LET’S SET THE RECORD STRAIGHT
There has been confusion on when to fertilize and apply herbicides to our four warm season turfgrasses (centipede, zoysia, Bermuda and St. Augustine).
FERTILIZING
Fertilize the above mentioned turfgrasses with a fertilizer recommended from a soil analysis when green growth begins in April. No nitrogenous fertilizer, the first number on the bag, should be applied before April and after August 15. Nitrogen after this date can make turf “Happy “and reluctant to become “Sleepy”, dormant, for the late fall and winter low temperatures. Winter damage may occur.
It is a green industry practice to apply potassium 0-0-50 at the rate of 1.5 to 2 lb. per 1,000 sq. ft. after the August 15 date to (1) improve winter hardiness (2) improve resistance to certain fungal diseases and (3) counteract some of the detrimental effects of excess nitrogen.
HERBICIDES
There are 2 major types of herbicides, (1) pre-emergent and (2) post emergent. The difference is pre-emergent is applied before the weed seeds germinate, therefore killing the young germinating plant. Post emergent kills the susceptible weeds after growing to the young and adult life stages. Most of the turfgrass problems I see when inspecting yards is the misuse of pre-emergent hebicides.
Now this is where the picture gets fussy. We have the host plant (turfgrass), the pesticide (herbicide) and the pest (weeds).
Turfgrasses have a certain tolerance to pre-emergent herbicides. Herbicide means “plant-killer” or to put it another way “turf killer”. Pre-emergent Herbicides are ok IF applied at the right time of year (stage of turfgrass development) and recommended rates. The beginning of the time to use pre-emergent herbicide is around the first of February and the cut off date is around the end of March or the beginning of the dogwood bloom date for control of most spring and summer weed pests. Some pre-emergents will have a duration of activity from 3 or 4 months to 8 months.
“What will kill the goose will kill the gander” The mode of action of pre-emengent herbicides is preventing the elongation of young root cells, causing little or no water and nutrient uptake to the plant. Germinating weeds are killed and young developing roots of turfgrass are stubbed and stunted resembling nematode infestation. This stubbing and stunting is called root pruning by some in the chemical industry. This is a play on words.
To avoid trouble, read the herbicide label, follow the instructions and remember a long duration of action will interfere with the developing turfgrass root system when stolen runners begin to grow across the ground.
