Weed Related Field Tour Dates

June 24 , Weed Tour, 1 pm, Haskell Ag Lab-UNL, Concord

July 6 , "Sandbur control in corn" (by Brunswick) starting at 10 am and "Buckbrush control in pasture" (west of Niobrara State Park) starting at 2 pm.

For the Sandbur Tour, near the town of Brunswick, take 4th street west which turns into 863 road (gravel), drive for about 2 miles outside of town. Plots are at the south side of the road, next to a turkey farm. This study has 22 treatments, combinations of PRE and POST products.

For the buckbrush study, from Verdigre take 881 (paved road) west, after about 12 miles turn north on 512 (gravel road), follow the road for about 11 miles, it will turn east, after 2 miles take road 514 north, drive over Niobrara river to the top of the bluffs. Tour is on the top of the hill, road 892. You will see vehicles there, can't miss it. This study has 38 treatments of different modes of action.

European Corn Borer Moths Are Flying

European corn borer moths have been flying for a while now. As corn (non-Bt) grows it will become susceptible to the first generation of corn borers. Current information on black light trap catches for several sites in Nebraska can be found at http://entomology.unl.edu/fldcrops/index.htm . Peak flight occurred at the Haskell Ag Lab the night of June 7 th . Egg masses and small shotholes should be visible now on early planted (tallest) corn. While not a bumper crop of moths, we should not be complacent about the European corn borer in non-Bt cornfields. Now is the time to scout non-Bt corn fields and/or refuges.

Timely and accurate scouting is the key to managing European corn borer in standard (non-Bt) corn hybrids. Remember that conditions are localized and fields must be scouted on an individual basis to make accurate decisions.

Corn borer larval survival is dependent upon several factors. High humidity and warm temperatures are ideal for establishment of larvae in the whorl. Egg masses are white, with 5 to 40 eggs in each mass, and laid on the underside of leaves near the midrib. The masses look like fish scales flattened against the leaf. In 4 to 7 days the heads of the developing larvae will be visible, and the eggs will appear spotted. This is the "blackhead" stage, and these eggs normally hatch within 24 hours. As the larvae enter the whorl to feed on the developing tissue, the feeding scars (shot-holes) appear as the leaves emerge from the whorl. Larvae will remain within the whorl for 7 to 14 days before boring into the stalk.

Corn that is below about 16" extended leaf height (distance from the tip of the leaf pulled up vertically to ground, about six-leaf stage) is unlikely to support young larvae because of the presence of a substance known as DIMBOA, a natural resistance factor. As the plants grow the level of DIMBOA decreases, so plants above the 16" extended leaf height will generally support corn borers. First generation corn borers prefer taller plants for egg laying, therefore, the earliest planted fields are more likely to have higher populations. Scout these fields first, but do not neglect other fields because any cornfield is a potential target and should be scouted.

Now that Bt corn is being planted widely, be sure you know whether the field you are scouting was planted to Bt corn. In Bt corn, corn borer injury to whorl stage plants should be limited to a few tiny pinholes where larvae initially fed before ingesting a lethal dose of Bt toxin. However, seed lots may contain a small percentage of off-type seed (typically less than 4%), which does not produce sufficient toxin levels to kill corn borer larvae. If greater than 4% of plants show significant leaf feeding damage in a Bt cornfield, check to confirm it is corn borer causing the injury (other caterpillars such as corn earworms, or common stalk borer are not controlled by B.t. corns currently available). If you believe that corn corer is causing the injury, contact a representative of the company who sold the seed to investigate the situation more completely.

To determine the need for treatment, scout at least 20-25 consecutive plants in at least 4-5 different places in the field (100 plants minimum per field). The scouting locations should be randomly selected and representative of the field as a whole. At each scouting location, randomly select the first plant that will be sampled. If you do not and always start sampling at an infested plant, the counts may be inflated by 5%. Count the number of plants showing shot-hole feeding and determine the percent of infested plants. Next, pull the whorls from at least two randomly selected infested plants in each set of 20-25 plants. Unroll the leaves and count the number of larvae in the whorl and determine the number of larvae per infested plant. Young corn borers usually suffer from 60 to 85% or higher mortality due to natural enemies, weather and disease, so try to wait to make treatment decisions until most of the borers are second instar to take advantage of natural larval mortality.

Use the information gathered from field scouting to complete the accompanying worksheet. This takes you through the calculations needed to estimate the preventable loss if an insecticide is used. Compare the preventable loss to the total cost of insecticide application. An insecticide application is economically justified if preventable loss exceeds the total cost of insecticide application. An interactive version of the worksheet is available at http://www.ianr.unl.edu/forms/forms.skp/ecb_1st.html.

Treatments will be effective only if borers are still feeding in the whorl. Treatments made after corn borers begin to bore into the stalk (when they are about half grown) will not be effective. Based on research data, the best control is achieved with aerial or ground applied granular formulations or liquid applications through sprinkler irrigation systems, which provide the best penetration of insecticide into the whorl where the corn borer larvae feed.

Worksheet for First Generation European Corn Borer: To estimate the cost/benefits of applying an insecticide for European corn borers, you also need to know the cost per acre of the insecticide application ($/acre), the anticipated price of grain ($/bu), and yield potential (bu/acre) of your hybrid. Assume 5% yield loss/borer/plant and a proportion of larval population reduction by insecticide application of 0.75. Here is an example with a 200 bushel yield goal at $2.75. Scouting has found an average of 50% plants infested with 4 borers found in the whorl of each infested plant:

Average number of larvae/plant (percent of injured plants X number of larvae/injured plant) 50% x 4 = 2	2
Potential yield loss if all larvae survive (number of larvae/plant X 5% loss/borer/plant) 2 x 5% = 10%	10%
Potential bushel loss (potential yield loss X yield potential) 10% X 200 = 20	20 bu
Potential dollar loss (potential bushel loss X estimated price of corn) 20 X $2.75 = $55	$55.00
Preventable loss (potential dollar loss X proportion of larval population reduction) 55 X 0.75 = $41.25	$41.25

In the above case a $12.00 application would more than pay for itself by preventing a $41.25 loss. All of the above numbers are variable and are unique to each field and farm management operation. Use the formula several times using different figures for yield, price, and cost of application to see how each one affects the outcome. Use the figures closest to your situation to make the final determination.

Many insecticides are registered for control of first generation European corn borers and most will do a good job if applied properly at the right time. Chlorpyrifos (Lorsban, Nufos), bifenthrin (Capture) and permethrin (Pounce) granules are preferred by air because the whorl will act as a funnel and bring the granules to the larvae. Liquids work extremely well if chemigated due to the coverage provided by the pivot. Included in this list are Baythroid, Ambush, Pounce, Capture, Asana, Lorsban, Mustang Max, Penncap-M and Warrior. Bt products such as DiPel and Javelin will work well but should not be applied to refuge areas for resistant management purposes.

Additional information on first generation European corn borer management is available in First Generation European Corn Borer Scouting and Treatment Decisions , NebFact 98-364. This publication is available from your local cooperative Extension office or at http://entomol /ecb/ecb1.htm (TH&KJ)

Purple Loosestrife – Biology and Control (PART II)

This is the second part of the article about the Purple Loosestrife published in the 8th issue.

4. Herbicides : Herbicides alone cannot provide economical control of this weed, however they are necessary part of an integrated approach to stop the expansion of currently infested acres. Herbicides are especially important for ‘spot spraying' and control of this weed along roadsides and ditches. For example, there are many loosestrife plants along the shores of Niobrara and Missouri. They are especially evident along the two rivers at the town of Niobrara and Niobrara State Park. Herbicides can be used for spot spraying along roadsides, especially along Hwy-12, at the section from Santee Indian Reservation to town of Niobrara.

Recommended herbicides include Rodeo (4-6 pts), Habitat (1 pt/a) Garlon 3A (3-5 pts), Escort (2-4 oz/acre), and 2, 4-D (3-5 pts/acre), and Arsenal under special circumstances (see further). Before using any herbicide check the label carefully for recommended rates, appropriate additives and plant species sensitivity. Each of the recommended herbicides has benefits and risks associated with its use. The question may still remain as to “which herbicide to use?”

Garlon or 2.4-D, or the mix of the two will prevent seed production and provide short-term suppression, which means yearly applications for at least several years, but annual expenses will be low. Longer-term control, which means spraying once in several years, can be achieved with Rodeo (and other aquatic glyphosates), Habitat, Escort, Arsenal and a mixture of Escort and 2,4-D. Arsenal should be used for specifically targeted and controlled sites. Due to non-selective nature of these herbicides, they should be used as part of an integrated and site-specific approach. Furthermore, these non-selective herbicides should not be used at the same site continuously for more than 2-3 years in order to allow the native vegetation to regrow.

There are four aquatic herbicides (glyphosate, aquatic 2,4-D and aquatic triclopyr (Garlon) and Habitat) that are currently registered in Nebraska for use in aquatic sites (sites that are continuously under water). Do not use non-aquatic glyphosates (e.g. Roundup-named products, and other generic glyphosates registered for use in Roundup-Ready soybeans) for spraying aquatic sites. They are toxic to aquatic wildlife (e.g. fish, frogs, etc).

The best time to apply herbicide is at beginning of the flowering stage, which usually occurs from mid June to end of July. Early flowering time is a preferred application time for few practical reasons: (a) easy identification by landowners (purple flowers), and (b) flowering time is one of the most vulnerable stages for chemical control of perennial species. Herbicide solutions can be applied using a back- pack sprayer, tractor mounted or pulled sprayer, from a boat or aerial application in solutions ranging from 10-20 gallons per acre.

For those of you who want to do some ‘spot spraying' with a back pack sprayer, for example use 1 pint of Rodeo + 3 oz NIS per 3 gallons of water. The spray solution volume is on a spray-to-wet basis. The product is non-selective, therefore, avoid injuring native vegetation. As always, read and follow the product label directions.

5. Biological control using insects does not eliminate the target weeds, but in general, it can suppress weed population to a non-significant level. Bio-control agents alone cannot provide long-term control of purple loosestrife, however they are necessary part of an integrated approach to stop the expansion of currently infested acres. Several insect species were introduced from Europe, where the loosestrife originated. The list of insects includes: root weevil (Hylobius sp.), two beetles (Galerucella sp.), and two flower-feeding weevils (Nanophyes sp.). They are highly host specific to purple loosestrife, defoliating the plant as both adults and larvae. These insects, in combination with other plant species, so called natural competitors, have historically kept loosestrife under control at the European continent.

It is believed that insects alone cannot provide adequate control of purple loosestrife here in North America. Experience from other parts of the USA and Canada suggest that it takes 7-15 years to observe some effect of insect feeding. If you are interested in rearing biocontrol agents, for more information see NebGuide (G01-1436-A), "Rearing and Releasing Galerucella Beetles to Control Purple Loosestrife" (by Knezevic and Smith).

Rearing and releasing insects however is just one step in the process of biocontrol. Monitoring insect establishment, spread, and impact is crucial for the success of the biological control program. Monitoring programs will determine the effectiveness of Galerucella beetles throughout Nebraska to optimize the beetle release program. For more information see Extension Publication (EC02-175) “Biological Control of Purple Loosestrife: Monitoring Galerucella Establishment and Impact ” (by Hunt and Knezevic).

6. Monitoring: Monitor the sites for several years. New shoots may come up from plant remnants.

HOW CAN YOU HELP? Stop the spread. It is the best course of action currently available. We must all work together to prevent further planting and natural spread. If we do not stop purple loosestrife now, the economic burden to taxpayers will only increase as our vital waterways and wetlands become chocked with this weed.

In local plantings and flower gardens, you can do your part by pulling and burning any plant, root and seed material. You can help your friend and neighbors to do the same. Discourage any and all new purple loosestrife planting. Landscapers and gardeners have a wide variety of alternative perennial plants that are as ‘pretty ' as loosestrife but pose no threat to the environment. Some examples are: spiked speedwell, lilies, Siberian iris, spiked gayfeather and garden sage. Check with your local extension office or horticultural organization for information on alternative landscape species. There are also several useful extension publications including “Growing Perennials (G-828), “Perennials” (G-1015) and “Perennial Flowers Water Wise Garden (G-1214), that can help in the alternative species selection process.

SUMMARY: Purple loosestrife is a serious, perennial, weed found in wetlands of the Prairie states, including Nebraska. Due to major characteristics of the loosestrife habitat (e.g. marshy land) it is believed that neither herbicides nor biocontrol agents used alone can provide long term control of this weed. However, if they are integrated with other weed management methods the long term and cost effective control goal may be achieved. Each management plan would work best when designed for a specific area. (SK)