Mike Raupp, "The Bug Guy" for the University of Maryland Extension, explains how, like a crime scene investigator, you can use clues to find out what types of insects are causing damage in your garden. Look for telltale signs like chewed leaves, discoloration, distortion, dieback, and insect products.
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From the look of these shredded leaves, it appears that something has tried to turn these cabbages into coleslaw.
Hi, I'm the bug guy here for university of Maryland extension. Insects and diseases are going to wreak havoc in your vegetable garden. Oftentimes when you arrive at the crime scene, the perpetrator's not going to be there. All you're going to have is the victim, but like a crime scene investigator, you can use the clues. These are the symptoms and signs that insects and diseases leave behind to identify the perp. Just as criminals have specific weapons of choice, insects also leave characteristic damage behind and the damage is caused by their mouth parts. There are fundamentally two types of mouth parts. The first is called a chewing mouth part. Insects like beetles and caterpillars have chewing mouth parts and they leave behind a characteristic signature. The other type of mouth part is a beat, a sucking mouth part. As you might guess, when an aphid or a stinkbug gyms that into a plant, it's gonna leave behind characteristic symptoms. There are five types of symptoms that insects cause when they damage plants. First they can chew the leaves. They can also discolor the leaves. Their feeding can cause distortion. It can also cause die-back. And finally, as insects move about the world, they leave behind a variety of products. We'll look at these.
These coarse holes in a squash leaf are a sure sign of an insect with chewing mouth parts. In this case, cucumber beetles fed on this leaf early in the season. It's going to wear this damage all season long. Smaller insects with chewing mouth parts cause a different kind of damage. Basically they feed between the lines. This type of damage is called skeletonization and it's caused by the Mexican bean beetle. Really small insect with tiny mouth parts make very small holes. Flea beetles create a type of damage called shot hole. It looks like somebody blasted this with a shotgun. This is clearly a case of double homicide, death by discoloration. You can see Harlequin bugs have been feeding on this. They take their beaks, jam them in the plants to create proteolytic enzymes that cause these lesions. And look at these potatoes. Thousands of leafhoppers have moved over here. They put their beaks in. They suck the juice out and cause discoloration called hopper burn. These two plants are in real trouble right now.
Another type of insect damage is dastardly distortion. As you can see early in the season, these bean leaves were big and beautiful, but leafhoppers have moved in, they're taking their beaks. They're damaging those tender young leaves. These leaves are looking gnarly. They're not going to be able to photosynthesize. They're not going to be productive. Leafhoppers distortion.
Sometimes we find a victim that's been dead a while. This little squash plant died from a bacterial wilt disease that was carried by a cucumber beetle earlier in the season. Whenever we see die back, we know the vascular system has been damaged. Usually damage to the vascular system can be lethal.
As insects move their way through the world, they leave stuff behind. Hey, they're just like us. Sometimes we can use these insect products to help us detect the presence of insects or mites on our plants. When caterpillars feed, they often leave behind silk. On these cucumber leaves, we can find the telltale signs of the silk of a little leaf tie and Caterpillar that's going to defoliate these things. As insects feed, let's face it, they're going to leave behind stuff. Excrement. We call this frass. If we look at these stalks of corn, we can see the frass being excoriated and forced out of the stems by European corn borer. So we know there are corn borer larvae inside the stems. Another sign that's readily apparent are the eggs of insects. Here we see the eggs of the squash bug. These little bronze bombs are going to hatch. The nymphs are going to come out and feed, but we can detect those eggs, eliminate them, and this is going to reduce our problem down the road. So if you use the five symptoms, chewing damage, discoloration, distortion, die back, and insect products, you'll nail the perp every time.
Guess what, mr Harlequin bug. You've just received the death sentence.
