The number of acres planted to sorghum in Nebraska is expected to be 45% higher than last year, when this harvest photo was taken. Photo by Brett Hampton

May 2, 2003

Choose a top sorghum hybrid. Select a top performing hybrid from one of the seed companies that is proud to sell sorghum seed. Don't be afraid of taller hybrids. Many times these are top performers and, with today's combines, height is not a real issue. Height also doesn't appear to be closely related to stalk rot or standability. As a general guideline, I recommend planting 80,000 seeds per acre in any row spacing of dryland acres in Gage County or any southern county east of Gage. For each county west of Gage in southern Nebraska, drop the plant population by 5,000 seeds per acre.

Fertilize for top yields. Grain sorghum needs 1.1 lbs of nitrogen per bushel for top economic production. Soil test results will indicate how much nitrogen to add and the response you might expect from adding phosphorus and zinc. If the phosphorus level in the field is low, starter fertilizer is an excellent way to get the phosphorus efficiently placed for top response. Today when we rely so much on postemergent herbicides for weed control, starter fertilizer usually will help provide a larger plant sooner and aid in weed control.

Limit tillage. Grain sorghum yields have been excellent under no-till systems. If you feel you have to part the residue, avoid moving soil. Residue cover keeps the soil temperature a bit cooler and reduces stalk rot problems. This is particularly true as you move west in Nebraska to dryer and warmer summertime soil temperatures.

Control grasses. If you have a terrible grass or shattercane problem in the field, plant corn or soybeans rather than sorghum because of the limited herbicide choices available for grain sorghum. Early preplant herbicide applications in April are the best choice for grain sorghum. The herbicide will be in place for the later planted crop which saves moisture and gives the producer added options for both grass and broadleaf control. Spraying part of the Bicep, Bullet, Guardsman, etc. behind the planter and/or using Roundup behind the planter extends weed control and ensures a clean field at planting without using tillage to dry the soil and plant more weed seed. There are limited herbicide options for post grass control, so it's important to scout early and respond aggressively to escapes while they are small.

Scout for greenbugs. Scout fields carefully and often during July to determine the need for greenbug control. If you wait until August for treatments, the damage will already have been done.

Trifold chinch bug plan. Chinch bugs are a threat to sorghum and corn at three stages. First, in the seedling stage when chinch bugs are present because of poor or late control of grasses like volunteer wheat. Second, when wheat or oats ripen and the chinch bugs move to nearby grain sorghum or corn fields. Third, after heading when the second generation flies into the grain sorghum or corn and sets up housekeeping. Signs point to a higher population of chinch bugs this year so stay alert to the potential and be prepared to choose the best treatment option for your farm. (Also see story below on insect control in sorghum.)

Timely harvest. Often sorghum is not treated as a priority crop and is left to dry while corn is harvested. This may not be the best choice for top sorghum yields.

Exceptions to this are when sorghum is planted next to wheat where chinch bugs are abundant and in fields with a history of severe wireworm damage (greater than 20% stand reduction). Although planting time treatments are effective in controlling early season greenbugs, our studies indicate that seedling greenbug damage is uncommon in Nebraska.

Chinch bugs

Chinch bugs

Dry weather, poor wheat stands, and planting sorghum into wheat stubble with volunteer wheat can contribute to increased damage from chinch bugs. Chinch bug numbers and damage have been increasing in southeastern Nebraska the past several years and we expect some localized, heavy damage this year, particularly in sorghum planted next to wheat. In some fields, particularly in areas that had noticeable levels of chinch bugs last year, using seed treated with Gaucho or Cruiser or applying Furadan 4F at planting to the outer rows of sorghum next to wheat could be beneficial.

Southern corn leaf beetle Corn damage caused by the southern corn leaf beetle

The adult corn leaf beetle overwinters in sheltered areas and becomes active in April. In addition to corn it may feed on weeds, including cocklebur. The adults are about 0.20 inch long, grey to dark brown and often covered with soil particles, making them difficult to see. They hide in the soil during the day and are difficult to find. They feed on the stems of corn seedlings and the edges of leaves, producing a notched appearance. If abundant they may cause severe damage to seedling corn.

While some basic facts are known about the southern corn leaf beetle's life cycle, there has been little biological research since the early 1900s. This beetle has one generation a year. The beetle lays eggs in the soil around the base of corn plants, and the larvae hatch out in 6-10 days and feed on corn roots for about 10 weeks. Larvae pupate in the soil and adults emerge from mid July to August. Adults feed for a short while and then in late summer seek overwintering sites.

Stripe rust and leaf rust continue to develop in the southern plains (see map). By mid-April leaf rust had moved into southern Oklahoma, but severities were still low. However, with increased rainfall and warmer temperatures, the incidence and severity of leaf rust could increase rapidly.

Stripe rust was severe in central and northern Texas and southern Arkansas but had not been reported in Oklahoma by mid April. It’s northward progression will be monitored as the season progresses. In the 2001 outbreak, Nebraska fields planted to 2137 or Lakin were the most severely affected by stripe rust.

In many cases, it may be advisable to take the first cutting before buds develop. Cutting healthy, vigorously growing alfalfa after it gets about 15 inches tall has several advantages. First, the weather may be better than later in spring. Second, cutting some alfalfa early allows for staggering the work load and provides more time management options. Third, an early harvest can reduce some insect and disease problems. Most importantly, feed value from an early cutting can be very high and the second cutting probably will be ready before summer heat lowers forage quality.

With an early cut, however, yield will be lower than if the cutting were delayed, although much of the loss will be made up in later harvests. Regrowth for second harvest probably will be slower than if alfalfa had been cut at a more advanced growth stage, especially if your alfalfa experienced winter injury this year.

If you take an early cutting, be sure to allow a longer than normal recovery after either the first or the second cutting if you want to maintain long-term stands.

Clover leaf weevils are occasionally problems but are very vulnerable to fungus disease and haven't been pests since the late 80s and early 90s when spring rains were rare. Clover leaf weevil larvae will be in the debris around the crowns during day.

To determine the degree of clover leaf weevil infestation, scratch in the soil around the crowns and count the number of larvae found per crown. Their brown heads will help distinguish them from the black headed alfalfa weevil. The table compares some of the distinguishing characteristics between the alfalfa and clover leaf weevils.

Both the alfalfa and clover leaf weevils feed on first cutting alfalfa as larvae, and on regrowth of the first cutting as adults. While research conducted in northeast Nebraska indicates that clover leaf weevil larvae feeding does not cause yield reduction to first cutting alfalfa, alfalfa weevil feeding can cause severe losses to yield and quality of the first cutting.

Alfalfa weevil development in the Panhandle tends to lag behind the rest of the state. In many years, weevil larvae will survive the first cutting and feed on the regrowth. This phenomena also has been observed occasionally in northern Nebraska, as far east as Boyd County. While most regrowth problems will be caused by adult weevils, growers in the Panhandle and northern Nebraska need to be aware that either larvae or adults may hold back regrowth after the first cutting.

Figure 1. Vertical pump

Most irrigation in Nebraska uses groundwater, which is pumped using a vertical turbine pump (Figure 1). The University of Nebraska has field tested hundreds of pumping plants over the years. Based on these field tests and on laboratory tests of engine efficiency, the University has developed the Nebraska Pumping Plant Performance Criteria, also known as the NPPPC or NPC. This criteria states the amount of useful work (water horsepower - hours, whp-h) to reasonably expect a pumping plant to achieve in the field for each unit of energy consumed.

In a pumping plant test, the technician measures total head (lift plus system pressure), flow rate (gallons per minute), and rate of energy consumption. The performance of the pumping plant is stated in terms of whp-h per unit of fuel. The performance rating is the performance of the particular pumping plant compared to the Nebraska Performance Criteria and is expressed as a percentage of the NPC. A rating of 100% indicates the pumping plant is operating as expected.

A rating below 100% indicates the pumping plant is using more energy that called for by the criteria. For example, a pumping plant operating at 70% of the NPC is only producing 70% of the useful work it should for the energy it is consuming.

The most recent NU statewide pumping plant efficiency study tested 180 pumping plants. As one might expect, the efficiency of the pumping plants varied considerably. Some achieved good efficiency, including 15% which actually exceeded the NPC. (Performance ratings over 100% of the NPC are possible when a highly efficient motor is attached to a well-designed pump that is not worn or misadjusted). The fact that some pumping plants exceed the criteria indicates that the criteria is a reasonable target for all pumping plants. The other 85% of the pumping plants were found to use more energy per unit of work than would be expected by the Nebraska Performance Criteria. The average pumping plant in Nebraska was found to be operating at only 77% of the NPC. To put it another way, the average pumping plant in the study was using 130% as much energy as it would if it were operating at the NPC (1.0 / 0.77 = 130%).

When the efficiency of a pumping plant is not what it should be, the problem may be in the power unit or in the pump or both. Internal combustion power units on irrigation pumps can have the same problems as those in cars and trucks. About the only thing that will cause poor electric motor efficiency is if the bearings are bad or the motor is far larger than is needed for the job.

Causes for poor pump performance include:

Figure 2. Vertical turbine pump performance curve. (Click to link to a larger version.)

• pump designs that are poorly matched to their current job (perhaps because the operator has switched from gated pipe to a center pivot sprinkler or from a high pressure to a lower pressure sprinkler); and
• pumps that had worn impeller vanes and/or internal seals as a result of pumping sand, or impellers that were not properly adjusted within the pump bowls.

In the recent pumping plant tests, 57% were determined to potentially benefit from adjustments. Adjustments either to the engine or pump or both resulted in 14% average savings in energy costs over the initial test results. An equally important result of the tests was that inefficient pumping plants were identified and the feasibility of more extensive repairs beyond the field adjustments were calculated. On some pumping plants, the potential savings in energy costs from major repair or even replacement of the pump would pay for itself in only a few years.

If there isn't a water meter on the system, a short-term pumping plant test can be run using one of a variety of devices to measure the flow rate. Contact a reputable well driller to see if they can run a short-term pumping plant efficiency test. At today's energy prices, identifying a pumping plant that needs adjustment or repair could result in saving hundreds or even thousands of dollars each year.

The Clearfield sunflower was developed using conventional breeding techniques and is not considered to be a genetically modified organism (GMO). Myocgen and Seeds 2000 are offering a limited quantity of Clearfield hybrid seed this year. The seed is expected to be more widely available next year. Beyond herbicide is applied early postemergence at a rate of 4 oz of product per acre to sunflower with two to eight leaves. Weeds should be actively growing at the time of application and broadleaf weeds should be less than 3 inches tall. Grass weeds should not have more than four to five leaves. A nonionic surfactant and nitrogen-based fertilizer must be added to the spray solution for optimum weed control.

It is recommended that a soil-applied grass herbicide, such as Prowlr or Dual Magnumr, be applied before Beyond is applied. Beyond herbicide will control many broadleaf weeds that are troublesome in Nebraska sunflower fields including pigweed, kochia, Russian thistle, and nightshade; however, Beyond is an ALS-inhibitor and will not effectively control ALS-resistant kochia or Russian thistle. There also is some concern about the risk of transferring the gene conferring tolerance to Beyond herbicide from the commercial sunflower hybrid to wild sunflower. This technology should be avoided in fields where wild sunflower is present.

The other new herbicide label in sunflower for 2003 is Dual Magnum (s-metolachlor). Dual Magnum may be applied preplant incorporated or preemeergence to sunflower to control grass weeds. Rates range from 1 to 2 pints of product per acre depending on soil texture and organic matter content. Dual Magnum provides a similar level of grass control as Prowl herbicide, but it is not as susceptible to photodegrada-tion or volatilization. When it is applied preplant or preemergence in a no-till system, it can wait for rain longer than Prowl without losing its activity. Prowl does provide a little better control of small-seeded broadleaf weeds than Dual Magnum, but this may not be critical if broadleaf weeds are not a problem or if the field will also be treated with Spartanr or Beyond herbicide.

Spartan herbicide has provided excellent control of troublesome broadleaf weeds, such as kochia, Russian thistle, and pigweed in no-till sunflower. Spartan should be tank-mixed with Prowl or Dual Magnum herbicide at labeled rates for control of many grass weeds. If grass weeds are not a concern, an alternative strategy to tank mixing Prowl or Dual Magnum with Spartan is to plan on a postemer-gence treatment of either Poastr or Selectr herbicides if grasses become a problem. The disadvantage to this strategy is higher costs.

Some crop injury has been reported from using Spartan. The injury, which has typically been restricted to high pH, low organic matter soils on hilltops, consisted of leaf chlorosis, plant stunting, and occasionally plant death. Injured plants generally grew out of the injury within a few weeks and yield differences were minimal at harvest.

Spartan use rates range from 2.0 oz of product per acre on coarse soils with less than 1.5% organic matter to 5.33 oz of product per acre on medium or fine textured soils with organic matter content greater than 3%. Consider applying Spartan, with or without a soil-applied grass herbicide, two to four weeks before planting to allow ample time for rainfall to activate the herbicide. Follow up with glyphosate at planting to control any emerged weeds.

The preliminary All Farm Products Index is up 7 points (7.4%) from April, 2002. Higher prices for cattle, corn, soybeans, and broilers more than offset lower prices for potatoes, dry beans, celery, and lemons.