Taming Turf Pests

Insect pests are thorns in the sides of lawn care companies. You can provide perfect fertility and weed control and still end up terminated by a customer because of insect damage to their lawn.

The greatest pest dilemma is in deciding when to use insecticides. Overuse of insecticides to compensate for poor cultural practices can lead to secondary pest problems arising from the loss of earthworms, soil compaction, a build-up in thatch and the loss of insect predators and parasites.

A lawn is a living, breathing web of microbes, plants and insects that need to be considered when planning the turf care program. Pesticide applications can have an effect on the balance of decomposers, predators and pests for as long as six months. Even so, preventive pesticide applications are useful for lawns with chronic insect pest infestations, and spot treatments are necessary for unexpected infestations reported during the growing season.

The best tools we have for tackling turf pests are a knowledge of pest management strategies that complement judicious pesticide applications, host plant resistance and scouting and the use of the most selective pesticides available for the pest problem in question.

Recent research has yielded some new approaches to pest management, and industry has developed several new products that are more selective yet highly effective.

TURF MANAGEMENT PRACTICES. The most important cultural prac-tice that prevents turf injury from insects is irrigation. Three key pests of home lawns — billbugs, chinch bugs and grubs — are not nearly as damaging to irrigated lawns as to water-stressed lawns.

Frequent watering increases the activity of Beauveria, a fungal disease of chinch bugs and billbugs, and allows turf to recover from the root-pruning injury caused by grubs. Turf injury from grubs is most severe when lawns are water-stressed in September or October, a time when grubs are actively feeding on turf roots. Keeping lawns irrigated during drought-type weather in the fall is very effective for preventing grub injury.

If a homeowner balks at the cost of irrigation, you can explain to them that in most cities the cost of 1 inch of irrigation per week or 1/10 inch per day is approximately $1 per day for an average size lawn (10,000 square feet). Daily irrigation is particularly effective in preventing damage from European chafer grubs because it actually reduces the number of grubs found in turf. European chafer is the most damaging of all grubs to home lawns in its range (New York, Pennsylvania, Ohio and Michigan).

This is not the case for Japanese beetle grubs. They survive better in irrigated turf than in dry turf. That is why a golf course in New York or Michigan may have Japanese beetle grubs in the fairway and European chafer grubs in the rough. Even though Japanese beetle grubs survive better in irrigated turf, irrigation still reduces the amount of damage sustained by the infested turf.

Another way to prevent pest problems is to avoid overusing insecticides or to use selective insecticides instead of broad spectrum insecticides (Table 1). Broad spectrum insecticides eliminate predators that keep chinch bugs, webworms and cutworms under control. It also causes a build-up of thatch, and lawns with a thick thatch layer are most likely to harbor chinch bugs.

NEW STRATEGIES. A new resource is now available for the identification and management of turf insects. The Handbook of Turfgrass Insect Pests, edited by Brandenburg and Villani, is available from the Entomological Society of America for $35 (9301 Annapolis Road, Lanham, MD 20706-3115, phone: 301/731-4535). This book has color photographs of all the insect pests found on turf, range maps to show where they are found, a description of their life cycles and management strategies. It should be on the shelf of every lawn care professional.

Homeowners can help themselves by adjusting the mowing height of their mowers. It has been well established that turf maintained at 2½ to 3 inches is much healthier than 1-inch turf. Now recent studies have shown that increasing the mowing height may also increase predator activity as well as turf vigor. Tell homeowners to crank-up their mowers to the highest level — 3 inches is not too high.

Insect resistance can be “built in” when establishing a lawn if a turf cultivar is chosen that contains endophytes (fungi that live inside grass plants and produce substances toxic to some insects). Some perennial ryegrass, tall fescue and fine fescue cultivars with endophytes are resistant to chinch bugs, greenbug (an aphid that feeds on turf), cutworms and webworms.

Unfortunately, they are not resistant to grubs. Look for seed that is marked as endophyte enhanced.

NEW PRODUCTS. Astro™ from FMC is a py-rethroid insecticide, active against a broad range of insects in turf. According to the label, it can be applied to lawns and grass nurseries. Although Astro is broad spectrum and highly toxic to predators and parasites, it is not as damaging to earthworms as other products on the market today because it tends to bind to organic matter and not move into the soil very well.

For the same reason, Astro is not the best product to use for grubs. The best fit for Astro is for use against webworms, cutworms and chinch bugs. Astro will probably be used more extensively for tree and shrub insects than for turf. Astro is marked with a “caution” on the label, has a 24-hour re-entry interval and can not be used within 25 feet of streams or ponds.

Scimitar™ and Battle™ are formulations of a new generation pyrethroid insecticide. They will be very useful against chinch bugs, webworms, cutworms and other surface insects. Scimitar and Battle are also less likely to affect earthworm populations as other broad spectrum insecticides. They are not very effective against grubs and should not be used near streams or ponds because of their toxicity to fish. Scimitar and Battle will also be useful for many tree and shrub pests.

A new insecticide that has been used extensively in the last two years for grub control is Merit™. Merit is a nicotinyl insecticide, similar in structure to nicotine. It is highly effective against grubs when applied at the time of egg laying or young larval development. In Ohio, late June is the optimum time to apply Merit for Japanese beetle, although April and May applications are also effective for control of eggs and young larvae in July and August. Merit is not very effective against large grubs when applied from late September to May.

Other than price and timing of applications, Merit is an ideal product for grubs. It is fairly specific for grubs, long lasting and is a relatively safe product to use. The biggest problem with Merit is that it must be applied before you can sample for grubs to see how many are there. This limits the use of Merit for IPM programs in areas with low numbers of grubs, where lawns are sampled to see if grubs are above or below threshold levels before treating. However, Merit is an excellent choice for sites with a chronic grub problem.

PRODUCTS UNDER DEVELOPMENT. The chemical manufacturing industry is working on some excellent new products. RohMid, a Rohm & Haas and American Cyanamid joint venture, is expecting a label for MACH 2™ in 1997. MACH 2 is an insect growth regulator that interferes with molting. It is very safe to use and highly effective against grubs, cutworms, armyworms and webworms. MACH 2 has the added advantage of being almost nontoxic to predators, parasites and decomposers.

Another new insect control product, spinosad, is being developed by DowElanco under the trademark Conserve™ SC with hopes of reaching the market in 1997. The active ingredient in Conserve is made by culturing a specific bacterium and extracting the spinosad made by the bacteria. It is fairly safe and specific to certain groups of insects, leaving predators unharmed. For turf, Conserve will be particularly useful against cutworms and webworms. It will also be labeled for many ornamental insect pests.

Nematode products have not been a reliable method of grub control for lawn care companies thus far. One of the most effective nematodes for grubs, Heterorhabditis sp., is being developed by Ecogen as Cruiser™. They are hoping to increase production and start marketing in 1997.

Cruiser is more effective than Steinernema carpocapsae (Vector™) for grubs and is reported to have a better shelf life. Cruiser is another potential product for controlling grubs without eliminating beneficials.

Although Vector (Biosys) nematodes are not consistent for grub control, they are still a good choice for cutworms, webworms and billbug larvae.

Another microbial insecticide now under development is M-Press™ (Bacillus thurin-giensis japonensis, ‘buibui’ strain). In testing, M-Press has worked well against Japanese beetle and green June beetle. Mycogen will have an Experimental Use Permit for M-Press sometime in 1997. M-Press could become a key product for grub control because like most Bt products, M-Press is very specific for the targeted pest and almost completely harmless to predators, parasites, earthworms and mammals.

CHOOSING A SELECTIVE PRODUCT. When a pest problem surfaces despite your preventive strategies, scout the lawn and treat only the infested area with an insecticide that is the least harmful to beneficial insects and earthworms, yet still effective.

At this time, Merit is the best choice for lawns that suffer grub injury every year. Merit should be applied in June or July to prevent grub injury in the fall. Soon, MACH 2 will also be available for tough grub problems. Similar to Merit, MACH 2 will need to be applied in June or July to provide satisfactory fall grub control.

A different approach is necessary for marginal grub infestations. For grub problems that surface in September or October, sample to determine how many grubs are present. If lawns or portions of lawns average more than five per square foot (nonirrigated) or 15 per square foot (irrigated), spot treat with products that do not persist for more than a few weeks, like Sevin™ or Dylox™. Sevin and Dylox are both pH sensitive and should not be used when the pH of the irrigation water is above 7.5.

In the future you may be able to choose selective products like M-Press or Cruiser for grub control.

For cutworms and webworms, Vector and neem products are effective and relatively harmless to predators and earthworms. When MACH 2 and Conserve become available, they will be even more effective than nematodes or neem for cutworm and webworm control, yet still harmless to most beneficials.

The author is professor of entomology at Michigan State University, East Lansing.