![]() Second, milky spore affects only one species of white grubs and, in some situations, the Japanese beetle may not be the only or the predominant species. First, it can be very difficult to determine results because other microorganisms (for example, predators and pathogens) in the soil may kill Japanese beetle grubs more rapidly than milky spore. However, the use of milky spore disease is not without problems or concerns. The goal when using milky spore disease is to keep Japanese beetle levels below damaging thresholds (10 to 12 grubs per square foot). Milky spore disease is a population suppressant. It has been thought that milky spore may remain in the soil in a dormant but viable state until new infestations of grubs are present In fact, studies have demonstrated that milky spore can last 15 to 20 years in the soil. Persistence in the soil ranges from 2 to 10 years with persistence as long as 30 years if grub recycling continues. Spores bind tightly to soil particles and are normally located near the soil surface where grubs are likely to be located. In addition, infected grubs may eventually spread through the soil profile, increasing the likelihood of spreading the bacteria.īacterial spores tend to be concentrated in areas with high grub numbers. As a result, the higher the density of the grub population, the faster milky spore will become established. The density of the grub population is important in the establishment and buildup of the bacteria in the soil. ![]() Milky spore does not spread unless grubs are present in the soil. It is important to know the soil temperatures within the profile during the fall and early spring when grubs are active. In cooler climates, like the Northeast, milky spore may take longer to spread than in warmer climates. Ideal soil temperatures for spore development during grub attack are between 60° and 70 ☏ (19° and 21☌). Efficacy of the disease may vary depending on cold temperatures the spores are very cold-sensitive. Successful use of milky spore disease requires attention to environmental conditions, including temperature, moisture, soil structure, pH, and soil type. An earlier, more efficient, and consistent formulation method is now being used to produce milky spore disease. As a result, products were withdrawn from the marketplace. In the 1980s, it turned out that a different but related bacteria was actually being produced, which had little activity on Japanese beetle grubs. This is normally accomplished by injecting live grubs with bacterial spores. Nor will the bacteria develop on a dead insect, so infection needs to be induced through artificial means. Milky spore disease does not germinate well on an artificial medium or in test tubes. Milky spore disease was produced initially by collecting thousands of Japanese beetle larvae from the wild each spring and fall and bringing them to a laboratory for processing. Ingestion of the bacteria does not always produce infection as spores may pass through the gut and be discharged with fecal matter. Infested grubs eventually die, and bacterial spores disperse into the surrounding soil. The bacterial spores reproduce within the grub, eventually turning the hemolymph, the internal insect fluids, an opaque white. Japanese beetle grubs must ingest the bacteria because the primary mode of entry is through the mouth. However, all larval stages are susceptible to the bacteria. It is effective only in controlling Japanese beetle grubs it has virtually no activity on other grub species. The bacterium is applied to turfgrass as a dust. Milky spore disease is a bacterium that was initially referred to as Bacillus popillae, but it is now known as Paenibacillus popillae. It became available commercially for use on turfgrass in 1948. This bacterium was first detected in New Jersey in 1933. One of the first microbial insecticides ever registered in the United States was milky spore disease. However, there is growing interest in the use of alternative pest control materials such as beneficial nematodes and microbial-based insecticides. All these materials are highly effective in maintaining Japanese beetle grub numbers below damaging levels. The primary method of managing Japanese beetle grubs in turfgrass is with the use of insecticides such as trichlorfon (Dylox), halofenozide (Mach 2), and imidacloprid (Merit).
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