Residues of three winter cover crop legumes currently recommended for use with cotton (Gossypium spp.) inLISA (Low Input Sustainable Agriculture) systems, i.e., Berseem clover (Prifolium alexandrinum L.), hairy vetch (Vicia hirsuta (L.) S. F. Gray) and crimson clover (Trifolium incarnatum L.), have distinctive volatile emissions profiles which contain C₂-C₁₀ hydrocarbons, alcohols, aldehydes, ketones, esters, furans and monoterpenes (4). Many of these simple organic volatiles strongly inhibited onion, carrot, and tomato seed germination (1, 2, 4), but germinating cotton seeds were relatively resistant (2, 3). However, when seedlings of the cotton variety, Coker 315, were grown in 20 or 30 C soil to which had been added 2 µM/cm³ (or lower) levels of C₄-C₉ ketones emitted by these cover crops (4), significant inhibition of both root and shoot growth was observed. The relationships between chemical structure and inhibitory activity in these seedling growth responses duplicated those seen in the earlier seed germination studies (1, 2, 4). Because these naturally-occurring inhibitors are active in the volatile phase and not in aqueous solution, inhibition of cotton seedling growth was greater at the higher soil temperature.