If the mint leaves have holes, the mint leaf beetle is usually behind them. You can take action against the bug with a few simple measures.
Mint dominates the picture in the herb garden. Nothing seems to be able to harm the lush growing aromatic herbs. Because the menthol it contains has a deterrent effect on vermin.
Only the mint leaf beetle seems to like the plants. Anyone who discovers the small, beautifully colored beetles on their mint usually does not need to fear for the plant. Because the mint usually grows much faster than the mint leaf beetle can eat the leaves. To prevent a permanent infestation, gentle control of the mint leaf beetle is a good idea.
Recognizing mint leaf beetles
The mint leaf beetle belongs to the leaf beetle family. About 50,000 species exist worldwide. The well-known Colorado potato beetle is a close relative of the less common mint leaf beetle.
The beetles have a short and rounded body. The elytra are highly arched. The shimmering blue-green coloring is characteristic of the beetle, which is about eight millimeters in size. The body looks as if it is surrounded by a layer of lacquer and has fine dotting. The pairs of antennae on the head are clearly visible.
In the spring, the mint leaf beetles lay their eggs. The orange-brown eggs can be seen on the underside of the leaves. They are placed in groups of about 15. The larvae hatch after about ten days. The voracious larvae are brown in color and have a black head.
After the larvae, which are about five millimeters long, have fed on the mint leaves for about four weeks, they pupate. The striking yellow pupae can be spotted by hobby gardeners in the upper layers of the earth under the mint plant. After about two weeks, the second generation of beetles hatch, feed on the mint leaves and then hibernate in the ground.
The mint leaf beetles are active between May and August and can be fought directly on the plant.
Spread of the mint leaf beetle
The mint leaf beetle occurs almost everywhere in Germany. It prefers to stay in wet meadows and in inhabited settlements. In Maythe beetle leaves its winter location and the mating season begins. In warm and dry weather, there is a strong increase and a correspondingly large-scale infestation.
Pest of the Mint Leaf Beetle
The beetles are easy to spot on the mint plants due to their size and iridescent colour. Furthermore, the damage pattern provides clear indications of an infestation. The larvae often eat the leaves completely. Many smaller holes in the mint leaves also indicate an infestation.
The first signs of feeding appear from May, preferably on the tender tips of the shoots. Several feeding spots can occur per leaf. These are about one centimeter in size and therefore clearly visible. A heavy infestation can cause defoliation. Only the middle ribs remain of the mint plant.
If the larvae become active in June, this is indicated by holes in the leaf blades. The dark brown droppings provide another clue.
Control measures
If the mint leaf beetle appears on the plants, there is usually no reason to worry. The mint can hold its own very well against the pest with its vigour. Completely bare plants remain the absolute exception.
The mint leaf beetle infestation can be contained with a few simple countermeasures.
Collecting the Mint Leaf Beetle
Pests are reluctant to use their wings. This makes it easy for the hobby gardener to collect the mint leaf beetle directly from the plants. The larvae can also be removed in this way.
Hint: Make sure you catch all the animals and don't let any bugs and larvae fall on the ground. These return to the plant quickly.
Pruning of the mint plant
Mints can easily withstand heavy pruning and usually grow back all the faster. Several prunings per year are possible without any problems. If the infestation is severe, it is advisable to cut the mint close to the ground and to dispose of the leaves and pests. Again, it's important to pick up the bugs and larvae on the ground.
Spraying the plant with soapy water
A harmless biological control measure is treating the mint plant with soapy water. Add about 20 milliliters of liquid soap to one liter of water and mix the solution. The plant should be sprayed several times with the soapy water at intervals of two to three days.
If you want to use commercially available products, you can use the pesticides approved in Germanybased on rapeseed oil or pyrethrins, such as COMPO Schädlings-frei plus AF.
Prevent mint leaf beetle infestation
An infestation can be prevented by deploying crop protection nets. One danger to the beetles that overwinter in the ground is abundant watering in late winter. Pruning measures in early spring also lead to a significant reduction in the population.
In general, he althy and vigorous plants are well-armed against mint leaf beetle infestation and usually grow faster than the plant is clearly damaged.