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Q

If Japanese beetle grubs eat my tall fescue roots, why don't they eat the dandelions in my lawn? — via e-mail

A

Japanese beetle grubs don't like dandelions. In fact, they won't eat dandelions even if there is nothing else to eat. A study from The Ohio State University recently proved this. They grew pots of dandelion and dandelion mixed with either perennial rye or tall fescue and infested them with the grubs. They found that grubs in pots with only dandelion, looked starved, had very low dry weights and did not affect the health of dandelions at all. In pots with only tall fescue or perennial rye, grubs reduced the number of grass tillers and above and below-ground biomass. However, in a mixed stand of fescue and dandelions, the presence of grubs actually increased the number of dandelion leaves and biomass, while reducing the number of tillers on fescue.

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I've heard that there can be problems if a phosphorus fertilizer is put down at the same time as lime. Is there any truth to that?

A

The results of applying phosphorus and lime together are not so much a problem as a management issue. Lime is calcium carbonate, magnesium carbonate or a combination of calcium and magnesium carbonate. When phosphorus comes in contact with either calcium or magnesium they react to become a solid (a rock, you might say). For the plants to use phosphorus (or any other nutrient), it has to be dissolved in the soil water, so over the short-term the applied phosphorus is not available for plant uptake. The good news is the situation is not permanent. After a time, some of the phosphorus will dissolve and become available. How you manage the two applications depends on your situation. If your plants are in immediate need of phosphorus, apply P fertilizer without lime. Work the fertilizer into the soil around the plants, if possible, or in a turf situation, apply after core aerating or powerraking. Some of the phosphorus will react with calcium and magnesium already in the soil, but not as much as when applied with lime. If needed, you can apply lime in three to four weeks. For less “urgent” situations, where you are building up phosphorus levels in the soil and need to raise the pH, the two can be applied together. Over time, the calcium and phosphorus will reach equilibrium and the phosphorus will continuously, slowly dissolve and become available for the plants.

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