Controlling grubs in your lawn
Controlling grubs in your lawn
Not all lawn grub species are the same, so it’s crucial to understand their life cycles to apply insecticides correctly. Although we use the same product, the control methods are applied differently depending on the grub species.
Grass grub life cycle
Brown Beetles, commonly referred to as Grass Grub beetles, is the most common pest in New Zealand lawns, closely followed by Porina. The main difference is that Grass Grubs feed below the surface on your lawn’s roots, while Porina grubs come to the surface to feed at night.
Brown Beetles are only present from October to early January, often flying at dusk, and are attracted to street lighting and other light sources. The adults start flying in the South Island and colder regions slightly later in the year.
Brown beetles live for only two to three weeks, growing about 1cm long. During their life cycle, female beetles will lay eggs 10cm to 15cm under the soil of your lawn. Female beetles can lay two to three batches of about 30 eggs during this period. The eggs are vanilla white in colour, oval-shaped and 1.5mm in diameter.
Larvae hatch after about three weeks and start feeding on lawn roots. The most damage is done during the larvae stage. There are three stages of development called instars. It takes about one year from the bug to develop from egg to adult, however in colder regions it’s not uncommon for the life cycle to last two years.
During the second instar – mid-January to late February – they move closer to the surface of the soil and are often found as shallow as 5cm below the surface.
During the final stage of instars, they develop in the top few centimeters of soil, which is when the most damage is done, before burrowing down 20cm to 30cm over winter. The grubs are translucent, 25mm long, with six legs and a light brown head. One-year-old grass grubs pupate and transform into adult beetles in spring.
Control grubs in your lawn
Grub+ insecticide provides unmatched, season-long grub and caterpillar control in a single application. Grub+ does not need to be reapplied like other products available in New Zealand for controlling grubs.
Grub+ controls a wide range of insect pests including African Black Beetle, Argentinian Scarab, Billbugs, Grass Grubs and several species of caterpillars including Cutworm, Porina, Sod Webworm and Lawn Armyworm.
For superior results, apply Grub+ the first week of October at an application rate of 15ml per 100m2 followed by 3mm to 6mm of irrigation. This can then be repeated six months later in March.
NZLA Grub+
Controls and protects for 6 month's against a range of New Zealand grub species.
Only 15ml/100m²
Porina life cycle
Porina eggs are 1mm in diameter and white when laid, turning black within 24 hours. When they hatch, Porina will be 2-3mm in length and will grow up to 70mm long, with a yellow underbelly and greyish body. Pupae can be found in tunnels under the soil prior to emerging, similar to Grass Grub. Females generally lay up to 3000 eggs, usually around the point where they originally emerged from. Eggs are laid between November and January.
Larvae will hatch about one month after eggs are laid. Larvae will live near the surface for six weeks and begin to tunnel in the soil once they reach 10-15mm in length. Like Grass Grub, they can be found as deep in the soil as 30cm.
Porina will rise at night to feed on nearby leaves. Their tunnels will often have areas with bare patches near the entrance where they have cultivated the surrounding grass. Castings can sometimes be noticed on top of the soil in these areas.
Over winter they remain in these tunnels, pupating starts in September. Porina moth generally emerge from October and fly until mid-February. Similar to other lawn pests, they’re also attracted to light sources, and fly in the dusk.
How to control porina in your lawn
When treating for Porina delay irrigation for 24 hours, leaving the product on the surface of your lawn. This is due to the surface feeding habits of Porina.
Black beetle life cycle
Bleak Beetle grubs are normally a problem north of Lake Taupō and in warmer regions – the further north the bigger the problem they can be.
The adult beetle starts off a similar colour to the Grass Grub beetle but soon changes to a shiny black. The male beetle is normally slightly smaller than the female, which is an average of 15 millimeters in length.
The damage accrued from Black Beetle is similar to Grass Grub; the two suspects often get mixed up. One particular difference is all development stages of this beetle is underground. Warmer summer temperatures than normal can see a rise in the number of Black Beetles. The beetles are usually found in the top 15mm of soil.
The beetles and larvae are both responsible for damage, which is more visible during dry hot summers. Larvae feed on the roots very close to the surface. Damage can present similar to Grass Grub damage, with yellow patches, because larvae feed close to the surface on the roots. The grass in affected areas can easily be pulled out of the ground.
The eggs, about 2mm in diameter, can be found close to the surface from late September to early December.
The larvae are often confused with Grass Grub larvae due to a similar appearance, although Black Beetle larvae are larger when fully grown. Black Beetle larvae have breathing pores (spiracles) along the length of their body – these are more visible and look like orange spots.
Pupation occurs from the end of January and, like grubs, they have three instars. The pupas are a pale yellow to light brown, which turns reddish-brown before the adult emerges. Beetles emerge from February to April but won’t lay eggs until the following spring.
How to control black beetle in your lawn
Apply Grub+ the first week of October at an application rate of 15ml per 100m².
Grub+ does not control adult black beetles, but it is effective at controlling the larval (grub) stage, which tends to cause the most damage to lawns and gardens. The chlorantraniliprole (also sold as Acelepryn) in Grub+ works by interfering with muscle regulation in susceptible larvae.
