Broadleaf Weeds, Frost Injury and Disease Highlights

July 7, 2015

April 22, 2010, Current Problems Noted on Lawns:

Lawns may still have damaged areas from snow removal equipment or other damage experienced during the winter months. In many cases, these areas need to be renovated which may include filling in depressed areas and reseeding. The key item to remember in these situations is that if a crabgrass material is applied to prevent the germination of crabgrass seed, some materials will also interfere with the germination and development of the desired grass seed. So areas that are being renovated and seeded should not receive many of the pre-emergence herbicides products.

Broadleaf Weed Control

During this period with abundant dandelions in bloom, many applications of broadleaf weed control are being made. Several factors should be kept in mind.  bygl 1 4-29-10

Avoid non-target plants. When making applications care should be taken around flowers and plants that are starting to grow, such as perennials and newly planted annuals. Drift or direct contact from herbicides can be injurious to these new, tender, rapidly growing plants.   bygl 2 4-29-10

Heavy frost, close to the day of broadleaf weed applications, will often result in reduced herbicide efficacy. The frost may affect the weed cuticle and reduce the amount of herbicide absorbed resulting in reduced broadleaf weed control efficacy. Weeds may curl but recover over time.

Frost injuries on tall fescues

This has been noted in various parts of the state. Often this appears as a white or light yellow band across the leaf blade. Tissue that is in the bud stage is sensitive to cold temperatures and these result in damaging the chlorophyll which result in these white or light colored bands across leaf blades. Leaf tip dieback has also been noted. This is a temporary situation and with several mowings the lawns will appear normal again.

Disease Highlights

At this time most lawns have shown significant or full recovery from snow mold damage experienced past winter. The next disease that appears to be emerging is leaf spot. Leaf spots are most prevalent on common Kentucky bluegrass lawns. During early stages, they pose minimal injury or problems on turf. However, if lawns are known to be susceptible to leaf spots and the disease progresses and becomes severe in the spring period, often this will result in severe decline from a condition known as melting out later in the year.

The melting-out stage usually occurs as temperatures increase in early summer. Lawns with this condition should be properly maintained with good mowing practices and adequate fertilizer, but not excessive fertilizer. If there are known cases of severe disease problems year after year, an application of fungicide may be considered to manage the disease. For specific fungicide recommendations, refer to OSU Extension bulletin L-187 “Management of Turfgrass Pests”. Go to the section on disease management (table 2) for specific recommendations for fungicides for leaf spot. The 2010 version of this bulletin can be found under publications on this web site.