When determining the timing of any control, be aware that evidence of moles is not necessarily a sign of grubs. The greater the number of grubs, the faster the disease will spread. Milky spore cannot be effective if there are too few grubs to spread the disease. It is much easier to apply but must be applied three times a year for two years as opposed to just once. Some newer formulations allow for application through a drop spreader. Milky spore powder is typically applied in a matrix pattern, a teaspoonful every four feet in rows four feet apart. If milky spore powder is applied to frozen ground, it may wash away during heavy rainfall. The spore is a dormant organism, and it only becomes active after a warm Japanese beetle larva has ingested it (larvae are cold blooded and may not activate a Bp spore if ingested by a grub that’s not warm enough). Timing with milky spore is not as important. Applying after rain or irrigation is best. Nematodes move through soil moisture and can migrate easily into a moist soil. They don’t usually need to be watered in but should not be introduced to a dry soil. Applying them on a cloudy day is fine and during rain is ideal. Nematodes should be applied early morning or early evening to avoid direct sunlight. In fact, timing is important regardless of the control you choose. For this strategy to work, the repellent must be applied before the beetles arrive, which requires some knowledge of the pest’s life cycle. Products containing garlic, pepper, or other repelling extracts can persuade adult beetles to oviposition elsewhere. The Importance of TimingĪnother grub control strategy that may work is to repel adult beetles before they lay eggs. Heterorhabditis are asexual and one can multiply by itself. are sexual and at least two need to enter a larvae to multiply.

They can still infect and kill larvae but cannot multiply. If, however, they are exposed to direct sunlight for more than a few minutes during the application phase, the UV light will sterilize them. Nematodes multiply inside the grub host from one or two to hundreds of thousands in just a few weeks.

When larvae are infected with Heterorhabditis, they usually turn shades of red. These nematodes can be found much deeper in the soil than Steinernema and may be more appropriate for controlling scarab larvae. are typically hunters that can track grubs by following trails of exudates. Steinernema spp., for example, are typically an ambushing strain and dwell closer to the soil’s surface than Heterorhabditis spp. The species of nematode applied is also an important consideration. If nematodes are applied only once and hot dry conditions persist after application, they may have to be re-applied at some point. There is no data available, however, that suggests how long they will last. If nematodes are applied once or twice per year, there is evidence that their populations begin to sustain themselves after two to three years. Nematodes may be the only natural option available to you. There are species of Bacillus bacteria that cause milky disease in other scarab larvae, but they are not currently available. If the grubs in your lawn are identified as chafers or any species other than Japanese beetle larvae, Bp probably won’t be effective.

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