Downy mildew is a potentially devastating disease to cucurbits. It usually affects cucumbers and cantaloupes first; later in the season it can be found on summer squash and zucchini. During some seasons, downy mildew can spread to winter squash and watermelons. Growers need to be monitoring their fields. This short video shows the different stages of the disease and possible outcomes if it is not controlled.

From Margaret McGrath, Cornell
Producing a high-quality cucurbit crop necessitates effectively managing downy mildew. This foliar disease is common in the northeast because the pathogen produces a large quantity of asexual spores that are easily dispersed long distances by wind, which enables it to spread widely. There has been no evidence that the pathogen is surviving between growing seasons where winter temperatures kill cucurbit crops (outdoors above the 30th latitude); however, recently both mating types have been found, albeit typically on different cucurbit crop types, thus there is the potential for the pathogen to produce oospores (sexual spores) that could enable the pathogen to survive in northern areas of the USA. The downy mildew forecasting program has documented based on downy mildew occurrence movement of the pathogen throughout the eastern USA each year via its wind-dispersed asexual spores. The pathogen does not affect fruit directly; however, affected leaves die prematurely which results in fewer fruit and/or fruit of low quality (poor flavor, sunscald, poor storability).

The most important component of an effective management program for downy mildew is an effective, properly-timed fungicide program. And the key to that is applying mobile fungicides targeted to the pathogen starting when there is a risk of the pathogen being present. Mobile (or translaminar) fungicides are needed for control on the underside of leaves. Each year there often are changes to the fungicides recommended as the pathogen develops resistance or new products are registered. Because these fungicides have targeted activity, additional fungicides must be added to the program when there is a need to manage other diseases such as powdery mildew. Most targeted fungicides effective for downy mildew are also effective for Phytophthora blight.

This reference sheet lists the herbicides that are labeled for cucurbits in New York and which species are controlled, as well as other important considerations and photos of weeds. While this is a handy references, it is critical to read the product labels thoroughly.

There are several different copper fungicides approved for use in organically-produced crops. Copper fungicides are important tools for managing diseases that cannot be effectively managed with cultural practices alone.

While no one wants to think about the possibility of hail hitting their beautiful crops just as they start to respond to the heat and take off, the likelihood that we will see more hail seems pretty high. So let's talk about it.

Download a report on using buckwheat strips to attract native pollinators to vine crops (2008). This project was funded by the Organic Farming Research Federation.