A highly virulent cotton wilt pathogen, Fusarium oxysporum f. sp. vasinfectum VCG0114 (race 4) was found in West Texas in 2017, after being known in California since 2001. Isolates obtained from wilted plants collected in 2017 from Texas, in 2015 from China, and during 2001 to 2014 from California and isolates from historical collections including the race 4 reference isolate were characterized by soil-infestation pathogenicity assays, DNA sequence analysis, and vegetative compatibility analysis. All obtained F. oxysporum f. sp. vasinfectum isolates belonged to VCG0114. All of these isolates, except one isolate from China, caused disease in a soil-infestation assay without nematodes. Thus, they belong to the nematode-independent pathotype. Texas isolates were significantly more virulent than were isolates from China or California on Gossypium barbadense ‘Pima S-7’. Four different genotypes (N, T, MT, and MiT) were identified based on the transposable element Tfo1 insertion into the PHO gene and independent MULE or MITE insertions into the Tfo1 transposon. Some significant differences in virulence were detected among the genotypes in some locations. No differences in pathogenicity were observed between the California and China collection isolates on Pima S-7, and the virulence of the major genotypes was similar on the Gossypium hirsutum cultivar ‘Stoneville 474’ or the Barbren 713 germplasm line. Simple polymerase chain reaction (PCR) methods were developed to specifically determine and detect the four genotypes within VCG0114. A specific PCR method to detect all VCG0114 isolates was also developed. These methods will facilitate the timely identification of infested fields and seed lots and the elucidation of evolutionary relationships among the isolates. This should help to closely monitor the movement of the pathogen and reduce dissemination of these devastating pathogens.

The production of hybrid cotton (Gossypium hirsutum L.) seed requires both a system of sterilizing one parent in the crossing block and the effective use of a pollen vector. This paper reports results from studies in which a systemic gametocide was used to produce male‐sterile flowers and also reports behavioral responses of honeybees (Apis mellifera L.) to the gametocide. Field and greenhouse tests were conducted during 1984 and 1985 to determine the quantity of the foliar‐applied systemic gametocide, TD‐1123, that was translocated to the floral and bracteal nectar of cotton (G. hirsutum L. and G. barbadense L.). Field observations and a laboratory bioassay evaluated honeybee response to TD‐1123 in nectar or to TD‐1123‐ laced sucrose solutions. The gametocide was fonnd in floral nectar in the field (<1‐542 mg L‐1) (bracteal nectar not collected) and in both floral and bracteal nectar (11‐151 mg L‐1) in the greenhouse studies. The highest concentrations of TD‐1123 were found in the floral nectar of upland cotton sampled 1 day after spraying (542 mg L‐1). Honeybee consumption of 0.84 M sucrose solutions that included TD‐1123 was not significantly increased at 50 mg L‐1 but significantly increased at 75 mg L‐1 of the gametocide. Floral visitation by foraging honeybees as measured in the field was not affected by the gametocide. We concluded that although the gametocide occurs in the nectar of treated cotton plants, it should not pose a threat to adequate pollination activity by the honeybee.