this time, but we need to look at management changes to avoid the problem in the future.
For less obvious symptoms, plant analysis is an excellent tool for diagnosing these problems. Be sure to follow the sampling recommendations from the lab. A good way to determine the problem using plant analysis is to take a sample from the problem area and a similar sample from a nearby normal area and compare the results.
High temperatures and limited rainfall have created stress conditions in many cornfields across Ohio. Average water use by a corn crop during pollination and early grain fill is about 1/3 inch per day. Evapotranspiration rates in corn depends on temperature, humidity, wind, solar radiation and total leaf area of the crop. (Evaporation from the soil surface combined with transpiration from plants is evapotranspiration). When temperature is relatively low and humidity is high as on a calm, cloudy day, the evapotranspiration rate will be low. If temperature is high and humidity low as on a sunny, windy day, the rate will be high.
As drought-like conditions appear to be increasing in parts of the state, especially areas which have received negligible rainfall since early June, questions have arisen as to how much of the corn crop's water needs can be met by subsoil moisture. After all, excessive rainfall occurred earlier in the spring.
The following is information from the National Corn Handbook - Chapter NCH-20
"Irrigation Scheduling for Corn-Why and How"
(http://www.agcom.purdue.edu/AgCom/Pubs/NCH/NCH-20.html)
to help address these questions
Soil textural characteristics dictate the water holding capacity, intake rate and drainage rate. Soils may have available water capacity of as little as 4 inches or may exceed 8 inches in 4 feet of soil. Table 1 gives the available-water holding capacities of ten different soil types. Soils also differ as to depth adequate for active root development; some have underlying layers of gravel or hard pan that would restrict root growth.
Information in this table might be used to estimate the number of days that moisture stored in the soil could "carry" a corn crop. For example, with a storage capacity of 1.8 in./ft, a fully charged silty clay loam soil might carry corn with a 3 foot rooting depth up to 18 days during silking and early grain fill stages (1.8 in/ft times 3 foot depth= 5.4 inches available water; 5.4 in. divided by 0.3 inch/A/day water requirement = 18 days). Although corn roots can grow as deep as 8 feet, when actively growing, corn obtains 90% of its water requirements from the top 3 feet of the soil profile.
A major factor determining the ability of corn to extract available soil water is soil compaction. In many Ohio corn fields, surface compaction, combined with excessive soil moisture early in the season, late plantings, etc. have resulted in corn root systems restricted to the top few inches of the soil profile. These flat, shallow root systems make the crop especially vulnerable to drought. In addition to soil compaction, when relating the information from Table 1 to various Ohio soil types, keep in mind that other factors may influence water availability. Differences in soil organic matter and texture often occur at different rooting depths, for example the top foot of soil may be a silty clay loam but underlying layers may be clay, sand, or gravel.
Most soybeans blooming or developing pods, and thus, are in the most critical stage in terms of damage from insect defoliation. Numerous insects will feed on soybeans, and although most will not reach economic levels by themselves, the level of feeding can become serious when numerous insects are working on the crop. The insects that we are seeing to watch out for are Japanese beetles, first generation bean leaf beetles that are now present, and grasshoppers. Treatments should be applied if defoliation levels reach 15% and insects are active and feeding. A consideration for growers is that most soybeans are relative short in stature, and thus, the defoliation percentages will become greater much more quickly than if the plants were taller and their canopies were full. Numerous insecticides are labeled for all these insects.
Reports of corn fields with large numbers of rootworm beetles and some silk clipping are coming in from throughout the state. In addition to rootworm beetles, some areas also have large numbers of Japanese beetles that may be clipping silks, especially around the edges of the fields. Rescue treatment for rootworm beetle silk clipping is warranted if 5 or more beetles are found per silk mass when 75% of the plants have silked and silk clipping to 1/4 inch or less is observed. Rescue treatment for Japanese beetle silk clipping may be warranted if there are 3 or more beetles per silk mass and pollination has not occurred. The important thing to check for in corn at this time is whether or not the corn has pollinated. If pollination has occurred, then silk clipping by rootworm or Japanese beetles will not affect yield.
Because of uneven silking, there may be only a small portion of the field that has fresh silks at any one time. In these cases, the beetles will congregate on those emerged silks and populations per plant may be larger than if the whole field had silked. As more plants silk, the population may become dispersed throughout the field and reduce the beetle numbers per plant and thus the need for treatment.
Chemicals that labeled for silk-feeding beetles include:
Ambush*
Asana XL*
Capture 2E*
Lannate*
Dimethoate
Malathion
Mustang*
Penncap-M*
Warrior 1CS*
--- Use is restricted to certified applicators only.
The summer and fall after wheat harvest is an excellent time to control many annual and perennial weeds, and reduce weed populations in future years. Benefits of controlling weeds at this time include the following:
- Reduces weed seed production and prevents increases in the soil weed seedbank for many summer annual weeds.
- Prevents increase in the seedbank of ALS-resistant ragweeds and marestail as well as other resistant weeds.
- Controlling volunteer wheat, quackgrass, and other grasses reduces the risk of several wheat diseases in future years.
- Controlling purple deadnettle reduces its potential to serve as a host for soybean cyst nematode.
- Late summer and fall allows application of glyphosate/2,4-D when perennials are in an appropriate growth stage to get maximum movement of herbicide into their roots.
- Late-fall applications are an excellent tool to manage dandelion and winter annual weed populations, which have been increasing in recent years.
When planning a strategy for weed control in wheat stubble, it is essential to decide which weeds are most important to target, since there is no single application timing that works well for all weed types. The single biggest challenge may be determining how to prevent summer annual weeds from going to seed, while also targeting cool-season perennials and winter annuals with a late-fall application. Some things to consider:
- summer annuals (ragweeds, foxtails, etc) and marestail should be controlled by about mid-August to prevent seed production. This can be accomplished with herbicides. Mowing by early August will greatly suppress these weeds, but some of them they may still regrow and produce seed if not killed by frost or a later herbicide application (although seed production will be much less than if they are not disrupted in August).
- Winter annuals emerge in late summer through mid-fall, so a late-fall herbicide application is a very effective tool for control.
- Cool-season perennials such as Canada thistle, quackgrass, and dandelion survive light frosts, and are most effectively controlled with herbicide applied through late-October or early November. Thistle plants should be at least 8 to 12 inches tall for best results.
- Warm-season perennials such as hemp dogbane and milkweeds will complete their life cycles by late summer and do not tolerant frost well, so herbicide applications cannot be delayed until late fall.
- Tank-mixtures of 2,4-D with glyphosate can antagonize the activity of glyphosate on Canada thistle and perennial grasses.
To control summer annual weed seeds, an application of glyphosate (13 to 26 oz of UltraMax or 16 to 32 oz of other glyphosate products) and/or 2,4-D ester (1-2 pts/A) will be necessary. A combination of glyphosate plus 2,4-D can be more effective than either herbicide alone, allows lower rates of glyphosate, and slows the rate of development of glyphosate-resistant weed populations. If the weeds are large or tough to control species such as velvetleaf, smartweed, horseweed/marestail and morningglory, high rates of glyphosate may be necessary when applied without 2,4-D. Mowing the wheat stubble at a height of 4 to 6 inches when any weed species has started to flower and then mowing as low as possible when these species begin flowering again is another method of reducing, although not eliminating, seed production of summer annual weeds in wheat stubble.
Mowing wheat stubble fields as soon as possible (before August) will allow for maximum regrowth of perennial weeds. Mowing prevents summer annual weeds from producing large amounts of seeds, allows for regrowth of perennial weeds, and helps reduce the wheat residue that can interfere with spray coverage. Applying glyphosate and/or 2,4-D in July or August will prevent seed production by annual weeds, but can actually reduce the control of perennial weeds, which are more difficult to control in the following year's crop. The most effective timing for perennial weed control is generally mid-September through late October depending upon the species. Herbicide effectiveness at that time will be maximized by applying after several days of warm weather when perennial weeds are fairly large and/or in the bud to flower stage. Perennial weed regrowth should be at least 8 to 12 inches in order to obtain maximum control of the roots or rhizomes for next year. For warm-season perennials such as johnsongrass, hemp dogbane, milkweeds, common pokeweed, and bindweeds, application of glyphosate and/or 2,4-D in mid- to late September should provide the most effective control. Cool-season weeds such as Canada thistle, quackgrass, dandelion, and Canada bluegrass will be most effectively controlled with a glyphosate application after a light frost in mid- to late October.
Control of volunteer wheat and perennial grasses, especially quackgrass, should help reduce the risk of wheat diseases in future wheat crops. To most effectively reduce wheat streak mosaic virus, rust, stagonospora blotch, and powdery mildew, the volunteer wheat should be controlled before September 1st. Control of quackgrass and other perennial grasses before September will reduce the future risk to take-all root rot. To selectively control the volunteer wheat and other grass species, an application of Select (8.0 oz/A) could be applied before August 15th, followed by glyphosate and/or other products later to control winter annuals and perennials. Glyphosate should effectively control volunteer wheat. Purple deadnettle, field pennycress and shepherd's-purse have been documented as hosts of the soybean cyst nematode, and may have a role in increasing the nematode populations. Therefore control of these species may reduce soybean cyst nematode populations. The control of chickweed and other species may help in reducing cutworm and slug populations in the spring.
In a study conducted in 1993 through 1995, we examined the effect of Roundup/2,4-D applications in wheat stubble on annual weed populations the following year. The Roundup/2,4-D (1 quart + 1 pint/A) combination was applied in late July, late August, or late September, and weed populations were measured the following year. The July application controlled the foxtail, common ragweed, and other summer annual weeds most effectively and reduced seed production almost completely. This did tend to reduce annual weed populations the following year, but we saw little impact on control where an effective preemergence corn herbicide was used the next spring. Control of perennial and winter annual weeds was most effective with the late September application, which resulted in a more weed-free seedbed the following spring. Weeds in the 1994-95 study included marestail, Philadelphia fleabane, curly dock, and mustards. Control of these weeds the following spring ranged from 83 to 100 percent with the September application, 30 to 64 percent with the August application, and 9 to 45 percent with the July application. In our opinion, control of the winter annual and perennial weeds in wheat stubble is more important than control of summer annual weeds. For this reason, we recommend that applications of glyphosate and 2,4-D be delayed until later in the fall. Mowing fields now will help reduce seed production by summer annual weeds. However, under the current dry conditions, it is possible that perennials may not regrow sufficiently to allow for effective control with herbicides later in the fall. We speculate whether it may be better to not mow at all this summer if perennial weed control is a primary goal, in order to have perennials at the appropriate size this fall.
Most of the soybean varieties grown in Ohio have indeterminate growth, i.e., vegetative growth continues after flower initiation. Leaves and flowers originate from the area on the main stem called nodes. As the plant grows in height it produces new nodes. Not all of the flowers will set and become pods, and some pods may abort during stress periods. However, additional nodes (potentially more flowers and pods) will develop during periods of adequate growing conditions. During periods of stress (extended dry weather) development of new nodes may temporary stop or at least take much longer to develop (now occurring in the dry areas of Ohio). Once the plant reaches the seed fill stage, vegetative growth ceases and plant will reach its maximum height. Any flowers that do not set, or pods that abort at this time will not be replaced with new flowers. Agronomists call seed fill growth stage R5, where a pod at any of the four uppermost nodes contains a bean 1/8 inch long. To count the uppermost four nodes, start with the top leaf on the main stem where leaflet margins do not touch, and then move down the main stem four more leaves. The node is where the leaf stalk (petiole) attaches to the main stem. Seed fill has begun if any pods at these leaf axils have beans greater than 1/8 inch long. Fortunately, the plant has four to six weeks after the first flower before growth stage R5. For the past three years I have staged the variety 'Sandusky' (Group 2.9) in one of my research studies at the Northwestern Branch of OARDC. This variety reached growth stage R5 by August 10 in each of these years. Thus we are approaching a critical time for soybean yields. However, new nodes will develop with timely rains. The extended dry period has reduced soybean yields, but the amount of yield reduction will be determined by the amount of rainfall over the next several weeks.
The Field Crops Day scheduled for this Thursday, July 25 at the Research Branch between Hoytville and Custar will have a special emphasis on the summer drought Northwest Ohio is presently experiencing. The field day will be held from 6:00 to 9:00 p.m. Thursday, July 25th at the OARDC Northwest Branch located at 4240 Range Line Road, Custar, Ohio. Leading the discussion on the drought will be several state specialists from Ohio State University including Dr. Ann Dorrance, Dr. Jim Bauerlein, Dr. Ron Hammond, Dr. Ed Lentz, Dan Frobose from the ABE Center and several area County Extension Agents. The discussion on the drought will help determine how much the crops have suffered, probable yield outcomes, and forage and livestock utilization.
Other topics to be covered at the field day will include new technologies in
precision agriculture and how weed populations change with tillage rotation
and herbicides. This field day is free and open to the public and free refreshments
will be available.
Readers can subscribe electronically to this newsletter by sending an e-mail message to: corn-out-on@postoffice.ag.ohio-state.edu. A successful subscription message will receive by an automatic reply from the listserv. Contact your local Ohio State University Extension Office or e-mail labarge.1@osu.edu if you have problems subscribing.
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.
State Specialists: Pat Lipps, Anne Dorrance & Dennis Mills (Plant Pathology), Peter Thomison (Corn Production), Mark Sulc (Forage Production), Mark Loux & Jeff Stachler (Weed Science), and Bruce Eisley & Ron Hammond (IPM). District Agents: Ed Lentz & Robert Fleming (Northwest) Extension Agents: Barry Ward (Champaign), Greg Labarge (Fulton), Gary Wilson (Hancock), Howard Siegrist (Licking), Jim Lopshire (Paulding), Glen Arnold (Putnam), Roger Bender (Shelby), and Dave Jones (Allen).Editor: Dave Jones Web Editor: Tom Rosati
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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