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Extension > Minnesota Crop News > July 2012

Monday, July 30, 2012

Performance problems surface again with Bt corn rootworm traits

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.

Small grains disease update

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.

Thursday, July 26, 2012

Using Drought-Stressed Corn for Forage

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.

Wednesday, July 25, 2012

Spider mites: some points to consider

From the University of Minnesota Extension Southeast Crop Connection newsletter

spider mites
Photo 1. 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.

Monday, July 23, 2012

Crop revenues and costs resulting from drought

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

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.

Wednesday, July 18, 2012

Small Grains Disease Update

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.


Thursday, July 12, 2012

What is the next step this season in N management for corn?

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.

Tuesday, July 10, 2012

Small Grains Disease Update

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.

Monday, July 9, 2012

Dry Conditions During Corn Pollination in Minnesota

By Jeff Coulter, Extension Corn Agronomist

Tassels became visible in early-planted corn fields around Minnesota at the beginning of last week, coinciding with unusually hot and continued dry weather. While some isolated areas in Minnesota received a little rain late last week, most did not.

This week, a large percentage of the corn in Minnesota will be pollinating. Although air temperatures across Minnesota during the next ten days are forecast to be near optimal for corn (mid- to upper 80s), there is little chance of rain during this time. How will these weather conditions affect the corn crop?


The critical period for avoiding stress in corn is during the two weeks before and two weeks after tassel emergence, with the most important time being about eight days after tassels emerge. Drought and heat stress around tassel emergence can affect the success of pollination and the number of kernels per ear.

Sunday, July 8, 2012

Spider Mites in Soybeans


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!

Monday, July 2, 2012

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 dependent upon a clear 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

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.

Jochum Wiersma, Small Grains Specialist

Variable wheat height
Photo 1. Variable wheat height.
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.
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