INTERACTIONS OF TEMPERATURE AND DORMANCY-RELIEVING COMPOUNDS ON THE GERMINATION OF WEED SEEDS

Dormant weed seeds were germinated at constant and alternating tempera tures using five chemicals. Germination of Chenopodium album when expr essed in normal equivalent deviates, increased linearly with the logar ithm of chemical dose up to an optimal concentration. Ethephon (2-chlo roethyl phosphonic acid) and sodium azide slightly stimulated germinat ion of C. album seeds at 20 degrees C while potassium nitrate, thioure a and azide each interacted positively with alternating temperatures ( 5 degrees/25 degrees C). Relief of Avena fatua dormancy by azide exhib ited a positive interaction with cool constant temperatures (3-10 degr ees C), and chemicals had smaller or no effects at higher and alternat ing temperatures. No chemical mixture, including that of nitrate, thio urea, ethephon, azide and hydrogen peroxide, promoted more germination than azide on its own in A. fatua or nitrate together with ethephon i n C.album. In C. album, this result arose largely because nitrate and azide antagonized each other in the presence of ethephon. Peroxide and thiourea together relieved this antagonism so that the fourth order i nteraction was positive. The negative interaction of nitrate, azide an d ethephon in C. album was avoided in a sequential treatment with nitr ate plus ethephon for seven days followed by sodium azide. Relief of d ormancy by nitrate and ethephon was optimized at 67mM nitrate with 1.4 mM ethephon for C. album at 20 degrees C and 20 mM nitrate with 1.4mM ethephon for A. fatua at 15 degrees C. None of the chemicals used in this investigation stimulated the germination of Rumex crispus seeds. The results are discussed with respect to chemical control of soil see d banks.