Grubs are frequently found feeding on the roots of turf and pasture grasses. Damage caused by white grubs initially resembles drought stress. As grub feeding continues, areas of grass begin to wilt and turn brown. In areas where their numbers exceed five to 10 per per1 sq. ft., dead patches of turf will result. Turf that has been damaged by white grubs will lift away from the soil easily because the roots have been eaten and they no longer anchor the turf to the soil. Often, skunks and other small mammals will pull back the turf in search of a meal of grubs. This damage is usually more extensive than that caused by the grubs, but can be repaired by replacing the sod, tamping or rolling the surface and watering the area.
In parts of Ontario, there are three species of white grubs, which infest lawns – European chafer, June beetle and Japanese beetle. The most common species is the European chafer, which has come from Europe and has invaded much of the southern portion of the province. It occurs along Lake Erie and has spread to areas north of London and Kitchener and east of Toronto. Another species, also imported, is the Japanese beetle and it has become established in some areas of the Niagara Peninsula and Hamilton-Wentworth region. Grubs of both species cause considerable damage to turfgrass, while the Japanese beetle adult is a serious pest of a large number of fruit and ornamental trees and shrubs. June beetles are native to North America, with approximately 152 species occurring in the United States and Canada. In Ontario there are three principal species.
Grubs of all species have soft, white, C-shaped bodies with tan or brown heads and six prominent, spiny legs. They are quite small when first hatched (3 to 4 mm long), but at maturity reach a length ranging from 2 cm (3/4 inches) for a Japanese beetle larvae to 4 cm for the June beetle grub. A healthy grub is milky white in colour.
Each species of grub has a different life history with events or specific behaviour occurring during their life cycle that may be of use in control programs.
June beetles emerge from the soil during the latter part of May and early June and fly in large numbers. They take to the air at dusk and feed and mate on the foliage of broad-leaved trees and shrubs. At daylight they seek out grassy areas or weedy places and burrow into the soil where the females lay their eggs. The eggs hatch in a few weeks and for the remainder of the summer the young grubs feed on the roots of plants and decaying organic matter. In the fall, when the temperature drops, they go down deep in the soil and remain there during the winter. In the spring, when the soil warms, they return to the surface and feed ravenously on the roots during the spring and summer. This is the second-year of their three-year life cycle. Grubs cause the greatest damage during this period of their life cycle.
In the fall, they again go deep into the soil for the winter and again return to the surface the following spring. At that time, the grubs feed for only a few weeks before pupating and changing to beetles. The beetles, however, remain inactive in the soil until the next spring before taking flight. The life cycle is then complete and a new generation is started.
White grubs require three years to complete their life cycle and while it is possible to find all stages in any one year, the majority will follow a three-year pattern. In the past, outbreaks of white grubs have occurred every third year with the most severe damage caused by second-year grubs.
European chafers emerge from turf in mid-June to mid-July, with variation across the province. At dusk, the adults congregate in large numbers to mate on trees which are isolated in large grassy areas or provide a silhouette effect near a large area of turf. Beetle activity occurs about the time hybrid-tea roses and catalpas are in full bloom. Very little feeding takes place, but the flights at dusk allow the beetles to mate. Females then return to the surrounding turfgrass areas and deposit their eggs in the soil below. The eggs require two weeks to hatch into small grubs, which feed near the surface. If moisture is not available, this process can be delayed by a couple of weeks. During periods of summer drought, grubs may remain deep in the soil where moisture is available. Once rainfall resumes, the grubs will migrate up to the soil/thatch interface to feed. By the end of September, most of the grubs are at their mature size and begin to seriously damage the turf. Cool weather does not seem to deter them, as they will remain near the surface if there is adequate moisture until frost begins to drive them down in November or December. They prefer to dig below the frost, but can withstand freezing if they cannot penetrate deeper.
In the spring they migrate to the surface when the frost leaves, even before the snow melts. Feeding at this time can cause damage with the grubs consuming the shallow roots and crowns. By mid- to late May they cease feeding and begin to transform into the resting pupal stage. They remain in this state until they emerge as adults in mid- to late June, completing a one-year life cycle. A flight of adults at dusk on warm evenings in June or early July may result in damage to surrounding turfgrass in the fall. Skunk damage to turf in the spring and fall as well as flocks of starlings or blackbirds feeding on turfgrass areas are signs of grub infestations.
Japanese beetles emerge in early July and actively feed on a wide variety of trees and shrubs, including foliage, flowers and fruit for 30 to 45 days. After mating female beetles enter the soil under turf to a depth of 3 to 5 cm and deposit one to four eggs in one location. Females may lay as many as 60 eggs in their lifetime. Larvae hatch in two weeks and begin feeding on the roots in the upper 10 cm of soil. During drier periods, eggs may be killed and surviving larvae will be found deeper in the soil. In late summer and early fall, the grubs reach maturity and are generally found near the surface. As the soil temperature drops below 15°C (60°F), the grubs migrate downward and will remain below the frost line during winter. When the soil temperature begins to warm above 15°C in the spring, the grubs will approach the surface again to feed.
Japanese beetle grubs are much more sensitive to soil temperature changes than European chafers and normally have migrated downward by mid- to late October and do not return to the surface until late April or May. Clues to infestations are the presence of adults on shrubbery, flowers, or fruit and damage to turf by skunks or other small mammals in the spring and fall. Traps containing a combination of both female attractants (pheromones) and a floral lure may be used to capture male beetles. Both attractants must be used together and traps should be placed every 2000 m2 (1 acre) from late June to mid-September.
In recent years, chinch bug damage to lawns has increased in Ontario. The first chinch bug damage was reported in 1971. Since then they have become a common home lawn problem in many provinces. Many lawns are only partially damaged, but in severe cases the entire lawn will be damaged to such an extent that it must be entirely renovated.
Chinch bugs have piercing mouth parts. They suck the sap from the crown and stems of turfgrass plants. Populations of chinch bugs tend to be aggregated which initially results in localized dead patches. These dead areas are brown, irregular sunken patches, which can coalesce into larger dead areas . All common turfgrass species in Ontario are susceptible to chinch bug feeding but some varieties may be more susceptible to chinch bug injury. However, research has shown that turf cultivars containing high levels of endophytic fungi show some resistance to chinch bug feeding.
There are several species of chinch bug, but the one causing damage to lawns in Ontario is the hairy chinch bug. This insect is quite small, the adults are 4 mm in length .
The immature nymphs are bright red in colour when they first hatch, and begin to darken from brick red to grey/brown when they are nearly mature.
The immature nymphs have a characteristic white band across their abdomen which is eventually covered by the enlarging wings as the insects become larger and mature.
If lawns are suspected of having chinch bug infestations, this can be accurately determined using the following method:
- obtain a large can which has a circular area of approximately 200 centimetres
- cut out the bottom and the top to form a cylinder and force this into the turf fill the cylinder with water, the chinch bugs will soon float to the surface where they can be seen
The adult chinch bug spends the winter congregated under trees and shrubs and on the edges of lawns under hedges and in flower beds. As the temperatures become warmer in the spring, the adults move into the lawn and begin depositing eggs. As many as 20 eggs per female may be laid during May and June. Light damage does not usually appear until the middle of July. In most of Ontario severe damage is not noticed until August after the occurrence of several weeks of hot, dry weather. In lawns with no visible damage, the best time to check for chinch bug infestations is the second to third week of July. This will vary from year to year and from one locality to another. At this time, most eggs have hatched and the initial stages of damage are minimal.