by Kephas Mphande, ISU PhD candidate (kephas@iastate.edu)

 

Organic growers of muskmelon and other cucurbit crops in the US lose millions of dollars every year due to bacterial wilt, which is caused by Erwinia tracheiphila. Bacterial wilt is spread by striped cucumber beetle (Acalymma vittatum) and spotted cucumber beetle (Diabrotica undecimpunctata). There are no reliable organic insecticides, and no resistant muskmelon varieties are available. Mesotunnels were developed to help organic muskmelon growers in developing a production system that consistently delivers profitable yields.

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2020 year was an unprecedented year. On top of the COVID19 pandemic, we experienced an unusually violent derecho storm. Our mesotunnel covers were ripped off by 100-mph winds in early August. Luckily, however, our crop was ready for harvest when the storm hit and did not suffer much yield damage.

At ISU during 2020 season we had two muskmelon field trials: a pollination trial and a mulch trial. Pollination and weed control are concerns in mesotunnel systems because the nylon-mesh nets covering the plots could restrict bee movement and prevent in-season weed management. Treatments in the pollination trial, in 150-ft-long, triple-row plots, were:  1. full-season (one bumblebee hive installed at bloom; covers stayed on all season), 2. on-off-on (nets were removed when first female flowers appeared, then replaced two weeks later) and 3. Open ends (two ends opened at the start of bloom, then re-closed two weeks later).

We surveyed bee activity during the crop’s bloom period. We also scouted for pests and diseases, and measured marketable yield at the end of the season.

Pollination trial results. There were significant differences between treatments in weight of marketable fruit. The full-season mesotunnel treatment had the highest marketable yield (40,000 lb/A), followed by the open-ends treatment (33,000 lb/A and on-off-on treatment (19,000 lb/A). Non-marketable (cull) fruit weight was higher in the on-off-on treatment (17,000 lb/A) than in the full-season mesotunnel treatment (5,067 lb/A). In the open-ends treatment, we observed a trend of declining marketable yield from plots ends toward the center of the subplot. The same trend was seen in bee activity, pest incidence and disease incidence. These position effects were not observed in the other two treatments. The on-off-on treatment had the highest incidence of bacterial wilt (11%) and Alternaria leaf spot (ALS) (15.8%). The open-ends treatment had a bacterial wilt incidence of 4.3% and ALS at 9%, whereas the full-season mesotunnel treatment had the lowest disease incidence, with bacterial wilt at 1.5% and ALS at 5.3%.

 

 

 

 

 

 

 

 

 

 

 

 

Mulch trial results. We had four mulch treatments in triple-row 30-ft-long subplots: landscape fabric; two seeding rates of teff (Eragrostis tef) at 4 lb/acre, and 8 lb/acre; and a bare ground control. We measured aboveground weed biomass and marketable yield. There were significant differences in marketable yield among treatments. The weed fabric had the highest yield (44,370 lb/A), more than twice as much as the other treatments. There were no significant differences between teff treatments, with 20,400 lb/A for the 8lb/acre seeding rate and 19,130 lb/A for the 4 lb/acre seeding rate. The bare ground control recorded 20,900 lb/A marketable fruit weight. We think that the suppressive effect of teff on yield may be due to competition for nutrients, light, and water between teff and the crop. There were significant differences between treatments in terms of weed biomass. As expected, and bare-ground treatment had the most weeds: 17x the amount for teff at 4 lb/acre seeding rate, compared to almost no weeds at the 8 lb/acre seeding rate. The landscape-fabric treatment had no weeds.