Impact of Brassica Cover Crops On Eggplant Transplant Growth and Muskmelon Seed Germination Under Field Conditions

A field experiment was conducted at the Southwest Michigan Research and Extension Center in Berrien County, Michigan in the summer of 2008 to determine the effects of three Brassica cover crops on eggplant and muskmelon growth and yield. The treatments consisted of oilseed radish (20 lbs/acre), yellow mustard (9 lbs/acre), Oriental mustard (8 lbs/acre), methyl bromide (the positive control), and no treatment (the negative control). The experiment used a randomized complete block design with 6 replications.  Methyl bromide (400 lbs/acre 50:50 methyl bromide:chloropicrin) was applied in mid May. The cover crops were planted on 4 April, then disked and tilled into the soil on 3 June, after which black plastic mulch was immediately put in place. Eggplant seedlings were transplanted and muskmelon seeds were direct-seeded into the beds on 10 June. Plots were evaluated for stand count, transplant height, and Verticillium wilt incidence based on a subjective score of 1 to 10 (1 being ‘dead’ and 10 being ‘no disease’).  The eggplant in the yellow mustard plots consistently had the lowest subjective scores (indicating more disease).  Although eggplant stand was not affected, transplant height was generally reduced in the cover crop plots early in the season. Further, the cumulative yield of grade 1 eggplant was significantly less in the yellow mustard plots than in the methyl bromide and no treatment plots. Muskmelon stand counts were reduced in the cover crop plots. Melon stand was 0, 12, and 40% for oilseed radish, Oriental mustard, and yellow mustard, respectively, compared to 100% for the methyl bromide plots and the untreated control plots.  The results suggest that the use of these three cover crops is not advisable in systems where the cash crop will be direct seeded immediately after tilling the cover crop into the soil. Additional studies are needed to determine a safe period of time between cover crop incorporation into the soil and cash crop seeding, and to determine the susceptibility of cash crop cultivars to cover crop residue.