We developed a model and subsequently simulated robust white foxtail (Setaria viridis var. robusta-alba Schreiber) or robust purple foxtail (Setaria viridis var. robusta-purpurea Schreiber) growth. SETSIM (SETaria SIMulation) uses the GASP IV simulation language which allows for both continuously changing variables and discrete events. GASP IV provides the necessary integrations and automatic time-stepping essential in simulation. SETSIM uses the materials-flow concept to simulate foxtail growth and development on a population basis. Carbohydrate flow among six compartments (leaf, stem, and root total nonstructural carbohydrate pools; leaf, stem, and root tissue) is governed by nine physiological rates. Each rate is dependent on the physiological state of the foxtail population and the environmental conditions prevailing. Simulation of carbohydrate flow in and out of each compartment results in the net growth of that compartment. By considering all six compartments simultaneously, the vegetative growth and development of a foxtail population can be simulated. Validation of SETSIM with field data recorded over a 2-yr period has shown that this simulator can accurately predict foxtail growth parameters such as dry matter accumulation, plant height, leaf area index, and leaf to stem ratio. SETSIM could serve as a framework for other weed models because of its modular structure. Such models can benefit weed science by predicting the active stage of weed growth, predicting whether a weed could become a problem under different climatic conditions, interfacing with existing crop models to predict yield and harvest restriction, pointing out gaps in our present knowledge in weed biology, and serving as teaching aids.

Research was conducted to determine effects of glyphosate [N-(phosphonomethyl)glycine] on the chlorophyll and carotenoid and on the catalase specific activity in purple nutsedge (Cyperus rotundus L.). The isopropylamine salt of glyphosate caused chlorosis to appear on the center leaves of plants maintained under lighted conditions after treatment. Glyphosate-induced chlorosis was delayed by darkness but occurred when treated plants were placed in the light. Glyphosate caused significant reducations in the chlorophyll and carotenoids content of purple nutsedge leaves. Based on levels in untreated plants, carotenoid content was reduced more rapidly than chlorophyll in glyphosate-treated plants. The catalase specific activity was reduced by glyphosate to about 70% of the level in untreated plants. Interrelationships among the effects of glyphosate on the carotenoid and chlorophyll content and catalase activity were not determined but possible interactions are discussed.

In six years of field studies, early-season releases of the native moth Bactra verutana Zeller were evaluated as a biological control for purple nutsedge (Cyperus rotundus L.). Establishment from adult releases required at least 10 pairs of moths per release; establishment from larval release could be achieved with a single release of two or five newly-emerged larvae per shoot. When shoots averaged 4 or 7.5 cm high at the time of such releases, aboveground growth was reduced 32 to 62% after 30 days. Three to eight weekly releases of larvae reduced the topgrowth of nutsedge planted in rows of cotton (Gossypium hirsutum L. ‘Stoneville 213’) 30 to 68% 6 to 8 weeks after the last release. Weekly releases of about five larvae per shoot repeated three, four, or five times in 1976 and 1977 reduced nutsedge growth so that seed cotton yield equalled that of cotton in plots without nutsedge. MSMA (monosodium methanearsonate) applied at the rate of 2.2 kg/ha 5 and 7 weeks after cotton emergence gave greater control of purple nutsedge topgrowth and a yield of seed cotton equal to that resulting from three to five larval releases of about five larvae per shoot beginning when purple nutsedge averaged 7.5 cm high. When MSMA was applied at 7.5 and 8.5 weeks after cotton emergence, the addition of two early-season releases of larvae were also necessary to achieve nutsedge control and seed cotton yield equal to that produced by three to five releases of larvae.

We previously reported that napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] was highly toxic to achlorophyllous callus of tomato (Lycopersicon esculentum Mill. ‘San Marzano’), whereas foliar application to seedlings was almost without effect. Experiments were performed to ascertain the effects of napropamide on green and achlorophyllous calli of tomato and broadleaf dock (Rumex obtusifolius L.). The growth of achlorophyllous tissues was more severely inhibited. Foliar applications were not as inhibitory in both species. Napropamide was applied to tomato seedlings via roots and cut shoots and root growth was more inhibited than shoot growth. Thus napropamide is toxic to achlorophyllous tissue and is either less toxic to, or detoxified by green tissue.

Four weed species, eragrostis (Eragrostis tenella Roem. and Schult), cogongrass [Imperata cylindrica (L.) Beauv.], synedrella (Synedrella nodiflora Gaertn.) and tridax (Tridax procumbens L.) were planted at 5, 10, 15, 20 or 25 plants per pot. Competition affected shoot and root dry weights, height, and leaf number of all species and the reproductive characteristics of eragrostis and tridax. The interaction between species and plant density was also highly significant for shoot and root dry weights, height and leaf number. Individual plant height, shoot and root dry weights, leaf and node numbers, percent flowering per pot and the number of inflorescences produced decreased with increase in population density. This reduction was greatest in eragrostis followed by tridax. Synedrella (both disk and ray floret seeds) were least affected. There was no significant difference in the response of plants from disk floret seeds and ray floret seeds of synedrella.