Mike Staton                                                Dan Rajzer
MSUE Agricultural/Natural                           County Extension Director, Cass County
Resource Agent, Van Buren Co.

Table 2. Soybean yield when glyphosate was applied to 4 & 8 inch weeds (Saginaw, MI 2004). Dr. Christy Sprague, MSU Extension Weed Scientist.

Maximizing Glyphosate Performance
By Mike Staton, Extension Agricultural Educator

• Know your glyphosate formulation. You need to know the glyphosate concentration expressed as pounds of acid equivalent per gallon and if the formulation contains a surfactant. If the product does not contain a surfactant, add a non-ionic surfactant at 0.25% by volume. MSU weed scientists have determined that some glyphosate products that include a surfactant will perform better under adverse conditions if additional non-ionic surfactant is added at a rate of 0.25% by volume. These products will have an “S” in the “Surfactant is Needed” Column in Table 10 on the next page of this newsletter.
• Always add spray grade ammonium sulfate (17 lbs. of ammonium sulfate per 100 gallons of water) before adding your glyphosate. MSU weed scientists evaluated several commercially available water conditioners and found straight ammonium sulfate performed the best.
• Apply glyphosate at the proper rate. Consider weed species and weed heights to determine your application rate. The full rate of glyphosate (.75 a.e./acre) must be applied to provide consistent control of velvetleaf, common lambsquarters and giant ragweed.
• Time your glyphosate application properly. Control barnyardgrass, crabgrass and nightshade before they reach 4 inches tall. Proper timing also reduces yield losses from weed competition. Apply glyphosate before the weeds reach 4 inches tall in corn and narrow row soybeans and before they reach 6 inches tall in soybeans planted in 30 inch rows to minimize yield losses.
• Rain-free periods range from 1 to 6 hours for glyphosate products. Check the product label or the MSU Weed Control Guide for this information and follow the recommendations. Allow at least 6 hours for Glyphomax Plus and Touchdown under cool, cloudy conditions. According to product labels, heavy rainfall within two hours may wash the following products off the foliage: Touchdown, Glyphomax, Glyphomax Plus, Glyphos, Gly-4, Gly Star Original, Credit Extra and Credit Duo.
• Avoid making applications during extended periods of hot, dry conditions. Herbicide absorption is decreased due to thickening of the waxy epidermis of the leaves of certain weed species.
• Do not spray velvetleaf after the leaves have begun to tip in the evening.
• Let the dew evaporate prior to applying glyphosate.
• Avoid glyphosate antagonism when making foliar applications of manganese to soybeans. The surest method for achieving maximum weed control and alleviating manganese deficiency symptoms is to make separate applications of manganese sulfate and glyphosate. Always apply the glyphosate before the manganese. If you must mix manganese and glyphosate in the same tank, make sure to use the chelated manganese (Mn-EDTA). Do not use other chelated materials as some of these have demonstrated significant antagonism. Mn-EDTA must be applied at lower rates to avoid burning soybean leaves so more that one application may be required.

What does this mean for SBA numbers in soybean this year? Based on the lack of fall aphid flight, low overwintering egg numbers, and lack of colonies on buckthorn, I expect early season aphid colonization will be low on beans in Michigan. The one unknown is what will happen later in the season. We could get flights on aphid in late July or early August.

Check Alfalfa Re-growth for Alfalfa Weevil
Alfalfa producers should check the regrowth in their fields for the first three to five days after cutting to make sure that weevil larvae and adults are not still present in damaging numbers and feeding on the regrowth. Look for larvae and adults on the soil surface around alfalfa crowns. They often can be found under leaf litter or at the juncture between soil and crown. During cool, cloudy weather, you may find them feeding on new alfalfa buds during daylight hours. An insecticide application is warranted when 6 to 8 larvae and adults per square foot are present or when 50% of the stems have feeding injury.

National Soybean Rust Commentary from the USDA SBR Web Site (updated: 05/24/06)
Alabama reported today that the kudzu patch in Henry County in SE Alabama, where soybean rust had successfully overwintered, was destroyed earlier this month. This was the only rust positive kudzu patch in Henry County. Scouting continues on kudzu patches from Florida northward to southern Illinois, and westward to Texas and Nebraska. Many of the soybean sentinel plots have been planted throughout the country with the most advanced ones in the south starting to fill pods. Currently, there are no reports of rust on newly planted soybean in 2006 including volunteer plants. Rust has been confirmed in five counties in Alabama, 11 in Florida, four in Georgia, and one in Texas. You can access the USDA SBR web site at http://www.sbrusa.net/.

Pre-sidedress Soil Nitrate Testing
Testing your soil for nitrate nitrogen is an excellent way to evaluate how much nitrogen is available to your corn crop. Numerous research and demonstration studies have shown that many farmers in Michigan could reduce their nitrogen fertilizer application rates without risk of reducing yields if they used the nitrate soil test. To get an accurate test result and maximize your economic return from nitrate testing, you will need to understand a few things about soil nitrogen. Nitrogen existing in the soil is in three forms (organic nitrogen, ammonium nitrogen and nitrate nitrogen). The nitrate test measures only the nitrate form. The reason why we measure the nitrate form is that soil microbes convert most of the organic nitrogen and ammonium nitrogen to nitrate nitrogen by early June. If you take your soil samples too early before this conversion is completed, the nitrate test will underestimate the amount of nitrogen available for your crop. Therefore, you want to wait until June to take soil samples. The highest nitrate levels typically occur in manured and legume fields. Fine-textured soils will also have higher nitrate levels than coarse-textured soils.

Send your soil samples to a qualified lab for nitrate analysis as soon as the samples are dry. The MSU Soil and Plant Nutrient Lab performs soil nitrate tests for a fee of $9.00 per sample. There is an additional $1.00 per sample charge if you would like to have the results faxed or e-mailed. You can expect the results back in 48 hours after the samples have reached the lab.

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The information given herein is supplied with the understanding that no discrimination is intended and no endorsement by MSU Extension is implied.