Skip to main content

Cucurbit Check In: Squash Bug & Powdery Mildew

Author: Marissa Schuh, Integrated Pest Management Extension Educator, University of Minnesota Extension. Reviewed by Annie Klodd.

Depending on your market, you are a month or two out from pumpkin prime-time.  After dodging the early season weeds and persistent cucumber beetles, it can be tempting to focus on other crops or prepping for fall visitors.  However, this point in the season is a good time to check in for some late-season pests that can cause big issues.

Squash Bugs

Pumpkin and squash fields across Minnesota are seeing squash bugs emerge, lay eggs, and grow their populations.   Populations are variable in fields that I’ve been in -- some fields have  adults are mating and laying eggs, while others have nymphs of all ages everywhere.

Squash bug nymphs are small and grey. Photo: Whitney Cranshaw, Colorado State University,

Why does life stage matter for this pest?  The earlier in their life you catch squash bugs, the easier they are to control.  

  • Clusters of eggs can easily be scraped off of leaves

  • Small nymphs are the easiest to control with insecticides, large nymphs and adults are able to persist through sprays

Squash bugs are worth monitoring and controlling, as they feed in large number.  On leaves this can caused leaves to become crispy and die, on fruit they cause unsightly marking that can allow for secondary rot to invade the fruit.

Because of their numbers and damage they cause, the threshold for treatment is low, with treatment being justified if you are finding an average of more than one egg mass per plant.

Squash bug eggs are highly scrape-able, allowing you to quickly dispense with a dozen pests in one swipe. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo,

Recently hatched squash bug nymphs. This is the ideal life stage of squash bug to control with insecticides. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo,

The easiest life stage to control is when nymphs have recently hatched (see photo above).  Nymphs tend to hide on the underside of leaves and deep in the foliage, so spray coverage is important.

For insecticide control options, see the Midwest Vegetable Production Guide.  Kaolin clay has helped plants fend off squash bugs and boost yields in trials in Iowa.  For a list of organic controls, with notes on known efficacy, see Cornell’s Organic Production Guide for Squash.

Adult squash bug has no issue dodging an application of koalin clay. Video: Marissa Schuh, UMN Extension.

Powdery Mildew

While this dry growing season has limited pressure for most diseases, diseases that aren’t dependent on water have still cropped up this year.  This includes viruses (which are spread by pests that love hot weather) and powdery mildew.

Powdery mildew crops up in Minnesota every year.  The disease needs water to get started, but once it gets established, it can spread to new plants with limited water.  In the pumpkin and squash fields I was in last week, its presence varied greatly by location and variety.  In all cases, powdery mildew wasn’t something you would see from the truck or gator.  

It is important to catch diseases early.  Unlike insects, where allowing some level of insect pressure is tolerable because insecticide treatments can knock them down, diseases don’t work this way.  Sick plants cannot be cured, and disease can only be prevented.  This means catching powdery mildew early is important, especially if it is a disease you want to prevent because of past yield losses.

Weekly, scout at least five plants.  In larger fields, do this in at least ten locations.  Look deep within the canopy, on older leaves, and on the underside of leaves. These are the first parts of the plant to become infected.

Check for powdery mildew on older leaves and those deep in the canopy. Video: Marissa Schuh, UMN Extension.

Fungicide treatment may be necessary, depending on your variety and market.  Powdery mildew can kill off leaves, leading to premature plant death and loss of leaf cover, potentially allowing for pumpkins to get sunburned. It can also infect handles, causing them to fall off.  This isn’t ideal for wholesale or direct markets.

If you’ve had losses to powdery mildew in the past, a suggested treatment threshold is spray when you are seeing one out of every 50 scouted leaves with powdery mildew.  Spray weekly, and continue until 21 days to last harvest

For recommended products, refer to the Midwest Vegetable Production Guide.

Check in on Stragglers

While scouting for squash bug eggs or flipping leaves for powdery mildew, check in on plants that have crashed.  Keep an eye out for wilted plants, and check for root and fruit rots.  The dry weather may have kept some soil borne issues at bay, but recent rains may cause things to pop up in low spots.  It is good to know where the problem areas are before harvest to keep equipment from moving soilborne disease around and to help keep diseased pumpkins out of harvested bins.

Wilted plants afflicted with phytophthora in a part of a field where water gathers. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo,

Viruses are another thing to look for.  Many viruses can infect pumpkins and squash, but all produce similar symptoms. The symptoms include off coloring, twisting leaves and stems, and mosaic patterns on foliage. Pull out infected plants to keep viruses from being spread by insects.  Insect feeding can move the virus into other cucurbit plans as well as into perennial weeds (which can act as a reserve of the virus when the weed plant grows next year).

There are numerous viruses that can cause similar symptoms. Photo: Paul Bachi, University of Kentucky Research and Education Center,

Print Friendly and PDF