Controlling a Squash Beetle Invasion
This August we were away for more than three weeks leaving the garden to mostly fend for itself. This is only possible because I companion plant, rotate our crops each year, have good soil management and mostly importantly a wonderful husband who diligently kept the garden hydrated during the heat of the summer. But even with the best practices in place it seems that while the gardener is away the insects will play.
Our watermelon vines were invaded by a lady beetle look alike, known as the squash beetle (Epilachna borealis). This beetle is a native to Eastern North America and is larger than your typical beneficial lady beetle.
Unlike most lady beetles which are a gardener's friend, since they eat loads of aphids and scale insects which feed on our fruits, vegetables and flowers, the squash beetle attacks the leaves of cucurbits which include squash, pumpkins, cucumbers, gourds, watermelons and cantaloupes; sucking on the tasty juices.
The squash beetle has an odd behavior of circling the leaf area that it feeds on. A study at the University of Delaware found that this feeding method preserves the leaf tissue's suitability for feeding because it reduces the influx of chemical defenses from the injured plant (source: Purdue University Extension). This typically creates a skeletonized appearance on the upper side of the leaves.
The larvae are yellow, alien looking creatures found mostly on the underside of the leaves. Aren't they creeping looking things?
According to the University of Purdue Extension the best time to control these insects is at noon since the beetles are easiest to find. They can be hand picked and placed in a container of soap and water. Be sure to check the underside of the leaves for eggs and larvae. I usually remove the entire leaf if their are eggs present or you can try to scrape them off.
The photo above shows old eggs but it will give you an idea of what to look for. They are very similar to the beneficial lady beetle eggs (yellow, bullet-shaped) but if you find them on cucurbits your probably safe in assuming they are from the squash beetle.
If you are not inclined to remove them by hand you can make a homemade spray of liquefied ingredients: garlic clove, small onion, fresh or powdered hot pepper (habanero, jalapeno or cayenne). Add this to a quart of water and let steep for an hour. Strain off the solids and then add a drop of dish soap to your liquid solution. Spray this mixture onto the lady beetles (adults and larvae) that are on your cucurbits. If your not one to make your own spray Neem Oil is an option.
At the end of the growing season be sure to dispose of all the plant residue so you won't have any overwintering beetles in your soil. Rotating crops is a good practice to keep diseases and insects in check too but diligently attending a garden to catch the signs early is the best way to go!