When they appear en masse, white grubs can cause a great deal of damage to many lawns, as they feed on the roots of the grasses. Usually, however, the damage is not noticed until the lawn has brown spots. They can live in the soil for up to four years in the larval stage. When they then pupate, however, they can still be found in the soil for some time. We have some tips and tricks for you on how to get after the grubs in an environmentally friendly way.
Not every white grub is harmful to the lawn; for example, those from the rhinoceros beetle and rose chafer are not. These beetles are protected by law. The rose chafer larvae, for example, are important beneficial insects for the compost pile. The grubs of May and June beetles can reach a length of five to six centimeters. They are about the same thickness at the back and front and have very long, strong legs on the head. The head and legs are darker in color than the pale, yellowish to brownish rest of the larva and take on an orange, brown to black coloration depending on the larval stage. If you have a lot of grubs in your lawn and don’t know exactly which beetle larvae they are, the following test can help you figure out which grubs they are:
Place the grubs on a flat surface, such as a patio tile or wooden board. May and June beetles try to get away on their bellies or in a sideways position. The rose chafer grub, on the other hand, first turns onto its back and then crawls away much like a caterpillar. In addition, its abdomen is much thicker than its front part.
Use of nematodes
In large lawns, picking out the grubs is very tedious and actually almost impossible. Often, the entire lawn must also be freshly seeded. However, useful nematodes (nematodes) can help you control a massive grub infestation. Predatory HM nematodes (Heterorhabditis sp.) are used for the larvae of dung beetles, garden leaf beetles, May beetles and June beetles, and they are also commonly used in the control of thick grub larvae. You can obtain the nematodes from various insect companies, where you can also send in the grubs for identification. This way you can be completely sure you are applying the correct nematodes.
Always mix the package contents with the nematodes according to directions and use a watering can to apply to the lawn. Pay attention to the soil temperature. The nematodes work most successfully at about 12 °C. The most favorable time to apply the nematodes outdoors is between April/May and September and, of course, depends on the weather. Approximately 10 million nematodes are needed for a lawn area of about 20 square meters.
Tip: After treatment, keep the lawn moist for about six to eight weeks to allow the nematodes to take full effect.
Use of grub traps
You can also set traps with nutrient-rich contents for annual white grubs. And do so in a way that will distract them from the lawn. To do this, it’s best to take large planters or water buckets and fill them with horse manure or compost. Leave a top edge about a hand’s width clear. Then dig the buckets or planters about 40 to 50 inches deep into the garden soil and fill in the top with soil. Carefully mark the spots with the buried traps so you can find the buckets later. To mark them, you can use sticks or stones that you place all around the buckets.
Tip: It’s best to bury the grub traps in the ground in the spring and not remove them until a year later. Then fill the buckets fresh and start the procedure all over again.
Reserve garden area for white grubs
In a natural garden, grubs can hardly be avoided and are also on the menu of hedgehogs and Co. Therefore, it is rather advisable to attract the grubs specifically to a garden area, which is best located in the area of the compost and allowed to run wild. Let dandelion grow preferably, whose roots are only too gladly eaten by grubs. Or, in addition, bring horse manure into the corner so that the grubs have no choice but to come here.
Tip: Limit the area of the grubs with lawn edging, sheet metal or buried grates so they can’t wander up to your lawn and stay just as far away from the rest of the garden. Additionally, install solar-powered garden lights, as the bugs are attracted to the light. Then they prefer to lay their eggs in that area.
Attract beneficial insects to the garden
Martens, hedgehogs, birds and mice love to eat the grubs and therefore often dig in the ground for them. You can recognize this in your garden by the many holes after heavy rainfall, when the grubs are washed to the surface of the soil and can then be more easily rooted out by hedgehogs.
Let the useful animals run free and do not close the holes tightly. Because the animals are industrious garden helpers and save you from regular digging. In addition, digging aerates the soil. Rather, set up natural corners in your garden for them, where you and your family have no access and the useful animals can develop and reproduce freely. This includes, for example, bird protection hedges and brushwood piles. But also install accessible watering and feeding stations that you can always refill.
Regular dethatching loosens the soil in the lawn and makes it more difficult for grubs to settle there. Therefore, scarify regularly to prevent a heavy infestation of grubs.
Plants against grubs
There are some plants that are toxic to grubs and that you can use to reduce an infestation, for example geranium and delphinium. Therefore, plant these plants in large numbers near your lawn or dig shredded plant parts into the lawn after scarifying or mulch with them.
As a preventive measure against the infestation of your lawn with white grubs, garlic tea works very well, which you spread over the entire lawn. The white grubs are deterred by the active ingredients in garlic.
Blackworms in the lawn can cause a lot of damage once they are in the ground in large numbers. However, you can counteract this ahead of time by attracting beneficial insects to your garden, driving the grubs away with garlic, regularly dethatching, or reserving an overgrown corner in the garden for the grubs. If the infestation is very severe, nematodes and traps are helpful. Keep in mind, however, that there are a few white grubs in every good garden soil. So if you find a grub here or there while weeding, just take it to the compost with the weeds. The birds are happy when they can pick it out there.