Grubs: How to manage them in an organic landscape.
How to monitor for grub infestations in your landscape
June beetles are a common and seemingly harmless part of our Texas summers. While the adult beetles are not destructive in our landscapes, their larvae, known as grubs, can do damage to your lawn if populations get out of control. Grubs typically feed on organic matter in the soil, but will move on to plant roots when organic matter is limited and their population is high. When grubs feed on your lawn’s roots, patches of lawn can turn brown and die.
While there are almost 100 different species of beetle that are referred to as June beetles, or Junebugs, there are three in particular that can cause damage in Texas lawns and landscapes.
1. June Beetle Phyllophaga crinita
2. Southern Masked Chafer Cyclocephala lurida
3. Green June Beetle Cotinis nitida
#1 & #2 look similar to one another, with a classic reddish brown color. #3, the green June beetle, is bright iridescent green in color.
In late-spring or early summer, the adult June beetles emerge from the soil and mate. They then lay their eggs in the soil and then die. About two weeks later, the eggs hatch small white larvae. It’s these larvae (grubs) that will feed on grass roots mid-summer through early fall as they grow and do the most damage to your lawn. Treatments for grubs should be applied mid-summer. Damage from grubs will be apparent from June through October.
Winter and spring chemical treatments have little to no impact on grubs.
Once soil temperatures begin to drop in late-fall, the grubs burrow deeper into the soil to over-winter dormant. While dormant, the grubs are not feeding. The following spring, the larvae transition into pupa and then return to the upper layer of soil. Once temperatures are warm enough, the pupa transition into adults that emerge in summer to mate and lay new eggs.
Grubs can cause the most damage when they reach a length of 1⁄2- to 1-inch.
Damage to your Lawn
Warm season grasses like St. Augustine grass, bermudagrass, and zoysiagrass are often targeted by the larvae of the first two species of June beetle. Most of the damage occurs during summer and fall when the grubs are small and situated shallowly in the soil. The large larvae of the green June beetle can harm plant roots simply as a result of their burrowing in the soil. Diseases like Take-all Root Rot are often mistaken for grub damage. Timing is the first way to distinguish between the two: TARR damage will show up in spring and early summer, while grub damage appears mid-summer through fall. Roots of TARR infected grass will also appear rotted.
Do You Have an Infestation?
If you think you might have a grub infestation, you’ll first need to examine several areas of landscape by digging up 4- to 5-inch sections of soil. Count the number of grubs you find. If you discover more than five grubs per square foot, then you may need to treat your landscape.
It’s common to find at least a few grubs in landscape beds, especially foundation plantings, where higher levels of organic matter are typically present. These grubs generally don’t do much damage to your plants. By keeping soil healthy, bioactive and rich in organic matter, you can discourage grubs from feeding on plant roots.
Do you need chemicals treatments?
A grub infestation doesn’t require chemical treatments. We successfully use organic treatments, such as beneficial nematodes, to significantly reduce grub populations in lawns and landscapes. Beneficial nematodes are predatory, microscopic organisms applied to the soil that feed on the larvae of insects such as grubs, fire ants, and fleas. Through our Soil Building Program, we apply beneficial nematodes at optimal times each year to help prevent and control grubs naturally. (Milky spore is not an effective treatment in our Texas climate).
Applying chemical pesticides when it isn’t necessary can cause more problems than it solves.
Most chemical grub treatments persist in the soil, but are only effective at killing grubs while they are small; within their first three instars of growth. Therefore, timing is crucial when using chemicals. Often, they are applied at the wrong time in spring, which is too early to be effective. Chemical treatments must be applied within six weeks of egg-laying, or they’re ineffectual at controlling grubs. However, most of the chemical treatments on the market are also detrimental to many beneficial soil organisms, such as earthworms. Therefore, we only recommend building healthy soil and using organic treatments in order to control grubs.
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