A New Sericea Lespedeza Cover Crop to Reduce Incidence of Aphid-borne Viruses in Pumpkin.

Inter-row cover crops (Sericea lespedeza SL, Sunn Hemp and weeds) were evaluated comparatively with a conventional, bare soil treatment for their ability to reduce the aphid-borne virus, Watermelon mosaic virus (WMV), incidence and associated yield losses in pumpkin.  It was hypothesized that inter-row cover crops would provide consistency in color or reflectance observed by incoming aphids thereby being less attractive than the high contrast between pumpkin plants and soil.  In addition, upon landing on the cover crop, the viruliferous aphids would lose virus during test probes of leaves to determine suitability as a food source.  These aphids would then be virus-free upon moving to pumpkin. In 2006, inter-row cover crops included a new low growing selection of SL [Lespedeza cuneata (Dumont de Courset)] G. Don], and sunn hemp (Crotalaria juncea L.)  The low growing SL was used in the 2007 trial; but naturally occurring weed species were used instead of sunn hemp.  Watermelon mosaic virus (WMV) was detected in the 2006 trial and Papaya ringspot virus (PRSV) and WMV were detected in the 2007 trial.  In 2006, significantly more aphids were identified on pumpkin plants in the SL treatment; however, no differences were observed for WMV incidence among treatments.  Enzyme-linked immunosorbent assay absorbance values for WMV accumulation in pumpkin plants for whole treatment, and for samples shown to be infected, were significantly lower in the SL treatment indicating less virus accumulation in these samples. In the 2007 trial, WMV incidence was significantly less in pumpkin plants in the weed treatment compared with SL early in the season, but incidence did not differ among treatments later in the season.  PRSV incidence did not differ among treatments early in the season but was significantly lower in pumpkin plants in the SL treatment than the conventional treatment later in the season. Pumpkin plants in the weed treatment had more aphids than those in SL and conventional whereas those in SL had more than in the conventional treatment. Marketable pumpkin fruit numbers, total weight and weight per fruit were significantly greater for the SL treatment than the conventional in both years.  Results indicate that pumpkin plants grown with the low growing SL as inter-row cover crop may have less aphid-borne virus despite greater numbers of aphids and produce higher yields.