Research and Education Project, Region: North Central. The management of watermelon vine decline through sustainable management practices
Data from the 2009 season contrasts with the data from the 2007 and 2008 season. Prior to the 2009 season, the data indicated a possible advantage to using cover crops and biological treatments. However, the 2009 data did not reveal any significant difference in growth or yield to using cover crops or biological treatments. The reason for this difference in data between the seasons may be that the 2009 season was exceptionally cool. July 2009 was the coolest July in Indiana in recorded history. Although the third season of data for this study is a bit of a disappointment, the pint can be made that none of the sustainable treatments explored in this study will have a beneficial effect every season.
Information Growers can use to avoid mature watermelon vine decline:
The data from the 2009 season differed in almost every way from data for the 2007 and 2008 season. Whereas data from the previous two seasons suggested a benefit from cover crops and biological treatments at planting, the data from the 2009 season showed little benefit for either cover crops or biological treatments. The reason for this is most likely the significantly wetter and colder year for 2009 than for the previous two seasons. July 2009 was the coldest such month for Indiana on record. The ‘take-home’ message is that neither cover crops nor biological treatments will offer benefits to watermelon crops each year. This message is similar to that given in the brassicas and mustards chapter in “Managing Cover Crops Profitably” (3rd Edition, Sustainable Agriculture Network). Certainly, growers can not expect to use cover crops to solve their disease problems every year. The cover crop and biological treatments used here did not hurt the crop, but little benefit was observed in 2009.
The following is a discussion of the data for all three seasons. (tables are located at the end of the report in the attached full report including tables):
In general, early vine growth was better for untreated (control) vines than vines treated with either of the biological treatments at planting (Tables 1 and 6). In 2008, the vines growth was equal for all treatments by 2 Jul (Table 6). In the 2009 season, BioYield was unavailable for testing, so Actinovate was used instead. No differences of any kind were observed in the vine growth of watermelons treated with biological compounds (Table 13 and 14). It is interesting to note that on 5 August 2008 (Table 12), treatments that had been on bare ground yielded better when planted with BioYield or T22 than when no biological treatments were included at planting. This was not the case when either canola or rye had been the cover crops in those plots. (There was an interaction between cover crop and biological treatment on this harvest date-thus, the data was presented by individual treatment on this date.) Although biological treatments seem to have slowed early vine growth in 2007 and 2008, in overall yield data, biological treatments increased yields in 2007 and had little affect on yield data in 2008 (Table 4, 8 and 11). In general, biological treatments have had more influence on yields than cover crops. In 2007, the bare ground treatment had a greater yield than the rye treatment (Table 5). In 2008, there were no differences in yield due to cover crop (Table 10). In 2009, no yield differences were noted for cover crop or biological treatments (tables 15 and 16). In 2009, yield was not influenced by cover crop (table 16) or biological treatment (18).
In 2007, several elements (phosphorus, zinc, sulfur and copper) were significantly higher in watermelon planted in plots where canola had been the cover crop than any other cover crop treatment (Table 3). In 2008, potassium and zinc were higher in canola plots than in any other cover crop treatment (Table 7). Only zinc was consistently higher in canola plots both years. Biological treatments did not influence elemental analysis in either year (data not shown). No differences in elemental content were observed in watermelon in any cover crop (Table 17) or biological treatment (data not shown).
Of great interest to the watermelon growers in Indiana was whether cover crops or biological treatments would ameliorate the general vine collapse symptoms that have been observed over the years. The vine collapse has been named Mature Watermelon Vine Decline (MWVD). These symptoms have not been associated with any particular pathogen. In fact, it has not been clear that the vine collapse that has been observed is in fact caused by a soil microorganism or is the result of horticultural problems such as too much soil moisture or a lack or roots to maintain the fruit load. A greenhouse experiment conducted in November 2009 suggests that a biological factor in the soil is responsible for the vine decline of watermelon. Soil was collected from a commercial watermelon field that had a history of vine decline. The soil was placed in 5-gallon pots and either fumigated with dazomet or left unfumigated. Seedlings of either watermelon or muskmelon were planted and grown to maturity in a factorial design with 4 replications.
Only watermelon in unfumigated soil had symptoms of vine decline (Table 9). Fumigation apparently destroyed a biological component of the soil responsible for vine decline. Muskmelon plants had few symptoms of vine decline in this greenhouse experiment. The same situation has been observed in commercial fields-muskmelon have not been observed with vine decline.
Since the cause ofMWVD is not known, the occurrence of this disease cannot be predicted. Although the commercial field chosen for this experiment has a history of MWVD, the disease occurred only sporadically during the 3 years of this project. Symptoms of MWVD were observed in the 2007 season. Watermelon in plots that had been in canola had less MWVD than cereal rye on 12 July (Table 2). However, by 14 Aug, there was no difference in vine collapse in any cover crop treatments.
MWVD is characterized by root rot. Although root rot was observed in the 2010 season, there was no statistically significant difference (Table 19). The hypocotyl (crown) of the plants were observed at the same time, however and there were significantly different amounts of rot due to treatment. Watermelon plants in plots that had been in cereal rye had significantly more hypocotyl rot than rye plots that been treated with either T22 or Actinovate plus T22 (Table 19).
Changes in watermelon culture by growers-As a result of the data supported by this grant, growers are more likely to try a cover crop in general and a brassica cover crop specifically. As a result of the greenhouse study reported here, growers are more likely to use longer crop rotations between watermelon crops.
More sustainable culture of watermelon-Both the use of cover crops and the use of longer crop rotations are more sustainable practices. Crop rotation allows the crop residue to decay and thus disease pressure to lessen as well as helping the fertility and tilth of the soil. The use of cover crops helps add organic matter to the soil, helps reduce the disease pressure (in the case of brassica cover crops) and helps reduce erosion
Impacts and Contributions/Outcomes
At the technical meeting of the Southwest Melon and Vegetable Growers Association, data from the two years of experiments was presented: “The Use of Cover Crops to Manage Soilborne Diseases of Watermelon”. 77 growers attended. Several questions were asked both during and immediately after the presentation as well as individuals who asked questions privately.
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