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

Final 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
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Project Information

Summary:

The goal of our research and outreach project was to enhance sustainability of muskmelon disease, weed, and insect pest management while reducing pesticide inputs. Muskmelon, a key high value crop, relies heavily on costly synthetic pesticides and fertilizers that endanger grower and consumer health, kill non-target organisms, and pollute the environment.

Our research clearly demonstrated the effectiveness of row covers in reducing insecticide use, decreasing the incidence of bacterial wilt, and increasing muskmelon yields. This outcome provides muskmelon growers with a practical alternative for control of bacterial wilt that is likely to improve profitability and reduce insecticide use compared to conventional management practices. In addition, cooperating commercial muskmelon growers successfully utilized row covers in their own operations. These results are published in a peer-reviewed journal and in extension and trade-journal publications. We also presented these results to growers at field days and workshops.

Using the Melcast warning system with input weather data from either on-site weather sensors or commercially available site-specific estimates reduced fungicide sprays compared to conventional, calendar-based spray program and provided equivalent control of anthracnose, caused by Colletotrichum orbiculare. These findings benefit growers by providing a convenient, reliable alternative to using on-site weather sensors in implementing a disease-warning system. Weather sensors and dataloggers are expensive, require regular maintenance, and demand time to download weather data. Growers can obtain site-specific weather estimates far more easily, via e-mail or the Web, than making on-farm measurements; our work shows that these data will reduce fungicide sprays while providing good disease control.

Our weather modeling work showed the feasibility of using near-field weather sensors as another alternative to within-field sensors that are subject to damage from tillage and other agronomic activities. The near-field sensors provide another option for growers to make implementation of disease-warning systems more convenient and practical. Three publications in peer-reviewed research journals resulted from this effort.

We experienced problems with current strategies to use trap crops to reduce the incidence of bacterial wilt in muskmelons by reducing cucumber beetle feeding. We found that trap crops commonly used may not be the most effective species and cultivars, so we devised a Year 3 trial to determine which species and cultivars might work better. Our results point to several cucurbit varieties that have good potential to serve as effective, season-long trap crops. Future trials should deploy these trap crops to test their ability to reduce bacterial wilt.

Our experiments with using a hairy vetch-rye cover crop to control weeds in muskmelon gave inconsistent results, with weeds sometimes becoming a major problem in these trials. An unanticipated disadvantage of this strategy in Iowa is that muskmelons cannot be planted into the cover crop until the vetch flowers; this occurs in mid-June in Iowa, which means that melons will be harvested from these plots too late (e.g., late August) to fetch adequately profitable prices at local markets or supermarkets. We concluded that the hairy vetch/rye strategy may be better suited to warmer climates than Iowa, and that further experimentation is needed to develop an optimal method for pushing the cover crop down to soil level before transplanting melons.

Introduction:

Muskmelons are among the top 5 vegetable crops in the North Central Region in number of growers (2,000), acreage (8,000 acres), and farm gate value ($25 million) (NASS, 2001). As a high-value annual crop, muskmelons offer rapid diversification and enhanced cash flow for grain and livestock operations seeking to diversify, as well as for conventional and organic vegetable growers.

Muskmelons in the North Central Region are heavily dependent on synthetic chemical inputs. Current Cooperative Extension guides recommend up to 15 fungicide, insecticide, herbicide, and fertilizer applications per season (Foster et al., 2001). This chemical intensive regime is not sustainable because it poses a significant risk of pesticide injury to growers who apply the chemicals, kills many vulnerable non-target organisms in and near fields, and can endanger the general population through residues on melons and pollution of drinking water sources.

Until now, alternatives to reliance on synthetic chemical inputs have been unavailable. Genetic resistance to the most important insect pests (cucumber beetles) and most of the major diseases (including anthracnose, gummy stem blight, Alternaria leaf blight, and bacterial wilt) is absent in commercial muskmelon cultivars (Foster et al., 2001). Total yield losses from these pests and diseases can exceed 70% for North Central Region growers (Latin, 1993). Traditional cultural techniques like crop rotation, while helpful, are insufficient to reduce reliance on synthetic pesticides. Monitoring of cucumber beetles as a management decision aid is difficult on muskmelons because the action threshold is extremely low (one beetle per plant) (Foster et al., 2001). Traditional clean-cultivation practices for weed control are time-consuming, energy intensive, and worsen wind and water erosion of topsoil.

Economic pressures have made pesticide intensive muskmelon culture even more untenable. Profitability of using synthetic pesticides in agriculture has declined steadily, and is now only 1/3 the level of 1970 (Carter, 2001). Steadily increasing national and global competition has squeezed profits and forced muskmelon growers to seek new ways to control costs of off-farm inputs, including pesticides.

Project Objectives:

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

OBJECTIVE 2: Alternative strategies against the fungal disease complex of anthracnose, gummy stem blight, and Alternaria leaf blight.

OBJECTIVE 3: Evaluate the ability of a hairy vetch-rye cover crop to suppress weeds, reduce applications of conventional herbicides, and add nitrogen to soils.

OBJECTIVE 4: Combine the most promising component strategies from Objectives 1-3 into systems-level strategies that integrate weed, insect, and disease management.

OBJECTIVE 5: Document economic costs and benefits of these new management tactics in comparison to conventional practices.

OBJECTIVE 6: Transfer the project’s findings to muskmelon growers through on-farm demonstration trials, a WWW site, quarterly newsletter articles, presentations at regional grower meetings, annual field days, press releases, and an extension bulletin.

Research

Materials and methods:

Objective 1

Two sets of experiments evaluating several strategies for managing cucumber beetles were established in June 2004 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 were 1) Entrust (an organically approved spinosad insecticide), 2) Admire (a single application of the systemic insecticide Imidacloprid), 3) Admire applied at planting + Sevin or Capture applied after flowering, and 4) Invite (a cucurbitacin-impregnated compound that is highly attractive to cucumber beetles) + Sevin or Capture. A conventional control (Sevin alternated with Capture) and a non-treated 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.

Objective 2

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.

All rows were inoculated on 13 Jul in Muscatine and 14 Jul in Ames with a pathogenic isolate of Colletotrichum orbiculare isolated from melon plants in 2003. 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 using Horsfall-Barrett scale, and the weight and number of marketable and cull melons was determined at harvest. Disease data were converted to midpoints prior to analysis.

Objective 3

Four weed management strategies were tested in Ames and Muscatine, Iowa in 2004. These management strategies are similar to those 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 2003. In mid-June of 2004, when the hairy vetch was flowering, the plots were crushed using a cultipacker. Four rows were marked out in each plot and ‘Athena’ muskmelon seedlings were planted into the mulch. 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.

Research results and discussion:

Objective 1

Row covers. There was a clear benefit to covering plants with Reemay from transplanting until bloom, as it increased both the number and weight of melons harvested. Some of the yield benefits of these covers are likely to be due to a warming effect in the spring. However, the row covers also decreased the incidence of bacterial wilt and delayed its onset, indicating that they effectively protected the plants from cucumber beetles, and that this early-season protection had continuing impact even after the covers were removed.

Of the insecticide treatments evaluated, all resulted in yields greater than the non-treated control. This is mostly from the increase in marketable fruit. There was no correlation between yield and either beetle population. There was a significant negative correlation between bacterial wilt incidence at later dates and marketable melon number and weight (P<0.001).

Trap cropping. In a second trial, the feasibility of a trap crop strategy was investigated. The trap crop used was ‘Black Beauty’, a zucchini cultivar that that is highly attractive to cucumber beetles. It is hypothesized that the melons will be ignored by cucumber beetles when a more attractive alternative (‘Black Beauty’ zucchini) is available to the beetles. The trap crop selection is different from 2003 (Turk’s Turban). Problems from 2003 were that the trap crop wilted early in the season, leaving the fields without their trap crop. The ‘Black Beauty’ zucchini is still highly attractive to the beetles, yet has some resistance to bacterial wilt (according to a source from Connecticut).

At two locations in Iowa, three small fields of ‘Athena’ muskmelons were established at least 1000 feet from one another to evaluate the efficacy of ‘Black Beauty’ zucchini as a trap crop alone and in combination with an insecticide. In two of the fields, a row of zucchini was established between every five rows of muskmelons. Admire (imidacloprid) at planting, and Capture (bifenthrin) or Sevin (carbaryl) applied weekly were the insecticides for the treated zucchini 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 treated zucchini than fields with just melons or non-treated zucchini (p<0.05). This means that some of the trap crop fields are a regional attractant to beetles. However, having more beetles in a trap cropped field is only a problem if they move from zucchini plants to melon plants. The trap crop may attract 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.

We hoped to slow the dispersal of beetles from zucchini plants to melon plants by making weekly sprays of insecticide 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 non-sprayed rows. It appears, from average beetle counts and wilt ratings, that a zucchini trap crop, sprayed or unsprayed, did not decrease the incidence of bacterial wilt in muskmelon under the conditions tested.

Yield data from these three fields, however, show that the field without a trap crop and the insecticide-treated trap crop field produced fewer melons and total weight of melons than did the non-sprayed trap crop field. This is exactly opposite of the data from 2003. Also, there was no correlation between bacterial wilt development and beetle population dynamics this season (P<0.05).

From the two years of data, most fields with a trap crop had more trapped beetles in the trap crop than in the adjacent melons. However, this did not decrease the number of beetles in the melon rows compared to fields that had no trap crop. Furthermore, the trap crop did not have any influence on the number of wilted plants in either year. As for marketable melons, there were conflicting results from year to year; suggesting that more factors than beetle populations, bacterial wilt, and presence of trap crops influence the number and weight of melons.

Objective 2

At Ames, the Melcast disease warning system suggested only one spray during the season for the on-site weather data, the SkyBit weather data, and the corrected SkyBit data. Scheduled sprays called for 3 to 6 sprays, indicating that the Melcast system used with any source of weather data saved several sprays. Compared to the non-sprayed control, all treatments had significantly lower disease. However, this did not result in an increase in the number or weight of marketable melons.

At Muscatine, the Melcast disease warning system suggested only 2 sprays during the season for the SkyBit weather data, the on-site and the corrected SkyBit data. Scheduled spray treatments called for 2 to 4 sprays, indicating that the Melcast system used with any source of weather data saved two sprays compared to the 7-day spray schedule.

The final percent of foliage infected was approximately equal in all of the treatments, and was extremely high throughout the field. The non-sprayed control and the plots treated with Kaligreen had significantly higher final percent disease than chlorothalonil sprayed every 7 days. The number of marketable melons was approximately equal among treatments, though the weight of melons was significantly lower in the non-treated plots compared to most of the treated plots.

Overall, all treatments had significantly less disease than the unsprayed control at both locations. However, at Muscatine, none of the fungicide treatments were effective at controlling disease. Many of the plants died prematurely. The Melcast system did save a few sprays at Ames, but it is unclear how often sprays would have been needed in Muscatine for adequate disease control. A few differences from 2003 were that a more pathogenic isolate of C. orbiculare was used for inoculations and all rows were inoculated, instead of guard rows only.

A second goal of Objective 2 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. Leaf wetness sensors were also placed at 5 established CR-10 stations across Iowa. SkyBit data for each of these locations was collected as well. Cloud cover data were obtained from the ISU Mesonet, http://wepp.mesonet.agron.iastate.edu/GIS/rainfall.phtml. Data from all of the Iowa sites are being compiled and modeling efforts are underway.

The results of the wetness modeling work indicated that off-site measurements of leaf wetness duration could readily be substituted for measurements made at the top of the plant canopy in a muskmelon field. This approach offers practical advantages, because sensors located within cultivated fields are often at risk from damage due to spraying and cultivation activities, and are difficult to access frequently after heavy rains or after vines close, whereas off-site but nearby sensors can be located conveniently (e.g., on mowed turfgrass) for downloading by scouts or growers. This result means that muskmelon growers have new options to implement weather-based warning systems that are faster, easier, safer, and equally as reliable as using in-field sensors.

Objective 3

In Ames, the weed pressure in the vetch-rye plots was so high that it quickly became unrealistic to count and weigh weed samples from the whole plot. The high weed pressure resulted in very few melons and no marketable ones. In Muscatine, we also found that cover cropped plots had lower yields than plastic mulched plots (P<0.0001). The weed pressure was not as severe in Muscatine. However, the rye that was knocked down in June started to re-seed and became established during the growing season, potentially creating competition with the muskmelon crop.

Overall, half of the field locations using the hairy-vetch/rye cover crop had a significant decline in yield compared to the black plastic mulch. Even in the years with comparable yields, there was a long delay in harvest time (3-4 weeks) from delaying planting until mid-June, which would be likely to result in much lower prices for marketable melons. As a result, the project decided not to pursue this strategy further in Year 3 due to its apparent unsuitability to commercial melon production in Iowa.

Objective 4

Faced with inconsistent success of strategies to control cucumber beetles and bacterial wilt with recommended trap crops, we sought new strategies. It had become clear, from results of our field trials, that if the trap crop strategy were to be effective, a highly beetle-attractive, but also bacterial wilt-resistant, trap crop would be essential. In 2005, therefore, we devised a new field experiment, at the ISU Horticulture Research Farm near Gilbert, IA, to evaluate which cucurbit variety was best suited for use as a trap crop (attractive to cucumber beetles yet not susceptible to wilt). The experiment included 50 varieties of cucurbits. Squash types included acorn (4 varieties), buttercup (7 varieties), butternut (3 varieties) Delicata (5 varieties), Hubbard (3 varieties), spaghetti, Turks Turban, green zucchini (7 varieties), yellow zucchini, yellow straightneck (2 varieties), yellow crookneck (2 varieties), patty pan (2 varieties), pumpkins (5 varieties), cucumber (3 varieties), watermelon (3 varieties), muskmelon and ornamental gourds. Numbers of striped and spotted cucumber beetles were tracked weekly. The survival of the cucurbit plants were evaluated at 6 weeks and 10 weeks. Four replicates of the varieties were planted in a single plot at the Horticulture Research and Demonstration Farm near Ames, IA. Each 20 ft subplot consisted of 10 plants spaced 2 ft apart, with a gap between subplots in a row of 8 ft. Rows were spaced 8 ft apart. Bravo Ultrex was applied to the plot every 14 days and no insecticides were used.

We considered a variety a good trap crop if the variety had over 50% of the plants survive and had an average of at least 6 cucumber beetles / five plants. Butternut, delicate winter squash and yellow crookneck summer squash showed the most potential for use as trap crops.

Objective 5

Disease management

We compared the return in melon count and weight with the cost of conventional fungicide sprays timed using Melcast calculated with on-site weather data, site specific weather data collected from satellites (SkyBit) and SkyBit weather data that had been corrected based on previously developed models. Using weather data to time fungicide sprays had a greater economic return than conventional practices. Using Melcast to time sprays reduced the number of fungicide sprays without a loss in crop yield.
We found that fungicides timed with on-site weather data consistently did slightly better than SkyBit or corrected SkyBit weather data. However the difference was only $0.01-0.04 per pound of melons, so the convenience of SkyBit must be weighed against the cost and environmental impact of an unnecessary spray.
We also compared the costs of a conventional fungicide (Bravo Ultrex) applied at 7 or 14 days with alternative fungicides (Kaligreen and Serenade) applied on a 7-day schedule. Kaligreen cost 2 or 3 times more than the conventional fungicide and Serenade cost 9 to 11 times more. However our economic analysis does not take into account the possibility of melons treated with alternative sprays that are organic may be sold for a higher profit or the benefits to the grower, consumer and environment of utilizing lower risk fungicides.

Insect pest management

Our research focused on alternative methods to manage both spotted and striped cucumber beetles. Reemay row covers reduced insecticide use by two sprays (from 5 sprays to three sprays). We calculated the cost of treatments with the different insecticides used in our trials and from that we calculated the total cost of insecticide treatments for number and weight of melons.

In both 2003 and 2004 Reemay row covers were considerably more expensive than insecticides alone. However, in both years yield was greatest in the Reemay covered fields and there was reduced incidence of bacterial wilt. In addition, Reemay row covers have been demonstrated to decrease ripening time, and early melons will sell for more than later melons. This will help cover the additional cost of the Reemay. Also, Reemay covers can be reused, thereby eliminating the cost of the Reemay in subsequent years.

Objective 6

We have prepared an introductory website (http://www.public.iastate.edu/~cucurbitipm/). It includes background information on the biology of cucumber beetles, anthracnose, gummy stem blight, Alternaria leaf blight, and common weeds in Iowa, Minnesota, and Colorado, as well as some basic management strategies. We are currently adding the results of our 2003 and 2004 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 Practical Farmer’s of Iowa Field Days in July.

Research conclusions:

The short-term impact of our research was to demonstrate the feasibility of using row covers and remote weather data to reduce reliance on pesticides in muskmelons. Through our collaborations with growers we also provided farm-specific advice and networking. The intermediate-term impact of our research is presenting our results to a wider audience through publications and field days and the internet. Finally, in the long-term more growers will have the research based tools needed to implement IPM tactics in their operations.

Economic Analysis

Disease management

We compared the return in melon count and weight with the cost of conventional fungicide sprays timed using Melcast calculated with on-site weather data, site specific weather data collected from satellites (SkyBit) and SkyBit weather data that had been corrected based on previously developed models. Using weather data to time fungicide sprays had a greater economic return than conventional practices. Using Melcast to time sprays reduced the number of fungicide sprays without a loss in crop yield.

We found that fungicides timed with on-site weather data consistently did slightly better than SkyBit or corrected SkyBit weather data. However the difference was only $0.01-0.04 per pound of melons, so the convenience of SkyBit must be weighed against the cost and environmental impact of an unnecessary spray.

We also compared the costs of a conventional fungicide (Bravo Ultrex) applied at 7 or 14 days with alternative fungicides (Kaligreen and Serenade) applied on a 7-day schedule. Kaligreen cost 2 or 3 times more than the conventional fungicide and Serenade cost 9 to 11 times more. However our economic analysis does not take into account the possibility of melons treated with alternative sprays that are organic may be sold for a higher profit or the benefits to the grower, consumer and environment of utilizing lower risk fungicides.

Insect pest management

Our research focused on alternative methods to manage both spotted and striped cucumber beetles. Reemay row covers reduced insecticide use by two sprays (from 5 sprays to three sprays). We calculated the cost of treatments with the different insecticides used in our trials and from that we calculated the total cost of insecticide treatments for number and weight of melons.

In both 2003 and 2004 Reemay row covers were considerably more expensive than insecticides alone. However, in both years yield was greatest in the Reemay covered fields and there was reduced incidence of bacterial wilt. In addition, Reemay row covers have been demonstrated to decrease ripening time, and early melons will sell for more than later melons. This will help cover the additional cost of the Reemay. Also, Reemay covers can be reused, thereby eliminating the cost of the Reemay in subsequent years.

Farmer Adoption

Our advisory panel includes the following growers: Ray Jensen (Greenfield), 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 15 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. We also cooperated with several growers in Iowa on strategies for cucurbit pest management during the 2003 field season:

We also cooperated with several growers in Iowa on strategies for cucurbit pest management:

Phil and Nancy Funk (Dallas Center, IA) and Richard, Bill, and Sharon Dix (Janesville, IA) managed two rows 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. The Melcast system saved them at least one or two sprays this season, without an increase in foliar disease symptoms. Both growers were very happy with this strategy.

Gary Guthrie (Nevada, IA) and Ray Jensen (Henry Wallace Country Life Center, Greenfield, IA) evaluated row covers for control of bacterial wilt. At both places, one of two 100-foot rows was covered with Reemay row cover until bloom. The treated row sections were compared with the non-covered row section. ISU scouts visited every week to assess wilt and count striped and spotted beetles on a sticky card in each plot. At the Guthrie farm, there were both striped and spotted beetles this summer. Beetle counts were take five times this summer and averaged. There were more beetles found in the non-covered row (11.2 striped and 24.8 spotted) than the covered row (7.4 striped and 15.2 spotted), however, there was no bacterial wilt in either row. There were very few beetles found at the Henry Wallace Farm (an average of 0-3 per week in both rows), yet there were 13.3% wilted plants in the non-covered row and 6.7% wilted plants in the covered row.

Greg Hoffman (Waterloo, IA) treated one row of his muskmelon plants with a single application of the systemic insecticide Admire at planting. He also planted one row of melons that was treated with Gaucho (same active ingredient as Admire). We visited three times to look for beetles and signs of bacterial wilt. There were more beetles found in the ‘Gaucho’ row (average of 48.3 striped and 6.3 spotted) than the ‘Admire’ row (17.3 striped and 2.3 spotted). There were 7.3% of the plants wilted in the ‘Gaucho’ row compared to 7.3% in the ‘Admire’ row.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

Gleason, M. L., Mueller, D. S., Havlovic, B., Lawson, V. 2005. A row cover and low-risk insecticide strategy for cucumber beetle management. Annual Fruit/Vegetable Progress Report 2004. Iowa State University Extension: FG 601: 37-38.

Mueller D. S., Gleason, M.L., Sisson A. J., Massman J. M. 2006. Effect of row covers on muskmelon production, cucumber beetle populations, and bacterial wilt. Plant Health Progress: doi: 10.1094/PHP-2006-1020-02-RS.

Sentelhas, P.C., Gilllespie,T.J., Gleason, M.L., Monteiro, J.E.B.A., and Helland, S.J. 2004. Operational exposure of leaf wetness sensors. Agricultural and Forest Meteorology 126:59-72.

Sentelhas, P.C., Gillespie, Y.J., Batzer, J.C., Gleason, M.L., Monteiro, J.E.B.A., Pezzopane, J.R.M., and Pedro, M.J., Jr. 2005. Spatial variability of leaf wetness duration in different crop canopies. International Journal of Biometeorology 49:363-370.

Sentelhas, P.C., Gillespie, T.J., Gleason, M.L., Monteiro, J.E.B.M., Pezzopane, R.M., and Pedro, M.J., Jr. 2006. Evaluation of a Penman-Monteith approach to provide “standard” and crop leaf wetness duration estimates. Agricultural and Forest Meteorology: in press.

Project Outcomes

Recommendations:

Areas needing additional study

1) The project revealed major gaps in our knowledge of the melon bacterial wilt pathosystem. The principal shortfall is in knowledge of vectoring of the pathogen, Erwinia tracheiphila, by cucumber beetles. In order to control the disease better, we need to understand:

• Factors that affect acquisition and transmission of the pathogen by both striped and spotted cucumber beetles, including plant age, generation of beetles (whether overwintered adults or later-emerging generations), stage of infection, feeding time on infected plants, duration of transmissibility by infested beetles, etc.

• Factors that affect epiphytic survival of the bacterium on the surface of melon plants and in cucumber beetle excrement, and whether epiphytic bacteria can give rise to systemic infections.

• The relative risk of disease transmission by the striped and spotted cucumber beetles.

• The biology of attraction of cucumber beetles to melon plants. It was evident from our failures with traps using volatile attractants that we need a clearer understanding of the full range of cues that draw these beetles to host plants, including sex pheromones and other possible attractants such as volatiles released from wounded or stressed plants.

2) Our project also clearly revealed serious weaknesses in applying the hairy vetch/rye cover crop strategy for weed management in muskmelons in Iowa:

• The most significant limitation is economic: hairy vetch and rye do not mature enough to be flattened as weed barriers in Iowa until late June, so transplantation is also delayed until then. Muskmelons transplanted so late in the season will mature several weeks after conventional melons, so the market price will be substantially lower than for these earlier melons. As a result, the late-transplants melons are likely to be unprofitable.

• Crushing the vetch/rye mixture, creating slits or holes for transplants, and keeping weeds out of these slits or holes after transplanting require specialized equipment (for crushing the cover crop) and expertise (to avoid dragging the cover crop through the field when creating slits) that, when combined with the lateness of harvest inherent in the strategy, they are unlikely to be attractive to growers.

3) The Melcast disease-warning system is clearly practical for Iowa muskmelon growers to use, and site-specific weather estimates can be substituted for on-site weather measurements, making the warning system more convenient and less laborious to use. An additional advantage of the site-specific weather data is that it does not require growers to invest in weather-monitoring equipment, but merely subscribe to a service that sends data to them by Internet or email.
Additional important remaining questions include:

• It is unclear how economical the Melcast system would be in general use. In particular, cultivar resistance to anthracnose and Alternaria leaf spot may differ. Therefore, it would be prudent to adjust the action threshold for Melcast to accommodate significant differences in cultivar resistance.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.