Squash bugs and blueweed


Squash bugs are destroying my many vining plants–zucchini, pumpkins… What can I do to keep them off?

I am also having trouble with blueweed, which is toxic to horses, in my pasture field.  What chemicals can I buy, not being liscened, to eradicate this blueweed?



The squash bug, Anasa tristis, primarily attacks squash and pumpkins but can also attack other cucurbits.

Squash bugs overwinter in sheltered places under plant debris, rocks, or around buildings.  They emerge in the spring and fly to growing cucurbit plants to feed and mate.  The egg clusters are typically found on the undersides of leaves, especially between the veins where they form a “V”.  Eggs may also be deposited on stems.  The females usually start appearing in gardens in early June and continue to lay eggs through mid-summer.  In the fall, especially after the vines have died, the adults often congregate on the squash fruits.  As the temperature drops to freezing, they retreat to sheltered places to overwinter.

Squash bugs are sap-suckers.  Although damage is not usually serious, and they are not vectors for diseases (unlike the cucumber beetle), a severe infestation can potentially destroy a crop, especially when young.

The most important times to control squash bugs are when the plants are young seedlings and when they are flowering.  Early detection of nymphs is important because adult squash bugs are difficult to kill.  Starting in June, inspect the plants regularly.  Knock off and kill nymphs and adults by dropping them into a pail of soapy water.  Pick off and crush the eggs.  Also, set up traps by laying out boards or pieces of newspaper – the squash bugs will congregate under the boards at night, and in the morning you can collect and destroy them.  Remove plant debris around the garden during the growing season to reduce hiding places. Consider not mulching around the cucurbits to further reduce hiding sites.  In the fall, clean up and dispose of cucurbits and other plant matter thoroughly to reduce the number of overwintering sites.  Also consider crop rotation if the squash bugs return.

Squash bugs are difficult to kill using insecticides because egg masses, nymphs, and bugs are often hidden near the crown of the plant and difficult to reach with sprays.  Several insecticides are available that are less toxic to the environment, i.e. products containing soaps and horticultural oils.  These soaps and oils are most effective on the smallest nymphs, but good penetration throughout the canopy is essential so that nymphs under the leaves and deep within plants will be covered.

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Blueweed (Echium vulgare), also known as Viper’s bugloss, is an invasive species in Canada and toxic to horses and cattle due to its pyrrolizidine alkaloid content.  It is a biennial or short-lived perennial that primarily spreads by seed.  An effective mechanical control is repeated mowing, in order to deplete root reserves of current plants and also to prevent flowering so that the seed bank in the pasture is diminished.

The Ontario Ministry of Agriculture, Farm and Rural Affairs should be contacted for more information and help with an eradication or control method.  The Agricultural Information Contact Centre of OMAFRA an be reached at 1-877-424-1300.  Alternatively, you can email them at the email address below:


Give them your geographic location and what weed or pest you have.  They will respond with the contact information of the Municipal Weed Inspector in your area, who can set up a site visit and draw up a plan to address the problem.

Included below is a link to an OMAFRA newsletter article regarding weed control in horse pastures.


Here is the Guide to Weed Control.


Also, see this factsheet on blueweed published by the Alberta Invasive Spieces Council with information on chemical control.


And finally, the MDSD of Weed B Gon.