Feasibility Study on Application of Different Polyethylene Mulch types to Control of Important Virus Diseases and Sucking pests in Melon

Introduction: Virus diseases are a worldwide problem for cucurbit production, which cause economic losses. In fact, more than 35 different viruses have been isolated from cucurbits. The main symptoms include mosaic, yellowing, vein clearing, leaf and fruit malformation in the crops. Until now, 13 viruses have been detected on cucurbits in Iran. CMV, ZYMV, WMV, CABYV and CVYV have been confirmed in field-grown cucurbit crops in Khorasan razavi province (Bananej & Vahdat, 2008). Mulch has been used to obtain good vegetable growth and yield in crops like cucumber, tomato and pepper (Kring & Schuster, 1992). Stylet borne virus transmission can be decreased only by applying preventive methods like mulching during the production. The research on the insect repelling effect of reflective surfaces has been done by many researchers (Kring & Schuster, 1992). They have achieved statisfactory outcome in decreasing virus incidence in vegetables using reflective surfaces. The silver reflective plastic mulch reflects ultraviolet (UV) wavelengths, unlike black or clear plastic mulches. Flying aphids as plant virus vectors are repelled by these UV wavelengths. The outcome is to delay and reduce the incidence of aphid-borne viruses. The aim of this project was to assess and select suitable plastic mulches that can act versatile and perfectly meet the needs of farmers for controlling pests and viruses in melon prodcution.

Materials and Methods: The experiment was carried out with six treatments including polyethylene plastic mulch in four colors, including a colorless transparent plastic, white plastic (milky), silver, black plastic mulch and two controls including hand weeding and weed-free mulch in a randomized complete block design with four replications during two growing seasons in 2013 and 2014 near Saaleh Abad in Torbat Jam. Each experimental unit comprised 5 rows(70 cm spacing) of 10 m long with a drip irrigation system. Serological surveys were conducted during three plant growth stages including the first week after transplanting (to remove possible infection), flowering(30 days after transplanting), and four weeks after the flowering (50 days after transplanting). A sampling of the middle leaves of the plant from three rows in the middle of each experimental unit was performed.
Assessment for viral factors CMV, CABYV, ZYMV and WMV was performed using a polyclonal antibody. The aphids pests population was studied at a 10-day interval from the beginning of flowering and until three weeks after the first fruit harvest.

Results and Discussion: There were statistically significant differences among the aphids pests population on different treatments during the two years of experiments. The comparison of means between the first, second and third stages of sampling showed a significant difference. The silver treatment had the lowest aphids pests population, followed by white and black treatments. However, some researchers have recorded different results in their studies . Since the four viral diseases studied in this work are common in the aphid vector, the frequency of these four viruses was calculated during two sampling stages. The frequency of the viruses in the first stage of sampling in the two years of the experiment under silver mulch was recorded as 3.573% and 7.14%, which was the lowest. Similar results were observed by Jalali et al., 2016.
It is noteworthy that in the first stage of sampling(30 DAT) in both years, the lowest number of aphids observed was fully consistent with the lowest infection rate by the viruses. But in the second stage sampling, the results did not follow certain orders. This was due to the alteration of the physical properties of silver mulch under the environmental conditions such as UV sunlight, which led to its degradation. The results of analysis of variance for the total melon yield in the two years between treatments were significant. The highest yields were obtained with black and silver mulch, respectively.

Conclusion: The results of this project showed that silver mulch had the highest efficiency in reducing aphids pests population by 43/75% and 36/73% in the first and second years, respectively. Silver mulch reduced aphid-borne viral diseases in the first sampling in two years of experiment by 88/8% and 77/1% as compared to control, respectively. The highest yield was achieved with both black and silver mulches.