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CONTENTS

75 ...............................................................DOES OILSEED RADISH PROVIDE NITROGEN CREDITS?

75 ...............................................................CORN ROOTWORM BEETLE SCOUTING

77 ...............................................................SOYBEAN APHIDS

78 ...............................................................MORE FIELD CROP INSECT UP-DATES

78 ...............................................................2020 WISCONSIN WINTER WHEAT PERFORMANCE TRIALS RESULTS

79 ...............................................................NATIONAL SUSTAINABILITY PRO-GRAMS AND LINKS TO ON-FARM DOCUMENTATION

79 ...............................................................OTHER NEWSLETTER LINKS

DOES OILSEED RADISH PROVIDE NITROGEN CREDITS?MIKE BALLWEG, SHEBOYGAN COUNTY EXTENSION AGRICULTURAL AGENT – CROPS AND SOILS, UNIVERSITY OF WISCONSIN-MADISON, DIVISION OF EXTENSION, RICHARD PROOST, SOUTHESAST REGIONAL AGRONOMIST, NUTRIENT & PEST MANAGEMENT PROGRAM, UNIVERSITY OF WISCONSIN-MADISON, MATT RUARK, PROFESSOR AND EXTENSION SOIL FERTILITY SPECIALIST, UNIVERSITY OF WISCONSIN-MADISON

Oilseed radish (Raphanus sativus L.) is a member of the Brassicaceae or Crucif-erae plant family commonly referred to as the mustard family. This plant family includes broccoli, kale, cauliflower and cabbage. There has been considerable interest in growing oilseed radish as a cover crop in Wisconsin due to claimed benefits such as alleviating soil compaction and scavenging excess plant nutri-ents. This research summary specifically addresses the uptake of nitrogen and its availability for the next season’s corn crop.

One concern is that the majority of the radish cover crop research has been conducted in the Mid-Atlantic region of the United States, a region with vastly different agronomic conditions than in the Upper Midwest. Research for this publication summarizes six site-years of data collected in east central Wiscon-sin and is developed to help growers better understand the limitations and benefits of growing oilseed radish. View the 3 page document at the end of this newsletter.

CORN ROOTWORM BEETLE SCOUTINGBRYAN JENSEN, UW-MADISON DEPT. OF ENTOMOLOGY AND INTEGRATED PEST MANAGEMENT PROGRAM

Now is that time of year when scouting adult corn rootworm beetles can pay dividends for next year. Beetle populations during the egg laying period (now and through early Sept.) will help predict if rootworm protection is needed next year and which practice will provide economic control and provide infor-mation that is useful to delay resistance to the Bt hybrids.

UNIVERSITY OF WISCONSIN CROP MANAGER AUGUST 13, 2020

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Beetle populations have been historically low the last 3 years according to statewide surveys conducted by DATCP staff. If populations remain the same, decrease or increase can only be determined by field scouting. I am a fan of the whole plant count method not because of reliability but because I get information the first time I am in the field. This method is simple but does take time and corn is not easy to walk in this time of year. However, the information gained will be extremely helpful. More detailed information can be found in the attached reference card Field Scouting for Corn Rootworms or if you prefer the YouTube version How to scout for Corn Rootworm Beetles

Briefly, count the number of beetles on 50 plants/field/sampling date. Keep samples distributed within a field. I would suggest counting beetles on 5 plants in each of 10 areas of a field. When approaching a plant, cover the silks with one hand before counting beetles on the rest of the plant. You will find them on the tassel, upper and lower leaves as well as in leaf axils. Remove your hand to count beetles on and in the silk. Don’t count beetles on adjacent plants because they are easily disturbed and will drop off or fly away.

If the field average is greater than 0.75 beetles/plant you will need root protec-tion if you plant corn in the same field next year. One more count in 7-10 days will give you additional comfort in knowing if populations are increasing which help choose an effective, yet economical, management practice. If you stay be-low 0.75 beetles/plant for a minimum of two weekly counts during egg laying you will not need root protection next year.

An alternative method is to use the Pherocon AM unbaited yellow sticky traps. For every 10-50 acres, 6 traps should be deployed in two transects (12 total traps) across the field at least 330 feet apart. Each trap within a transect should be 165 feet apart. These traps are a visual attractant. I would suggest stripping leaves on adjacent plant to make sure the traps are visible. Check traps on a weekly schedule and count both northern and western adults. If an average of 2 or more beetles are caught/trap you should consider using a rootworm management practice on next year’s corn.

One final thought on rootworms. There have been several reports of lodged corn after strong storms moved through the state earlier this summer. Don’t assume lodged corn is the result of rootworm feeding. The window may be closing on assessing root damage. Late July is better only because corn can re-generate roots and mask earlier damage but it is still worth your time to check.

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SOYBEAN APHIDSBRYAN JENSEN, UW-MADISON DEPT. OF ENTOMOLOGY AND INTEGRATED PEST MANAGEMENT PROGRAM

The calls about soybean aphids have started to come in but let me put this comment in perspective. Those calls have usually been a curiosity and prompt-ed because of a gradual increase in aphid number. Certainly, high numbers have not been reported. However, a little spraying has started.

We have a few things on our side to help with your aphid management de-cisions. First, a lot of our soybean were planted earlier than the previous two years. Which means as each day goes by, we have banked more yield so there is less yield to protect. We are also getting reports of summer dwarfs which are shorter lived and have a lower reproductive rate.

Soybean aphid populations have been relatively low all season. Certainly, we need to continue to use and respect the long-established threshold of 250/plant (80% of plants infested and the aphid populations must be increasing) but another way to look at it is how long have the aphids been feeding. My point is a population of 250/plant for 3 days is less problematic than the same populations that was present for 3 weeks. That scenario is a bit simplistic, but it does indicate my point. A population that spikes to 250/plant may not need immediate spraying if, for example you are close to R6 (when little if any yield response would be expected) and/or natural enemies are building and/or hot weather is expected that should slow reproduction.

In addition to using the 250/plant threshold also consider looking at cumula-tive aphid days. One aphid day equals 1 aphid feeding on a plant for one day. Ten aphids feeding on one plant for one day equals 10 cumulative aphid days. That same 10 aphids feeding for 10 days equals 100 cumulative aphid days. The economic threshold for cumulative aphid days is 5,500 days. I am hopeful this alternative method of using the same threshold will help you put the need for control in perspective and is especially useful if you have weekly scouting data.

The closer we get to the end of season soybean aphid population crash the lower your probability of a return on investment that your spray decision should provide. Keep in mind if using ground application equipment wheel traffic will slight reduce yield. With that in mind, I do think you want to be rel-atively confident that an insecticide application is necessary. These and other reasons make late season economic spray decision very difficult. I guess at this time of the growing season I try to come up with reasons not to apply an insec-ticide. If I can’t? I feel more confident I made the right decision. Also spray deci-sions usually do not have to be made on the spot. Often decision can be delay for a few days to allow more time for observations and to build confidence.

When deciding to make a spray decision be sure to check for the presence of economic populations of two-spotted spider mites. Some areas of Wisconsin have been dry and spider mites may be a concern. If present in low numbers, it puts more pressure on making a correct spray decision. Insecticides used to control soybean aphids will kill beneficial arthropods which could easily flare spider mite (and aphid) populations. If spider mites are present in economic numbers it should also impact your spray decision to choose a product with aphid and spider mite activity.

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MORE FIELD CROP INSECT UPDATES

BRYAN JENSEN, UW-MADISON DEPT. OF ENTOMOLOGY AND INTEGRATED PEST MANAGEMENT PROGRAM

Potato leafhoppers. By most reports are still going strong. Continue to sweep until there is a consistent drop in populations over a couple weeks. Be especial-ly concerned with new seedings. When will leafhopper populations decline? It is very hard to predict. Usually by mid August, sometimes not until early September.

Armyworms. There have been few reports regarding the summer generation. But now is the time when significant damage can be spotted in corn.

Corn Rootworm Adults. Monitor late planted fields for silk clipping. Adults are mobile and will move around the landscape looking for pollinating fields. We will soon approach the best time to scout beetles to determine the need for and/or the most appropriate control decision in next year’s corn.

Two-spotted spider mites. Droughty areas should be monitored for damage and signs of live mites.

Soybean aphids. Scout. We still have time for populations to increase but eco-nomic control decisions get more difficult.

Soybean Defoliators. Grasshoppers have been reported in some areas. Dry weather tends to increase grasshopper populations both for the current year and the following year. Especially when populations peak late season. Japa-nese beetles are still active but potential for damage is diminished as the grow-ing season progress. Other caterpillars have been reported but remember the economic threshold for defoliating insect is 20% defoliation. Those decisions should be made based on the leaf area of the whole plant, not just the upper leaves.

2020 WISCONSIN WINTER WHEAT PERFORMANCE TRIALS RESULTSSHAWN P. CONLEY, SOYBEAN AND WHEAT EXTENSION SPECIALIST, DEPARTMENT OF AGRONOMY, UNIVERSITY OF WISCONSIN-MADISON

New publication>> 2020 Wisconsin Winter Wheat Performance Trials (A3868)

Introduction: 2020 Acreage and Growing Conditions

Wisconsin saw a 18% decrease in winter wheat acres planted (160,000) in the 2019-2020 growing season compared to the previ-ous year; 120,000 acres are fore- casted to be harvested for grain, compared to 150,000 in 2019. The forecasted yield for the 2020 crop is 70 bu/a, up 6 bu/a from 2019. Some wheat was planted late due to delayed corn and

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soybean harvest caused by substantial rains and early snow falls. Mild winter conditions resulted in good winter survival. Wheat broke dormancy in early April and crop development was delayed all season due to lower than average GDU accumulation. In general, the crop was relatively short in stature.

The Wisconsin Winter Wheat Performance Trials are conducted each year to give growers information to select the best-performing varieties that will sat-isfy their specific goals. The performance trials are conducted each year at four locations in Wisconsin: Arlington, Chilton, Fond du Lac and Sharon. Trials in-clude released varieties, experimental lines from University breeding programs and lines from private seed companies. The primary objective of these trials is to quantify how varieties perform at different locations and across years. Grow-ers can use this data to help select which varieties to plant; breeders can use performance data to determine whether to release a new variety.

NATIONAL SUSTAINABILITY PROGRAMS AND LINKS TO ON-FARM DOCUMENTATIONDEANA KNUTESON, HEALTHY GROWN COORDINATOR, NPM PROGRAM, UW-MADISON

As the requirements for sustainability becomes more evident in the market-place, and as more, complex data is collected on the farms, it is important for growers to understand these trends so that they are aware, prepared and proactive. On-farm data can be used to respond and document production practices, and can be used for promotions to show your own farm advances.

National sustainability programs emphasize environmental, economic and so-cial components of sustainability and are looking at how to calculate and track progress along the sustainability continuum.

Some examples are Field To Market (https://fieldtomarket.org/), the Steward-ship Index for Specialty Crops (https://www.stewardshipindex.org/), and the Cool Farm Tool (https://coolfarmtool.org/). Growers can use these to track and document specific practices for their farms and see where adjustments could be made. Additionally, some retailers have developed their own sustaina-bility efforts, and many retailers are using these for corporate responsibility programs and to have on-farm data to track improvements overtime. Incen-tives for growers for sustainability tracking can be as simple as a premium for product, preferential buying, or in more complex ways such as reduced insur-ance rates or via public investments such as tax breaks or direct payments for practice adoption.

OTHER NEWSLETTER LINKS

08/13/2020 - Wisconsin Pest Bulletin

08/07/2020 – Welcome to Wisconsin Fruit News Vol 5 Issue 8

Wisconsin Vegetable Updates

Oilseed radish (Raphanus sativus L.) is a member of the Brassicaceae or Cruciferae plant family commonly referred to as the mustard fami-ly. This plant family includes broccoli, kale, cauliflower and cabbage. There has been considerable interest in growing oilseed radish as a cover crop in Wisconsin due to claimed benefits such as alleviating soil compaction and scavenging excess plant nutrients. This research sum-mary specifically addresses the uptake of nitrogen and its availability for the next season’s corn crop. One concern is that the majority of the radish cover crop research has been conducted in the Mid-Atlantic region of the United States, a region with vastly different agronomic conditions than in the Upper Midwest. Research for this publication summarizes six site-years of data collected in east central Wisconsin and is developed to help grow-ers better understand the limitations and benefits of growing oilseed radish in Wisconsin.

SEEDING RATES AND ESTABLISHMENT

The daikon type of oilseed radish used in this study has a large taproot, which can grow 2 or more inches in diameter and more than a foot in length with adequate growing degree-days and soil fertility. It was planted in mid-August following the harvest of a winter wheat crop. Seeding rates were 10–12 pounds per acre (lb/acre). Oilseed radish is best used in a crop rotation planted after short season crops such as winter wheat, snap beans, peas or other vegetable crops. Planting by mid-August is recommended for oilseed radish in order to produce adequate biomass before the end of the growing season. Oilseed rad-ish will winter kill following several days when temps are below 20°F. Planting in September usually does not result in sufficient plant biomass.Oilseed radish is drilled, either conventionally or no-tilled, to a depth of 1/4 to 1/2 inch, or broadcast and incorporated with light tillage. With adequate moisture, oilseed radish establishes quickly. Research conducted in Michigan found that seeding rates of 10, 15 and 20 lb/acre all produced similar amounts of biomass. Lower seeding rates resulted in larger individual plants producing larger tubers. Although oilseed radish is often established without the addi-tion of supplemental nitrogen, it may be necessary for adequate growth.Radish planted in late summer can be overly competitive when established in combination with other cover crop species. Consequently farmers are planting oilseed radish at 1–3 lb/acre in combination with other crops such as barley, oats, berseem, crimson, and/or other clovers.

Does Oilseed Radish Provide Nitrogen Credits? Mike Ballweg, Sheboygan County Extension Agricultural Agent - Crops and Soils, University of Wisconsin-Madison, Division of Extension

Richard Proost, Southesast Regional Agronomist, Nutrient & Pest Management Program, University of Wisconsin-Madison

Matt Ruark, Professor and Extension Soil Fertility Specialist, University of Wisconsin-Madison

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FALL GROWTH AND NITROGEN UPTAKE

Analysis of whole plant oilseed radish grown as a cover crop clearly shows that large amounts of soil nitrate are captured in the plant biomass. This study found that oilseed radish planted after winter wheat in mid-August showed nitrogen uptake in 2012 of 48 and 120 lb/acre, and 110 and 124 lb/acre in 2013 (Table 1).At the end of the radish-growing season, radish significantly reduced soil nitrate in the 0–12-inch sampling depth in all six site years, and in four site years in the 12–24 inch sampling depth. At corn planting, radish significantly reduced nitrate in three of the six site years at the 0–12 inch and 12–24 inch sampling depth.

DOES OILSEED RADISH PROVIDE A NITROGEN CREDIT WHEN CORN FOLLOWS RADISH?

In this study, there was no significant difference in corn yield between radish cover crop and nitrogen rates (data not shown). When corn yield was aver-aged over all nitrogen rates, significant differences between a radish cover crop and no radish cover crop were found in three of the six site years, and in those cases the no radish cover crop had higher grain yields than the radish cover crop (Figure 1). The carbon to nitrogen (C:N) ratio of the whole radish plant biomass ranged from 11–19.3, with the above ground biomass ranging from 9.02–16.0 and the below ground biomass ranging from 11.7–25.1 (data not shown). This data was averaged from across all site locations in 2012 and 2013. These C:N

Table 1 SOIL NITRATE NITROGENfall sampling at corn planting radish

0”-12” 12”-24” 0”-12” 12”-24” biomass N uptake--------------------lb N/acre------------------- ton/acre lb/acre

2011 – 2012

Sheboyganno radish 50a* nc** 29 16 -- --radish 11b nc 39 9 -- --Washingtonno radish 7a nc 64 21 -- --radish 4b nc 68 22 -- --

2012 – 2013

Sheboyganno radish 28a 22a 18a 15a -- --radish 5b 3b 13b 3b 3.1 120Washingtonno radish 35a 17a nc nc -- --radish 3b 2b nc nc 1.19 48

2013 – 2014

Sheboyganno radish 26a 17a 10a 11a -- --radish 6b 3b 7b 4b 2.42 110Washingtonno radish 39a 30a 34a 21a -- --radish 5b 3b 14b 10b 2.78 124

* Means (in columns, within site years) followed by different letters were statistically different (A=0.10) ** nc = not collected

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ratios would suggest a net nitrogen mineralization rather than a net nitrogen immobilization during the radish decomposition. C:N ratios of 20 or less re-lease nitrogen, whereas C:N ratios greater than 30 tie-up nitrogen (see chart for examples). However, results showed that while the uptake of N by oilseed radish can be substantial, there was no corresponding nitrogen credit. What is not clear is the fate of the nitrogen released from the decomposing radish biomass. As mentioned, there seems to be a potential N credit based on the amount of N in the whole plant biomass and the favorable C: N ratio for net mineralization. However, this study found no N credit for the next season’s crop as determined through nitrogen response curves (data not shown). This research supports radish use as a cover crop to trap fall N. From an environmental perspective, this uptake of nitrogen has the potential to re-duce nitrate nitrogen from making its way to the groundwater, however, the release of nitrogen from decomposing radish biomass was not available to a subsequent corn crop as indicated by the corn yield, showing that the fate of this nitrogen is unclear.

Material C:N RatioSoil microorganisms 8Soil organic matter 10Alfalfa 12Radish (average) 12Rotted manure 20Corn residue 60Grain straw 80Sawdust 300

ReferencesChawner, M.M., Assessing the Benefits of Radish as a Cover Crop. Thesis: Master of Science (Soil Science and Agroecology) University of Wisconsin-Madison, 2015. Chawner, M.M., M. Ruark, M. Ballweg, R. Proost, F. Arriaga and J. Stute. Does cover crop radish supply nitrogen to corn in Wisconsin. Jacobs, A.A. 2012. Plant Guide for oilseed radish (Raphanus sativus L.). USDA-Natural Resources Conservation Service.Ruark, M., K. Shelley and J. Stute. Radish as a cover crop. New Horizons in Soil Science. Issue 11-01.Ngouajio, M. and D.R. Mutch. 2004. Oilseed Radish: A New cover Crop for Michigan. Bulletin E 2907.Michigan State University, East Lansing.Shelley, K., Cover Crop Options for Winter Wheat in Wisconsin. Cover Crop in Wisconsin – The Wisconsin Crop Team.

Treatment Yield (bu/a) Treatment Yield (bu/a) Treatment Yield (bu/a)

Sheboyganradish 177b radish 175b radish 83no radish 183a* no radish 190a no radish 83

Washingtonradish 97 radish 105 radish 152bno radish 99 no radish 107 no radish 162a

*Means followed by different letters were statistically different (A=0.10)

180 bu/a

140 bu/a

100 bu/a

60 bu/a

Sheboygan Washington

2012Sheboygan Washington

2014ra

dish

no ra

dish

radis

h

no ra

dish

Sheboygan Washington

2013

radis

h

no ra

dish

radis

h

no ra

dish

radis

h

no ra

dish

radis

h

no ra

dish

0 bu/a

Figure 1

An EEO/AA employer, University of Wisconsin-Madison Division of Extension provides equal opportunities in employment and program-ming, including Title VI, Title IX, the Americans with Disabilities Act (ADA) and Section 504 of the Rehabilitation Act requirements.

This publication is available from the Nutrient and Pest Management (NPM) Program. (608) 265-2660, npm@hort.wisc.edu or visit our website: ipcm.wisc.edu

NPM

Field Scouting for Corn Rootworm: An Integrated Pest Management (IPM) practice

Scouting for corn rootworm (CRW)beetles can help determine the need for rootworm control in continuous corn.

If beetle numbers are below thresholds, no field treatment for CRW is needed. (See the back of this card.)

Bt CRW hybrids is known to occur in areas of the Midwest and is suspected in areas of Wisconsin. Collecting field scouting information can fine-tune management strategies to reduce reliance on Bt CRW hybrids and adopt an IPM program for corn production.

A well balanced IPM program includes scouting for CRW beetles, crop rotations, use of soil applied insecticides on conventional hybrids, seed treatments (low to moderate CRW populations only), and Bt CRW Hybrids.

What is a corn rootworm’s life cycle?

Northern and Western corn rootworms have similar life cycles. They overwinter as eggs laid in the upper soil profile and hatch in early June. First instar larvae

feed on the smaller branching corn roots. Second and third instars feed on larger roots at the base of the corn plant.

Adult beetles emerge late June through August and lay eggs almost exclusively in corn fields from early August through early September. There is one complete generation/year. In the southeast part of Wisconsin, Western corn rootworm adults may lay eggs in soybean fields.

Scan the QR code to see a video: How to scout for corn rootworm beetles

This card and video produced by Integrated Pest Management (IPM) program University of Wisconsin-Madison

Using accurate field information can help delay CRW resistance to the Bt CRW hybrids by matching appropriate corn rootworm management practices with actual beetle populations.

Western corn rootworm resistance to

Lodged corn is not a good indicator of CRW presence.

Corn-rootworm-card2015h.indd 1 9/16/15 12:32 PM

How to scout: Count the number of CRW beetles on 50 corn plants. Visit 5 random areas of the field and count beetles on 10 plants in each area. Do not pick plants directly adjacent to each other. Count the beetles found on the tassel, silk, top and bottom of leaves, and feeding on the ear tip.

First, trap beetles in the silk by firmly grabbing the silk end of the ear. Count beetles on the rest of the plant before slowly opening your hand to count beetles feeding on the silk and ear tip.

For pollination protection, scout fields before 70% of the field has silked.

For root protection, scout fields during the egg-laying period from early August to early September. Repeat this scouting procedure on 7-10 day intervals one or two more times during the egg-laying period.

Pollination Protection: Treat corn fields if silks are clipped to 1/2-inch or less from the ear and pollination is less than 50% complete. This usually requires approximately 5 beetles per plant.

Root Protection following corn: Treat if scouting counts from the previous year’s egg-laying period reached a field average of 0.75 beetles per plant.

Root Protection following soybean: Treat corn if yellow sticky trap catches average more than 5 Western corn rootworm beetles/trap/day during the egg-laying period from early August to early September.

UW-Madison IPM program, http://ipcm.wisc.edu I-10-2015-2M An EEO/Affirmative Action employer, the University of Wisconsin-Extension, provides equal opportunities in employment and programming, including Title IX and ADA requirements.

Western CRW beetle Northern CRW beetle Silk clipping

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