Nebraska ranks fourth nationally in corn for grain production with 940,800,000 bushels in 2002, according to the Nebraska Agriculture Fact Card. Over 40% of the feed grains grown in Nebraska are fed to livestock in this state. This issue and the April 11 issue of CropWatch will spotlight corn production and pest management. Photo by Brett Hampton

April 4, 2003

No-till protects the soil surface with crop residue, reducing erosion and crusting. The residue acts as a mulch to reduce evaporation and keeps the soil surface cooler. In drought conditions, unprotected soils may be too hot and dry for proper root development.

Too often the soil will dry to the depth of tillage. An average silt loam soil can hold about 2 inches of available soil moisture per foot of soil. Tilling 6 inches deep and allowing the soil to dry to the depth of tillage could result in a loss of up to 1 inch of soil moisture with each trip. Shallower tillage, even row crop cultivation, can still result in moisture losses of about ½ inch. By not tilling or cultivating, you can minimize these moisture losses.

Greater yet are the soil moisture losses from evaporation once tillage destroys residue cover. The residue mulch reduces evaporation in several ways: by reducing solar heating of the soil, by keeping drying winds off the soil surface, by insulating the soil to keep it cooler, and by intercepting some of the water as it evaporates. Research has shown that the residue mulch can reduce water losses from evaporation by as much as 3 inches during the season.

While flattened residue makes a better mulch, standing residue is preferred in crop production. Any residue that is standing up and still anchored to the soil is more effective in keeping the wind off the soil surface, reducing wind blown soil losses and the dust storms common in the spring. In addition, anchored standing residue doesn’t have to be cut or handled during subsequent field operations and is far less likely to move with the wind, surface water runoff, or during furrow irrigation. Unlike a flattened mat of residue which may keep the soil surface too cold and wet for planting, the air movement among the standing residue allows more timely field operations while maintaining the benefits of the residue.

Disking dries the soil and destroys soil structure.

Some say the soil needs to be tilled to “open it up to let water in”. Unfortunately it dries to the depth of tillage so the initial water let into the soil just replaces what was lost rather than adding to the soil moisture reserve. Tillage breaks up and pulverizes the soil surface, making the soil prone to crusting from raindrop impact. Tillage actually creates a condition that seals the soil, resulting in more runoff and less effective rainfall or irrigation.

Tillage also destroys the residue cover that protects the soil from raindrop impact, reducing erosion and crusting of the soil and allowing more rainfall to soak in. The residue also slows water runoff allowing time for infiltration and acts as a mulch to reduce moisture evaporation from the soil.

Some people recommend tillage for herbicide incorporation for better weed control. While very shallow tillage with good soil mixing may help weed control, it also dries the soil and “plants” weed seeds. Deeper tillage dilutes the herbicide with more soil and dries the soil even more. Rainfall will incorporate herbicides more uniformly than a tillage operation, provided the herbicide label allows it and the herbicide is applied early enough to receive adequate rainfall. Usually there is enough rain in early April to activate an early preplant preemergence herbicide; however the chances diminish by waiting until late April or until after planting when weeds may have already started growing.

Higher fuel costs — about 30% more this year — also are a factor when considering tillage. The diesel fuel requirements for the typical disk-disk-field cultivate tillage system is about 3.77 gallons per acre including knifing in fertilizer, planting, and one row crop cultivation. By switching to a no-till system, the fuel use decreases to about 1.43 gallons per acre including knifing in fertilizer, planting, and two sprayings. By eliminating preplant tillage, labor requirements decrease and there is improved timeliness of planting.

Choosing an effective herbicide strategy is not always an easy task. Producers need to consider many aspects, including economics such as herbicide costs, fuel and time, and biological and environmental factors such as weed species spectrum, soil type, organic matter, herbicide efficacy, herbicide restrictions, annual precipitation, precipitation at application, and the ability to make a timely treatment application. Even when all of these factors are considered, often there is still no perfect choice.

Corn /weed competition

All weeds are not created equal. Each weed species competes differently with corn with some species being much more competitive than others. For example, common sunflower has a competitive index of 10 and is much more competitive than lambsquarters, which has a competitive index of about 2. Understanding the differences between each species and their competitive factors can be very important in determining what weed management strategy will provide the best return on investment.

Since weeds are not created equal we should acknowledge that neither are crops. Each crop differs in its competitive ability as well. Corn is one of the most competitive row crops planted in Nebraska. The relative competitive load necessary to cause a specific yield loss quantifies the competitiveness of a crop. For corn, it would take a competitive load of around 36, per 100 square feet, to cause a 5% yield loss. (100 square feet is approximately 40 feet of row in 30-inch rows.) Sunflower has a competitive index of 10, therefore it would take 3.6 sunflower plants per 100 square feet (3.6 x 10 = 36) to cause a 5% yield reduction in corn. This assumes that the weeds emerge at the same time as the crop.

Accurately calculating yield loss, especially when several species of weeds are present in the field, can be difficult. WeedSOFT, a computer-aided weed management decision support tool, can be purchased from the University of Nebraska to supply this information at the click of a button. Using this type of technology allows for more accurate yield loss analysis and better information for making weed management decisions.

Early preplant and preemergence weed management

Table 1. Pre-emergence herbicide terms Acronym Treatment Timing EPP Early Preplant 10-30 days prior to planting PP Preplant 0-10 days prior to planting PPSA Preplant Surface Applied 0-30 days on the surfaec PPI Preplant Incorporated 0-30 days incorporated PRE Preemergence Planting time until crop emerges Table 2 is available in a pdf format.

Controlling weeds before they become a problem just makes good sense. The old saying – “An ounce of prevention is worth a pound of cure” – is true with weed control in corn. Various techniques are available and depending on individual circumstances, one may be better than another. Producers need to determine their seasonal goals before committing to any one strategy.

Before we dive into all of the strategies available, be sure to refer to Table 1 for an explanation of all the terms and acronyms used for preemergent weed control in corn.

Early preplant herbicide applications 10-30 days before planting offer many advantages to most producers, especially no-till farmers. First, early preplant treatments allow producers to burndown winter annuals including henbit and mustards and early summer annuals, including giant ragweed, common sunflower and lambsquarter. This can be very important in a year characterized by drought conditions as these early weeds, while not competing directly with the crop, can quickly rob precious soil moisture.

Second, an early preplant treatment reduces most if not all weed competition as the crop emerges from the soil. Although this early competition may not be the most critical with respect to yield, it can quickly reduce yield as corn enters the two-leaf stage. Another advantage is that in years with limited moisture, the herbicide has a greater chance of being activated before the crop emerges. A disadvantage of the early preplant treatment is decreased longevity of residual activity. Common sense tells you the earlier a herbicide is applied to the soil, the earlier it will stop working. Postemergence programs need to be carefully evaluated before decisions are made and some knowledge of the field’s weed history will be helpful.

Preplant is similar to early preplant in that many of the same herbicides can be used. Treatments are typically made 0-10 days before planting. Preplant doesn’t give you the advantage of catching early weeds, but it may provide the needed residual to set the stage for a good postemergence treatment.

A preemergence treatment, applied after the crop is planted but before emergence, offers many of the same advantages. An additional advantage is that it allows the producer to increase the longevity of the herbicide. This works well with conventionally tilled fields and provides increased management flexibility later in the season as summer annuals begin to emerge.

Monsanto has received EPA registration of the MON863 event expressing this protein, and several companies will be marketing YieldGard^® hybrids which utilized this event. An article in the March 7 CropWatch described the refuge requirements for MON863 hybrids, which differ in several ways from the refuge requirements for previous Bt corn hybrids.

The table below summarizes results from a replicated small plot (4 row x 30 feet) trial conducted in 2002 at the South Central Research and Extension Center Research Farm near Clay Center. The trial evaluated a MON863 hybrid and its sister line for efficacy against western corn rootworms. Levels of feeding injury were assessed in mid-July using the 0-3 node injury rating scale developed at Iowa State University. This scale is different than the 1-6 scale commonly used in the past for corn rootworm insecticide efficacy trials across the Midwest. On the 0-3 scale, 1=1 node of roots pruned to within 1.5 inches of the stalk, 2=2 nodes pruned, and 3=3 nodes pruned. Partial units represent the fractional portion of a node pruned.

This study was planted in an area late planted to corn the year before, so there was heavy rootworm pressure (2.96) in the untreated isoline. The YieldGard hybrid has significantly lower root injury than any of the soil insecticide or seed treatment rootworm insecticides evaluated. The best soil insecticide treatment was significantly less effective than the YieldGard hybrid, although all the soil insecticide and seed treatments did provide significant root protection, compared with the untreated isoline. Similar results were obtained in a study at Clay Center in 2001. Limited seed was available for these trials, and no yield data were taken in either year.

Nozzles break the liquid into droplets, form the spray pattern, and propel the droplets in the proper direction. They determine the amount of spray volume at a given operating pressure, travel speed, and spacing. Drift can be minimized by selecting nozzles that produce the largest droplet size while providing adequate coverage at the intended application rate and pressure.

Table 1. Spray nozzle selection guide for broadcast application.* ---- Herbicides ---- Soil-Inc. Pre-Emerge Post-Emerge Liquid fertilizer Contact Systemic Turbo Jet Good Good Good Good++ Good Air induction Good+ Good+ Good Good++ Good+ Extended range flat fan — — Good++ Good Good Pre-orifice flat fan Good+ Good+ Good Good+ Good Standard flat fan — — Good Good — Twin orifice flat fan — — Good+ — — Turbo Floodjet Good++ Good++ — Good Good++ TurfJet Good++ Good++ — Good Good++ Solid cone — — — — Good+ * Mention of trade and company names does not imply endorsement or preferential treatment of the product names by the University of Nebraska-Lincoln. — Information not available or not applicable.

Spray particle size

The size of the spray particle is important because it affects both efficacy and spray drift of the pesticide. If you double the size of the spray particle (for example 300 to 600 microns) and the application volume stays the same, you have only 1/8 as many spray droplets. For optimum efficacy and 10 to 20 gallon spray volumes a medium droplet size is suggested for contact non-translocating herbicides and a coarse droplet size for contact translocating herbicides. Concern for drift may cause you to consider larger droplet sizes and higher spray volumes.

For preplant and preemergence herbicide application without a burndown herbicide and with liquid fertilizer, use nozzle tips which produce a very coarse or extremely coarse droplet size. The larger spray particles help reduce drift and evaporation. This is because nozzle tips which produce larger spray particles produce less small droplets.

Table 1 is a spray nozzle selection guide for broadcast applications. Remember, if you are banding use an even flow nozzle. An example of this nozzle would be AI9504E. The E tells you that this is an even flow nozzle tip which applies the same amount across the entire spray pattern.

The sum of average temperatures for December, January and February. Areas below 80oF are expected to see below average survival of flea beetles, areas above 98oF are expected to see above average survival of flea beetles. Corn flea beetle feeding causes direct damage, but perhaps more importantly, the beetle is a vector of Stewart’s Wilt. (Map developed by Al Dutcher, State Meteorologist, High Plains Climate Center.)

Corn flea beetles overwinter as adults in protected areas near corn fields. They become active in April and feed on a variety of grasses before corn emerges. Corn flea beetles can directly injure corn by feeding on seedling plants; however, probably more importantly they vector the bacterium which causes Stewart’s wilt. (For more information, see the NebGuide, “Stewart’s Wilt of Corn in Nebraska,” G1462.)

To minimize damage caused by flea beetle feeding:

• Avoid hybrids or inbreds known to be more susceptible to Stewart’s wilt (see seed catalog or local seed company representative).
• Avoid early planting dates if susceptible inbreds or hybrids are planted.

Scout for corn flea beetles on seedling corn. Postemergence treatment may be warranted on dent corn if 50% of plants show severe flea beetle injury (plants look silvery or whitish, or leaves begin to die), and five or more flea beetles per plant are found. If susceptible inbreds or hybrids are grown, an insecticide may be needed when two to three flea beetles per plant are present and 10% of the plants show severe flea beetle injury.

A variety of foliar insecticides are effective in controlling flea beetles. They include: Lorsban 4E, 2-3 pt/acre; Sevin XLR Plus, 1-2 quarts per acre, Asana XL, 5.8-9.6 fl. oz per 1000 row-feet; Lannate LV 0.75-1.5 pt/acre; Pounce 3.2 EC 4-8 fl. oz per acre; Warrior 2.56-3.84 fl. oz per acre), Mustang Max 2.72-4.0 oz per acre; Baythroid 2 1.6-2.8 oz per acre.

• Section 18 registration for using Spartan (broadleaf herbicide) in chickpeas, March 27-July 1;
• Section 18 registration for using Spartan (broadleaf herbicide) in potatoes, effective April 10-June 30;
• Section 18 registration for using Spartan (broadleaf herbicide) in sunflowers, effective April 1- July 1;
• Section 18 registration for using Outlook (herbicide) in sugarbeets, effective April 10 - July 31;
• Section 18 registration for using Checkmite on bee hives; effective March 17 - Dec. 31.

What I can report on now is the status of leaf and stripe rusts in Texas. If you remember stripe rust was widespread and damaging in the southern and central plains including Nebraska in 2000 and 2001 and leaf rust was moderately severe in 2002.

The following information is based on the most recent update from the USDA’s Cereal Disease Lab. In mid-February they reported light amounts of leaf rust in central Texas. Cool temperatures restricted leaf rust development, so the situation had not changed by early March.

By mid-February there were several hot spots of stripe rust in central Texas and by early March stripe rust was spreading in that area. When this disease occurred in Nebraska in 2001, the varieties 2137 and Lakin showed the highest rust severities. The northward progression of both rusts will be monitored as our growing season begins. Critical factors that will determine if we will have problems are how rapidly these rusts build up in Texas, Oklahoma and Kansas, a pattern of southerly winds that blow rust spores north and our May and early June weather once rust reaches Nebraska.

Wheat stem cut off at the top of roots and then split lengthwise to reveal hollow stem and the growing point. Return per acre in a wheat grain-stocker cattle enterprise is strongly influenced by when cattle are removed from the pasture. (Photo and illustration used with permission from “Economic Impact of Grazing Termination in a Wheat Grain-Stocker Cattle Enterprise” Oklahoma State University researchers Gene Krenzer and Gerald Horn. Also see the OSU publication, “Wheat Pasture Grazing Termination Makes Dollars and Sense”.

The developing grain head on all small grains (winter wheat, rye, triticale, barley) is located just above the highest stem node of the plant. Grain yield is jeopardized when this structure elongates and elevates to a height that is susceptible to being removed by grazing livestock. Generally, this occurs when the growth stage we call ‘jointing’ begins, usually about mid-April (earlier in southern Nebraska and later in the northern counties). Maintaining a 2- to 3-inch minimum stubble helps.

The jointing growth stage is easy to identify. Before jointing, all nodes are small and grouped together at or below the soil surface. Only a ‘pseudo’ stem comprised of tightly wrapped sheaths of leaves gives the plant erect growth. When jointing occurs, the first node becomes swollen and appears above the soil surface. It can be seen or felt. This begins formation of the true stem with the grain spike just above this first node. A sharp knife can split the stem lengthwise to see the location of the hollow (in most varieties) true stem, the hard and swollen node, and an elongated, triangular shaped developing grain spike.

Grazing tends to slightly delay the onset of jointing. Thus, a good way to avoid grain yield reduction is to protect a small area of the field from grazing and observe ungrazed plants for the onset of jointing. If animals then are removed from the small grain pasture, little grain yield reduction will have occurred as a result of grazing removing grain heads. Grazing often can continue for a week to 10 days beyond the onset of jointing with only slight grain yield reduction as long as a minimum of 2 to 3 inches of stubble remains ungrazed. Both irrigated and dryland fields respond similarly.

If the primary grain head is removed, plants sometimes produce new tillers but these new tillers usually do not produce grain.

Spring small grains, like oats, behave similarly. They will not elevate their seed heads until about one month later than winter small grain. Tillers stimulated by early grazing can form some grain.

Disadvantages to no-till include relying solely on clipping or post-emergence herbicides for weed control. Fortunately, we have good post-emergence herbicides available. Another problem is ridges from prior row crops that can interfere with uniform seeding as well as make fields rough for future haying operations. And finally, some drills do not work well for no-till seeding so equipment might limit your options.

If you can do it, no-till alfalfa is worth trying. It works really well in bean stubble and almost as well in small grain stubble. No-till is a bit more difficult in corn and milo stubble, especially if there is much row ridging. Be sure to kill any early weeds with Roundup or Gramoxone before planting. And last but not least, use a drill that places seed about one-half inch deep and then covers seed with soil using a good press wheel.

Field of irrigated proso millet in western Nebraska.

As a dryland crop grown without fallow, proso is a very efficient user of soil water and can produce a grain crop with 13 to 14 inches of annual moisture. Studies at Akron, Colo., indicated that proso begins producing grain after only 6 inches of total water use, while winter wheat requires 9 to 10 inches of water before grain production begins. Proso also has worked well under irrigation after a row crop like corn or sorghum because proso tolerates atrazine that may remain in the soil after the corn or sorghum crop. It also can be planted after beans, beets, potatoes or alfalfa if residual grass herbicides are not an issue.

Proso has a shallow rooting system. Its rooting depth is generally limited to the upper 6 to 12 inches. It is one of the most efficient crops at removing moisture from the topsoil and converting it to dry matter. Proso requires approximately 270 pounds of water to produce 1 pound of dry matter; wheat requires approximately 530 pounds of water to produce 1 pound of dry matter.

For these reasons proso may be a valuable alternative for irrigated land with less than normal available irrigation water. Irrigated yields may be as high as 40 cwt per acre, although yield might more typically range from 30 to 35 cwt per acre. Proso has minimal straw strength relative to wheat so production practices targeting yields higher than this usually result in lodging and significant yield losses. The most serious problem with irrigated proso production is wild proso. Select fields where there is no history of wild proso. Buffalo-bur also can cause the crop to be rejected. Most broadleaves can be controlled, but sandbur can be a serious competitor.

The bulk of proso sold in the cash trade is marketed through elevators in the counties where it is grown most extensively. This grain is cleaned further, processed, and used for bird seed. Both domestic and wild bird seed is packaged by adding other grains for color and nutrition. Some proso goes through a dehulling process and supplies both human and animal needs. Some is exported and some is used for specialty purposes, such as mushroom production. Proso is the only millet of quantity involved in world trade. As a feed grain, some cracking improves utilization.

Proso prices have historically been higher than corn or sorghum, but this varies dramatically from season to season. When the premium human food and bird seed markets are saturated, the price quickly drops to feed grain values or less as conversion from corn to proso can cost some money. Proso prices have ranged from $1.50 to $20 per cwt over a five-year period.