April Articles

Tis the Season to Spray Thistles

April 3, 2002

In spring, before trees leaf out, is the best time to control thistles in pastures. The trouble with that advice is no one worries about thistles when they can't be seen from the pickup truck. The calls start coming in midsummer when thistles are blooming.

In early spring thistles are in the rosette stage with the primary leaves spread flat, close to the ground. They are easier to control soon after they become established, before they grow into thick patches and spread thousands of seed.

There are lots of herbicides that will work on thistle at this stage. But 2,4-D works very well and is fairly inexpensive. 2,4-D should be used before leaves begin to appear on trees and shrubs. Vapors from 2,4-D can drift to vegetable gardens and rosebushes with deadly results.

A new University of Missouri guide sheet, IPM 1015 "Thistle and Thistle-like Plants of Missouri, has pictures to identify the prickly pests. The guide, prepared by Fred Fishel, MU extension IPM specialist, can help identify the thistle in the pasture. MU manual MP 581, "Weed and Brush Control in Forages, Pastures and Non-Cropland," has a separate section on thistle control. Herbicides approved for use in Missouri are listed. These publications are available at local MU Extension offices.

For the widespread musk thistle, MU specialists encourage landowners to allow natural predators to provide control. Two introduced weevils are found in thistle patches across the state. One weevil attacks the rosettes. Another bores into the seed and prevents germination. The major reason central Missouri has so few musk thistles is from the weevils controlling vast patches across the Ozarks. In the early “80s, I spent many a rewarding spring day at roundups herding weevils from one musk thistle patch to another – Yaw Hoo! The only local infestations large enough to get weevils were along Route A between I-70 and Route B in Callaway and west of Midway on old 40 in Boone County in the mid ‘70s and early ‘80s. Only an occasional musk thistle remains there today.

Spraying or mowing the musk thistle at the wrong time destroys habitat for the weevil populations that can keep the weeds under control. There are no known natural predators for the other thistles.

The method of spraying depends on the extent of the thistle infestation. For localized patches, spot spraying with a hand sprayer works well. An all-terrain vehicle provides a convenient way to get around the pasture for spot applications. For larger infestations, a tractor-mounted sprayer or commercial applicator may be needed. Broadcast spraying of herbicides may also kill legumes in the pasture. This time of year, before the grass starts growing, the rosettes are exposed. The secret to success is to spray early in the growth cycle. Usually, pests are easier to control when they are young.

Thistles are biennial, becoming established in the fall of one year and growing into seed-producing plants the next year. A thistle patch that is not sprayed this spring will have rosettes to be sprayed again this fall.

The sources for this article are Bill Johnson, weed specialist at the University of Missouri (573) 882-0619 and Jim Jarman, Agronomy Specialist, (573)642-0755. University of Missouri Extension programs are open to all. 

I got a call the other day from a farmer wanting to know where he could buy soy diesel. If he grew it, he figured he should burn it in his diesel engines. He had heard that a filling station was selling soy diesel. Soy diesel would be made from only soybean oil. The commercial biodiesel product is known as B20 or a blend of 20 percent soybean and 80 percent petroleum diesel. Diesel engines need very little or no modification to run on B20. A quick bit of information on the politically correct term for soy diesel is “biodiesel”. 

Warm Winter Puts Fall Nitrogen At Risk - Dry Weather Helps?

April 10, 2002

Fall-applied nitrogen fertilizer at risk of loss because soil temperatures stayed above normal through early winter. Below normal rainfall across northern and western Missouri has helped to keep the nitrogen in place, ready for spring planting.  

Farmers gambled and probably won -- so far. Luckily we had dry conditions along with the warm weather. The nitrogen is probably still there. The nitrogen can still be lost if above-normal rain falls in April and May.

  April showers are needed after corn planting, especially on dry soils coming out of winter. However, a lot of rain will wash nitrogen down into the subsoil. Missouri corn growers applied a record-setting 60,000 tons of nitrogen last fall. That is up from 38,000 tons applied in 1999, which had been the previous high in recent years. 

Corn growers took advantage of the open season to apply fertilizer. Fall application saves time in the spring as farmers rush to control weeds and start planting. They took calculated risks. If the winter is mild and wet, risk of nitrogen loss is high. Fall nitrogen is applied as anhydrous ammonia, a gas that converts to ammonium, which is stable in the soil. Ammonium slowly converts to nitrate, which becomes mobile. The conversion is faster at warmer temperatures.

  Across a broad area soil temperatures did not drop below 50 degrees until early December. At that temperature, conversion slows. Anhydrous applied before November 15 has a good chance of having turned to nitrate. Once the fertilizer changes to the nitrate form, any water moving through the soil will carry the nitrate with it. Because it has been a dry winter for parts of Missouri, not much water has moved through the soil. In a normal Missouri winter, the soil cools in fall and then freezes.  

Most of the anhydrous was applied in November and December, according to the fertilizer inspection service of the MU Agricultural Experiment Station.  

Sampling soil to test for fall-applied nitrogen is complicated and must be done well to be meaningful. If you do not know where the anhydrous knifed bands are, you must take many soil probes to get an accurate sample. More than 30 deep probes (at least 24 inches) are needed for a good sample. A 6-inch probe is used for a regular soil test. It is better to test one or two fields really well, than to do a fair job on all of the fields. 

Peter Scharf, University of Missouri soil scientist, and MU soil technicians will make deep probes, down to 36 inches, in test fields across the state this spring. If they find low nitrogen levels, the soil scientists will issue advisories to regional extension agronomists and the media.  

Even if the nitrate has moved down into the soil, the nitrogen is not likely to be lost to the corn crop. In the growing season, corn roots reach deep into the subsoil for water and nutrients.  

The sources for information in this article are Peter Scharf, University of Missouri soil scientist (573) 882-0777 and Pat Guinan, Extension climatologist (573) 882-5908 (Pronunciation guide: Peter Scharf: Say Skârf; Pat Guinan: Say gâ-NÂN) and Jim Jarman, Agronomy Specialist, (573)642-0755.  

A regional Grazing School will be held on April 23 and 24 at the Russellville Fire Department. Contact the Callaway County MU Extension Center for more information at (573) 642-0755.  

Watch for notification of Advanced Master Gardener training at the Callaway County Callaway County MU Extension Center coming soon. University of Missouri Extension programs are open to all.

Look Now for Alfalfa Weevil

April 17, 2002

Look Now for Alfalfa Weevil

Alfalfa weevil (AW) infestations are being reported south and central Missouri. Warm weather will stimulate their growth. Early infestations may require treatment now. This is long before the alfalfa will be mature enough to harvest but gives plenty of time for preharvest intervals to expire. During past springs many producers have been able to avoid costly sprays and just harvest a little early. This year the weather has not been favorable for this excellent management option. Our warm winter has allowed AW to lay eggs which may continue to hatch up to harvest. We will need to watch our alfalfa closely.

At this time, alfalfa growers should be scouting for AW larvae by collecting 10 alfalfa stems at each scouted locations in a field. (Alfalfa plants on south facing slopes often exhibit early damage due to warmer temperatures and earlier egg hatch.) The stems should be carefully removed by cupping one hand around the top of the stem during picking. Holding the terminal while pulling the stem prevents the larvae from being lost. As soon as a stem is removed, it should be tapped inside a light colored (white if you got one) bucket to shake the larvae off. If a field averages 1 or more larvae per stem, the economic threshold has been reached and control is recommended.

If early harvest of alfalfa is used as a control method, then the crop should be harvested about 7 to 10 days prior to usual at the one-tenth bloom stage. A recent study in Missouri shaowed AW larval numbers are reduced by about 98% with mechanical harvest and about 90% by cattle grazing in a management intensive grazing system (MiG). This control can stop the risk as long as most spring-laid eggs have hatched. Producers using grazing for control must be aware of the bloat risk to cattle grazing green alfalfa and the risk to alfalfa stands due to trampling and root injury during wet conditions and soil compaction. If a producer decides to use an insecticide application, insecticides recommended for alfalfa weevil control are listed below. Rates are given as amount of product applied per acre. You may notice that Ambush and Pounce are not listed. Although they are economical and excellent insecticides against many other pests, they may not perform well against alfalfa weevils. Wait to use them against potato leaf hopper infestations.

It is possible a disease will control the alfalfa weevil larval. Cool, wet weather promotes a fungus which usually causes most of the AW larvae to die within 2 to 3 weeks after infection. Although, infected larvae have not been as of yet this spring. Sick larvae lose their green color and turn tan to brown.

Something to think about next year is removing the fall regrowth after it turns brown. AW need the stems to lay their eggs. Momma AW chews a small hole in the stem and lays her eggs in there. Several methods are effective such as winter grazing when the soil is firm, brush hogging just after the stems turn brown or burning. Late spring laid eggs may hatch from early growth. These weevils are usually late enough to be controlled by early harvest management.

Baythroid 2* 1.6 to 1.8 oz 7 days
Dimethoate See label See label
Furadan 4F* 0.5 to 1 pt 7 to 10 days (see rate)
Imidan 70-W 1.3 lbs 7 days
Lorsban 4E 1 to 2 pts 7 to 21 days (see rate)
Mustang 1.5EC 2.6 to 4.3 oz. (see label) 3 days
Penncap-M* 2 to 3 pts 14 days
Warrior T* 2.56 to 3.84 oz 1 day forage - 7 days hay

Read and follow all label instructions.

Information on the alfalfa weevils and pesticide recommendations is from Wayne Bailey, University of Missouri College of Agriculture, Food, and Natural Resources Associate Professor of Entomology, 573-882-2838 and Jim Jarman, Agronomy Specialist 573-642-0755. For more information on alfalfa, alfalfa weevils or other topics, contact the Callaway County Extension Center. University of Missouri Extension programs are open to all.

April 24, 2002

Look for early corn damage. Farmers are finding cutworms in cornfields well ahead of normal, High temperatures last week spurred cutworm growth. Those who haven't looked should check now.

With normal temperatures, we would see the first black cutworm damage on April 27 based on cutworm moth captures earlier this month. Wayne Bailey received calls on April 19 of the first larvae found in cornfields. Cutworms are being found as far north as Marshall and Carrollton, Mo., where heavy early planting was under way.

Control may be delayed because of the weather. We need calm winds and the ground must be dry enough to drive across. Many fields are too wet now, from weekend rains.

Pat Guinan, extension climatologist with the Commercial Agriculture Program, said temperatures for several days in mid-April averaged 20 to 25 degrees above seasonal norms.

Black cutworm larvae, the worm stage, cause economic damage by cutting newly emerged corn plants. The larvae cut seedlings at the base and sometimes drag them into their burrows.

The growth of cutworms is determined by the accumulated degree days. Computer models can project the expected first outbreak of cutworm damage when 300 degree days have accumulated. The degrees counted are those above 50 degrees Fahrenheit.

We saw the first heavy flight of black cutworm moths the night of April 6. That was earlier than usual. This flight was recorded in Callaway County’s trap on Monday the 8^th with 34 black cutworm moths caught. A total of 121 moths were caught here that week.

Normally the adult black cutworm moths arrive from the Gulf Coast on southern winds. We may be seeing local moths that survived the warm winter. Although, the moths in our traps looked fresh. Like they came out this spring in the southern U.S.

After arrival, each female lays more than a thousand yellowish-white eggs. With warm weather, the eggs hatch in three days. Immature cutworms go through six or seven growth stages, or instars. Larger larvae cause more cutting damage, with one larva cutting several plants in a single night.

Cutworms start causing damage when they are a half-inch long or in the fourth instar. Field crop scouts or crop consultants use "head gauges" to determine the growth stages of black cutworms. Each time a black cutworm sheds its skin to grow, its head grows at a predictable rate. Head gauges are a valuable management tool for telling farmers about how many more days until the cutworms stops cutting and about how many more corn plants will be cut.

Cutworms have several generations in a season, however the first hatch causes most damage to corn. The larvae have rough, grainy skin that ranges in color from light gray to black. When disturbed, they curl into a "C" shape.

We have a lot of early corn available for cutting. Cutting of seedling corn can be heavy enough to require replanting. Insecticides are available for rescue applications, but that requires early scouting and identification of the problem. Corn may outgrow the cutworms once it gets six inches tall.

A new MU extension guide sheet, by Bailey and Michael L Boyd, entomologist at the MU Delta Center, has been published this spring. "Black Cutworm in Missouri," G7112, is available at county Extension Centers, or from extension publications by credit-card order; call toll-free 1-800-292-0969.

The source of information in this article were Wayne Bailey, extension entomologist at the University of Missouri (573) 882-2838 and Pat Guinan, extension climatologist with the Commercial Agriculture Program (573) 882-5908 and Jim Jarman, Agronomy Specialist, (573)642-0755. University of Missouri Extension programs are open to all.

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	Jim Jarman, jarmanj@missouri.edu Agronomy Specialist, (573) 642-0755 Site maintained by: Jen Pauley, pauleyj@missouri.edu Last update: 04/27/06