1. Chinch Bugs
The Southern chinch bug is the most important insect pest of St. Augustine grass in Florida. (Figure 1) It is not a serious pest on any of the other lawn grasses. The eggs begin hatching in March/April and there are 3-4 generations per year. The immature chinch bugs (nymphs) are about the size of a pinhead and are bright red with a white band across the back. Late stage nymphs and adult chinch bugs are about 1/5 inch long and black. The adults have white wings.
Chinch bugs suck the plant juices from grass and also
apparently causes other injury to the grass, resulting in yellowish to brownish
patches in the lawns. These injured areas are often first noticed in water
stressed areas along edges of lawns and in particular during dry periods
and in full sun. The bugs can be found in sunny and off-color areas by parting
the grass at the margin of the yellowed areas and closely examining the
soil surface and base of the turf.
Rapid grass growth resulting from water-soluble inorganic nitrogen fertilizers increases the chance of chinch bug attack. Best is to use minimum applications (in March and September) of complete slow release nitrogen fertilizers (such as 6.25 lbs. of 16-4-8 fertilizer corresponding to a rate of 1 pound nitrogen per 1000 ft2). Avoid further fertilization in summer. Use Ironite to green up lawn without rapid flushes of growth during the rainy season.
Frequent intense rainfall normally occurs during summer. Therefore, irrigate to prevent drought stress only on an as needed basis. Wait until lawn shows signs of wilting (blue-gray color or footprinting) before irrigating again with ¾ inches of water.
Excessive water or fertilization can cause lawns to develop a thick, spongy mat of live, dead and dying shoots, stems and roots which accumulate as thatch above the soil surface. This thatch provides an excellent home for the chinch bugs and chemically ties up insecticides and therefore reduces control. It may be necessary to remove the thatch mechanically via vertical mowing, power raking, etc.
Proper mowing can make the grass more tolerant to chinch bugs and greatly improve the appearance of the lawn. St. Augustine grass should be mowed to a height of 3-4 inches (as high as possible with a home mower) and it is very important to keep the mower blade sharpened (sharpen once per month). The grass should be mowed often enough so that no more than 1/3 of the leaf blade is removed at each mowing. Do not remove the clippings.
Floratam, Floralawn and Floratine are St. Augustine varieties with some degree of resistance to chinch bugs. There are a few predatory insects like the 'Big-eyed bug' and the 'earwig' which feed on chinch bugs. However, if chinch bugs are found at 20-25 chinch bugs per ft2, than products containing Diazinon, Dursban or Orthene can be applied (follow directions on label). The jar attachment to a garden hose is the best application device. Irrigate lightly after spraying. To limit use of pesticides, spot treatments can be applied when infestations are first noticed and the damaged area is very small. Treat the off-color area and about a 5-foot buffer area surrounding it. In some areas chinch bugs have developed resistance to Dursban and Diazinon. If the chemicals don't work a synthetic pyrethrin such as Tempo can be applied. Be careful while using any of these chemicals since all are poisonous.
2. Take-all Root Rot
The pathogen (Gaeumannomyces graminis var. graminis ) is naturally present on warm-season turfgrass roots. The trigger for disease is high rainfall and stressed turfgrass, so it is observed during the summer and early fall months when Florida receives the majority of its rainfall. Prolonged periods of rainfall are most conducive to this disease. Any stress placed on the turfgrass will encourage or worsen the disease.
Symptoms/Signs: This is a root rot disease. Symptoms observed on the leaves are the result of pathogen activity on the root system. The fungus does not attack leaves. Initial symptoms above-ground are irregular, yellow (chlorotic) or light green patches ranging in diameter from a few inches to a few feet. Roots will initially be thin and off-white in color with isolated black lesions. Eventually, roots will become very short, black and rotted. Stolons and rhizomes may have black lesions and, under severe disease conditions, begin to rot. Entire plants may die resulting in irregular patches of thinning grass, and if not controlled, bare patches may develop
Cultural Controls: This disease is very difficult to control once the aboveground symptoms are observed. Therefore, measures that prevent or alleviate stress are the best methods for completely controlling the disease or at least decreasing the potential damage. Stress on turfgrass can result from many factors and are addressed below.
The turfgrass must be mowed at the correct height during the summer Turfgrass must be mowed as frequently as necessary so that only one third (1/3) of the leaf tissue is removed during any one mowing event. Scalping the grass damages the growing point.
Balance nitrogen applications with equal amounts of potassium. For every pound of nitrogen applied, an equal amount of elemental potassium (K) should be applied. Slow-release nitrogen and slow-release potassium sources should be used. Avoid nitrate-nitrogen products and quick-release urea products (e.g., uncoated urea). If slow-release potassium is not readily available, then apply quick-release potassium to the turfgrass between nitrogen applications. Extra potassium may be useful in late summer and early fall.
Frequent foliar (leaf) feeding of all nutrients (N, P, K and micronutrients) in small amounts will be necessary if the root system is severely damaged. The roots are not functioning properly, and so will not be able to efficiently obtain nutrients from the soil. Apply micronutrients, especially manganese. Micronutrients should be applied in the sulfate form as foliar applications. Do not apply lime to the turfgrass. Apply herbicides only as needed and according to the label. St. Augustinegrass is especially sensitive to herbicides. Even when herbicides are applied correctly, there will be some stress placed on St. Augustinegrass. Avoid herbicides by learning how to manage the turfgrass to limit weeds!
Chemical Controls: azoxystrobin, myclobutanil, propiconazole, thiophanate methyl, triadimefon These systemic fungicides are not as effective as the use of cultural controls once the disease symptoms are observed. These fungicides may be useful when used preventively. This means they must be applied prior to symptom development. Start applying the fungicides at least one month prior to when you normally observe aboveground symptoms. Continue applying once a month until the weather is no longer conducive for disease development. It is beneficial to lightly water-in these fungicides, but it must be done immediately after application.
3. Gray Leaf Spot
Pathogen: Pyricularia grisea
Occurrence: This disease of St. Augustinegrass is most often observed from late spring to early fall, especially during prolonged periods of rainfall. Excessive applications of quick-release nitrogen sources enhance disease severity, as does compacted soil. Application of the herbicide atrazine increases the susceptibility of St. Augustinegrass to this disease.
Symptoms/Signs: Initial symptoms include small pinhead size spots that are olive-green to brown in color. These enlarge and form circular to oblong spots that are tan to brown colored with distinctive dark brown margins. Under humid conditions, the fungus produces abundant spores in the center of these spots, giving them a velvety-gray appearance.
Many spots can occur on a single leaf, such that severely affected leaves wither and turn brown. No distinct patches are observed, but areas may appear thin. A severely affected turfgrass area may appear as though it is suffering from drought. Once St. Augustinegrass is established in the landscape, the disease is chronic but not severe. During the summer months, individual St. Augustinegrass plants will always have a few spots on the leaf blades, but the overall health of the turfgrass is not affected unless the grass is placed under severe stress.
Cultural Controls: Avoid excess nitrogen during potential disease development periods. Do not use readily available forms of nitrogen such as soluble liquids or quick-release nitrogen sources just prior to or during these periods. Instead, use slow-release nitrogen sources. Apply a balanced fertilizer containing equivalent amounts of potassium, preferably a slow-release potassium form. If soils are compacted (walking paths for example), alleviate the compaction or reduce traffic in those areas. Limit atrazine herbicide applications. If it is necessary to use atrazine, only apply to weed infested areas and not the entire lawn. Before and after atrazine applications, be sure the turfgrass is being managed correctly - fertility, mowing and water. Monitor the turfgrass area for disease development. Avoid herbicides by learning how to manage the turfgrass to limit weeds.
Chemical Controls: azoxystrobin, propiconazole, thiophanate methyl, and trifloxystrobin.
Weeds can be bad too in summer, but they are best pulled or dug out until September or October when a herbicide can be used. Applying any 'post emergence' herbicides during summer may result in objectionable turf injury. St. Augustine grass is damaged by certain herbicides (e.g., MSMA, DSMA). Follow label directions and use with caution, and only when grass and weeds are actively growing and not suffering from drought stress and air temperatures are below 85 degrees F.
References used for this article:
· 'Florida Lawn Handbook - An environmental approach to care and maintenance of your lawn' by Kathleen C. Ruppert & Robert J. Black, University of Florida - Institute of Food & Agricultural Sciences, 1997.
· University of Florida - Turfgrass Science website at http://turf.ufl.edu/residential/residential.htm
(This is an excellent resource for any and all information on St. Augustine and other lawn grasses)
· Advice from Tom MacCubbin, Urban Horticultural agent of the Orange County Cooperative Extension Service.
This page was updated 8/29/2001