Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/2014
Publication Date: 9/30/2014
Publication URL: http://DOI:10.1094/PHP-RS-14-0009
Citation: Kousik, C.S., Ikerd, J.L., Harrison Jr, H.F. 2014. Pre- and post-harvest development of Phytophthora fruit rot on watermelons treated with fungicides in the field. Plant Health Progress. 15(3):145-150.
Interpretive Summary: For the past several years, fruit rot of watermelon caused by a fungus has resulted in severe losses to watermelon growers in southeastern states and hence it is considered an important problem and a top research priority by producers and watermelon commodity groups. In 2013, the disease was particularly severe in Georgia. In many instances, the watermelon fruit rotted during transport due to post-harvest fruit rot caused by the same fungus. We have been testing fungicides (chemicals that can kill or slow down fungus) to manage Phytophthora fruit rot of watermelon before and after harvest (pre- and post-harvest) of the watermelon fruit since 2010. The tests were conducted at Charleston, SC, for 3 years. Based on these tests, ARS scientists have identified several existing and new fungicides with varying levels of effectiveness for management of pre- and post-harvest Phytophthora fruit rot of watermelon. Some of these fungicides applied in the field protected the fruit for up to 9 days under storage conditions favorable for development of fruit rot. This research also found that, despite using some of the recommended fungicides, severe losses still followed because of unfavorable weather conditions and intense disease pressure. These fungicides can be used by growers to manage fruit rot of watermelon. However, growers should keep in mind that there is always a possibility of the fruit rot fungus developing resistance to these new fungicides, thus rendering them ineffective. Therefore, to prolong the life of these fungicides, they should be rotated with some of the available new and other older fungicides. Fungicides should be part of an overall disease management strategy that also includes the use of well drained fields, water management, and crop rotation. These research results will be of use to commercial growers, researchers and extension agents who are working to manage Phytophthora fruit rot of watermelon
Technical Abstract: Fruit rot, caused by Phytophthora capsici, is a serious disease in most watermelon producing regions in southeastern U.S., and has caused devastating loss over the past few years. In many instances, severe losses occurred after harvest during transportation. Experiments were conducted in 2010, 2011, and 2013 in a P. capsici infested field to identify fungicides effective for managing pre- and post-harvest development of Phytophthora fruit rot. Weekly treatments of OXTP (Oxathiapiprolin), V-10208 (ethaboxam), Zampro (ametoctradin+dimethomorph), Forum (dimethomorph), Prophyt (potassium phosphite) + Kocide 2000 (copper hydroxide), Revus (mandipropamid) rotated with Prophyt + Kocide, and rotation of Revus with Presidio (fluopicolide) significantly reduced pre-harvest fruit rot compared to non-treated control. Rotations of Actigard with Revus also reduced pre-harvest fruit rot. However, Actigard alone significantly reduced fruit rot only in 2010. Symptomless fruit harvested 4 days after the last spray were inoculated with P. capsici and maintained in a humid chamber to evaluate for post-harvest fruit rot. OXTP, Zampro, Forum, V-10208, Presidio rotated with Revus, and Actigard rotated with Revus applied in the field provided extended post-harvest protection against Phytophthora fruit rot compared to non-treated control. Many fungicides belonging to different FRAC groups are now available to rotate and manage Phytophthora fruit rot of watermelon. However, fungicide applications should be part of an overall management strategy that also includes the use of well drained fields, proper irrigation practices and crop rotation.