107th Annual Midwest Food Processors Association Convention
84th Annual Processing Crops Conference
Title: Determining the Risk Window for Aster Yellows in Carrots: New Technologies for an Old
Problem
Project History. The research conducted in 2011 is a new field research project focused on the
development of sustainable and long-term solutions for the key insect and nematode pests of
processing carrots. Objectives outlined in this research are directly related to the problematic
management and control of carrot insect pests including, Aster leafhopper (ALH: Macrosteles
quadrilineatus), Aster Yellows phytoplasma (AYp), and the northern root-knot nematode
(NRKN:Meloidogyne hapla) in Wisconsin.
Principal Investigators
Russell L. Groves, Assistant Professor and Entomology Extension Specialist, 537 Russell
Laboratories, University of Wisconsin, Madison 53706 groves@entomology.wisc.edu (608) 2623229.
Ken Frost, Graduate Research Assistant, Department of Plant Pathology, 537 Russell Laboratories,
University of Wisconsin, Madison 53706 kfrost@plantpath.wisc.edu (608) 262-9914.
Amanda Gevens, Plant Pathology Extension Specialist, Russell Laboratories, University of
Wisconsin, Madison 53706 gevens@plantpath.wisc.edu (608) 890-3072.
Ann MacGuidwin, Plant Pathology Extension Specialist, Russell Laboratories, University of
Wisconsin, Madison 53706 aem@plantpath.wisc.edu (608) 263-6131.
Randy Van Haren, Pest Pros Inc. LLC, 10086 1st Street, Plainfield, WI 54966-9407,
pestpros@uniontel.net (715) 335-4046.
Scott Chapman, Associate Research Specialist, 537 Russell Laboratories, University of Wisconsin,
Madison 53706 chapman@entomology.wisc.edu (608) 262-9914.
Zsofia Szendrei, Assistant Professor and Entomology Extension Specialist, Department of
Entomology, Michigan State University, 439 Natural Science Building, East Lansing MI 48824,
szendrei@msu.edu, (517) 974-8610.
Adam Byrne, Research Technician, Department of Entomology, Michigan State University, 439
Natural Science Building, East Lansing MI 48824, byrnea@msu.edu, (517) 355-4633.
Cooperator (s)
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Jeffrey Krumm, Syngenta Crop Protection, N3847 Airport Road, Cambridge, WI 53523,
jeffrey.krumm@syngenta.com, (608) 320-2014 (office / mobile).
Greg Miller, Seed Technology Specialist, Nunhems USA Inc., 1200 Anderson Corner Road,
Parma, ID 83660-6188, (208) 674-4000, greg.miller1@bayer.com.
Paul Miller, Paul Miller Farms, N4481 4th Avenue, Hancock, WI 54943-8917
pmfarms@uniontel.net,
(715) 249-5160.
Abstract. Insect and nematode management programs on processing and fresh market carrot crops
in Wisconsin rely heavily on the use of frequent foliar applications of insecticides. Many of the
pesticides used are broad spectrum chemicals that present considerable, well documented risks to
the safety of farm workers and the environment including at-plant treatments of oxamyl and
successive foliar applications of synthetic pyrethroids and protectant fungicides. This research
attempts to refine and replace current practices, which rely on frequent foliar sprays of broad
spectrum insecticides with an economically viable system that relies on reduced-risk and
carbamate-alternative insecticides applied as seed treatments or as in-furrow applications to
minimize farm worker exposure to pesticides and mitigate adverse effects on human health, the
environment, and non-target organisms. An outcome of this integrated research and extension
program in Wisconsin is a management approach which can be tailored to meet the needs of a
diversity of stakeholders representative of processing producers and an emerging potential market
for a fresh, cut-n-peel segment. Compared to current IPM practices, these reduced-risk systems
will increase the sustainability and thus the profitability of carrot production, enhance natural
enemy populations and biological control, and reduce adverse effects on farm workers and
applicators.
Rationale and Significance. Effective, economical, and efficient long term management of the key
insect pests in carrot (e.g. PLH, AYp, RLN, RKN) continues to be a challenge using combinations
of both pre-plant, broadcast and foliar insecticides. In particular, the AYp continues to be a high
pest priority for Wisconsin carrot growers as problematic populations are regularly the result of
migrating populations from southerly latitudes. The AYp pathogen is vectored primarily by the
ALH in a persistent and propagative manner. The leafhopper acquires AYp by feeding on infected
plants and may carry and transmit AYp over great distances. A defining feature of the aster
leafhopper’s biology is the early season migration of the insect from the Gulf-states to Upper
Midwest. Aster yellows disease is caused by the AYp, which is a small prokaryote that is
taxonomically placed in the provisional genus, Candidatus. As noted previously, this organism is
obligately associated with its plant and insect host(s) and has not been successfully cultured in the
laboratory to date (which has slowed research progress due to the inability to obtain a “pure”
culture). The symptoms caused by AYp are as varying as the number of plant species infected by
AYp, but these symptoms lead to direct yield and quality losses and processing problems which
results from malformed roots challenges associated with cleaning raw product. Currently, the
decision to intercede and implement a pest control practice (e.g. insecticide spray) is based upon
calculation of the Aster Yellows Index (AYI). Control practices strictly utilize insecticide sprays
(primarily Group 3 synthetic pyrethroids, IRAC, Mode-of Action Classification http://www.iraconline.org/) that target not only the aster leafhopper, but will impact all other beneficial insects
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present in the crop. These materials currently comprise the backbone of low-cost registrations
which are relied upon for use against the aster leafhopper in support of the AYI. The synthetic
pyrethroids were conditionally registered beginning in 1984 for use on selected crops and currently,
EPA is assessing risks to non-target organisms. Several of these synthetic pyrethroids remain
conditionally registered for use on vegetables grown in muck soils, however, each of these
chemicals is highly lipophilic and in aquatic environments tend to strongly adsorb to sediments.
Under section 4 of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), US EPA
continues to re-evaluate existing pesticides to ensure that they meet current scientific and
regulatory standards. US EPA has recently completed several Reregistration Eligibility Decisions
(RED) for the synthetic pyrethroid group is insecticides and will continue to do so in the future
under section 4(g)(2)(A) of FIFRA. These compounds are broadly characterized as having a wide
spectrum of activity often with acute oral neurotoxicity to mammals, notable chronic effects as
endocrine disruptors, and are classified as both mutagenic and carcinogenic. With the advent of
novel, reduced risk, and less broad spectrum seed treatment registrations for many homopterous,
sucking insect pests (e.g. thiamethoxam), the continued RED eligibility of this important class of
insecticides could be in jeopardy.
Root-knot nematodes are major pathogens of vegetables throughout the United States and the
world, and particularly in carrot production in the upper Midwest where they impact both the
quantity and quality of marketable yields. In addition, root-knot nematodes interact with other
plant pathogens, resulting in increased damage caused by other diseases including the foliar
pathogens. Only the northern root-knot nematode (NRKN; Meloidogyne hapla) has been
documented in carrot grown on organic or mineral soil in Wisconsin, as it is able to survive the
extreme low temperatures during winter. The NRKN has a wide host range consisting of more
than 500 crop and non-crop weed species, including weeds common to both muck and mineral
soils. The increasing occurrence and damage of this nematode to carrots grown on muck and
mineral soils in Wisconsin has been so severe in certain circumstances to cause marketable yield
losses of carrots reduced by as much as 45% in commercial fields and even complete rejection of
whole loads. Roots of severely infected carrots exhibit forking, galls, hairiness, and even stubby
roots as typical symptoms. Adversely affected root systems of carrots heavily infected by M. hapla
are also not efficient in the uptake of water and nutrients that are necessary for normal plant growth
leading to susceptibility to other foliar pathogens. Rotating carrot with a non-host crop such as
sweet corn and other grain crops, if economically possible, can be effective in reducing damage
levels of NRKN, however current crop rotations on many commercial farms are of limited value as
most crops grown, including potatoes, snap beans, onion, and carrot are susceptible. Effective and
economical control is most often achieved with the use of pre-plant nonfumigant-type nematicides
including oxamyl (Vydate® L); the primary pesticide tool registered for use in Wisconsin. Oxamyl
is a carbamate used to control insects, mites, and nematodes first registered in 1974 by DuPont, Inc.
Initial registered application methods included ground, foliar spray, soil spray, soil drench, root dip,
preplant incorporated, or transplant water. In recent years, the registrant has undertaken a number
of voluntary actions to reduce exposures human and environmental exposures to include the
deletion of specific uses (ornamentals, greenhouse, and soil mixing uses), lowered application
rates, and established seasonal maximums, restricted entry intervals, and extended pre-harvest
intervals. The potential for new, reduced risk, and less broad spectrum seed treatment registrations
targeting the NRKN (e.g. abamectin), increasingly provides pest management alternatives for long
term control of nematode pests and resulting infection.
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Objective. Current IPM practices for carrots and many other vegetable crops rely extensively on
frequent foliar sprays of older, broad spectrum insecticides including oxamyl (Vydate®)and
synthetic pyrethroids (Asana®, Permethrin®, etc.). Although successful from the perspective of
managing insect pests in a cost-effective manner, this approach presents considerable, well
documented risks to the safety of farm workers and the environment. We propose to refine and
implement a pest management program based on reduced risk insecticides and an application
technology that: 1) minimizes farm worker exposure to high-risk pesticides and newer RR
insecticides, 2) reduces environmental risks by utilizing insecticides with a more friendly
environmental profile on an as needed basis to reduce or eliminate drift and run-off into water
resources; and 3) creates incentives for adoption by the grower community by documenting
enhanced profitability.
Methods and Results. Experiments were conducted in two experimental field locations in central
Wisconsin on a sandy loam soils near Hancock, WI. The field sites have been selected based on a
field history of known pressure from both ALH (and associated AYp) plus NRKN which can result
in yield and quality losses. Experiments were arranged as a randomized stripped block design with
10 experimental replications of the insecticide main effects to include: 1) untreated control
(fungicide only seed treatment, 2) Cruiser seed treatment (0.1 mg a.i. / seed), 3) Avicta® seed
treatment (0.116 mg a.i. / seed), and 4) a conventionally managed at-plant oxamyl (Vydate®)
broadcast application (Table 1). At each experimental field site, replicates will vary in plot length
according the total length of the field. In the slicing carrot variety (cv. Enterprise), the
experimental plots were approximately 2,400’ in length with 10 experimental replicates resulting in
plots that are 240’ in length resulting in a plot size of 0.99 acres. Plots will be arranged as a
randomized complete block design (RCBD) and the experimental site will be located at Field
‘HAI’. Each experimental treatment will consist of 3 carrot rows spaced 19” apart on a single 72”
bed. The slicing variety ‘Enterprise’ is seeded at a rate of 600,000 seeds /acre and our request will
be for 630,000 seeds with an estimated 10% overage. Total seed amounts will be split into 3 equal
parts and seed treatments applied. In the dicing carrot variety (cv. Canada) the experiment will be
2,390’ in length with 10 experimental replicates resulting in plots that are 239’ in length resulting
in a plot size of 0.99 acres (Fig. 2). Plots will also be arranged as RCBD and the experimental site
will be located at Field ‘Kellerman’. Each experimental treatment will consist of 3, paired carrot
rows spaced 19” apart on a single 72” bed. The dicing variety ‘Canada’ is seeded at a rate of
225,000 seeds /acre and our request will be for 237,000 seeds with an estimated 10% overage.
Total seed amounts will be split into 3 equal parts and seed treatments applied.
Table 1. At-plant, seed-treatment insecticides for the control of Aster leafhopper (ALH), Aster Yellows
phytoplasma (AYp), and northern root-knot nematode (NRKN) applied to both a slicing (cv. Enterprise) and a
dicing carrot variety (cv. Canada), Paul Miller Farms, HancockWI 2011.
Trt
Product
1
Untreated Control
(fungicide only)
2
Cruiser 5FS
(plus fungicide)
Active
Ingredient
metalaxyl
fludioxonil
thiamethioxam
metalaxyl
fludioxonil
Rate
7.5 g ai / kg
2.5 g ai / kg
0.1 mg ai / seed
7.5 g ai / kg
2.5 g ai / kg
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Application Method1
ST
ST
1
3
Avicta 400FS
4
Vydate CLV
5
Sepresto
6
Sepresto / Votivo
abamectin
thiamethoxam
metalaxyl
fludioxonil
oxamyl
iprodione
thiram
clothianadin
imidacloprid
clothianadin
imidacloprid
Bacillus firmus
0.016mg ai / seed
0.1 mg ai / seed
7.5 g ai / kg
2.5 g ai / kg
2 gal / acre
9.5 g ai / kg
3.0 g ai / kg
0.15 mg ai / seed
0.08 mg ai / seed
0.15 mg ai / seed
0.08 mg ai / seed
CFU / mg
ST
PPB
ST
ST
ST
ST
Denotes application method for insecticides to include seed treatment (ST) and pre-plant, broadcast (PPB) applications.
Approximately 3 weeks after planting, initial stand counts were obtained to determine and estimate
a baseline plant emergence. At weekly intervals after this count, the number of damaged or
missing plants were recorded over 20 feet of row in each replicate to investigate the potential for
phytotoxicity and direct stand loss due to phytophagous insect pests (e.g. seed corn maggot,
wireworms, etc). Adult and nymphal ALH populations were surveyed weekly by counting all
lifestages (nymphs & adults) collected from 100 random sweeps in each experimental plot. The
percentage of symptomatic plants in a smaller, 25’ bed section of each experimental plot were also
recorded to measure the extent of Aster Yellows disease present in each plot. Infection of AYp
will be confirmed through established PCR-based protocols using nested-primers. At 2 intervals
during the course of the study (e.g. mid-June and Mid- September) and within each experimental
replicate, populations of NRKN were assessed using soil core samples according to the protocols
outlined by Pest Pros, Inc. At the completion of the experiment, total crop yield and crop quality
(e.g. percentage of forked and hairy-roots) were recorded from each plot. Data were analyzed
using ANOVA, with mean separation by Fisher’s protected LSD at P <0.05. ALH count data and
yield and quality data were transformed using a log10 (x + 1) function prior to analysis while
percent infection estimates of AYp will be transformed using an arc-sine, square root function prior
to analysis.
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