Implementing Sustainable Management of Muskmelon Diseases, Weeds, and Insect Pests in Partnership with Iowa Growers

2003 Annual Report for LNC02-213

Project Type: Research and Education
Funds awarded in 2002: $95,441.00
Projected End Date: 12/31/2006
Region: North Central
State: Iowa
Project Coordinator:
Dr. Mark Gleason
Iowa State University

Implementing Sustainable Management of Muskmelon Diseases, Weeds, and Insect Pests in Partnership with Iowa Growers

Summary

The goal of our three-year, multidisciplinary research project is to enhance sustainability of muskmelon disease, weed, and insect pest management. Muskmelon, a key high-value crop in the North Central region, relies heavily on costly synthetic pesticides and fertilizers that endanger grower and consumer health, kill non-target organisms, and pollute the environment. We will investigate innovative tactics that can reduce or replace these toxic inputs.
Field trials will use mass trapping augmented by trap crops, row covers, neem, and kaolin clay to deter bacterial wilt transmission and feeding injury by cucumber beetles. Another field experiment will evaluate control of anthracnose, gummy stem blight, and Alternaria leaf blight by Bacillus subtilis, potassium bicarbonate, and the Melcast disease-warning system, which allows growers to time fungicide sprays efficiently. We will also assess suitability of a hairy vetch-winter rye mulch to replace synthetic herbicides and fertilizers in managing weeds and N fertility. We will integrate the most promising new strategies into systems-level field trials and determine input costs, profitability, and risks associated with all strategies. Growers will learn about the new methods through eight on-farm trials per year, field days, a website, newsletter articles, press releases, and an Extension bulletin.
Muskmelon growers are full partners in the project from start to finish. Growers have provided feedback on the proposal, and a 10-grower Advisory Panel will help to design field trials, interpret findings, and prioritize education efforts.
Short- and intermediate-term outcomes include identifying practical management tactics that reduce reliance on synthetic chemical inputs, participation of 15 growers in on-farm trials, and (as determined by Year 1 and Year 3 surveys) adoption of one or more of the new methods by 50 growers and increased willingness of 100 growers to adopt these methods. Long-term outcomes include higher profits for growers, reduced environmental pollution, and healthier and more stable rural communities.

Objectives/Performance Targets

  1. Suppress bacterial wilt and cucumber beetle feeding injury on muskmelons as effectively as conventional insecticide-based methods by integrating mass trapping, trap crops, row covers, neem, and kaolin clay.

    Validate ability of a) the Melcast disease-warning system using site-specific weather estimates as inputs, b) Bacillus subtilis sprays, and c) potassium bicarbonate sprays to reduce or replace conventional fungicide sprays for control of muskmelon anthracnose, gummy stem blight, and Alternaria leaf blight.

    Evaluate ability of a hairy vetch-rye cover crop to suppress weeds, reduce applications of conventional herbicides, and add nitrogen to soils.

    Combine the most promising component strategies from Objectives 1-3 into systems-level strategies that integrate weed, insect, and disease management.

    Document economic costs and profitability of these new management tactics in comparison to conventional practices.

    Transfer the project’s findings to North Central region muskmelon growers through on-farm demonstration trials with eight growers per year, a website, quarterly newsletter articles, presentations at regional grower meetings, annual field days, annual press releases, and an Extension bulletin.

Accomplishments/Milestones

SARE 2003 Annual Report
GROWER INVOLVEMENT
Our advisory panel includes the following growers: Phil Funk (Dallas Center),
Laura Krouse (Mt. Vernon), Greg Hoffman (Waterloo), Michael Nash and Solveig
Hanson (Postville), Richard and Sharon Dix (Janesville), Gary Guthrie (Nevada),
Dean Henry (Nevada), John Kiwala (Muscatine), Bob Furleigh (Clear Lake), and
a group of Amish farmers from Davis County. We met in Ames on December 8 to
discuss the results of last year’s experiments and plans for next year. The
meeting allowed the growers to ask questions about our results, and brought
to light several ideas for next year’s project. Specifically, several growers
had ideas about our hairy vetch/rye mulch, and many growers were interested
in learning more about the impact of weather on beetle behavior and survival.
We also cooperated with several growers in Iowa on strategies for cucurbit pest
management during the 2003 field season:
– Phil and Nancy Funk (Dallas Center, IA) and Richard, Bill, and Sharon Dix
(Janesville, IA) managed one row of muskmelons at each of their farms according
to the Melcast system. In each of these trials, ISU personnel managed the weather
data, and worked with each grower to determine spray timing. Iowa had the driest
late summer on record this year, and the Dixes and Funks made zero and one spray,
respectively, throughout the season. The Melcast system saved them three and
two sprays this season, without an increase in anthracnose symptoms. Both growers
were very happy with this strategy. They are interested in learning to manage
the sprays on their own using the Melcast computer program.
– Greg Hoffman (Waterloo, IA) treated one row of his muskmelon plants with
a single applications of the systemic insecticide Admire at planting. He called
ISU at the first sign of bacterial wilt in his fields, and we compared the number
of wilted plants in the Admire-treated plots with his conventionally-managed
plots at the beginning and end of the season. However, because there were very
few cucumber beetles present in his fields this year, we couldn’t draw many
conclusions about the success of Admire.
– Laura Krouse (Mt. Vernon, IA) tested the cucumber beetle attractant Invite
for management of beetles in zucchini. She conducted a trial with three replications
of three treatments (Invite + Sevin, Invite + Boric Acid, and Sevin). ISU scouts
visited her farm each week until harvest to spray the plots and count striped
and spotted beetles on a sticky card placed in each plot.
There was no difference among treatments in the average population of striped
beetles in this trial, however the spotted beetles were more numerous in plots
treated with the attractant + organic insecticide than in plots treated with
Sevin alone (Table 1). This suggests that boric acid may not be an effective
control for spotted cucumber beetle, but we see no reason that striped and spotted
beetles should respond differently to boric acid. The differential effect of
these chemicals on the two species may have occurred in response to this year’s
beetle flight times or low population sizes, and will require further investigation.
There was also no difference among treatments in the total number of wilted
plants in a plot. This means that, in this case, a 10% rate of Sevin is as effective
for control of bacterial wilt as the full rate when it is applied in combination
with an attractant. Further testing will be required before this strategy can
be recommended to other growers, but it may be one method to reduce the amount
of insecticides applied to cucurbit fields.

– Gary Guthrie (Nevada, IA) tested the effect of row covers and Pyola (an
organic insecticide) for control of striped and spotted cucumber beetles in
muskmelon. He covered one of two 100-foot rows with Reemay row cover until bloom,
and sprayed half of each row with Pyola after every rain. The treated row sections
were compared with the uncovered, unsprayed row section. ISU scouts visited
every week to assess wilt and count striped and spotted beetles on a sticky
card in each plot.

Although there were both striped and spotted beetles in on Gary’s farm this
summer, there was no bacterial wilt (Table 2). Beetle counts suggest that spraying
Pyola did not protect the plants from beetle infestation any better than the
untreated control.

– Joe Lynch (Ames, IA) tested row covers and a trap crop strategy in winter
squash. He covered his squash with row covers from planting until bloom. Following
this, ISU scouts treated one of every 10 squash plants with Invite + boric
acid weekly. The goal was to create an attractive but toxic trap plant by spraying
it with the Invite/boric acid mixture. Striped and spotted beetles on sticky
cards placed next to squash trap plants and next to regular squash plants were
compared, and bacterial wilt was assessed weekly. Joe, like Gary Guthrie, had
beetles but no bacterial wilt in his plots (Table 3). His data indicate that
plants treated with Invite and boric acid did not attract significantly more
beetles to sticky cards near them. Without data on bacterial wilt and further
years’ data on beetle populations, however, we can’t draw any conclusions about
the utility of this product in creating a trap crop.

OBJECTIVE 1: Control cucumber beetle damage by mass trapping and augmentation
strategies.
After careful analysis of 2002 mass trapping results, we concluded that the
traps did not control cucumber beetles or bacterial wilt- in fact, they appeared
to make the problem worse. We decided to focus on other strategies while working
with Trecé, Inc. on possible revisions of the trap design. Two sets of experiments
evaluating several strategies for managing cucumber beetles were established
in June 2003 at three university farms in Iowa. These locations include the
ISU Horticulture Research Station in central Iowa, the Armstrong Research and
Development Farm in Southwest Iowa, and the Muscatine Island Research Station
in Southeast Iowa.

In one trial, five insecticide treatments were applied to 20-foot rows of ‘Athena’
in four replications. These treatments were applied to two fields at each farm,
one of which was covered with ‘Reemay’ spun cotton row covers at the time of
planting. The row covers were removed at bloom. Insecticide applications were
made every two weeks. They began at the time of planting in the uncovered field
and at bloom in the covered field. The evaluated insecticides include: Entrust
(an organically approved spinosad insecticide), Admire (a single application
of the systemic insecticide Imidacloprid), and Invite (a cucurbitacin-impregnated
compound that is highly attractive to cucumber beetles) in combination with
either Sevin (carbaryl) or boric acid (an organically-approved insecticide).
A conventional control (Sevin) and an untreated plot were also included in the
trial. Striped and spotted beetle populations on five plants per plot, as well
as the number of plants with bacterial wilt, were recorded each week. The number
and weight of melons harvested per plot was measured twice per week at maturity.

There was a clear benefit to covering the plots with Reemay, as it increased
both the number and weight of melons harvested (Table 4). Some of the yield
benefits of these covers may have been due to a warming effect in the spring,
but they also decreased the incidence of bacterial wilt, indicating that they
protected the plants from cucumber beetles. The row covers delayed the first
onset of bacterial wilt by three weeks in Ames and one week in Muscatine.
Of the insecticide treatments evaluated, none resulted in yields greater than
the untreated control (Table 5). In fact, plots treated with the attractant
(Invite) + an organically-approved insecticide (boric acid) had lower yields
than the control. Furthermore, attempts to find a correlation between yield
and either beetle populations or bacterial wilt incidence for the insecticides
failed. This means that, although the insecticides sometimes reduced beetle
populations or bacterial wilt below the levels found for the control, these
reductions did not always lead to higher yield. This result was very surprising,
as more beetles should lead to more disease, and more disease should lead to
dead plants and fewer melons. One reason this may have occurred is the fairly
low populations and seemingly late arrivals of striped and spotted cucumber
beetles in Iowa this year. Perhaps a certain population of beetles or early
epidemics of bacterial wilt are necessary to see an impact on yield. We look
forward to testing these insecticides next year, when beetle populations may
be higher.

In a second trial, the feasibility of a trap crop strategy was investigated. The
trap crop used was ‘Turks Turban,’ an ornamental gourd that is highly attractive
to cucumber beetles. It is hypothesized that the melons will be ignored by cucumber
beetles when a more attractive alternative (‘Turk’s Turban’) is available to the
beetles. At three locations in Iowa, three small fields of ‘Athena’ muskmelons
were established at least 1000 feet from one another to evaluate the efficacy
of ‘Turks Turban’ as a trap crop alone and in combination with an insecticide.
In two of the fields, a row of gourds was established between every five rows
of muskmelons. Sevin (carbaryl) was applied weekly to the rows of gourds in one
field. As a control, only muskmelons were planted in the third field. Striped
and spotted beetle populations on five plants per row, as well as the number of
plants with bacterial wilt, were recorded each week. The number and weight of
melons harvested per plot was measured at maturity.
Overall, more striped and spotted beetles visited fields with ‘Turk’s Turban’
than fields with just melons (P<0.05). This means that our trap crop makes a melon
field a regional attractant to beetles. However, having more beetles in a trap
cropped field is only a problem if they move from gourd plants to melon plants.
We found that there were more striped beetles in gourd rows than in melon rows
throughout the season (Table 6), but there were the same number of beetles on
melon rows in the trap crop and control fields (Table 3). Furthermore, melon rows
more distant from the gourd rows had no fewer beetles in them than rows right
next to gourd rows. The trap crop attracts more beetles to the field, and doesn’t
distract all beetles from the melon plants. Consequently, there was the same average
number of wilted plants in melon rows from fields with and without the trap crop
(Table 6).

We hoped to slow the dispersal of beetles from gourd plants to melon plants by
making weekly sprays of carbaryl in the trap crop in one field. These sprays did
not reduce the average number of beetles or wilted plants in melon rows when compared
to unsprayed rows (Table 6). It appears, from average beetle counts and wilt ratings,
that a ‘Turk’s Turban’ trap crop, sprayed or unsprayed, does not decrease the
incidence of bacterial wilt in muskmelon.

Yield data from these three fields, however, show that the field without a trap
crop and the carbaryl-treated trap crop field produced a greater number and total
weight of melons than did the unsprayed trap crop field (Table 6). Our average
beetle counts and wilt data do not reflect this trend, so we tracked beetle populations
and bacterial wilt development over time for each field. For the first two rating
dates with wilt signs (fourth and fifth), the unsprayed trap crop field had significantly
more bacterial wilt incidence than the control or sprayed trap crop plots (P<0.05).
Perhaps this early infection had a great impact on yield.

Oddly, there was no correlation between bacterial wilt development and beetle
population dynamics this season (P<0.05). This may have occurred because beetle
populations were very low, a phenomenon that may also have masked the impact
of our treatments. We did note that the population of striped beetles on melon
plants in the trap crop fields appeared to increase sharply when most of the trap crop wilted (about the seventh and eight rating date). This shows that to effectively use this trap crop, we will need to keep it alive for the entire season.

We will repeat this experiment next season with different beetle populations; possible changes to the trap crop strategy will be discussed in our December and February meetings. One potential improvement may be the use of a highly effective systemic imidacloprid insecticide with the gourd trap plants. This may keep the gourds alive for the entire season. It may be more toxic to visiting beetles, preventing them from moving to a melon plant after feeding on squash plants.

OBJECTIVE 2: Evaluate the Melcast disease-warning system (using site specific
weather estimates as inputs), Bacillus subtilis, and potassium bicarbonate
in comparison to conventional methods for control of anthracnose, gummy stem blight,
and Alternaria leaf blight.

This trial was located in central and southeast Iowa. Seedlings of ‘Athena’
muskmelon were transplanted into black plastic in a randomized complete block
with eight treatments and four replications. Plots were 25-ft-long rows with
2-ft spacing between plants and 8 ft between row centers. Treatment rows alternated
with guard rows. Treatments included Bravo Ultrex (chlorothalonil) applied at
7 and 14-day intervals, as well as Serenade (Bacillus subtilis) and Kaligreen
(potassium bicarbonate) applied at 7-day intervals. In addition, three treatments
were sprayed according to the Melcast disease-warning system: a treatment based
on weather data collected from a CR10 weather data logger located on-site, another
treatment based on remotely-estimated SkyBit weather data, and a final treatment
based on SkyBit weather data that was corrected using models developed in previous
years of the study.

Guard rows were inoculated with a suspension of Colletotrichum orbiculare (muskmelon anthracnose) in early July. Immediately prior to inoculation, all treatments except the non-sprayed control were applied with a backpack sprayer for the first time when vines first touched between rows. Subsequent sprays were applied either on a calendar-based schedule or according to the Melcast system. Percentage of foliage covered with anthracnose lesions was measured each week, and the weight and number of marketable and cull melons was determined at harvest. We will not report results for Ames, as significant symptom development did not occur at this location and the fungicides treatments were not truly tested by disease pressure. Our inoculation may have failed because the isolate used to produce the spores lost virulence after storage on agar media for over five years, and/or because it was very dry throughout the summer. We collected leaf samples from infected plants at Muscatine and made several anthracnose isolations; we are currently identifying a virulent strain of Colletotrichum orbiculare for use in next year’s trials.

At Muscatine, the Melcast disease warning system suggested only one spray during the season for the SkyBit weather data, and zero sprays for the on-site and the corrected SkyBit data (Table 7. Scheduled spray treatments called for four to eight sprays, indicating that the Melcast system used with any source of weather data saved several sprays. The final percentage of foliage infected was approximately equal in all of the treatments, and was fairly low throughout the field (Table 7). The unsprayed control and the plots treated with the two low-risk fungicides had significantly higher AUDPCs (areas under the disease progress curve) than any of the chlorothalonil-sprayed treatments. This shows that the Melcast system and the scheduled sprays of chlorothalonil slowed the spread of anthracnose. The marketable weight and number of melons were approximately equal among all plots, though the unsprayed plot had a lower
yield than several of the other treatments.

Overall, any version of the Melcast system was successful in this dry year; it saved four to eight sprays without an increase in foliar damage or a decrease in yield. We will continue to test the system in future years with wetter conditions and more severe anthracnose infections.

A second goal of objective two for summer 2003 was to collect data for use in
better estimating leaf wetness. Weather stations, including thermometers, pyranometers,
relative humidity sensors, rain gauges, wind speed sensors, and leaf wetness sensors
were established in central and southeastern Iowa. Leaf wetness sensors were placed
at various heights in and outside of the muskmelon canopy. Data were measured
hourly for all instruments, and files were downloaded from the weather station
each week. Remotely-estimated SkyBit data were ordered from June 1 to Sept 15
for each of these locations. Cloud cover data were obtained from the ISU Mesonet (http://wepp.mesonet.agron.iastate.edu/GIS/rainfall.phtml). Data from the two Iowa sites have been compiled and modeling efforts are underway.

OBJECTIVE 3: Evaluate ability of a hairy vetch-rye cover crop to suppress weeds and reduce sprays of conventional herbicides.

This experiment was modified to focus more on weed control after previous years’
results showed that additional N is necessary for adequate fertilization of muskmelon crops grown on mulch. Four weed management strategies were tested in Ames and Muscatine, Iowa in 2003. These strategies included conventional mulch or cover crop mulch combined with either “weed-free” hand weeding or “weed-management” hand weeding. Treatments include all possible combinations of conventional mulch, cover crop mulch, “weed-free” hand weeding, and “weed-management” hand weeding. The objective of ‘weed management’ hand weeding is to simulate the realistic (i.e. incomplete) on-farm weeding effort required to keep weed competition in check and to limit increases in the soil weed seed bank.

Hairy vetch and rye were seeded in eight 30’ x 32’ plots at each location in September 2002. In mid-June of 2003, when the hairy vetch was flowering, the plots were crushed using a cultipacker. Four slits were cut into the mulch in each plot using a cutting coulter, and ‘Athena’ muskmelon seedlings were planted into the furrow. Another eight “conventional” plots were established at the same time using pre-emergence herbicide and black plastic mulch. The conventional plots received tillage as needed until the vines touched between the rows. One-m2 weed samples were collected at the time of planting in each plot, and weeds were separated by species and weighed. This type of sampling was repeated in early August and at the time of harvest. In “weed-free” plots, weeds were removed weekly, and in “weed-management” plots, weeds were removed at 3, 6, and 9 weeks after planting. The person-hours spent weeding and the species and weight of
weeds removed during each weeding event were recorded. The number and weight
of melons harvested from each plot was measured at maturity.

In Ames, we found no difference in the number or total weight of marketable melons
harvested from cover cropped vs. plastic mulched plots. This result is consistent
with previous years’ positive experience with the cover crop. In Muscatine, however,
we found that cover cropped plots had lower yields than plastic mulched plots
(P<0.0001; Table 8). The cover crop in Muscatine was very, very sparse and brittle
this year, possibly due to dry weather in the autumn of 2002 and a cool spring
in 2003. It did very little to subdue weeds. The repeated foot traffic and soil
disturbance caused by our extensive weeding efforts at this site, as well as high
weed pressure, likely caused a yield decline. Although there was obvious visual
evidence of this difference in weed pressure in the field, we did not find significant
differences in the average weight of weeds collected from cover cropped vs. plastic
mulched plots. We plan to take larger samples per plot next year to better document
this difference. Although there appeared to be no difference in yield or weed
pressure due to our two weeding treatments (“weed management” and “weed-free”)
at Ames or Muscatine, efforts to simulate the difference in weed seed contributed
to the plots are underway. Increased sampling next season may also be necessary
to learn more about this effect.

OBJECTIVE 4: Integrating sustainable management strategies.
One of the major goals of our advisory panel and PI meetings in December will
be to decide which strategies to combine for next year’s trials.

OBJECTIVE 5: Document costs and profitability of strategies in Objectives 1-4.
Economic analyses are ongoing.

OBJECTIVE 6: Transfer project findings to North Central region muskmelon
growers.

Although newsletter articles and press releases will not be written until our
experiments are complete, we have prepared an introductory website. It includes
background information on the biology of cucumber beetles, anthracnose, gummy
stem blight, Alternaria leaf blight, and common weeds in Iowa, as well as some
basic management strategies. We are currently adding the results of our 2003
experiments.
We have also completed a web-based extension bulletin, “Melcast: A Weather-based
Disease Warning System for Muskmelon Anthracnose,” that describes the system
and publicizes a newly-developed Excel computer program that growers can download
from our website to help them use the Melcast system. This computer program
will be modified at the end of these experiments to incorporate an improved
leaf wetness model developed from ongoing modeling efforts. Furthermore, we
presented our research to approximately 75 growers at an Iowa Fruit and Vegetable
Grower’s field day in July, as well as at two Practical Farmer’s of Iowa Field
Days in June and July.
Finally, a “pre-project” survey was mailed to 437 Iowa cucurbit growers in April
2002. Because this project has much in common with a three-state cucurbit pest- management project, a total of 667 growers from Iowa, Minnesota, and Colorado were asked to share their experiences and perspectives on cucurbit IPM practices. Most Iowa
and Minnesota growers have fewer than five acres, while 55% of Colorado growers
have over 50 acres. Nearly all of the surveyed growers sell their produce on-farm, but 46% also sell them at farmer’s markets or through CSAs (57% in Iowa,
34% in Minnesota, and 9% in Colorado). Of four sources of management information
(field days, grower’s meetings, extension publication, crop newsletters, and
IPM websites) written sources are considered slightly more helpful than meetings
or presentations. Seventy percent of growers consider the sources somewhat to
very important to their cucurbit pest management decisions, and credit them
for slight to moderate increases in their motivation to try IPM strategies in
the last year.

Sixty-two percent of growers practice IPM some or all of the time, and most
know about crop scouting, reduced-risk insecticides, and disease resistant cucurbit
varieties. They currently know little about disease warning systems, alternative
cucumber beetle control strategies, and use of traps to monitoring cucumber
beetle. The most often used IPM tactic is reduced-risk insecticides for cucumber
beetle control, and they have found living mulches for weed management to be
the least successful method. The most common reason growers fail to use IPM
practices is a lack of knowledge. Other reasons commonly listed are increased
time inputs and satisfaction with current strategies. Growers are not inclined
to farm organically due to perceived cost increases and skepticism about the
possibility of growing cucurbits organically.

Seventy percent of growers consider cucumber beetles the most serious pest of
cucurbits, with squash bugs a distant second. They find anthracnose and powdery
mildew to be the most serious diseases of cucurbits. Most of the growers are
extremely interested in receiving more information about all IPM strategies,
especially living mulches and alternative cucumber beetle control.

Impacts and Contributions/Outcomes

The impacts and contributions will be determined when research in subsequent years is complete. Some promising results gleaned from 2003 data are listed below.

-There was a clear benefit to covering the plots with Reemay, as it increased both the number and weight of melons harvested. Some of the yield benefits of these covers may have been due to a warming effect in the spring, but they also decreased the incidence of bacterial wilt, indicating that they protected the plants from cucumber beetles. The row covers delayed the first onset of bacterial wilt by three weeks in Ames and one week in Muscatine.

-Melon plots were treated with different fungicides applied using either the Melcast System or on a set spray schedule. The unsprayed control and the plots treated with low-risk fungicides had significantly higher disease than any of the chlorothalonil-sprayed treatments. This shows that the Melcast system and the scheduled sprays of chlorothalonil slowed the spread of anthracnose. The marketable weight and number of melons were approximately equal among all plots, though the unsprayed plot had a lower yield than several of the other treatments. Overall, any version of the Melcast system was successful in this dry year; it saved four to eight sprays without an increase in foliar damage or a decrease in yield. We will continue to test the system in future years with wetter conditions and more severe anthracnose infections.