Huangjun Lu

Effect of Silicon on Resistance of St. Augustinegrass to Southern Chinch Bugs (Hemiptera: Blissidae) and Plant Disease

Abstract Silicate slag was applied to soil of Captiva, Floratam, and Raleigh varieties of St. Augustinegrass to measure the effect of plant silicon on resistance of the varieties to southern chinch bugs, Blissus insularis Barber, and plant disease. In general, silicate slag addition increased Si and Cu content in leaves but tended to decrease P and Mg concentrations. Tissue nutrient contents were generally lowest for Floratam; this trend occurred both with and without silicate slag amendment, indicating a lower nutrient requirement than with other varieties. Chinch bug survival was lowest and development slowest on Captiva which was the only variety with resistance to the insects. There were no significant differences in survival or developmental rates of chinch bugs between silicon treatments within any of the 3 varieties. In disease assessments, Raleigh was more susceptible to gray leaf spot than Captiva or Floratam. However, the addition of Si resulted in significant disease reduction in Raleigh. The addition of Si resulted in disease reduction in Floratam as measured by disease incidence, but not severity. The addition of Si slag caused significant increases in stolon number, stolon length, and leaf blade width in 1 - 2 varieties. Varieties varied in response to Si fertilization among 6 growth characters measured.

Morphological and Nutrient Changes in St. Augustinegrass Caused by Southern Chinch Bug (Hemiptera: Blissidae) Feeding Damage

Abstract The southern chinch bug, Blissus insularis Barber, is the most damaging insect pest of St. Augustinegrass, Stenotaphrum secundatum (Walt.) Kuntze. However, there is little understanding of the impact of the insect feeding on the plant biomass or nutrient flux in tissues. The objective of this study was to measure biomass and nutrient change in St. Augustinegrass caused by feeding of southern chinch bugs. Chinch bugs were collected by vacuuming infestations in commercial and residential lawns in southern Florida. After collection, chinch bugs were placed in buckets containing St. Augustinegrass potted plants whereas controls were plants with no chinch bugs. Nutrient concentrations were measured for nine elements (N, P, K, Ca, Mg, Mn, Fe, Cu, Zn) in leaf and stolon tissue. At the termination of the test, chinch bug treated buckets had >100 chinch bugs/bucket in them and controls had none. Stolons were 31% shorter in chinch bug exposed plants than controls with no chinch bugs. Above-ground dry matter was reduced by 37% by chinch bug feeding. Plant leaf color was also significantly changed by chinch bug feeding from dark green to yellow. In general, chinch bug feeding decreased all nutrient concentrations, suggesting that the damage was broad in scale and reduced the plants ability to maintain nutrients.

Effect of Time and Testing Method in Determining St. Augustinegrass Resistance to Southern Chinch Bugs (Hemiptera: Blissidae)

Abstract St. Augustinegrass, Stenotaphrum secundatum (Walt.) Kuntze, is used as lawn grass throughout the southern United States for its wide adaptation to varying environmental conditions. The southern chinch bug, Blissus insularis Barber, is the plants most damaging insect pest. Host plant resistance of St. Augustinegrass has been determined in numerous studies using various techniques. However, efficacy of these various procedures in determining St. Augustinegrass resistance to southern chinch bug has not been determined. The objective of this study was to determine the effect of time and methodologies in assesing St. Augustinegrass resistance to southern chinch bugs. Four varieties were tested for resistance using 4 methods (bag, jar, box, tube) and 5 time intervals to measure chinch bug mortality. Overall, survival was greater in whole-plant methods (box and tube) than excised stolon methods (bag and jar). The bag test gave the most erratic results of the 4 methods. The effect of time in determining resistance was also evident. In our tests, it was clear that shorter time intervals in measuring mortality may result in not measuring resistance in a variety. In summary, researchers should carefully consider method, time and temperature as important variables in determining St. Augustinegrass resistance to southern chinch bugs.

New Sources of Southern Chinch Bug (Hemiptera: Blissidae) Resistance in St. Augustinegrass Varieties

Abstract The southern chinch bug, Blissus insularis Barber, is the most damaging insect pest of St. Augustinegrass, Stenotaphrum secundatum (Walt.) Kuntze. Historically, host plant resistance has been important for control of southern chinch bugs in St. Augustinegrass. In this study we screened 36 St. Augustinegrass varieties for resistance to southern chinch bugs. Four varieties were shown to have significant resistance using 2 different testing methods. Morphological data for these 4 varieties also were measured.

Morphological and Physiological Responses of St. Augustine Grass Cultivars to Different Levels of Soil Moisture

Understanding responses of turf grasses to drought stress is important for water resource management to maintain an acceptable level of quality for turfs under prolonged drought conditions. Four cultivars of St. Augustine grass (SA) (Stenotaphrum secundatum [Walt.] Kuntze) were evaluated for morphological and physiological responses to four watering treatments in greenhouse studies. Soil moisture treatments had greater impact on stolon number, photosynthetic rate, and dry matter production than on leaf sheath length and chlorophyll fluorescence. Full irrigation and the 75% field capacity (FC) did not result in significant differences in most of the characteristics, whereas the 25% FC significantly reduced morphological growth, physiological activities, and dry matter production of cultivars. The time when the morphological characteristics started showing differences among the watering treatments varied, with stolon numbers beginning to show response to watering treatments at week 2 (two weeks after watering treatment) and leaf sheath length not differing significantly until week 5 (five weeks after watering treatments). Cultivars differed in response to soil watering treatments among the characteristics. Floratam had the longest stolons, largest leaves, and greatest dry matter accumulation among cultivars across the environments. Raleigh had the lowest dry matter production at all levels of soil moisture but the least reduction of dry matter at 25% FC.

Southern Chinch Bugs (Hemiptera: Blissidae) Increase Severity of Plant Disease in St. Augustinegrass

Abstract  The southern chinch bug, Blissus insularis Barber, is the most damaging insect pest of St. Augustinegrass. Numerous studies have shown direct damage to the plant by chinch bugs. However, these studies did not determine if the insect may be causing indirect damage to the plant by making it more susceptible to disease. The study reported herein demonstrates that the fungal plant disease, gray leaf spot (Magnaporthe grisea [T.T. Hebert]), significantly increased in St. Augustinegrass after being infested with chinch bugs. Damage by the insect to other morphological and growth traits is also reported. This study emphasizes the complexity of southern chinch bug damage to St. Augustinegrass by direct damage and by indirect damage making the plant more susceptible to disease.

Comparison of the New Southern Chinch Bug-Resistant Lines with Commercial Cultivars of St. Augustinegrass

St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] is a warm season turfgrass and is widely used for lawns and landscapes in the southern United States of America. The southern chinch bug (Blissusinsularis Barber) is the most damaging insect of St. Augustinegrass. Use of resistant cultivars is an environmentally sound and sustainable method to control this insect pest. Two newly identified resistant St. Augustinegrass lines (NUF3231 and NUF4872) were compared with three commercial cultivars for turfgrass quality and other important traits. The two lines had turf color and turf visual quality similar to those of Captiva and similar to or better than those of Floratam and Palmetto during the experiment. NUF4872 had higher level of resistance to gray leaf spot than Floratam and Palmetto. Stolon architectures of NUF3231 were similar to those of Captiva whereas NUF4872 had the stolons similar to those of Floratam. The results indicated that the two lines could potentially be released as commercial cultivars for use on lawns to battle against the southern chinch bug.

Effect of Temperature on Resistance of St. Augustinegrass to Southern Chinch Bugs {Hemiptera: Blissidae}

Abstract St. Augustinegrass, Stenotaphrum secundatum (Walt.) Kuntze, is used as lawn grass throughout the southern United States for its wide adaptation to varying environmental conditions. The southern chinch bug, Blissus insularis Barber, is the plants most damaging insect pest. Host plant resistance of St. Augustinegrass to southern chinch bugs has been determined in numerous studies using various techniques. However, temperature has been shown to affect plant resistance to insects; this has not been determined for St. Augustinegrass resistance to southern chinch bugs. In our study, 4 varieties were tested for resistance to adult chinch bugs at 5 temperatures. These varieties were Floratam (susceptible), Captiva (resistant), NUF-216 (resistant), and FX-10 (resistant). The temperatures were 15°, 20°, 25°, 30° and 35°C, and adults were held 7 days at each temperature. Analysis of mean mortalities showed cooler temperatures reduced the ability of LSD tests to statistically determine which varieties were resistant compared with the susceptible variety Floratam. Linear regression analysis showed that mortality was not significantly correlated with temperature in Floratam. In contrast all 3 resistant varieties showed significant positive correlations of mortality versus temperature. These correlation data are consistent with LSD analysis which showed that higher temperatures were better than lower temperatures for discerning St. Augustinegrass resistance to southern chinch bugs held for 7 days.