There's a better way than lawn weed-and-feed products
"Fielding Questions" columnist Don Kinzler also advises readers on how to treat a sick pine shrub and what to do about lawn bumps caused by night crawlers.
Q: I have a pine shrub that is sick. It’s shedding needles and the needles have white spots on them. Do you know the best way to treat this? I wasn’t sure if I should spray an insecticide or a fungicide. — Kimberly K.
A: The white spots on the needles are the insect called pine needle scale. The insects hide under the white, waxy coating, where they suck the needle’s sap. In May they begin what is called the "crawler stage" in which they begin moving.
There are two methods of control. Apply a product called horticultural oil now, which is sold at garden centers, following label directions.
Then, when the insects begin their crawler stage and begin moving on your mugo pine shrub, apply the insecticide Sevin, or another insecticide labeled for pine needle scale. This is the most successful stage to control this insect, and often occurs in May approximately the time lilacs are blooming in the area.
It might be necessary to follow these procedures again next year to completely reduce the insects.
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Q: When I mow our lawn, it’s like going on a roller coaster up and down. How do I get rid of the night crawlers that are causing this? I’m going to have power raking done, which has not been done for quite a few years, and also aerating. — Patty K.
A: Walking across a lawn affected by night crawlers is like walking across a field of golf balls. The bumps are called "worm castings." Night crawlers and earthworms are considered protected species, and there are no pesticides labeled for legal control. Efforts must be aimed at minimizing their effects.
Bumps caused by the night crawlers can be leveled by light power raking. Core aeration can also help. Both operations help, at least temporarily. As lawns dry, worms tend to move deeper into the soil. When watering lawns, water deeply and less often to encourage worms to move deeper.
Although the bumps are annoying, the presence of earthworms in the lawn indicates a healthy soil environment. Earthworms and night crawlers aid in the breakdown of thatch and other organic matter and create tunnels, which promote water infiltration, oxygen movement, microbial activity and deeper grass rooting.
Rich in nutrients, their castings are a combination of minerals moved from deep in the soil and from their main food sources, which are grass clippings and thatch.
Q: When is the best time to put weed-and-feed products on the lawn? — Curt W.
A: I’d like to suggest a better way. Granular weed-and-feed products that combine fertilizer and herbicide are often not the most effective for either fertilizing or weed control. Most research universities strongly recommend alternative methods, instead of applying these granules.
Most lawns aren’t a carpet of weeds, so applying a blanket of herbicide granules to the entire lawn is usually unnecessary, wastes product and money, and increases the possibility of collateral damage to trees, shrubs, flowers and vegetable gardens.
Some weed-and-feed product labels indicate that granules must be applied to a damp lawn so the product sticks to the leaves of actively growing weeds. Such products don’t prevent weeds — they only kill weeds already growing, if the little granules stick to the leaves long enough. Labels must be followed exactly.
The large number of emails I receive about disappointing weed-and-feed results prompts me to suggest an alternative. Fertilize the lawn in a separate procedure in May when the grass is green and actively growing. Then, if weeds appear in May or early June, apply a liquid lawn weed herbicide, spot-spraying only the weeds in a targeted application, instead of wasting spray where there are no weeds. For hard-to-control weeds, apply herbicides both in early summer and again in September.
If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at email@example.com. Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.