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Weed management programs in corn typically include herbicides applied both preemergence (PRE) and postemergence (POST) for season-long weed control. Mesotrione is a new triketone herbicide registered for PRE and POST control of broadleaf weeds in corn. Triketone herbicides function through inhibition of the enzyme p-hydroxyphenylpyruvate dioxygenase. Mesotrione applied PRE did not adequately control common lambsquarters (Chenopodium album L.), smooth pigweed (Amaranthus hybridus L.), common ragweed (Ambrosia artemisiifolia L.), or morningglory species (Ipomoea spp.) in conventional tillage corn, but control of these weeds was generally improved in no-till corn. Mesotrione combinations with acetochlor did not always improve control of broadleaf weeds, but increased control of smooth pigweed and giant foxtail (Setaria faberi Herrm.). POST applications of mesotrione at 105 g ai/ha controlled most annual broadleaf weeds except common ragweed, but did not control giant foxtail. The addition of atrazine at 280 g ai/ha to mesotrione, however, improved control of common ragweed. Tank-mixtures of glyphosate, imazethapyr, or imazethapyr plus imazapyr with mesotrione improved control of giant foxtail in herbicide-resistant corn. Corn injury was usually low from PRE and POST mesotrione applications in non-genetically modified corn, however, greater injury occurred in glyphosate-resistant varieties. Corn treated with mesotrione combinations generally yielded similar to corn treated with commercial standards. Mesotrione applied POST also suppressed the perennial weeds horsenettle (Solanum carolinense L.) and Canada thistle [Cirsium arvense (L.) Scop.]. Additions of atrazine increased the rate of plant tissue necrosis on these perennial weeds as compared to the slower bleaching symptoms associated with mesotrione applied alone. In general, Canada thistle plants were more susceptible to mesotrione in the rosette stage of growth than when bolting. Absorption, translocation, and metabolism of 14C mesotrione in Canada thistle was generally low. However, higher levels of absorption and translocation and lower root metabolism of mesotrione in rosette stage plants compared to bolting stage plants may explain why Canada thistle is more susceptible to mesotrione in the rosette stage of growth. The changes in symptomology and increased control from mesotrione plus atrazine tank-mixtures is likely due to the interrelationship between the modes of action of atrazine and mesotrione. / Ph. D.

Weeds pose a challenge to cotton production, and herbicides have been the primary means of control. However, there is growing concern over weed resistance to herbicides. To address this issue, we evaluated three cover crop species and six cotton accessions for weed suppression. The study found that hairy vetch, wheat, and B16 cotton CS line effectively suppressed Amaranthus species, while MNTN 4-15, B16, hairy vetch, and wheat were correlated with the highest cotton yield. Cover crops were also analyzed for chlorogenic acid content, with wheat, MNTN 4-15, and hairy vetch producing the highest amounts. The greenhouse tray study showed that wheat and hairy vetch cover crops were among the best treatments for weed suppression. These findings suggest that cover crops may provide effective weed control and improve crop yield.

Inter-row mechanical cultivation was proposed as a supplement to or substitute for conventional weed control methods currently used in snap bean, carrot and lettuce production. Several types of cultivators were assessed and compared. The effect of mechanical cultivation on crop yield and quality was studied by counting, weighing and grading bean pods, carrot roots and lettuce heads. The effect of mechanical cultivation on disease incidence was studied by surveying fields during the season and by determining the number and weight of diseased pods, roots and heads at harvest. The relationship between the level of Cercospora blight on carrots and potential impacts on yield was also investigated by measuring plant characteristics and the amount of force needed to separate carrot foliage from root. The effect of mechanical cultivation on the phenology of snap bean flowering was studied by determining how long it took for a plant to produce 50% of its flowers and counting how many flowers and pods a plant produced. In general, mechanical cultivation did not affect normal crop production and may be used to replace or complement conventional weed control methods. There was little variation among different cultivators within one season, but cultivator effects differed among crops and from one year to the next.

Mississippi ranks among the leading states in sweetpotato production in the US. However, managing weeds in sweetpotato fields presents a significant challenge, and the limited availability of herbicides labeled for use in sweetpotato makes it even more challenging. The widespread and repeated use of herbicides has led to the development of weed resistance. In addition, herbicides are incompatible with the organic production system. Finding sustainable weed management strategies to provide weed control options for organic cultivation and detain the development of herbicide-resistant weeds under conventional crop production is imperative. The natural chemicals released by the plants, also called allelochemicals, can potentially suppress weeds and be used for weed management under conventional and organic cultivation systems. The current study aimed to 1) screen the sweetpotato varieties for their weed-suppressing effect on the growth of weeds in controlled conditions using a stair-step structure, 2) evaluate the allelopathic suppression of selected sweetpotato varieties under field conditions, and 3) identify and quantify allelochemicals released by the roots of seventeen sweetpotato varieties. Results of the current study on the availability of allelopathic sweetpotato varieties will benefit organic producers by enhancing crop productivity. They will decrease reliance on synthetic herbicides in conventional farming systems. Identifying and quantifying allelochemicals will also improve our knowledge of allelopathy and provide valuable information for developing allelopathic sweetpotato varieties.

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Typescript (photocopy). / Digitized by Kansas Correctional Industries

Typescript (photocopy). / Digitized by Kansas Correctional Industries

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