Leaf spot and crabgrass
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EmailEditor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
High
temperatures, lack of rain in many places and high humidity, have put
the hurt on turfgrass in many areas across the state. The early season
sightings of diseases on lawns, such as red thread, have now been
replaced by sightings of leaf spot. Leaf spot is generally active during
warm summer weather. The symptoms are water-soaked spots on leaf blades
that turn purple/brown/black. Turf infested with leaf spot will appear
yellowish to reddish-brown, and a general thinning of the turf with no
distinct pattern may occur if conditions are ideal. The best management
strategy to alleviate damage is to irrigate lightly and frequently,
preferably around mid-day (noon) and apply a light fertilizer
application (0.5 lb. N/1000 ft.2 or less). Avoid irrigating at night
because it results in the leaf blades remaining moist throughout the
night and, therefore, more susceptible to disease infection. Another
cultural management option is to raise the mowing height to reduce
turfgrass stress. Fungicide applications to home lawns are generally not
recommended, as they can be expensive and often give unpredictable
results.
One grass that is currently thriving in the summer heat is crabgrass. In
most areas, crabgrass is really cutting loose and control with
Dimension, active ingrediant dithiopyr, which has early postemergence
activity is probably past. Probably the most common postemergence
crabgrass killer in the homeowner market contains the active ingredient
MSMA, usually sold as a product that has the phrase “crabgrass killer”
somewhere in the title. If you are going to use products that contain
MSMA, beware that at high temperatures (greater than 80º F) these
products might burn the turf a little, so you might need to decide how
important it is for you to eliminate the crabgrass from the turf.
Remember that sometimes green is better than brown even if it is a weed!
Another active ingredient that is now available in homeowner products
and is very effective for postemergence control of crabgrass is
quinclorac. Please remember that when using any pesticide to read and
follow all label directions.
