In this article you will learn how to identify signs of infestation, treat existing lawn grubs, and prevent future grubs from further damaging your clients’ lawns.
White grubs are serious pests and if left untreated can cause extensive damage to your lawn in a short amount of time. If grub damage has occurred, major repair such as removing the damaged turf and re-seeding may be needed, which is time consuming and expensive. Read on to learn how to identify signs of infestation, treat, and prevent lawn grubs.
Identify Signs of Grub Infestation:
First, it is important to understand that white grubs are the larvae of several different Scarab Beetles. See examples below for reference.
White Grubs have brown heads with soft, gray, or white c shaped bodies and live in the soil below the grass. White grub damage is usually most evident in August and September.
Early Grub Damage Symptoms Include:
- Gradual thinning of grass
- Yellowing of grass blades
- Scattered, irregular dead patches
The damage will continue to grow if left untreated, meaning the dead patches may increase in size. Healthy turf areas may look like they are wilting. When walking over the infested area, it may feel spongy. Another indication that white grubs may be present are moles, skunks, and raccoons as these creatures feed on grubs. If you are noticing damage from them, you most likely have a grub problem.
Soil sampling and early recognition of a grub problem can prevent turf loss and costly renovation.
Test Your Lawn for Grubs:
- Pull Test: If the turf is heavily grub-damaged, it will not be well anchored to the ground. Grub infested turf can be pulled easily from the soil by hand. If the grass you are testing is still anchored to the soil, the problem is probably related to other causes. This can include: dry spots, dog urine damage, fertilizer burn, or disease.
If the turf does pull up easily, inspect the top 1 to 2 inches of soil for the white larvae. Soil sampling and early recognition of a grub problem can prevent turf loss and costly renovation.
- Shovel Test: To determine the extent of the infestation, sample the turf in several locations throughout the lawn. In each location, cut out one square-foot piece of turf and closely inspect the roots and soil for white grubs. The depth should be around 6 to 8 inches.
After the sample is inspected, replace and tamp back into place. Water it well to start the regrowth process.
Note: The presence of a few white grubs per square foot on lawns is normal and not a cause for concern. Healthy turf can easily outgrow the root loss caused by a small number of grubs. However, if there is an average of ten or more grubs per sample this indicates a need for treatment; especially if the lawn is under heat and drought stress. When the weather is cooler and soil moisture adequate, turf can tolerate higher grub activity without being damaged.
White Grub Life Cycle:
To accurately treat and prevent grubs, it is important to understand their life cycle. The following information and the infographic below are based upon the life cycle of a Japanese Beetle. From January through March grubs are deep in the soil in their winter cells. Many grubs die from the freezing temperatures over winter, but it is possible for them to survive and start eating your grass roots during the spring. In the months of March, April and May grubs are closer to the surface and are larger as they get closer to becoming a beetle. In June and July the beetles emerge from the soil. In July and August the adult beetles descend into the soil to lay their eggs. As shown in the image below, it is best to apply grub control in July and August in order to prevent any eggs that have been laid from hatching. In September and October the eggs hatch and the grubs immediately start feeding on grass roots, which is why grub damage is most prevalent during these months. Then finally in November, the grubs descend further into the soil to prepare for winter.
Treating a lawn for grubs may seem overwhelming at first, but it does not have to be complicated. Jonathan Green has five great professional options for controlling grubs in your client’s lawns. See below for more details on each product:
- Two-part premium formula contains Merit® to kills grubs and lambda-cyhalothrin to kill insects.
- Preventative and Curative (1st and 2nd instar)
- Kills grubs deep down in the soil where the lawn roots are growing.
- Also controls: ants, fleas, crickets, chinch bugs, earwigs, and ticks.
- Apply in July or August when the lawn is dry and then irrigate the lawn lightly with ¼ to ½ inch of water immediately after to activate the product.
- Dylox 6.2
- Granular insecticide contains 6.2% Trichlorofhon and provides rapid grub control in as little as 24 hours.
- Curative only, works by both contact and ingestion.
- Kills second and third instar grubs on contact.
- Also controls: annual bluegrass weevils (larvae & adults), armyworms, chinch bugs, cutworms, and sod webworms.
- Most often applied in late summer and fall to target second and third instar grubs or in early spring for overwintering grubs.
- Fertilizer + Imi-Lambda
- NPK ratio: 12-0-0
- Preventative and Curative (1st and 2nd instar)
- Controls insects and fertilizes lawns in one step.
- Contains 20% slow-release nitrogen.
- Also kills: grubs, ants, armyworms, billbugs, chinch bugs, sod webworms, and several other listed insects.
- Apply in the summer time from late June to late August
- Organic Grub Control
- Preventative and Curative (1st, 2nd and 3rd instar)
- Family-friendly- allowing children and pets to get back in the yard immediately after application.
- When to apply:
- Springtime (shortly after the ground has thawed): controls grubs coming to the surface of your lawn to feed on roots.
- Middle to late summer: will target newly hatched grubs.
- Fall: for maximum protection, apply to help minimize over-wintering grubs and to start your next spring off strong.
- Contains 76.5% Cedarwood oil that immediately triggers the erosion of the exoskeleton of insect eggs and larvae, which results in their dehydration, rendering their pre-life status DBH (dead before hatch)
- Preventative with a 3-4 week residual
- Organic option that focuses on the larval stage insect in the soil like white grubs.
- Stifles grub’s ability to detect food, mates, and to reproduce.
- Non-toxic to all humans and pets.
To help keep a healthy lawn all season long, preventative maintenance is key. Applying Grub & Insect Control at the end of June or early July will help ensure your lawn is protected against grubs once fall arrives.
In addition, poor soil is often the problem in growing a great lawn. Jonathan Green Turf Pro has two great soil food products to balance pH and loosen compaction. Mag-I-Cal Soil Food for Lawns in Acidic Soil rapidly adjusts soil pH and stimulates soil microbial life. Love Your Soil loosens hard and compacted soil to improve porosity, making it easy for air and water to penetrate the soil. These products help strengthen and deepen roots and promote grass growth by increasing biological activity and releasing nutrients trapped in the soil.
Having a healthy lawn is crucial to prevent damage caused by grubs, insects, fungal infections, and drought. Fertilizing properly and watering regularly will help build a strong root system to survive any potential damage. If you found this article helpful visit our Turf Professional Library!
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