Digitized by Kansas Correctional Industries

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Typescript (photocopy). / Digitized by Kansas Correctional Industries

Bromegrass species (<i>Bromus</i>) can produce high forage yields under the short growing season of western Canada and have excellent nutritive value. Smooth bromegrass (<i>Bromus inermis</i> Leyss.) and meadow bromegrass (<i>Bromus riparius</i> Rehm.) are the most commonly cultivated bromegrass species. Hybrid bromegrass (<i>B. riparius X B. inermis</i>) was developed in Canada by hybridizing smooth and meadow bromegrass. Regrowth potential differs among these three bromegrass species, but the morphological and physiological basis for these differences is unclear. Regrowth characteristics of three bromegrass species following defoliation to 5cm at the vegetative and stem elongation stages of growth were studied in the field and greenhouse. Above-and below-ground dry matter production, leaf area index (LAI) development, individual leaf area expansion, leaf-to-stem ratio, photosynthetic rate, tiller and axillary bud development, etiolated regrowth, and nitrogen concentration in stem bases were evaluated.<p> Regrowth was similar among the three species when defoliated at the vegetative stage. Meadow bromegrass consistently produced more (P¡Ü0.05) above-and below-ground dry matter than smooth bromegrass following defoliation at the stem elongation stage, while that of hybrid bromegrass was generally intermediate to the other two species. Individual leaf photosynthetic rates did not differ among the three species. Individual leaf area expansion rate was faster (P¡Ü0.05) in smooth bromegrass than meadow and hybrid bromegrass. LAI of the three bromegrass species increased linearly with days of regrowth (r2¡Ý0.88, P¡Ü0.05), and the increase was greatest in meadow bromegrass, intermediate in hybrid bromegrass, and least in smooth bromegrass in all stages of defoliation. Similarly, the leaf-to-stem ratio was highest in meadow bromegrass, intermediate in hybrid bromegrass, and lowest in smooth bromegrass following all defoliations.<p> Defoliation at the vegetative stage had no effect (P¡Ý0.05) on tiller development relative to the undefoliated treatment, whereas tiller development was negatively affected by defoliation at the stem elongation stage. After 60 days of regrowth, final tiller density was greatest in meadow bromegrass, intermediate in hybrid bromegrass, and least in smooth bromegrass in the field. A lower proportion of tillers in meadow bromegrass reached the reproductive stage compared to the other two species. The final tiller density following defoliation was similar among species in the greenhouse. Total buds tiller-1 and elongated buds tiller-1 were similar (P¡Ý0.05) among three species following defoliation at each growth stage; however, defoliation at stem elongation stage visually delayed bud development. Etiolated regrowth was greater in meadow and hybrid bromegrass (P¡Ü0.05) than smooth bromegrass 10 days after defoliation, but was similar thereafter. Concentration of N in stem bases was similar among species, but decreased with advancing maturity.<p> Rapid regrowth of meadow bromegrass appears to be associated with more tillers, rapid remobilization of organic reserves during early regrowth, and allocation of more biomass to leaf tissue than to stems compared to the other two bromegrasses. Variation in regrowth among the species was not associated with expansion of individual leaf area, photosynthetic rates, total organic reserve remobilization, or nitrogen concentration in stem bases. Based on these characteristics, meadow bromegrass is the most suitable species for grazing, and smooth bromegrass the least suitable.

Bromegrass species (<i>Bromus</i>) can produce high forage yields under the short growing season of western Canada and have excellent nutritive value. Smooth bromegrass (<i>Bromus inermis</i> Leyss.) and meadow bromegrass (<i>Bromus riparius</i> Rehm.) are the most commonly cultivated bromegrass species. Hybrid bromegrass (<i>B. riparius X B. inermis</i>) was developed in Canada by hybridizing smooth and meadow bromegrass. Regrowth potential differs among these three bromegrass species, but the morphological and physiological basis for these differences is unclear. Regrowth characteristics of three bromegrass species following defoliation to 5cm at the vegetative and stem elongation stages of growth were studied in the field and greenhouse. Above-and below-ground dry matter production, leaf area index (LAI) development, individual leaf area expansion, leaf-to-stem ratio, photosynthetic rate, tiller and axillary bud development, etiolated regrowth, and nitrogen concentration in stem bases were evaluated.<p> Regrowth was similar among the three species when defoliated at the vegetative stage. Meadow bromegrass consistently produced more (P¡Ü0.05) above-and below-ground dry matter than smooth bromegrass following defoliation at the stem elongation stage, while that of hybrid bromegrass was generally intermediate to the other two species. Individual leaf photosynthetic rates did not differ among the three species. Individual leaf area expansion rate was faster (P¡Ü0.05) in smooth bromegrass than meadow and hybrid bromegrass. LAI of the three bromegrass species increased linearly with days of regrowth (r2¡Ý0.88, P¡Ü0.05), and the increase was greatest in meadow bromegrass, intermediate in hybrid bromegrass, and least in smooth bromegrass in all stages of defoliation. Similarly, the leaf-to-stem ratio was highest in meadow bromegrass, intermediate in hybrid bromegrass, and lowest in smooth bromegrass following all defoliations.<p> Defoliation at the vegetative stage had no effect (P¡Ý0.05) on tiller development relative to the undefoliated treatment, whereas tiller development was negatively affected by defoliation at the stem elongation stage. After 60 days of regrowth, final tiller density was greatest in meadow bromegrass, intermediate in hybrid bromegrass, and least in smooth bromegrass in the field. A lower proportion of tillers in meadow bromegrass reached the reproductive stage compared to the other two species. The final tiller density following defoliation was similar among species in the greenhouse. Total buds tiller-1 and elongated buds tiller-1 were similar (P¡Ý0.05) among three species following defoliation at each growth stage; however, defoliation at stem elongation stage visually delayed bud development. Etiolated regrowth was greater in meadow and hybrid bromegrass (P¡Ü0.05) than smooth bromegrass 10 days after defoliation, but was similar thereafter. Concentration of N in stem bases was similar among species, but decreased with advancing maturity.<p> Rapid regrowth of meadow bromegrass appears to be associated with more tillers, rapid remobilization of organic reserves during early regrowth, and allocation of more biomass to leaf tissue than to stems compared to the other two bromegrasses. Variation in regrowth among the species was not associated with expansion of individual leaf area, photosynthetic rates, total organic reserve remobilization, or nitrogen concentration in stem bases. Based on these characteristics, meadow bromegrass is the most suitable species for grazing, and smooth bromegrass the least suitable.

The timing of harvest aid application on cotton (Gossypium hirsutum L.) is critical, and poses potential problems when mistimed. The consequences of premature harvest aid application could result in reduced profit to the grower through the need for additional applications, reduced lint yield, poor fiber quality, and/or delayed harvest. A delayed application of harvest aid materials may also reduce lint yield and fiber quality if late season inclement weather patterns are established. Currently, there are many methods utilized for determining application of harvest aid materials. One method utilizes accumulated heat units, or growing degree days (HU or DD60??s), following plant physiological maturity. Physiological maturity (cutout) is identified as nodes above white flower equals 5 (NAWF=5). This method triggers the application of harvest aid chemicals when 850 HU have been accumulated beyond cutout. Due to differing environmental and edaphic characteristics across the Cotton Belt, application of harvest aid chemicals at this time may be premature in terms of optimizing lint yield and fiber quality. A two-year study was established to determine the proper timing of harvest aid application for picker harvested cotton in south central Texas. The design utilized a split-plot with four replications. The main plots consisted of three nodal positions(NAWF=3, 4, and 5), and the subplots were five HU accumulations (650, 750, 850, 950, and 1050) that corresponded to each of the nodal positions. In both years, lint yields increased with an increase in HU accumulation. Greater yields were achieved when HU accumulation was initiated after NAWF = 4. This two-year study indicates that harvest aid applications made at NAWF = 4 plus 1050 HU would optimize yield potential for picker harvested cotton in south central Texas.

Reviewed 06/2015; Originally published 02/2001 / 2 pp. / There are several factors which are important to consider in managing defoliation. Factors such as plant-water relations, Nitrogen (N) fertility status, the extent of honeydew deposits on the leaves from insects such as the sweet potato whitefly or aphids, and weather conditions following the defoliant application are all important in terms of the final defoliation results.

Revised 06/2015. Originally published 07/2001. / 3 pp. / This bulletin deals with the physiology of cotton defoliation and attempts to describe what conditions must exist inside the plant in order for defoliation to occur. It is important to understand the basic physiological processes involved in order for best crop management practices to accomplish a successful defoliation. The objectives of defoliating a cotton crop can be simply stated as: 1) to remove leaves to facilitate mechanical picking, 2) to maintain the quality of the lint, and 3) to complete defoliation with a single application of chemicals.

CANUSA, Canada/United States Spruce Budworms Program