Wet summer leads to diseases and more interest in high tunnels

Published: November 14, 2016

Missouri’s erratic weather always presents challenges, and 2016 was no exception. Some very chilly weather in May lead to some warm season vegetables being held back, and as the very hot and dry June weather settled in, some struggled to adjust well, notably peppers seemed stunted. And then just as drought concerns mounted, rain came in from July through September, of course varying around the state. But one could say, everyone seemed to get their fill by the time summer closed out on the equinox.

Heavy rains in July and August, high relative humidity between rains, and warm night temperatures were conducive for disease development. Then a very rainy September made harvesting challenging as well. Besides what is listed, numerous reports of severe foliar diseases were reported by home gardeners and commercial growers. A common scenario, this season, was the inability to get a preventative pesticide out between rains.

The rain kept soils saturated and promoted soil-borne diseases, especially those caused by Phytophthora and Pythium. These two fungal-like plant pathogens are called water molds and make a motile spore (zoospore) that easily moves from infected to healthy tissues. In some cases Phytophthora diseases could be associated with low areas or standing water (flooding). One squash sample came from a raised bed system and the only diseased areas were stems that were touching the ground on either side of the bed.

Below is a list of vegetable diseases diagnosed from the MU Plant Diagnostic Clinic:

The disease pressure this year has come on the heels of relatively rainy years every year since the drought of 2012, with 2015 being quite difficult statewide. Tomatoes were very short at farmers’ markets by September. This is leading some growers to consider further expanding the use of high tunnels or greenhouses.