February 12, 2018

Cucurbit Downy Mildew Sentinel Plots and Reports in Mississippi

By: Rebecca A. Melanson, MSU Extension Plant Pathologist, Central MS Research and Extension Center, Raymond, MS

     Sentinel plots for cucurbit downy mildew (CDM) were planted in the spring and fall of 2016 and 2017 at the Truck Crops Branch Experiment Station (TCBES) in Crystal Springs (Copiah County) and in the spring of 2016 and the fall of 2017 at the North Mississippi Research and Extension Center (NMREC) in Verona (Lee County). The purpose of the sentinel plots is to have hosts that are susceptible to CDM available to regularly monitor for the presence of the disease in order to detect when it first appears in the area and is active. The sentinel plots are maintained to keep plants healthy as much as possible, but fungicides that have activity against CDM are not applied. Sentinel plots included cucumber (‘Straight Eight’), cantaloupe (‘Hales Best’), pumpkin (‘Big Max’), acorn squash (‘Table Queen’), butternut squash (‘Waltham’), and watermelon (‘Mickey Lee’).

Figure: Spring (2016) CDM sentinel plot at the Truck Crops Branch Experiment Station in Crystal Springs. Photo credit: R. A. Melanson, MSU Extension.

     In 2016, CDM was not observed on any hosts in either of the spring sentinel plots, but it did appear in the fall sentinel plot (butternut squash, cucumber). The first confirmed report of CDM in 2016 in Mississippi was on cucumber in late-August in Hinds County. CDM was also later confirmed in Copiah (cucumber, pumpkin, squash), Lee (pumpkin), and Madison (cucumber, squash) counties in 2016.

     The first confirmed report of CDM in Mississippi in 2017 was on cucumber in late June in the sentinel plot at the TCBES. This report was about two months earlier than the first confirmed report of CDM in Mississippi in 2016. CDM appeared on all cucurbit hosts in the 2017 spring sentinel plot by mid-July. CDM was confirmed in the fall sentinel plots at the TCBES (acorn and butternut squash, cantaloupe, pumpkin, watermelon) and the NMREC (all hosts) in 2017. CDM was also confirmed in Copiah (cantaloupe, pumpkin, watermelon), Hinds (cucumber), Simpson (cucumber), and Yazoo (pumpkin) counties in 2017.

     Sentinel plots for cucurbit downy mildew are planned for the spring and fall of 2018 at the TCBES and the fall of 2018 at the NMREC. If downy mildew on a cucurbit crop is suspected in Mississippi, please contact your local county Extension agent or Dr. Rebecca A. Melanson (rebecca.melanson@msstate.edu) so that samples can be obtained for disease confirmation and outbreaks of downy mildew can be reported.

     For more information on cucurbit downy mildew, please see MSU Extension publication P3076 Cucurbit Downy Mildew.

January 26, 2018

Sample Collection and Assistance for Disease Identification

By: Rebecca A. Melanson, MSU Extension Plant Pathologist, Central MS Research and Extension Center, Raymond, MS

     Diagnosis is the first step in disease management. It is important to know what disease and pathogen is affecting a plant or crop so that appropriate disease management actions can be taken. When seeking assistance from county agents or specialists, it is important to provide relevant information that can help your local county agent or specialist to identify the problem in a timely manner and determine the best management options. It is always a good idea to provide at least the following information: the affected plant host and variety, the extent of the damage, a description of the symptoms, and your preferences for disease management, which may range from conventional to strictly organic. Additional information such as disease history and recent pesticide use is also valuable.

     Often times, digital images (photos) of plants are also received from growers or homeowners wanting to know what is wrong with their plant. These images can be very valuable and provide additional information regarding a situation, but it is often not possible to diagnose a disease problem from a digital image. Information about the types of images that are most useful and examples of good images are available in MSU Extension publication P3022 Taking Photos of Plant Disease Problems. If sending photos to your local county agent or specialist, please remember to make sure that your photos are in focus and that you also provide the information requested above.

     Despite the valuable information that can be provided through words and images, it is often still necessary to examine a physical sample for diagnosis. Samples submitted for diagnosis should not be in an advanced stage of decay. They should also be fresh and arrive undamaged. Instructions for collecting and packaging samples for diagnosis are available in MSU Exteension publication M1562 How to Collect and Package Plant Disease Specimens for Diagnosis.

(The majority of this article originally appeared in the April 2017 issue of the North MS Fruit and Vegetable Newsletter.)