Corn leaves exhibiting eyespot symptoms of yellow lesions with brown or purple borders.

Eyespot identified in Nebraska corn fields

Disease symptoms include small circular tan lesions (1-4 mm in diameter) that are surrounded by a brown or purple ring and a yellow, translucent halo (Figure 1) that can be seen when held up to sunlight, giving lesions the appearance of eyespots. The appearance of these lesions will vary by hybrid. They generally develop on lower leaves first and can fuse to cover the entire leaf. The pathogen survives on corn debris, so reduced tillage and continuous corn create a high-risk environment for development of eyespot, especially if there is heavy residue and a history of it in that location.

A few producers apply fungicides to control it, but you should carefully consider the economics of this decision, especially yield potential, crop value, associated costs of fungicide application, and the weather forecast. This disease is favored by cool, humid weather, like that experienced in many parts of Nebraska up until three weeks ago. The recent development of hot, drier weather will help slow the progression of this disease. Hybrids are available with resistance to eyespot and should be considered when you plant corn in that location again.

Tamra Jackson Extension Plant Pathologist

The first irrigation of the season is typically the least efficient. Often the crop roots have only penetrated 18 to 24 inches. Crop water use is at minimal levels so the depletion of water in the soil is minimal at deeper depths. Although the soil surface is likely to be dry, usually 2 to 3 inches of water is needed to refill the soil profile. The amount of water applied during the first irrigation is usually the largest of all irrigation events. This is due to the rough soil surface, clods, and residue in the furrow that slow water advance. After the first or second irrigation, the furrow surface is smooth and water advances at a much faster rate. Therefore the greatest savings of fine-tuning furrow irrigation sets will result from the first irrigation or two.

One challenge that faces most furrow irrigators is how to balance the amount of runoff that leaves the field and the amount of water that percolates below the active root zone. One management tool to improve efficiency is to use the Target Cutoff Ratio. This is the ratio of the time required for water to advance to the end of the furrow divided by total set time.

Research has been conducted to determine the “best” cutoff ratio for various types of furrow irrigation systems and soil types. Choosing the appropriate cutoff ratio depends on soil factors and irrigation system configuration. The cutoff ratio helps the furrow irrigator to minimize deep percolation and runoff. Table 1 lists the target cutoff ratios for several irrigation system/soil texture combinations.

Table 1. Target cutoff ratio based on soil and system considerations. Sandy soils Loamy soils Clayey soils Without reuse 0.50 0.70 0.90 With reuse 0.20 0.40 0.50 Blocked ends 0.70 0.85 0.95

By looking at the target cutoff ratios, you can see that for coarse soils, smaller ratios are recommended. Smaller ratios indicate a faster advance time so that the top end of the field would have a similar infiltration time as the lower end of the field. Smaller advance times would limit deep percolation that is inherent with coarse textured soils. Conversely, with finer texture soil, a larger advance time would encourage less runoff, since advance time and set time are similar.

The reason that systems with reuse systems have such a low cutoff ratio (faster advance time) is that when the water runs out of the field, it is collected and used to irrigate the same or a nearby field. Pumping water from a reuse pit to another field is less expensive than pumping water from under the ground. By having fast advance times, deep percolation will be virtually eliminated and water that leaves the field in the form of runoff will be used again, at a smaller cost.

The one telltale sign that indicates many furrow irrigators do not use the cutoff ratio is flags that mark furrow numbers at the end of the field. If irrigators use the cutoff ratio, even on clayey soils without reuse, water should advance to the end of the field in under 11 hours, on a 12-hour set time (12 hours x 0.90 cutoff ratio = 10.8 hours). If water was advancing in under 11 hours, there would not be a need to count rows (i.e. no need for flags) and leave gates open that have not advanced to the end of the field.

To use the cutoff ratio effectively, calculate an actual cutoff ratio. Take observations in the field and keep track of the amount of time it takes for half of the rows to reach the end of the field, this is the advance time. Divide this number by the total set time, typically 12 or 24 hours. If the observed cutoff ratio is greater than the recommended cutoff ratio from Table 1, open fewer gates on the next set. This will cause more water to enter each furrow, and will likely have a faster advance time.

With the proper cutoff ratio and gross water application, you can achieve uniform application and minimize both deep percolation and runoff. Experiment with different combinations of furrow stream size and set time to find the optimum settings for a particular irrigation in a particular field. The best combination is one that moves water to the end of the furrow within the requirements of the cutoff ratio, is less than the maximum non-erosive stream size and results in gross applications that are not excessive.

There are several generations per year in Nebraska, but typically the first generation on corn does the most injury. Field observations indicate that this first generation is near the end of its feeding. As corn matures the leaves thicken and the maggot tunnels in only the lower or upper half of the leaf, causing less damage.

Foliar insecticides are not recommended for these insects. The adult flies emerge over several weeks and would be difficult to economically control with insecticides. The egg and immature stages are inside the leaf and protected from insecticides.

Soybean stem damage caused by hail at the V7-V8 stage in 2004 (Photo by Lori Abendroth)

Some areas of central and eastern Nebraska recently sustained hail damage, leaving producers to consider whether to replant or stick with the current crop. For many producers, options may be limited by previous herbicide selection, timing (in many areas it's too late to replant corn), and wet fields. Producers will need to consider potential yield loss of the existing crop vs. replanting costs and potential reduced yields.

Before doing anything with the field, notify the proper government agency and, if you plan to make a claim, your insurance provider. Discuss replant options and limits; when they'll be able to determine the severity of the loss and their assessment of the loss. Next, consider your investment in the crop, additional expenses, and expected yield at this point. Weed and pest control will continue to be costly, and weed control may be even more difficult if the crop canopy is open. Be sure to consider herbicide replant options for this year as well as next year if applying herbicide this late in the season. Whenever you open the canopy, weeds will develop quickly. Timely rescue treatments when the weeds are small will be most effective and cost efficient. Hail and wind damaged fields also may face increased insect problems. Some insects prefer later maturing corn and may flock to those fields, requiring continued diligence in scouting.

Yield potential of soybean

Much of the research regarding soybean damage from hail gives yield loss values greater than what we’ve seen in recent research at the UNL South Central Agriculture Laboratory (SCAL) at Clay Center. Soybean compensated very well to stand reductions by branching outward instead of growing upward.

In our research at SCAL we reduced stands at the V6 and R1 stages. Reports this week indicate that much of the state’s crops may be at comparable stages. Based on our research, if producers lost half their stand (i.e., half of the plants were hit by hail at the stem baseand broken so that the plant could not regrow), we would estimate yield loss to be 12% and 18% of yield potential at V6 and R1, respectively.

Sometimes when hail hits a soybean crop most of the plants will appear undamaged, while they actually do incur damage. The hail will hit the stem and bruise it or open it up slightly, enabling disease pathogens to enter. The plant may still grow, but lodging may occur at harvest because the weight is too great for the stem.

Soybean also will lose leaves from hail, but as with corn, this is not the primary concern. New trifoliate leaves will emerge about every four days. A 50% loss in leaf area at R1-R2 will reduce yields by only 6% and a 100% leaf loss only equates to a 23% yield loss.

Market Journal This week's Market Journal, Cooperative Extension's Television for Ag Business Decisions, focuses on crop and livestock issues. Watch or listen using RealPlayer as host and Agricultural Economics Specialist Doug Jose visits with ag researchers and specialists. Water Supply for Irrigators (Length 3:11) Even with good rains in the Platte and Republican River Basins, irrigators will get less water. Ann Bleed, deputy director, Nebraska Department of Natural Resources, says some basins are considered to be fully or over-appropriated. Soybean Rust (Length 3:05) Loren Giesler, University of Nebraska extension plant pathologist, explains the role of weather in whether soybean rust moves into Nebraska and shows what to look for in the field. Ag weather (Length 2:57) Below normal precipitation is forecast over the next ten days in the grain producing states, according to University of Nebraska-Lincoln State Climatologist Al Dutcher. This will affect the markets. Visit the Market Journal Web site to view the whole program or individual segments. Market Journal is broadcast Fridays at 12:30 p.m. on the Disk Network NAUHS 9411, Saturdays at 6:30 a.m. on NETV, and Sundays at 9 a.m. on NETV2. Watch or Listen

Southeast Nebraska lies on the extreme western edge of a broad area of dryness that extends from eastern Texas and Oklahoma northeast through Arkansas, Missouri, Illinois, and Indiana. Within this area, much of central and northern Illinois are seeing some of their worst drought conditions since the late 1980s. As of June 26, Illinois corn condition was rated 29% good and 3% excellent.

While recent models indicate limited precipitation relief may occur across portions of the eastern corn belt, no significant reversal in the pattern is forecast in the next 14 days. Temperature forecasts do point to the central and eastern United States upper air ridge slipping westward, as an upper air trough digs into the eastern states. This may push temperatures back into the normal range as the corn crop moves into the critical pollination stage.

The ridge movement from a central/eastern to a western/central U.S. position during the next seven days should result in a rapid temperature warm-up for the July 4th weekend. After a couple of days of below normal temperatures, highs will again move back into the 90s across Nebraska, with 100s in central and southern Kansas. Precipitation chances will depend on whether thunderstorms can fire across the western third of the state and move eastward during the late evening and overnight hours.

Precipitation forecasts after the July 4th weekend will depend on the mean position of the western/central U.S. upper air ridge. If it pushes westward over the central Rockies, northwest flow aloft on the eastern edge of the ridge will allow systems to push southeast from the Dakotas. Since there has been an abundance of moisture across the Dakotas for the last 30 days, this type of pattern could tap surface moisture, giving the eastern half of the state a decent opportunity for beneficial rainfall. If the ridge establishes itself across the central United States, then the best precipitation chances will remain in the west, including western Nebraska. Under this scenario, further deterioration of soil moisture conditions in southeastern and portions of central Nebraska can be expected. Temperatures would be expected to remain in the 90s, depending on how far north the core of the upper air high reached into the central United States.

One of the unexpected consequences of the recent storm activity across central and western Nebraska during the last 30-45 days has been the reduction in irrigation demands. Lake McConaughy is a full 5 feet higher as of June 27 than it was at this time last year. Also encouraging is that above normal moisture has been consistently falling across a substantial portion of the Platte River valley in Wyoming.

Although we don't expect to see McConaughy improve significantly through the remainder of the growing season, conditions are in place to see more substantial recoveries this fall into next spring given a continuation of the current weather pattern. Forecasts for the next three months are positive as they continue to indicate a tendency for above normal precipitation across Wyoming, Montana and Idaho.

Confidence concerning a substantial recovery within the Republican river basin is a little more tempered. Although good rains have fallen on occasion across the watershed within the Nebraska borders, generous precipitation within the headwater area of east central Colorado has not been as common. Until these events occur on a regular basis, streamflow rates on the Republican, east of Colorado, will remain within the lower end of average flows and Harlan reservoir will be slow to improve.

Al Dutcher
Extension State Climatologist

Corn rootworm beetle

I have received some calls concerning how long rootworm larvae will feed. The table summarizes duration of immature stages of rootworms at constant temperature.

Regular scouting of rootworm beetles during late July and August, which corresponds with their egg-laying period, provides information on the potential for damage in that field if it is planted to corn next year. I will discuss rootworm beetle scouting recommendations fully in the next issue of CropWatch.

Be aware that rootworm beetles emerging before silks are available will feed on the corn leaf surface by scraping away the green surface tissue, producing a window-pane appearance on the leaf. This is not an economic concern.

As silks emerge beetles will concentrate in the first silking fields to feed on silks and pollen. Complete information on rootworm beetle scouting and thresholds is available in Corn Rootworm Management (EC 1563), available from local Extension offices.

Bob Wright
Extension Entomologist

Table 1. Duration of immature stages of western corn rootworm at constant temperatures. Days to complete stage Degree days to (male/female) at different complete stage constant temperatures (oF) (48.2oF base) Stage 64.4 69.8 75.2 Males Females 1st instar larva 8.1/8.6 5.6/6.2 4.8/5.3 70.4 77.7 2nd instar larva 6.8/7.1 4.9/5.4 4.3/4.9 61.7 70.6 3rd instar larva 15.0/15.5 11.2/11.9 9.4/10.4 140.5 149.2 Pupa 13.5/13.8 10.1/10.1 7.8/8.4 122.2 125.1 Hatch to adult emergence 43.4/45.0 31.8/33.6 26.3/28.9 394.8 422.6 Source: Jackson & Elliot, 1988, Environ. Entomol. 17:166-171.

Figure 1. Soybean aphids on a single leaf, 2002. In Minnesota, as many as 13,000 soybean aphids have been found on a single plant.

We have learned much about the insect, including two things which stand out as important to Nebraska farmers:

1. the seasonal occurrence of the soybean aphid has been different in Nebraska than in much of the rest of its range; and
2. late season infestations can cause significant yield loss.

Description

The aphid is light green to pale yellow, less than 1/16 inch long, and has two black-tipped cornicles (cornicles look like tailpipes) on the rear of the abdomen. It has piercing-sucking mouthparts and typically feeds on new tissue near the top of the soybean plant on the undersides of leaves. Later in the season aphids can be found on all parts of the plant. Its identification is often simplified by one fact — it is the only aphid in North America that forms colonies on soybean.

Aphid life cycle and crop injury

The seasonal life cycle of the soybean aphid is complex with up to 18 generations a year. It requires two species of host plant to complete its life cycle: common buckthorn and soybean. Buckthorn is a woody shrub or tree and is the overwintering host plant of the aphid. Soybean aphids lay eggs on buckthorn in the fall. These eggs overwinter and hatch in the spring, giving rise to wingless females. These females reproduce without mating, producing more females.

After two or three generations on buckthorn, winged females are produced that migrate to soybean. Multiple generations of wingless female aphids are produced on soybeans until late summer/fall, when winged females and males are produced that migrate back to buckthorn, where they mate. The females then lay eggs on buckthorn and the eggs overwinter, completing the seasonal cycle.

Soybean aphid populations can grow to extremely high levels under favorable environmental conditions. Reproduction and development is fastest when temperatures are in the 70s to mid 80s. The aphids do not appear to do well when temperatures are in the 90s, and are reported to begin dying when temperatures reach 95^oF. When populations reach high levels during the summer, winged females are produced that migrate to other soybean fields. Like a number of other insect species (e.g. potato leafhoppers), these migrants can be caught up in weather patterns, moved great distances, and end up infesting fields far from their origin. These summer migrants were most likely the major source of infestations in Nebraska during the last couple of years.

Begin scouting . . . soybean fields once or twice a week in late June to early July. The current recommended threshold for late vegetative through R5 stage soybeans is 250 aphids per plant (field average) with 80% of the plants infested and populations increasing.

Soybean aphids injure soybeans by removing plant sap with their needle-like mouthparts. Symptoms of soybeans infested by soybean aphid may include yellowed, distorted leaves and stunted plants. A charcoal-colored residue also may be present on the plants. This is sooty mold that grows on the honeydew that aphids excrete. Honeydew in itself makes leaves appear shiny. Soybean plants are most vulnerable to aphid injury during the early reproductive stages.

Soybean aphids in Nebraska

In much of the soybean aphid’s range, significant aphid infestation has occurred in the early vegetative stages. These infestations then undergo rapid population growth to reach high populations during the flowering stages (R1, R2). During the last three years in Nebraska, however, very few aphids have been found during the vegetative stages. We find a few in late June and early July, but it is usually mid-July, while soybeans are entering or in R3 (beginning pod stage), before we begin to regularly find aphids. During 2003 and 2004, most aphid populations in Nebraska reached economically damaging populations in mid to late August, while soybeans were in the mid-reproductive stages (R4-R5). During 2004 aphid populations peaked in many fields in late R5 (beginning seed) to early R6 (full seed). Can these late populations cause significant yield loss? Yes, it appears they can.

Figure 2. Yield loss by peak population, 2004, UNL Haskell Ag Lab.

A soybean yield trial was conducted at the Haskell Agricultural Laboratory at Concord in northeast Nebraska in 2004. It was part of a North Central Soybean Research Program Project that has been repeated in several states. In this study 16 soybean plots (irrigated) were infested with very low numbers of soybean aphids on July 23 and allowed to increase in population. Four additional plots were kept aphid-free.

The aphid populations peaked on approximately August 30, with average peak populations ranging from 952 aphids per plant to 3,634 aphids per plant. The results indicate that late season infestations can result in at least 20% yield loss (see graph). The major portion of the population curves and all population peaks occurred in soybean stage R5 to beginning R6. The data also indicate that the economic injury levels (EILs) would be approximately 1000 aphids per plant, depending on various factors including management costs and crop value. Because a farmer’s goal should be to keep the aphid populations from reaching the EIL, the economic threshold will be lower than the EIL and should allow the farmer time to set management tactics in motion.

Soybean aphid management

Begin scouting soybean fields once or twice a week in late June to early July. Check 20 to 30 plants per field. Aphids are most likely to concentrate at the very top of the plant, although they will move onto stems and within the canopy as populations grow and/or the plant reaches mid to late reproductive stages. As the season progresses, aphid numbers can change rapidly. (Populations can double in two to three days).

The current recommended threshold for late vegetative through R5 stage soybeans is 250 aphids per plant (field average) with 80% of the plants infested and populations increasing. This gives you about seven days to schedule treatment before populations reach damaging levels (if populations do not increase during these seven days, you may be able to eliminate or delay treatment). Determining if the aphid population is actively increasing requires several visits to the field. Factors favorable for aphid increase are relatively cool temperatures, plant stress (particularly drought), and lack of natural enemies.

Look for natural enemies such as lady beetles, green lacewings, and other insect predators. Aphid “mummies” (light brown, swollen aphids) indicate the presence of parasitoids. These predators and parasitoids may keep low or moderate aphid populations (under 200 aphids per plant) in check. The presence of “fuzzy” aphid carcasses indicates fungal pathogens are active, which can lead to dramatic reductions of aphid populations.

For more information on soybean aphid scouting and management, see: UNL Department of Entomology Web site: Soybean Aphid Management in Nebraska (NF04-599) found at Extension offices or on-line. Soybean Aphid Management on-line video. Using Real Player, view the video as Extension Entomologist Tom Hunt discusses soybean aphid scouting and management and demonstrates what to look for.

Look for winged aphids. If most aphids are winged or developing wings, the aphids may soon leave the field and treatment can be avoided.

If plants are covered with honeydew or sooty mold or are stunted, an insecticide treatment may help, but the optimum treatment time has passed.

Good insecticide coverage and penetration is required for optimal control of soybean aphid, as many aphids feed on the undersides of the leaves and within the canopy. Use high water volume and pressure. Aerial application works well when high water volume is used. (Five gallons of water per acre is recommended).

The first western bean cutworm moths of the season were caught late last week in light traps across the state. Moth numbers will continue to increase until mid to late July and then will decrease. There have been many reports of increased numbers of these pests in the region, with infestations reported throughout northeastern Nebraska and into South Dakota, Minnesota and Iowa. Infestations can be cyclical in eastern Nebraska and at this time appear to be increasing.

Farmers and crop consultants throughout Nebraska should scout fields during July for the white masses of western bean cutworm eggs. Since the moth overwinters as a prepupa in the soil, pupates in the soil and emerges from the soil as a moth, areas with heavier soils and rains may see a smaller moth populations than in recent years since it is harder for the moth to make its way out of the soil in a wet year. As moth numbers increase, mating will commence and the females will begin to lay eggs on corn. Female moths preferentially search out pre-tassel corn and later, if available, move to dry edible beans to lay their eggs. These eggs are laid in clusters of five to 200 on the top surface of the upper most leaf of a corn plant and on lower leaf surfaces of dry beans. The eggs require five to seven days to develop, during which time the egg color changes to tan and then to purple immediately before they hatch.

Western bean cutworm eggs

After the small, dark brown larvae hatch on corn plants, they move to the whorl or tassel to feed on the tender yellow leaf tissue or on the tassel itself. Once the tassel emerges or if it has already emerged when the eggs hatch, the larvae will move to the green silks. The developing larvae will feed on the green silks, moving down the silk channel until they reach the ear tip. The larvae will feed in the ear tip until they are fully developed. If the infestation on one ear tip is so great that the larvae become crowded, a few individuals may move outside the ear and begin to feed on the side of the ear. They will chew through the husks and eventually begin to feed on the developing kernels, causing extensive damage.

Western bean cutworm that hatch on dry bean plants, feed on blossoms and young, tender leaf material. The larvae will attack bean pods as they develop, eventually feeding on the developing seeds.

In corn

(Above) Figure 1. Uneven stand height typical of corn nematode damage. Figure 2. Corn root symptoms caused by stubby root nematode damage.

Recent changes in cultural practices and insecticide chemistries may inadvertently benefit corn nematodes. Planting continuous corn and using reduced tillage practices worsen many diseases, including those caused by corn nematodes. And, the use of transgenic corn and pyrethroid insecticides instead of the traditional organophosphates and carbamates favors nematodes. Only a limited number of chemicals are available for their control, although several companies are exploring new chemical options. The following is a list of corn nematodes that have historically caused significant disease to corn in Nebraska and possible management strategies for them.

• Needle (Longidorus spp.) The largest of these, needle nematodes, require sandy soil and are most damaging in soils that are more than 90% sand. They have been reported in the eastern half of the state in the Elkhorn, Loup, Platte, and Republican river waterways. The symptoms they cause can be dramatic (see photos in the June 17, 2005 CropWatch) and include root necrosis, pruning, plant stunting, and uneven heights (Figure 1). Needle nematode has a relatively narrow host range that includes sorghum, corn, and grassy weeds. There has been no evidence of feeding on soybean. Rotations with soybean or alfalfa and strict weed control can help reduce population densities. This nematode travels deeper into the soil as summer temperatures increase, so sample for it early in the season as soon as symptoms are visible.

• Sting (Belonolaimus spp.) The sting nematode, also a large nematode, has a wide host range that includes corn, sorghum, soybean, small grains, and numerous weeds, such as morning glory, crabgrass, ragweed, and cocklebur. Some species, however, such as soybean and alfalfa, do not support reproduction as well as corn. Like the needle nematode, sting requires sandy soil to increase to high numbers. It also can cause severe yield loss and travel deep into the soil.

• Dagger (Xiphinema spp.) Although large, dagger nematodes can be found in silt loams, but tend to cause the greatest damage in sandy soils. Dagger nematodes are most abundant in the upper soil layers and are sensitive to disturbance, making tillage a management option.

• Stubby-root (Trichodorus or Paratrichodorus spp.) These nematodes feed on root tips, causing the development of shortened, thickened roots that have a stubby appearance, as opposed to normal fibrous roots, like the ones in Figure 2. Damage is dependent upon which species is present. This nematode has a wide host range that includes soybean, but it favors corn and sorghum, limiting rotation as a management strategy. Stubby-root nematodes can exist deep in the soil, more than 8 inches, so some may be missed during routine soil sampling.

The previously described nematodes all spend their lives in the soil on the outside of the root, moving from root to root to feed. However, lesion and lance nematodes are endoparasites, spending most of their lives inside the roots. Therefore, root samples must be evaluated to accurately estimate their population densities.

• Lesion (Pratylenchus spp.) Lesion nematodes are believed to be the most economically important group of corn-pathogenic nematodes. These nematodes are small so they are not restricted by soil texture, occur in every corn field, and can reach high numbers. They can cause extensive damage and severe lesions by entering the root and migrating through the tissue while they feed. The resulting wounds are easy entry points for other pathogens. Numerous species are known to parasitize corn. Species identification is difficult, but is necessary for effective management recommendations for lesion nematodes.

• Lance (Hoplolaimus spp.) Although this nematode is large, it can be found in both silt loams and sand. The lance nematode has several species and a wide host range that includes both corn and soybean. This nematode can cause significant yield loss, particularly if it damages seedlings early in the season.

Tamra Jackson
Extension Plant Pathologist

Similar stresses can have very different effects on final yield depending on when they occur in the development of the corn plant. Therefore, it’s important to be able to identify the growth stage to properly assess the impact a stress may have on the crop. Learning how to identify growth stages is also important in determining if the crop is developing normally.

Staging corn by the leaf collar method requires splitting the stalk lengthwise. Noting growth stages and plan stressors now can provide valuable clues at harvest if yield levels are not as expected. (Lori Abendroth, 2005)

The leaf collar method is most often used in determining the developmental stage of corn. With this method, growth stage is determined according to the uppermost leaf with a visible collar. The collar is where the leaf blade visually breaks away from the sheath and the stalk. We still use this method at this point in the season, except it becomes more difficult since the first leaves have sloughed off. Now, the lower stalk must be split lengthwise to see the earlier nodes (see Figure 1). Each node appears as a line across the stalk. The first four nodes are condensed and cannot be distinguished from one another; they are located at the base of the crown. Approximately 1/4 to 1/2 inch above this condensed area will be the 5th node. In the figure you can see the 6th node is right above the ground; this is where the 6th leaf is attached.

Corn is in a rapid elongation phase right now and new leaves appear about every two days. The plant is increasing its rate of nutrient and dry weight accumulation now until R6. Between V8 and V12, the ear girth or the number of rows around the ear is determined. The number of rows is largely set by the genetics of the hybrid and can vary only with severe environmental conditions. If later stresses occur, this can be easily observed since the number of rows will be reduced part way up on the ear.

A reduction in the number of rows can be easily observed since they will be reduced part way up on the ear. The number of kernels per row or ear length will be determined from V12 until approximately one week before silking.

Corn hybrids will vary in the number of leaves they have, usually from 16 to 18. The final vegetative stage is VT. This occurs when the entire tassel is visible. The plant will not increase in vegetative stages once VT is reached. This stage occurs about two to three days before silks appear.

Table 1. The Nebraska Pumping Plant Performance Criteria (NPC) Engine output Pumping Plant Energy source hp-h whp-h Unit of energy Unit of energy Energy Units Diesel 16.66 12.50 Gallon Gasoline 11.50 8.66 Gallon Propane 9.20 6.89 Gallon Natural gas 82.20 61.70 mcf (1000 cu-ft) (925 BTU/cu-ft) Natural gas 88.90 6.67 Therm (100k BTU) Electricity 1.18 0.885 kWh

Using the NPC as a basis for comparison, you can calculate the expected difference in energy consumption between two energy sources. For example: the NPC for diesel is 12.5 water horsepower hours per gallon (whp-h/gal) and the NPC for liquid propane gas (LPG) is 6.89 whp-h/gal. A pumping plant using LPG could be expected to use 1.81 times (12.5/6.89) as many gallons per hour when connected to the same pump under the same operating conditions. Conversely, a pump that is switched from LPG to diesel would be expected to burn 0.55 times (6.89/12.5) as many gallons of diesel as LPG. Table 2 presents all possible equivalent fuel comparison multipliers for common energy sources for irrigation.

Lets look at an example. A producer is currently using a diesel engine to power his irrigation pump. He is wondering whether switching to a propane engine would decrease his energy cost. To answer this question, we need to know the prices of the energy sources being compared. Let’s say the local farm delivered price of LPG is $1.099 per gallon and diesel is $1.919 per gallon. We can use the relative work output to compare prices between the two alternative energy sources.

Since we can anticipate using 1.81 times as much LPG for the same amount of water pumped, we can compute an equivalent price for diesel. $1.099/gal for LPG x 1.81 = $1.989/gal for Diesel. The actual diesel price is $1.919 per gallon whereas the equivalent price to LPG is $1.989, therefore the energy cost to irrigate with Diesel is currently less than if we switched to LPG.

Alternatively, we could calculate the equivalent price for LPG based on the current price for diesel. $1.919 x 0.55 = $1.055. If LPG were priced at $1.055 per gallon the expected energy cost would be the same as diesel. Since it is actually $1.099 per gallon, the cost of LPG is slightly higher than that for diesel.

Sunflowers can tolerate a good deal of defoliation prior to bud formation without significant damage. At the V9-V11 stages, defoliation levels up to about 50% will result in only about 5% yield loss. This level of damage would be economic for irrigated flowers or dryland flowers with a good yield potential. Defoliation thresholds would be lowered dramatically after the flowers have started into the reproductive stages. From R1 (first bud) through R5 (flowering) defoliation levels of 15-25% will result in 5% yield loss. Treatment decisions for the thistle caterpillar should be based the size (stage) of the larvae that are present and on level of defoliation that has occurred. Treatments should be targeted at preventing defoliation from reaching these significant levels. Once larvae are close to 1 1/4 inch in length, they will soon stop feeding and treatments would not be necessary.

Another important sunflower insect that is becoming more important in the areas where sunflowers have been grown regularly in the past is the spotted sunflower stem weevil. This small weevil (about 1/8 inch long) is grayish-brown with white spots. It is perfectly camouflaged for concealment on the soil surface. Because of its small size and coloring it is very difficult to scout for.

The weevil lays eggs on the sunflower stems, and the larvae develop within the stem, weakening the stem and increasing the potential for lodging and the development of stem diseases. The potential for damaging populations is increased in areas where flowers have been grown in the past, especially if stem weevil infestations have been a problem in these areas.

Management of the stem weevil must rely on scouting for the adults during the V8-V14 stages in late June and early July. Sampling consists of counting the number of weevils on a number of plants across the field. Care must be taken not to disturb the weevils while counting as the weevils will drop from the plants if disturbed. Consider treatment if weevil counts average one insect for every three plants during the V8-V14 period.

• time of year (how much planting window is left for confection or oil),
• yield loss due to later planting,
• cost,
• moisture and seed availability,
• herbicide residual,
• available time to replant,
• observed populations, and
• uniformity of stand.
• Would stand uniformity yield performance overcome later season planting yield loss and additional expenses?
• Would additional/different herbicide need to be applied?
• Can the crop fully canopy to give adequate weed protection?
• If you replant could you have the same problem again?
• What do you do with the original survivors?
• Reducing populations in very high confection stands could be considered -- thinning manually or with tillage/cultivating equipment (at an angle) is possible.

One “rule of thumb” is that if you are within 25% of your yield goal, you may not do better by replanting at this time.

Bill Booker
Extension Educator in Box Butte County

Nitrogen deficiency . . . is showing up in northern Nebraska corn fields. The general pattern is that greener parts of the field may have been the wheel tracks of a large, floater type of fertilizer spreader. The reason for this is not certain, however, several factors combine to point toward increased nitrogen leaching in the non-wheel track areas. This area of northeast Nebraska has had higher than usual rainfall, much of it falling gently so infiltrated rain may have moved the nitrogen deep. Some soil tests indicate very little nitrogen in the top two feet. The fields that are worse tend to be fields with early nitrogen application. In addition, because the weather was cooler than normal, mineralization is probably reduced, so the nitrogen available from natural processes is reduced. What makes this an interesting case is that we tend to think of compaction as causing negative crop growth and that early nitrogen application avoids conditions for volatilization, hence more nitrogen is usually conserved. Charles Shapiro Extension Soils Scientist

Tom Dorn, Extension Educator in Lancaster County: Soybeans have five to seven trifoliate leaves and are still quite short (10-15 inches). Most fields are blooming at several nodes, but there is no pod development yet (R2 growth stage). Brown spot is common on lower leaves, but we aren’t seeing disease above second trifoliate leaf. No major insects have been detected. Corn development is somewhat more variable. Most corn ranges from the 8- to 12-leaf stage (leaf collar exposed). Some fields are quite uneven in height due to slow germination or arrested development due to cold weather during early growth stages. Wheat is mature and harvest is just beginning in a few fields. Yields will be lower than in 2004.

Keith Glewen, Extension Educator in Saunders County: Both the soybean and corn crops are progressing at a fast pace. Corn is at the stage where early season problems with stand establishment and uniformity are now being hidden by the stature of the corn. Dryland corn is rooting at the three foot depth and, even with high temperatures and lack of precipitation, it is looking good. Areas that missed the earlier rains will need precipitation soon. Adequate subsoil moisture going into the growing season plays an important role during these stressful days. The weather is pushing many irrigators to start watering sooner than they would like. Some irrigated corn and soybean growers were disappointed with profits last year due to high pumping costs. With rising fuel prices, profit margins may again be narrow.

F. John Hay, Extension Educator in Pierce, Madison and Wayne counties: The rain keeps falling and the weeds keep growing. Moisture has slowed weed control, but few are complaining. Hail hit western Pierce County and caused multiple corn and bean fields to be replanted, with some beans going in where corn had been. Oats are coming out for silage in a few places. Insect pests have been slow so far, but there is still a long way to go.

Andy Christiansen, Extension Educator in Hamilton County: This week I found soybean aphids in low numbers near Aurora. Also, western bean cutworm moths were found Saturday, for the first time this year, in a light trap in Aurora. This occurrence is about normal, but a little later than last year.

John Wilson, Extension Educator in Burt County: Crops are growing rapidly with warmer temperatures this week. There’s been some corn curling, but it comes out of it overnight. Good subsoil moisture, but not all crops are rooted down to it yet. Surface moisture conditions are drying out rapidly. Scattered showers this past week were not enough to provide relief from recent hot, dry weather. Insect problems are minimal, but we’re finding some potato leafhoppers in soybeans. So far, they haven’t gotten bad enough to hurt new alfalfa seedings. Second cutting alfalfa is underway. Pastures still looking good. Things just look pretty darned good right now, but we’ll need a good soaking rain soon or crop conditions will decline.

Paul Hay, Extension Educator in Gage County: Wheat yields in southeast Nebraska are across the board. From 25 bu/ac to 80 bu/ac and everything in between. Many operators have been pleasantly surprised that yields are a bit better than expected. We should end up a bit above the 42 bushel average. Crops are in need of rain, but still look quite good. The insect and disease situation is calm.

Doug Anderson, Extension Educator in Nuckolls and Thayer counties: Wheat harvest is underway and yields are going to be average but variable between some very good fields and some not so good fields. Test weights look good. Corn is getting ready to tassle, but beans look small. We haven’t seen anything major yet in the way of insects or disease.

Gary Lesoing, Extension Educator in Nemaha County: Wheat harvest is just getting started. With limited rainfall and temperatures in the 90s, corn is now showing stress. The northern part of the county was on the southern edge of the storm that dumped 0.75-1.00 inch of rain in Cass County Monday night while most of the county only received light showers. Last week most of the soybeans were sprayed and hay was harvested.

Crop report

Wheat conditions remained stable and rated 7% very poor, 13% poor, 36% fair, 34% good, and 10% excellent. Eighty-two percent of the fields were turning color, behind last year at 88% and the average at 83%. Seventeen percent of the crop was ripe, compared to 35% last year and 29% for the average. Five percent of the crop had been harvested, behind last year at 7% and average at 9%.

Corn condition was rated at 2% poor, 11% fair, 61% good, and 26% excellent. Irrigated fields rated 91% good or excellent while dryland fields rated 83%. Conditions continue higher than last year and normal. Three percent of the soybean crop has bloomed, the same as last year and average. Condition was rated at 1% very poor, 2% poor, 17% fair, 59% good, and 21% excellent, above last year and average.

Sorghum planting was virtually complete at 99%, behind last year and the average at 100%. Ninety-seven percent of the crop had emerged, ahead of last year at 95% and the average at 96%. Condition rated 3% poor, 27% fair, 55% good, and 15% excellent, above previous year and average. Oat condition rated 3% poor, 20% fair, 52% good, and 25% excellent. Ninety-two percent of the crop has headed, ahead of 91% last year and 89% for the average. Alfalfa conditions rated 4% very poor, 7% poor, 26% fair, 48% good, and 15% excellent. First cutting was 94% complete, behind last year at 95% and the average at 96%. Second cutting was 17% complete, ahead of 11% last year and 13% average.

Proso millet planting made good progress last week and was 61% complete, which was behind last year at 87%.

Dry bean planting was virtually complete, slightly ahead of last year and average at 98%. Eighty-seven percent of the crop had emerged, compared to 82% last year and the average at 84%.

The UNL Extension clinics begin each day with 7:30 a.m. registration at the Agricultural Research and Development Center near Mead and start at 8 a.m.

Participants can attend one or both of the clinics as subject matter will be different each day. July 14 topics will include: corn plant distribution -- population, twin rows and equidistance; corn rootworm technology; hands-on crop scene investigation (CSI); diagnostic lab update; Liberty Link vs. Roundup Ready weed control system; relay cropping -- wheat and soybeans; and soybean rust.

July 15 topics will include: occasional tillage for improvement of no-till systems and crop nutritional disorders; managing irrigation for maximum profits; root dynamics; corn nitrogen credits; hands-on crop scene investigation; nutrient management tools; and water optimizer software demonstration. Presenters include UNL extension educators and specialists.

Early registration is recommended to reserve a seat and resource materials. Cost for attending one clinic is $130 for those registering by July 7 and $180 after. Cost for attending both clinics is $225 before July 7 and $275 after.

Soybeans stored in all positions totaled 44.6 million bushels, up 14% from last year. On-farm stocks are 17.5 million bushels, more than double the level from a year ago. Off-farm stocks, at 27.1 million bushels, are down 12% from 2004.

Wheat stored in all positions totaled 16.1 million bushels, down 17 from a year ago. On-farm stocks of 1.6 million bushels are down 41% from 2004. Off-farm stocks, at 14.5 million bushels, are down 13% from last year.

Sorghum stored in all positions totaled 12.6 million bushels, up 7% from 2004. On-farm stocks are 2.6 million bushels, up 53% from a year ago. Off-farm stocks, at 10.0 million bushels, are 1% below last year.