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Extension > Minnesota Crop News > Archives > July 2012 Archives

July 2012 Archives

By Ken Ostlie and Bruce Potter, University of Minnesota Extension

Bt-RW problem field with lodged corn

Bt-RW problem field with lodged corn

Calls over the last two weeks indicate Bt-RW trait performance problems may be expanding in scope. Field observations suggest corn rootworm populations have increased markedly in corn after corn fields since 2011; recent calls indicate a major expansion of the geography of performance problems into SC and WC Minnesota. Unfortunately the drought has masked the primary tip-off to severe corn rootworm injury—lodging. With injury largely completed and corn rootworm emergence peaking, now is the time to check fields for signs or symptoms of performance problems with your Bt-RW traits. Getting a handle on Bt trait performance is critical before making seed purchases for 2013. You may need to change your corn rootworm management strategy/strategies.

corn rootworm map

2009-11 problem fields

Since the first reports surfaced in 2009, scattered performance-problem fields have been reported in a broad arc from NW Illinois through NE Iowa, W Wisconsin, SE Minnesota, SW Minnesota, E South Dakota, NW Iowa, and NE Nebraska. The map at the right indicates where Bt-RW performance problems have been previously reported in Minnesota (2009-2011 map). Field visits and phone calls in 2012 suggest an increase in the geographical scope of performance problems, especially in SC and WC Minnesota, and prospective resistance to more Bt-RW traits. Your help is needed in identifying where, and to which traits, these problems are occurring!

Drought this summer has been both a blessing and a curse when it comes to identifying performance problems. Typically, the most visual tip-off to corn rootworm injury and performance problems is lodging. But lodging is an imperfect indicator since besides corn rootworm injury, it also requires thunderstorm activity. The moist soils loosen root grip and strong winds generate strong force on the corn. Under drought conditions, thunderstorm prevalence has been minimal and offer little insight into status of the resistance problem. However, corn rootworm survival and injury is enhanced under drought conditions and above-ground, stress symptoms of this root injury (stunting, leaf roll) are magnified. For many growers this year, it's these symptoms and unusually high numbers of corn rootworm beetles that have been the tip-off to performance problems.

Click an image below for a closer look at symptoms.

If you identify fields with Bt-RW performance problems, and prospective resistance to a Bt-RW trait, it's critical to report the field ASAP to the seed company (whether or not the field is in compliance with respect to refuge)! Confirming resistance involves both field and lab verification. The process begins by contacting your seed dealer to report the problem. This page outlines this reporting process and what to expect. Field visits will gather field history, verify trait presence and corn rootworm injury of sufficient magnitude to report the problem, and possibly collect adult beetles to evaluate their progeny for resistance.

If you detect a performance problem field, we'd appreciate notification as well: www.extension.umn.edu/cornrootworm/. These reports will enable us to get a better handle on the geography of the problem and the traits involved so we can tailor our extension and research efforts, serve as an independent source of information, and improve transparency on the critical issue of Bt-RW trait resistance!

Small Grains Disease Update

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This year proved to be an interesting in more ways than one for the cereal crops in Minnesota. The mild winter and spring saw many growers planting their crops very early. However these same conditions conspired to give us early influxes of aphids carrying Barley yellow dwarf virus (BYDV). While this disease can always be found in low levels in wheat, barley and oats (characterized by yellowing and eventually drying of leaf edges originating for the leaf tip and progressing down towards the stem in wheat and barley and red to purple discoloration in oats), symptom severity this year was far more extreme in a lot of cases due to plants being infected at very early growth stages. This resulted in severe dwarfing and excessive tillering, something rarely, if ever, seen before in Minnesota.
By the same token, parts of Minnesota also experienced large populations of Aster leaf hopper early in the year which have the potential to transmit Aster Yellows (AY) to the crop. This disease can cause symptoms very similar to BYDV, and without lab testing it can be very difficult to distinguish between these two diseases. This trend was echoed in canola which is also susceptible to AY.
Another disease, stripe (or yellow) rust caused by Puccinia striiformis then became evident. This disease is also rarely seen in Minnesota and is more commonly seen in the Pacific North West, as conditions in the typical growing season here are more favorable to leaf rust. The stripe rust infections were able to continue despite warm daytime temperatures and little rain, probably due to much cooler night temperatures and the high humidity in late June. The difference between plants that had been sprayed at Feekes 5 with fungicide and those which had not became marked as the stripe rust infections continued. However, once temperatures really warmed up to the low to mid 90s F, stripe rust entered a decline and went in to its resting phase.
Tan spot as always, was ever present in many fields with the worst affected being those fields which had minimal fungicide inputs to control foliar diseases.
Fusarium head blight (FHB) did make an appearance later in the season but this year conditions were not optimal for FHB to really take hold as it has in previous years.
In addition to diseases this year, there were many reports of herbicide injury in the wheat crop. Again this was probably in part due to high temperatures and lack of moisture which left plants stressed and less able to cope with the demands placed on their metabolism by pesticide applications.
Despite such an atypical - and in parts of the State - extremely dry growing season, some farms are averaging 60-70 bushels an acre.
We wait with baited breath to see what next year's growing season brings us.

Sin-cereal-ly,

Madeleine Smith, Extension Plant Pathologist and Jochum Wiersma, Extension Agronomist.

Using Drought-Stressed Corn for Forage

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By Lizabeth Stahl, Extension Educator - Crops

Drought conditions continue to intensify in areas across the state including Southwestern Minnesota.  According to the July 24, 2012, U.S. Drought Monitor report, the southwest corner of the state is now rated in the "Severe" drought category.  The western half and southern counties of the state are also rated as "Abnormally Dry" or in the "Moderate" to "Severe" drought categories, and throughout this area soil moisture levels are low.  For example at the U of MN Southwest Research and Outreach Center in Lamberton, soil moisture levels are less than half the historic average for this time of year, and what moisture remains is almost all at a depth of more than 3 feet.  In areas hardest hit by the drought, growers are assessing grain yield potential and if or when to harvest drought-stressed corn for forage. 

Spider mites: some points to consider

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From the University of Minnesota Extension Southeast Crop Connection newsletter

spider mites

Spider mites are the concern today. Symptoms have become more obvious in some fields, especially along field edges, drought pockets and drier area in the region. Is this a "tornado watch" or "warning"? A watch in most fields, but we have touchdown (warning), with damage in some (more drought stressed conditions). You need to scout now. Here are some additional precautions and suggestions to consider.

  1. We are entering the critical time for soybean growth--pod set and fill, determining yield.
  2. When/If you pull the trigger and apply an insecticide now, this early in the season, plan on multiple application for multiple pests (aphids). You'll remove all beneficial insects and open the door to other pests.
  3. When making multiple applications it is imperative that you choose multiple modes of action.
  4. Canopy penetration is critical for good control.
    • Do not cheat on insecticide rates.
    • Do not cheat on water (gallons/acre applied).
    • Do not cheat on pressure--keep PSI up.
  5. Consider preharvest interval (PHI) when planning multiple applications of insecticides. Average range, 18-45 days. You may need to use a product with a longer PHI first followed by one with a different mode of action and a shorter PHI second.
  6. Insecticide/miticides will not kill spider mite eggs. Life cycle completed in 5-19 days (faster with temps above 90°)
  7. Remember buffer zones, and setbacks to sensitive areas for the insecticides you use. Read the label.
  8. Places to scout first: heaviest infestation usually occur along roadways, ditches, near alfalfa fields. Watch for spider mite movement from alfalfa to soybeans.

Read this article for more information on managing spider mites.

Don Nitchie, Extension educator, dnitchie@umn.edu

How quickly crop conditions have changed from the wet weather of May.

Extreme heat and lack of rainfall throughout June has resulted in USDA Crop reports having been dramatically revised to reflect deteriorating crop progress throughout the U.S. Corn Belt. At the moment, conditions appear not quite as severe in SW Minnesota as in other regions but, that could change soon. I hope it is for the better as the result of rainfall.

Dry conditions threatening to generally impact final yields across the U.S. Corn Belt have historically had significant impacts on "old crop" and "new crop" prices. We have certainly seen that in the last few weeks. If market demand for corn or soybeans remain the same and stocks are tight, a relatively small change in expected supply leads to a larger change in prices.

Relief spelled R-A-I-N for some

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Dan Martens, Extension educator, marte011@umn.edu

Rain during the last week to 10 days provided some relief to some crops through central Minnesota in various amounts. Crops are at a lot of different stages. Some scorched corn crop may not benefit much from rain anymore. Pollination may have been hurt for some corn. There is a large amount of corn, soybeans and hay crops that will benefit significantly from recent rains.

Where crops are starting to deteriorate, like corn turning brown, some farmers might think about saving some other stored feed and starting to chop some of this corn. For anything you might do with the crop, for those carrying crop insurance, have a good discussion on with your crop insurance rep first.

For day to day feeding I'd think about the following:

Small Grains DIsease Update

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Temperatures are set to be high again this week with maximum temperatures forecasted from the high 80s to mid 90s. Humidity will be lower than we have seen in the past week. Most of the wheat crop is now in the soft to hard dough stage of development.
With the warmer weather, stripe rust is finally entering the resting stage of its life cycle evident as black telial pustules on leaves. Leaf rust incidence is moving North and West through the state with the highest incidences (up to 100%) and severities (up to 30%) being reported in Otter Tail county.
Incidence of tan spot is on the increase as well - in some cases 100%,of affected - with low to moderate severity. This trend is likely to continue in the central and eastern parts of the state over the next few days.
Risk of leaf rust in the central and eastern part of the state will trend much higher in the next couple of days. The risk for tan spot remains high throughout the state.
Scab risk remains moderate to high in the north west of the state. Initial reports of scab infections have been confirmed, especially in the most northwestern portion of the State. This is the same area for which the risk model had shown a moderate risk for FHB 2 to 3 weeks ago. Incidence and severity are low at this point.

John Lamb and Daniel Kaiser
Extension Soil Specialists


The corn is tasseling, we are praying for rain, and the week of the 4th of July was hot and miserable.  It must be time to think about evaluating this year's nitrogen management program and making decisions about next year's nitrogen needs.  

Small Grains Disease Update

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07/10/2012

Temperatures are set to be slightly cooler this week than last, and expected to stay in the low to mid 80s. Humidity will be lower than we have seen in the past week. Most of the wheat crop is now in the late milk early dough stage of development.

Stripe rust is still prevalent across the state. However weather conditions are now becoming favorable for development of leaf rust which is evident in the south and west of the state with severity ranging from moderate to severe. Sibley county being the worst affected at present. Septoria diseases have progressed with 100% of some fields affected with moderate to high severity.

Risk of leaf rust in the central and eastern part of the state will trend much higher in the next couple of days . The risk for tan spot remains high throughout the state. Scab risk remains moderate to high in the north west of the state.

Reports of fields with a unusual amount of dead heads with little or no grain have been reaching us. Incidences as high as 15-20% have been reported. We are sampling some of the worst fields to determine the exact cause or causes and will share those results as they become available.

Dry Conditions During Corn Pollination in Minnesota

Spider Mites in Soybeans

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We've been getting calls about spider mites in soybeans, not surprising given our high temps and the dry conditions in some locations. As temps get into the 90's, spider mite reproduction and development rates increase significantly. Drought also exacerbates spider mite populations, and when drought conditions are relieved by rain, spider mite populations may not necessarily decrease. Consequently, even after drought conditions pass, best to continue scouting for spider mites damage.

Spider mites are tiny and only large females are visible to the naked eye (unless you've got really good eyesight!). The best way to see spider mites is to shake a plant over a piece of white paper - any moving pieces of dirt are likely spider mites... So to scout for something that small, it's best to look for damage. Spider mite damage will first appear as small yellow spots (stippling) on lower leaves. There is currently no solid treatment threshold in soybeans, but If stippling reaches mid-canopy leaves, a treatment is likely necessary. Pyrethroids may flare spider mite populations, spreading mites and increasing their populations.

A good source for information on spider mite biology, scouting and thresholds was prepared last year by Bruce Potter and Ken Ostlie and is available at:

http://www.extension.umn.edu/agriculture/soybean/pest/managing-two-spotted-spider-mites-on-soybeans/

Keep scouting!

Aphid Alert 2012 - Ian MacRae (UMN), Robert Koch (MDA)


The aphid monitoring network, Aphid Alert, lives again....

The network, which ran from 1997 through 2003, was designed to monitor the seasonal dynamics of aphid vectors of viral diseases of seed potatoes. The national epidemic of Potato Virus Y (PVY) has been increasingly impacting marketability of MN & ND seed potatoes. Vector control is an important part of PVY management, but is depedent upon a cleqar understanding of the spatial and temporal dynamics of vector populations. To provide this data to producers in MN and ND, we are re-establishing the Aphid Alert network.

Aphids have already been found in the Crookston location trap and in plots at the NWROC. It looks to be an early year!

Weekly results and updates can be found on:
aphidalert.blogspot.com

Small Grains Disease Update

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Weather conditions have been getting steadily warmer over the last week, routinely in the mid-80s° F. This trend is set to continue over the next week with temperatures reaching the low 90s° F. This unusually dry and warm weather is having a direct impact on the range and severity of diseases and plants reactions to other stresses such as herbicide drift and drought. With the majority of wheat in the end of milk and into the early dough stage, many plants are clearly showing evidence of heat stress. This heat stress is exacerbating other diseases that are not normally prevalent.

Stripe rust is still very evident across the state with high severity on spring and winter wheat in to the mid canopy. A number of fungicides will give good control of stripe rust provided they are applied before symptoms are evident on the flag leaf. Fungicide application will not cure already visible or latent infections. Although the warm temperatures will slow stripe rust development, cooler night time temperatures and the chance of stormy precipitation, will allow this disease to continue. If generic Folicur, Prosaro or Caramba were already applied at Feekes 10.51 to suppress scab, you can expect sufficient control for the remainder of the growing season for stripe rust.

Septoria species are also becoming prevalent in the west central portion of the state with low - mid severity on 20-50% in the fields scouted. Evidence of wheat stem maggot is now appearing in the south-west of the state. Typical symptoms of damage caused by this insect are white or blasted heads which will produce no grain, while the rest of the plants looks normal. The head can easily be pulled from the plant to reveal the feeding damage.

Because of the weather, the risk of scab is likely to be very low over the next week. These same conditions are more conducive to stem rust and leaf rust may become more evident, especially in the southern part of the state.

Tall Off Types in Wheat.

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A fair number of spring wheat fields appear to be quite variable in plant height this season. Obviously varying degrees of drought stress can create height differences that are, in some instances rather striking ( Photo 1). Differences in height, however, are more interspersed and without clear delineations and/or transitions as is the case in photo 1, it is probably not drought stress per se but one of three things:

  • a variety blend
  • a variety that is segregating for plant height
  • a variety that suffers from a genetics anomaly that results in a chromosome being lost across generations.
The first cause is rather straightforward; if during anytime in the previous generations seed of another variety inadvertently has been comingled with the variety you think you have, you will get mixtures of varieties. This happens more often than probably any of us want to admit and it's the reason why sanitation (i.e. cleaning equipment and bins) is so important to maintain variety purity.

The second reason for differences in plant height is much less common but the extreme growing conditions we are experiencing this year can bring some differences in plant height that previously had gone unnoticed. Without going into too much detail, you have to understand that most varieties that are released are actually number of sister lines derived from the same cross that are nearly identical. These lines only differ for a few percentage point of the total number of genes, most of which will go unnoticed. After all, to be recognized the Plant Variety Protection Act requires that the variety meets certain minimum for distinctness, uniformity, and stability or DUS requirements for wheat. Breeders will generally select a number of sister lines that phenotypically are hard to distinguish from another in an environment that shows differences well. Dr. Jim Anderson, for example, will often do this work in the winter nursery in Arizona to detect even the slightest of difference in plant height and/or maturity. The extreme conditions we are encountering this season may, however, trigger some differences that previously had gone unnoticed.

The third reason is related to a problem that is particularly unique to wheat. It can create challenges for the DUS requirements, especially if the enforcement of the PVP is strict as is the case in many European countries. With the introduction of the semi-dwarf genes, the breeders quickly noticed that in certain lines and genetic backgrounds a number of tall plants would appear at a low frequency from one generation to the next generation (Photo 2). Subsequent research showed that in certain wheat varieties up to 6% of the time something goes during the formation of the pollen grains in certain g. This, in turn, leads to some 1% of the next generation to be so-called aneuploids, meaning having an individual progeny with one of more chromosomes missing or extra. Monosomic deletions, i.e. plants missing one chromosome, are most commonly encountered. Most often you will never see a difference, except in the case of semi-dwarf wheat varieties.

The odds that a chromosome gets lost in the shuffle that is called meiosis during the formation of pollen grain appears to be equal for all 48 chromosomes that make up wheat. Consequently, ever so often the one of the two chromosomes that carries the semi dwarf genes goes missing. This in turn results in half the reduction in height compared to the genetically equivalent variety without the semi-dwarf genes (another way to think about this is that only one instead of two doses of a medicine are given to shorten the height of the patience). The frequency of this phenomenon appears to be rather constant in certain background and varieties like Vance were notorious for getting 'dirty' over time.

A nice article that describes this phenomenon in more detail can be found here. An interesting experiment to do is to safe some seed of these tall off-types and grows them out next year. Half the plants derived from these tall off-types should revert back to the original variety, the other half of the plant will be the taller off-type again.

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