University of Connecticut

White Grub Control

 

The number one insect problem that is responsible for killing turfgrass in the northeast is the damage created by the larva of many of the scarabaeid (beetles) pests. These larvae are commonly known as white grubs. White grub damage can be devastating to home lawns, athletic fields, parks, cemeteries, golf courses and other turfgrass areas. Damage typically shows up in September and is evident through October. In the spring as soil temperatures warm, grubs will resume feeding. Damage caused by white grubs is the result of the grubs eating the root system of the turf. Symptoms of white grub damage begin with the turf turning a bluish color (wilting), followed by the death of the turfgrass stand. Dead turf can be easily pulled up or rolled back, often exposing the grubs. (fig. 1 and 2).    

      

In New England there are many beetles that produce white grubs, five of the most likely to create lawn damage are the larvae of the: Japanese beetle, oriental beetle, northern masked chafer, European chafer, and the Asiatic garden beetle. To properly control, scout, and monitor for white grubs it is necessary to understand the life cycles of these pests. All of the above mentioned beetles have one generation per year. Generally the life cycles of these beetles are very similar. In Connecticut the adult beetles usually emerge from late June through July depending on the species. After emergence the beetles mate and lay eggs throughout July and August.  Newly hatched white grubs may be seen in late July through early August. White grubs are C shaped (figure 3) and undergo three stages of development (instars). Grubs start feeding on the root systems of grass immediately after hatching. By October many of the grubs are in the third instar of development. It is in this third stage that root consumption is at its highest level and damage rapidly occurs. As cold weather and winter approaches grubs will move downward into the soil and overwinter in their larval form. As spring approaches and soil temperatures rise, grubs will resurface to the rootzone and resume eating. In late May through June grubs stop eating and begin the transformation (pupate) into adult beetles. At this point the life cycle repeats (figure 4).

           

Scouting and Monitoring

To determine if a grub problem is imminent a homeowner can utilize a variety of techniques that may indicate a potential for white grub infestations. Records can be kept of locations with a past history of problems. Grub damage is usually most severe on lawns with south facing slopes and in full sunlight. Monitoring can be performed for both the adult and larval forms of the beetles.

Adult monitoring

 Begin looking for adults in late June through early August. Often adult beetles can be seen flying at dusk or seen on trees and shrubs. For example, the adult Japanese beetle can be found eating the foliage on many species of trees and shrubs including maple trees, crab apples, roses, and potentilla. The oriental beetle can often be found in swimming pool skimmers or resting on plants and shrubs. If adults are present, it is a good indication that the females may lay their eggs in the lawn nearby.  The use of sex pheromone traps (Japanese beetle traps) in gardens to attract adult beetles is not recommended. Pheromone traps will attract beetles from distances of up to several miles. Severe grub damage is often found in close proximity to where pheromone traps have been placed.

 

White grub monitoring

Monitoring for white grubs can begin in mid-August and continue through mid- October, resuming again in the following April and May. To sample and scout for grubs, use a pointed shovel and cut the turf on three sides. Cuts can be from 6 to 12 inches in length with a depth of approximately 3 inches. Roll the sod back and loosen the soil from the thatch and the root system and count the number of grubs present. It is a good idea to sample multiple locations in your lawn. Grubs may be present in one area while absent in another. Five to ten grubs per square foot would be the baseline for threshold levels. Tolerable threshold levels can be dependent on a variety of circumstances including the size of the grub, the health and vigor of the turfgrass and soil moisture.1 Turf growing under drought stress has a lower threshold level than turf that is growing with adequate moisture levels. It is important to point out that while grub damage may not be evident in a wet fall, it can show up in a dry spring.

Controlling White Grubs

Biological Control

There are a number of natural enemies including predators such as wasps, beetles and ants that control white grubs. Two biological control products that are presently available to the consumer are milky spore disease and parasitic nematodes. In New England, due to cooler soil temperatures, milky spore disease has not been very successful in controlling white grubs. However, a higher degree of success has been reported in the Mid-Atlantic States with this product. Another drawback to milky spore disease is that it is specific to Japanese beetle larva and is not effective on other species of beetles. An alternative biological control product that is presently on the market for white grub control is parasitic nematodes. Reports on the effectiveness of nematodes have been mixed. If choosing parasitic nematodes for control, it is important to purchase the nematodes fresh. Often nematodes will be shipped directly to the consumer. Upon receiving nematodes it is necessary to apply them right away. Nematodes must be kept moist. A good time to apply them would be in a light rain or a cloudy day followed with irrigation.

             

Presently, researchers are investigating the effectiveness of the fungal pathogen Metarhizium on the mortality of several species of white grub larva. However, more research is needed to determine the effectiveness of this fungus as a control method for white grubs.

Chemical Control

Chemical control for white grubs can be either curative or preventative. Curative control can be accomplished with a product such as the organophosphate, triclorfon (Dylox®). Organophosphates such as Diazinon® and Dursban® are no longer available for grub control in home lawns. There are a few disadvantage of a curative method of control. One disadvantage would be that if the homeowner or turf manager neglects to scout or monitor the site, grubs will go unnoticed and damage may not be caught in time resulting in severe turfgrass loss. Another disadvantage to curative control is that the insecticide used for control often has to be applied at higher rates to control mature grubs. If choosing a curative method, a strategy that should be used to improve pesticide performance would be to water before and after the insecticide is applied with at least 1/2" of water. Grubs will move to the surface with a "pre-watering" and the product moves to the grub with a "post watering".

Preventative control can be accomplished with applications products such as, halofenozide (Mach 2®), imidacloprid (Merit®), or clothianidin(Arena®). These products are extremely effective in controlling white grubs. Proper timing should be prior to egg hatch (figure 4). Recommendation for timing of applications with these products is June through July 15th. A target date of June 15th would be best. Preventative applications should be watered in with at least 1/2" of water. The advantages of preventative applications are that you greatly reduce the possibility of grub damage to the lawn. Also, preventative products tend to be more environmentally friendly than curative applications. The disadvantage of preventative insecticide applications is that a problem is anticipated and an insecticide is being applied whether it is warranted or not.

By: Steven Rackliffe Extension Instructor Turfgrass Science

 

Photo 3 -  Rackliffe

 

1 Turfrass Nutrient and Integrated Pest Management Manual. University of Connecticut College of Agriculture and Natural Resources. 2 For more information refer to the UConn IPM Web Site http://www.hort.uconn.edu/ipm/index.html

 

Information on our site was developed for conditions in the Northeast. Use in other geographical areas may be inappropriate.

The information in this material is for educational purposes. The recommendations contained are based on the best available knowledge at the time of printing. Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. The Cooperative Extension system does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available. All agrochemicals/pesticides listed are registered for suggested uses in accordance with federal and Connecticut state laws and regulations as of the date of printing. If the information does not agree with current labeling, follow the label instructions. The label is the law. Warning! Agrochemicals/pesticides are dangerous. Read and follow all instructions and safety precautions on labels. Carefully handle and store agrochemicals/pesticides in originally labeled containers immediately in a safe manner and place. Contact the Connecticut Department of Environmental Protection for current regulations. The user of this information assumes all risks for personal injury or property damage. Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Kirklyn M. Kerr, Director, Cooperative Extension System, The University of Connecticut, Storrs. The Connecticut Cooperative Extension System offers its programs to persons regardless of race, color, national origin, sex, age or disability and is an equal opportunity employer.