Although biological control of plant pests is being proposed as an alternative to chenical contral, the rational for such an alternative is weak when seed treatment is the pesticide delivery system. In contrast to all other applicatons of chemical pesticides, seed treatment provides effective, economic contral with small amounts of the active ingredient with very little exposure to man and his environment.

The limiting factor for root disease contral be seed treatment chemical pesticides is the duration of the contral. The physical saize of the seed and seed safety determine the amount of chemical that can be delizered be this method. The repid develoement in the size of the seedling quickly dilutes the chemical below effective levels. In addition, if the chemical does not have systemic activity it will have very limited movement within the seedling All of these factors limit the duration of control of seedling diseases, in most cases, to 21-28 days.

Biological systems, used in combination with chemical seed treatments, offer the potential for combining the benefits of both into a system which we refer to as Intergrated Plant Protection. The chemicals provvide the early control of the seedling disease complex. The biologicals can then colonize this protected developing root system and provide benefit to the plant well beyond the benefit obtained from the chemicals alone.

Field studies in 1991 concentrated on the interaction of various chemical combination with Bacillus subtilis as measured by stand and yield. The results of these studies are highlighted in Table 1. These data show that significant differences in yield are obtaing by treatment with Bacillus subtilis is an increase in the number of fruit and a decrease in the number of aborted fruit. These results are presented in Table 2.

These data are cinsisten with results obtained and reported previously with QUANTUM^® and Kodiak. The active ingredients in the two products are both Bacillius subtilis but different strains. QUANTUM^® contains Bacillus subtilis A-13 whereas Kodial contains a strain isolated from cotton seedlings growing in North Texas and designated GB03. Because of trademark difficulties, Kodiak is now referred to as QUORUM™. Both products have provided yield increases. In addition, observational data from our research plots have shown a mid-season vigor response by plants whose root systems have been colonized by Bacillus subtilis. These responses are most apparent during periods of drought stress. All of the responses that we have noted (vigor, increased fruiting, decrease abortion adn yield) are consistent with the hypothesis that the colonization of cotton root systems by Bacillus subtilis improves root health. How this improvement is achieved is still not clear. The determination of the benefit produced by the biological to the plant is the object of our current research. Using Bacillus subtilis strains GBO3 and GBO7 alone and in combination with chemicals, studies are in progress to determine the effect on various pathogens that attack cotton such as Pythium, Rhizoctonia, Fusarium, macropoomina, etc. These as well as other major and minor pathogens of cotton will be used to determine what is being controlled by the Bacillus on cotton roots. Also, the effect of the Bacillus on the pnysiology of the cotton plant will be determined.

Elucidation of this mode of action will allow us to explain the positive yield responses that nave been obtained with QUORUMtm and QUORUMtn Plus which are expected to be registered by EPA in 1992. QUORUMtn (previously called Kodiak) contains subtilis GBO3 as the active ingredient. QUORUMtmPlus is a combination product of the Bacillus with APRONO and PCNB.

A better understanding of tne mode of action will also allow us to be able to predict under what conditions (environmental, cultivar, disease inoculum, etc.) will the effect of the Bacillus be best expressed as well as helping to explain the variations in responses that are obtained.