Volume 10, Number 4 - April 2004

This Month in Ag Connection

• Alternative Insecticides to Diazinon
• Soybean Aphid Management Recommendations for 2004
• Lime Management in Missouri
• Taxation Tidbit: Asset Transfers to a Spouse
• Fertilizing Soybeans

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Alternative Insecticides to Diazinon

On December 5, 2000, the EPA released its revised risk assessment and announced an agreement with manufactures to phase-out/eliminate certain uses of the organophosphate pesticide diazinon with phase-out completion by 2004.

Alternative pesticides are:

White Grub
*Imidacloprid:	The product's brand names are Admire, Condifor, Gaucho, Premier, Premise, Provado, and Marathon.
*Halofenozide:	The product's brand names are Mach2, Grub-b-gon, and Grubex (interferes with the molting process).
*Paenibacillus popillae:	The product's brand name is "Milky Spore Disease" (a bacterial disease for Japanese beetle grubs only).
*Trichlorfon:	The product's brand name is Dylox.
*Carbaryl:	The product's brand name is Sevin.

Caterpillars, Ants, Mole Crickets and Chinch Bugs
*Bacillus thuringiensis (Bt)	Brand names may include Dipel, Javelin, Thuricide, and Bt as a general identifying pesticide abbreviation. Check the label to see if the variety of Bt is recommended to kill caterpillars, beetle larvae (grubs), or fly larvae (maggots and others) and if the particular pest is listed.
*Hydramethylnon	Brand names include Amdro and Maxforce.
*Abamectin	Brand names include Affirm, Agri-Mek, Avid, Dynamec, Vertimec and Zephyr.
Pyrethrins	Natural insecticide from a flower labeled under several brand names.
*Pyrethroids	Synthetic insecticides similar to pyrethrins but having greater activity and longevity. Common and brand names may include sumithrin (Anvil), resmethrin (Scourge), and other common and trade names.
*Propoxur	There are several brand names of which Baygon is the most common.
*Carbaryl	There are other brand names but Sevin is the most common.

*Please note that these are the names of pesticide (chemical or common names) active ingredients and brand names. There may be many end-use products on the market containing any single active ingredient or combinations of active ingredients. The attached pesticide label is the last word on its use.

(Author: Jim Jarman, Agronomy Specialist)

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Soybean Aphid Management Recommendations for 2004

The potential economic losses to Missouri farmers from soybean aphid infestations can be high. In a 2003 Minnesota study, soybean aphids damaged nearly 4 million acres of crops and cost Minnesota farmers about $80 million in damages. While the damages in Minnesota have been high, the economic threshold has been reached in few fields in Missouri.

What sets the soybean aphid apart from other corn and soybean insects is its ability to rapidly reproduce itself asexually -- populations typically double in 2-3 days. The optimum temperature for reproduction has shifted from 78 degrees to 82 degrees, indicating species adaptation to Missouri conditions. One expert described the battle against the tiny green insect as "clone warfare." All soybean-growing areas of Missouri are considered infested.

Management practices should include:

1. Scout once or twice a week beginning in late June or early July. Examine the entire plant, particularly new growth. Check 20 to 30 plants per field. Scout late-planted fields closely. Fields near buckthorn, the over-wintering host, may be colonized at emergence and require earlier scouting. In areas without buckthorn, winged aphids migrate from other areas in mid-season.
2. Use an action threshold of 250 aphids per plant if populations are actively increasing. In replicated research trials, this threshold has worked well in late vegetative (at first bloom) to R4 soybean. This threshold incorporates an approximately 7-day lead-time between scouting and treatment to make spray arrangements or handle weather delays. Keep in mind that populations can decline as rapidly as they can increase. Spraying after R6 has not been documented to increase yield.
   • To determine if an aphid population is actively increasing, check over several visits. Conditions that favor aphid population growth are cool temperatures, plant stress, drought stress, fields with low potassium and a lack of aphid predators.
   • Check for mummies (tan, swollen aphids infested by a parasitic wasp) and winged females. Do not spray if mummies are numerous or a majority of aphids are winged or developing wings, an indication that the aphids will soon leave the field.
   • Plants are likely to be considerably above threshold if stems or pods are covered with aphids and honeydew, sooty mold covers the bottom leaves, and plants are stunted. Insecticide treatment is probably still of value, but the optimal time for treatment (greatest economic return) is past.
3. Aphid kill, residual, and yield gains are not consistent among individual insecticides. Consider the product choices for your situation.
   • Organophosphate products have a fuming action, and may work better in heavy canopies or at higher temperatures. Pyrethroids (Warrior, Mustang, Asana, Baythroid) have a long residual, but are less effective at temperatures above 90°F.
   • Tank mixes of fungicides, herbicides, or foliar feedants, with an insecticide targeted for the soybean aphid are generally compatible, but a jar test is always recommended. Consider the optimal timing and method (GPA, pressure, nozzle type) for all the components in the tank mix. Check the labels for information on tank mixes.
   • Good coverage is important, particularly with aerial application. Higher spray volumes and higher pressure help to move the insecticide down into the canopy.
   • Adding insecticide to early-season glyphosate applications as "insurance" is not recommended unless aphids are at threshold levels and actively increasing.
4. Leave an unsprayed check strip to compare against sprayed areas to determine the performance of the insecticide and the value of the treatment. Predators and parasites surviving in check strips may aid biological control.
5. Communicate treatment plans to beekeepers and follow precautions to minimize bee kills. In areas with concern about honey bees, pyrethroids are a better choice for application than other formulations.

These recommendations are the cooperative effort of researchers throughout the North Central states, funded with soybean checkoff dollars through the North Central Soybean Research Program.

Links to additional information.

• NCR Recommendations: http://planthealth.info/soyaphid/sbamgmt.htm
• Reproductive Soybean Development Stages and Soybean Aphid Thresholds: http://planthealth.info/soyaphid/uwexsoystage.pdf
• SBA map 2003: http://www.ceris.purdue.edu/napis/pests/saphid/imap/agl2003.html

(Author: Jim Jarman, Agronomy Specialist)

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Lime Management in Missouri

Why is pH important to your crop? A low pH could result in aluminum toxicity (water pH less than 5.5 or a salt pH of less than 5.0), phosphorous (P) less available, slower nitrogen (N) release and reduced effectiveness of triazine herbicides. High pH (> 7.0) can result in carryover of atrazine, Peak, Canopy/Classic, increased nematode populations, and reduced availability of P and micronutrients.

Soil test results from the University of Missouri are reported as salt pH. Most other states and private labs report water pH. Salt pH is closer to the pH that the plant experiences and is more stable and quicker to measure than water pH. Water pH is about 0.5 units higher than salt pH. Different soils have different critical values for pH. Soil pH will affect the nutrient availability to crops. Depending on the soil, the yields will begin to decline at different pH levels. Also, crops respond differently to soil pH level. Forage grasses are the least sensitive to pH levels, followed by wheat, corn, clover, soybean and alfalfa the most sensitive.

Where does acidity originate? The long-term factor is climate. Typically, humid areas have acid soils while arid and semi-arid soils are neutral to alkaline. The short-term cause for acidity is nitrogen fertilizer. Acid is released by conversion of ammonium to nitrate. All N sources are equal in acid formation except for ammonium sulfate, which creates two times more acid. Each pound of N creates enough acidity to require 6 or 7 pounds of lime. In a corn-soybean rotation where an average of 150 pounds of nitrogen is applied each corn production year, you have a total of 600 pounds of N applied in an 8 year period. It will take about 2 tons of lime just to neutralize the acidity from the N fertilizer.

Different soils with the same pH will require different amounts of lime. Clay soils need more lime than loam soils and loam soils need more lime than sandy soils at the same pH. Neutralizable acidity is the lab measurement used to take into account this variability and determine the lime recommendation.

When ordering lime there are some terms that are important. Calcium carbonate equivalence (CCE) is measured on a lime sample by seeing how much acidity it will neutralize per ton in comparison with pure calcium carbonate. The CCE for pure calcium carbonate is 100%. Lime with impurities would be less than 100%. In Missouri, the Effective Neutralizing Material (ENM) is used to describe the effectiveness of the liming material for raising soil pH in the field. ENM = CCE x fineness factor x 800. The fineness factor accounts for how much of the lime will react with soil within 3-4 years.

Additional lime management considerations are needed as producers increase the use of minimum till and no-till. Surface applied N in no-till crop production can result in acidification of the top inch of soil. At low pH levels, atrazine is not as effective, resulting in a potential for weed escapes and increased risk of atrazine carryover. In contrast, surface applications of lime (2 tons for example) can result in high pH in the top inch of soil, and Atrazine carryover risk is increased.

Lime management in no-till or minimum till requires smaller and more frequent applications of lime. The same total amount of lime is still needed. Keep track of soil pH in the top two inches. Sample to two inches and to six inches and keep the samples separate.

(Author: Wayne Crook, Agronomy Specialist)

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Fertilizing Soybeans

The current price outlook for soybeans makes you wonder whether or not to fertilize soybeans. Fertilizer is usually applied before corn in a corn-soybean rotation. Typically there is no fertilizer applied directly to the soybean crop. This system works as long as there is enough fertilizer applied for both crops.

In 2000 and 2001, University of Missouri researchers conducted soybean fertility trials at 20 sites across the state, to tell if the current recommendations were appropriate. The fertility treatments evaluated included additional N, P, K, sulfur and boron. All sites had adequate nutrient levels, based on the University of Missouri soil test recommendation program.

The scope of this study could not determine if recommendations are too high. However, researchers concluded that recommendations for P and K are at least adequate. If you are following soil test recommendations and your soil nutrients are adequate, additional fertilizer will probably not provide an economic return.

(Author: Wayne Crook, Agronomy Specialist)

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