Effect of Pink Bollworm on Agronomic Properties of Resistant and Susceptible Cotton1

Abstract

Little is known about the differential effects of the attack of pink boilworm (PBW), Pectinophora gossypiella (Saunders), on agronomic properties of resistant and susceptible cottons, Gossypium spp. The major objective of this study was to determine and compare those effects in a susceptible cultivar and a resistant breeding stock of upland cotton, G. hirsutum L., and a susceptible cultivar of Pima cotton, G. barbadense L. Other objectives were to compare an x‐ray method with a visual boll‐grading method of determining damage done by the insect, and to study the relationship of seed damage with selected agronomic properties. The three cottons were grown for two seasons in untreated field plots and in plots treated for PBW control Seed cotton was harvested weekly as boils opened, seed samples were x‐rayed to determine seed damage, and agronomic properties were measured. At the end of the season, all bolls were removed from five plants/plot and boils were graded into damage classes. Pink bollworm mainly damaged rather than destroyed seed. Damaged bolls did not abscise but remained on the plant. The Pima entry, ‘Pima S‐5’ had more dry, unharvestable bolls than the two upland entries, ‘Deltapine 61’ and AET‐5. Damage was higher in unsprayed than in sprayed plots. The resistant AET‐5 had less seed damage and fewer damaged bolls than the other two entries, and its agronomic properties were less affected by PBW attack. The x‐ray method failed to integrate data from unharvestable bolls, and the graded‐boll method failed to quantify the amounts of damage in the damaged‐boll category. The percentages of variation in decreases in agronomic properties, attributable to increases in seed damage, were higher in unsprayed than in sprayed plots, but also differed among the three cottons. Thus, direct comparison of the effects of PBW on agronomic properties among cottons in unsprayed plots could be misleading because these effects would be superimposed on different natural patterns of decrease in those properties as the season progressed.