Field Crop News

Website Address: http://fcn.agronomy.psu.edu/

July 8, 2008 Vol. 08:18

IN THIS ISSUE:

Management of Foliar Diseases in Corn
Poisonous Plants in Summer Pastures
Weed Control in Small Grain Stubble
Insect Defoliation Assessment
Wheel Traffic Affects on Soybean Yield
Wheat Test Weights
Pre—mature Sprouting in Wheat
Register Now for the 2008 Agronomic Diagnostic Clinic

Management of Foliar Diseases in Corn — Del Voight, Interim Grain Crop Specialist

Corn tassels are emerging across the state the ideal window to apply a fungicide to corn will open and close fairly quickly. Many labels target 75% tassel emergence. With the high grain prices it may be tempting to consider treating the crop to increase yields and in some fields a response will be returned to the farm. Data from across the east and Midwest is variable and the key to determine the need to treat is related to specific field conditions.

In some studies completed with industry and Extension involvement it appears that fields that have observable disease infecting the lower leaves, fields with hybrids that are prone to disease infection, and reduced tilled fields that are showing signs of infection are fields that may prove to return a profit. In some industry hybrids 60% of hybrids showed a response above the economic return. Universities found that a fourfold response occurred in fields showing disease infection. Most of the studies suggested an average of 8 bu/acre resulted in fields where a disease is present in the east. In the southern climates responses to a fungicide treatment of 15 bu/acre, were observed by Universities.

The thresholds developed are based on typical crop markets. Current markets may certainly have changed but the key to the best response is the infield observation of what diseases exist and to what extent. From a practical stand point with the number of fields that were converted to no till this season growers that utilized the same hybrid in two consecutive years should take a serious look at fungicide applications on corn. In Pennsylvania research is underway looking at the affects of fungicides on grain and also the silage impact as well. If one does choose to apply a fungicide read and follow label directions and be sure the application equipment can get high enough above the canopy to provide proper coverage.

Poisonous Plants in Summer Pastures — Dwight Lingenfelter and Bill Curran, PSU Weed Specialists

Well it’s July and that means the potential for reduced pasture growth and a greater potential for overgrazing. Despite the fact that we have had moist conditions for good pasture growth thus far, we have already received some calls concerning potential livestock poisoning by weeds. Livestock may be forced to graze on weeds that normally they would not, or they may eat weeds out of curiosity. Scout your pastures and remove these weeds before they cause livestock health problems. Keep in mind there are numerous poisonous plants that could invade an area or pasture. Many plants contain potentially poisonous substances that may be toxic to livestock if consumed. In addition, certain plants may be problematic because of mechanical irritation when eaten, photosensitization, and disagreeable tastes or odors in meat, milk or milk products. If you suspect livestock poisoning, call your local extension educator or veterinarian immediately. If death occurs, the stomach contents should be examined for consumed herbage. Identify the suspected plants and remove livestock from the grazing area until all poisonous plants have been removed or destroyed. Table 1 lists only some common weeds and their poisonous properties; many other plants can be toxic to livestock.

Table 1. Selected poisonous plants of the Northeast (Information adapted from Fishel 2000; Hardin 1973; and Hill and Folland 1986 and D. Wolfgang, PSU)
Common name	Problem/symptoms	Toxic ingredient - toxicity dosage
Bouncing bet	Leaves and stem - delayed for several days; depression, vomiting, abdominal pain, diarrhea	Saponin - amount equivalent to 3% (dry wt.) of sheep wt. killed within 4 hr.
Buttercups	Leaves and stem especially in flower. Dried hay loses toxicity - anorexia, salivation, weakness, convulsions, breathing difficulty, death	Protoanemonin - toxicity reported to vary with species, age, and habitat. Generally 1-3% of body weight necessary.
Cherry, black	Leaves (wilted leaves are worse), stems, bark and fruit - anxiety, staggering, breathing difficulty, dilated pupils, bloat, death	Cyanogenic glycosides - Less than 0.25 lb leaves (fresh wt.) can be toxic to 100 lb animal. Leaves from several small to mid sized branches are sufficient to kill an adult animal.
Clover species	Vegetation - Hairballs; Sweet clover: nose bleeding, anemia, abdominal swelling	Coumarin with sweet clover - varies
Fern, bracken	Entire plant - Dullness, fever, bleeding, loss of appetite, and salivation	Glycoside thiaminase - Cattle fed 50% bracken for 30 to 80 days was toxic. Others report that only 20% of diet for 30-60 days was toxic.
Garlic, wild	All plant parts - tainted milk and meat.	Only toxic in large quantities
Hemlock, poison	All plant parts - nervousness, salivation, vomiting, diarrhea, weakness, paralysis, trembling, dilation of pupils convulsions, and coma, death	Coniine and others (pyridine alkaloids) - 0.5 to 4% (fresh wt.) equivalent of cattle wt. is toxic. In horses, 0.25% of body weight.
Jimsonweed	Entire plant (seeds are most toxic - Thirst, mood swings, convulsions, coma, death	Solanaceous alkaloids - 0.06 to 0.09% (dry wt.) equivalent of animal body wt. is toxic.
Locust, black	Leaves (especially wilted), seeds, and inner bark - Causes weakness, depression, anorexia, vomiting and diarrhea	Phytotoxin robin, glycoside robitinm - bark extract and powder in amount equivalent to 0.04 - 0.1% of animal wt. toxic to horses. Cattle 10-times more tolerant.
Milkweeds	Entire plant - depression, muscle tremors, spasms, bloat, difficult breathing.	Glycosides and galitoxin - 0.3 to 0.6% of body weight.
Mustards	All parts (especially seeds) - oral and gastrointestinal irritation, shaking, salivation, abdominal pain, vomiting, and diarrhea.	Thiocyanates, irritant oils, and nitrates (large quantities generally necessary for toxicity)
Nightshade species	Vegetation, unripe fruit - loss of appetite, salivation, weakness, trembling, paralysis	Solanine - toxic at 42 mg/kg (LD50). 0.1 to 0.3% of body weight.
Pigweed species	Foliage (worse in drought) - kidney disease, weakness, edema, rapid respiration	Nitrates nitrate oxalates, unknown - 0.5 to 1% of diet. Sheep, hogs, and young calves most susceptible.
Pokeweed, common	Entire plant, especially roots - gastrointestinal cramps, weakened pulse, respiration, salivation	Phytolacctinm - 10 or more berries can result in toxicity to humans. Unknown for livestock, but perhaps 100-200 berries/1000 lb.
Snakeroot, white	Leaves and stem - constipation, loss of appetite, salivation, rapid respiration. Toxin passes through milk (milksickness).	Trophine alkaloid - varies from 1 to 2% of animal body wt. after 2 weeks. Toxin cumulative.
St. Johnswort	Flowers and leaves - photosensitivity which leads to redness of muzzle, around eyes, and around white hair.	Hypercin - uncertain

Key points about weed forage quality and poisonous plants:

Some weeds have excellent nutritive quality.
Weeds in the vegetative stage of development usually are more nutritious than more mature weeds.
Regardless of weed quality, livestock may avoid grazing certain plants because of taste, smell, or toxicity.
Some plants contain potentially poisonous substances that may be toxic to livestock if consumed — properly identify potential problem weeds and consult with a veterinarian if necessary.
A productive pasture is important to reduce the potential incidence of toxic weed exposure to livestock. Remember to soil test and maintain the proper lime and fertility levels. If possible, routinely mow or spray to manage weed problems within and around pasture area.

For additional information and resources on plants that are poisonous to livestock see the University of Pennsylvania Web site, the Cornell site, and Purdue’s site. In addition, there are numerous other Web sites that contain information on this subject. Simply conduct a Web search for poisonous plants and livestock.

Weed Control in Small Grain Stubble — Kevin Fry, Armstrong County

Now is a good time for controlling problematic weeds in your small grain stubble, especially prior to forage seeding. Once the grain is harvested and the straw is baled, a systemic herbicide can be applied at this time to control actively growing weeds. Application should be made within 1 to 3 weeks after harvest. Glyphosate control is reduced as weed size increases above 6 inches.

Your goals will be to control summer annual seed production (lambsquarter, ragweed, foxtail, etc.). Mowing alone will not control seed production, they can regrow — this is especially true for annual grasses like foxtail which will require two to three mowings to prevent seed production. An application of Glyphosate and 2,4-D will be very effective on most weeds. If weeds are tall and beginning to flower, spraying the regrowth following mowing may provide better control, but wait two to three weeks before you make the herbicide application. This can be particularly effective on perennial weeds.

Speaking of perennials, this can be also an excellent time to control troublesome perennials. At this time of year, perennial’s root reserves are at their lowest which coincides with the bud to bloom stage of growth. Frequent rainfall and good soil moisture ensure healthy perennial weeds that are susceptible to systemic herbicides. Weeds in drought stress or flooded fields may not respond as favorably and you should probably mow to prevent seed production and make a later summer application. An application of Glyphosate and 2,4-D or dicamba (Banvel/Clarity) will be effective in controlling most of those troublesome perennial weeds.

Insect Defoliation Assessment — Del Voight, Interim Grain Crop Specialist

Insect Identification & Distribution

A host of insects are building in population and will begin feeding on corn and soybeans. The insect pest complex includes (1) the bean leaf beetle, (2) the Mexican bean beetle, (3) the Japanese beetle, (4) grasshoppers, and (5) the green cloverworm (6) rootworm beetles.

The bean leaf beetle is a beetle that varies in color from golden brown to green, generally has 4 black spots on the wing covers, and always has a black triangle on the shield directly behind the head. The larvae develop below ground on the root system. The first generation will emerge in the next week or two depending on weather conditions.
The Mexican bean beetle is a coccinelid beetle (i.e. the lady bug family). The adult is a gold color and rather oval shaped beetle having 16 black spots on the wing covers. The larvae have conspicuous spines and when fully grown measure approximately ½ inch in length. Although distributed throughout the state, this pest has been predominantly a pest in the southern and east central regions of Ohio.
The Japanese beetle is a scarab beetle. This bright metallic green and bronze beetle measures nearly ½ inch in length. The larvae is a typical grub similar but smaller than the grubs of June beetles. June Beetles are already emerged in the southern portion of the state and will be laying eggs in high organic matter areas. These beetles will seek the first silked corn fields so as the silks emerge be on the look out for this pest. If the damage is evident and the insect trims the silks to within a half inch of the ear tip; treatment is warranted to protect pollination. Once brown silks are evident damage to pollination is not an issue. Beetles also can severely attack soybeans as well.
Grasshoppers affecting soybeans and corn are primarily the differential grasshopper and the redlegged grasshopper. Economic activity of grasshoppers (both adult and nymph stages) is normally notes in areas near grassy areas. Reports from across the southeast of massive populations are being reported so it is wise to keep a eye on areas of fields bordering grassy areas.
The green cloverworm is a migratory moth that enters the state each year from the south. Reports from Maryland indicate heavier than normal populations and I observed feeding and collected larvae at the Southeast Research Center in Landisville. The larvae are green in color having 2 thin white stripes along each side of the body. Full grown larvae may reach 1 to 1 ½ inches in length.
Rootworm larvae are beginning to turn into adult beetles. After observing third instar larvae near Hershey I would expect them to begin emerging as adults in about a week or two depending on weather. Northern(green coloration) and Western beetles (yellow/black coloration) will begin searching for the first silked fields and feed heavily on silks the females will leave those fields and end up in the last silked fields to lay eggs. For this reason one may forecast next seasons populations based on in field diagnosis and observation. For now it is important to protect the silks of the plants and use the same guidelines for other beetles that feed on silks.
The new PIPE systems Web site allows you to check in at convenient times to check on the status. Click on this and follow it to rootworms and see what stage they are entering in your area.

Damage Assessment

During these tassel phase in corn and pod formation in soybeans it is critical to assess the potential of these complexes to maximize leaf loss and reduce pod and silk feeding.

After trifoliate leaves have formed, damage assessment is based on estimates of defoliation. To estimate defoliation, the following procedure is recommended:

Pick a trifoliate leaf from the top, middle and low third of 10 randomly selected plants. (It is suggested that one carry a plastic bag for collection of foliage so that damage assessment may be made at one time.)
From each trifoliate discard the most and least damaged leaflets. At this point one should have 30 leaflets upon which the defoliation estimate will be based.
Compare the selected leaflets to the illustration provided and record the average level of defoliation.

The action thresholds for determining the need for a rescue treatment varies with the stage of soybean development. Please note these are based on historic market prices current market prices may reduce the levels to compensate for the extreme change in markets. Recommended action thresholds include the following:

Pre—bloom 30%
Bloom to Pod—fill 15%
Pod—fill to maturity 25%

If defoliation exceeds the action threshold at a given stage of soybean development, then a rescue treatment may be warranted if the pest causing the injury is present and vulnerable to treatment.

Sampling foliage and assessment of defoliation should always be accompanied by observations of the defoliating pest complex present. Preferably, the field observer should take a minimum of 30 sweeps with a standard insect sweep net. Soybeans are generally swept parallel to the rows (not across the rows). In the process, the dominant pests present and their predominant stage of development should be noted. Maintenance of sweep catch records will enable comparison from time to time to determine whether pest activity is increasing or decreasing.

Here are some points to keep in mind when using insecticides for beetle control:

Japanese beetle flight is greatest on clear days with temperatures between 84° and 95° F and winds less than 12 miles per hour. This can bring new beetles into the field to challenge any control program that you may have. When these conditions exist, check plants frequently to see if beetles are starting to feed again.
A few beetles on plants, or some moderate damage, will bring in more. Japanese beetles apparently produce aggregation pheromones that will attract more males and females to feed and find potential mates. In addition, volatile odors from damaged plants may attract more beetles. These conditions also can keep beetle numbers high. Keeping numbers and damage low can mean fewer new arrivals.
Japanese beetles begin to feed at the tops of plants and move down as defoliation occurs. This makes damage obvious, in terms of brown leaves and esthetic damage, but also can pose coverage problems on large soybeans.
Some of the effective insecticides for Japanese beetle control, such as carbaryl (Sevin) and the pyrethroids (permethrin and others) can contribute to build-ups of mites or aphids. Watch closely for signs of these pests and use alternative products like Dimethoate and Lorsban. While these insecticides have a shorter residual life, they may help to reduce problems with secondary pests.

For a list of suggested insecticides, rates and restrictions for soybean and corn insect control follow the link to the PSU Agronomy Guide.

Wheel Traffic Affects on Soybean Yield — Del Voight, Interim Grain Crop Specialist

Dr. David Holshouser Extension Soybean Specialist Virginia Tech and Dr. Richard W. Taylor Extension Agronomist University of Delaware summarized results of studies into wheel traffic affects on soybeans. Here is the summary of the article. One may expect between 1 and 6% loss from running over soybean rows in the Mid-Atlantic region. The amount of loss will depend on the sprayer boom width, row spacing, and environmental conditions. There will likely be less of a loss in drilled rows than in 15&-inch rows because the resulting gap is smaller (22.5 inches versus 30 inches). Environmental conditions before and after the damage will affect the amount of compensation from neighboring rows.

Wheat Test Weights — Del Voight, Interim Grain Crop Specialist

Reports of high grain yields in the 80–100bu/acre range with little to no scab and high test weights are encouraging given the high input costs growers realized this season. Two issues to keep in mind as harvest continues. One is that test weight does suffer as harvest is delayed and also the concern for sprouted wheat. Below is an article from the June edition of the Mid Atlantic Agronomy Newsletter it details the impact of delayed harvest on wheat test weight. A discussion of the potential for pre mature sprouting and germination testing is discussed in the next article.

Wheat Test Weight Declines with Delayed Harvest. Wade Thomason, Carl Griffey and Kelly Burt. Virginia Tech. Univ. email: wthomaso@vt.edu

Test weight is the weight of grain contained in a bushel volume. A wheat sample with test weight equivalent to less than 58 lbs. per bushel may be subject to dockage; resulting in a reduction in the price received for wheat. Test weight is a function of both genetics and environment. So, test weight varies among varieties and from year-to-year for a single variety.

At physiological maturity, wheat grain moisture is about 37%, however at this high moisture level, the grain is too soft for combine harvest. Most producers harvest when the grain has dried to between 15 and 13% moisture. Delayed harvest is common in Virginia because of climatic conditions around harvest time. Rainfall between maturity and harvest is known to lower grain test weight.

Last season, plots from a number of commonly grown varieties were not harvested, but left in the field at the Eastern Virginia Agricultural Research and Extension Center, to study the effects of post-harvest weather on grain quality. The dates of sampling and cumulative rainfall between samples are shown in figure 1. While the 2007 harvest season was relatively dry compared to some, the plots did experience four rainfall events during the course of the study.

Figure 1. Cumulative rainfall by delayed harvest date, EVAREC, Warsaw, 2007.

Rainfall reduces test weight because grain that absorbs water swells. When the grain dries and shrinks, it typically does not return to exactly the same size and does not “pack” as well as it originally did. This results in more space between grains and lower test weight.

Figure 2 below illustrates the effects of wetting and drying on grain test weight. Consistent with reports from other researchers, we observed a loss of about 1 lb. per bushel in test weight with each rainfall event. The major influence is the number of wetting and drying cycles, not the total rainfall in each event.

Figure 2. Wheat test weight decrease with days after harvest maturity, EVAREC, Warsaw, 2007.

All varieties we evaluated last season responded similarly to weathering. This means that the main tool available to combat environmental conditions that cause poor test weights is choosing a variety with high genetic test weight potential.

Other than hoping nature provides ideal conditions, there are several things managers can do to increase the likelihood of harvesting high quality wheat.

Be ready. Equipment maintenance and repair should be completed well ahead of planned harvest time.
Timeliness depends on capacity. Attempt to have the combine, hauling, and storage/delivery capacity in place to harvest as much wheat as possible when weather is suitable. Understand the bottlenecks in your harvest operations and plan accordingly.
Start early. Harvesting high quality, high test weight wheat may mean that some wheat must be harvested at above 15% moisture and dried prior to storage.
Grow several (2 or more, depending on total acreage) wheat cultivars having distinctly different maturities (e.g. early, medium, late), which should reduce the risk and overall loss in test weight of the crop as a whole.

Pre-mature Sprouting in Wheat — Del Voight, Interim Grain Crop Specialist

We have not received any reports to date but conditions are set for a potential for kernels to begin sprouting in wheat if harvest is delayed and wet conditions persist. Normally dry conditions that favor development of quality grain for bread making exist during wheat harvest. With moist conditions, which delay harvest, the mature grain can sprout in the spike. Rain, heavy dew, and high humidity stimulate preharvest sprouting.

Moisture swells wheat kernels and activates enzymes that break down proteins, starches, lipids, and other constituents in the endosperm. Flour milled from the endosperm of sprouted wheat produces bread that is porous and sticky and has a low loaf volume. The grain has little value to the milling and baking industries. In past years growers reported sprouting in isolated areas of the field. The best tactic might be to scout fields if this condition does show up and select in the field the best place to harvest then harvest the poor quality last. I have received numerous calls into saving wheat and barley for seed and the PDA seed lab is useful to gain information as to the quality of the germination. Here is the link. http://www.agriculture.state.pa.us/agriculture/cwp/view.asp?a=3&q=128411

Register Now for the 2008 Agronomic Diagnostic Clinic — Dwight Lingenfelter, PSU CMEG

The Penn State Agronomic Field Diagnostic Clinic is approaching fast!
July 22 and 23, 2008, 9am – 4:30pm at the Penn State Agronomy Research Farm near Rock Springs, PA. Visit http://cropsoil.psu.edu/extension/clinic.cfm for more information about each topic. The cost is $60/person. ($80 after July 16—register now to avoid the late fee!)

To register, please visit: http://cropsoil.psu.edu/extension/clinic.cfm and use the “on-line” registration system or complete the hard-copy form and fax or mail it. Phone-in and email registrations are discouraged. Credit card payments will be accepted.

(Note: we are using a new registration system this year, so please make sure to complete the necessary procedure.)

We look forward to seeing you at this year’s Clinic!

If you have questions about the Clinic please contact Dwight Lingenfelter at 814–865–2242.

Contributors: Dept. Crop & Soil Science: Bill Curran, Dwight Lingenfelter, Marvin Hall and Sjoerd Duiker. Extension Agents: Andrew Frankenfield (Montgomery), Kevin Fry (Armstrong), Jonathon Rotz (Cumberland), and Mark Madden (Sullivan), Grant Troop (York) and Del Voight (Lebanon).

Editor: Marvin Hall

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