Growth of Johnsongrass Selections Under Different Temperatures and Dark Periods

Abstract

The differential response of three selections of johnsongrass (Sorghum halepense(L.) Pers.) to different temperatures and dark periods was studied in two experiments conducted in growth chambers. The three selections of johnsongrass were obtained from locations representing different climates. At 20 C all three selections grew equally with respect to most parameters of growth studied; however, at 35 C the selection from the southern climate produced more total fresh weight than the other two selections. Rhizome production and the number of stems also were greater in the southern selection at 35 C. An 8-hr dark period prevented flowering in all three selections and significantly reduced rhizome production in two selections compared to the 12-hr dark period. Flowering occurred most rapidly in the selection from a northern climate and most slowly in the selection from a southern climate. The results are discussed in relation to the possible plant adaptive changes and the possibility of weed control through dark period interruption.

The biology of Johnson grass (Sorghum halepense)

“…It was found that seed germination at 20°C was less than 10% for forty-three Johnson grass ecotypes and between 10% and 20% for one ecotype (Taylorson & McWhorter, 1969), With alternating tempera-Sorghum halepense 263 tures, twenty-three ecotypes had less than 10% germination, another twenty-one had more than 10%, one ecotype having 50-^0% germination. Control 5 weeks after dalapon application at 11 kg/ha varied from 36% for a Louisiana selection to 91% for a Georgia selection (McWhorter & Jordan, 1976b), The number of tillers produced by different ecotypes after a 14 week period varied from 7 to 12 (Wedderspoon & Burt, 1974), Production of rhizome nodes varied from 94 to 229 in 10 weeks (McWhorter & Jordan, 1976b), Burt & Wedderspoon (1971) showed ecotypic variation in flowering response to photoperiod, Spikelet production varied from 37 to 352 sessile spikelets per panicle and the incidence of shattering varied from 1 to 73% for sixteen American ecotypes (McWhorter, 1971), The same author reported that Johnson grass plants from Turkey, Ethiopia and the Dominican Republic did not overwinter in Mississippi unlike American, Indian, Pakistani, Iranian and Israeli ecotypes.…”

Effect of Spray Components on Glyphosate Toxicity to Annual Grasses

“…Observations in the greenhouse and field indicate that glyphosate phytotoxicity may be influenced by several application and environmental factors. Environmental variables such as soil moisture, air temperature, stage of plant growth, light, and relative humidity have been shown to affect the performance of foliar-applied herbicides (1,2,5,7,10,12,13). The addition of surfactants (11,18) and other additives such as inorganic salts (15,16) and carrier volume (11,15,16) also influences glyphosate phytotoxicity.…”

Rhizome depth: the critical factor in winter survival of Sorghum halepense (L.) Pers. (Johnson grass)

“…Depth of rhizome production in the field and tolerance to cold is not known for populations of this species at the northern extreme of its distribution in North America. Considerable intraspecific variability has been described for populations of S. halepense throughout its range, and this variability has been suggested as important for the rapid adaptability of this species to more northern climates (Burt & Wedderspoon, 1971). It was, therefore, of considerable interest to compare winter survival parameters in the two contrasting biotypes of 5".…”