Varietal and Nitrogent-level Effects on Sweepotato Whitefly Populations in Cotton

Transcription

1 Varietal and Nitrogent-level Effects on Sweepotato Whitefly Populations in Cotton Item Type text; Article Authors Watson, T. F.; Silvertooth, J. C.; Tellez, A. Publisher College of Agriculture, University of Arizona (Tucson, AZ) Journal Cotton: A College of Agriculture Report Download date 11/05/ :01:48 Link to Item

2 VARIETAL AND NITROGEN -LEVEL EFFECTS ON SWEETPOTATO WHITEFLY POPULATIONS IN COTTON T. F. Watson, J. C. Silvertooth, A. Tellez Abstract Four cotton varieties, each differing in leaf pubescence, and three nitrogen (N) levels were investigated for effects upon development of SPWF populations. The N treatments appeared to have no effect upon population development. However, there was a direct correlation of increased SPWF numbers with increased hairiness. Both DPL 5415 and SALCOTIO had significantly lower seasonal means of all stages than did the more hairy varieties of CB1135 and STV453. Introduction The sweetpotato whitefly (SPWF), Bemisia tabaci (Gennadius), has become a serious problem of a number of agricultural crops in the southern U.S. This is particularly true of cotton, Gossypium spp., in southern Texas, and in the lower desert areas of Arizona and southern California. Populations reached unprecedented levels in cotton during 1981 in Arizona and California (Duffus and Flock, 1982; Butler and Wilson, 1984) and in a number of vegetable crops in the southwestern U.S. and west coastal Mexico (Brown and Nelson, 1984). More recently, SPWF has proliferated to include additional crops over wider areas. For example, in Arizona, severe infestations have been found on such crops as alfalfa, Medicago sativa L., Broccoli, Brassica oleracea L., cauliflower, Brassica oleracea L., and peanuts, Arachis hypogaea L., (Watson et al., 1992). The increased problem with the SPWF has been attributed, in part at least, to the introduction of a new biotype (Biotype B) which apparently can adapt to a broader host range more quickly than the original biotype (Biotype A) (Brown et al., 1991). In the past, damage to cotton caused by whiteflies (SPWF) was mostly associated with sticky lint and sooty molds caused by the honeydew produced (Gerling et al., 1980) and, to a lesser extent, reduced yields (Mound, 1965). During recent years, however, serious yield losses have occurred in cotton, primarily as a result of the infestations occurring on younger cotton and reaching unusually high population levels earlier in the growing season (Watson, unpublished). This study was designed to determine the effects of two factors -degree of leaf pubescence and the amount of nitrogen fertilizer applied during the growing- season upon the rate of population development of SPWF in cotton. 352

3 Methods The experiment was arranged as a split -plot within a randomized complete block design with fourreplications. Plots were 40 ft. long by eight (40 ") rows wide, with 10 -foot alleys separating plots lengthwise. Whole plots consisted of four cotton varieties, ranging from smooth leaf to highly pubescent. These varieties were DPL5415, SALCOTIO, CB1135 and STV453, from least to most pubescent, respectively (Table 1). Sub -plots consisted of 3 nitrogen levels: N1 (check), N2 (100 lbs. N), and N3 (200 lbs. N). Applications of fertilizer N were split over three dates as shown in Table 2. The cotton was planted on March 31, 1993, at the Yuma Valley Agricultural Center. Yields were taken on September 17, 1993, by harvesting the two center rows of each plot. Sampling consisted of pulling 5 fully- expanded leaves from the 3rd to 5th node below the terminal in each plot and examining 1 -inch dia. leaf discs for egg and immature stages of the SPWF. Adult populations were sampled by beating plant terminals across on ordinary bread pan lightly coated with vegetable oil to which the adults adhered. Two, 50 sq. cm. sections were delineated in each half of the pan and adults within these squares were counted. No insecticide applications were made during the course of the SPWF study. Results The results of this experiment provided conclusive results of the effects of leaf pubescence upon SPWF populations. However, the correlation of SPWF populations with yields was less conclusive, possibly as a result of heavy lygus, Lygus hesperus (Knight), populations which affected all varieties. The sub -treatments of N showed an inverse relationship to yields (Table 3). The highest yield was obtained in the control treatment receiving no additional N. Petiole analyses showed that there was an adequate supply of N in all treatments for the greater part of the growing season (data not shown). Obviously, in order to obtain separation in the N levels among the treatments the experiment would need to be repeated on the same plots. The most plausible explanation for the lower yields in the higher nitrogen treatments involves a vegetative growth tendency with higher N regimes, a delay in maturity, and possibly greater effects of lygus feeding in the plots. Table 4 shows the effect of the more pubescent varieties on SPWF populations. All stages - egg, immatures and adults - were significantly higher in CB1135 and STV453, the most pubescent varieties (see Table 1). Both DPL5415 and SALCOT10 are relatively smooth -leaf varieties and had seasonal mean egg, immature and adult populations which were similar and significantly lower than both of the hairier varieties. The N level had no apparent effect upon any stage of SPWF. No significant differences occurred among N treatments relative to egg, immature and adult populations (Table 5). Seasonal development of the SPWF in this experiment was similar to that observed in previous studies. Populations started at relatively low levels and continued at about these same levels for several weeks and then increased at a much accelerated rate thereafter. This trend was similar in all varieties but at a higher rate in the two more pubescent varieties (Table 6). 353

4 References 1. Brown, J. K. and M. R. Nelson Geminate particles associated with cotton leaf crumple disease in Arizona. Phytopath. 74: Brown, J. K., H. S. Costa, and J. Bird Variation in Bemisia tabaci populations based upon geographic origin, silverleaf symptom induction, and esterase banding patterns. Phytopath. 81: Butler, G. D., Jr., and F. D. Wilson Activity of adult whiteflies (Homoptera: Aleyrodidiae) within plantings of different cotton strains and cultivars as determined by sticky -trap catches. J. Econ. Entomol. 77: Duffus, J. E., and R. A. Flock Whitefly- transmitted disease complex of the desert southwest. Calif. Agric. 36: Ellsworth, P. C., D. L. Meade, S. H. Husman, C. S. Ramsey, J. C. Silvertoth and J. E. Malcuit Sweetpotato whitefly preference and performance on medium maturity cotton varieties in Arizona. In J. C. Silvertooth [ed.], Cotton, A College of Agriculture Report. Series P. 94. University of Arizona, College of Agriculture, Tucson, AZ pp Gerling, D., U. Motro and R. Horowitz Dynamics of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) attacking cotton in the coastal plain of Israel. Bull. Entomol. Res. 70: Mound, L. A Effect of leaf hairs on cotton whitefly populations in the Sudan Gezira. Empire Cotton Grow. Rev. 41: Watson, T. F., J. C. Silvertooth, A. Tellez and L. Lastra Seasonal dynamics of sweetpotato whitefly in Arizona. Southwest. Entomol. 17:

5 Table 1. Cotton yields from four cotton varieties varying in density of leaf pubescence. Variety Interveinal leaf* hair /0.25 in2 Yield lbs. seed cotton /A. Stat. Sig. (0.05) DPL a SALCOT a b CB a STV b * Pubescence rating from Ellsworth et al. (1993). Table 2. Fertilizer N applications for each variety X N treatment, YVAC, Treatment Number Date Form Method* lbs. N /acre 23 April Urea ( ) SD May Urea ( ) SD June Urea ( ) SD TOTAL * SD = sidedress Table 3. Effect of three nitrogen levels on cotton yields across the four varieties. Nitrogen Level Yield ( #seed cotton /A) (All varieties combined) Stat. Sig. (0.05) Control (none added) 2563 a 1 x Rate (100 #N) 2231 b 2 x Rate (200 #N) 2242 b 355

6 Table 4. Effect of variety upon sweetpotato whitefly populations. Seasonal Means and Stat. Sig. (0.05) Variety Eggs Immatures Adults DPL a 3.4 a 8.3 a SALCOT a 4.3 a 9.7 a CB b 12.3 b 12.7 b STV b 16.5 c 16.5 c Table 5. Nitrogen -level effects upon sweetpotato whitefly populations. Seasonal Means (Stat. Sig 0.05) N Level Eggs Immatures Adults Control (none) 28.8 a 8.05 a 11.8 a 1 x (100 #N) 35.8 a a 11.9 a 2 x (200 #N) 38.4 a 9.45 a 11.6 a Table 6. Seasonal development of sweetpotato whitefly populations across four cotton varieties. Mean Numbers Per Samp e Datez Sample Dates' Eggs Immatures Adults a 0.88 a a 1.06 a a 0.14 a a 1.15 a 0.85 a a 2.69 a 1.29 a a 2.17 a 0.88 a a 2.64 a 5.10 b b b c b c 9.78 c c b d d c d ' Sampling was initiated on May 3 and terminated on July Egg and immature samples consist of mean numbers per 1" dia. leaf disc and adults are mean numbers per 50 sq. cm. in oil pan. 356