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6/20/2011 - 6/26/2011

Predicted Corn Rootworm Egg Hatch Approaching

Erin Hodgson, Department of Entomology and Adam Sisson, Corn and Soybean Initiative

Some people base the corn rootworm hatching date on the calendar, accumulating degree days or when they see fireflies. The first two are more reliable methods for predicting hatching dates. Corn rootworm egg hatch in Iowa can occur from late May to mid June depending on soil conditions, but the average hatching date is around June 6.

Research suggests about 50 percent of larval hatch occurs between 684-767 degree days (base 52 F soil). The cool spring weather in 2011 has slowed down predicted egg hatch and will be behind the normal date (Fig. 1). The southwest Iowa region is experiencing 50 percent larval hatch now and other parts of the state will approach it within 7-10 days depending on the temperature. 

 

Fig. 1. Accumulated degree days (base 52F, soil) Jan. 1-June 21, 2011. About 50 percent of larval hatch occurs between 684-767 degree days.


Shortly after egg hatch, young larvae will begin feeding on root hairs and inside roots. As they develop, larvae will begin feeding on root tips. A severe infestation can destroy nodes 4 to 6 which interferes with water/nutrient uptake and makes the plant unstable.

Saturated soils will diminish overall corn rootworm pressure, and the high adoption of Bt corn should decrease populations in most fields this year. However, every field should be scouted for corn rootworm larval feeding regardless of the seed selection (i.e., scout even if Bt proteins are used). Continuous corn fields and areas with persistent corn rootworm populations are the highest priority for inspection.

Sample for larvae by digging up corn plants and washing the roots in a bucket; larvae should float to the top of the water (Fig. 2). Sample corn plants in different areas of the field to estimate infestation levels. Determine the number of larvae per plant and/or the nodes pruned.
 


Fig. 2. Corn rootworm larvae are creamy white with a small, brown head. Photo credit Marlin E. Rice.


Corn rootworm rescue treatments should be made in June, but are not very practical or effective, as the corn is too tall for the product to sufficiently penetrate the soil and reach the larvae. But sampling and evaluating root systems this year will help assess corn rootworm management and seed selection for 2012. Here are two websites that may be of interest for corn rootworm management:

 

Erin Hodgson is an assistant professor of entomology with extension and research responsibilities; contact at ewh@iastate.edu or phone 515-294-2847. Adam Sisson is a program assistant with responsibilities with the Corn and Soybean Initiative. Sisson can be contacted by email at ajsisson@iastate.edu or by calling 515-294-5899.

Yellow Leaves Emerge from Twisted Whorls – 2011

By Roger Elmore, Department of Agronomy

Yellow leaves wave above V5 to V8 corn canopies in northern and central Iowa this week.   These sun-starved leaves freshly emerged from twisted whorls will turn green soon after they begin intercepting sunlight.

Potential causes are numerous:  rapid growth coupled with a wide range of temperatures, hail, strong winds or an application of a herbicide, insecticide or fungicide, etc. 

These two references describe these symptoms and causes in more detail: Twisted Whorls and Twisted whorls and ‘buggy whipped’ corn.


Yellow leaves resulting from twisted whorls associated with an application of a growth regulator herbicide. Broadleaf weeds in the photo were affected too.
  Photo by Brian Lang, ISU Extension Field Agronomist; 2011.


I would expect these plants to look almost normal within a few days to a week or so. If the malformation causes a delay in either growth or development, it could result in yield reductions. But any yield reduction would likely be hard to detect on a field basis unless the symptom is widespread.

See more images at our website Image Gallery: Crop Diagnostics, Early Season Diagnostics.  Click on the thumbnail images to see image descriptions.

 

Roger Elmore is a professor of agronomy with research and extension responsibilities in corn production. He can be contacted by email at relmore@iastate.edu or (515) 294-6655.

Flooding and Stored Grain

By Charles Hurburgh, Department of Agricultural and Biosystems Engineering and Dan Loy, Department of Animal Science
 
Iowa is facing its third significant flooding situation in five years, which again raises the possibility of stored grain being inundated with floodwater. With only a few exceptions, flood soaked grain is not useable for feed or food. Iowa Secretary of Agriculture Bill Northey reminded farmers in a June 21 news release  that grain impacted by flood waters, whether in the field or in a bin, is considered adulterated and cannot be used for feed or food. Flooding affects both the stored grain and the storage structures. The best option is to move the grain before the flood reaches the bin, but stop using underfloor conveyors and legs once the water starts entering the pits.

Grain and Grain Products

Flood damaged grain is adulterated grain because of the potential for many contaminants to enter through the water. This grain should be destroyed, never blended. Contact the Department of Natural Resources (DNR) Environment Services regional office for the best disposal process in your area.
 
Water coming up from tiles and pits is just as suspect because storm and sanitary sewers are usually compromised in floods. Even field tile water may contain high chemical levels and other contaminants. 
 
Corn will stay at 30 percent moisture after the water drains off; soybeans about 25 percent moisture. The moisture won't travel more than a foot above the floodline.
 
Good grain on top of flooded grain must be removed from the top or side, not down through the damaged grain. The reclaim conveyors and pits under bins are likely to contain flood water as well. Remove all the good grain before doing anything with the bad portion. Do not start aeration fans on flooded bins.
 
Mold toxins are likely in rewetted grain. Warm wet conditions are ideal for mold growth. Soaked grain will spoil within a day or two at high moisture and summer temperatures.

Moldy grain is a safety hazard. The attached fact sheet prepared by the Iowa Department of Health for the 2010 flooding gives guidance on the hazards and protective equipment to use when working with moldy grain. Assume that flood soaked grain will be moldy by the time the water has receded enough to permit access to bins.

Take care not to track or mix mud or gravel from flooded grounds into good grain during salvage operations. These materials are potentially toxic for the same reasons as the floodwaters.
 
FDA allows for reconditioning (washing and drying at high temperatures) in cases where the flood water did not remain long and it is known that the water did not contain contaminants. This situation would be very rare, to know that floodwater was clean.  In both the 2008 and 2010 situations, the water was determined to be contaminated; expect that to be true in this case as well.

Structures

Grains swell when wet so bin damage is likely; more so with soybeans. Bolts can shear or holes can elongate. Look for signs such as stretched caulking seals, doors misaligned or similar structural problems.
 
Check bins with stirring devices carefully. The bin must be perfectly round for them to work correctly.
 
Bin foundations can shift, float or deteriorate from flooding. Inspect structures and foundations carefully, and have an engineering evaluation for larger bins.
 
Expect electric wiring, controls, motors and fans to be ruined. Do not energize wet components. Be sure the power is off and locked out before touching any electrical components of flooded systems.
 
Wood structures will be hard hit and may retain mold and contaminants.
 
Clean facilities and grounds completely. Then do a careful food safety inspection before returning facilities to operation. Maintain records of cleaning.

Salvage

In the rare situations where the water was not contaminated, the grain may be reconditioned. If the grain is to be sold, reconditioning has to be done with the written consent of FDA. For feed on site, producers have three alternatives.

  • Dry the grain
  • Feed it immediately to their livestock
  • Ensile the grain for livestock feed.

Decisions need to be made quickly. The good grain should be removed immediately, again not down through the soaked grain. No flooded grain can be sold to the market without approval of FDA, to document its exposure only to uncontaminated water, with subsequent  reconditioning and intended use.
 
There is no problem, other than spoilage within a day or two, with using uncontaminated soaked corn as a livestock feed. Just replace the corn in the animals' current diet with the wet corn. Remember to adjust amounts fed for moisture.
 
Wet, whole soybeans can be fed to cattle if the soybeans are limited to 10 to 12 percent of the ration's dry matter. Soybeans substitute well for the protein in soybean meal, but they need to be fed with a vitamin-mineral-additive premix if substituted for a complete protein supplement.
 
It is not necessary to heat-treat the soybeans for cattle. Also, if adding whole soybeans to diets high in distillers' grains, watch the total ration fat content. For hogs, raw soybeans can only be fed to mature sows. The soybeans need to be heat treated if fed to younger pigs.

The Missouri River situation of 2011 is not likely to create salvageable situations.
 

 

Charles Hurburgh is a professor of Agricultural and Biosystems Engineering and professor in charge of the Iowa Grain Quality Initiative. Dan Loy is a professor of animal science with research and extension responsibilities for livestock nutrition.

Oats for Forage

By Steve Barnhart, Department of Agronomy

Oats have been an important crop in Iowa. In addition to being a favored spring-planted companion or cover crop for forage seedings, they have historically been harvested as a cash grain crop. In recent years, as market demands and cropping systems have changed, oats are more often being harvested as hay or silage for livestock.  

One of the important decisions producers must make when using oats for forage is when to harvest the crop. This decision has several implications. Early removal of the cover crop from a new forage seeding reduces shade and moisture competition; a benefit to the new forage seedlings. And, harvest timing affects the forage yield and forage feeding value of the harvested corp.  

Producers often use visual traits of the developing oat crop when making harvest decisions. Figures 1, 2 and 3 illustrate some of the most commonly used visual guides.
   
 

Figure 1.
a. ‘Boot’ stage. The developing seedhead is still in the leaf sheath of the uppermost leaf.
b
. ‘Milk’ stage. The seedhead is green, the developing grain has a liquid, milky color starch.
c. ‘Dough’ stage. The seedhead color is changing from green to yellow; the grain starch is changing from soft to hard consistency.


The forage yield and forage feeding value of the harvested crop change as the oat plant matures through its growth stages. (See Figure 2 and Tables 1 and 2). Note that these changes occur relatively quickly. Producers are encouraged to consider the nutrient requirements of the livestock being fed as a guide to timing of their oat forage harvest. 


 

                            The harvested yield of oats forage increases rapidly with increasing maturity until early dough stage.


 

 

 


For lactating dairy cattle, oat forages should be harvested as the first grain heads appear in a field (late boot stage). Oat forage at this stage will provide a feed with more energy and similar protein levels to late-bud alfalfa and similar energy but higher protein content than corn silage. Many producers harvesting oats for feeding to gestating beef cows will delay harvest until the dough stage, to gain slightly more forage yield.

 

Stephen K. Barnhart is the ISU Extension forage agronomist. He can be contacts by phone at 515-24-7835 or by e-mail at sbarnhar@iastate.edu.

SCN Females Now Apparent on Soybean Roots

By Greg Tylka, Department of Plant Pathology

A very quick and easy way to check for the soybean cyst nematode (SCN) is to dig roots and look for the presence of the telltale, swollen, white females on soybean roots.  This technique is effective for checking fields for the presence of this serious yield-limiting pest and also for checking to see if SCN populations are building up on SCN-resistant soybean varieties.  But checking roots in this manner can only be done during the growing season and only once females from the first generation of the season become apparent.

On Monday, June 20, I observed swollen, adult SCN females on roots of susceptible soybeans in Hamilton County and Franklin County, Iowa.  The soybeans in Hamilton County were planted on May 18 near Williams and were in the V4 to V5 growth stage.  Those in Franklin County, near Hampton, were planted on May 6 and were at V6 growth stage.  The appearance of the SCN females indicates that growers and agribusiness personnel can begin checking fields for SCN.


White, adult SCN females on soybean roots.

Over the course of a week or two, the white, adult SCN females will turn yellow then tan, and eventually brown, as the female dies.  And the brown, dead, egg-filled females (called cysts) will easily dislodge from the roots.  But new, white adult SCN females will appear continuously throughout the growing season. 

New SCN females appear on young soybean roots and those roots are deeper in the soil and farther laterally from the seed row later in the season (August and September) than in late June or early July.  So one has to dig deeper as the season progresses in order to recover the young soybean roots on which new adult SCN females will appear.

The next four to six weeks (through July) are prime time to dig roots and check for SCN females. 

Roots should not be pulled from the soil because the young roots with the SCN females attached will be stripped off.  Roots should be dug with a shovel or spade and soil carefully removed from the roots.


Brown SCN cyst (dead female) on older soybean root.

 

Greg Tylka is a professor of plant pathology with extension and research responsibilities in management of plant-parasitic nematodes.

Scouting Reveals a Mixture of Caterpillars in Corn

Erin Hodgson, Department of Entomology  and John Holmes, Extension Field Agronomist

A recent scouting adventure in northeast Iowa resulted in finding a few different caterpillars infesting corn. The most abundant plant damage was from black cutworm. They have been feeding for several weeks throughout Iowa, and are reaching near maturity (Fig. 1). Black cutworm treatment thresholds for caterpillars over ¾ inches in length is five percent of the field with cut plants. But nearly fully developed larvae will stop feeding soon and drop to the soil to pupate. A foliar treatment now may not be warranted. 

 
black cutworm
Fig. 1. Black cutworms make an entry hole just above the soil surface and move up into the stalk to feed. Nearly full-grown caterpillars are 1 ½ inches long. Photo credits Erin Hodgson.

We also saw several “dead head” weeds along the field edge borders, indicating that stalk borers were potentially in the area. Dissecting grass stems revealed copious amounts of frass pellets from stalk borer (Fig. 2). Some stems were still infested, but others were empty. This matches up fairly well with our predicted cutting dates for stalk borer in northeast Iowa this year. 

 
stalk borer dead head
Fig. 2. Grasses with dead heads are an indicator of stalk borer infestations. Splitting open the grass stems will help determine if caterpillars are still feeding or starting to migrate.
Photo credits Erin Hodgson.

By looking for shredded corn plants adjacent to grassy field edges, we were able to find small stalk borer larvae infesting corn (Fig. 3). Infested older plants (V4-V7) will be discolored, wilted or dead. Plants older than V7 are unlikely to be killed. A timely stalk borer application must be made to migrating caterpillars. 

 
stalk borer
Fig. 3. Stalk borer larvae attack corn plants from the top or tunnel into the side of the stalk. Foliar treatments are not effective once the caterpillar is inside the stalk.
Photo credits Erin Hodgson.

John found a single spotted fireworm caterpillar in corn (Fig. 4). Not much is known about these rare corn pests, and a treatment threshold has not been developed. You may find them rolled up in a leaf with webbing and frass pellets. 

 
spotted fire worm
Fig. 4 Spotted fireworm caterpillars are rare corn pests in Iowa. The body is dark purple and covered with long hair and bumpy white spots.
Photo credits Erin Hodgson.

Some fields in that area were suspected to have hop vine borer in corn (Fig. 5), although we did not find any in our search. These caterpillars can cause stand loss in corn, particularly in northeastern Iowa. Hop vine borers attack the corn from underground and hollow out the base of the stalk, and shouldn’t be confused with cutworm or stalk borer damage. But like stalk borer, foliar treatments must be made before they enter the stalk.

hop vine borer 
Fig. 5. Hop vine borer caterpillars are creamy white with an orange head and dark patches along the abdomen. Photo credit Marlin E. Rice.

 

Erin Hodgson is an assistant professor of entomology with extension and research responsibilities; contact at ewh@iastate.edu or phone 515-294-2847.  John Holmes is an ISU Extension field agronomist serving north central Iowa. He can be reached at 515-532-3453 or by emailing jdholmes@iastate.edu.



This article was published originally on 6/27/2011 The information contained within the article may or may not be up to date depending on when you are accessing the information.


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