KNOTWEED. Knotweed is easily controlled with most pre-emergent herbicides. Yet, it always seems to be a problem in areas where the soil is compacted. Knotweed is the earliest germinating summer annual weed. For this reason, by the time most preemergent herbicides have been applied, knotweed has already germinated.
PREEMERGENT APPLICATIONS. Effectiveness of many preemergent herbicides for crabgrass control is determined by timing. Although many factors, including soil moisture and turf density are involved, temperature is a major key. The ideal situation is to apply a preemergent herbicide just prior to crabgrass germination. At this point in time, your herbicide will prevent germination and last longer through the growing season. Plant phenological keys are often used to time crabgrass herbicide applications. The Eastern redbud tree is an example of a phenological timing event. As the redbud tree approaches full bloom, crabgrass germinates. Obviously a drawback to this plant is that redbuds are not found in every landscape. The most common plant used is forsythia. When forsythia bloom, crabgrass will start germinating. The problem with timing based on flowering is the wide variation in air temperature that can occur. For example, in some years, forsythia may bloom multiple times based on the spring weather.
RED THREAD. Red thread (causal agent: Laetisaria fuciformis) attacks Kentucky bluegrass, fine fescue and especially perennial ryegrass during periods of heavy dew, fog and light rain. Circular to irregular shaped patches that are straw to pinkish in color. A diagnostic key is the presence of read threads (stroma) protruding from the leaf blade. In addition, pink cottony balls (small in diameter) may be present (especially on perennial ryegrass). Sometimes this heavy reddish mass of mycelium causes confusion with pink snow mold. Red thread is especially severe on slow growing, nitrogen deficient turf. Nitrogen applications may help reduce the severity of the disease, but avoid excessive nitrogen applications during the spring.
FACTS ABOUT POA ANNUA. Annual bluegrass is capable of profuse seed production from the middle spring to early summer. At mowing heights of an eighth of an inch or less, annual bluegrass incredibly produces a seedstalk. From a golfer’s point of view, seedhead production causes a disruption in the aesthetic and quality of a putting surface. However, from an agronomic view, the ability to produce seed on such a scale is amazing. Dr. Mary Lush (Lush, W.M. 1998. Journal of Applied Ecology 25: 977-988.) has studied the life cycle of annual bluegrass and has reported some interesting characteristics of annual bluegrass:
- Annual bluegrass uses 4 to 35 percent of its top growth (dry weight) for seed production. As a reference, annual plants like cereals invest 20 to 50 percent of their top growth for seed production.
- Annual seed production on a golf green is between 150,000 to 650,000 seeds per meter squared, per year (177,000 to 767,000 seeds per square yard per year). The majority of this seed would be produced from May through early August.
- Approximately 75,000 to 225,000 tillers per meter squared per year flower (88,000 to 265,000 per square yard per year).
- During the growing season, annual bluegrass tiller mortality is roughly 100,000 tillers per meter squared per month (118,000 tillers per square yard per month). Annual bluegrass has a strong potential for replacing dying tillers with new ones. Obviously, sustaining favorable growth through the season is critical in maintaining annual bluegrass turf.
- Annual bluegrass dispersal is passive. The mechanism of dispersal is by human (animal) or equipment. Annual bluegrass has followed human disturbance over all seven continents.
SOIL TEMPERATURES.
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