Submitted to: Plant Disease Management Reports
Publication Type: Research Notes
Publication Acceptance Date: July 6, 2010
Publication Date: September 1, 2010
Citation: Kousik, C.S., Adkins, S.T., Webster, C.G., Turechek, W., Roberts, P.D. 2010. Effect of Reflective Plastic Mulch and Insecticide Sprays on Viral Watermelon Vine Decline in Florida, 2009. Plant Disease Management Reports. 4:V149. Technical Abstract: Watermelon vine decline (WVD) caused by Squash vein yellowing virus (SqVYV) is a new and emerging disease in southwest and west central Florida that is transmitted by the silver-leaf whitefly (Bemisia tabaci). Symptoms of WVD typically manifest as sudden decline of vines at harvest time or one to two weeks prior to harvest and can also affect fruit quality. The experiment was conducted in Immokalee, FL. Four-week old plants of the seeded watermelon cultivar ‘Crimson Sweet’ grown in 50-cell Jiffy trays were transplanted onto raised beds covered with either reflective (silver) or non-reflective (white) plastic mulch on 6 Oct. The soil was Immokalee fine sand. The experimental design was a split plot. Whole plot treatments were arranged in a randomized complete block design with four blocks and consisted of the plastic mulch treatments: reflective and non-reflective. Split plots were insecticide treated and untreated check. Each split plot had 27 plants and plant to plant spacing within plot was 24-inches. Thus the whole plots (mulch) had 54 plants each. Guidelines established by the University of Florida/IFAS were followed for land preparation, fertility, irrigation, and weed management. A 4-wk old squash plant inoculated with SqVYV was planted at both ends of each split plot to serve as a source of initial inoculum. Soon after transplanting, Admire Pro (imidacloprid) was applied at the rate of 8 fl oz/A as a soil drench on plants in the insecticide treated plots for managing whiteflies. Whitefly management was continued with two sprays of Oberon 2SC (spiromesifen) at the rate of 7 fl oz/A, applied only to the insecticide treated plots on 18 Oct and 30 Nov. The sprays were applied using a pressurized sprayer calibrated to deliver 30 gal/A. Plants were monitored for symptom appearance on a regular basis. Plants were rated on a 1-9 scale for percent of plant foliage affected and severity of symptoms as indicated: 1=0% (no symptoms), 2=1-3% (very minor chlorosis/vein yellowing, no necrosis), 3=4-10% (minor chlorosis/vein yellowing plus mild epinasty of youngest upper leaves), 4=11-25% (chlorosis/vein yellowing plus severe epinasty of youngest upper leaves, no necrosis), 5=26-35% (chlorosis of most basal leaves, necrotic streaks in petioles and/or tendrils), 6=36-50% (necrosis of most basal leaves, petiole collapse), 7=51-65% (necrosis of most leaves, total petiole collapse, main stem mostly green/yellow), 8=66-80% (necrosis of most leaves, stem necrosis and slight collapse, stem tip dead), 9=81-100% (plant dying or dead). Disease ratings were recorded on 30 Sep, 18 Oct, 30 Nov and 17 Dec and used to calculate Area under the disease progress curves (AUDPC). Whitefly counts were recorded on the same days when disease data were recorded. The numbers of adult whiteflies were counted on the underside of 15 leaves per plot early in the morning when temperatures were still low and whiteflies were not very active. The numbers of watermelon fruits with internal greasy or necrotic rinds and rotting flesh, which are also important diagnostic symptoms of WVD were recorded on 17 Dec. Data were fit to a general linear model and contrast statements were constructed to determine differences among treatments. The analysis was performed with the GLM procedure of SAS. Symptoms of WVD were first observed on the leaf petioles about a month after transplanting. The initial appearance of symptoms was on the plants adjacent to the inoculated squash plants. However, it became difficult to rate the plants for WVD from the middle to end of the season because of gummy stem blight infection on leaves and stems. The percentage of fruits with WVD symptoms were significantly less (P=0.0033) in insecticide treated plots compared to untreated plots. Total adult whitefly counts were significantly lower in treated plots compared to unsprayed plots (P=0.0253). Whitefly counts in untreated reflective mulch plots were significantly lower compared to the untreated no-reflective mulch plot. Insecticide treatments to manage whitefly populations can help in management of WVD of watermelon.